ABSTRACT
Relative measurements are, in most cases, easier than absolute measurements. This chapter discusses the factors that should be taken into account in performing absolute and relative measurements. The geometry may affect the measurement in two ways. First, the medium between the source and the detector may scatter and may also absorb some particles. Second, the size and shape of the source and the detector and the distance between them determine what fraction of particles will enter the detector and have a chance to be counted. A general method that can be used with any geometry is based on a Monte Carlo calculation, which simulates, in a computer, the emission and detection of particles. Radioactive substances are deposited on a backing material in thin deposits. In most measurements, the source is located outside the detector. Charged particles moving through matter will always have Coulomb interactions with the electrons and nuclei of that medium.
