Diapositive 1

Energy Dependence

Intrinsic energy dependence

Detector reading to the average dose to the material of the sensitive detecting element

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

med

(Q) = f(Q) · D

det

(Q) =f

· 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

med

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:

med

det

÷ + -

(

)

med

det

Alan E. Nahum