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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A New Approach for Calculating the Alpha-Decay Half-Life for the Heavy and Super-heavy Elements and an Exact A Priori Result for Beyllium-8

A new general method for calculating the alpha decay half-life is presented. The method predicts an a priori exact value for the beryllium-8 half-life. Beryllium-8 is an exception to the current alpha decay theory captured in the Geiger-Nuttal law. The new method predicts the beryllium-8 alpha half-life using only constants and measured isotopic mass. The method also reliably predicts all the heavier isotope alpha decay half-lives consistent with the Geiger-Nuttal law. With respect to current theory, the inability of the Geiger-Nuttal Law to predict the alpha-decay half-life in the case of beryllium-8 has led to consideration of other decay mechanisms for this isotope, such as fission for example. One result is that given the consistency of the new method presented here for all isotopes including an exact a priori result for beryllium-8, the evidence strongly suggests that the beryllium-8 decay is in fact an alpha decay. A second result is that the method definitively demonstrates that the entire rest mass of the two helium-4 electrons is converted to energy in the decay process and this energy becomes part of the emitted alpha particle kinetic energy.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2024

Properties of the 256 Db decay chain

Experiments were performed at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron Facility to study the decays of neutron-deficient dubnium isotopes. These isotopes were produced in the 206 Pb( 51 V, xn) 255,256 Db reaction, and excitation functions were measured. This article reports on the observed properties of the 256 Db decay chain. The produced 256 Db nuclei were separated from unreacted-beam material and reaction byproducts with the Berkeley Gas-filled Separator (BGS) before being implanted into a double-sided silicon strip detector at the BGS focal plane. Decay properties of 256 Db and its daughters were then extracted from the analysis of correlations between implanted Db nuclei with α decay chains and spontaneous fission (SF) events. In total, 86 decay chains and 38 SF events were observed, giving increased statistics as compared to previous studies. In conclusion, improved decay data are presented for 256 Db and its daughter isotopes 252 Lr, 252 No, 248 Md, 248 Fm, 244 Es, and 244 Cf.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Determining g A / g V with High-Resolution Spectral Measurements Using a LiInSe 2 Bolometer

Neutrinoless double beta decay (0νββ) processes sample a wide range of intermediate forbidden nuclear transitions, which may be impacted by quenching of the axial vector coupling constant (g A /g V ), the uncertainty of which plays a pivotal role in determining the sensitivity reach of 0νββ experiments. Here we present measurements performed on a high-resolution LiInSe 2 bolometer in a “source = detector” configuration to measure the spectral shape of the fourfold forbidden β decay of 115 In . The value of g A /g V is determined by comparing the spectral shape of theoretical predictions to the experimental β spectrum taking into account various simulated background components as well as a variety of detector effects. We find evidence of quenching of g A /g V at >5 σ with a model-dependent quenching factor of 0.655 ± 0.002 as compared to the free-nucleon value for the interacting shell model. We also measured the 115 In half-life to be [5.18 ± 0.06(stat) $^{+0.005}_{- 0.015}$(sys)] x 10 14 yr within the interacting shell model framework. This Letter demonstrates the power of the bolometeric technique to perform precision nuclear physics single-β decay measurements, which along with improved nuclear modeling can help reduce the uncertainties in the calculation of several decay nuclear matrix elements including those used in 0νββ sensitivity calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

R&D Towards CUPID, a Ton-Scale Bolometric 0νββ Experiment

CUPID, the CUORE Upgrade with Particle IDentification, is a next-generation experiment to search for neutrinoless double beta (0νββ) decay and other rare events using scintillating bolometers with 100 Mo. This award supported simulation and design work on the muon tagger system for CUPID as well the development of a plan and protocol for the irradiation and fabrication of the NTD thermal sensors for CUPID.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Overview of the ASDEX Upgrade results

