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1. 1
Nuclear Physics and Society
Physics Department
University of Richmond
Nuclear Basics

2. Motivation:
Educate the Public and University
communities about basic nuclear physics
ideas and issues
2
U.S. Department of Energy Workshop
July 2002, Washington D.C.
Role of the Nuclear Physics Research Community (universities
and national laboratories) in Combating Terrorism
Education and Outreach
•Community
•Local PD and FD

3. DOE Workshop …
3
Border Control/ US Customs
•1,000,000 visas/year
•422 ports of entry
•1700 flights / day
•290 ships / day
•60 trains / day
•1200 busses / day
•540,000,000 border entries /
year
Time per primary inspection
8 seconds => 1 hour delay
Cargo Containers
10,000,000 per year … 10,000 per
ship!
5 / minute @ L.A.
< 3% inspected

4. What the Course is/is not
4
This is not a radiation workers course
This is not a course that will certify you for anything
We hope that we can introduce you to some basic facts about
nuclear physics, about radiation, about detectors etc., which
may be useful for you to know.

5. Who are We
5
Con Beausang
Chairman & Associate Professor Physics Department
Jerry Gilfoyle
Professor, Physics Department
Paddy Regan
Professor Physics Department, University of Surrey, U.K.

6. 6
Monday April 13th
Lecture 1:
The types of radiation, their properties and how these can be used to detect them.
Some basic definitions.
Introduction to radiation detectors.
Tuesday April 14th
Laboratory Session: 12:15  3:30 pm
Environmental Radiation Laboratory experience
Measurement of half-life
Demonstration of shielding
Find the source
Lecture 2:
The creation of the elements. Nuclear physics in the cosmos.
Wednesday April 15th
Laboratory Session 2: 12:15  3:30
Repeat of Tuesdays experience
Lecture 3:
Applications of Nuclear Physics: Nuclear weapons, nuclear power and nuclear medicine.
Thursday April 16th
Lecture 4
Some of the frontiers of modern nuclear physics research
Nuclear Physics and Society

7. 7
The Cookie Quiz
Alpha
cookie
Beta
cookie
Gamma
cookie
Neutron
cookie

8. 8
The Cookie Quiz
Alpha
cookie
Beta
cookie
Gamma
cookie
Neutron
cookie
Throw away
Put in pocket
Hold in clenched fist
Eat one … GOAL: Minimize your
radiation exposure

9. 9
The Cookie Quiz: Answer 1
Alpha
cookie
Beta
cookie
Gamma
cookie
Neutron
cookieThrow away
Put in pocket
Hold in clenched fist
Eat one …

10. 10
The Cookie Quiz: Correct Answer
Alpha
cookie
Beta
cookie
Gamma
cookie
Neutron
cookie
Throw away
Put in pocket
Hold in clenched fist
Eat one …
GOAL: Minimize your
radiation exposure
Mutiny at once
Retire from the navy and
Toss ALL cookies away

11. … when I was
young(er), I was curious
…
What are we made of ?
… sugar and spice and all things nice
… that’s what little girls are made of
… snips and snails and puppy dogs tails
… that’s what little boys are made of.
… ok mum, … so what
are sugar, spice and
snails etc. made of? … cells
… molecules
… atoms
… nuclei

12. The Uncertainty Principle
Heisenberg (Quantum Mechanics)
∆(position) ∆(momentum) > Constant
Beausang (Teaching)
∆(truth) ∆(clarity) > Constant

13. Atoms … are made of …
Electrons
… very light, but occupy most of the volume
inside an atom
Nuclei
… lie at the Core of Atoms
… very heavy, very small, very compact
…occupies almost none of the volume inside
the atom

14. How do we know?
How to see the invisible?
… size of your probe
… scattering
Alpha-particle beam
Detector
Zinc-sulfide
screen
Discovery of the
nucleus
~1910
The eyes of
Geiger and
Marsden
16-inch
Battleship
shells and
tissue paper

