SEARCH · Engineering Papers
Results for “GAMMA DECAY”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Identification of $\gamma$-decaying resonant states in 26 Mg and their importance for the astrophysical s process
The 22 Ne(α, n) reaction is expected to provide the dominant neutron source for the weak s process in massive stars and intermediate-mass (IM) Asymptotic Giant Branch (AGB) stars. However, the production of neutrons in such environments is hindered by the competing 22 Ne(α,γ) 26 Mg reaction. Here, the 11 B( 16 O,p) fusion-evaporation reaction was used to identify γ-decay transitions from 22 Ne + α resonant states in 26 Mg. Spin-parity restrictions have been placed on a number of α-unbound excited states in 26 Mg and their role in the 22 Ne(α,γ)26Mg reaction has been investigated. In particular, a suspected natural-parity resonance at E c.m. = 557(3) keV, that lies above the neutron threshold in 26 Mg, and is known to exhibit a strong α-cluster character, was observed to γ decay. Furthermore, a known resonance at E c.m. = 466(4) keV has been definitively assigned 2 + spin and parity. Consequently, uncertainties in the 22 Ne(α,γ) stellar reaction rate have been reduced by a factor of ~20 for temperatures ~0.2 GK.
Excitation and $\gamma$-decay coincidence measurements at the GRAF beamline for studies of pygmy and giant dipole resonances
Physical studies of electric dipole excitations in atomic nuclei e.g. the structure of pygmy dipole resonances and isovector giant dipole resonances are attracting much attention recently. In this article, we describe a technical development in the coincidence measurement of the excitation processes with the Grand Raiden high-resolution magnetic spectrometer and the γ-decay processes by the CAGRA and SCγ LLA efficient γ-detector arrays at the Research Center for Nuclear Physics at Osaka University. Specifically, we describe how we developed a new beamline (GRAF), for γ detection at the target position by placing the spectrometer at an angle of 4.5-19.0° and by transporting the primary beam to a well-shielded beam dump. Experimental conditions and representative data are shown for each of the two γ-detector arrays.
Properties of $\gamma $-decaying Isomers in the $^{100}$Sn Region Revisited
The study of nuclei in the region around the N = Z doubly-magic nucleus 100Sn has been of long standing interest for the nuclear structure and nuclear astrophysics. Recently, Park et al. have reported on properties of γ-decaying isomers and isomeric ratios in the vicinity of 100Sn. That experiment was performed at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center in Japan as a part of the EURICA campaign. Neutron-deficient nuclei were produced in a fragmentation reaction of a 124 Xe primary beam on a 9 Be target at an energy of 345 MeV/A. Secondary ions were separated and identified in the BigRIPS fragment separator and implanted in the silicon detector array WAS3ABi. The data presented here were obtained in another experiment performed at the RIBF using the same reaction but slightly different separator settings. New results of ratios of isomeric population and half-lives of γ-decaying isomers populated in the experiment are presented.
Experimental Status of b -> s(d) gamma Decays
Explore the source record for details and available documents.
Measurement of the Direct CP Asymmetry in b --> s gamma Decays
Explore the source record for details and available documents.
Factorization in B to V gamma Decays
Explore the source record for details and available documents.
The Sign of The pi_0 ->Gamma Gamma Decay Amplitude
Explore the source record for details and available documents.
CHIRAL CORRECTIONS TO THE ANOMALOUS 2 GAMMA DECAYS OF PI0, ETA AND ETA-PRIME
Explore the source record for details and available documents.
SNAP-8 post shutdown gamma radiation approximations
Detector responses were calculated for normalized sources in the Perkins and King energy group structure for a SNAP 8 power system on a NASA space station. Gamma decay rates were then calculated by using an expanded, updated list of isotopic decay data, and from these, actual detector responses were found for the SNAP 8 system. The results indicate that energy-dependent calculations must be made to determine decay gamma dose rates for actual reactor configurations. A simplified method for making these calculations has been devised.
Searches for exclusive Higgs boson decays into D *$\gamma$ and Z boson decays into D 0 $\gamma$ and K $^{0}_{s}$$\gamma$ in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector
Searches for exclusive decays of the Higgs boson into D*$\gamma$ and of the Z boson into D 0 $\gamma$ and K$_{s}^{0}$$\gamma$ can probe flavour-violating Higgs boson and Z boson couplings to light quarks. Searches for these decays are performed with a pp collision data sample corresponding to an integrated luminosity of 136.3 fb -1 collected at $\sqrt{s}$ = 13TeV between 2016–2018 with the ATLAS detector at the CERN Large Hadron Collider. In the D*$\gamma$ and D 0 $\gamma$ channels, the observed (expected) 95% confidence-level upper limits on the respective branching fractions are B(H→D*$\gamma$) < 1.0(1.2)×10 -3 , B(Z→D 0 $\gamma$) < 4.0(3.4)×10 -6 , while the corresponding results in the K$_{s}^{0}$$\gamma$ channel are B(Z→K$_{s}^{0}$$\gamma$) < 3.1(3.0)×10 -6 .
