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Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Chapter 23: Nuclear Chemistry 23.1: The Nature of Nuclear Reactions Nucleons: - the particles that make up a nucleus of an atom (protons,( 11 p+ or 11 H) and neutrons, ( 01 n)). Isotopes: - atoms that have different mass number but the same atomic number or number of protons. Nuclide: a particular atom or isotope containing specific numbers of protons and neutrons Mass Number (# of p+ and n)
A Z
+
Atomic Number (# of p )
X
Element Symbol (based on Atomic #)
Radioactivity: - the particles and/or electromagnetic radiation that are emitted due to unstable nuclei. - all elements having atomic number 84 (Polonium) and greater are radioactive. Nuclear Transmutation: - a process where radioactivity is resulted from the bombardment of nuclei by neutrons, protons or other nuclei. - in most cases, heavier elements are synthesized from lighter elements. History of Radioactivity • In 1896, Wilhelm Roentgen discovered X-ray by examining ray emitting from the outside of the cathode ray glass tube. It has the capability of ing through solid materials, but can be blocked by denser matters. It can also be exposed to photographic plate, resulting from an image of “seeing through” an container made of less dense material. • In the same year, Antoine Becquerel discovered that uranium emits a ray onto a photographic plate in the absence of sunlight or other forms of energy. • A few years later, Marie and Pierre Curie demonstrated that radiation can be emitted by other elements. They discovered two new elements (polonium and radium) based on their tendency to emit radiation (radioactivity). Types of Radioactive Particle and Decay 1. Alpha Particle (α particle): - basically a helium nucleus ( 42 He), commonly found during radioactive decay from heavier nuclide (the net result is to increase the neutron to proton ratio – more explanation in the next section). Example:
218 84
Po →
214 82
Pb + 42 He
2. Beta Particle (β particle): - basically an electron ( −01 e or −01 β) that is emitted when the neutron to proton ratio is higher than the zone of stability (a neutron is transformed to a proton and an electron as a result – more explanation in the next section). - electrons have a mass number of 0 and an atomic number assignment of −1, due to its charge. Example:
Page 230.
214 82
Pb →
214 83
Bi +
0 −1
e
( 01 n → 11 p +
0 −1
e)
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
3. Gamma Ray (γ ray): - also known as a high-energy photon ( 00 γ) that is usually a by-product of an alpha-particle decay. - photon has no mass and no atomic number. 238 92
Example:
U→
234 90
Th + 42 He + 2 00 γ
4. Positron (e+): - an antimatter of electron ( 10 e or 10 β) that is emitted when the neutron to proton ratio is lower than the zone of stability (a proton is transformed to a neutron as a result more explanation in the next section). - positrons have a mass number of 0 and an atomic number of 1, due to its charge. - when a positron and an electron collide, they annihilate themselves to produce energy (matter-antimatter reaction).
O→
15 8
Example:
15 7
( 11 p → 01 n + 01 e)
N + 01 e
5. Electron Capture: - an inner-orbital electron is “captured” by the nucleus to increase neutron to proton ratio. It is usually accompanied by an emission of gamma ray. 73 33
Example:
0 −1
As +
e→
73 32
Ge + 00 γ
Balancing Nuclear Equations: - the total atomic number (Z) and the total atomic mass (A) have to balance on both sides. Example 1: Balance the following nuclear equations. 222 86
a.
222 86
49 21
11 6
1 1
Po +
48 22
0 −1
Ti +
11 5
B+
0 1
e
H reacts with
H + 20 9
4 2
A: 222 = (218) + (4) Z: 86 = (84 → Po) + (2)
He
1 0
e+
C produces a β particle.
14 6
14 6
C →
14 7
N+
0 −1
A: 14 = (14) + (0) Z: 6 = (7 → N) + (−1)
e
n A: 49 = (48) + (0) + (1) Z: 21 = (22 → Ti) + (−1) + (0)
C produces a positron.
C → 1 1
f.
218 84
b.
Sc produces a β particle and a neutron.
Sc →
11 6
d.
g.
Rn →
49 21
c.
Rn produces an α particle.
15 7
F→
N → 20 10
12 6
15 7
A: 11 = (11) + (0) Z: 6 = (5 → B) + (1)
C +
4 2
He +
Ne + _____
F→
20 10
40 19
K captures an electron to produce γ ray
40 19
K +
e→
0 −1
40 18
Ar +
0 0
γ
A: 40 + (0) = (40) + (0) Z: 19 + (−1) = (18 → Ar) + (0)
N to produce an α particle with γ ray.
A: 20 = 20 + (0) Z: 9 = 10 + (−1) 20 9
e.
Ne +
γ
A: 1 + 15 = (12) + (4) + (0) Z: 1 + 7 = (6 → C) + (2) + (0)
h. 0 −1
0 −1
0 0
e
e
239 94
Pu + ____ →
A: 239 + (4) Z: 94 + (2) 239 94
Pu +
4 2
Copyrighted by Gabriel Tang B.Ed., B.Sc.
242 96
4 2
He →
Cm + 01 n
He 242 96
= 242 + 1 = 96 + 0 Cm + 01 n
i.
54 27
Co → ______ + 10 e
A: 54 = (54) + 0 Z: 27 = (26 → Fe) + 1 54 27
Co →
54 26
Fe + 10 e
Page 231.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
23.2: Nuclear Stability Strong Nuclear Force: - a force of attraction that is present over extremely short distance (1 × 10−15 m) between all nucleons (protons and neutrons). - it is much stronger than electromagnetic force in short distances. However, electromagnetic force is more significant over longer distances. Properties of Neutrons: 1. Neutrons serve as “nuclear cement”, gluing neighbouring protons together despite the electric repulsion of positive charges, but only over short distances. 2. At large distances, strong nuclear force become less significant. Hence, the MORE Protons in the nucleus (Heavier Atoms), the MORE Neutrons are needed to hold them together. Sometimes this means for every 1 proton, there are 1.5 times to twice as many neutrons. 3. SMALLER Atomic Nuclei usually have the SAME Number of Protons as Neutrons. 4. A Single Neutron is rather UNSTABLE. It will CONVERT itself to a Proton and an Electron. 1 0
Strong Nuclear Force
n → 11 H +
0 −1
e → (basically a hydrogen atom)
Electric Repulsion Force
For Small Nucleus, Strong Nuclear Force is MORE significant compared to electric repulsive force between protons due to small distances between nucleons.
Weaker Nuclear Force
Stronger Electric Repulsion Force
For Large Nucleus, Electric Repulsive Force between Protons is MORE significant compared to strong nuclear force because of the large distances between nucleons. Hence, they are inherently unstable and likely undergo alpha decay (see below).
Radioactive Decay: - when a heavier nucleus loses nucleons to become a smaller but more stable nucleus. In the process, it gives off radiation products like alpha-, beta- particles and/or gamma rays. Zone of Stability: - a graph that depicts the relationship between the number of neutrons versus the number of protons, and the area where there are stable nuclides.
Page 232.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Common Observations of Radioactive Decay 1. When a nuclide has 84 or more protons (Z ≥ 84), it tends to be unstable and likely undergo radioactive decay. 2. Lighter nuclides are stable when Z = n (or n : p+ ratio = 1). However, heavier nuclides are stable only when Z < n (or n : p+ ratio > 1).
Too Many Neutrons (Spontaneous β production)
( 01 n → 11 p +
0 −1
e)
