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4. RADIATION Energy in the form of particles or electromagnetic waves
Energy
in the form of particles
or electromagnetic waves
emitted from the nuclei of unstable atoms 4

5. RADIATION
The term really includes all forms of electromagnetic radiation
Radio Waves, Infrared, Visible Light
Ultraviolet, X-rays, -rays
Commonly used today to describe particle radiation 5

6. NUCLEAR REACTIONS PRODUCE RADIATION
Protons and neutrons determine nuclear reactions
One must understand atomic structure to understand radiation 6

7. NUCLEAR PARTICLES
Protons and Neutrons are the two basic nuclear particles. Together they contain practically all the mass of an atom and are determinants of an atom’s nuclear characteristics. 7

8. RADIOACTIVE DECAY
Radioactive decay refers to the spontaneous emission of radiation from the nucleus of an unstable atomic nucleus 8

9. DEFINITION OF RADIOACTIVE DECAY
DEFINITION OF RADIOACTIVE DECAY
“Radioactive decay is the process of spontaneous emission of radiation in the form of particles or photons from the nuclei of unstable atoms” 9

10. CHARACTERISTICS OF RADIOACTIVE DECAY
CHARACTERISTICS OF RADIOACTIVE DECAY
It is a natural process in our universe
It is spontaneous – we cannot predict when an atom will undergo decay 10

11. BASIC TYPES OF RADIOACTIVE DECAY
BASIC TYPES OF RADIOACTIVE DECAY
Alpha () decay
Occurs when atomic nuclei have too many protons and neutrons (i.e., Are heavy) 11

12. ALPHA PARTICLE 12

13. CHARACTERISTICS OF ALPHA PARTICLES
CHARACTERISTICS OF ALPHA PARTICLES
Consist of 2 protons and 2 neutrons
Mass of an alpha particle is 4 amu
Charge = +2
The isotope’s Atomic Mass goes down four;
The Atomic Number goes down two
Are highly ionizing
Have low penetrating abilities (only cm in air and mm in water) 13

14. MORE ABOUT ALPHA PARTICLES
MORE ABOUT ALPHA PARTICLES
Easily shielded; common types of shielding are paper, cardboard, air, clothing; will not penetrate skin
Health hazard when taken internally
Not commonly used in medicine
Common sources = smoke detectors (Am-241) and lantern mantles (thorium nitrate) 14

15. ALPHA PARTICLE DECAY
Changes both the mass and identity of the nucleus of the parent radionuclide
This means that the decay results in the formation of a new element as the daughter product 15

17. QUESTIONS? ? 16

18. NEGATIVE BETA (ß-) DECAY
Occurs when atoms have too many neutrons (i.e., Are “neutron-rich”) and decay by emitting a negative beta particle (ß-) 17

20. WHAT ARE NEGATIVE BETA PARTICLES?
During negative beta decay, neutrons are converted into protons and electrons. The protons remain in the nucleus but the new electrons are emitted as negative beta particles (ß-) or negatrons. You may
wish to think of them as
“nuclear electrons.” 18

21. CHARACTERISTICS OF NEGATIVE BETA DECAY
Less ionizing than alphas due to decreased mass of negatrons
Changes the identity of the nucleus but not the mass
The Atomic Number is increased by one due to conversion of neutrons into protons 19

22. CHARACTERISTICS OF NEGATIVE BETA PARTICLES (NEGATRONS)
Negatrons consist of nuclear electrons
The mass is the same as electrons
There is a charge of –1 in negatrons
More penetrating than alpha particles; ~ 12 meters in air
They can penetrate skin– best shielding is wood, plastics, thick cardboard, etc. 20

23. QUESTIONS? ? 24

24. GAMMA () EMISSION
Is a form of pure electromagnetic radiation emitted from nuclei that have excess energy. It is sometimes called gamma photon radiation. 25

25. GAMMA RAYS
Are photons emitted from unstable nuclei to rid themselves of excess energy.
Gamma photons are subatomic packets of pure energy. They are higher in energy and more penetrating than the photons that make up visible light. 26

26. PROPERTIES OF GAMMA () RAYS
Charge is 0 (no charge)
Mass is 0 (no mass)
Low ionization
Penetration abilities can be extremely high; – penetrating power is dependent upon the energy of the emitted photons 28

