1. Radioactivity & Nuclear Chemistry
OAKTON
Community College
101 • Introductory Chemistry
Dr. Maria Yermolina
Radioactivity & Nuclear Chemistry

2. Depicting Atoms Depicting Atom Basic Chemistry I
Lecture 3, September 14

3. Depicting Atoms Depicting Atom Basic Chemistry I
Lecture 3, September 14

4. Isotopes
Isotopes
Basic Chemistry I
Lecture 3, September 14

5. Skillbuilder Skillbuilder A. Basic Chemistry I Lecture 3, September 145

6. Skillbuilder
Skillbuilder A.
Basic Chemistry I
Lecture 3, September 14

7. The strong nuclear force acts between two nucleons:
Skillbuilder
Skillbuilder
How do protons and neutrons are held together so tightly in the nucleus?
The strong nuclear force acts between two nucleons:
Four Fundamental Forces: the gravitational and electromagnetic interactions, which produce significant long-range forces whose effects can be seen directly in everyday life, and the strong and weak interactions, which produce forces at subatomic distances and govern nuclear interactions.
The strong force is one of the four basic forces in nature and is about 100 times stronger than the electric force. The attractive forces between all the protons and neutrons in a nucleus keep the nucleus together. However, protons and neutrons have to be close together, like they are in the nucleus, to be attracted by the strong force. The strong force is a short-range force that quickly becomes extremely weak as protons and neutrons get farther apart. The electric force is a long-range force, so protons that are far apart still are repelled by the electric force, as shown in
Nucleon: a proton or a neutron

8. The Strong Nuclear Force Skillbuilder
How do protons and neutrons are held together so tightly in the nucleus?
The strong nuclear force acts between two nucleons:
> m
The strong force is one of the four basic forces in nature and is about 100 times stronger than the electric force. The attractive forces between all the protons and neutrons in a nucleus keep the nucleus together. However, protons and neutrons have to be close together, like they are in the nucleus, to be attracted by the strong force. The strong force is a short-range force that quickly becomes extremely weak as protons and neutrons get farther apart. The electric force is a long-range force, so protons that are far apart still are repelled by the electric force, as shown in
Nucleon: a proton or a neutron

9. A Multinucleon Nucleus
Skillbuilder
Protons and neutrons are held together less tightly in large nuclei. The circle shows the range of the attractive strong force.
Small nuclei have few protons, so the repulsive force on a proton due to the other protons is small. (A) A proton on the surface is attracted by the six or seven nearest nucleons.
In large nuclei, the attractive strong force is exerted only by the nearest neighbors, but all the protons exert repulsive forces. The total repulsive force is large. (B)

10. Radioactivity Skillbuilder
If a strong force is not large enough (atoms with more than 83 protons) to hold a nucleus together tightly, the nucleus can decay and give off matter and energy to adjust the neutron-proton imbalance.
Radioactivity (or radioactive decay): a spontaneous process of nuclei undergoing a change by emitting particles or rays.
Nuclide (or radionuclide): nuclei that undergo spontaneous decay (=disintegration). Example: 238U or 14C.
Discovered by Henri Becquerel in 1896.
Pier and Marie Curie discovered Po, U and Ra. Nobel Prize in 1903.

11. Three Components of Radiation
Skillbuilder
An electric field separates the rays from a radioactive source or a heavy nuclides, such as uranium, into:
alpha (a) particles = positively charged helium nuclei, 42He;
beta (b) particles = negatively charged electrons;
neutral gamma (g) rays = high –energy electromagnetic radiation
General Nuclear Equation:
A ➝ B + b
A = the parent nucleus, B = the daughter nucleus, b = the emitted particle or ray

12. General Terms
Nuclide: a nucleus with a specified number of neutrons (almost synonymous with “isotope”, “isotone”, “isobar”, etc)
Refers more to the “thing” rather than the “type of matter”
Radioactive Nuclide: a nuclide that undergoes a spontaneous nuclear decay process
With a corresponding release of some energetic particle (or photon)
Radiation: general (historic) term for the kind of energetic particles (or photons) that are emitted from a sample containing radioactive nuclides. Many kinds:
Alpha, beta, gamma, positron
Stable Nuclide*: a nuclide that does not undergo any spontaneous nuclear decay process. *more on “stable” later