15. Think of atoms as being like a mini solar system
… The sun at the center is the nucleus, the electrons
orbit the nucleus, like the planets orbit around the
sun
Bohr Model

16. Electrons
•Very small
•Point-like particles (i.e.nothing inside an electron)
•Very light ~ 1/2000th
of proton mass
•Negatively charged (-1 elementary charge)
•Electrons occupy almost all the space in the atom (orbiting the
nucleus like the earth and other planets orbit the sun)
•Have almost none of the mass of the atom
•All of chemistry has to do with electrons from different atoms
interacting with each other

17. The Nucleus
•Made up of protons and neutrons
•Almost all of the mass of the atom is
concentrated in the nucleus.
• >99.9% of the known mass in the universe.
•Occupies almost none of the volume of the
atom.
•Radius < 1/10,000
•Volume < 1/1,000,000,000,000

18. •The nucleus is the source of almost all the
things we commonly think of as being
radioactive.

19. The Nucleus Protons
•Positively charged
(+1 elementary charge)
•Size ~ 1 fm (10-15
m)
•Mass 938 MeV/c2
= 1
Neutrons
•Neutral
(0 charge)
•Size ~ 1 fm (10-15
m)
•Mass 939 MeV/c2
~ 1
Neutrons are slightly more massive than
the protons!!!
This has huge consequences for us!

20. Delicate Balances
Laws of Physics
1) If it can happen … it will happen …
2) If some law forbids it to happen … it will happen more
slowly …
3) If a process is really REALLY forbidden to happen …
it just takes a long time …

21. Standard Model:
Neutron and proton are
very close relatives
quark structure
… proton (uud)
… neutron (udd)
Many laws allow neutrons to `change into’
into protons … change a d-quark into a u-
quark (or vice versa)
… beta-decay

22. The half life of a free neutron (i.e., one not inside a
nucleus) is only about 12 minutes!!!
Mass Neutron = 939.565330 MeV/c2
Mass Proton = 938.271998 MeV/c2
But …
Inside a nucleus … neutrons are stable
The half life of a free proton is > 1031
years
Inside some nuclei protons can ‘decay’ into neutrons
Imagine … if they were not!
Then in ~ 1-2 hours the entire universe
would be made of Hydrogen
E = mc2

23. The Nucleus
•Atoms are electrically neutral
•The number of protons in a nucleus is equal to and determines the number
of orbiting electrons
the chemistry
the element name
•Hydrogen (1
1H)
1 proton, 0 neutrons
Mass = 1
•Helium (4
2He) (Alpha-particle)
2 protons, 2 neutrons
Mass = 4
•Uranium (238
92U)
92 protons, 146 neutrons
Mass = 238

24. The Nucleus
Many elements have several stable nuclei with the
same number of protons but different numbers of
neutrons …
same name
same chemistry
different mass
Isotopes

25. The Periodic Table of the Elements

26. Chart of the Nuclei
1
H 2
D
3
He 4
He
6
Li 7
Li
n
9
Be
3
T
5
He 6
He
5
Li
6
Be 7
Be 8
Be
8
Li
7
He
9
Li
10
Be
10
Li 11
Li
8
He 9
He
11
Be 12
Be
10
B 11
B9
B
14
Be
12
B 13
B 14
B 15
B8
B7
B
12
C 13
C 14
C 15
C 16
C 17
C11
C10
C9
C8
C
Z=No.ofProtons
0
1
2
3
4
5
6
N = No. of Neutrons
0 1 2 3 4 5 6 7 8 9

27. Chart
of the
Nuclei
The Landscape
~300 stable
~ 7000 unstable … radioactive.

28. Half Life
28
Time taken for half of the substance to decay away
Example:
If you have 1000 radioactive nuclei
and
If their half life is 30 minutes
After 30 minutes 500 nuclei remain
After 60 minutes 250 remain
After 90 minutes 125 remain
After 120 minutes 62 remain
There is a huge variation in
half lives of different isotopes
…. From a tiny fraction of a
second to roughly the age of the
universe.