29. QUESTIONS? ? 29

30. What is a “packet” of light energy that behaves like a particle?
Positron
Negatron
Megatron
Photon

31. Which form of radiation penetrates the least?
Alpha Decay
Beta Decay
Gamma Decay
Delta Decay

32. Which radioactive particle increases the Parent Nucleus’s atomic number?
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle

33. Which form of radiation penetrates the most?
Alpha Decay
Beta Decay
Gamma Decay
Delta Decay

34. Which particle drops the Parent Nucleus’s atomic number by two?
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle

35. Which particle resembles a Helium nucleus?
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle

36. Which particle isn’t a particle but a photon?
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle

37. Decay Systems
Each radioactive element will undergo various forms of radiation until it becomes stable
The particular elements that a “Parent Nucleus” changes into are always the same
This “path” is a Decay System

39. Half-life Original Amount # of  Current Amount 100g 1 50g 2 25g 34
6.25g 5
3.125g
The amount of time it takes for HALF of an amount of a radioactive material to decay
One symbol for half-life is  (lambda)

44. A Decay System showing half-lives

45. Nuclear Processes Fission
The splitting of a large, unstable nucleus into two or more stable nuclei
Scientists can cause fission by injecting a neutron at high speed
These are the uses associated with nuclear fission:
Power plants / reactors
Bombs
“Dirty bombs”

48. Nuclear Processes Fusion
The joining of two or more smaller nuclei into one larger, more stable nucleus
Scientists are working on fusion using high pressures, temperatures, and lasers
The only place that fusion occurs naturally is stars

50. Chernobyl Disaster
April 26, 1986 – flawed reactor design was operated by inadequately trained personnel and w/o regard to safety

51. Chernobyl Disaster
Result – steam explosion and fire released at least 5% of the radioactive reactor core into the atmosphere & downwind
28 people died within 4 months from radiation or thermal burns
19 subsequently died and 9 deaths from thyroid cancer

53. TERMS TO REVIEW Radiation Alpha decay Alpha particle Radioactive decay
Negatron Negative beta decay
X-ray
Gamma ray Photon
Half-Life
Decay Systems
Mother Nucleus Daughter Nuclei
Fission Fusion 30

54. Half-Life Problems
1. An isotope of cesium (cesium-137) has a half-life of 30 yrs. If 1.0 mg of cesium-137 disintegrates over a period of 90 yrs., how many mg of cesium-137 would remain?

55. Half-life
2. A 2.5 gram sample of an isotope of strontium-90 was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test site. The half-life of strontium-90 is 28 yrs. In what year will only grams of this strontium-90 remain?

56. Half-life
3. Actinium-226 has a half-life of 29 hours. If 100 mg of actinium-226 disintegrates over a period of 58 hours, how many mg of actinium-226 will remain?

57. Half-life
4. Thallium-201 has a half-life of 73 hours. If 4.0 mg of thallium-201 disintegrates over a period of 6.0 days and 2 hours, how many mg of thallium-201 will remain?

58. Half-life
5. Sodium-25 was to be used in an experiment, but it took 3.0 minutes to get the sodium from the reactor to the laboratory. If 5.0 mg of sodium-25 was removed from the reactor, how many mg of sodium-25 were placed in the reaction vessel 3.0 minutes later if the half-life of sodium-25 is 60 seconds?

59. Half-life
6. The half-life of isotope X is 2.0 years. How many years would it take for a 4.0 mg sample of X to decay and have only 0.50 mg of it remain?

60. Half-life
7. Selenium-83 has a half-life of 25.0 minutes. How many minutes would it take for a 10.0 mg sample to decay and have only 1.25 mg of it remain?

61. Half-life
8. Element-106 has a half-life of 0.90 seconds. If one million atoms of it were prepared, how many atoms would remain after 4.5 seconds?

62. Half-life
9. The half-life of Po-218 is three minutes. How much of a 2.0 gram sample remains after 15 minutes? Suppose you wanted to buy some of this isotope, and it required half an hour for it to reach you. How much should you order if you need to use 0.10 gram of this material?

63. Half-life
10. Three grams of Bismuth-218 decay to grams in one hour. What is the half-life of this isotope?

64. Half-life
11. The half-life of francium is 21 minutes. Starting with 4 x 1018 atoms of francium, how many atoms would disintegrate in 1 hour and 45 minutes? What fraction of the original sample remains?

65. Half-life
12. The half-life of a radioactive element is 30 seconds. In what period of time would the activity of the sample be reduced to one-sixteenth of the original activity?