13. Not all nuclear reactions are decay!
Kinds of Nuclear Reactions
Not all nuclear reactions are decay!
Spontaneous Nuclear Decay (discussed first)
Radioactive nuclides (only)
one (“reactant”) nuclide turns into another nuclide
not initiated (just happens)
Other nuclear reactions (later)
Generally involve initiation & more than one nuclide as “reactants”.
Fission and Fusion
Transmutation (bombardment) reactions

14. a Emission Skillbuilder
Alpha emission: the expulsion of an alpha particle from an unstable, disintegrating nucleus; travels from 2 to 12 cm through the air, depending on the NRG source; easily stopped by a sheet of paper close to the nucleus.
Notice:
The total charge is conserved during a nuclear reaction.
This means that the sum of the subscripts for the products must equal the sum of the subscripts for the reactants.

15. Skillbuilder b Emission
2. Beta emission: ejecting electron at a high speed; increasing the amount of protons in a nucleus; more penetrating than a particles; may travel several hundreds cm thought the air; stopped by a thin layer of metal. +
Transmutation: the process of changing one element to another through nuclear decay.

16. Skillbuilder g Emission
3. Gamma emission: a high-NRG burst of electromagnetic radiation (photon) from an excited nucleus so it can return to a lower NRG state; can completely pass a person but can be stopped by a 5 cm thick piece of lead or concrete close to the source; no change in the number of nucleons. or

17. Positron Emission Skillbuilder
4. Positron emission: occurs when an unstable nucleus emits a positron; positron is the antiparticle of the electron: the same mass but opposite charge.
If a positron collides with an electron, the two particles destroy each other, releasing energy in the form of gamma rays. In positron emission, a proton is converted into a neutron and emits a positron:

18. Electron Capture Skillbuilder
5. Electron Capture: involves a particle being absorbed by instead of emitted from an unstable nucleus. Electron capture occurs when a nucleus assimilates an electron from an inner orbital of its electron cloud. Like positron emission, the net effect of electron capture is the conversion of a proton into a neutron.

19. Summary: Modes of Radioactive Decays
Skillbuilder

20. Overview: Table 20.1 in Tro (2nd part)
Summary: Modes of Radioactive Decays
Overview: Table 20.1 in Tro (2nd part)

21. Skillbuilder
What Kind of Decay and How Many Protons and Neutrons Are in the Daughter?, Continued ?
5 p+
4 n0
= proton
= neutron
= positron
Positron emission giving a daughter nuclide with
four protons and five neutrons

22. b emission giving a daughter nuclide with
Skillbuilder
What Kind of Decay and How Many Protons and Neutrons Are in the Daughter?, Continued ?
9 p+
12 n0
= proton
= neutron
= electron
b emission giving a daughter nuclide with
10 protons and 11 neutrons

23. Skillbuilder
What Kind of Decay and How Many Protons and Neutrons Are in the Daughter? ?
11 p+
9 n0
= proton
= neutron
a emission giving a daughter nuclide with
nine protons and seven neutrons

24. Write a nuclear equation for each of the following:
Skillbuilder
Write a nuclear equation for each of the following:
alpha emission from U–238
beta emission from Ne–24
positron emission from N–13
electron capture by Be–7
Tro: Chemistry: A Molecular Approach

25. Band of Stability Skillbuilder
What does stable mean? Stable means atom does not undergo radioactive decay.
a-emission
As the number of protons increase, the neutron-to proton ratio of the stable nuclei also increases in a band of stability: the region in which stable nuclides lie in a plot of number of protons against number of neutrons.
When you plot each stable nuclide on a graph of protons vs. neutrons, stable nuclei fall in a certain region, or band. Nuclei outside this band of stability are radioactive.
b-emission

26. there are no stable nuclei
Band of Stability
Skillbuilder
a-emission
for Z = ,
stable N/Z ≈ 1
b-emission
for Z = ,
stable N/Z approaches 1.25
for Z = ,
stable N/Z approaches 1.5
for Z > 83,
there are no stable nuclei

27. Number of Stable Nuclides with Even and Odd Numbers of Nucleons
Band of Stability
Skillbuilder
Number of Stable Nuclides with Even and Odd Numbers of Nucleons
Even numbers (of nucleons) appear to correlate with stability. Theory of nucleon energy levels is beyond the scope of this course.

