Stephan Pomp

Nucleon-induced reactions at intermediate energies: New data at 96 MeV and theoretical status

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 deg. -160 deg. ). 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.

Light‐Ion Production in the Interaction of 96 MeV Neutrons with Silicon

Double-differential cross sections for light-ion (p, d, t, He and α) production in oxygen, 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 energydifferential and production cross sections are reported. Experimental cross ∗Corresponding author, Tel. +46 18 471 6850, Fax. +46 18 471 3853, E-mail: stephan.pomp@tsl.uu.se

The New Uppsala Neutron Beam Facility

A new quasi‐monoenergetic neutron beam facility has been constructed at the The Svedberg Laboratory (TSL) in Uppsala, Sweden. Key features include an energy range of 20 to 175 MeV, high fluxes, and the possibility of large‐area fields. Besides cross‐section measurements, the new facility has been designed specifically to provide optimal conditions for testing of single‐event effects in electronics and for dosimetry development. First results of the beam characterization measurements performed in early 2004 are reported.

OBSERVATION OF PHI-PHI PRODUCTION IN THE REACTION (P)OVER-BAR-P-]4K(+/-) AT 1.4 GEV/C INCIDENT (P)OVER-BAR MOMENTUM

Abstract The JETSET (PS202) experiment at CERN-LEAR searches for hadronic resonances by means of in-flight antiproton-proton annihilations in the reaction p p → φφ . In order to obtain sufficient luminosity and good final-state mass resolution, this experiment uses an internal hydrogen-cluster jet target intersecting the LEAR antiproton beam. We report on the study of the reaction p p → 4K ± at 1.4 GeV / c incident p momentum, and we present the first experimental observation of a stro φφ signal in this reaction.

Total Monte Carlo evaluation for dose calculations

Total Monte Carlo (TMC) is a method to propagate nuclear data (ND) uncertainties in transport codes, by using a large set of ND files, which covers the ND uncertainty. The transport code is run multiple times, each time with a unique ND file, and the result is a distribution of the investigated parameter, e.g. dose, where the width of the distribution is interpreted as the uncertainty due to ND. Until recently, this was computer intensive, but with a new development, fast TMC, more applications are accessible. The aim of this work is to test the fast TMC methodology on a dosimetry application and to propagate the (56)Fe uncertainties on the predictions of the dose outside a proposed 14-MeV neutron facility. The uncertainty was found to be 4.2 %. This can be considered small; however, this cannot be generalised to all dosimetry applications and so ND uncertainties should routinely be included in most dosimetry modelling.

An iterative procedure to obtain inverse response functions for thick-target correction of measured charged-particle spectra

A new method for correcting charged-particle spectra for thick-target effects is described. Starting with a trial function, inverse response functions are found by an iterative procedure. The variances corresponding to the measured spectrum are treated similarly and in parallel. Oscillations of the solution are avoided by rebinning the data to finer bins during a correction iteration and back to the original or wider binning after each iteration. This thick-target correction method has been used for data obtained with the MEDLEY facility at the The Svedberg Laboratory, Uppsala, Sweden, and is here presented in detail and demonstrated for two test cases.

Elastic neutron scattering at 96 MeV from {sup 12}C and {sup 208}Pb

A facility for detection of scattered neutrons in the energy interval 50-130 MeV, SCANDAL, has recently been installed at the 20-180 MeV neutron beam line of the The Svedberg Laboratory, Uppsala. Elastic neutron scattering from {sup 12}C and {sup 208}Pb has been studied at 96 MeV in the 10 deg. -70 deg. interval. The achieved energy resolution, 3.7 MeV, is about an order of magnitude better than for any previous experiment above 65 MeV incident energy. The present experiment represents the highest neutron energy where the ground state has been resolved from the first excited state in neutron scattering. A novel method for normalization of the absolute scale of the cross section has been used. The estimated normalization uncertainty, 3%, is unprecedented for a neutron-induced differential cross section measurement on a nuclear target. The results are compared with modern optical model predictions based on phenomenology or microscopic nuclear theory.

Comment on "Piezonuclear decay of thorium" [Phys. Lett. A 373 (2009) 1956]

Subjecting a solution of 228 Th to ultrasound (20 kHz, 100W), Cardone et al. [Phys. Lett. A 373 (2009) 1956] claim to observe an increase in the transformation or decay rate of 228 Th by a factor of 10 4 . The evidence provided seems however far from conclusive and in part contradictory to the claims made. In fact, looking at the presented data we find it cannot be taken as justification to discard the null hypothesis, namely, that the data from exposed and non exposed samples are drawn from the same distribution. We suggest a number of additional tests that should be made in order to improve the quality of the study and test the hypothesis of so-called piezonuclear reactions.

Experimental determination of the complete spin structure for (p)over-barp -g(Lambda)over-bar Lambda at p((p)over-bar)=1.637 GeV/c

The reaction anti-proton + proton -> anti-\Lambda + \Lambda -> anti-proton + \pi^+ + proton + \pi^- has been measured with high statistics at anti-proton beam momentum of 1.637 GeV/c. The use of a transversely-polarized frozen-spin target combined with the self-analyzing property of \Lambda/anti-\Lambda decay allows access to unprecedented information on the spin structure of the interaction. The most general spin-scattering matrix can be written in terms of eleven real parameters for each bin of scattering angle, each of these parameters is determined with reasonable precision. From these results all conceivable spin-correlations are determined with inherent self-consistency. Good agreement is found with the few previously existing measurements of spin observables in anti-proton + proton -> anti-\Lambda + \Lambda near this energy. Existing theoretical models do not give good predictions for those spin-observables that had not been previously measured.

A new facility for high-energy neutron-induced fission studies

A new facility is constructed for measurements of neutron‐induced fission cross sections in the 20–180 MeV energy region versus the np scattering cross section, which is adopted as the primary neutron standard. The advantage of the experiment compared to earlier studies is that the fission‐fragment detection and the neutron‐flux measurement via np scattering are performed simultaneously and at the same position in the beam, and, therefore, many sources of systematic errors cancel out. Further reduction of systematic errors is achieved due to “embedded” determination of effective solid angle of particle detectors using α‐particles from the radioactive decay of the target nuclei. The performance of the facility is illustrated by first data obtained for angular distributions of fission fragments in the 238U(n,f) reaction.