3. Nuclides with even # of p+ with even # of n are more stable than nuclides with odd # of p+ and odd # of n.
Example: Most Stable to Least Stable Nuclides ( 126 C, 136 C , 199 F , 63 Li ) Nuclide +
12 6
# of p # of n Stability:
C 6 (even) 6 (even) Most
13 6
C 6 (even) 7 (odd)
19 9
F 9 (odd) 10 (even)
6 3
Li 3 (odd) 3 (odd) Least
Too Many Protons (Spontaneous Positron production)
( 11 p → 01 n + 01 e)
4. Magic Numbers of protons or neutrons (2, 8, 20, 28, 50, 82 and 126) results in very stable nuclides. Thermodynamic Stability: - amount of potential energy inside a nucleus versus total potential energy of all nucleons. - the difference in energy can be calculated using Einstein’s equation (ΔE = Δmc2), where Δm is referred to as mass defect. Mass Defect (Δm): - the change in masses during a nuclear transformation. (Δm = mproducts − mreactants) - sometimes masses for subatomic particles is measured in amu (atomic mass unit) (1 kg = 6.022 × 1026 amu , or 1 g = 6.022 × 1023 amu = 1 mole amu). Subatomic Particle Neutron Proton
Mass (kg) 1.67497 × 10−27 1.67357 × 10−27
Atomic Mass Unit (amu) 1.008665 1.007825
Binding Energy (ΔEbind): - the amount of energy released during a nuclear transformation because of a mass defect. It is used to bind the nucleons in the reactant nuclide. - we often convert the unit to electron volt (1 eV = 1.69 × 10−19 J or 1 MeV = 1.69 × 10−13 J). - higher the ΔEbind per nucleon means more mass is turned into pure energy to bind the nucleons together. Hence, bigger ΔEbind means more stable nuclei (the most stable nuclei is 26Fe). Einstein’s Mass-Energy Conversion ΔEbind = −Δmc2 ΔEbind = Binding Energy Δm = mass defect (kg) c = speed of light (3.00 × 108 m/s)
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Nuclei need to break up to achieve maximum stability (fission) Nuclei need to combine to achieve maximum stability (fusion)
Page 233.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Example 1: Calculate the binding energy for carbon-13 (13.003355 amu) in J/nucleon and MeV/nucleon. m of 136 C = 13.003355 amu m of (6p+ and 7n) = 6(1.007825 amu) + 7(1.008665 amu) = 13.107605 amu Δm = m of 136 C − m of (6p+ and 7n) = 13.003355 amu − 13.107605 amu
Δm = −0.104250 amu
1 kg ⎛ ⎞ 8 2 −11 ΔE = −Δmc2 = −(−0.104250 amu) ⎜ ⎟ (3.00 × 10 m/s) = 1.5580372 × 10 J 26 6.022 × 10 a m u ⎝ ⎠ −11 1.5580372 × 10 J ΔEbind per nucleon = ΔEbind = 1.20 × 10−12 J/nucleon 13 nucleons 1 MeV ΔEbind = 7.09 MeV/nucleon ΔEbind = 1.20 × 10−12 J/nucleon × 1.69 × 10 −13 J Example 2: Calculate the energy released per mole of 235 92
( 235 92 U = 235.0439 amu; minitial of
235 92
141 56
U + 01 n →
141 56
235 92
U reacted when it undergoes nuclear fission:
Ba +
92 36
Ba = 140.9144 amu;
Kr + 3 01 n
92 36
Kr = 91.9262 amu)
U + 01 n = 235.0439 amu + 1.00899 amu = 236.05289 amu
92 1 mfinal of 141 56 Ba + 36 Kr + 3 0 n = 140.9144 amu + 91.9262 amu + 3(1.00899 amu) = 235.86757 amu Δm = mfinal − minital = 235.86757 amu − 236.05289 amu Δm = −0.18532 amu 1 kg ⎞ ⎛ 8 2 −11 ΔE = −Δmc2 = −(−0.18532 amu) ⎜ ⎟ (3.00 × 10 m/s) = 2.76964464 × 10 J/nucleus 26 ⎝ 6.022 × 10 amu ⎠ −11 ΔEbind = 2.76964464× 10 J/nucleus × (6.022 × 1023 nucleus/mol) = 1.66788 × 1013 J/mol
ΔEbind = 1.67 × 1010 kJ/mol = 16.7 TJ/mol
1 TJ (Tera-Joules) = 1 × 1012 J
Assignment 23.1 pg. 994−995 #1 to 6, pg. 996 #55 23.2 pg. 995 #7, 8, 11, 12, 14, 16, 18 to 20; pg. 998 #80 21.3: Natural Radioactivity Decay Series: - a succession of decays from a particular radioactive nuclide until the formation of a stable nuclide. Rate of Decay: - the rate at which a given radioactive nuclide decays over time. - the negative of the change in the number of nuclides per unit of time (measured in reciprocal time unit).
Page 234.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Kinetic Stability: - sometimes called radioactive decay (a process where a nucleus decomposes into a different nucleus to achieve more stability). Derivation Using Calculus: (k = Rate Constant, ΔN Rate = − = kN N = Amount of Nuclide) Δt (Rearrange for Integration, 1 N ΔN = −kΔt ΔN = dN ; Δt = dt)
Non-Calculus Explanation: N = N0e−kt N N0
(Continuous Exp Decay)
= e−kt
(Solving for −kt)
( ) = ln (e−kt) ln ( ) = −kt ln e ln
N
∫
(Natural log both sides)
N N0
N0
(ln e = 1)
N N0
t
1 N
dN = − k ∫ dt
(Integrate Both Sides:
0
∫
1 x
dx = ln x)
(Use Logarithm Law: log A − log B = log ( BA ) )
ln N − ln N0 = −kt ⎛ N ⎞ ⎟⎟ = −kt ln ⎜⎜ ⎝ N0 ⎠
(Radioactive Decay Equation)
Half-Life (t½): - the amount of time it takes to half the amount of radioactive nuclides. - at half-life, t½,, the amount of radioactive nuclides ½ N0 = N : ⎛ N ⎞ ⎛ (1 N ) ⎞ ⎟⎟ = −kt ⇒ ln ⎜⎜ 2 0 ⎟⎟ = −kt½ ⇒ ln (½) = −kt½ ⇒ ln (2) = kt½ ln ⎜⎜ ⎝ N0 ⎠ ⎝ N0 ⎠
t½ =
ln 2 0.693 = k k
Radioactive Decay Equations t
⎛ N ⎞ ln 2 0.693 ⎛ 1 ⎞ t1/2 ⎟⎟ = −kt t½ = = N = N0 ⎜ ⎟ ln ⎜⎜ k k ⎝ 2⎠ ⎝ N0 ⎠ N = Amount of Nuclide at time t N0 = Amount of Nuclide at time 0 k = Rate Constant (s−1, min−1, hr−1, day−1, yr−1) t = total decay time t½ = half-life
Example 1: Technetium-99, the first synthetic element in the Table, is used as a radiotracer for many organs such as heart, liver and lungs. It has a half-life of 6.0 hours. Draw a graph showing how 99 100 mg of 99 43 Tc decays over time. What is the radioactive amount of 43 Tc after 2.00 days?
N=? t
⎛ 1 ⎞ t1/2 N = N0 ⎜ ⎟ ⎝ 2⎠ 48.0 hrs
⎛ 1 ⎞ 6.0 hrs N = (100 mg) ⎜ ⎟ ⎝ 2⎠
N = 0.391 mg
ln 2 k ln 2 k= t1 / 2
Radioactive Decay of Tc-99
t½ =
ln 2 k= 6 hr
⎛ N ⎞ ⎟⎟ = −kt ln ⎜⎜ ⎝ N0 ⎠ N = N0 e−kt
N = (100 mg) e
N = e−kt N0
120 Amount N (mg)
N0 = 100 mg t½ = 6.0 hrs t = 2.00 days = 48.0 hrs
At t½, N = 50 mg (half of 100 mg)
100 80 60 40 20
ln 2 − ( 48.0 hr ) 6 hr
N = 0.391 mg
Copyrighted by Gabriel Tang B.Ed., B.Sc.
0 0
6
t½ = 6 hrs
12
18
24
30
36
42
48
Time (hours)
Page 235.
Unit 4: Thermochemistry and Nuclear Chemistry Example 2:
131 53
Chemistry AP 131 53
I is a radiotracer used to detect thyroid activity. The half-life of
a. Determine the rate constant of
131 53
I.
b. How long will it take a patient to have her initial dosage of initial value? t½ = 8.1 days N N 0 = 0.01
ln 2 k ln 2 k= 8.1 days
a. t½ =
k=? t=?
ln 2 t1 / 2
k=
131 53
I to decrease to 1.00 % of its t
k = 0.086 day−1
t1 / 2
( ) log( ) =t N N0
log( 12 ) (8.1 days)log(0.01) = 53.815 days t= log(0.5)
N N0
N N0
ln 2 8.1 days
t = 54 days Example 3:
222 86
t = 54 days
Rn is a natural alpha particle producer. Due to its noble gas characteristic, it can cause
damage to tissues as it can be easily inhaled into the body. uranium mine because it is a decay product of
238 92
45.7 mg in 24.0 hours. Determine the half-life of N0 = 50.0 mg N = 45.7 mg t = 24.0 hrs
t½ = ? k=?
t
N ⎛ 1 ⎞ t1/2 ⎛ 1 ⎞ t1/2 N = N0 ⎜ ⎟ → =⎜ ⎟ N0 ⎝ 2⎠ ⎝ 2⎠ N t log N0 = t1 / 2 log (½)
( )= −kt ln ( ) ln (0.01) = t= −( −k ) = 53.815 days
b. ln
I is 8.1 days.
222 86
Rn can be found quite easily in
U. In an analysis 50.0 mg 222 86
Solving t½ first:
ln
⎛ 1 ⎞ t1/2 N = N0 ⎜ ⎟ ⎝ 2⎠ log NN0 =
t
N N0
N N0
−t
45.7 mg 50.0 mg
)
( )
− 24.0 hrs
k = 0.00375 hr−1
t½ =
t log( 12 ) (24.0 hrs ) log(0.5) = 45.7 mg log NN0 log(50 .0 mg )
( )
Then solve for k: ln 2 ln 2 ln 2 t½ = k= = k t1 / 2 185 hrs
t½ = 185 hours = 7.71 days
k = 0.00375 hr−1 14 6
C can be found naturally in organic material
and the atmosphere. It decays as soon as the organism dies ( 146 C → - uses the known ratio of
14 6
0 −1
e+
14 7
N).
12 6
C/ C of similar organic sample of the day with the ratio in the
artefact and the half-life of
Page 236.
t
N ⎛ 1 ⎞ t1/2 → =⎜ ⎟ N0 ⎝ 2⎠ t t1 / 2 log (½)
t½ = 185 hours = 7.71 days
Then, solve for t1/2: ln 2 ln 2 t½ = = k 0.0037468628 hr −1
Radiocarbon Dating: - sometimes called carbon-14 dating.