29. Some Isotopes & Their Half LivesSome Isotopes & Their Half Lives
ISOTOPEISOTOPE HALF-HALF-
LIFELIFE
APPLICATIONSAPPLICATIONS
Uranium billions
of years
Natural uranium is comprised of several different isotopes.
When enriched in the isotope of U-235, it’s used to power
nuclear reactor or nuclear weapons.
Carbon-14 5730 y Found in nature from cosmic interactions, used to “carbon
date” items and as radiolabel for detection of tumors.
Cesium-137 30.2 y Blood irradiators, tumor treatment through external
exposure. Also used for industrial radiography.
Hydrogen-3 12.3 y Labeling biological tracers.
Irridium-192 74 d Implants or "seeds" for treatment of cancer. Also used for
industrial radiography.
Molybdenum-99 66 h Parent for Tc-99m generator.
Technicium-99m 6 h Brain, heart, liver (gastoenterology), lungs, bones, thyroid,
and kidney imaging, regional cerebral blood flow, etc.
29

30. The Amount of Radioactivity isThe Amount of Radioactivity is
NOT Necessarily Related to SizeNOT Necessarily Related to Size
• Specific activity is the amount of
radioactivity found in a gram of
material.
• Radioactive material with long half-
lives have low specific activity.
1 gram of Cobalt-60
has the same activity as
1800 tons of natural Uranium
30

31. 31
For Example: Suppose we have
1,000,000,000 atoms of material A with a half life of 1 second
and
1,000,000,000 atoms of material B with a half life of 1 year
(real sources have many more atoms in them)
Suppose they both decay by alpha emission.
In the First Second
Substance A: Half the nuclei will decay
… 500,000,000 alpha particles will come zipping out at you.
1 year = 365 days * 24 hours * 60 minutes * 60 seconds = 31,536,000 seconds
In the First Second for substance B
Only ~ 500,000,000 / 31,536,000 = 16 nuclei will decay
… only 16 alpha particles will come zipping at you

32. 32
On the other hand …
In 10 seconds … almost all of the radioactivity in substance A is gone away
But it takes years for the activity of substance B to go away!
Nuclear Bombs …
The fissile material (U or Pu) has a long half-life. Low specific activity. Not
much activity on the outside.
Dirty Bombs …
The radioactive material wrapped around the explosive would probably
have a much shorter half-life. Perhaps significant activity on the outside.

33. Types of Radioactivity
33
Each type of radiation has
different properties which affect
the hazards they pose, the
detection mechanism and the
shielding required to stop them.
Five Common Types
Alpha Decay
Beta Decay
Gamma Decay
Fission
Neutron Emission
Each of the particles emitted in the decay carries a lot of
kinetic energy. Damage can be caused when this energy
is absorbed in a human cell.

34. Alpha Decay
34
An alpha particle (α) is an energetic, He nucleus
(4
2He2)
Alpha decay mostly occurs for heavy nuclei
Example
238
94Pu  234
92U + 4
2He
Half-life: 88 years
Energy α =5.56 MeV

35. Alpha Decay
35
Very easy to shield
A sheet of paper, skin, or a few cm (~inch)
of air will stop an alpha particle
External Hazard: Low
Internal Hazard: High

36. Alpha Decay
238
94Pu144 234
92U142 + α
• Parent nucleus 238
94Pu144
• Daughter Nucleus 234
92U142
–Often the daughter nucleus is also
radioactive and will itself subsequently
decay.
–Decay chains or families (e.g. uranium,
thorium decay chains). 36

