Physics and Engineering of Radiation Detection

120 Chapter 2. Interaction of Radiation with Matter

Energy(MeV)

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Range (mm)

0

10

20

30

40

50

60

Figure 2.4.7: Range ofα-particles in air

as computed from equations 2.4.23 (solid

line) and 2.4.24 (dashed line).

Example:

Compute the range of 4MeV α-particles in air and tissue.

Solution:

Using equation 2.4.23 we get

Rαair =(0. 05 Eα+2.85)Eα^3 /^2

=24. 4 mm=2. 44 cm.

To calculate the range in tissue we can make use of the simplified Bragg-

Kleeman identity 2.4.25

Rtissue=3. 37 × 10 −^4 Rairα

√

Atissue

ρtissue

.

Substitutingρtissue=1g/cm^3 andAtissue≈9 in the above equation, we get

Rtissueα ≈ 3. 37 × 10 −^42. 44

√

9

1

=10. 1 × 10 −^4 cm=10. 1 μm.

As an exercise, let us also compute the range in air using equation 2.4.24.

Rairα =1. 24 Eα− 2. 62

=2. 34 cm

This shows that the relative difference between the ranges calculated from the

relations 2.4.23 and 2.4.24 is only 4% for 4MeV α-particles.