Dosimetry requirements in support of an in-reactor radiation chemistry programme

Reactors are now used as radiation sources in a wide range of studies. In some, the changes observed result from the interaction of the irradiated material with only one type of radiation present in the reactor; in others, a number of different radiations may produce the observed effect. In any investigation of the effects of radiation on matter, it is necessary to know the spectrum of the radiation used. This information should be available in the form of the variation of photon or particle flux density with photon or particle energy. The amount of change observed in an irradiated material will always be the product of the radiation flux density and an interaction function, integrated over the radiation spectrum. The nature of this interaction function will vary with the type of study being performed. The radiation spectra in reactors are complex in form and cover wide ranges of photon and particle energies. Given sufficient information about the fission reaction, and about the geometry and materials of construction of a reactor, it is possible, in principle, to calculate the spectra of the reactor radiations. It is then possible, in principle, to calculate the rates of production of change in irradiated materials. In this paper the conventions used in radiation chemistry are discussed. This is followed by a discussion of the various types of calorimeters which can be used for dosimetry, with some remarks about their limitations. The reasons for choosing an isothermal-type calorimeter for the work at the Atomic Energy Research Establishment (AERE) are given, followed by a description of the construction, characteristics, and calibration of the calorimeters in use. It is shown that under the proper conditions these calorimeters measure the ideal absorbed dose-rate, or kerma rate. By the use of three calorimeters, as described, containing respectively graphite, anthracene, and an empty can, measurements were made of the dose rates in graphite and in anthracene, and in the reactor BEPO at AERE. The problem of correlating the calorimetric experiment with the chemical experiment is discussed. Ionization chambers are also being used at AERE and a description of their construction, characteristics, and calibration is given. The ionization chambers described measure the ideal absorbed dose-rates in graphite. A comparison is made of calorimeters and ionization chambers, and it is concluded that both probably have a place in routine dosimetry. By intercomparison of the data obtained in the two ways something is learned about the loss of secondary radiation across a boundary between two materials