28. Band of Stability
The stable nuclides lie in a very narrow band of neutron-to-proton ratios.
The ratio of neutrons to protons in stable nuclides gradually increases as the number of protons in the nucleus increases.
Light, stable nuclides, such as 12C, contain about the same number of neutrons and protons.
Heavy, stable nuclides, such as 204Hg, contain up to 1.55 times as many n’s as p’s.
There are no stable nuclides with atomic numbers larger than 83 (209Bi is last stable one).
This narrow band (valley) of stable nuclei is surrounded by a sea of instability.
Nuclei that lie below the valley don't have enough neutrons and are therefore neutron-poor. They tend to decay via P.E. or E.C.
Nuclei that lie above the valley have too many neutrons and are therefore neutron-rich. They tend to decay via b-decay
Nuclei that lie “beyond” the valley have too much of both. They tend to decay by a-decay

29. Radioactive Decay Series
The stable nuclides lie in a very narrow band of neutron-to-proton ratios.
The ratio of neutrons to protons in stable nuclides gradually increases as the number of protons in the nucleus increases.
Light, stable nuclides, such as 12C, contain about the same number of neutrons and protons.
Heavy, stable nuclides, such as 204Hg, contain up to 1.55 times as many n’s as p’s.
There are no stable nuclides with atomic numbers larger than 83 (209Bi is last stable one).
This narrow band (valley) of stable nuclei is surrounded by a sea of instability.
Pa = PROTACTINIUM
Nuclei that lie below the valley don't have enough neutrons and are therefore neutron-poor. They tend to decay via P.E. or E.C.
Nuclei that lie above the valley have too many neutrons and are therefore neutron-rich. They tend to decay via b-decay
Nuclei that lie “beyond” the valley have too much of both. They tend to decay by a-decay

30. Band of Stability NOTE:
40K half-life 1.3 x 109 yr
NOTE:
The farther away a nuclide is from the valley of stability, the shorter its half life.
“Farther = less (kinetically) stable”
261Db half-life 27 s
15C half-life s
214Po half-life 164 ms

31. Rules of Nuclear Stability
Skillbuilder
All isotopes with an atomic number greater than 83 have an unstable nucleus.
Isotopes that contain 2, 8, 20, 28, 50, 82, or 126 protons or neutrons in their nuclei are more stable than those with other numbers of protons and neutrons.
Pairs of protons and pairs of neutrons have increased stability, so isotopes that have nuclei with even numbers of both protons and neutrons are generally more stable than those that have nuclei with odd numbers of both protons and neutrons.
Isotopes with an atomic number less than 83 are stable when the ratio of neutrons to protons in the nucleus is about 1:1 in isotopes with up to 20 protons, but the ratio increases in larger nuclei in a band of stability. Isotopes with a ratio to the left or right of this band are unstable and thus will undergo radioactive decay.
200 80 Hg

32. Rules of Nuclear Stability
Skillbuilder
All isotopes with an atomic number greater than 83 have an unstable nucleus.
Isotopes that contain 2, 8, 20, 28, 50, 82, or 126 protons or neutrons in their nuclei are more stable than those with other numbers of protons and neutrons.
Pairs of protons and pairs of neutrons have increased stability, so isotopes that have nuclei with even numbers of both protons and neutrons are generally more stable than those that have nuclei with odd numbers of both protons and neutrons.
Isotopes with an atomic number less than 83 are stable when the ratio of neutrons to protons in the nucleus is about 1:1 in isotopes with up to 20 protons, but the ratio increases in larger nuclei in a band of stability. Isotopes with a ratio to the left or right of this band are unstable and thus will undergo radioactive decay. 4 2 He 16 8 O 58 28 Ni
118 50 Sn

33. Rules of Nuclear Stability
Skillbuilder
All isotopes with an atomic number greater than 83 have an unstable nucleus.
Isotopes that contain 2, 8, 20, 28, 50, 82, or 126 protons or neutrons in their nuclei are more stable than those with other numbers of protons and neutrons.
Pairs of protons and pairs of neutrons have increased stability, so isotopes that have nuclei with even numbers of both protons and neutrons are generally more stable than those that have nuclei with odd numbers of both protons and neutrons.
Isotopes with an atomic number less than 83 are stable when the ratio of neutrons to protons in the nucleus is about 1:1 in isotopes with up to 20 protons, but the ratio increases in larger nuclei in a band of stability. Isotopes with a ratio to the left or right of this band are unstable and thus will undergo radioactive decay. 60 27 Co

