1. Mr. Hollister Holliday Legacy High School Chemistry
Radioactivity & Nuclear
Chemistry
Mr. Hollister Holliday
Legacy High School
Chemistry

2. The Discovery of Radioactivity
Antoine-Henri Becquerel designed an experiment to determine if phosphorescent minerals also gave off x-rays.

3. Becquerel’s Plate

4. The Discovery of Radioactivity, Continued
Bequerel discovered that certain minerals were constantly producing penetrating energy rays he called uranic rays.
Like x-rays.
But not related to fluorescence.
Bequerel determined that:
All the minerals that produced these rays contained uranium.
The rays were produced even though the mineral was not exposed to outside energy.
Energy apparently being produced from nothing?

5. Marie Curie
Marie Curie used an electroscope to detect the radiation of uranic rays in samples.
By carefully separating minerals into their components, she discovered new elements by detecting the radiation they emitted.
Radium named for its green phosphorescence.
Polonium named for her homeland.
Since the radiation was no longer just emitted from of uranium, she renamed it radioactivity.

6. Electroscope +++ When charged, the metal foils spread apart due to
like-charge repulsion.
When exposed to ionizing radiation, the radiation knocks electrons off the
air molecules, which jump onto the foils and discharge them, causing them to
drop down.

7. Properties of Radioactivity
Radioactive rays can ionize matter.
Cause uncharged matter to become charged.
Basis of Geiger counter and electroscope.
Radioactive rays have high energy.
Radioactive rays can penetrate matter.
Radioactive rays cause phosphorescent chemicals to glow.
Basis of scintillation counter.

8. What Is Radioactivity?
Radioactivity = release of tiny, high-energy particles from an atom.
Particles are ejected from the nucleus.

9. Types of Radioactive Rays
Rutherford discovered there were three types of radioactivity:
1. Alpha rays (𝝰):
Have a charge of +2 c.u. and a mass of 4 amu.
What we now know to be helium nucleus.
2. Beta rays (β):
Have a charge of -1 c.u. and negligible mass.
Electron-like.
3. Gamma rays (𝜸):
Form of light energy (not particle like α and β).

10. Rutherford’s Experiment g b a

11. Penetrating Ability of Radioactive Rays
0.01 mm mm mm
Pieces of Lead

12. Facts About the Nucleus
Very small volume compared to volume of the atom.
Essentially entire mass of atom.
Very dense.
Composed of protons and neutrons that are tightly held together.
Nucleons.

13. Facts About the Nucleus, Continued
Every atom of an element has the same number of protons; equal to the atomic number (Z).
Atoms of the same elements can have different numbers of neutrons.
Isotopes.
Different atomic masses.
Isotopes are identified by their mass number (A).
Mass number = number of protons + neutrons.

14. Facts About the Nucleus, Continued
The number of neutrons is calculated by subtracting the atomic number from the mass number.
The nucleus of an isotope is called a nuclide.
Less than 10% of the known nuclides are non-radioactive, most are radionuclides.
Each nuclide is identified by a symbol.
Element − mass number.

15. Important Atomic Symbols
Particle
Symbol
Nuclear symbol
Proton p+
Neutron n0
Electron e-
Alpha a
Beta
b, b-
Positron
b, b+

16. Radioactivity
Radioactive nuclei spontaneously decompose into smaller nuclei.
Radioactive decay.
We say that radioactive nuclei are unstable.
The parent nuclide is the nucleus that is undergoing radioactive decay; the daughter nuclide are the new nuclei that are made.
Decomposing involves the nuclide emitting a particle and/or energy.
All nuclides with 84 or more protons are radioactive.

17. Transmutation
Rutherford discovered that during the radioactive process, atoms of one element are changed into atoms of a different element—transmutation.
In order for one element to change into another, the number of protons in the nucleus must change.

18. Chemical Processes vs. Nuclear Processes
Chemical reactions involve changes in the electronic structure of the atom.
Atoms gain, lose, or share electrons.
No change in the nuclei occurs.
Nuclear reactions involve changes in the structure of the nucleus.
When the number of protons in the nucleus changes, the atom becomes a different element.

19. Nuclear Equations
We describe nuclear processes using nuclear equations.
Use the symbol of the nuclide to represent the nucleus.
Atomic numbers and mass numbers are conserved.
Use this fact to predict the daughter nuclide if you know parent and emitted particle.

20. Alpha Emission (Decay)
An ά particle contains 2 protons and 2 neutrons.
Helium nucleus.
Loss of an alpha particle means:
Atomic number decreases by 2.
Mass number decreases by 4.

21. ά Decay

22. Beta Emission (Decay) A β particle is like an electron.
Moving much faster.
Produced from the nucleus.
When an atom loses a β particle, its:
Atomic number increases by 1.
Mass number remains the same.
In beta decay, a neutron changes into a proton.

