Double-differential cross sections for light charged particle production (up to A=4) were measured in 96 MeV neutron-induced reactions, at the TSL Laboratory Cyclotron in Uppsala (Sweden). Measurements for three targets, Fe, Pb, and U, were performed using two independent devices, SCANDAL and MEDLEY. The data were recorded with low-energy thresholds and for a wide angular range (20°–160°). The normalization procedure used to extract the cross sections is based on the np elastic scattering reaction that we measured and for which we present experimental results. A good control of the systematic uncertainties affecting the results is achieved. Calculations using the exciton model are reported. Two different theoretical approaches proposed to improve its predictive power regarding the complex particle emission are tested. The capabilities of each approach is illustrated by comparison with the 96 MeV data that we measured, and with other experimental results available in the literature.
Recently, many new applications of fast neutrons are emerging or under development, like dose effects due to cosmic ray neutrons for airplane crew, fast neutron cancer therapy, studies of electronics failure induced by cosmic ray neutrons and accelerator-driven incineration of nuclear waste and energy production technologies. In radiation treatment, the kerma (Kinetic energy release in matter) coefficient, which describes the average energy transferred from neutrons to charged particles, is widely used. The kerma coefficient can be calculated from microscopic nuclear data. Nuclear data above 20 MeV are rather scarce, and more complete nuclear data libraries are needed in order to improve the understanding of the processes occurring on a cellular level. About half the dose in human tissue due to fast neutrons comes from proton recoils in neutronproton (np) scattering, 10-15% from nuclear recoils due to elastic and inelastic neutron scattering and the remaining 35-40% from neutron-induced emission of light ions. Experimental data on elastic and inelastic neutron scattering at 96 MeV from C-12 and O-16 have been obtained recently at The Svedberg Laboratory in Uppsala, Sweden. These data are shown to be relevant for the determination of nuclear recoil kerma coefficients from elastic and inelastic neutron scattering at intermediate energies.
In fast neutron cancer therapy, similar to 50% of the cell damage is caused by recoil protons from neutron-proton (np) scattering. In the intermediate energy region, there is a need for unambiguous np scattering data with good precision in both the shape of the angular distribution and the absolute normalisation. The normalisation techniques have been reviewed for np scattering measurements as well as recent experimental results, particularly the data obtained at The Svedberg Laboratory at 96 and 162 MeV. In addition, to what extent systematic uncertainties in the np differential cross section might affect the determination of proton recoil kerma coefficients is investigated.
A tagged medium-energy neutron beam was used in a precise measurement of the absolute differential cross section for np backscattering. The results resolve significant discrepancies within the np database concerning the angular dependence in this regime. The experiment has determined the absolute normalization with +/- 1.5% uncertainty, suitable to verify constraints of supposedly comparable precision that arise from the rest of the database in partial wave analyses. The analysis procedures, especially those associated with the evaluation of systematic errors in the experiment, are described in detail so that systematic uncertainties may be included in a reasonable way in subsequent partial wave analysis fits incorporating the present results.
Double-differential cross sections for light-ion (p, d, t, 3He, and α) production in silicon, induced by 96 MeV neutrons, are reported. Energy spectra are measured at eight laboratory angles from 20° to 160° in steps of 20°. Procedures for data taking and data reduction are presented. Deduced energy-differential, angle-differential, and production cross sections are reported. Experimental cross sections are compared to theoretical reaction model calculations and experimental data in the literature.
Double-differential cross sections of inclusive light-ion (p, d, t, He-3 and alpha) production in carbon induced by 96 MeV neutrons have been measured at eight laboratory angles from 20 to 160 in steps of 20 degrees. Experimental techniques, as well as procedures for data taking and data reduction, are presented. Deduced energy-differential and production cross sections are herewith reported. Experimental cross sections are compared with theoretical reaction model calculations and experimental data in the literature. The measured production cross sections for protons, deuterons, tritons, He-3, and alpha particles support the trends suggested by data at lower energies. Deduced partial kerma coefficients for carbon are also shown.