37. Decay Chains
37
238
94Pu  234
92U + α t1/2 = 88 yrs
234
92U  230
90Th + α t1/2 = 2.5 105
yrs
230
90Th  226
88Ra + α t1/2 = 8.0 104
yrs
226
88Ra  222
86Rn + α t1/2 = 1.6 103
yrs
222
86Rn  218
84Po + α t1/2 = 3.8 days
218
84Po  214
82Pb + α t1/2 = 3.1 min
214
82Pb  214
83Bi + β t1/2 = 27 min
214
83Bi  214
84Po + β t1/2 = 20 min
214
84Po  210
82Pb + α t1/2 = 160 µs

38. Decay Chains
38
210
82Pb  210
83Bi + β t1/2 = 22 yrs
210
83Bi  210
84Po + β t1/2 = 5 days
210
84Po  206
82Pb + α t1/2 = 138 days
206
82Pb is STABLE

39. Decay Chains
39
Pu
U
Th
Ra
Rn
Po
Pb
Hg
Au

40. Beta Decay
• The neutron and the proton are very similar to
each other (very closely related).
• A neutron can ‘change into’ a proton, or vice
versa.
• When this happens, an energetic electron (or
positron) is emitted.
• This is called beta-decay
40
A beta-particle is an electron (e) or
its anti-particle the positron (e+
)
n  p + e-
+ ν
p  n + e+
+ ν

41. Beta Decay
41
In terms of nuclei beta-decay looks like
As in the case of alpha decay the daughter nuclei are
usually radioactive and will themselves decay.
•Beta-particles are HARDER to stop
Since the electron is lighter than an alpha-particle
and carries less charge.
•Therefore, the range of a beta-particle is greater and it
137
55Cs82  137
56Ba81 + e-
+ ν

42. Beta-Decay
42
•Beta-particles are HARDER to stop
Since the electron is lighter than an alpha-
particle and carries less charge.
•Therefore, the range of a beta-particle is greater
and it takes more shielding to stop beta-particles
(electrons or positrons) than alpha particles
~ few mm or 1 cm of lead
~ few feet of air

43. Gamma-Decay
43
•A beta-decay or alpha-decay typically leaves the
daughter nucleus in a highly excited state.
•To get to the ground state the nucleus (rapidly …
almost instantly) emits one or more gamma-rays
•Gamma-rays are a very energetic form of light.
More energy and more penetrating than x-rays.
•No charge
•Much more penetrating than either alpha or beta.
•Few inches of Pb, many feet of air

44. Gamma-Decay
44
•Gamma-ray energies are characteristic of the nucleus.
•Measure the energies … identify the nucleus.
(just like atoms or molecules give off characteristic
colors of light).
Measuring the gamma-ray is by far the best and easiest
way to measure what type of radioactive substance you
are dealing with.

45. Fission
45
What holds nuclei together?
•Protons repel each other (opposites attract, like
repel)
•Coulomb Force
Some other force must hold nuclei together
The STRONG FORCE
•Attractive and Stronger than the Coulomb Force
•But short range

46. Fission
46
What happens if you have a lot of protons (i.e in a
heavy nucleus)?
…Eventually the Coulomb repulsion will win
… and the nucleus will fall apart into two smaller
(radioactive!!) nuclei.
FISSION
An enormous amount of energy is released.
This energy is utilized in power plants and in fission
bombs.

47. Fission
47
The heavy parent
nucleus fissions …
into two lighter fission
fragment nuclei …
Plus some left over bits
… energetic neutrons
Example:
252
Cf is a spontaneous fission source …
Sometimes this
process happens
spontaneously …
sometimes you can
‘poke’ at the
nucleus and induce
it to fission

48. Fission …Fission Fragments
48
Are emitted with a huge energy but stop very quickly
(very short range).
Are all radioactive nuclei and will decay usually by
beta-and gamma-decay
Mass 
Probability Heavy
fragment
Light
fragment
They have a broad
range of masses

