Jean-Pierre Meulders

Cross sections for neutron-induced fission of U-235, U-238, Bi-209, and Pb-nat in the energy range from 33 to 200 MeV measured relative to n-p scattering

Abstract The cross sections for neutron-induced fission of 235U, 238U, 209Bi, and natPb in the intermediate-energy region were measured using parallel plate fission ionization chambers. The experiments were carried out relative to the differential n-p scattering cross section using quasi-monoenergetic neutron beams with peak energies ranging from 33 to 200 MeV. The experimental cross sections were compared to International Nuclear Data Committee reference fission cross sections, to results of nuclear model calculations, and to cross sections calculated with the nuclear models implemented in the radiation transport code MCNPX. The experimental results for 235U and 209Bi are consistent with the available reference cross sections and theoretical data while the 238U(n,f) cross section exceeds the reference cross section systematically by ˜7% between 30 and 60 MeV. The experimental results for natPb agree with a parameterization of other experimental data for natPb(n,f).

Secondary light charged particle emission from the interaction of 25- to 65-MeV neutrons on silicon

Abstract Double-differential cross sections for the production of protons, deuterons, tritons, and alpha particles from a silicon target were determined using fast incident neutrons. The inclusive charged particle emission spectra were measured at six laboratory angles, 20, 40, 60, 70, 110, and 140 deg, over the neutron energy range of 25 to 65 MeV. Representative results are shown for the cross-section differentials in energy and angle as well as for angle-integrated cross sections. The spectra are compared to existing data and with predictions from nuclear model calculations. Since the data for 62.7-MeV incident neutrons are the most complete, we emphasized these results; from the experimental energy-differential cross sections, the total charged particle production cross sections are determined as well as the partial and total kerma coefficients for silicon. Moreover, a comparison is done with our data on aluminum, for which exists a consistent set of measured cross sections in the same neutron energy region.

New neutron sources for radiotherapy

All existing neutron sources suffer from disadvantages which would not be tolerated in modern megavoltage X-ray equipment. Experimental work with 30-60 MeV protons on beryllium and other elements has shown how these difficulties can to a large extent be overcome. Angular distributions and kerma rates as a function of proton energy are presented for various targets. Thin targets are found to be a better method than filtration for improving the penetration of the beam. A 237Np fission counter and a GM counter have been used to decompose stray radiation into its neutron and gamma-ray components. A model of a treatment head was found to attenuate the neutron component to less than 1% of its value in the useful beam.

Fast neutron-induced emission of light charged particles on aluminum (E/sub n/=25 to 55 MeV)

Abstract Double-differential cross sections (spectra) for light charged particle (proton, deuteron, triton, and alpha) emission in fast neutron-induced reactions on aluminum are reported for eight incident neutron energies between 25 and 55 MeV, augmenting previous results at 63 MeV. Angular distributions were measured at 15 laboratory angles between 20 and 160 deg. Procedures for data taking and data reduction are presented. Deduced energy-differential and total production cross sections are also reported. Experimental cross sections are compared to existing experimental proton-induced data and to nuclear model calculations that include preequilibrium and compound nucleus decay mechanisms. These calculations formed the basis of a recent set of higher-energy ENDF/B-VI data evaluations (the LA150 Library), and therefore, the present measurements facilitate a testing of the accuracy of these evaluated cross sections. This is important for accelerator-driven-systems design, where radiation transport simulation codes require accurate nuclear data to guide engineering design. Comparisons between the experimental data and the calculated values indicate that while proton, triton, and alpha-particle emission are modeled fairly accurately, deuteron emission is only poorly described, and further improvements to the nuclear reaction models for preequilibrium cluster emission are needed.

Secondary Light Charged Particle Emission from the Interaction of 25-65 MeV Neutrons on Uranium

Double-differential cross sections for light charged particle production in fast-neutron induced (n, px), (n, dx), (n, tx) and (n, αx) reactions on uranium were measured in the incident neutron energy range 25-65 MeV and at laboratory angles from 20° to 160°. In this paper, only a quick review of the experimental arrangement and data reduction procedures will be given. Preliminary inclusive emission spectra for hydrogen isotopes will be shown. From the double-differential cross sections, angle- and energy-differential cross sections as well as total production cross sections are deduced. The measurements are compared to nuclear model calculations which include preequilibrium and equilibrium decay mechanisms: the Liège intranuclear cascade model (INCL) and the GNASH nuclear data code.

Survey of the “Pretherapeutic” Experiments with Fast Neutrons Produced with the 50 Mev Deuteron Beam of Cyclone

The physical and radiobiological experiments performed with the fast neutron beams at the cyclotron of the University of Louvain are described and discussed in view of their therapeutic applications.