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The Nature of Radiation

January 10, 2001

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Learning Objectives

Know basic constituents of the atom Define and give an examples of:

Isotopes Nuclides Radionuclides Radioisotopes Radiations

Know major radiation interactions in matter

Become familiar with and use equations to describe radiation interactions

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Learning Objectives

List charged and uncharged particles Write the equation that describes how

uncharged particles are attenuated Describe/draw an image of how

uncharged particles penetrate into matter

Calculate the: Range of an alpha particle in air Range of a beta particle in a known

material Attenuation of a photon beam Attenuation of a neutron beam

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Basic Nuclear Particles

Neutron, mass = 1.008665 amu

Proton, mass = 1.007277 amu

Atom: consists of protons,neutrons & electrons

Electron, mass = 0.000549 amu

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Basic Nuclear Particles

Alpha (), mass = ~4 amu

Beta (-), mass = 0.000549 amu

Positron (+), mass = 0.000549 amu

Gamma ray, no mass

X ray, no mass

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Nuclear Terms Nucleons

Protons and neutrons Nuclide

Species of atom defined by Z and A 1H, 238U, 2H are all nuclides

Isotopes Nuclides of same element (Z),

different number of neutrons (N) 1H, 2H, 3H are isotopes of H

Isotones Nuclides with same number of

neutrons 206Pb and 204Hg

N

A

Z X

Mass number

= Z + N

Atomic number

Neutron

number

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Nuclear Terms, continued

Radionuclide Radioactive nuclide

Radioisotope Radioactive isotope

Radiation Particles or waves with

sufficient energy to interact with or cause ionization of the atoms with which they interact

N

A

Z X

Mass number

= Z + N

Atomic number

Neutron

number

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Classification of Nuclear Particles

alpha (), + 2 charge

beta (-), -1 charge

positron (+), + 1 charge

Proton, +1 charge

Electron, -1 charge

Charged Particles

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Classification of Nuclear Particles

Uncharged

Particle

s

Neutron

Gamma ray

X ray

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e -e - e -

e -

e -

e - e -

e -

e -

e -

e -

e -

e -e -

e -

e -

e -

e -

e -

e -

e -e -

e -

e +

alpha ()

beta (-)

positron (+)

ionization

ionization

Ionizationandannihilationradiation

annihilation radiation0.511 MeV

annihilation radiation0.511 MeV

Charged Particle Interactions

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fast neutron

thermal neutron

elastic scatteringof nuclei and production of recoil nuclei

diffusion Absorption with (n,) reaction

photon

recoil nuclei

recoil nuclei

recoil nuclei

e -

e -

e -

e -photons

Uncharged Particle Interactions

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Important Radiation Interactions in Matter Production of Bremsstrahlung Photon Interactions

Photoelectric Effect Compton Effect Pair Production Positron Annihilation

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e -

e -e -

Electrons are deflected and accelerated in theCoulomb field of the nucleus.

Bremsstrahlung Radiation

Accelerated electriccharges emit electromagnetic waves (X-rays)

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Photon Interactions - Photoelectric Effect

e -

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Photon Interactions - Compton Effect

e -

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Photon Interactions – Pair Production

e -e +

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Photon Interactions – Positron Annihilation

e -e +

e -e +

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Important Equations

Alpha Particle Range Beta Particle Range Proton Range Photon Absorption Neutron Absorption

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Alpha Particle Range

Where: R = range in cm of air at 1

atm and 15oC E = energy in MeV

Note…this is an empirically derived equation, the units don’t “work out”

2/3318.0 ER

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Sidebar: Types

of equations Dimensionally correct

Internally consistent May be physics based May include empirically derived

Example: Velocity (m/s) = distance (m) / time (t) Units “work out”

Examples Radiation attenuation equations Radioactive decay

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Empirically derived Experimental method of science

applied to the creation of equations. Hypotheses generated to test theory Data collected and analyzed. Patterns extracted to describe

observed behavior Units may not “work out”

Examples Many “rules of thumb” Range equations

Sidebar: Types

of equations

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Beta Particle Range

For particles 0.01<E<2.5 MeV Where

R = range expressed in mg/cm2

E = maximum energy in MeV

Note…this is also an empirically derived equation, the units don’t “work out”

EER ln0954.0265.1412

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Proton Range

Where Rp = range expressed in

meters of air E = energy in MeV (few MeV to

200 MeV)

Note…this is also an empirically derived equation, the units don’t “work out”

8.1

3.9

E

Rp

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The “one-size fits all” equation

teAA 0

 

xeII 0

teNN 0

Activity decay equation

Atom decay equation

Photon attenuation equation

And many more….

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Photon Absorption

Where I0 is the original exposure rate or

beam fluence or flux I is the attenuated exopsure rate,

fluence or flux is the linear absorption coefficeint

(cm-1) x is the thickness of the absorber e is the base of the natural logarithm

(2.718..)

xeII 0

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Neutron Absorption

Where I0 is the original neutron intensity I is the attenuated neutron intensity N is the number of atoms per cm3 in the

absorbing material is the cross section of the abosrber

(capture coefficient (cm2) x is the thickness of the absorber (cm) e is the base of the natural logarithm

(2.718..) is the macroscopic cross section of the

absorber

xNx eIeII 00

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Behavior of Exponential Functions

t, x, or Z

N0

N

Linear plot

t, x, or Z

ln (N0)

ln N

Semi-log plot

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The Chart of the Nuclides

Still available See Jean Robinson, NE Office

A portable resource Known elements

Stable and radioactive forms Periodic table Brief description of nuclear

properties Conversion tables!

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Chart of the Nuclides

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Chart Information

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Chart Information, cont’d

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Chart Information, cont’d

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Chart Information, cont’d

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Summary

Basic constituents of the atom Defined and give an examples of

nuclear terms Described major radiation

interactions in matter Listed equations to describe

radiation interactions Layout of the Chart of the

Nuclides