Rn decayed to
Rn and its rate constant.
Solving k first:
( )= −kt ln ( ) ln ( = k=
222 86
14 6
C being 5730 years to determine the age of the artefact.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Example 4: An ancient wooden artefact found in China has a 146 C decay rate of 5.2 counts per minute per gram of carbon. A comparison to a freshly cut piece of wood has a count of 13.6 counts per minute per gram of carbon. Given the rate of carbon-14 decay is 5730 years, determine the age of this artefact. kN Final Rate at t 5.2 counts/ (min • g ) = = 13.6 counts/ (min • g ) Initial Rate at t = 0 kN 0
t=?
t½ = 5730 yrs
First, we solve for k. ln 2 ln 2 ln 2 t½ = → k= = k = 1.209680943 × 10−4 yr−1 k 5730 yrs t1 / 2 Next, we solve for t. ln NN0 ⎛ N ⎞ ln (135..26 ) ⎟⎟ = −kt → = ln ⎜⎜ t= = 7947.642495 yrs t = 7948 years ln 2 − − k ( ) N ⎝ 0⎠ 5730 yrs
( )
Uranium-238 Dating: - due to its lengthy half-life (4.5 × 109 years), it is used to date rocks and other 206 238 206 ancient inorganic material. 238 92 U/ 82 Pb ratio is used as 92 U eventually decays to stable 82 Pb. 238 92
U →
Example 5: A piece of ore containing Suppose that no life of
238 92
206 82
206 82
238 92
Pb + 8 42 He + 6
U and
206 82
0 −1
t½ = 4.51 × 109 years
e
Pb was found. The ratio between
206 82
Pb to
238 92
U is 0.432.
Pb was originally present. Determine the age of the ore given that the half-
U is 4.5 × 109 years.
N of 206 N of 238 N 432 92 U still present 82 Pb at t = = = 0.432 = ⇒ 238 N0 1000 N of 92 U at t N of 238 92 U before t½ = 4.5 × 109 yrs
238 92 238 92
U now 1000 1000 = = 206 U + 82 Pb 1000 + 432 1432
t=?
First, we solve for k. ln 2 ln 2 ln 2 k = 1.54032707 × 10−10 yr−1 t½ = → k= = k t1 / 2 4.5 ×10 9 yrs Next, we solve for t. ln NN0 ⎛ N ⎞ ln (1000 1432 ) ⎜ ⎟ = = 2,331,141,717 yrs ln ⎜ = − kt → t = t = 2.3 billion years ⎟ −k − 4.5×ln1029 yrs ⎝ N0 ⎠
( )
(
)
Potassium-40 Dating: - used mainly in geochemistry to determine the age a metal ores. Its main mode of 9 40 decay via electron capture 40 19 K turns it into 18 Ar with a half-life of 1.2 × 10 years. Using a mass spectrometer, we can easily measure the amount of inside the lattice mineral. By calculating the of a metal ore. 40 19
K +
0 −1
e →
40 18
Ar
40 18
Ar /
40 19
40 18
Ar trapped
K, we can determine the age
t½ = 1.2 × 109 years
Assignment 23.3 pg. 995 #21, 23 to 26, 28, 29; pg. 997−998 #66 to 68, 85 Copyrighted by Gabriel Tang B.Ed., B.Sc.
Page 237.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
23.4: Nuclear Transmutation Nuclear Transmutation: - the reaction where one element is converted to another element by changing the number of protons. Transuranium Elements: - elements that have been synthesized by nuclear transformation after the last natural element, uranium. Example:
244 94
Pu +
48 20
Ca →
289 114
Uuq + 3 01 n
(Discovered in 1998 and t1/2 = 30 seconds)
Particle Accelerator: - a device that alternates electric field to speed up a particle to add into a target nuclide. a. Cyclotron: - a type of particle accelerator that utilizes a changing electric field along with a magnetic field to increase the speed of an ion around a disc before hitting a target nuclide. COMET: A medical superconducting cyclotron. It is used to generate thallium-201 (coronary arteries) and gallium-67 (soft-tissue tumors). It can also produce radiopharmaceutical needed for PET and SPECT scans Schematic of Accelerated charged particle a Cyclotron to collide with target nuclide
b. Linear Accelerator: - a particle accelerator that speeds up a particle by using an alternating electric field at different segment of a linear tube to add an ion into a target nuclide. Left: Schematic of a Linear Accelerator Right: Stanford Linear Accelerator Linear Accelerator Computer Program is used to control radiotherapy Multileaf treatment by a Collimeter medical linear to shape the accelerator beam Schematic of a Medical Linear Accelerator
Page 238.
Assignment 23.4 pg. 996 #33 to 36
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
23.5: Nuclear Fission Nuclear Fission: - the breaking up of a heavier nucleus into two nuclei with small mass number. Example:
235 92
U + 01 n →
141 56
Ba +
92 36
Kr + 3 01 n
ΔH = 2.0 × 1010 kJ/mol
Chain Reaction: - when the nuclear fission is self-sustaining. a. Subcritical: - when there is on average, less than one neutron produced per 235 92 U is consumed. The fission will eventually stop. b. Critical: - when there is on average, exactly one neutron produced per 235 92 U consumed. The fission can then be self-sustaining at the same level. c. Supercritical: - when there is one average, more than one neutron produced per 235 92 U is consumed. The fission can increase its rate rapidly and a violent explosion can result. Critical Mass: - the minimum mass of fissionable material required for the generation of a self-sustaining nuclear chain reaction. Spontaneous Fission: - when a heavy nuclide splits into two lighter nuclides and sometimes neutrons. Example:
256 100
Fm →
140 54
Xe +
112 46
Pd + 4 01 n
Atomic Bomb: - an uncontrolled nuclear fission device that releases large amount of energy. - in 1939, just before WWII, Einstein and other scientists wrote to President Roosevelt that Nazi was researching ways to purify U-235 for the purpose of an atomic bomb. This led to the US initiation of the “Manhattan Project” (a secret project to develop the atomic bomb by the US). - the first atomic bomb test was conducted at Jemez Mountains in northern New Mexico on July 16, 1945 at 5:29:45 AM (Mountain War Time). Less than a month later, an atomic bomb (code name: Little Boy) was dropped on Hiroshima, Japan on Aug 6. It had a yield of 15 kilotons of TNT (6 × 1010 kJ ≈ 750 g of U235) and it killed an estimated 80,000 people with 60,000 died later of radiation poisoning. Three days later, another atomic bomb (code name: Fat Man) was dropped on Nagasaki. It had a yield of 21 kilotons of TNT (8 × 1010 kJ ≈ 1 kg of Pu-239) and killed 74,000 people with several hundred thousands died from disease due to radiation. - the “gun-type assembly” design detonation starts with conventional TNT explosion at one end of the device, pushing half the U-235 / Pu-239 subcritical mass into another half of the U-235 / Pu-239 subcritical mass located at the other end of the bomb. When the two masses connect, a supercritical chain reaction takes place and releases a large amount of heat energy. The “implosion” design involves detonate surrounding TNT to ignite a nuclear fission core. Plutonium Implosion Uranium “Gun” Atomic Bomb (Little Boy) Length: 10 ft / 3 m Diameter: 28 in / 71.1 m Weight: 9,700 lbs / 4,400 kg Yield: 15 kilotons
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Atomic Bomb (Fat Man) Length: 10.7 ft / 3.25 m Diameter: 5 ft / 1.5 m Weight: 10,265 lbs / 4,656 kg Yield: 21 kilotons
Page 239.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Nuclear Reactors: - fission reactors where enriched 235 92 U is placed in the reactor core. The heat is generated in the reactor is used to heat water. This water also acts as the (a substance that slows down neutrons emitted and reduces their kinetic energy). Control rods (usually made of carbon, cium, or boron to absorb extra neutrons) can be lifted or lowered to control the rate of the fission process. The super-heated water from the reactor core heats another tank of water, but the water is recycled back into the reactor. As the water in the tank is heated into steam, it turns the steam turbine to generate electricity. This water is then cooled in a cooling tower and recycled (the hot water cannot be discharged into nearby lake or stream to avoid thermal pollution). Since large amount of cold water is needed for the cooling process of steam, most nuclear power plants are built near a large river or lake. - the by-products of 235 92 U fission have a very long half-lives and can remain radioactive for a long time. Great efforts are needed to dispose of the wastes properly. The danger of a nuclear meltdown is also a constant danger as in the cases of Three Mile Island, Pennsylvania in 1979 and Chernobyl, Ukraine in 1986.
