Nuclear data needs for the space exploration initiative

On July 20, 1989, the President of the United States announced a new direction for the US Space Program. The new Space Exploration Initiative (SEI) is intended to emplace a permanent base on the Lunar surface and a manned outpost on the Mars surface by 2019. In order to achieve this ambitious challenge, new, innovative and robust technologies will have to be developed to support crew operations. Nuclear power and propulsion have been recognized as technologies that are at least mission enhancing and, in some scenarios, mission enabling. Because of the extreme operating conditions present in a nuclear rocket core, accurate modeling of the rocket will require cross section data sets which do not currently exist. In order to successfully achieve the goals of the SEI, major obstacles inherent in long duration space travel will have to be overcome. One of these obstacles is the radiation environment to which the astronauts will be exposed. In general, an unshielded crew will be exposed to roughly one REM per week in free space. For missions to Mars, the total dose could exceed more than one-half the total allowed lifetime level. Shielding of the crew may be possible, but accurate assessments of shield composition and thickness are critical if shield masses are to be kept at acceptable levels. In addition, the entire ship design may be altered by the differential neutron production by heavy ions (Galactic Cosmic Rays) incident on ship structures. The components of the radiation environment, current modeling capability and envisioned experiments will be discussed

Neutron induced fission cross section measurements of 240

Accurate neutron induced fission cross section of 240Pu and 242Pu are required in view of making nuclear technology safer and more efficient to meet the upcoming needs for the future generation of nuclear power plants (GEN-IV). The probability for a neutron to induce such reactions figures in the NEA Nuclear Data High Priority Request List [1]. A measurement campaign to determine neutron induced fission cross sections of 240Pu and 242Pu at 2.51 MeV and 14.83 MeV has been carried out at the 3.7 MV Van De Graaff linear accelerator at Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig. Two identical Frisch Grid fission chambers, housing back to back a 238U and a APu target (A = 240 or A = 242), were employed to detect the total fission yield. The targets were molecular plated on 0.25 mm aluminium foils kept at ground potential and the employed gas was P10. The neutron fluence was measured with the proton recoil telescope (T1), which is the German primary standard for neutron fluence measurements. The two measurements were related using a De Pangher long counter and the charge as monitors. The experimental results have an average uncertainty of 3–4% at 2.51 MeV and for 6–8% at 14.81 MeV and have been compared to the data available in literature

MULTI: a FORTRAN code for least-squares shape fitting of neutron cross- section data using the Reich--Moore multilevel formalism

The FORTRAN code MULTI shape fits a multilevel R-matrix formula to experimental neutron cross-section data by the leastsquares technique. The program utilizes the multilevel formalism developed by Reich and Moore for neutron reactions involving 0, 1, or 2 fission channels per spin state. Each spin state may be chosen to represent s-, p-, d-, f-, or g-wave neutron reactions. The cross sections can be Doppler-broadened and resolutionbroadened by a Gaussian function, an exponential function, or a convolution of a Gaussian and an exponential function. The program can simultaneously fit all four neutron cross sections, can handle a maximum of 1600 data points and 100 resonances, and search on at most 150 parameters. Nine sample problems and a FORTRAN listing are given in the Appendices. (auth

Fast neutron capture with a white neutron source

A system has been developed at the Los Alamos National Laboratory to measure gamma-rays following fast neutron reactions. The neutron beam is produced by bombarding a thick tantalum target with the 800 MeV proton beam from the LAMPF accelerator. Incident neutron energies, from 1 to over 200 MeV, are determined by their times of flight over a 7.6-m flight path. The gamma-rays are detected in five 7.6 x 7.6-cm cylindrical bismuth germanate (BGO) detectors which span an angular range from 45/sup 0/ to 145/sup 0/ in the reaction plane. With this system it is possible to simultaneously measure the cross section and angular distribution of gamma-rays as a function of neutron energy. The results for the cross section of the /sup 12/C(n,n'..gamma..=4.44 MeV) reaction at 90/sup 0/ and 125/sup 0/ show good agreement with previous measurements while the complete angular distributions show the need for a large a/sub 4/ coefficient which was not previously observed. Preliminary results for the /sup 12/C(n,n'..gamma..=15.1 MeV) reaction have also been obtained. The data obtained for the /sup 40/Ca(n,..gamma../sub 0/) reaction in the region of the giant dipole resonance demonstrate the unique capabilities of this system. Future developments to the neutron source which will enhance the capabilities of the system are presented. 14 references

High resolution measurement of the /sup 231/Pa(n,f) cross section from 0. 4 eV to 12 MeV

The /sup 231/Pa(n,f) reaction was studied to shed light on the existence of a shallow third minimum in the /sup 232/Pa fission barrier. Results are plotted along with data points derived from ENDF/B-V. The occurrence of a pure vibrational state at E/sub n/ = 156.7 keV (3/sup +/) together with a nearby state of opposite parity favors the evidence for a third asymmetrically deformed minimum in the /sup 232/Pa fission barrier. 2 figures. (RWR

WNR/PSR facility: neutron physics capabilities from sub-thermal to 800 MeV

The Weapons Neutron Research facility (WNR) is a versatile pulsed neutron source used in a variety of research programs ranging from fundamental neutron properties with ultra cold neutrons to medium energy charge exchange reaction studies. Here we describe the WNR facility and the improvements presently in progress as the Proton Storage Ring (PSR) becomes operational. 14 refs., 11 figs