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Energy Dependence
Intrinsic energy dependence
Detector reading to the average dose to the material of the sensitive detecting element
D
det
(Q) = F
cal
(Q)· M
det
(Q)
Ion chamber: F
cal
=1 (W/e constant)
TLD: TLD response per unit of dose varies between 5% and 15% for low energy photons
Absorbed dose- energy dependence
Relates the dose to the detector material to the dose to the medium
D
med
(Q) = f(Q) · D
det
(Q) =f
Q
· D
det
(Q)
Burling
f(Q) is calculated by MC
Cavity Theory
Cavity Theory
g sections the following two limiting cases have been analyzed:
rs that are large compared to the electron ranges, and in which, there-
E is approximately established (photon radiation only): section 2.
rs that are small compared to the electron ranges and which there-
as “sensers” of the electron fluence existing in the uniform medium
Gray cavities): section 3.
s involve measuring the dose from photon (or neutron) radiation
that fall into neither of the above categories (see next section); for
there is no exact expression for the ratio
D
med
/
D
det
. Burlin (1966)
so-called “General Cavity Theory” to treat these cases approxi-
osed a factor, which is a weighted mean f the s opping-power ratio
nergy absorption coefficient ratio; this factor, slightly simplified
(3.29a)
ighting actor which v ri s etween unity for small (or Bragg-Gray)
ro for large cavities (or photon detectors). Burlin provided a formula
ased on the exponential attenuation of the electron fluence entering
ugh the wall (build-down), balanced by the exponential build-up of
rated electron fluence:
D
D
d
L
d
med
med
en
det
det
=
æ
è
ç
ç
ö
ø
÷
÷ + -
(
)
æ
è
ç
ç
ö
ø
D
r
m
r
1
÷
÷
med
det
,
Alan E. Nahum