Bruce Power Nuclear Plant at Tiverton (Lake Huron), Canada
Light Water Reactor: - uses light water (regular H2O) as . - all US nuclear reactors are light-water reactors and they use cium or boron control rods. - since light water is a good absorber of neutrons, the uranium fuel used has to be enriched (the same initial process is used to make weapon-grade uranium, 235U). Heavy Water Reactor: - uses heavy water (D2O – deuterium water - 21 H2O) as . - D2O dose not absorb neutrons as well as H2O (it has a neutron in the hydrogen atom already). Hence, the nuclear reactor is more efficient (more neutrons are left to do more fission collisions). As a result, uranium enrichment is not necessary. This eliminates the potential of a country to develop nuclear weapons. - D2O can be expensive to produce due to the amount of water needed for operating a nuclear power plant. Currently, Canada is the only country that uses heavy water reactor (CANDU reactor). Breeder Reactor: - due to the limited resources of enriched uranium 235 92 U, the excess neutrons in the fission reactor can be used to convert uranium-238 to plutonium-239 to be used as an alternate nuclear fuel. 238 92
U + 01 n →
239 94
Pu + 2
0 −1
e
- it is the most expensive type of reactor due to the its technical aspects. Currently, only Russia and have a handful of breeder reactors.
Page 240.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
23.6: Nuclear Fusion Nuclear Fusion: - the combining of two light nuclei into a heavier and more stable nucleus. Example:
2 1
H + 31 H → 42 He + 01 n
ΔH = 1.7 × 109 kJ/mol
- the availability of hydrogen isotopes, deuterium ( 21 H) and tritium ( 31 H), in sea water and the harmless product, 42 He, makes nuclear fusion an environmental friendly alternative to generate power. - however, fusion reactions such as the one above usually require an initial temperature above 4 × 107 K to overcome the strong electrostatic repulsion between the two protons (the release of significant binding energy can only achieve when the distance between the two protons is approximately 10−15 m). High-powered laser and heating by electric currents are being studied as Fusion reaction is the driving methods to attain this high temperature to initial a control fusion reaction. force of our sun’s energy.
European Tokamak Fusion Test Reactor Vacuum Vessel employs the design of a toroid with a super strength magnetic field to contain plasma without having it touch the wall of the reactor. A similar experimental fusion reactor can also be found at Princeton, USA.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Propose Schematic of a Fusion Reactor to Generate Electricity
Page 241.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Hydrogen Bomb: - also called a thermonuclear bomb that uses fusion reaction to destroy a large target area. - the device contains solid lithium deuteride (LiD or Li 21 H) which can be packed tightly. The detonations involve a fission reaction to generate the initial heat to start the fusion reaction. 2 1
H + 21 H → 31 H + 11 H
- fusion reaction is not limited by a critical mass as in fission reaction. Hence, the size of the explosion depends on the amount of fusion material. - besides the intense heat to incinerate a large area, the damaging radiation effects come from the products of the fission starter and the product of the fusion reaction, tritium, has a half-life of 12.5 yrs. However, other radioactive material with longer half-life, such as Co-59, can be used to spread harmful radiations.
Differences in yields between atomic (fission) and thermonuclear (fusion) bombs
Thermonuclear Hydrogen Bomb (Teller-Ulam) Length: 18.8 ft / 5.7 m Diameter: 5 ft / 1.5 m Weight: 39,600 lbs / 18,000 kg Yield: 13.5 megatons
Thermonuclear Hydrogen Bomb (Tsar Bomba) Length: 26.6 ft / 8 m Weight: 59,400 lbs / 27,000 kg Diameter: 6.6 ft / 2 m Yield: 50 megatons Tested on Oct 30, 1961at Novaya Zemlya Island, (north of the Russia)
See Tsar Bomba explosion: http://www.youtube.com/watch?v=FfoQsZa8F1c and http://www.youtube.com/watch?v=BmQIkDkZ7sk
Assignment 23.5 & 23.6 pg. 996 #38, 40, 41, 44 to 46 Page 242.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
23.7 & 23.8: Uses of Isotopes & Biological Effects of Radiation Some Uses of Isotopes: 1. Structural Determination: - when a molecular or polyatomic ion structure is difficult to determine, an isotope of an element in the chemical can be used to study the mechanism of decomposition. This in addition of Infrared Spectral Analysis, we can determine the correct chemical structure of otherwise an ambiguous scenario. 2_ S
Example: Using
35 16
S, thiosulfate, S2O32− is determined to be
O
S
O
instead of
2_ O
S
O
S
O
.
O
Radioactive Tracers: - radioactive elements that leave a path of radiation that can be imaged to determine how the material is taken up by an organism. 2. Study of Photosynthesis: - radioactive tracers like 14C and 18O can be included in determine the path of carbon and oxygen during the process of photosynthesis and other nutrient uptakes 3. Isotopes in Medicine: - compound that contain a radioactive tracer (carrier compound), can be introduced to a patient. An device that can pick up radiation produces an image for the purpose of diagnosis (medical imaging). Some Common Radioactive Tracers and their Usages: Radiotracers
Area of the Body Examine / Treatment
131 53 I
Thyroid
59 26 Fe
Red Blood Cells, Metabolism
Metallic Welds, Corrosion Mechanisms, Engine Wears
Cf
Cervical and Brain Cancer Treatments
Detections of Metal Fatigue and Explosives
P
Eyes, Liver, Tumours
Path and Rate of Adsorption of Plant Nutrients
Radiation Source of Radiotherapy
Food Irradiation, Sterilization of Medical Equipment
Localize Prostate and Cervical Cancer Treatments
Metal Integrity Tests
51 24 Cr
and
252 98 32 15
60 27 Co
192 77 87 38 Sr
Ir
and
47 20 Ca
99 42 Mo
99 43 Tc
Bones Parent Generator of
99 43 Tc
Brain, Myocardium, Thyroid, Lungs, Liver, Gallbladder, Kidneys, Skelton, Blood Flow and Tumours
241 95 Am 133 54
Other Usages
Xe
24 11 Na
Equipment Calibration and Nanoscale Nuclear Batteries Smoke Detection
Heart, Lungs, Brain and Blood Flow Extracellular Fluids, Circulatory System
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Detection of Leaky Pipes
Page 243.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Detecting Radiations: 1. Geiger-Müller Counter: - sometimes refer to as the Geiger Counter. (Hans Geiger worked with Rutherford on his gold-foil experiment. The counter was invented to count the number of α-particles.) - argon gas becomes ionized and when struck by high-energy particle from radioactive decay. The resulting electric potential is amplified and the current can show as the intensity of the radioactivity. Argon ion
Radiation
Argon
2. Scintillation Counter: - zinc sulfide and other substances give off light when struck by high-energy particle from radioactive decay. A photocell measures the intensity of the light produced and gives the measure as the number of decay events per unit of time.
Radiation Damages: - high-energy particles generated by nuclear decays can cause damage to organisms. Depending on the doses, it can be shown either immediately or years after exposure. a. Somatic Damage: - radiation damage to the organism’s tissues or cell structures causes sickness or death. Examples: Sunburn, hear rash, cancer, and cataracts b. Genetic Damage: - radiation damage to the genetic code or reproduction process of the organism, which causes mutations in the offspring. Examples: Genetic and DNA mutations
Page 244.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Sources of Radiation: 1. Natural Radiations: - small amounts of radiation happened naturally from the environment. ¾ Cosmic radiation from outer space and the sun (amounts vary by elevation from sea level). ¾ Ground radiation from Earth’s interior that is responsible from heat of hot springs and geyser to the molten core of the planet. It is also present in organic food and water, building material such as bricks and wood products. ¾ Air radiation from randon-222 (inert gas from natural uranium deposits); easily inhale from basement cracks. Randon-222 is also found in tobacco smoke (man-made radiation). ¾ Human tissues contains about 20 mg of potassium-40 that emit pulses of radioactivity over time. 2. ¾ ¾ ¾ ¾ ¾
Man-Made Radiations: - radiations that are artificially created (intentional and unintentional). Medical procedures such as X-ray and radiotherapy and radio-diagnostic procedures. Consumer products like television tubes. Proximity to Power Generators like nuclear and coal power plants. Aviation from airline travels. Nuclear Weapon Testing Fallouts can travel all around the globe.
Biological Effects from Radiation 1. Radiation Energy Level: - the higher the energy levels (doses), the more the severe are the damages. - radiation doses are measured in rads (radiation absorbed doses – now an obsolete unit), 1 rad = 10 mJ. - rems (roentgen equivalent in man), measures the ability to radiation to cause harm biologically. - it takes 500 rems to be considered lethal radiation dosage if it was given in a short period of time. - smaller radiation on a body can be measured in millirems. (1000 millirems = 1 rem) 2. Penetrating Ability: - the lighter the particles, the more penetrating they can be. In of penetrating ability: γ ray is the strongest, follows by β particles and α particle is the least penetrating. 3. Ionization Ability: - as high-energy particles through tissue, it can cause ionization that is damaging to the organism. α particles ionize the most along its path whereas γ ray does not. Therefore, α particle producers like plutonium and radon can cause severe radiation damage if ingested or inhaled.
4. Radiation Source’s Chemical Properties: - the length of the half-life of a radioactive nuclide can also affect radiation damage. Generally, the longer the half-life, the more damage it can cause. This is because it can reside in the organism for a longer period of time. This is why most radiotracers used in medical diagnosis have half-lives that are at most in days.
Assignment 23.7 & 23.8 pg. 996 #50 Copyrighted by Gabriel Tang B.Ed., B.Sc.
Page 245.
