Physics and Engineering of Radiation Detection

102 Chapter 2. Interaction of Radiation with Matter

I 0

d

Source

I

Detector

Collimator Collimator

Detector

Figure 2.3.10: Sketch of a simple

setup for determining the atten-

uation coefficient of a material.

The incident and transmitted in-

tensities (I 0 andI)aremeasured

through two detectors before and

after the slab of the material of

which attenuation coefficient is to

be determined.

B.2 Mixtures and Compounds

The attenuation coefficient of a compound or mixture at a certain energy can be
obtained by simply taking the weighted mean of its individual components according
to

μt =

∑

i

wiμit and (2.3.44)

μm =

∑

i

wiμim, (2.3.45)

wherewiis the weight fraction ofith element in the mixture or compound having
total linear and total mass attenuation coefficients ofμitandμimrespectively.
Fig.2.3.11 shows the dependence of mass attenuation coefficients of water and
dry air on energy.

Energy(MeV)

10 -3 10 -2 10 -1 1 10

2 /g)

(cmm

μ

10 -1

1

10

102

103

Figure 2.3.11: Depen-

dence of mass attenua-

tion coefficients of water

(solid line) and dry air

(dotted line) on energy.