23. β Decay

24. Gamma Emission Gamma (𝜸) rays are high-energy photons of light.
No loss of particles from the nucleus.
No change in the composition of the nucleus, however, the arrangement of the nucleons changes.
Same atomic number and mass number.
Generally occurs after the nucleus undergoes some other type of decay and the remaining particles rearrange.

25. Positron Emission (Decay)
Positron has a charge of 1+ c.u. and negligible mass.
Anti-electron.
When an atom loses a positron from the nucleus, its:
Mass number remains the same.
Atomic number decreases by 1.
Positrons appear to result from a proton changing into a neutron.

26. β + Decay

27. Nuclear Equations
In the nuclear equation, mass numbers and atomic numbers are conserved.
We can use this fact to determine the identity of a daughter nuclide if we know the parent and mode of decay.

28. Practice—Write a Nuclear Equation for Each of the Following:
Alpha emission from U-238.
Beta emission from Ne-24.
Positron emission from N-13.

29. Practice—Write a Nuclear Equation for Each of the Following, Continued:
Alpha emission from U-238.
Beta emission from Ne-24.
Positron emission from N-13.

30. Decay Series
In nature, often one radioactive nuclide changes in another radioactive nuclide.
Daughter nuclide is also radioactive.
All of the radioactive nuclides that are produced one after the other until a stable nuclide is made is called a decay series.
To determine the stable nuclide at the end of the series without writing it all out:
Count the number of a and b decays.
From the mass nunmber, subtract 4 for each a decay.
From the atomic number, subtract 2 for each a decay and add 1 for each b.

31. U-238 Decay Series

32. Practice—Write All the Steps in the U-238 Decay Series and Identify the Stable Isotope at the End of the Series.
a, b, b, a, a, a, a, b, a, b, a, b, b, a

33. Practice—Write All the Steps in the U-238 Decay Series and Identify the Stable Isotope at the End of the Series, Continued.
a, b, b, a, a, a, a, b, a, b, a, b, b, a
Great
granddaughter
Great great
granddaughter a b
Po-214 Pb-210 Bi-210 Po-210 Pb-206
Ra-226 Rn-222 Po-218 At-218 Bi-214
U-238 Th-234 Pa-234 U-234 Th-230
Daughter
Granddaughter

34. Practice—Determine the Stable Isotope at the End of the U-238 Decay Series.
a, b, b, a, a, a, a, b, a, b, a, b, b, a

35. Practice—Determine the Stable Isotope at the End of the U-238 Decay Series, Continued.
a, b, b, a, a, a, a, b, a, b, a, b, b, a
238 92 U
8 a ?
6 b
76 + 6
206 82 Pb =

36. Selected Types of Radioactive Decay

37. Detecting Radioactivity
To detect when a phenomenon is present, you need to identify what it does:
Radioactive rays can expose light-protected photographic film.
Use photographic film to detect the presence of radioactive rays — film badges.

38. Detecting Radioactivity, Continued
2. Radioactive rays cause air to become ionized.
An electroscope detects radiation by its ability to penetrate the flask and ionize the air inside.
Geiger-Müller counter works by counting electrons generated when Ar gas atoms are ionized by radioactive rays.

39. Detecting Radioactivity, Continued
3. Radioactive rays cause certain chemicals to give off a flash of light when they strike the chemical.
A scintillation counter is able to count the number of flashes per minute.

40. Natural Radioactivity
There are small amounts of radioactive minerals in the air, ground, and water.
It’s even in the food you eat!
The radiation you are exposed to from natural sources is called background radiation.

41. Radioactivity in Medicine
An isotope scan Technetium-99 is often used as the radiation source for bone scans such as this one.
Phosphorus-32 is used to image tumors because it is preferentially taken up by cancerous tissue.
Iodine-131 is used to diagnose thyroid disorders.

42. Radiotherapy for Cancer
Treatment involves exposing a malignant tumor to gamma rays, typically from radioisotopes such as cobalt-60.
The beam is moved in a circular pattern around the tumor to maximize exposure of the cancer cells while minimizing exposure of healthy tissues.

43. Half-Life Each radioactive isotope decays at a unique rate.
Some fast, some slow.
Not all the atoms of an isotope change simultaneously.
Rate is a measure of how many of them change in a given period of time.
Measured in counts per minute, or grams per time.
The length of time it takes for half of the parent nuclides in a sample to undergo radioactive decay is called the half-life, t1/2.