In recent years, an increasing number of applications involving fast neutrons have been developed or are under consideration, e.g. radiation treatment of cancer, neutron dosimetry at commercial aircraft altitudes, soft-error effects in computer memories, accelerator-driven transmutation of nuclear waste and energy production and determination of the response of neutron detectors. Data on light-ion production in tight nuclei such as carbon, nitrogen and oxygen are particularly important in calculations of dose distributions in human tissue for radiation therapy at neutron beams, and for dosimetry of high-energy neutrons produced by high-energy cosmic radiation interacting with nuclei (nitrogen and oxygen) in the atmosphere. When studying neutron dose effects, it is especially important to consider carbon and oxygen, since they are, by weight, the most abundant elements in human tissue. Preliminary experimental double-differential cross sections of inclusive light-ion (p, d, t, He-3 and alpha) production in carbon induced by 96-MeV neutrons have been presented. Energy spectra were measured at eight laboratory angles: 20, 40, 60, 80, 100, 120, 140 and 160 degrees. Measurements were performed at The Svedberg Laboratory (TSL), Uppsala, using the dedicated MEDLEY experimental setup. The authors have earlier reported experimental double-differential cross sections of inclusive light-ion production in oxygen. In this paper, the deduced kerma coefficients for oxygen has been presented and compared with reaction model calculations.
Data on light-ion production in light nuclei such as carbon, nitrogen and oxygen are particularly important in calculations of dose distributions in human tissue for radiation therapy at neutron beams, and for dosimetry of high energy neutrons produced by high-energy cosmic radiation interacting with nuclei (nitrogen and oxygen) in the atmosphere. When studying neutron dose effects, special consideration on carbon and oxygen is needed since they are, by weight, the most abundant elements in human tissue. The MEDLEY setup at The Svedberg Laboratory (TSL), Uppsala, Sweden has been used to measure such data with double-differential cross sections (DDX) for the (n, xp), (n, xd), xt), (n,(3)He), and (n,alpha) reactions from C, 0, Si, Ca, Fe, Pb, and U around 96 MeV. At the new Uppsala neutron beam facility the available energy range of quasi mono-energetic neutron beams is extended up to 175 MeV. The detector setup used in MEDLEY consists of eight so-called telescopes mounted at different angles inside all evacuated reaction chamber. Each of the telescopes consists of two fully depleted Delta E silicon surface barrier detectors (SSBD) and a CsI(Tl) crystal. In order to make measurements at this higher neutron energy possible some changes in the detector setup compared to the campaign at 96 MeV were applied Accordingly, the second Delta E detectors have been replaced by 1000 mu m thick SSBDs as well as the size of the crystals used as E detectors was increased to a total length of 100 mm and a diameter of 50 mm. The Delta E - E technique is used to identify the light ions, and cutoff energies as low as 2.5 MeV for protons and 4.0 MeV for alpha particles are achieved. The data are normalised relative to elastic up scattering measured in one of the telescopes at 20 degrees. Preliminary DDXs for oxygen are presented and compared with theoretical calculations.
Data on elastic scattering of 96 MeV neutrons from Fe-56, Y-89, and Pb-208 in the angular interval 10-70 degrees are reported. The previously published data on Pb-208 have been extended, as a new method has been developed to obtain more information from data, namely to increase the number of angular bins at the most forward angles. A study of the deviation of the zero-degree cross section from Wick's limit has been performed. It was shown that the data on Pb-208 are in agreement with Wick's limit while those on the lighter nuclei overshoot the limit significantly. The results are compared with modern optical model predictions, based on phenomenology and microscopic nuclear theory. The data on Fe-56, Y-89, and Pb-208 are in general in good agreement with the model predictions.
Elastic neutron scattering from (12)c, N-14, O-16, Si-28, (40) Ca, Fe-56, Y-89 and Ph-208 has been studiedl at 96 MeV in the10-70 degrees interval, using the SCANDAL (SCAttered Nucleon Detection AssembLy) facility. The results for C-12 and Pb-208 have recently been published, while the data on the other nuclei are under analysis. The achieved energy resolution, 3.7 MeV, is about an order of magnitude better than for any previous experiment above 65 MeV incident energy. A novel method for normalisation of the absolute scale of the cross section has been used. The estimated normalisation uncertainty, 3%, is unprecedented for a neutron-induced differential cross section measurement on a nuclear target. Elastic neutron scattering is of utmost importance for a vast number of applications. Besides its fundamental importance as a laboratory for tests of isospin dependence in the nucleon-nucleon, and nucleon-nucleus, interaction, knowledge of the optical potentials derived from elastic scattering come into play in virtually every application where a detailed understanding of nuclear processes is important. Applications for these measurements are dose effects due to fast neutrons, including fast neutron therapy, as well as nuclear waste incineration and single event upsets in electronics. The results at light nuclei of medical relevance (C-12, N-14 and O-16) are presented separately. In the present contribution, results on the heavier nuclei are presented, among which several are of relevance to shielding of fast neutrons.