After a 26-month vent ASDEX Upgrade (AUG) went back in operation with a newly designed upper W-divertor suitable for alternative divertor configurations (featuring in-vessel coils and cryo-pump). Parameter scans and an extensive set of measurements were obtained and their interpretation is ongoing. Prompted by the ITER wall change, dedicated experiments on non-boronized plasma startup were contrasted to that employing asymmetric and more symmetric boronizations. The asymmetric boronization proved to be as beneficial as the more symmetric one, which is in contrast to previous model calculations assuming perfect sticking of boron (measurements suggest sticking ≈ 0.3). In the startup phase also the impurity influxes at the outboard limiters were investigated contrasting the unboronized case featuring cold edges (low- Z radiation) to the boronized case, in which the lifetime of the boron layers could be estimated. Pedestal stability investigations revealed that the quasi-continuous exhaust (QCE) regime is obtained when ballooning modes are active in the vicinity of the separatrix and the global peeling-ballooning stability is high enough. Thus, at high enough shaping and high gas flux both can be achieved and QCE is a consequence. The closely related enhanced D-alpha (EDA) mode is not clearly distinguishable from QCE, e.g. the quasi-coherent mode characteristic for EDA also shows up in QCE. In QCE the impurity transport is behaving benign as could be measured for Ne with a novel analysis method making use of a comprehensive set of CXRS measurements. For high radiative fractions the regime of the X-point radiator (XPR) is accessible at AUG and the understanding of its access conditions and behaviour is further developed. Due to the localized radiative cooling at the X-point the XPR can be well diagnosed and thus controlled. For negative triangularity shapes, further experiments at increased shaping resulted in strongly heated L-mode plasmas avoiding ELMs. Two integrated modelling approaches towards ITER suggested that core W-accumulation will be no issue for ITER and that the fusion yield in ITER may be Q = 12 (i.e. ITPA20-IL scaling is too pessimistic). Further, investigations of the ITER ramp-down in AUG provide insights into maintaining position control. Various aspects of shattered pellet injection were investigated in AUG and one of the results show that with increasing Ne fraction the radiation during the current quench increases and the current decay becomes faster.

ASDEX Upgrade↗
DOE OSTI2020

Fundamental problems in astroparticle physics and cosmology (Final Technical Report)

In the standard cosmological model, structure forms when gas cools and condenses to the center of dark matter halos. The onset of structure is governed by rapid star formation and subsequent evolution of the first massive stars. One of the endpoints of stellar evolution is the formation of a black hole. We showed that all black hole merger events must occur after the universe is about 85 million years old. This prediction is important because it means that if a future experiment makes a detection of a black hole merger event at an earlier time then our understanding of cosmology and the onset of structure formation is not fully developed. In addition, we explored dark matter models that have either self-interactions or experience decays. In the first case, self-interactions may lead to the formation of a thick disk that can be co-planar to the Galactic disc due to correlations in angular momentum between dark matter and baryons that are predicted by tidal torque theory. We showed that for heavy dark matter particles, either the self interaction may not be strong enough to solve the small scale structure motivation or a dark disc cannot be present in the Milky Way. In the second-case, we showed that if dark matter experiences decays into two particles, one of which behaves like radiation, then it is possible to relieve the tension that exists between measurements of the local expansion rate. Finally, we developed methods on how to distinguish gamma-ray excesses from promising dark matter targets as compared to conventional astrophysical sources. This is an important toolset that is applicable to any suspected dark matter source.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Beyond-mean-field approaches for nuclear neutrinoless double beta decay in the standard mechanism

Nuclear weak decays provide important probes to fundamental symmetries in nature. A precise description of these processes in atomic nuclei requires comprehensive knowledge on both the strong and weak interactions in the nuclear medium and on the dynamics of quantum many-body systems. In particular, an observation of the hypothetical double beta decay without emission of neutrinos (0νββ) would unambiguously demonstrate the Majorana nature of neutrinos and the existence of the lepton-number-violation process. It would also provide unique information on the ordering and absolute scale of neutrino masses. The next-generation tonne-scale experiments with sensitivity up to 10 28 years after a few years of running will probably provide a definite answer to these fundamental questions based on our current knowledge on the nuclear matrix element (NME), the precise determination of which is a challenge to nuclear theory. Beyond-mean-field approaches have been frequently adapted for the study of nuclear structure and decay throughout the nuclear chart for several decades. In this review, we summarize the status of beyond-mean-field calculations of the NMEs of 0νββ decay assuming the standard mechanism of an exchange of light Majorana neutrinos. In conclusion, the challenges and prospects in the extension and application of beyond-mean-field approaches for 0νββ decay are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Aspects of gravitational portals and freeze-in during reheating