34. Rules of Nuclear Stability
Skillbuilder
All isotopes with an atomic number greater than 83 have an unstable nucleus.
Isotopes that contain 2, 8, 20, 28, 50, 82, or 126 protons or neutrons in their nuclei are more stable than those with other numbers of protons and neutrons.
Pairs of protons and pairs of neutrons have increased stability, so isotopes that have nuclei with even numbers of both protons and neutrons are generally more stable than those that have nuclei with odd numbers of both protons and neutrons.
Isotopes with an atomic number less than 83 are stable when the ratio of neutrons to protons in the nucleus is about 1:1 in isotopes with up to 20 protons, but the ratio increases in larger nuclei in a band of stability. Isotopes with a ratio to the left or right of this band are unstable and thus will undergo radioactive decay. 40 20 Ca 14 6 C 3 1 T
not radioactive
radioactive

35. K Ne Pb Pu Skillbuilder Skillbuilder 40 24 128 214
Predict if the the following nuclei are radioactive or stable.
Give your reasoning behind each prediction. 40 K
Radioactive, having an odd number of protons (19) and an odd number of neutrons (21). 24 Ne
Stable, because even numbers of protons and neutrons are usually stable.
128 Pb
Stable, because there are even numbers of protons and neutrons and because 82 is a particularly stable number of nucleons
214 Pu
Radioactive, an atomic number greater than 83.

36. Al Tc Sn Hg Skillbuilder Skillbuilder 25 95 120 200
Predict if the the following nuclei are radioactive or stable.
Give your reasoning behind each prediction. 25 Al
Radioactive, have an odd number of protons (13) and an even number of neutrons (12), not 1:1ratio. 95 Tc
Stable, have an odd number of protons (43) and an even number of neutrons (52) in 1:1.25 ratio, falls into a band of stability.
120 Sn
Stable, because there are even numbers of protons and neutrons and because 50 is a particularly stable number of nucleons
200 Hg
Stable, because even numbers of protons and neutrons are usually stable.

37. Summary of Strategy for Predicting Decay Type
First determine if “above, below, or beyond” the valley of stability:
If Z > 83, it is “Beyond”
Not always “correct”, but correct prediction
If Z ≤ 83, Figure out if the nuclide has:
“too many neutrons” (“Above”) OR
“too few neutrons” (“Below”)
(NOTE: long way or shortcut way*; even if you use shortcut, be able to relate it to the n/p ratio!)
Then make conclusion by noting which process makes daughter closer to the “valley”
*Discussed later

38. Summary of Strategy for Predicting Decay Type
It turns out that…
A radioactive nuclide tends to decay in such a way that its daughter nuclide is closer to the valley of stability
b decay: turns n to p
 used by nuclides above valley (“neutron rich”)
PE or EC: turns p to n
 used by nuclides below valley (“neutron poor”)
a decay: lose both n and p
 used by nuclides beyond valley (too many of both)

39. How to determine if a nuclide is “above”, “below”, or “beyond”?
Summary of Strategy for Predicting Decay Type
How to determine if a nuclide is “above”, “below”, or “beyond”?
(if you don’t have a valley of stability table)
Long way:
Calculate n/p (=N/Z) ratio
Compare actual n/p ratio to ~stable n/p ratio:
Know that for Z = 1-20, n/p = ~1 is stable
Know that for Z = ~80, n/p = ~1.5 is stable
Know that for Z = ~40, n/p ~1.25 is stable
Example: 114Ag, 60Co, 21Na, 226Ra, 59Fe?
Short way: (next slide)

40. Skillbuilder Half -Life
The rate of radioactive decay is usually described in term of its half-life: time required for one-half of the unstable nuclei to decay.
- different for different isotopes
- measured in fractions of seconds or minutes, hours, days, months, years, or
billions of years.