Chemistry AP
Chapter 23: Nuclear Chemistry 23.1: The Nature of Nuclear Reactions Nucleons: - the particles that make up a nucleus of an atom (protons,( 11 p+ or 11 H) and neutrons, ( 01 n)). Isotopes: - atoms that have different mass number but the same atomic number or number of protons. Nuclide: a particular atom or isotope containing specific numbers of protons and neutrons Mass Number (# of p+ and n)
A Z
+
Atomic Number (# of p )
X
Element Symbol (based on Atomic #)
Radioactivity: - the particles and/or electromagnetic radiation that are emitted due to unstable nuclei. - all elements having atomic number 84 (Polonium) and greater are radioactive. Nuclear Transmutation: - a process where radioactivity is resulted from the bombardment of nuclei by neutrons, protons or other nuclei. - in most cases, heavier elements are synthesized from lighter elements. History of Radioactivity • In 1896, Wilhelm Roentgen discovered X-ray by examining ray emitting from the outside of the cathode ray glass tube. It has the capability of ing through solid materials, but can be blocked by denser matters. It can also be exposed to photographic plate, resulting from an image of “seeing through” an container made of less dense material. • In the same year, Antoine Becquerel discovered that uranium emits a ray onto a photographic plate in the absence of sunlight or other forms of energy. • A few years later, Marie and Pierre Curie demonstrated that radiation can be emitted by other elements. They discovered two new elements (polonium and radium) based on their tendency to emit radiation (radioactivity). Types of Radioactive Particle and Decay 1. Alpha Particle (α particle): - basically a helium nucleus ( 42 He), commonly found during radioactive decay from heavier nuclide (the net result is to increase the neutron to proton ratio – more explanation in the next section). Example:
218 84
Po →
214 82
Pb + 42 He
2. Beta Particle (β particle): - basically an electron ( −01 e or −01 β) that is emitted when the neutron to proton ratio is higher than the zone of stability (a neutron is transformed to a proton and an electron as a result – more explanation in the next section). - electrons have a mass number of 0 and an atomic number assignment of −1, due to its charge. Example:
Page 230.
214 82
Pb →
214 83
Bi +
0 −1
e
( 01 n → 11 p +
0 −1
e)
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
3. Gamma Ray (γ ray): - also known as a high-energy photon ( 00 γ) that is usually a by-product of an alpha-particle decay. - photon has no mass and no atomic number. 238 92
Example:
U→
234 90
Th + 42 He + 2 00 γ
4. Positron (e+): - an antimatter of electron ( 10 e or 10 β) that is emitted when the neutron to proton ratio is lower than the zone of stability (a proton is transformed to a neutron as a result more explanation in the next section). - positrons have a mass number of 0 and an atomic number of 1, due to its charge. - when a positron and an electron collide, they annihilate themselves to produce energy (matter-antimatter reaction).
O→
15 8
Example:
15 7
( 11 p → 01 n + 01 e)
N + 01 e
5. Electron Capture: - an inner-orbital electron is “captured” by the nucleus to increase neutron to proton ratio. It is usually accompanied by an emission of gamma ray. 73 33
Example:
0 −1
As +
e→
73 32
Ge + 00 γ
Balancing Nuclear Equations: - the total atomic number (Z) and the total atomic mass (A) have to balance on both sides. Example 1: Balance the following nuclear equations. 222 86
a.
222 86
49 21
11 6
1 1
Po +
48 22
0 −1
Ti +
11 5
B+
0 1
e
H reacts with
H + 20 9
4 2
A: 222 = (218) + (4) Z: 86 = (84 → Po) + (2)
He
1 0
e+
C produces a β particle.
14 6
14 6
C →
14 7
N+
0 −1
A: 14 = (14) + (0) Z: 6 = (7 → N) + (−1)
e
n A: 49 = (48) + (0) + (1) Z: 21 = (22 → Ti) + (−1) + (0)
C produces a positron.
C → 1 1
f.
218 84
b.
Sc produces a β particle and a neutron.
Sc →
11 6
d.
g.
Rn →
49 21
c.
Rn produces an α particle.
15 7
F→
N → 20 10
12 6
15 7
A: 11 = (11) + (0) Z: 6 = (5 → B) + (1)
C +
4 2
He +
Ne + _____
F→
20 10
40 19
K captures an electron to produce γ ray
40 19
K +
e→
0 −1
40 18
Ar +
0 0
γ
A: 40 + (0) = (40) + (0) Z: 19 + (−1) = (18 → Ar) + (0)
N to produce an α particle with γ ray.
A: 20 = 20 + (0) Z: 9 = 10 + (−1) 20 9
e.
Ne +
γ
A: 1 + 15 = (12) + (4) + (0) Z: 1 + 7 = (6 → C) + (2) + (0)
h. 0 −1
0 −1
0 0
e
e
239 94
Pu + ____ →
A: 239 + (4) Z: 94 + (2) 239 94
Pu +
4 2
Copyrighted by Gabriel Tang B.Ed., B.Sc.
242 96
4 2
He →
Cm + 01 n
He 242 96
= 242 + 1 = 96 + 0 Cm + 01 n
i.
54 27
Co → ______ + 10 e
A: 54 = (54) + 0 Z: 27 = (26 → Fe) + 1 54 27
Co →
54 26
Fe + 10 e
Page 231.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
23.2: Nuclear Stability Strong Nuclear Force: - a force of attraction that is present over extremely short distance (1 × 10−15 m) between all nucleons (protons and neutrons). - it is much stronger than electromagnetic force in short distances. However, electromagnetic force is more significant over longer distances. Properties of Neutrons: 1. Neutrons serve as “nuclear cement”, gluing neighbouring protons together despite the electric repulsion of positive charges, but only over short distances. 2. At large distances, strong nuclear force become less significant. Hence, the MORE Protons in the nucleus (Heavier Atoms), the MORE Neutrons are needed to hold them together. Sometimes this means for every 1 proton, there are 1.5 times to twice as many neutrons. 3. SMALLER Atomic Nuclei usually have the SAME Number of Protons as Neutrons. 4. A Single Neutron is rather UNSTABLE. It will CONVERT itself to a Proton and an Electron. 1 0
Strong Nuclear Force
n → 11 H +
0 −1
e → (basically a hydrogen atom)
Electric Repulsion Force
For Small Nucleus, Strong Nuclear Force is MORE significant compared to electric repulsive force between protons due to small distances between nucleons.
Weaker Nuclear Force
Stronger Electric Repulsion Force
For Large Nucleus, Electric Repulsive Force between Protons is MORE significant compared to strong nuclear force because of the large distances between nucleons. Hence, they are inherently unstable and likely undergo alpha decay (see below).
Radioactive Decay: - when a heavier nucleus loses nucleons to become a smaller but more stable nucleus. In the process, it gives off radiation products like alpha-, beta- particles and/or gamma rays. Zone of Stability: - a graph that depicts the relationship between the number of neutrons versus the number of protons, and the area where there are stable nuclides.
Page 232.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Common Observations of Radioactive Decay 1. When a nuclide has 84 or more protons (Z ≥ 84), it tends to be unstable and likely undergo radioactive decay. 2. Lighter nuclides are stable when Z = n (or n : p+ ratio = 1). However, heavier nuclides are stable only when Z < n (or n : p+ ratio > 1).
Too Many Neutrons (Spontaneous β production)
( 01 n → 11 p +
0 −1
e)
