Basic Radiation Physics Detection and Measurement of Radiation

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Nuclear Physics and SocietyPhysics
DepartmentUniversity of RichmondNuclear
Basics
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Motivation Educate the Public and University
communities about basic nuclear physics ideas and
issues
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

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DOE Workshop

• 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 gt 1 hour delay

Cargo Containers 10,000,000 per year 10,000 per
ship! 5 / minute _at_ L.A. lt 3 inspected
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What the Course is/is not
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.
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Who are We
Con Beausang Chairman Associate Professor
Physics Department Jerry Gilfoyle Professor,
Physics Department Paddy Regan Professor Physics
Department, University of Surrey, U.K.
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Nuclear Physics and Society
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 1215 ? 330
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 1215 ? 330 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
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The Cookie Quiz
Alpha cookie
Beta cookie
Neutron cookie
Gamma cookie
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The Cookie Quiz
Beta cookie
Alpha cookie
Gamma cookie
Neutron cookie
Throw away
Put in pocket
Hold in clenched fist
GOAL Minimize your radiation exposure
Eat one
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The Cookie Quiz Answer 1
Neutron cookie
Throw away
Beta cookie
Put in pocket
Gamma cookie
Eat one
Alpha cookie
Hold in clenched fist
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The Cookie Quiz Correct Answer
Alpha cookie
Beta cookie
Throw away
Gamma cookie
Neutron cookie
GOAL Minimize your radiation exposure
Put in pocket
Mutiny at once Retire from the navy and Toss ALL
cookies away
Hold in clenched fist
Eat one
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What are we made of ?
when I was young(er), I was curious
sugar and spice and all things nice thats
what little girls are made of snips and snails
and puppy dogs tails thats what little boys
are made of.
ok mum, so what are sugar, spice and snails
etc. made of?
cells molecules atoms nuclei
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The Uncertainty Principle
Heisenberg (Quantum Mechanics) D(position)
D(momentum) gt Constant
Beausang (Teaching) D(truth) D(clarity) gt
Constant
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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
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How do we know?
Detector Zinc-sulfide screen
How to see the invisible? size of your probe
scattering
The eyes of Geiger and Marsden
Alpha-particle beam
16-inch Battleship shells and tissue paper
Discovery of the nucleus 1910
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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
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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

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The Nucleus

• Made up of protons and neutrons
• Almost all of the mass of the atom is
  concentrated in the nucleus.
• gt99.9 of the known mass in the universe.
• Occupies almost none of the volume of the atom.
• Radius lt 1/10,000
• Volume lt 1/1,000,000,000,000

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

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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!
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Delicate Balances

• Laws of Physics
• If it can happen it will happen
• If some law forbids it to happen it will happen
  more slowly
• If a process is really REALLY forbidden to happen
  it just takes a long time

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quark structure proton (uud) neutron (udd)
Standard Model Neutron and proton are very close
relatives
Many laws allow neutrons to change into into
protons change a d-quark into a u-quark (or
vice versa)
beta-decay
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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 gt 1031 years
Inside some nuclei protons can decay into
neutrons
E mc2
Imagine if they were not! Then in 1-2 hours
the entire universe would be made of Hydrogen
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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 (11H)
• 1 proton, 0 neutrons
• Mass 1
• Helium (42He) (Alpha-particle)
• 2 protons, 2 neutrons
• Mass 4

• Uranium (23892U)
• 92 protons, 146 neutrons
• Mass 238

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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
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The Periodic Table of the Elements
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Chart of the Nuclei
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Chart of the Nuclei
The Landscape 300 stable 7000 unstable
radioactive.
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Half Life
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.
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Some Isotopes Their Half Lives
ISOTOPE HALF-LIFE APPLICATIONS
 Uranium billions of years  Natural uranium is comprised of several different isotopes. When enriched in the isotope of U-235, its 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.
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The Amount of Radioactivity is NOT 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-60has the same activity as
  1800 tons of natural Uranium

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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
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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.
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Types of Radioactivity
Five Common Types Alpha Decay Beta Decay Gamma
Decay Fission Neutron Emission
Each type of radiation has different properties
which affect the hazards they pose, the detection
mechanism and the shielding required to stop them.
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.
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Alpha Decay
An alpha particle (?) is an energetic, He nucleus
(42He2) Alpha decay mostly occurs for heavy nuclei
Example 23894Pu ? 23492U 42He Half-life 88
years Energy ? 5.56 MeV
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Alpha Decay
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
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Alpha Decay

• 23894Pu144 ? 23492U142 a
• Parent nucleus 23894Pu144
• Daughter Nucleus 23492U142
• Often the daughter nucleus is also radioactive
  and will itself subsequently decay.
• Decay chains or families (e.g. uranium, thorium
  decay chains).

