Bandsaw - A proposal for remeasuring delayed neutron energies, yields and half-lives in AFSR-type reactors

Traditionally, delayed neutrons have been measured by means of a 'rabbit' experiment in which a sample of the fissionable isotope is irradiated in a neutron flux and rapidly transferred to a neutron counting geometry. Here we consider attacking the problem by means of a 'long foil' sample in the form of an endless tape passing bandsaw fashion through the 'glory hole' of a small reactor such as the Argonne Fast Source Reactor. This new approach in a field that has not really been, examined since the Los Alamos work was completed nearly ten years ago, has a number of advantages: It permits of delayed neutron counting under steady-state conditions; there is a chance of observing very short-lived delayed neutrons that might have been overlooked in a rabbit experiment; and it provides by a very wide margin the best look yet at delayed neutron energies. An endless uranium bearing sample tape runs at a constant speed through the glory hole of AFSR and then through a neutron counting geometry located as closely as possible to the reactor core. At various tape speeds the various delayed neutron groups attain their maximum emphasis'. The design of a suitable uranium bearing tape and the best detector arrangement using a 3He-filled proportional counter operating into a multichannel pulse-height analyser are discussed in detail. Such a system would enable the calculation of relative yields, and the data can be re-analyzed for delayed neutron energies. The same equipment used with a gamma spectrometer can be used to analyse the energies of early fission fragment decay gammas. This is of particular value in the calculation of delayed photo-neutron production in reactors containing beryllium or heavy water. Obviously, the overwhelming quantity of data produced by Bandsaw does offer considerable advantage in determining yields and decay constants. Nevertheless, the outstanding advantage of the method is that it permits steady state measurement of delayed neutron spectra. The most suitable sites for performing the experiment are reactors of the AFSR type. However, 236U might be investigated in almost any university reactor thermal column if cadmium tubing is used to define the region of irradiation. (author)