The effect of particle leaking and its implications for measurements of the (n,¿) reaction on light elements by using ionisation chambers (original) (raw)
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Nucl Instrum Meth Phys Res a, 2005
A new technique for the spectrometry of (n,a) reactions on light elements at MeV energies has been developed and successfully used for the measurement of the 10 B(n,a) 7 Li reaction at the 7 MV Van de Graaff accelerator of IRMM. The basic elements of the new technique are a gridded ionisation chamber, a fast waveform digitizer and advanced off-line analysis. The powerful data visualisation allowed the discovery of the effect of particle leaking. Particle leaking arises from the simultaneous emission of more than one reaction products in forward angles and the inability of the detector to resolve multiple particles. It is an inherent property of all GIC spectrometers used for the study of (n, charged particle) reactions on light-element solid targets. The measurement of the cross section strongly benefits from it, but the determination of other measurables is negatively affected. Cross sections at seven energies between 1.5 and 3.8 MeV have been obtained by using the new technique. Compared to evaluations the IRMM cross sections are close to the JENDL-3.2 data for energies from 1.5 to 2.15 MeV and above 2.5 MeV they have values between those of JENDL-3.2 and JEF-2.2, but strongly deviate from the ENDF/B-VI data with the exception of very good agreement at 2.5 MeV. Forward angular distributions are truncated at large emission angles by the effect of particle leaking and appears depleted of reaction products between a kinematically determined angle y 0 and 901. It is shown that all values of the branching ratio a 0 /a 1 of the 10 B(n,a) 7 Li reaction published up to now in refereed journals and obtained by using ionisation chambers and face-to-face surface-barrier detectors contain inaccuracies caused by particle leaking which was not considered.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
A new technique for the spectrometry of (n,a) reactions on light elements at MeV energies has been developed and successfully used for the measurement of the 10 B(n,a) 7 Li reaction at the 7 MV Van de Graaff accelerator of IRMM. The basic elements of the new technique are a gridded ionisation chamber, a fast waveform digitizer and advanced off-line analysis. The powerful data visualisation allowed the discovery of the effect of particle leaking. Particle leaking arises from the simultaneous emission of more than one reaction products in forward angles and the inability of the detector to resolve multiple particles. It is an inherent property of all GIC spectrometers used for the study of (n, charged particle) reactions on light-element solid targets. The measurement of the cross section strongly benefits from it, but the determination of other measurables is negatively affected. Cross sections at seven energies between 1.5 and 3.8 MeV have been obtained by using the new technique. Compared to evaluations the IRMM cross sections are close to the JENDL-3.2 data for energies from 1.5 to 2.15 MeV and above 2.5 MeV they have values between those of JENDL-3.2 and JEF-2.2, but strongly deviate from the ENDF/B-VI data with the exception of very good agreement at 2.5 MeV. Forward angular distributions are truncated at large emission angles by the effect of particle leaking and appears depleted of reaction products between a kinematically determined angle y 0 and 901. It is shown that all values of the branching ratio a 0 /a 1 of the 10 B(n,a) 7 Li reaction published up to now in refereed journals and obtained by using ionisation chambers and face-to-face surface-barrier detectors contain inaccuracies caused by particle leaking which was not considered.
2005
The B(n,α)Li reaction was studied in the energy range between 1.5 MeV and 5.6 MeV at the 7-MV Van de Graaff accelerator of IRMM by using a gridded ionisation chamber, signal digitisation, and an intrinsic U neutron monitor. The aim was to obtain accurate data for the IAEA Coordinated Research Project (CRP) on the improvement of standard cross sections for light elements. The effect of particle leaking was discovered and its implications investigated. The determination of the cross section σ(α0+α1) strongly benefits from it but measurements of angular distributions, individual cross sections σ(α0) and σ(α1), and the branching ratio α0/α1 are negatively affected. The correct number of reaction events was obtained by identification of unknown particle signatures in the energy spectra as B(n,α)Li events in the form of quasi Li+α particles created by particle leaking. The cross-section ratio B(n,α)Li/U(n,fission) was measured and the excitation function of B(n,α)Li determined by simultan...
Journal of Physics: Conference Series, 2010
The 10 B(n,α 0 ) 7 Li and 10 B(n,α 1 γ) 7 Li angular distributions have been measured at the GELINA time-of-flight spectrometer in the incident neutron energy range from 0.1 keV to 1 MeV by means of a twin Frisch-grid ionization chamber. With this type of detector it is possible to measure the angular distribution of the charged reaction fragments in a close to 2x2π solid angle with ~100% efficiency and a clear separation of both reaction channels: emission to the 7 Li ground state (α 0 ) or to its first excited state (α 1 ). A strong angular anisotropy was observed at ~ 520 keV. In order to extend the energy range up to 2.5-3 MeV and to measure, also, the reaction cross sections, a double twin Frisch-grid ionization chamber was constructed. It is loaded with two very thin 94% 10 B-enriched samples, mounted back-toback with 235 U samples on the common cathodes. New data acquisition, visualization and analysis software is used in a new set of long-term measurements, which are still going on.