3. Nuclides with even # of p+ with even # of n are more stable than nuclides with odd # of p+ and odd # of n.
Example: Most Stable to Least Stable Nuclides ( 126 C, 136 C , 199 F , 63 Li ) Nuclide +
12 6
# of p # of n Stability:
C 6 (even) 6 (even) Most
13 6
C 6 (even) 7 (odd)
19 9
F 9 (odd) 10 (even)
6 3
Li 3 (odd) 3 (odd) Least
Too Many Protons (Spontaneous Positron production)
( 11 p → 01 n + 01 e)
4. Magic Numbers of protons or neutrons (2, 8, 20, 28, 50, 82 and 126) results in very stable nuclides. Thermodynamic Stability: - amount of potential energy inside a nucleus versus total potential energy of all nucleons. - the difference in energy can be calculated using Einstein’s equation (ΔE = Δmc2), where Δm is referred to as mass defect. Mass Defect (Δm): - the change in masses during a nuclear transformation. (Δm = mproducts − mreactants) - sometimes masses for subatomic particles is measured in amu (atomic mass unit) (1 kg = 6.022 × 1026 amu , or 1 g = 6.022 × 1023 amu = 1 mole amu). Subatomic Particle Neutron Proton
Mass (kg) 1.67497 × 10−27 1.67357 × 10−27
Atomic Mass Unit (amu) 1.008665 1.007825
Binding Energy (ΔEbind): - the amount of energy released during a nuclear transformation because of a mass defect. It is used to bind the nucleons in the reactant nuclide. - we often convert the unit to electron volt (1 eV = 1.69 × 10−19 J or 1 MeV = 1.69 × 10−13 J). - higher the ΔEbind per nucleon means more mass is turned into pure energy to bind the nucleons together. Hence, bigger ΔEbind means more stable nuclei (the most stable nuclei is 26Fe). Einstein’s Mass-Energy Conversion ΔEbind = −Δmc2 ΔEbind = Binding Energy Δm = mass defect (kg) c = speed of light (3.00 × 108 m/s)
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Nuclei need to break up to achieve maximum stability (fission) Nuclei need to combine to achieve maximum stability (fusion)
Page 233.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Example 1: Calculate the binding energy for carbon-13 (13.003355 amu) in J/nucleon and MeV/nucleon. m of 136 C = 13.003355 amu m of (6p+ and 7n) = 6(1.007825 amu) + 7(1.008665 amu) = 13.107605 amu Δm = m of 136 C − m of (6p+ and 7n) = 13.003355 amu − 13.107605 amu
Δm = −0.104250 amu
1 kg ⎛ ⎞ 8 2 −11 ΔE = −Δmc2 = −(−0.104250 amu) ⎜ ⎟ (3.00 × 10 m/s) = 1.5580372 × 10 J 26 6.022 × 10 a m u ⎝ ⎠ −11 1.5580372 × 10 J ΔEbind per nucleon = ΔEbind = 1.20 × 10−12 J/nucleon 13 nucleons 1 MeV ΔEbind = 7.09 MeV/nucleon ΔEbind = 1.20 × 10−12 J/nucleon × 1.69 × 10 −13 J Example 2: Calculate the energy released per mole of 235 92
( 235 92 U = 235.0439 amu; minitial of
235 92
141 56
U + 01 n →
141 56
235 92
U reacted when it undergoes nuclear fission:
Ba +
92 36
Ba = 140.9144 amu;
Kr + 3 01 n
92 36
Kr = 91.9262 amu)
U + 01 n = 235.0439 amu + 1.00899 amu = 236.05289 amu
92 1 mfinal of 141 56 Ba + 36 Kr + 3 0 n = 140.9144 amu + 91.9262 amu + 3(1.00899 amu) = 235.86757 amu Δm = mfinal − minital = 235.86757 amu − 236.05289 amu Δm = −0.18532 amu 1 kg ⎞ ⎛ 8 2 −11 ΔE = −Δmc2 = −(−0.18532 amu) ⎜ ⎟ (3.00 × 10 m/s) = 2.76964464 × 10 J/nucleus 26 ⎝ 6.022 × 10 amu ⎠ −11 ΔEbind = 2.76964464× 10 J/nucleus × (6.022 × 1023 nucleus/mol) = 1.66788 × 1013 J/mol
ΔEbind = 1.67 × 1010 kJ/mol = 16.7 TJ/mol
1 TJ (Tera-Joules) = 1 × 1012 J
Assignment 23.1 pg. 994−995 #1 to 6, pg. 996 #55 23.2 pg. 995 #7, 8, 11, 12, 14, 16, 18 to 20; pg. 998 #80 21.3: Natural Radioactivity Decay Series: - a succession of decays from a particular radioactive nuclide until the formation of a stable nuclide. Rate of Decay: - the rate at which a given radioactive nuclide decays over time. - the negative of the change in the number of nuclides per unit of time (measured in reciprocal time unit).
Page 234.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Kinetic Stability: - sometimes called radioactive decay (a process where a nucleus decomposes into a different nucleus to achieve more stability). Derivation Using Calculus: (k = Rate Constant, ΔN Rate = − = kN N = Amount of Nuclide) Δt (Rearrange for Integration, 1 N ΔN = −kΔt ΔN = dN ; Δt = dt)
Non-Calculus Explanation: N = N0e−kt N N0
(Continuous Exp Decay)
= e−kt
(Solving for −kt)
( ) = ln (e−kt) ln ( ) = −kt ln e ln
N
∫
(Natural log both sides)
N N0
N0
(ln e = 1)
N N0
t
1 N
dN = − k ∫ dt
(Integrate Both Sides:
0
∫
1 x
dx = ln x)
(Use Logarithm Law: log A − log B = log ( BA ) )
ln N − ln N0 = −kt ⎛ N ⎞ ⎟⎟ = −kt ln ⎜⎜ ⎝ N0 ⎠
(Radioactive Decay Equation)
Half-Life (t½): - the amount of time it takes to half the amount of radioactive nuclides. - at half-life, t½,, the amount of radioactive nuclides ½ N0 = N : ⎛ N ⎞ ⎛ (1 N ) ⎞ ⎟⎟ = −kt ⇒ ln ⎜⎜ 2 0 ⎟⎟ = −kt½ ⇒ ln (½) = −kt½ ⇒ ln (2) = kt½ ln ⎜⎜ ⎝ N0 ⎠ ⎝ N0 ⎠
t½ =
ln 2 0.693 = k k
Radioactive Decay Equations t
⎛ N ⎞ ln 2 0.693 ⎛ 1 ⎞ t1/2 ⎟⎟ = −kt t½ = = N = N0 ⎜ ⎟ ln ⎜⎜ k k ⎝ 2⎠ ⎝ N0 ⎠ N = Amount of Nuclide at time t N0 = Amount of Nuclide at time 0 k = Rate Constant (s−1, min−1, hr−1, day−1, yr−1) t = total decay time t½ = half-life
Example 1: Technetium-99, the first synthetic element in the Table, is used as a radiotracer for many organs such as heart, liver and lungs. It has a half-life of 6.0 hours. Draw a graph showing how 99 100 mg of 99 43 Tc decays over time. What is the radioactive amount of 43 Tc after 2.00 days?
N=? t
⎛ 1 ⎞ t1/2 N = N0 ⎜ ⎟ ⎝ 2⎠ 48.0 hrs
⎛ 1 ⎞ 6.0 hrs N = (100 mg) ⎜ ⎟ ⎝ 2⎠
N = 0.391 mg
ln 2 k ln 2 k= t1 / 2
Radioactive Decay of Tc-99
t½ =
ln 2 k= 6 hr
⎛ N ⎞ ⎟⎟ = −kt ln ⎜⎜ ⎝ N0 ⎠ N = N0 e−kt
N = (100 mg) e
N = e−kt N0
120 Amount N (mg)
N0 = 100 mg t½ = 6.0 hrs t = 2.00 days = 48.0 hrs
At t½, N = 50 mg (half of 100 mg)
100 80 60 40 20
ln 2 − ( 48.0 hr ) 6 hr
N = 0.391 mg
Copyrighted by Gabriel Tang B.Ed., B.Sc.
0 0
6
t½ = 6 hrs
12
18
24
30
36
42
48
Time (hours)
Page 235.
Unit 4: Thermochemistry and Nuclear Chemistry Example 2:
131 53
Chemistry AP 131 53
I is a radiotracer used to detect thyroid activity. The half-life of
a. Determine the rate constant of
131 53
I.
b. How long will it take a patient to have her initial dosage of initial value? t½ = 8.1 days N N 0 = 0.01
ln 2 k ln 2 k= 8.1 days
a. t½ =
k=? t=?
ln 2 t1 / 2
k=
131 53
I to decrease to 1.00 % of its t
k = 0.086 day−1
t1 / 2
( ) log( ) =t N N0
log( 12 ) (8.1 days)log(0.01) = 53.815 days t= log(0.5)
N N0
N N0
ln 2 8.1 days
t = 54 days Example 3:
222 86
t = 54 days
Rn is a natural alpha particle producer. Due to its noble gas characteristic, it can cause
damage to tissues as it can be easily inhaled into the body. uranium mine because it is a decay product of
238 92
45.7 mg in 24.0 hours. Determine the half-life of N0 = 50.0 mg N = 45.7 mg t = 24.0 hrs
t½ = ? k=?
t
N ⎛ 1 ⎞ t1/2 ⎛ 1 ⎞ t1/2 N = N0 ⎜ ⎟ → =⎜ ⎟ N0 ⎝ 2⎠ ⎝ 2⎠ N t log N0 = t1 / 2 log (½)
( )= −kt ln ( ) ln (0.01) = t= −( −k ) = 53.815 days
b. ln
I is 8.1 days.
222 86
Rn can be found quite easily in
U. In an analysis 50.0 mg 222 86
Solving t½ first:
ln
⎛ 1 ⎞ t1/2 N = N0 ⎜ ⎟ ⎝ 2⎠ log NN0 =
t
N N0
N N0
−t
45.7 mg 50.0 mg
)
( )
− 24.0 hrs
k = 0.00375 hr−1
t½ =
t log( 12 ) (24.0 hrs ) log(0.5) = 45.7 mg log NN0 log(50 .0 mg )
( )
Then solve for k: ln 2 ln 2 ln 2 t½ = k= = k t1 / 2 185 hrs
t½ = 185 hours = 7.71 days
k = 0.00375 hr−1 14 6
C can be found naturally in organic material
and the atmosphere. It decays as soon as the organism dies ( 146 C → - uses the known ratio of
14 6
0 −1
e+
14 7
N).
12 6
C/ C of similar organic sample of the day with the ratio in the
artefact and the half-life of
Page 236.
t
N ⎛ 1 ⎞ t1/2 → =⎜ ⎟ N0 ⎝ 2⎠ t t1 / 2 log (½)
t½ = 185 hours = 7.71 days
Then, solve for t1/2: ln 2 ln 2 t½ = = k 0.0037468628 hr −1
Radiocarbon Dating: - sometimes called carbon-14 dating.