49. Induced Fission
49
Some nuclei can be made to fission when struck by
something …
Usually the something is a neutron
Example: 235
U + n  fission
Remember … in the fission process extra neutrons
are released
If some of these strike other 235
U nuclei … they can
induce another fission

50. Induced Fission
50
Chain Reaction
Controlled … nuclear power plant … exactly
one neutron per fission induces another fission.
Uncontrolled … nuclear bomb … more than one
neutron per reaction induces another fission

51. What is a “Dose” of Radiation?What is a “Dose” of Radiation?
• When radiation’s energy is deposited into our body’s
tissues, that is a dose of radiation.
• The more energy deposited into the body, the higher the
dose.
• Rem is a unit of measure for radiation dose.
• Small doses expressed in mrem = 1/1000 rem.
• Rad & R (Roentgens) are similar units that are often
equated to the Rem.
51
From Understanding Radiation, Brooke Buddemeier, LLNL

52. Typical DosesTypical Doses
Average Dose to US Public from All sources 360 mrem/year
Average Dose to US Public From Natural Sources 300 mrem/year
Average Dose to US Public From Medical Uses 53 mrem/year
Coal Burning Power Plant 0.2 mrem/year
Average dose to US Public from Weapons Fallout < 1 mrem/year
Average Dose to US Public From Nuclear Power < 0.1 mrem/year
Occupational Dose Limit for Radiation Workers 5,000 mrem/yr
Coast to coast Airplane roundtrip 5 mrem
Chest X ray 8 mrem
Dental X ray 10 mrem
Head/neck X ray 20 mrem
Shoe Fitting Fluoroscope (not in use now) 170 mrem
CT (head and body) 1,100 mrem
Therapeutic thyroid treatment (dose to the whole
52
From Understanding Radiation, Brooke Buddemeier, LLNL

53. Types of Exposure & Health EffectsTypes of Exposure & Health Effects
• Acute Dose
– Large radiation dose in a short period of time
– Large doses may result in observable health effects
• Early: Nausea & vomiting
• Hair loss, fatigue, & medical complications
• Burns and wounds heal slowly
– Examples: medical exposures and
accidental exposure to sealed sources
• Chronic Dose
– Radiation dose received over a long period of time
– Body more easily repairs damage from chronic doses
– Does not usually result in observable effects
– Examples: Background Radiation and
Internal Deposition
53
Inhalation
From Understanding Radiation, Brooke Buddemeier, LLNL

54. Dividing Cells are the MostDividing Cells are the Most
RadiosensitiveRadiosensitive
• Rapidly dividing cells are more susceptible to
radiation damage.
• Examples of radiosensitive cells are
– Blood forming cells
– The intestinal lining
– Hair follicles
– A fetus
54
This is why the fetus has a exposure limit (over gestation period)
of 500 mrem (or 1/10th
of the annual adult limit)
From Understanding Radiation,Brooke Buddemeier, LLNL

55. At HIGH Doses, We KNOWAt HIGH Doses, We KNOW
Radiation Causes HarmRadiation Causes Harm
• High Dose effects seen in:
– Radium dial painters
– Early radiologists
– Atomic bomb survivors
– Populations near Chernobyl
– Medical treatments
– Criticality Accidents
• In addition to radiation sickness, increased cancer rates
were also evident from high level exposures.
55
From Understanding Radiation,Brooke Buddemeier, LLNL

56. Effects of ACUTE ExposuresEffects of ACUTE Exposures
Dose (Rads*) Effects
25-50
First sign of physical effects
(drop in white blood cell count)
100
Threshold for vomiting
(within a few hours of exposure)
320 - 360
~ 50% die within 60 days
(with minimal supportive care)
480 - 540
~50 % die within 60 days
(with supportive medical care)
1,000 ~ 100% die within 30 days
56
* For common external exposures 1 Rad ~ 1Rem = 1,000 mrem
From Understanding Radiation,Brooke Buddemeier, LLNL