41. Skillbuilder Half -Life t1/2 = 0.693/k
The rate of radioactive decay is usually described in term of its half-life: time required for one-half of the unstable nuclei to decay.
- different for different isotopes
- measured in fractions of seconds or min, hrs, days, months, yrs, or billions of yrs.
Rate of Radioactive Decay
first-order kinetics, so the rate of decay in a particular sample is directly proportional to the number of nuclei present:
rate =kN
N is the number of radioactive nuclei and k is the rate constant.
It was discovered that the rate of change in the amount of radioactivity was constant, and different for each radioactive “isotope”
change in radioactivity measured with Geiger counter
counts per minute
Each radionuclide had a particular length of time it required to lose half its radioactivity
a constant half-life
we know that processes with a constant half-life follow first order kinetic rate laws
The rate of radioactive change was not affected by temperature
meaning radioactivity is not a chemical reaction!
Therefore, t1⁄2
t1/2 = 0.693/k

42. Skillbuilder Skillbuilder
The half-life of iodided-131 is 8 days. How much of a 1.0 oz sample of iodine-131 will remain after 32 days?
Solution:
1. 32 days is four half-lives /8 = 4
2. After the first half life (8 days), 1/2 oz will remain.
3. After the second half-life (8 + 8, or 16 days), 1/4 oz will remain.
4. After the third half-life ( , or 24 days), 1/8 oz will remain.
5. After the fourth half-life ( , or 32 days), 1/16 fraction will remain.
6. What is 1/16 of 1.0 oz? It’s 1.0 oz x 1/16 = 6.3 × 10–2 oz.

43. Skillbuilder Skillbuilder
The half-life of zinc-71 is 2.4 minutes. If one had g at the beginning, how many grams would be left after 7.2 minutes has elapsed?
Solution:
/ 2.4 = 3 half-lives
2. (1/2)3 = fraction (the amount remaining after 3 half-lives)
g x = 12.5 g remaining

44. Skillbuilder Skillbuilder
Osmium-182 has a half-life of 21.5 hours. How many grams of a 10.0 gram sample would have decayed after exactly three half-lives?
Solution:
(1/2)3 = fraction (the amount remaining after 3 half-lives)
10.0 g x = 1.25 g remain
g g = 8.75 g have decayed
Note that the length of the half-life played no role in this calculation. In addition, note that the question asked for the amount that decayed, not the amount that remaining!

45. The Integrated Law
Skillbuilder

46. Skillbuilder
If you have a 1.35 mg sample of Pu–236, calculate the mass that will remain after 5.00 yrs
Given:
Find:
mass Pu–236 = 1.35 mg, t = 5.00 yr, t1/2 = 2.86 yr
mass remaining, mg
Conceptual Plan:
Relationships:
t1/2 k
m0, t mt +
Solve:

47. Skillbuilder
Rn–222 is a gas that is suspected of causing lung cancer as it leaks into houses. It is produced by uranium decay. Assuming no loss or gain from leakage, if there is g of Rn–222 in the house today, how much will there be in 5.4 weeks? ( Rn–222 half-life is 3.8 Days)
Given:
Find:
mass Rn–222 = g, t = 5.4 wks, t1/2 = 3.8 d
mass remaining, g
Conceptual Plan:
Relationships:
t1/2 k
m0, t mt +
Solve: 51

48. Background Radioactivity
Skillbuilder
Background radioactivity: the ionization radiation present in the environment, to which we all are exposed, even in the absence of an actual radioactive source.
Originates from a variety of natural sources: soil, rocks, water, and vegetation from which it is inhaled or ingested into the body - internal exposure. Or external exposure: radioactive materials that remains outside the body and from cosmic radiation from space.
For example, about one out of every trillion carbon atoms is 14C, which emits a b particle when it decays. With each breath, you inhale about 3 million 14C atoms.
A small amount of mass can be converted into an enormous amount of energy. For example, if one gram of mass is con- verted to energy, about 100 trillion joules of energy are released.
A chain reaction occurs when a neutron emiitted from a split nucleus cause othe nuclei to split and emit additional neutrons
Tremendous amounts of energy can be released in nuclear fission. In fact, splitting one uranium-235 nucleus produces about 30 million times more energy than chemically reacting one molecule of dynamite. Even more energy can be released in another type of nuclear reaction,

49. Radioactive Dating Skillbuilder Isotopes = nuclear “clocks”
Radiocarbon dating (also referred to as carbon dating or C-14 dating) is a method for determining the age of an object containing organic material by using the properties of radioacarbon, a radioactive isotope (half-life = 5730 yr)
14C is constantly formed:
14C is constantly decays:
While still living, C–14/C–12 is constant because the organism replenishes its supply of carbon
CO2 in air ultimate source of all C in organism
Once the organism dies the C–14/C–12 ratio decreases
By measuring the C–14/C–12 ratio in a once living artifact and comparing it to the C–14/C–12 ratio in a living organism, we can tell how long ago the organism was alive
The limit for this technique is 50,000 years old
about 9 half-lives, after which radioactivity from C–14 will be below the background radiation
Basic Chemistry I
Lecture 3, September 14