We conduct a systematic investigation of freeze-in during reheating while taking care to include both direct and indirect production of dark matter (DM) via gravitational portals and inflaton decay. Direct production of DM can occur via gravitational scattering of the inflaton, while indirect production occurs through scattering in the Standard Model radiation bath. We consider two main contributions to the radiation bath during reheating. The first, which may dominate at the onset of the reheating process, is produced via gravitational scattering of the inflaton. The second (and more standard contribution) comes from inflaton decay. We consider a broad class of DM production rates parametrized as R χ ∝ T n + 6 / Λ n + 2 , and inflaton potentials with a power-law form V ( ϕ ) ∝ ϕ k about the minimum. We find the relic density produced by freeze-in for each contribution to the Standard Model bath for arbitrary k and n , and compare these with the DM density produced gravitationally by inflaton scattering. We find that freeze-in production from the gravitationally produced radiation bath can exceed that of the conventional decay bath and account for the observed relic density provided that m χ > T RH , with additional k - and n -dependent constraints. For each freeze-in interaction considered, we also find m χ - and T RH -dependent limits on the beyond the Standard Model scale, Λ , for which gravitational production will exceed ordinary freeze-in production. Published by the American Physical Society 2025

Henrich, Stephen E. (ORCID:0000000323669519)↗
DOE OSTI2024

Gallium oxide semiconductor-based large volume ultrafast radiation hard spectroscopic scintillators

We report on the development of the first-ever inorganic radiation-hard moisture-insensitive large volume spectroscopic semiconductor-based scintillator with less than 2 ns decay time and light yields as high as 8000 ph/MeV. Despite extensive research into scintillator materials, the quest for an ideal scintillator combining ultrafast decay times (akin to BaF 2 and Yb-doped scintillators such as Lu 2 O 3 :Yb), high light yields (exceeding 2000 photons per MeV), spectroscopic capabilities, and exceptional radiation hardness remain unfulfilled. In this study, we demonstrate and report for the first time the viability of large-volume (up to 20 mm thickness) gallium oxide (β-Ga 2 O 3 ) semiconductor-based scintillators for applications requiring these properties. These β-Ga 2 O 3 scintillators were grown using the fast turnaround (~2 days) crucible-free optical float zone (FZ) technique. The high light yield and ultrafast decay time of these high-purity n-type semiconductors with free carrier concentration of 6 × 10 17 cm –3 are attributed to native defects, specifically oxygen vacancies (V O ) and gallium–oxygen vacancy pairs (V Ga –V O ), generated during optimized FZ growth. The ultrafast decay, along with high light yield, enables excellent timing resolution and high count rate detection for applications like time-of-flight positron emission tomography, physics experiments, and nuclear safety. The radiation hardness of these devices has been documented in a separate publication.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Proton Decay of 21 Na for 20 Ne Energy Levels

The 24 Mg(p,α) 21 Na transfer reaction has been previously studied for a spectroscopic study of 21 Na. In this follow-up analysis, the proton decays of the excited states of the radionuclide 21 Na, which were measured simultaneously, are reported. By investigating the coincidence between the reaction α-particles and decay protons, we were able to identify three groups of events that are associated with the energy levels in 20 Ne. The 20 Ne excitation energy plot was obtained as a result. Here, the four lowest known energy levels in 20 Ne (the ground state and excited states at E x = 1.633, 4.247 and 4.966 MeV) were clearly observed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Demonstrating the β-Ga 2 O 3 Schottky diodes for alpha radiation detection

Schottky barrier diodes were fabricated on (001) monoclinic β-Ga 2 O 3 wafers with low doped epitaxial layers of 7.0 × 10 15 cm −3 . Circular Ni Schottky contacts with area 2 mm 2 were deposited by electron beam evaporation. Devices were characterized electrically by performing forward and reverse current-voltage sweeps with a range of −100 V–2 V, as well as capacitance-voltage sweeps to −30 V. The breakdown voltage was also determined to be −180 V for the devices. Experiments measuring the electrical response from incident X-ray radiation was performed. A response time to X-ray radiation of less than 1 s was recorded and a decay time of approximately 2 s after removing X-ray source, which primarily attribute to X-ray switching on and off time. Energy spectra of alpha particles from a 0.9 μCi 241 Am button source was collected at various voltage biases using devices with the lowest measured leakage current while reverse biased. The total count rate was observed to increase linearly with increasing device bias. In conclusion, the peak channel number was observed to increase with increasing bias with the best resolution of 9.5% at −100 V reverse bias.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

New constraints on the Al 25 ( p , γ ) reaction and its influence on the flux of cosmic γ rays from classical nova explosions

