Fission Fragments Angular Measurements
Fission Fragment Angular Distribution Measurements in the Energy Interval 20-200 Mev on a Spallation Neutron Source; Method Development, Manufacturing of Installation and Performing Measurements
Tech Area / Field
- FIR-NOT/Nuclear and Other Technical Data/Fission Reactors
3 Approved without Funding
Khlopin Radium Institute, Russia, St Petersburg
- NRG an ECN KEMA company, The Netherlands, Petten\nJAERI / Tokai Research Establishment, Japan, Tokai Mura
Project summaryNuclear data on fission cross-sections in the range of intermediate neutron energies are obtained in measurements of two types, absolute and relative, and also by calculations with the use of nuclear models. In this field the present point is, that an increase in the body of experimental data only slightly aids in development of the calculation procedures. The intermediate energy range is featured by changes in reaction mechanisms and not only the values of cross-sections themselves but also other data on the fission reaction are required to adjust the calculation codes.
With the aim to obtain such data we propose to perform an inpidual experiment in which the value to be measured is the angle between the directions of two fragments escaping nucleus which fissions under the bombarding neutrons.
Our preliminary study showed that this angle is an explicit, model depending parameter for the fission reaction in the range of intermediate neutron energies. It relates to the momentum delivered to the target nucleus and, hence, to the energy received by the nucleus. The use of this parameter in calculations contributes to separations of two components of fission cross-section, i.e. separating a part corresponding to compound process from the part in which the direct reactions participate.
We plan the experiment to base on technique of relative measurements with “spallation” neutron source; the technique has been used in the ISTC project no. 609. We propose to modernize this system in two ways. In the detector unit the ionization chamber will be replaced with a more complicated device in which both fission fragments are registered by coordinate-sensitive detectors. The data acquisition system of the installation will be upgraded for multi-parameter analysis of signals.
The new procedure makes it possible to obtain two dependences: the previous dependence of fission cross-section on the energy of bombarding neutrons in the range 20-200 MeV and a new dependence of fission cross- section on the energy received by the nucleus in interaction with this neutron. This procedure requires higher neutron flux in comparison with the procedure of one-parameter relative measurements.
The experimental installation will be produced in Khlopin Radium Institute. The fission target (a film transparent to fission fragments, with dimensions more than 8 cm) and coordinate-sensitive wire detectors of the “avalanche” type (with the step of 2 mm) will be arranged in a vacuum-processed vessel with the size nearly 1 m and adjusted for operation as a single unit - a fission detector. The electronic modulus and computer software needed for data acquisition, processing, and displaying will be made. Khlopin Radium Institute has fissionable materials, can manufacture two-side targets and coordinate detectors, and has also experience in experimental work with a “spallation” neutron source. Components of the installation will be tested on the Gatchina’s accelerator.
Neutron source is very important for the project results achievements. We propose to design the installation under the parameters of the WNR neutron source in Los Alamos, because of its highest intensity at present. Travel budget of the Project allows transportation, mounting, and adjusting of the equipment. The results of the Project will be (1) development of the measurement procedure, (2) manufacturing of installation, and (3) performing measurements for three fissionable nuclei which are recognized fission cross-sections standards - 235U, 238U, and 232Th.
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