50. % C-14 (compared to living organism) Object’s Age (in years)
Radioactive Dating
Skillbuilder
% C-14 (compared to living organism)
Object’s Age (in years)
100%
90%
870
80%
1850
60%
4220
50%
5730
40%
7580
25%
11,500
10%
19,000 5%
24,800 1%
38,100

51. Skillbuilder Skillbuilder Solution:
An old scroll (like the Dead Sea Scrolls) is found in a cave that has a carbon-14 activity of
4 counts/min per gram of total carbon if originally had an activity of 16 counts/min per gram of carbon. Approximately how old is the scroll?
Solution:
How many half-lives of 14C that have passed?
16 counts (t1/2) 8 counts (t1/2) 4 counts half-lives have elapsed
2. Knowing that the half-life of 14C is 5730 years
2 x 5730 years = 11,460 years
Answer: The parchment is between approximately 11,000 to 12,000 years old!
Basic Chemistry I
Lecture 3, September 14
Tro: Chemistry: A Molecular Approach, 2/e

52. Skillbuilder Skillbuilder Solution:
An archeology dig unearths an old skeleton. Analysis shows that there is a 14C activity of 1 count/min per gram of total carbon if originally had an activity of 16 counts/min per gram of carbon. Approximately how old is the skeleton?
Solution:
How many half-lives of 14C that have passed?
16 counts (t1/2) 8 counts (t1/2) 4 counts (t1/2) 2 counts (t1/2) 1 counts
4 half-lives have elapsed
2. Knowing that the half-life of 14C is 5730 years
4 x 5730 years = 22,860 years
Answer: The parchment is between approximately 22,000 to 23,000 years old!
Basic Chemistry I
Lecture 3, September 14
Tro: Chemistry: A Molecular Approach, 2/e

53. Skillbuilder
An ancient skull gives 4.50 dis/min∙gC. If a living organism gives 15.3 dis/min∙gC, how old is the skull?
Given:
Find:
ratet1/2 = 4.50 dis/min∙gC, ratet1/2 = 15.3 dis/min∙gC
time, yr
Conceptual Plan:
Relationships:
t1/2 k
rate0, ratet t +
Solve:

54. Skillbuilder
Archeologists have dated a civilization to 15,600 yrs ago. If a living sample gives 20.0 counts per minute per gram C, what would be the number of counts per minute per gram C for a rice grain found at the site?
Given:
Find:
t = 15,600 yr, rate0 = 20.0 counts/min∙gC
ratet, counts/min∙gC
Conceptual Plan:
Relationships:
t1/2 k
rate0, t
ratet +
Solve: 58

55. Nuclear Reaction: Nuclear Fission
Skillbuilder
1939, Lise Meitner: offered a theory of nuclear fission: the process of splitting a nucleus into several smaller nuclei. The 235U nucleus is distorted so divides into two smaller nuclei. The word fission means “to divide.”
the physicist Enrico Fermi: bombarding nuclei with neutrons heavier nuclei would be produced.
1938, Otto Hahn and Fritz Strassmann: experiment with 235U - the nucleus splits apart into smaller nuclei.
When a neutron hits a uranium-235 nucleus, the ura- nium nucleus splits into two smaller nuclei and two or three free neutrons. Energy also is released.
A few nuclei are so unstable that if their nucleus is hit just right by a neutron, the large nucleus splits into two smaller nuclei — this is called fission
Small nuclei can be accelerated to such a degree that they overcome their charge repulsion and smash together to make a larger nucleus - this is called fusion
Both fission and fusion release enormous amounts of energy
fusion releases more energy per gram than fission

56. Nuclear Reaction: Nuclear Fusion
Skillbuilder
Small nuclei can be accelerated to such a degree that they overcome their charge repulsion and smash together to make a larger nucleus - this is called fusion
Chain reaction: the series of reported fission reactions caused by the release of neutrons in each reaction.
Critical mass: the amount of material required so the at each fission reaction produces approximately one more fission reaction.
Splitting one 235U nucleus produces ≈ 30 million times > NRG than chemically reacting one molecule of dynamite.
The fission of a 235Unucleus produces two or three neutrons along with other products. These neutrons
can each move to other uranium-235 nuclei where they are
absorbed, causing fission with the release of more neutrons,
which move to other uranium-235 nuclei to continue the process.
A reaction where the products are able to produce more
reactions in a self-sustaining series is called a chain reaction.

