1. The Nucleus and Radioactivity
Radioactivity: Spontaneous changes in the nucleus that emit energy as radiation (particles or rays)
Nuclei contain protons and neutrons; some combinations of these particles are unstable
Examples of Radioactive Nuclei Include:
Uranium, Plutonium
Hydrogen-3
Potassium-38

2. Types of Radiation Include:
Radioactive Decay: Emission of radiation produced by unstable nuclei changing to a more stable state
Types of Radiation Include:
Alpha rays a: positive charge
Beta rays b: negative charge
Gamma rays g: no charge
a and b rays consist of streams of particles
g rays consist of electromagnetic radiation

3. A positron has a +1 charge and is called a “positive electron.”
positron: an antiparticle of a β particle (their charges are opposite, but their masses are the same)
A positron has a +1 charge and is called a “positive electron.” +1 e
positron: β+ or
A positron is formed when a proton is converted to a neutron. 1 p 1 n +1 e +
proton
neutron
positron 3

4. a particle:
contains 2 protons and 2 neutrons
identical to helium nucleus
travel only short distances
b particle:
electrons produced in the nucleus, then emitted
travel greater distances than a particles

5. g Ray:
High-energy ray similar to an X ray
Travel great distances
Daughter Nuclei: New nuclei that result from unstable nuclei undergoing radioactive decay
Example: Uranium-238 gives up an a particle, resulting in a daughter nucleus of a different element, Thorium (Th)

6. Summary of Radiation Types

7. Alpha Decay
When a radioactive nucleus emits an alpha particle, a new nucleus results.
The mass number of the new nucleus is 4 less than that of the initial nucleus.
The atomic number is decreased by 2.

8. Nuclear Reactions: Alpha Emission
Alpha emission is the decay of a nucleus by emitting
an a particle. 8

9. In a balanced nuclear equation, the sum of the mass numbers and the sum of the atomic numbers for the nuclei of the reactant and the products must be equal.
251Cf Cm He Am + Np
241 4 He
237 95 2 93

10. Write an equation for the alpha decay of Rn-222.
222Rn new nucleus He
Mass number: 222 – 4 = 218
Atomic number: 86 – 2 = 84
Symbol of element = Po
222Rn Po He

11. Beta Decay
The unstable nucleus converts a neutron into a proton (emitting an electron from the nucleus)
The mass number of the new nucleus remains the same
The atomic number of the new nucleus increases by 1
1n e + 1H

12. Nuclear Reactions: Beta Emission
Beta emission is the decay of a nucleus by emitting a β particle; 1 neutron is lost and 1 proton is gained. 12

13. Example: Potassium - 42 is a beta emitter.
42K new nucleus e
Mass number : (same) = 42
Atomic number: A = 20
Symbol of element = Ca
42K Ca e

14. Learning Check Write the nuclear equation for the beta decay of Co-60.27

15. Solution Write the nuclear equation for the beta decay of Co-60.
60Co Ni e 1

16. Nuclear Reactions: Positron Emission
Positron emission is the decay of a nucleus by emitting a positron, β+; 1 proton is lost and 1 neutron is gained. 16 16

17. Gamma  Radiation
Gamma radiation is energy emitted from an unstable nucleus indicated by m.
In a nuclear equation for gamma emission, the mass number and the atomic number are the same.
99mTc Tc 

18. Summary of Radiation

19. Some radioactive isotopes are more stable than others, and therefore decay more slowly
Half-Life: Time required for half of the unstable nuclei in a sample to decay
Example: A Potassium-38 sample weighs 100 grams. 8 minutes later, the sample is weighed again and found to weigh 50 g. The half-life of potassium-38 is 8 minutes

20. Note: The half-life of a radioactive isotope is a property of a given isotope and is independent of the amount of sample, temperature, and pressure. 20

21. Half-Lives Vary Dramatically Between Elements

22. Half-Life Calculations
After one half-life, 40 mg of a radioisotope will decay to 20 mg. After two half-lives, 10 mg of radioisotope remain.
40 mg x x = 10 mg
1 half-life 2 half-lives
Initial
40 mg
20 mg
10 mg

23. Determine how many half-lives occur in the given amount of time.
Practice:
If the half-life of iodine-131 is 8.0 days, how much of a 100. mg sample remains after 32 days?
Determine how many half-lives occur in the
given amount of time.
1 half-life
8.0 days
32 days x =
4.0 half-lives 23

24. For each half-life, multiply the initial mass by one-half to obtain
the final mass: 1 2 1 2 1 2 1 2
100. mg x x x x
= mg
initial mass
final mass
The mass is halved four times. 24

25. Learning Check
The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours?

26. Solution Half life = 13 hrs Number of half lives = 2
Amount remaining = 64 mg x 1 x 1 = 16 mg
13 hrs hrs
64 mg mg mg

27. Radiation and Health
Free Radicals: Very reactive compounds that can cause mutations, cancer; usually caused by long-term exposure to low-level radiation
Radiation Sickness: Illness and symptoms caused by short-term exposure to intense radiation

28. Uses of Radioisotopes
Medical: diagnosing and disease (cancer, thyroid, brain scans)

29. Common Imaging Techniques
PET Scans (Positron Emission Tomography): gamma rays create a 3D image of organs, used to analyze blood flow, metabolic activity and brain function
CT (Computed Tomography): X-rays are used to create series of images of the brain, identifying brain damage and hemorrhaging
MRI (Magnetic Resonance Imaging): H protons in magnetic field are used to create color images of soft tissue

30. Health/Agriculture: food irradiation
Radioactive dating: determine age of fossils

31. Nuclear Power Plants: Alternative energy source

32. Units of Radiation
Curie (Ci): number of disintegrations per second per gram of radium; 3.7 x 1010 disintegrations per second
Rad (Radiation Absorbed Dose): amount of material able to deliver 2.4x10-3 cal of energy to 1 kg of tissue
Rem (Radiation Equivalent in humans): amount of biological damage caused by different types of radiation

34. In 1934 Radioactivity was Artificially Induced for the first time!!
High-energy particles (such as neutrons) can create unstable nuclei that then undergo radioactive decay (Cyclotrons and Linear Accelerators)

35. Nuclear Fission: Process in which large nuclei split into smaller nuclei when bombarded with neutrons, releasing large amounts of energy
Example: When a neutron bombards U-235, an unstable nucleus of U-236 forms smaller nuclei such as Kr-91 and Ba-142.

36. Chain Reaction: Nuclear reaction in which the products of a reaction cause that reaction to occur repeatedly
Nuclear Fusion: Process in which small nuclei combine (fuse) to form larger nuclei
Example: Hydrogen nuclei combine to form Helium nuclei