44. Half-Lives of Various Nuclides
Half-life
Type of decay
Th-232
1.4 x 1010 yr
Alpha
U-238
4.5 x 109 yr
C-14
5730 yr
Beta
Rn-220
55.6 sec
Th-219
1.05 x 10–6 sec

45. Decay Series of Uranium-238

46. How “Hot” Is It?
When we speak of a sample being hot, we are referring to the number of decays we get per minute.
For samples with equal numbers of radioactive atoms, the sample with the shorter half-life will be hotter.
That is, more atoms will change in a given period of time.

47. Half-Life
Half of the radioactive atoms decay each half-life.

50. Radiocarbon Dating
All things that are alive or were once alive contain carbon.
Three isotopes of carbon exist in nature, one of which, C-14, is radioactive.
C-14 radioactive with half-life = 5730 years
Atmospheric chemistry keeps producing C-14 at nearly the same rate it decays.

51. Radiocarbon Dating
While an organism is still living, C-14/ C-12 is constant because the organism replenishes its supply of carbon.
CO2 in air is the ultimate source of all C in an 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

52. Practice—Radon-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 1024 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.)

53. Practice—Radon-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 1024 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.), Continued
5.4 weeks x 7 days/wk = 37.8  38 days
Amount of Rn-222
Number of Half-lives
Time
(days)
1024 g
512 g 1
3.8
256 g 2
7.6
128 g 3
11.4
64 g 4
15.2
32 g 5
19.0
Amount of Rn-222
Number of Half-lives
Time
(days)
16 g 6
22.8
8 g 7
26.6
4 g 8
30.4
2 g 9
34.2
1 g 10 38

54. Practice — How Much of a Radioactive Isotope, Rn-224 (with Half-Life of 10 Minutes) Did You Start with if, After One Hour if You Have 2 g?

55. Practice—How Much of a Radioactive Isotope, Rn-222(with Half-Life of 10 Minutes) Did You Start with if, After One Hour if You Have 2 g?, Continued
Fill in the “Number of half-lives” and “Time…” columns first, then work backwards up the “Amount…” column.
Amount of Rn-222
Number of half-lives
Time
(min)
128 g
64 g 1 10
32 g 2 20
16 g 3 30
8 g 4 40
4 g 5 50
2 g 6 60

56. Nonradioactive Nuclear Changes
A few nuclei are so unstable, that if their nuclei are 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.

57. Fission
+ energy!!

58. Fission Chain Reaction
A chain reaction occurs when a reactant in the process is also a product of the process.
In the fission process it is the neutrons.
So you only need a small amount of neutrons to start the chain.
Many of the neutrons produced in the fission are either ejected from the uranium before they hit another U-235 or are absorbed by the surrounding U-238.
Minimum amount of fissionable isotope needed to sustain the chain reaction is called the critical mass.

59. Fission Chain Reaction, Continued

60. Fissionable Material
Fissionable isotopes include U-235, Pu-239, and Pu-240.
Natural uranium is less than 1% U-235.
The rest is mostly U-238.
Not enough U-235 to sustain chain reaction.
To produce fissionable uranium the natural uranium must be enriched in U-235:
To about 7% for “weapons grade.”
To about 3% for “reactor grade.”

61. Nuclear Power Nuclear reactors use fission to generate electricity.
About 20% of U.S. electricity.
The fission of U-235 produces heat.
The heat boils water, turning it to steam.
The steam turns a turbine, generating electricity.

62. Nuclear Power Plants vs. Coal-Burning Power Plants
Use about 50 kg of fuel to generate enough electricity for 1 million people.
No air pollution.
Use about 2 million kg of fuel to generate enough electricity for 1 million people.
Produces NO2 and SOx that add to acid rain.
Produces CO2 that adds to the greenhouse effect.

63. Nuclear Power Plant

64. Nuclear Power Plants—Core
The fissionable material is stored in long tubes, called fuel rods, arranged in a matrix.
Subcritical.
Between the fuel rods are control rods made of neutron absorbing material.
B and/or Cd.
Neutrons needed to sustain the chain reaction.
The rods are placed in a material to slow down the ejected neutrons, called a moderator.
Allows chain reaction to occur below critical mass.

65. PLWR
Containment
building
Turbine
Boiler
Condenser
Core
Cold
water

66. PLWR—Core
Hot
water
Control
rods
Fuel
rods
Cold
water

67. Problems with Nuclear Reactors
Fukushima
Chernobyl

68. Nuclear Fusion
Fusion is the combining of light nuclei to make a heavier one.
The sun uses the fusion of hydrogen isotopes to make helium as a power source.
Requires high input of energy to initiate the process.
Because need to overcome repulsion of positive nuclei.
Produces 10x the energy per gram as fission.
No radioactive byproducts.
Unfortunately, the only currently working application is the H-bomb.

69. Fusion + 2 1H 3 4
2He 1 0n
deuterium + tritium
helium-4 + neutron