423Chapter 7
Position Sensitive Detection and Imaging
The spatial variation in energy and intensity of radiation has been found to be a
very useful tool in many disciplines. For example medical x-ray diagnostics utilize
the change in radiation intensity due to relative attenuation coefficients of different
organs and bones inside the body to create a two-dimensional image. In fact, with
the advent of electronic detectors, a lot of progress has been made in building two-
and three-dimensional imaging systems for medical diagnostic purposes. However
the development has not been limited to medical applications. Other fields, such as
particle physics research, environmental radiation monitoring, and non-destructive
testing of materials have equally benefited from these developments. Latest advance-
ments, such as charged coupled devices, multistrip silicon detectors, and microstrip
gas chambers have taken this field of research and development to a higher level of
sophistication and utility.
Position sensitive detection and imaging are two fields that have some overlapping
areas in terms of technology. For example the detector technologies used in both
systems are very similar but the processing of data for imaging systems is much
more involved than for position sensitive detectors. By position sensitive detector
we mean a system with which one could find the position of an interacting particle
up to a certain resolution. In such a system the radiation is allowed to interact
directly with the detector. An imaging system, on the other hand, is concerned
about creating the image of an object by exposing it to radiation and then detecting
the reflected or transmitted radiation.
In this chapter we will first discuss the position sensitive detection and then
move on to the imaging devices. But before we do that it is worthwhile to introduce
the reader to some terminologies and quantities that are used to characterize the
operation of these devices.7.1 Some Important Terminologies and Quantities
Since position sensitive detectors and imaging devices are essentially based on similar
concepts of particle detection, therefore most of the terminologies and quantities that
will be introduced here are common to both of them.7.1.A SpatialResolution
A basic requirement of all position sensitive and imaging detectors is that they must
be able to distinguish between intensities at two closely spaced points in space. The