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Decay Chains
23894Pu ? 23492U ? t1/2 88 yrs
23492U ? 23090Th ? t1/2 2.5 105 yrs
23090Th ? 22688Ra ? t1/2 8.0 104 yrs
22688Ra ? 22286Rn ? t1/2 1.6 103 yrs
22286Rn ? 21884Po ? t1/2 3.8 days

21884Po ? 21482Pb ? t1/2 3.1 min
21482Pb ? 21483Bi ? t1/2 27 min
21483Bi ? 21484Po ? t1/2 20 min
21484Po ? 21082Pb ? t1/2 160 ?s
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Decay Chains
21082Pb ? 21083Bi ? t1/2 22 yrs
21083Bi ? 21084Po ? t1/2 5 days
21084Po ? 20682Pb ? t1/2 138 days
20682Pb is STABLE
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Decay Chains
Pu
U
Th
Ra
Rn
Po
Pb
Hg
Au
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Beta Decay
A beta-particle is an electron (e) or its
anti-particle the positron (e)

• 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

n ? p e- ?
p ? n e ?
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Beta Decay
In terms of nuclei beta-decay looks like
13755Cs82 ? 13756Ba81 e- ?

• 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 takes more shielding to stop
  beta-particles (electrons or positrons) than
  alpha particles
• few mm or 1 cm of lead
• few feet of air

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Beta-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 takes more shielding to stop
  beta-particles (electrons or positrons) than
  alpha particles
• few mm or 1 cm of lead
• few feet of air

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Gamma-Decay

• 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

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Gamma-Decay

• 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.

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Fission

• 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

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Fission
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.
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Fission
The heavy parent nucleus fissions
into two lighter fission fragment nuclei
Sometimes this process happens spontaneously
sometimes you can poke at the nucleus and
induce it to fission
Plus some left over bits energetic neutrons
Example 252Cf is a spontaneous fission source
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Fission Fission Fragments
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
Light fragment
Heavy fragment
They have a broad range of masses
Probability ?
Mass ?
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Induced Fission
Some nuclei can be made to fission when struck by
something Usually the something is a
neutron Example 235U n ? fission
Remember in the fission process extra neutrons
are released If some of these strike other 235U
nuclei they can induce another fission
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Induced Fission
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
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What is a Dose of Radiation?

• When radiations energy is deposited into our
  bodys 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.

From Understanding Radiation, Brooke Buddemeier,
LLNL
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Typical 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 lt 1 mrem/year
Average Dose to US Public From Nuclear Power lt 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 body) 7,000 mrem
From Understanding Radiation, Brooke Buddemeier,
LLNL
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Types 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 andaccidental
  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 andInternal
  Deposition

Inhalation
From Understanding Radiation, Brooke Buddemeier,
LLNL
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Dividing Cells are the Most Radiosensitive

• Rapidly dividing cells are more susceptible to
  radiation damage.
• Examples of radiosensitive cells are
• Blood forming cells
• The intestinal lining
• Hair follicles
• A fetus

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
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At HIGH Doses, We KNOW Radiation 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.

From Understanding Radiation,Brooke Buddemeier,
LLNL
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Effects 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
For common external exposures 1 Rad 1Rem
1,000 mrem
From Understanding Radiation,Brooke Buddemeier,
LLNL
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At LOW Doses, We PRESUME Radiation 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

From Understanding Radiation Brooke Buddemeier,
LLNL
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Radiation Detectors
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
• Get to and b) Get into your detector

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Radiation Detectors

• 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).

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Radiation Detectors
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
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Radiation Detectors
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
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Radiation Detectors
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.
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Types of detector
Alpha, Beta and Gamma radiation Film Badges Gas
Counters (Geiger counters) Scintillators Solid
State Detectors
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Film Badges
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
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Gas Counters
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
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Scintillators
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
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Semiconductor Detectors
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.
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Spare Transparencies
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Radioactive Decay
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

• 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

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Beta Decay
n ? p e- ?

• Various laws must be obeyed, including
• 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
• Conservation of Charge
• An electron is produced
• Conservation of Lepton Number
• a very nebulous particle called a neutrino is
  also produced