Study Of Neutron-induced Reactions Research Articles

Isomeric Cross Section Study of Neutron Induced Reactions on Ge Isotopes

In the present work, natural Ge targets have been irradiated by neutron beams of 17.7 and 19.3 MeV, at the 5MV tandem accelerator of NCSR "Demokritos". The cross section of the 72,74Ge(n,α)69,71Zn and 76Ge(n,2n)75Ge reactions, leading to the population of isomeric states, has been deduced with respect to the 27Al(n,α)24Na and 93Nb(n,2n)92mNb reference reactions. After the neutron irradiations, the induced γ-ray activity of the Ge target and reference foils, was measured with high-resolution HPGe detectors.

First results of the 230Th(n,f) cross section measurements at the CERN n_TOF facility

The study of neutron-induced reactions on actinides is of considerable importance for the design of advanced nuclear systems and alternative fuel cycles. Specifically, 230Th is produced from the α-decay of 234U as a byproduct of the 232Th/233U fuel cycle, thus the accurate knowledge of its fission cross section is strongly required. However, few experimental datasets exist in literature with large deviations among them, covering the energy range between 0.2 to 25 MeV. In addition, the study of the 230Th(n,f) cross-section is of great interest in the research on the fission process related to the structure of the fission barriers. Previous measurements have revealed a large resonance at En=715 keV and additional fine structures, but with high discrepancies among the cross-section values of these measurements. This contribution presents preliminary results of the 230Th(n,f) cross-section measurements at the CERN n_TOF facility. The high purity targets of the natural, but very rare isotope 230Th, were produced at JRC-Geel in Belgium. The measurements were performed at both experimental areas (EAR-1 and EAR-2) of the n_TOF facility, covering a very broad energy range from thermal up to at least 100 MeV. The experimental setup was based on Micromegas detectors with the 235U(n,f) and 238U(n,f) reaction cross-sections used as reference.

Study of Neutron Induced Reactions on 7Be Using Large Angle Coincidence Spectroscopy

Neutron induced reactions on the radioactive nuclei 7Be represent a unique tool for study of the 8Be nuclear structure in the high-energy region. The interactions of thermal neutrons with 7Be is dominated by the strong 7Be(nth,p)7Li reactions. While 8Be in the ground state disintegrates rapidly into two α particles, the alpha decay from the 2− neutron capture state is prohibited because of the parity violation. The study of the 7Be(nth,α)4He reaction (with two 9496 keV α particles) is then a unique tool to study parity violation in strong interactions. The test was carried out on the collimated thermal neutron beam at NPI Rez using the large angle coincidence spectroscopy. The 7Be nuclei were prepared at the ISOLDE facility by implantation of the 60 keV 7Be ions into 5μm Al foil. The results showed that the ratio of the cross sections is σ(p1)/σ(p0) = (1.58 ± 0.06) x 10-2, and in the coincidence measurement simultaneous emission of two 8775 keV α particles is observed. This reaction channel corresponds to a two-stage process comprising transition from the neutron capture state (18991 keV) to an intermediate state by emission of γ photon that is followed by the decay into two alphas. The intermediate state in the highly excited 8Be nuclei is the level at 17640 keV (1+), which is in contrast to the previous reported data. In the experiment no α particles with the energy 9495 keV were observed.

Neutron cross-sections for advanced nuclear systems: the n_TOF project at CERN

The study of neutron-induced reactions is of high relevance in a wide variety of fields, ranging from stellar nucleosynthesis and fundamental nuclear physics to applications of nuclear technology. In nuclear energy, high accuracy neutron data are needed for the development of Generation IV fast reactors and accelerator driven systems, these last aimed specifically at nuclear waste incineration, as well as for research on innovative fuel cycles. In this context, a high luminosity Neutron Time Of Flight facility, n_TOF, is operating at CERN since more than a decade, with the aim of providing new, high accuracy and high resolution neutron cross-sections. Thanks to the features of the neutron beam, a rich experimental program relevant to nuclear technology has been carried out so far. The program will be further expanded in the near future, thanks in particular to a new high-flux experimental area, now under construction.

Use of shell model calculations in R-matrix studies of neutron-induced reactions

Abstract R-matrix analyses of neutron-induced reactions for many of the lightest p-shell nuclei are difficult due to a lack of distinct resonance structure in the reaction cross sections. Initial values for the required R-matrix parameters, Eλ and γλc for states in the compound system, can be obtained from shell model calculations. In the present work, the results of recent shell model calculations for the lithium isotopes have been used in R-matrix analyses of 6Li+n and 7Li+n reactions for En 8 MeV. Consequences of the shell model redictions for the level structure of 7Li and 8Li on the 6Li+n and 7Li+n reaction mechanisms and cross sections are discussed.