Chinese Physics C, 2019
Differential and angle-integrated cross sections for the 10B(n, α)7Li, 10B(n, α 0) 7Li and 10B(n, α 1) 7Li* reactions have been measured at CSNS Back-n white neutron source. Two enriched (90%) 10B samples 5.0 cm in diameter and ~85.0 μg/cm2 in thickness each with an aluminum backing were prepared, and back-to-back mounted at the sample holder. The charged particles were detected using the silicon-detector array of the Light-charged Particle Detector Array (LPDA) system. The neutron energy En was determined by TOF (time-of-flight) method, and the valid α events were extracted from the En -Amplitude two-dimensional spectrum. With 15 silicon detectors, the differential cross sections of α-particles were measured from 19.2° to 160.8°. Fitted with the Legendre polynomial series, the (n, α) cross sections were obtained through integration. The absolute cross sections were normalized using the standard cross sections of the 10B(n, α)7Li reaction in the 0.3 – 0.5 MeV neutron energy region. ...
Angular Distribution and Cross Section Measurement of the 6 Li( 3 He,n) 8 B Reaction at 5.8 MeV
EPJ Web of Conferences, 2014
The reaction 6 Li(3 He,n) 8 B was studied at Laboratori Nazionali di Legnaro in the framework of the EUROnu Design Study for a Beta Beam facility at CERN. The 8 B production cross section was determined through neutron angular distribution by using the time-of-flight technique. Thanks to the high statistics achieved, the neutron angular distribution for the population of the 8 B first excited state has been measured for the first time. Discrepancies with other available data sets for 8 B ground state population are discussed and interpreted in the framework of DWBA calculations. Further measurements at beam energies above 10 MeV are needed to clarify the behaviour of the angular distribution.
Particle emission in light and heavy ion reactions
Nuclear Physics A, 1983
... Q, involved into central Ar+KCl collisions Q = n^t - 2 n^- - (rip^ n^ ) (?) where n^ and nn-are the number of all charged particles and negative pions, npry is the number of leading fragments tra-velling with the ... H.Stocker, Lawrence Berkeley Laboratory preprint No 12302 (1981). ...
Li, Be, and B production in reactions of 45-100 MeV protons withC:12Astrophysical implications
Physical Review C, 1976
Cross sections for the production of mass 6 to 11 isobars from proton spallation of carbon targets have been measured at bombarding energies of 45, 55, 60, 65, 75, and 100 MeV. Isotopic cross sections for Li and Be have also been measured at 100 MeV. The excitation functions for these reactions have been used to test theories of Li, Be, and B nucleosynthesis. The measured abundance ratios for "B/' B and B/Be can be reproduced using the experimental cross sections and astrophysical models which propose LiBeB synthesis in nuclear reactions well above the threshold energy. In order to obtain the natural 'Li/ Li, Li/Be, and Li/B abundance ratios, however, it is concluded that a substantial amount of 'Li must be synthesized via some lower energy mechanism. NUCLEAR REACTIONS C(P, HI); HI Mass numbers A = 6, 7, 9, 10, and 11; E =45, 55, 60, 65, 75, 100 MeV; HI Li and Be at 100 MeV; measured cr, o(0), and o'(E); astrophysical implications of the data are discussed.
2011
Earlier we reported theoretical studies on the probable production of astatine radionuclides from 6,7Li- and 9Be-induced reactions on natural lead and thallium targets, respectively. The production of astatine radionuclides were investigated experimentally with two heavy-ion-induced reactions: 9Be + natTl and 7Li + natPb. Formation cross sections of the evaporation residues, 207,208,209,210At, produced in the (HI,xn) channel, were measured by the stacked-foil technique followed by off-line gamma spectrometry at low incident energies (<50 MeV). Measured excitation functions were interpreted in terms of a compound nuclear reaction mechanism using Weisskopf-Ewing and Hauser-Feshbach models. Measured cross-section values are lower than the respective theoretical predictions.
Physical Review C
Different modes of fusion phenomena observed in the isolated experiments are not yet fully understood. To comprehend these fusion mechanisms, more experimental studies are necessary. In view of this, a new measurement of residual cross sections from the 7 Li-induced reaction on 89 Y has been reported in this article within the 2.7-5.7 MeV/nucleon energy range. The γ-ray spectrometry has been used to identify the residues 93m Mo, 92m Nb, 89 Zr, 91m Y, and 90m Y produced in the reaction. A systematic analysis of the complete and incomplete fusion dynamics has been carried out by comparing the measured excitation functions with the equilibrium and pre-equilibrium reaction models in the framework of EMPIRE3.2.2 and ALICE19. A strong indication of the occurrence of incomplete fusion has been realized within the energy range considered; hence the incomplete fusion strength is discussed in detail. The product yield of 93m Mo, which is a candidate radionuclide for radiopharmaceuticals, has been estimated.