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 similiarly 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.Comment: 14 pages, 8 figures, submitted to NIM

Entrance channel dependence in compound nuclear reactions with loosely bound nuclei

The measurement of light charged particles evaporated from the reaction 6,7Li+6Li has been carried out at extreme backward angle in the energy range 14 - 20 MeV. Calculations from the code ALICE91 show that the symmetry of the target-projectile combination and the choice of level density parameter play important roles in explaining the evaporation spectra for these light particle systems. In above barrier energy region the fusion cross-section is not suppressed for these loosely bound nuclei.Comment: 2 pages, 1 figur

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 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 degrees). 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 approches 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.Comment: 21 pages, 28 figure

Experimental kerma coefficients of biologically important materials at neutron energies below 75 MeV.

The present work summarizes our results already published on cross sections and partial kerma coefficients for hydrogen, carbon, and oxygen and then applies them for determining experimental partial and total kerma coefficients of composite biologically important materials. Double-differential cross sections for light-charged particle production (proton, deuteron, triton, and alpha particle) induced by fast neutrons on hydrogen, carbon, and oxygen have been experimentally measured at several incident energies from 25 to 75 MeV. The measurements covered the laboratory angular range 20 degrees to 160 degrees and were extended to very forward and very backward angles by using a reliable extrapolation procedure. Energy-differential, angle-differential, and total production cross sections were derived from the measured data. The experimental methods and data reduction procedures are briefly presented here. The experimental cross sections were compared to existing data in the literature for nucleon-induced reactions and against prediction of nuclear models. Partial and total elemental kerma coefficients were deduced on the basis of the measured cross sections. Procedures for extrapolating the partial kerma coefficients down to the reaction threshold energies for each of the measured ejectile species have been applied to carbon and oxygen. A simple-to-use analytical formula to describe the experimental hydrogen kerma coefficients was proposed which provides the recoil kerma coefficients in the incident neutron energy range 0.3 to 100 MeV. The present article reports for the first time experimental partial kerma coefficients for composite materials of biological interest. Resulting total kerma coefficients are compared to theoretical predictions and to other experimental data

Mesures de sections efficaces doublement différentielles de particules chargées légères induites par neutrons rapides sur 12C aux énergies En = 42.5, 62.7 et 72.8 MeV

Doctorat en sciences physiques -- UCL, 199

The influence of a southward and northward turning of the interplanetary magnetic field on the geomagnetic cut-off of cosmic rays, on the mirror points positions of geomagnetically trapped particles, and on their rate of precipitations in the atmosphere

A number of geomagnetic observations indicate that the orientation of the interplanetary magnetic field (IMF) plays a definite role in triggering several magnetospheric processes. In this theoretical study based on the superposition of a dipole geomagnetic field model and an uniform IMF, it is shown that when the northward component of the IMF decreases (dB(z)/dt < 0), the geomagnetic cut-off surface moves to larger equatorial distances, the altitude of the mirror points of charged particles trapped in the geomagnetic field increases, and the value of their equatorial pitch angle decreases. Furthermore, we show that the loss cone angle of trapped particles decreases when dB(z)/dt is negative. The southward component of the magnetic field generated by an enhancement of the ring current produces similar effects everywhere inside this ring current loop. &COPY; 2005 Elsevier Ltd. All rights reserved

Geometry and Energy-loss Features of Charged-particle Production in Fast-neutron Induced Reactions

Raw data reduction of charged particle production in fast neutron induced reactions must take into account specific characteristics of this type of experiment. A calculation procedure is presented which considers particular features such as: the thickness of targets, beam dimensions on the target, the beam profile, relative target-telescope angular position etc. It results in a simulation programme (Perten) of the experiment. The way the above mentioned particularities are considered, is exemplified in calculating solid angles and fractions of target producing charged particles with enough energy to be registered by the detector

SCANDAL - a facility for elastic neutron scattering studies in the 50-130 MeV range

A facility for detection of scattered neutrons in the energy interval 50 130 MeV, SCAttered Nucleon Detection AssembLy (SCANDAL), has recently been installed at the 20-180 MeV neutron beam facility of The Svedberg Laboratory, Uppsala. It is primarily intended for studies of elastic neutron scattering, but can be used for (n,p) and (n,d) reaction experiments as well. The performance of the spectrometer is illustrated in measurements of the (n,p) and (n,n) reactions on H-1 and C-12. In addition, the neutron beam facility is described in some detail. (C) 2002 Elsevier Science B.V. All rights reserved