The astrophysical 25 Al(p,γ) 26 Si reaction represents one of the key remaining uncertainties in accurately modeling the abundance of radiogenic 26 Al ejected from classical novae. Specifically, the strengths of key proton-unbound resonances in 26 Si, that govern the rate of the 25 Al(p,γ) reaction under explosive astrophysical conditions, remain unsettled. Here, we present a detailed spectroscopy study of the 26 Si mirror nucleus 26 Mg. We have measured the lifetime of the 3 + , 6.125-MeV state in 26 Mg to be 19(3) fs and provide compelling evidence for the existence of a 1 – state in the T = 1, A = 26 system, indicating a previously unaccounted for ℓ = 1 resonance in the 25 Al(p,γ) reaction. Using the presently measured lifetime, together with the assumption that the likely 1 – state corresponds to a resonance in the 25 Al + p system at 435.7(53) keV, we find considerable differences in the 25 Al(p,γ) reaction rate compared to previous works. Furthermore, based on current nova models, we estimate that classical novae may be responsible for up to ≈ 15% of the observed galactic abundance of 26 Al.

20 ≤ A ≤ 38↗
DOE OSTI2021

Potential neutron-induced γ-ray background on natural tellurium relevant to 130 Te 0 ν ββ decay searches at the CUORE and SNO+ detectors

Gamma-ray production cross-section data have been obtained for the inelastic neutron scattering reactions 126,128,130 Te(n,n'γ) at five neutron energies between 3.6 and 10 MeV. We report data for the γ-ray energy region relevant to 0ν ββ decay of 130 Te with a Q ββ value of 2527.515 keV, assuming natural-abundance tellurium, as used at CUORE and SNO+. The natural abundance of 130 Te, 128 Te, and 126 Te is 34%, 32%, and 19%, respectively. For CUORE the γ-ray cascades from the excited state in 130 Te at 2527.06 keV and in 126 Te at 2533.85 keV are of concern. For SNO+, accounting for its inferior energy resolution, an additional four levels are important in 130 Te, an additional nine levels in 128 Te, and an additional eight levels in 126 Te. Of these, we report neutron-induced γ-ray production cross sections for the strongest transitions: the 2581.15 keV level in 130 Te, the 2494.20, 2508.06, and 2630.14 keV levels in 128 Te, and the 2496.83 and 2585.46 keV level in 126 Te. Here, the largest cross-section values were found for cascade γ-ray transitions to the ground state, while direct transitions to the ground state are very weak and were not observed in the present work. Both the CUORE and SNO+ detectors, however, may not be able to distinguish between cascade transitions and direct transitions to the ground state, making the neutron-induced excitation of the 2527.06 keV state of 130 Te in particular a potential problem for 0νββ decay searches of 130Te, because it matches its Q ββ value.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Opportunities in the Synthesis and Design of Radioactive Thin Films and Nanoparticles

Studies of radioactive isotopes at the liquid-solid or gas-solid interface are enabling a detailed mechanistic understanding the effects of radioactive decay on physical, biological, and chemical systems. In recent years, there has been a burgeoning interest in using radioactive isotopes for both imaging and therapeutic purposes by attaching them to the surface of colloidal nanoparticles. By merging the field of nanomedicine with the more mature field of internal radiation therapy, researchers are discovering new ways to diagnose and treat cancer. In this perspective, we discuss state-of-the-art radioactive thin films as applied to both well-defined surfaces and more complex nanoparticles. Here, we highlight the design considerations that are unique to radioactive films, which originate from the damaging and potentially self-destructive emissions produced during radioactive decay and highlight future opportunities in the largely underexplored area between radioisotope chemistry and nanoscience.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Enhancement of α -particle formation near Sn 100

The superfluid tunneling model is applied to the calculation of ground-state-to-ground-state α decay in the even-even neutron-deficient Te-Ba nuclei. Here, we show that there is a larger α-particle formation probability in nuclei of this region above 100 Sn when compared to analogous nuclei above 208 Pb. This is consistent with the expected systematic variation of the pair gap Δ as a function of mass number. Finally, the recent experimental data on the α decay of the N=Z nuclei 104 Te and 108 Xe are shown to leave open the possibility of enhanced α-particle formation involving nucleon correlations beyond the standard treatment of like-nucleon pairing, which is the mechanism suggested as underlying "superallowed" α decay.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

A method to load tellurium in liquid scintillator for the study of neutrinoless double beta decay

Herein, a method has been developed to load tellurium into liquid scintillator so as to permit searches for neutrinoless double beta decay with high sensitivity. The approach involves the synthesis of an oil-soluble tellurium compound from telluric acid and an organic diol. The process utilises distillable chemicals that can be safely handled underground and affords low radioactive backgrounds, low optical absorption and high light yields at loading levels of at least several percent Te by weight.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