57. E = mc2 (joules) =kg x (m/s)2
Nuclear Energy
Skillbuilder
238
234 4 U Th + He 92 90 2
The nuclear mass from equation:
u u u
It seems to be a loss of mass in the reaction.
u u u = u
This change in mass is related to the energy change: 4.6 x 10-6 kg releases 4.14 x 1011 J
Mass is not the same!!! The products of a mole of uranium-238 decaying to more
stable products (1) have a lower energy of 4.14 Å~ J and
(2) lost a mass of 4.6 Å~ 10–6 kg. As you can see, a very small
amount of matter was converted into a large amount of energy
in the process, forming products of lower energy.
When a neutron hits a uranium-235 nucleus, the ura- nium nucleus splits into two smaller nuclei and two or three free neutrons. Energy also is released.
Albert Einstein (1905): mass can be converted to energy and energy can be converted to mass. The relation between mass and energy is given by this equation:
E = mc2 (joules) =kg x (m/s)2

58. Nuclear Energy Skillbuilder U Th He 238 234 4 + 92 90 2
The nuclear mass from equation:
u u u
It seems to be a loss of mass in the reaction.
u u u = u
This difference u between the m of the individual nucleons making up a
nucleus & the actual m of the nucleus is called the mass defect of the nucleus.
When nucleons join to make a nucleus, NRG is released as the more stable nucleus is formed = to binding NRG: the energy required to break the nucleus into individual protons and neutrons.
1 MeV (megaelectron volt) = x 10−13 J
1 amu of mass defect = MeV
the greater the binding energy per nucleon, the more stable the nucleus is
Mass is not the same!!! The products of a mole of uranium-238 decaying to more
stable products (1) have a lower energy of 4.14 Å~ J and
(2) lost a mass of 4.6 Å~ 10–6 kg. As you can see, a very small
amount of matter was converted into a large amount of energy
in the process, forming products of lower energy.
When a neutron hits a uranium-235 nucleus, the ura- nium nucleus splits into two smaller nuclei and two or three free neutrons. Energy also is released.

59. Nuclear Energy Skillbuilder
The binding NRG of the nucleus of any isotope can be calculated from the mass defect of the nucleus.
The ratio of binding energy to nucleon number is a reflection of the stability of a nucleus.
The maximum binding NRG per nucleon occurs around mass number 56, then decreases in both directions.
As a result, fission of massive nuclei and fusion of less massive nuclei both release energy.
A small amount of mass can be converted into an enormous amount of energy. For example, if one gram of mass is con- verted to energy, about 100 trillion joules of energy are released.
A chain reaction occurs when a neutron emiitted from a split nucleus cause othe nuclei to split and emit additional neutrons
Tremendous amounts of energy can be released in nuclear fission. In fact, splitting one uranium-235 nucleus produces about 30 million times more energy than chemically reacting one molecule of dynamite. Even more energy can be released in another type of nuclear reaction,

60. Nuclear Reaction: Nuclear Fusion
Skillbuilder
Even more energy can be released in another type of nuclear reaction, called nuclear fusion:
two nuclei with low masses are combined to form one nucleus of larger mass. Fusion fuses atomic nuclei together, and fission splits nuclei apart.
Nuclear fusion and the Sun:
An isotope of 3He is produced when a proton (H+) and the hydrogen isotope H-2 (2D) undergo fusion.
For nuclear fusion to occur, posi- tively charged nuclei must get close to each other. However, all nuclei repel each other because they have the same positive elec- tric charge. If nuclei are moving fast, they can have enough kinetic energy to overcome the repulsive electrical force between them and get close to each other.
Remember that the kinetic energy of atoms or molecules increases as their temperature increases. Only at temperatures of millions of degrees Celsius are nuclei moving so fast that they can get close enough for fusion to occur. These extremely high temperatures are found in the center of stars, including the Sun.
The Sun is composed mainly of hydrogen. Most of the energy given off by the Sun is pro- duced by a process involving the fusion of hydrogen nuclei. This process occurs in several stages, and one of the stages is shown in Figure 18. The net result of this process is that four hydrogen nuclei are converted into one helium nucleus. As this occurs, a small amount of mass is changed into an enormous amount of energy. Earth receives a small
amount of this energy as heat and light.
As the Sun ages, the hydrogen nuclei are used up as they are con- verted into helium. So far, only about one percent of the Sun’s mass has been converted into energy. Eventually, no hydrogen nuclei will be left, and the fusion reaction that changes hydrogen into helium will stop. However, it is estimated that the Sun has enough hydrogen to keep this reaction going for another 5 billion years.

