Physics and Engineering of Radiation Detection

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Chapter 12

Radiation Spectroscopy

Radiation spectroscopy refers to a class of techniques that utilize different properties

of radiation to study materials and particles. Its usefulness in research and indus-

trial environments is well established. Perhaps the biggest advantage of radiation

spectroscopy is that it is essentially a non-destructive technique.

Because of its direct industrial applications and research value, radiation spec-

troscopy has seen immense developments not only in techniques but also in related

instrumentation. Even though this entire chapter has been devoted to the discussion

of this field, it is not intended to be a comprehensive guide. However every attempt

has been made to give an overall picture of different techniques and spectrometers

that are in common use.

Most of the discussions in this chapter have been organized with respect to the

types of radiation. That is, the spectroscopy of different radiation types have been

discussed separately. This was necessary due to the differences in the techniques and

instruments that are used for different kinds of radiation. At the end of the chapter,

the technical aspects ofmass spectroscopyandtime spectroscopyare also discussed.

12.1SpectroscopyofPhotons.........................

12.1.Aγ-RaySpectroscopy

Because of their deep penetrating power,γ-rays are routinely used for nuclear spec-

troscopy. The lower energy photons that originate from electronic transitions (such

as x-rays) are not suitable for this purpose mainly due to their lower penetration

power as compared toγ-rays.

The standard system used forγ-ray spectroscopy consists of aNaI(Tl) scintil-

lator and a photomultiplier tube. The scintillator converts theγ-ray photons into

visible light photons, which are detected by the photomultiplier tube. A photo-

multiplier tube is not absolutely necessary since, in principle, any photodetector

with appropriate efficiency and sensitivity can be used. However, the scintillator

and photomultiplier combination is more popular. The reader is encouraged to go

through the relevant sections in the chapter on scintillators and photodetectors for

more details. Here we will concentrate on their use inγ-ray spectroscopy.

Atypicalγ-ray spectroscopy setup usingNaIscintillator is shown in Fig.12.1.1.

The shield shown in the figure has two purposes. One is to protect the personnel from

radiation exposure and the other is to minimize the background in the detector. The

source and the detector are positioned such that most of theγ-ray photons from the