Rn decayed to
Rn and its rate constant.
Solving k first:
( )= −kt ln ( ) ln ( = k=
222 86
14 6
C being 5730 years to determine the age of the artefact.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Example 4: An ancient wooden artefact found in China has a 146 C decay rate of 5.2 counts per minute per gram of carbon. A comparison to a freshly cut piece of wood has a count of 13.6 counts per minute per gram of carbon. Given the rate of carbon-14 decay is 5730 years, determine the age of this artefact. kN Final Rate at t 5.2 counts/ (min • g ) = = 13.6 counts/ (min • g ) Initial Rate at t = 0 kN 0
t=?
t½ = 5730 yrs
First, we solve for k. ln 2 ln 2 ln 2 t½ = → k= = k = 1.209680943 × 10−4 yr−1 k 5730 yrs t1 / 2 Next, we solve for t. ln NN0 ⎛ N ⎞ ln (135..26 ) ⎟⎟ = −kt → = ln ⎜⎜ t= = 7947.642495 yrs t = 7948 years ln 2 − − k ( ) N ⎝ 0⎠ 5730 yrs
( )
Uranium-238 Dating: - due to its lengthy half-life (4.5 × 109 years), it is used to date rocks and other 206 238 206 ancient inorganic material. 238 92 U/ 82 Pb ratio is used as 92 U eventually decays to stable 82 Pb. 238 92
U →
Example 5: A piece of ore containing Suppose that no life of
238 92
206 82
206 82
238 92
Pb + 8 42 He + 6
U and
206 82
0 −1
t½ = 4.51 × 109 years
e
Pb was found. The ratio between
206 82
Pb to
238 92
U is 0.432.
Pb was originally present. Determine the age of the ore given that the half-
U is 4.5 × 109 years.
N of 206 N of 238 N 432 92 U still present 82 Pb at t = = = 0.432 = ⇒ 238 N0 1000 N of 92 U at t N of 238 92 U before t½ = 4.5 × 109 yrs
238 92 238 92
U now 1000 1000 = = 206 U + 82 Pb 1000 + 432 1432
t=?
First, we solve for k. ln 2 ln 2 ln 2 k = 1.54032707 × 10−10 yr−1 t½ = → k= = k t1 / 2 4.5 ×10 9 yrs Next, we solve for t. ln NN0 ⎛ N ⎞ ln (1000 1432 ) ⎜ ⎟ = = 2,331,141,717 yrs ln ⎜ = − kt → t = t = 2.3 billion years ⎟ −k − 4.5×ln1029 yrs ⎝ N0 ⎠
( )
(
)
Potassium-40 Dating: - used mainly in geochemistry to determine the age a metal ores. Its main mode of 9 40 decay via electron capture 40 19 K turns it into 18 Ar with a half-life of 1.2 × 10 years. Using a mass spectrometer, we can easily measure the amount of inside the lattice mineral. By calculating the of a metal ore. 40 19
K +
0 −1
e →
40 18
Ar
40 18
Ar /
40 19
40 18
Ar trapped
K, we can determine the age
t½ = 1.2 × 109 years
Assignment 23.3 pg. 995 #21, 23 to 26, 28, 29; pg. 997−998 #66 to 68, 85 Copyrighted by Gabriel Tang B.Ed., B.Sc.
Page 237.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
23.4: Nuclear Transmutation Nuclear Transmutation: - the reaction where one element is converted to another element by changing the number of protons. Transuranium Elements: - elements that have been synthesized by nuclear transformation after the last natural element, uranium. Example:
244 94
Pu +
48 20
Ca →
289 114
Uuq + 3 01 n
(Discovered in 1998 and t1/2 = 30 seconds)
Particle Accelerator: - a device that alternates electric field to speed up a particle to add into a target nuclide. a. Cyclotron: - a type of particle accelerator that utilizes a changing electric field along with a magnetic field to increase the speed of an ion around a disc before hitting a target nuclide. COMET: A medical superconducting cyclotron. It is used to generate thallium-201 (coronary arteries) and gallium-67 (soft-tissue tumors). It can also produce radiopharmaceutical needed for PET and SPECT scans Schematic of Accelerated charged particle a Cyclotron to collide with target nuclide
b. Linear Accelerator: - a particle accelerator that speeds up a particle by using an alternating electric field at different segment of a linear tube to add an ion into a target nuclide. Left: Schematic of a Linear Accelerator Right: Stanford Linear Accelerator Linear Accelerator Computer Program is used to control radiotherapy Multileaf treatment by a Collimeter medical linear to shape the accelerator beam Schematic of a Medical Linear Accelerator
Page 238.
Assignment 23.4 pg. 996 #33 to 36
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
23.5: Nuclear Fission Nuclear Fission: - the breaking up of a heavier nucleus into two nuclei with small mass number. Example:
235 92
U + 01 n →
141 56
Ba +
92 36
Kr + 3 01 n
ΔH = 2.0 × 1010 kJ/mol
Chain Reaction: - when the nuclear fission is self-sustaining. a. Subcritical: - when there is on average, less than one neutron produced per 235 92 U is consumed. The fission will eventually stop. b. Critical: - when there is on average, exactly one neutron produced per 235 92 U consumed. The fission can then be self-sustaining at the same level. c. Supercritical: - when there is one average, more than one neutron produced per 235 92 U is consumed. The fission can increase its rate rapidly and a violent explosion can result. Critical Mass: - the minimum mass of fissionable material required for the generation of a self-sustaining nuclear chain reaction. Spontaneous Fission: - when a heavy nuclide splits into two lighter nuclides and sometimes neutrons. Example:
256 100
Fm →
140 54
Xe +
112 46
Pd + 4 01 n
Atomic Bomb: - an uncontrolled nuclear fission device that releases large amount of energy. - in 1939, just before WWII, Einstein and other scientists wrote to President Roosevelt that Nazi was researching ways to purify U-235 for the purpose of an atomic bomb. This led to the US initiation of the “Manhattan Project” (a secret project to develop the atomic bomb by the US). - the first atomic bomb test was conducted at Jemez Mountains in northern New Mexico on July 16, 1945 at 5:29:45 AM (Mountain War Time). Less than a month later, an atomic bomb (code name: Little Boy) was dropped on Hiroshima, Japan on Aug 6. It had a yield of 15 kilotons of TNT (6 × 1010 kJ ≈ 750 g of U235) and it killed an estimated 80,000 people with 60,000 died later of radiation poisoning. Three days later, another atomic bomb (code name: Fat Man) was dropped on Nagasaki. It had a yield of 21 kilotons of TNT (8 × 1010 kJ ≈ 1 kg of Pu-239) and killed 74,000 people with several hundred thousands died from disease due to radiation. - the “gun-type assembly” design detonation starts with conventional TNT explosion at one end of the device, pushing half the U-235 / Pu-239 subcritical mass into another half of the U-235 / Pu-239 subcritical mass located at the other end of the bomb. When the two masses connect, a supercritical chain reaction takes place and releases a large amount of heat energy. The “implosion” design involves detonate surrounding TNT to ignite a nuclear fission core. Plutonium Implosion Uranium “Gun” Atomic Bomb (Little Boy) Length: 10 ft / 3 m Diameter: 28 in / 71.1 m Weight: 9,700 lbs / 4,400 kg Yield: 15 kilotons
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Atomic Bomb (Fat Man) Length: 10.7 ft / 3.25 m Diameter: 5 ft / 1.5 m Weight: 10,265 lbs / 4,656 kg Yield: 21 kilotons
Page 239.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Nuclear Reactors: - fission reactors where enriched 235 92 U is placed in the reactor core. The heat is generated in the reactor is used to heat water. This water also acts as the (a substance that slows down neutrons emitted and reduces their kinetic energy). Control rods (usually made of carbon, cium, or boron to absorb extra neutrons) can be lifted or lowered to control the rate of the fission process. The super-heated water from the reactor core heats another tank of water, but the water is recycled back into the reactor. As the water in the tank is heated into steam, it turns the steam turbine to generate electricity. This water is then cooled in a cooling tower and recycled (the hot water cannot be discharged into nearby lake or stream to avoid thermal pollution). Since large amount of cold water is needed for the cooling process of steam, most nuclear power plants are built near a large river or lake. - the by-products of 235 92 U fission have a very long half-lives and can remain radioactive for a long time. Great efforts are needed to dispose of the wastes properly. The danger of a nuclear meltdown is also a constant danger as in the cases of Three Mile Island, Pennsylvania in 1979 and Chernobyl, Ukraine in 1986.
Bruce Power Nuclear Plant at Tiverton (Lake Huron), Canada
Light Water Reactor: - uses light water (regular H2O) as . - all US nuclear reactors are light-water reactors and they use cium or boron control rods. - since light water is a good absorber of neutrons, the uranium fuel used has to be enriched (the same initial process is used to make weapon-grade uranium, 235U). Heavy Water Reactor: - uses heavy water (D2O – deuterium water - 21 H2O) as . - D2O dose not absorb neutrons as well as H2O (it has a neutron in the hydrogen atom already). Hence, the nuclear reactor is more efficient (more neutrons are left to do more fission collisions). As a result, uranium enrichment is not necessary. This eliminates the potential of a country to develop nuclear weapons. - D2O can be expensive to produce due to the amount of water needed for operating a nuclear power plant. Currently, Canada is the only country that uses heavy water reactor (CANDU reactor). Breeder Reactor: - due to the limited resources of enriched uranium 235 92 U, the excess neutrons in the fission reactor can be used to convert uranium-238 to plutonium-239 to be used as an alternate nuclear fuel. 238 92
U + 01 n →
239 94
Pu + 2
0 −1
e
- it is the most expensive type of reactor due to the its technical aspects. Currently, only Russia and have a handful of breeder reactors.
