ch2 interaction with matter
TRANSCRIPT
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Chapter 2: Gamma Ray
Interactions with MatterDr. Phillip C. Womble
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Mean Free Path• Consider a radiation withan initial intensity of I0
• The intensity diminishes
every m it travels in anexponential manner soI(x) is the intensity in xmeters
• The mean free path is
dened aso vera!e distan"e that a
!amma ray travels beforeintera"tin!
α
α
1
)(0
=
=−
x
e I x I x
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Making It Look Like the
Book• Consider a radiation
with an initialintensity of I
0
• µl is the linear
atten#ation "oe$"ientin "m%&.
µ
µ
1
)( 0
=
=−
x
e I x I x
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Photon Interactions• Whether x%ray or γ %
ray' we examine
their absorption• Two fa"tors of x%ray
absorptiono The spa"in! between
atoms (density)
o
The n#mber of ele"tronson ea"h atom
• This n#mber is "alledthe * n#mber
• Is e+#al to then#mber of protons
,
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Transmission Thru Lead
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Linear AbsorptionCoefficients
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Density is Important
• The tro#ble with µl is that it does not ta-e mass
into a""o#nt
• ass atten#ation "oe$"iento /atio of µl to ρ (µlρ)
• Density in !"m1 is ρ.
• Cal"#latin! mass atten#ation "oe$"ient of"ompo#ndo
Wei!ht fra"tion 2 per"enta!e of the total wei!ht that an element"omprises' wi
∑=i
iicompound w µ µ
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3 Interactions of GammaRays with Materials
• Photoele"tri" 34e"t
• Compton 5"atterin!
• Pair Prod#"tion
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Photoelectric Effect
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Compton Scattering
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Practical Effect on Spectra
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Pair Production
Must have at least 2 xrest mass of electronenergy or 1.022 MeV
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Filters
Usually used in measurement of Pu gamma rays
ALL Pu samples have241
Am as an indicator
Thin Cd sheet
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Shielding Information