Hans-Hermann J. Knitter and Carl Budtz-Jørgensen

Commission of the European Communities,
Joint Research Centre - Geel-Establishment,
Central Bureau for Nuclear Measurements, 2440 Geel, Belgium

Progresses in the development of experimental techniques for fission data measurements are reviewed briefly. This review comprises techniques for the preparation of special compound nuclei leading to fission (fission entrance) as well as experimental techniques which permit the measurement of the diversified characteristics of the emitted radiations in fission (fission exit). The latter developments are only considered when also other parameters than yield, mass, and energy of fission fragments are determined. Ionization chambers developed at CBNM are described in more detail. A simple ionization chamber with Frisch grid was used to determine fission layer characteristics, e.g. the number of fissile nuclei of a sample with an accuracy of smaller than 0.3%. A twin ionization chamber is described which has an advantageous 2×2π solid angle for fission fragment detection, a timing jitter of less than 0.7 ns, an energy resolution of smaller than 500 keV for fission fragments, and an angular resolution of ΔcosΘ < 0.05. Also the nuclear charge distribution of the fragments can be determined. A pulse pile-up rejection circuit was developed, which reduces pulse pile-up by more than a factor 30.

This detector is well suited for correlation measurements between fission fragment parameters, like mass and total kinetic energy, and the characteristics of the different radiations emitted from the fragments. This type of ionization chamber was successfully used in several experiments and some results are shown to demonstrate its capabilities.

KEYWORDS: Fission fragment detectors, neutron-fragment correlations, ternary fission