61. Application of Radioactive Isotopes
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A radioactive tracer is a very small amount of radioactive isotope added to a chemical, biological, or physical system to study the system.
– A series of experiments using tracers was carried out in the 1950s by Melvin Calvin at the University of California at Berkley, to discover the mechanism of photosynthesis in plants.
Another example of radioactive tracers is isotopic dilution, a technique to determine the quantity of a substance in a mixture. Human blood volumes are determined using the technique of isotopic dilution.
Using the carbon-14 isotope as a tracer, Calvin, Andrew Benson and James Bassham mapped the complete route that carbon travels through a plant during photosynthesis, starting from its absorption as atmospheric carbon dioxide to its conversion into carbohydrates and other organic compounds.[7][8]

62. Biological Application of Radioactivity
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Iodine tracers in the thyroid:
The thyroid gland produces chemical compounds called hormones that help regulate several body processes, including growth.
Iodine accumulates in the thyroid, therefore, radioisotope 131I can be used to diagnose thyroid problems.
As 131I atoms absorbed by the thyroid, decay, emitting b particles and g rays.
The thyroid gland is located in your neck and pro-duces chemical compounds called hormones. These hormones help regulate several body processes, including growth. Because the element iodine accumulates in the thyroid, the radioisotope iodine-131 can be used to diagnose thyroid problems. As iodine- 131 atoms are absorbed by the thyroid, their nuclei decay, emitting beta particles and gamma rays. The beta particles are absorbed by the surrounding tissues, but the gamma rays penetrate the skin. The emitted gamma rays can be detected and used to determine whether the thy- roid is healthy, as shown in Figure 19. If the detected radi- ation is not intense, then the thyroid has not properly absorbed the iodine-131 and is not functioning properly. This could be due to the presence of a tumor. Figure 20
The emitted g rays are detected; if the detected radiation is not intense, then the thyroid has not properly absorbed the 131I.

63. Biological Application of Radioactivity
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When a person has cancer, a group of cells in that person’s body grows out of control and can form a tumor. Radiation can be used to stop some types of cancerous cells from growing. Remember that the radiation that is given off during nuclear decay is strong enough to ionize nearby atoms. If a source of radiation is placed near cancer cells, such as those shown in Figure 21, atoms in the cells can be ionized. If the ionized atoms are in a
critical molecule, such as the DNA or RNA of a cancer cell, then the molecule might no longer function properly. The cell then could die or stop growing.
When possible, a radioactive isotope such as gold-198 or iridium-192 is implanted within or near the tumor.
The radiation that is given off during nuclear decay is strong enough to ionize nearby atoms, therefore, the cells can be ionized.
If the ionized atoms are in a critical molecule, such as the DNA or RNA of a cancer cell, then the molecule might no longer function properly. The cell then could die or stop growing. (198Au or 192Ir)

64. Biological Application of Radioactivity
Skillbuilder
Other times, tumors are treated from outside the body. Typically, an intense beam of gamma rays from the decay of cobalt-60 is focused on the tumor for a short period of time. The gamma rays pass through the body and into the tumor. How can physicians be sure that only the cancer cells will absorb radiation? Because cancer cells grow quickly, they are more susceptible to absorbing radiation and being damaged than healthy cells are. However, other cells in the body that grow quickly also are damaged, which is why cancer patients who have radiation therapy some- times experience severe side effects.
Other times, tumors are treated from outside the body with an intense beam of g rays from the decay of 60Co is focused on the tumor for a short period of time. The g rays pass through the body and into the tumor. How can physicians be sure that only the cancer cells will absorb radiation?