Page 240.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
23.6: Nuclear Fusion Nuclear Fusion: - the combining of two light nuclei into a heavier and more stable nucleus. Example:
2 1
H + 31 H → 42 He + 01 n
ΔH = 1.7 × 109 kJ/mol
- the availability of hydrogen isotopes, deuterium ( 21 H) and tritium ( 31 H), in sea water and the harmless product, 42 He, makes nuclear fusion an environmental friendly alternative to generate power. - however, fusion reactions such as the one above usually require an initial temperature above 4 × 107 K to overcome the strong electrostatic repulsion between the two protons (the release of significant binding energy can only achieve when the distance between the two protons is approximately 10−15 m). High-powered laser and heating by electric currents are being studied as Fusion reaction is the driving methods to attain this high temperature to initial a control fusion reaction. force of our sun’s energy.
European Tokamak Fusion Test Reactor Vacuum Vessel employs the design of a toroid with a super strength magnetic field to contain plasma without having it touch the wall of the reactor. A similar experimental fusion reactor can also be found at Princeton, USA.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Propose Schematic of a Fusion Reactor to Generate Electricity
Page 241.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Hydrogen Bomb: - also called a thermonuclear bomb that uses fusion reaction to destroy a large target area. - the device contains solid lithium deuteride (LiD or Li 21 H) which can be packed tightly. The detonations involve a fission reaction to generate the initial heat to start the fusion reaction. 2 1
H + 21 H → 31 H + 11 H
- fusion reaction is not limited by a critical mass as in fission reaction. Hence, the size of the explosion depends on the amount of fusion material. - besides the intense heat to incinerate a large area, the damaging radiation effects come from the products of the fission starter and the product of the fusion reaction, tritium, has a half-life of 12.5 yrs. However, other radioactive material with longer half-life, such as Co-59, can be used to spread harmful radiations.
Differences in yields between atomic (fission) and thermonuclear (fusion) bombs
Thermonuclear Hydrogen Bomb (Teller-Ulam) Length: 18.8 ft / 5.7 m Diameter: 5 ft / 1.5 m Weight: 39,600 lbs / 18,000 kg Yield: 13.5 megatons
Thermonuclear Hydrogen Bomb (Tsar Bomba) Length: 26.6 ft / 8 m Weight: 59,400 lbs / 27,000 kg Diameter: 6.6 ft / 2 m Yield: 50 megatons Tested on Oct 30, 1961at Novaya Zemlya Island, (north of the Russia)
See Tsar Bomba explosion: http://www.youtube.com/watch?v=FfoQsZa8F1c and http://www.youtube.com/watch?v=BmQIkDkZ7sk
Assignment 23.5 & 23.6 pg. 996 #38, 40, 41, 44 to 46 Page 242.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
23.7 & 23.8: Uses of Isotopes & Biological Effects of Radiation Some Uses of Isotopes: 1. Structural Determination: - when a molecular or polyatomic ion structure is difficult to determine, an isotope of an element in the chemical can be used to study the mechanism of decomposition. This in addition of Infrared Spectral Analysis, we can determine the correct chemical structure of otherwise an ambiguous scenario. 2_ S
Example: Using
35 16
S, thiosulfate, S2O32− is determined to be
O
S
O
instead of
2_ O
S
O
S
O
.
O
Radioactive Tracers: - radioactive elements that leave a path of radiation that can be imaged to determine how the material is taken up by an organism. 2. Study of Photosynthesis: - radioactive tracers like 14C and 18O can be included in determine the path of carbon and oxygen during the process of photosynthesis and other nutrient uptakes 3. Isotopes in Medicine: - compound that contain a radioactive tracer (carrier compound), can be introduced to a patient. An device that can pick up radiation produces an image for the purpose of diagnosis (medical imaging). Some Common Radioactive Tracers and their Usages: Radiotracers
Area of the Body Examine / Treatment
131 53 I
Thyroid
59 26 Fe
Red Blood Cells, Metabolism
Metallic Welds, Corrosion Mechanisms, Engine Wears
Cf
Cervical and Brain Cancer Treatments
Detections of Metal Fatigue and Explosives
P
Eyes, Liver, Tumours
Path and Rate of Adsorption of Plant Nutrients
Radiation Source of Radiotherapy
Food Irradiation, Sterilization of Medical Equipment
Localize Prostate and Cervical Cancer Treatments
Metal Integrity Tests
51 24 Cr
and
252 98 32 15
60 27 Co
192 77 87 38 Sr
Ir
and
47 20 Ca
99 42 Mo
99 43 Tc
Bones Parent Generator of
99 43 Tc
Brain, Myocardium, Thyroid, Lungs, Liver, Gallbladder, Kidneys, Skelton, Blood Flow and Tumours
241 95 Am 133 54
Other Usages
Xe
24 11 Na
Equipment Calibration and Nanoscale Nuclear Batteries Smoke Detection
Heart, Lungs, Brain and Blood Flow Extracellular Fluids, Circulatory System
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Detection of Leaky Pipes
Page 243.
Unit 4: Thermochemistry and Nuclear Chemistry
Chemistry AP
Detecting Radiations: 1. Geiger-Müller Counter: - sometimes refer to as the Geiger Counter. (Hans Geiger worked with Rutherford on his gold-foil experiment. The counter was invented to count the number of α-particles.) - argon gas becomes ionized and when struck by high-energy particle from radioactive decay. The resulting electric potential is amplified and the current can show as the intensity of the radioactivity. Argon ion
Radiation
Argon
2. Scintillation Counter: - zinc sulfide and other substances give off light when struck by high-energy particle from radioactive decay. A photocell measures the intensity of the light produced and gives the measure as the number of decay events per unit of time.
Radiation Damages: - high-energy particles generated by nuclear decays can cause damage to organisms. Depending on the doses, it can be shown either immediately or years after exposure. a. Somatic Damage: - radiation damage to the organism’s tissues or cell structures causes sickness or death. Examples: Sunburn, hear rash, cancer, and cataracts b. Genetic Damage: - radiation damage to the genetic code or reproduction process of the organism, which causes mutations in the offspring. Examples: Genetic and DNA mutations
Page 244.
Copyrighted by Gabriel Tang B.Ed., B.Sc.
Chemistry AP
Unit 4: Thermochemistry and Nuclear Chemistry
Sources of Radiation: 1. Natural Radiations: - small amounts of radiation happened naturally from the environment. ¾ Cosmic radiation from outer space and the sun (amounts vary by elevation from sea level). ¾ Ground radiation from Earth’s interior that is responsible from heat of hot springs and geyser to the molten core of the planet. It is also present in organic food and water, building material such as bricks and wood products. ¾ Air radiation from randon-222 (inert gas from natural uranium deposits); easily inhale from basement cracks. Randon-222 is also found in tobacco smoke (man-made radiation). ¾ Human tissues contains about 20 mg of potassium-40 that emit pulses of radioactivity over time. 2. ¾ ¾ ¾ ¾ ¾
Man-Made Radiations: - radiations that are artificially created (intentional and unintentional). Medical procedures such as X-ray and radiotherapy and radio-diagnostic procedures. Consumer products like television tubes. Proximity to Power Generators like nuclear and coal power plants. Aviation from airline travels. Nuclear Weapon Testing Fallouts can travel all around the globe.
Biological Effects from Radiation 1. Radiation Energy Level: - the higher the energy levels (doses), the more the severe are the damages. - radiation doses are measured in rads (radiation absorbed doses – now an obsolete unit), 1 rad = 10 mJ. - rems (roentgen equivalent in man), measures the ability to radiation to cause harm biologically. - it takes 500 rems to be considered lethal radiation dosage if it was given in a short period of time. - smaller radiation on a body can be measured in millirems. (1000 millirems = 1 rem) 2. Penetrating Ability: - the lighter the particles, the more penetrating they can be. In of penetrating ability: γ ray is the strongest, follows by β particles and α particle is the least penetrating. 3. Ionization Ability: - as high-energy particles through tissue, it can cause ionization that is damaging to the organism. α particles ionize the most along its path whereas γ ray does not. Therefore, α particle producers like plutonium and radon can cause severe radiation damage if ingested or inhaled.
4. Radiation Source’s Chemical Properties: - the length of the half-life of a radioactive nuclide can also affect radiation damage. Generally, the longer the half-life, the more damage it can cause. This is because it can reside in the organism for a longer period of time. This is why most radiotracers used in medical diagnosis have half-lives that are at most in days.
Assignment 23.7 & 23.8 pg. 996 #50 Copyrighted by Gabriel Tang B.Ed., B.Sc.
Page 245.
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