57. At LOW Doses, We PRESUMEAt LOW Doses, We PRESUME
Radiation Causes HarmRadiation Causes Harm
• No physical effects have been observed
• Although somewhat controversial, this
increased risk of cancer is presumed to be
proportional to the dose (no matter how small).
The Bad News: Radiation is a carcinogen
and a mutagen
The Good News: Radiation is a very weak
carcinogen and mutagen!
Very Small DOSE = Very Small RISK
57
From Understanding Radiation
Brooke Buddemeier, LLNL

58. Radiation Detectors
58
Range of Radiation
Alpha: Small. Shield with a piece of paper
Beta: Smallish Shield with a ½ inch or so of Pb
Gamma: Long Shield with a few inches of Pb
Neutron: Very long Shield with many inches of parafin
To detect the radiation it has to
a) Get to and b) Get into your detector

59. Radiation Detectors
59
Almost all work on the same general idea
When an energetic charged particle passes through matter it will
rapidly slow down and lose its energy by interacting with the
atoms of the material (detector or body)
•Mostly with the atomic electrons
It will ‘kick’ these electrons off of the atoms leaving a trail of
ionized atoms behind it (like a vapor trail of a jet plane)
Radiation detectors use a high voltage and some electronics to
measure these vapor trails. They measure a (small) electric
current).

60. Radiation Detectors
60
Like a bullet going through something
A friction force will slow it down and stop it
Friction
More Charge  More friction
More Massive  More friction
More friction  Shorter Range

61. Radiation Detectors
61
It has to get into your detector
e.g. Alpha …. A few inches of air or a piece of paper
stops it … if your detector is a few feet away, it will not
detect the alpha …
e.g. Alpha … if the sides of the detector are too thick the
alpha will not get in and will not be detected

62. Radiation Detectors
62
Neutrons and gamma-rays are neutral
No charge … much less friction … much longer range
When they penetrate matter eventually they also will interact
somehow (gamma-rays interact via Compton scattering,
photoelectic effect or pair production, neutrons will collide with
protons in the nuclei) and these interactions produce energetic
charged particles.
The detectors are sensitive to these secondary particles.

63. Types of detector
63
Alpha, Beta and Gamma radiation
Film Badges
Gas Counters (Geiger counters)
Scintillators
Solid State Detectors

64. Film Badges
64
Will detect: beta, gamma and neutron
Need to send away and develop the film and then later will tell
you what does you received
Used by radiation workers
TLC devices … similar idea but with real-time readout

65. Gas Counters
65
e.g. Geiger Counters
Will Detect: Alpha, Beta, some gamma
No identification … just tells you something is there
With a thin entrance window GM-tube is sensitive to alphas

66. Scintillators
66
Make a flash of light when something interacts
Sodium Iodide
Cesium Iodide
Will Detect: Alpha (with thin window), beta (with thin window)
and gamma.
Gives moderate to bad energy information … some information
on the type of radiation

67. Semiconductor Detectors
67
Germanium
Silicon
Will Detect: Gamma rays (also beta and alphas in a
laboratory, not in the field)
Excellent energy resolution: Can measure exactly was source
you are looking at.

68. Spare Transparencies
68

69. Radioactive Decay
69
When can a nucleus decay? …
•When there is a lighter nucleus for it to decay into
•When this decay is allowed by certain conservation laws ….
•Conservation of energy
•Conservation of charge
•Certain other ‘quantum numbers’
When a physical process can
happen … it will happen.
When it is forbidden to happen
… it just takes a little longer!
If a nucleus can decay
… it will

70. Beta Decay
70
Various laws must be obeyed, including
1. Conservation of Energy
• E = mc2
… a heavy particle can decay into
lighter one(s).
• The excess energy is turned into kinetic
energy of the light particles
2. Conservation of Charge
• An electron is produced
3. Conservation of Lepton Number
• a very nebulous particle called a neutrino is
also produced
n  p + e-
+ ν