Angular distribution and correlation measurements are an essential tool in nuclear structure experiments, especially when spectroscopic information on a specific nucleus is unknown. In most cases, ...the experimental determination of the spins and parities of the studied nuclear states, as well as the possible mixing between two electric/magnetic multipoles of a transition are determined using angular correlation measurements. In this work, the full effect of directional
γ
correlations is simulated, by using the formal theory of angular correlations. The statistical tensor formalism is employed, enabling to perform a full simulation of the angular correlation effects in a cascade of an arbitrary number of
γ
transitions. The present approach was coupled with the Monte Carlo code FIFRELIN, which can simulate the de-excitation of fission fragments or of excited nuclei after neutron capture. It provides a complete description of the spatial distributions of all the
γ
rays in the cascade, that can be used for simulation purposes in various applications both in nuclear and particle physics. The potential for a novel approach in data analysis of angular correlation measurements is discussed thoroughly.
The orbital M1 scissors resonance has been measured for the first time in the quasicontinuum of actinides. Particle-γ coincidences are recorded with deuteron and (3)He-induced reactions on (232)Th. ...The residual nuclei (231,232,233)Th and (232,233) Pa show an unexpectedly strong integrated strength of B(M1)=11-15μ(n)(2) in the E(γ)=1.0-3.5 MeV region. The increased γ-decay probability in actinides due to scissors resonance is important for cross-section calculations for future fuel cycles of fast nuclear reactors and may also have an impact on stellar nucleosynthesis.
The relation between the neutron background in neutron capture measurements and the neutron sensitivity related to the experimental setup is examined. It is pointed out that a proper estimate of the ...neutron background may only be obtained by means of dedicated simulations taking into account the full framework of the neutron-induced reactions and their complete temporal evolution. No other presently available method seems to provide reliable results, in particular under the capture resonances. An improved neutron background estimation technique is proposed, the main improvement regarding the treatment of the neutron sensitivity, taking into account the temporal evolution of the neutron-induced reactions. The technique is complemented by an advanced data analysis procedure based on relativistic kinematics of neutron scattering. The analysis procedure allows for the calculation of the neutron background in capture measurements, without requiring the time-consuming simulations to be adapted to each particular sample. A suggestion is made on how to improve the neutron background estimates if neutron background simulations are not available.
Coherent elastic neutrino-nucleus scattering and low-mass dark matter detectors rely crucially on the understanding of their response to nuclear recoils. We report the first observation of a nuclear ...recoil peak at around 112 eV induced by neutron capture. The measurement was performed with a CaWO_{4} cryogenic detector from the NUCLEUS experiment exposed to a ^{252}Cf source placed in a compact moderator. We identify the expected peak structure from the single-γ de-excitation of ^{183}W with 3σ and its origin by neutron capture with 6σ significance. This result demonstrates a new method for precise, in situ, and nonintrusive calibration of low-threshold experiments.
MicroMegas detectors are versatile gaseous detectors which are used for ionizing particle detection. A MicroMegas detector consists of two adjacent gas-filled volumes. One volume acts as a drift ...region with an electric field operating in the ionization chamber regime, the second volume is the amplification region acting as a parallel-plate avalanche counter. The use of the microbulk technique allows the production of thin, radiation resistant, and low-mass detector with a highly variable gain. Such MicroMegas detectors have been developed and used in combination with neutron time-of-flight measurements for in-beam neutron-flux monitoring, fission and light-charged particle reaction cross section measurements, and for neutron-beam imaging. An overview of MicroMegas detectors for neutron detection and neutron reaction cross section measurements and related results and developments will be presented.
Abstract
The development of low-threshold detectors for the study of
coherent elastic neutrino-nucleus scattering and for the search for
light dark matter necessitates methods of low-energy ...calibration. We
suggest this can be provided by the nuclear recoils resulting from
the γ emission following thermal neutron capture. In
particular, several MeV-scale single-γ transitions induce
well-defined nuclear recoil peaks in the 100 eV range. Using the
FIFRELIN code, complete schemes of γ-cascades for various
isotopes can be predicted with high accuracy to determine the
continuous background of nuclear recoils below the calibration
peaks. We present a comprehensive experimental concept for the
calibration of CaWO
4
and Ge cryogenic detectors at a research
reactor. For CaWO
4
the simulations show that two nuclear recoil
peaks at 112.5 eV and 160.3 eV should be visible above background
simply in the spectrum of the cryogenic detector. Then we discuss
how the additional tagging for the associated γ increases the
sensitivity of the method and extends its application to a wider
energy range and to Ge cryogenic detectors.
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