BACK-TO-BACK GRIDDED IONIZATION DETECTOR TECHNIQUE FOR THE DETERMINATION OF FRAGMENT ANGLE AND ITS USE FOR THE MEASUREMENT OF NEUTRON ANGULAR-DISTRIBUTIONS IN U-235 (NTH, F)

A back-to-back gridded ionization chamber was used to measure the prom pt neutron angular distributions after determining the fission fragmen t angle with incorporation of energy loss correction in the target and backing material. The correspondence of the ratio (V(g)/V(c)) of the grid pulse height to the collector pulse height with cos theta is made use of to derive energy loss corrected V(g) and V(c) values. The frag ment angle is obtained from the corrected grid pulse heights after det ermining the calibration constants for 0-degrees and 90-degrees emissi on angles as a function of energy and mass of the fission fragments. A n angular resolution of 2-degrees to 3-degrees [FWHM] for each fragmen t could be obtained over a large angular range on each side of the ion ization chamber. The chamber was used along with a NE213 neutron detec tor to measure the angular distributions of the prompt neutrons emitte d in the thermal neutron induced fission of 235 U-235, and results of these are reported as an illustration of the present method.