1. Radioactivity Nuclear Chemistry

2. Radiation
Radiation: The process of emitting energy in the form of waves or particles.
Where does radiation come from?
Radiation is generally produced when particles interact or decay. A large contribution of the radiation on earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial).
Radiation is going through you at this very moment!

3. Background Radiation 13% are man-made Radon gas Food Cosmic rays
Gamma rays
Medical
Nuclear power

4. Review Atomic Terms
Nucleons – particles found in the nucleus of an atom ex. Neutrons and Protons
Nuclear Forces – strong nuclear force holds neutrons and protons together to form a nucleus
Isotopes – atoms with identical atomic numbers but different mass numbers

5. Writing Isotopes
Mass number
= number of protons + number of neutrons A X
Element symbol Z
Atomic number
= number of protons
Number of neutrons = Mass Number – Atomic Number

6. Writing Isotopes
An isotope is an atom with a different number of neutrons:
Notice that the mass number is different. How many neutrons does each isotope have? O 8 16 O 8 17 O 8 18
Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more.

7. Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the man-made isotopes are unstable.
Radioactive Decay– the spontaneous decomposition of a nucleus
Unstable isotopes can become stable by releasing different types of particles.
Radioactive - a substance that is capable of ALWAYS emitting radiation under any conditions
Radioisotope - simply an isotope that is radioactive or that undergoes radioactive decay.

8. Radioactivity Alpha particles (a) Beta particles (b) Gamma-rays (g)
Three types of radiation (or radioactivity):
Alpha particles (a)
Beta particles (b)
Gamma-rays (g)
Nothing will actually stop gamma but there are some materials that can greatly slow it down

9. Alpha Decay (a) 88 protons 138 neutrons 86 protons 136 neutrons
Unstable nucleus
New nucleus
Alpha particle
Alpha Decay (a)
Mass #
Radium
226Ra
Radon
Rn222 + p n n p
a (4He) 2
88 protons
138 neutrons
86 protons
136 neutrons
2 protons
2 neutrons
Note: The alpha particle is really a cation (+2) but shown with no charge cause it very rapidly picks up two electrons and becomes a neutral He atom instead of an ion.
Isotopes with a high number of protons tend to do this like #83 and up
The alpha-particle (a) is a Helium nucleus. It’s the same as the element Helium, with the electrons stripped off !

10. Alpha Decay Example 1 Example 2
These are examples of Radioactive Equations
Result: 2 less protons and 2 less neutrons
loss of 4 in mass number and loss of 2 in atomic number.

11. Rn + Y He Rn He + Po Alpha Decay, Practice #1 222 86 A Z 4 2 222 86 4
218 84

12. X + Th He He U + Th Alpha Decay, Practice #2 A Z 230 90 4 2 4 2 234 92

13. Th + Y He He + Ra Th Alpha Decay, Practice #3 230 90 A Z 4 2 4 2 22688 Th
230 90

14. X + Pb He He + Pb Po Alpha Decay, Practice #4 A Z 214 82 4 2 4 2 214
218 84

15. Beta Decay (b) Carbon C14 Nitrogen N14 + e- 6 protons electron
Unstable nucleus
New nucleus
Beta particle
Beta Decay (b)
Carbon
C14
Nitrogen
N14 + e-
6 protons
8 neutrons
Note that in beta decay, the atomic mass does not change, since the neutron and proton have nearly the same mass…
7 protons
7 neutrons
electron
(beta-particle)

16. Beta Decay
A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.
Beta decay occurs when a neutron changes into a proton and an electron.
Atoms with a high neutron to proton ratio tend to do this to level out the N to P ratio (Like Iodine)
Result: the nucleus has one less neutron, but one extra proton.

17. Beta Decay, Practice #1 Th
234 90 Y A Z + b -1 Th
234 90 Pa 91 + b -1

18. Beta Decay, Practice #2 X A Z Pb
210 82 + b -1 Tl
210 81 Pb 82 + b -1

19. Beta Decay, Practice #3 Bi
210 83 Y A Z + b -1 Bi
210 83 Po 84 + b -1

20. Beta Decay, Practice #4 X A Z Bi
214 83 + b -1 Pb
214 82 Bi 83 + b -1

21. Unstable nucleus
New nucleus
Gamma radiation
Gamma particles (g)
In much the same way that electrons in atoms can be in an excited state, so can a nucleus.
Neon
Ne20
Neon
Ne20 +
gamma
10 protons
10 neutrons (in excited state)
10 protons
10 neutrons (lowest energy state)
A gamma is a high energy light particle.
After  or  decay, surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed.

22. Gamma Decay
Gamma rays are not charged particles like a and b particles.
Gamma rays are electromagnetic radiation with high frequency.
When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable.
This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x J).