Physics and Engineering of Radiation Detection

134 Chapter 2. Interaction of Radiation with Matter

Thickness (arb. units)

0 2 4 6 8 10 12 14 16

N

0

200

400

600

800

1000

Thickness (arb. units)

0246810121416

log(N)

1.6

1.8

2

2.2

2.4

2.6

2.8

3

Figure 2.5.5: Plot of number

of electrons transmitted per unit

thickness of an arbitrary material

as computed from equation 2.5.26.

For this plot we have arbitrarily

taken the initial number of elec-

trons to be 10^3 andμ=1/5. The

plot is shown on both linear (upper)

and semilogarithmic (lower) scales.

Here the energy of the electronsEshould be taken in units ofMeV. The superscript
spofRspe specifies that the expression represents thespecific rangein units ofkg/m^2.
The range (or more specifically the specific range) as computed from these formulae
are independent of the material. This, up to a good approximation, is a correct
statement as can be seen from Fig.2.5.7. Here we have plotted the range using these
functions as well as the ESTAR provided values for aluminum and silicon. ESTAR
is an online database of parameters related to interaction of electrons in elements,
compounds and mixtures (23). It is based on the values tabulated in the ICRU
Report 37 (22). It is apparent from the figure that the variations are quite small
and unless the application requires high accuracy, the above formulae can be safely
used. The case of compounds and mixtures is a little bit complicated, though. For
such materials, these expressions do not give reasonably accurate results specially at