.
A recent theoretical prediction of a breaking of axial symmetry in quasi all heavy nuclei is confronted to a new critical analysis of photon strength functions of nuclei in the valley of stability. ...For the photon strength in the isovector giant dipole resonance (IVGDR) regime a parameterization of GDR shapes by the sum of three Lorentzians (TLO) is extrapolated to energies below and above the IVGDR. The impact of non-GDR modes adding to the low energy slope of photon strength is discussed including recent data on photon scattering and other radiative processes. These are shown to be concentrated in energy regions where various model calculations predict intermediate collective strength; thus they are obviously separate from the IVGDR tail. The triple Lorentzian (TLO) ansatz for giant dipole resonances is normalized in accordance to the dipole sum rule. The nuclear droplet model with surface dissipation accounts well for positions and widths without local, nuclide specific, parameters. Very few and only global parameters are needed when a breaking of axial symmetry already in the valley of stability is admitted and hence a reliable prediction for electric dipole strength functions also outside of it is expected.
We present new limits on exotic keV-scale physics based on 478 kg d of Majorana Demonstrator commissioning data. Constraints at the 90% confidence level are derived on bosonic dark matter (DM) and ...solar axion couplings, Pauli exclusion principle violating (PEPV) decay, and electron decay using monoenergetic peak signal limits above our background. Our most stringent DM constraints are set for 11.8 keV mass particles, limiting g_{Ae}<4.5×10^{-13} for pseudoscalars and (α^{'}/α)<9.7×10^{-28} for vectors. We also report a 14.4 keV solar axion coupling limit of g_{AN}^{eff}×g_{Ae}<3.8×10^{-17}, a 1/2β^{2}<8.5×10^{-48} limit on the strength of PEPV electron transitions, and a lower limit on the electron lifetime of τ_{e}>1.2×10^{24} yr for e^{-}→ invisible.
Abstract For next-generation neutrinoless double beta decay experiments, extremely low backgrounds are necessary. An understanding of in-situ cosmogenic backgrounds is critical to the design effort. ...In-situ cosmogenic backgrounds impose a depth requirement and especially impact the choice of host laboratory. Often, simulations are used to understand background effects, and these simulations can have large uncertainties. One way to characterize the systematic uncertainties is to compare unalike simulation programs. In this paper, a suite of neutron simulations with identical geometries and starting parameters have been performed with Geant4 and MCNP, using geometries relevant to the LEGEND-1000 experiment. This study is an important step in gauging the uncertainties of simulations-based estimates. To reduce project risks associated with simulation uncertainties, a novel alternative shield of methane-doped liquid argon is considered in this paper for LEGEND-1000, which could achieve large background reduction without requiring significant modification to the baseline design.
The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A=124, 128, 132, and 134 in nuclear resonance fluorescence ...experiments using the γELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIγS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides.
Cross sections for neutron capture in the range of unresolved resonances are predicted for more than 140 spin-0 target nuclei with A>50. Allowing the breaking of spherical and axial symmetry in ...nearly all these nuclei a combined parameterization for both level density and photon strength is obtained which employs with surprisingly few fit parameters only. The strength functions used are based on a global fit to IVGDR shapes by the sum of three Lorentzians. They are based on theoretical predictions for the A-dependence of pole energies and spreading widths and add up to the TRK sum rule. For the small spins reached by capture resonance spacings are well described by a level density parameter close to the nuclear matter value; a significant collective enhancement is apparent due to the deviation from axial symmetry. Reliable predictions for compound nuclear reactions also outside the valley of stability – important for nuclear astrophysics and for the transmutation of nuclear waste – are expected to result from the global parameterization presented.
Abstract
In the search for a monochromatic peak as the signature of
neutrinoless double beta decay an excellent energy resolution and an
ultra-low background around the
Q
-value of the decay are
...essential. The LEGEND-200 experiment performs such a search with
high-purity germanium detectors enriched in
76
Ge immersed in
liquid argon. To determine and monitor the stability of the energy
scale and resolution of the germanium diodes, custom-made,
low-neutron emission
228
Th sources are regularly deployed in
the vicinity of the crystals. Here we describe the production
process of the 17 sources available for installation in the
experiment, the measurements of their alpha- and gamma- activities,
as well as the determination of the neutron emission rates with a
low-background LiI(Eu) detector operated deep underground. With a
flux of
( 4.27 ± 0.60
stat
± 0.92
syst
) ×
10
-4
n / (kBq·s), approximately one order of
magnitude below that of commercial sources, the neutron-induced
background rate, mainly from the activation of
76
Ge, is
negligible compared to other background sources in LEGEND-200.
Paschen's law studies in cold gases Massarczyk, R.; Chu, P.; Dugger, C. ...
Journal of instrumentation,
06/2017, Letnik:
12, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The break-through voltage behavior over small gaps has been investigated for differing gap distances, gas pressures, and gas temperatures in nitrogen, neon, argon and xenon gases. A deviation from ...Paschen's law at micro gap distances has been found. At lower temperatures, a significant shift of the curve relative to the results at room temperature was observed. This behavior can be explained by combining Paschen's law and the ideal gas law.
Abstract
We detail the design of a variable energy, x-ray fluorescence source using a low activity (1.8×10
6
dpm)
99
Tc
β
source that irradiates thin foils. By rotating the source among foils of Ti, ...Zn, Nb, Ag, and Au, the device produces x rays between 4 and 70 keV at a rate near 1 Hz. When the source is placed in a storage position, the external radiation is non-detectable. The design of the shielding and rotation mechanism permits use in vacuum and at liquid nitrogen temperature. The design is intended for the study of the low energy response to radiation impinging upon Ge detector surfaces. The source will be useful for understanding the detector response in large-scale Ge arrays such as
Majorana
and LEGEND.
Neutrinoless double-beta decay searches seek to determine the nature of neutrinos, the existence of a lepton violating process, and the effective Majorana neutrino mass. The Majorana Collaboration is ...assembling an array of high purity Ge detectors to search for neutrinoless double-beta decay in 76Ge. The Majorana Demonstrator is composed of 44.8 kg (29.7 kg enriched in 76Ge) of Ge detectors in total, split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. The initial goals of the Demonstrator are to establish the required background and scalability of a Ge-based, next-generation, tonne-scale experiment. Following a commissioning run that began in 2015, the first detector module started physics data production in early 2016. We will discuss initial results of the Module 1 commissioning and first physics run, as well as the status and potential physics reach of the full Majorana Demonstrator experiment. The collaboration plans to complete the assembly of the second detector module by mid-2016 to begin full data production with the entire array.
Abstract
The
Majorana Demonstrator
comprises two arrays of
high-purity germanium detectors constructed to search for
neutrinoless double-beta decay in
76
Ge and other physics beyond
the Standard ...Model. Its readout electronics were designed to have
low electronic noise, and radioactive backgrounds were minimized by
using low-mass components and low-radioactivity materials near the
detectors. This paper provides a description of all components of
the
Majorana Demonstrator
readout electronics, spanning the
front-end electronics and internal cabling, back-end electronics,
digitizer, and power supplies, along with the grounding scheme. The
spectroscopic performance achieved with these readout electronics is
also demonstrated.
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