.
The neutron time-of-flight facility n_TOF features a white neutron source produced by spallation through 20GeV/
c
protons impinging on a lead target. The facility, aiming primarily at the ...measurement of neutron-induced reaction cross sections, was operating at CERN between 2001 and 2004, and then underwent a major upgrade in 2008. This paper presents in detail all the characteristics of the new neutron beam in the currently available configurations, which correspond to two different collimation systems and two choices of neutron moderator. The characteristics discussed include the intensity and energy dependence of the neutron flux, the spatial profile of the beam, the in-beam background components and the energy resolution/broadening. The discussion of these features is based on dedicated measurements and Monte Carlo simulations, and includes estimations of the systematic uncertainties of the mentioned quantities.
At the n_TOF experiment at CERN a dedicated single-crystal chemical vapor deposition (sCVD) Diamond Mosaic-Detector has been developed for (n,α) cross-section measurements. The detector, ...characterized by an excellent time and energy resolution, consists of an array of 9 sCVD diamond diodes. The detector has been characterized and a cross-section measurement has been performed for the 59Ni(n,α)56Fe reaction in 2012. The characteristics of the detector, its performance and the promising preliminary results of the experiment are presented.
•A large-area detector of 3 ×3 sCVD diamonds was built for (n, α) measurements.•The 59Ni(n, α)56Fe cross-section was measured successfully at n_TOF/CERN.•The energy resolution of the detector meets the expectations from simulations.•The reaction products during the measurement at n_TOF could clearly be separated.•The detector is suitable for (n, α) measurements in a heterogeneous beam.
A new simulation of nuclear γ cascades by the Monte Carlo method is described. It makes it possible to generate artificially individual events of the γ-cascade decay of an isolated, highly excited ...initial level in a medium and heavy nucleus. A broad class of quantities, associated with the process of γ-cascade de-excitation, can be modelled. The main advantage of the method is the possibility of a full quantitative control over the influence of the Porter–Thomas fluctuations of partial radiation widths on uncertainties of the modelled cascade-related quantities. For assessment of these uncertainties and a control over the accuracy of the method, a special statistical formalism has been developed.
Achievements in instrumentation for positron lifetime measurements are summarized with emphasis on digital spectrometric systems. The main part of the data presented are based on the long-term ...exploitation of a conventional positron lifetime spectrometer developed at Charles University in early 90s, on bench-mark testing measurements with this spectrometer working in conjunction with a pair of 8-bit ultra-fast digitizers and on analogous measurements with a new, recently assembled digital positron lifetime spectrometer. Perspectives of further improvements of positron lifetime instrumentation are discussed.
The n_TOF Collaboration has built and commissioned a high-performance detector for
(
n
,
γ
)
measurements called the Total Absorption Calorimeter (TAC). The TAC was especially designed for measuring ...neutron capture cross-sections of low-mass and/or radioactive samples with the accuracy required for nuclear technology and stellar nucleosynthesis. We present a detailed description of the TAC and discuss its overall performance in terms of energy and time resolution, background discrimination, detection efficiency and neutron sensitivity.
The neutron-capture reaction is fundamental for identifying and analyzing the γ-ray spectrum from an unknown assembly because it provides unambiguous information on the neutron-absorbing isotopes. ...Nondestructive-assay applications may exploit this phenomenon passively, for example, in the presence of spontaneous-fission neutrons, or actively where an external neutron source is used as a probe. There are known gaps in the Evaluated Nuclear Data File libraries corresponding to neutron-capture γ-ray data that otherwise limit transport-modeling applications. In this work, we describe how new thermal neutron-capture data are being used to improve information in the neutron-data libraries for isotopes relevant to nonproliferation applications. We address this problem by providing new experimentally-deduced partial and total neutron-capture reaction cross sections and then evaluate these data by comparison with statistical-model calculations.
The n_TOF facility at CERN has been designed for the measurement of neutron capture, fission and (
n
,
×
n
) cross-sections with high accuracy. This requires a flexible and—due to the high ...instantaneous neutron flux—almost dead time free data acquisition system. A scalable and versatile data solution has been designed based on 8-bit flash-ADCs with sampling rates up to 2
GHz and 8
Mbyte memory buffer. The software is written in C and
C
++
and is running on PCs equipped with RedHat Linux.
The asset of ultra-fast digitizers for positron-lifetime spectroscopy Bečvář, F.; Čížek, J.; Procházka, I. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2005, Letnik:
539, Številka:
1
Journal Article
Recenzirano
A spectrometer for positron-lifetime measurements assembled from two BaF
2 scintillation detectors and two 8-bit,
4
GS
s
-
1
digitizes in a master–slave configuration is described in detail. We ...report the results of comparative testing measurements of the lifetime of positrons annihilating in
α
-Fe using this setup and a setup formed by the same pair of detectors working in conjunction with analog electronics modules. The data from these measurements demonstrate for the first time that replacing the analog electronics chain by fast digitizers leads to a substantial improvement of the precision in positron-lifetime measurements. A record timing resolution of 131–136 ps has been achieved with the described spectrometer at coincidence counting rate comparable or virtually equal to that obtained with the fast–fast setup.
The nucleus 177Lu is characteristic by an unusually high value of the thermal-neutron capturing state spin, J = 13/2, and by distinct low-energy rotational bands built on the 7/2+ ground state and ...the 9/2− level at 150 keV. The γ cascades connecting the capturing state with the members of these bands carry unique information about the role of identical M1 scissors-mode resonances, built according to Brink hypothesis assumingly on each energy level, even in conditions of fast nuclear rotation. With this motivation we measured a set of spectra of two-step γ cascades following the thermal neutron capture in 176Lu. The measurement was performed at neutron beam of the LWR-15 Reactor in Řež. From the analysis of these spectra the common parameters of the scissors resonances were deduced. The obtained results are discussed.
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