Physics and Engineering of Radiation Detection

12.2. Spectroscopy of Charged Particles 697

points. The procedure would then be simply to first adjust the zero point of the
MCA, obtain the spectra of the two sources, and then draw the calibration curve.

A.1 Energy of an Unknownα-Source

In the previous section we saw how a detection system can be calibrated. After
the calibration has been performed, one could essentially place any source in the
vacuumed container, obtain the MCA spectrum, and determine the energies corre-
sponding to the various peaks observed. The peaks can then be used to identify the
isotopes present in the sample.

A.2 Range and Stopping Power ofα-particles in a Gas

Using the setup shown in Fig.12.2.1, one can determine the range and stopping
power ofα-particles in air provided the vacuum system is equipped with a precision
pressure gauge.

A.3 Activity of anαSource

A very commonly performed experiment in radiation laboratories is to find the
activity of anαsource. Anαspectroscopy system can be used for the purpose.
The experiment is fairly straightforward and involves capturing theαpeak of the
source. The source is placed at a known distance away from the detector as shown
in Fig.12.2.4 and the energy spectrum is captured for a known period of time. The
spectrum shows a peak (see Fig.12.2.5), which characterizes the activity due to the
αparticles.

r

d

Detector

d

r

Detector

Source

Source
Figure 12.2.4: Source-detector geometry for deter-
mination ofαactivity of a source.

Theαactivity can then be calculated from the relation

A=

Cα

T

4 πd^2

πr^2

. (12.2.2)