Effect of laser radiation on aqueous solutions of beta-active nuclides
Experimental data are presented on the effect of pulsed laser irradiation of aqueous {sup 234}Th, {sup 231}Th and {sup 137}Cs solutions on the concentrations of the beta-active nuclides in the solutions. Central to the investigation technique used is that the solutions contain nanoparticles resulting from the interaction of laser radiation with a target placed in the cuvette. The concentration of the radionuclides was evaluated before, during and after laser irradiation from the area under gamma-ray lines corresponding to spontaneous gamma decay. The gamma photon energies of {sup 234}Th, {sup 231}Th and {sup 137}Cs are 92, 186 and 661 keV, respectively. It has been shown that laser irradiation reduces the concentration of the three beta-active nuclides without excess gamma-ray emission in the energy range of their spontaneous decay. This is possible if decay follows another mechanism, activated by interaction of laser radiation with the aqueous solutions of the nuclides in the presence of nanoparticles.
Quantum imaging with positronium-decay-emitted gamma rays
The use of entangled gamma rays from positronium decay for quantum-enhanced imaging of dense materials is demonstrated. Quantum ghost images, where only one of the entangled 511-keV photons interacts with the object, are obtained for tantalum samples of varying density using a 210-ps time-resolution dual detector system and a Na-22 positron source. An analysis comparing both classical and quantum imaging modalities is employed to isolate true 511-keV events from background noise. Image quality is quantitatively assessed using transmission ratios and the Michelson contrast. Quantum-correlated images are found to exhibit superior (up to approximately 1.7x, from 0.49 to 0.83 in the thickest sample measured) contrast compared to classical methods and align well with theoretical expectations. These results suggest that quantum ghost imaging with positronium-based entangled gamma rays could significantly enhance noninvasive imaging of high-density objects, with potential applications in areas such as cargo inspection and security screening.
Gamma and Decay Energy Spectroscopy Measurements of Trinitite
We report gamma-ray spectroscopy measurements of trinitite samples and analogous samples obtained from detonation sites in Nevada and Semipalatinsk, as well as in situ measurements of topsoil at the Trinity site. We also report the first isotopic composition measurements of trinitite using the novel forensics technique of decay energy spectroscopy (DES) as a complement to traditional forensics techniques. Our gamma spectroscopy and DES measurements are compared to other published results.
Origin of High-Energy Protons Responsible for Late-Phase Pion-Decay Gamma-Ray Continuum from the Sun
Gamma-ray emission from solar eruptions can last far beyond the impulsive phase of the associated flares, and hence termed as sustained gamma-ray emission (SGRE). These gamma-rays result from the decay of neutral pions produced when >300 MeV protons collide with hydrogen and heavier elements in the solar photosphere. The source of protons producing SGRE has two possible origins: (i) particles accelerated in the associated flare are somehow trapped in magnetic structures and diffuse slowly to the chromosphere, and (ii) particles accelerated at the shock front that diffuse back to the Sun. In this presentation, we compile currently available observations and inferences that support these two possibilities. We use the gamma-ray data from the Fermi Large Area Telescope (Fermi/LAT) in conjunction with coronal mass ejection (CME) data from the Solar and Heliospheric Observatory (SOHO) and type II radio burst information from the Wind spacecraft. We also use the GOES soft X-ray flare information.
Analyses to support waste disposition of SNS Inner Reflector Plug
The Spallation Neutron Source Inner Reflector Plug (IRP) is scheduled for replacement. It reached end of life-time because of moderator neutron poison and decoupler burn-out, which is used for shaping neutron pulses. The replacement of IRP is a complex task due to its location in the area receiving high irradiation, being under significant amount of shielding, and size, which requires removal in segments. In order to support the disposal of spent IRP, waste characterization analyses are performed. These analyses include an accurate estimate of the radionuclide inventory and the residual dose rate. Using this data, the package class is determined for the and appropriate containers for temporary storage and subsequent transport are assigned. Analyses are performed in four steps: a radiation transport analysis of the radiation environment for producing the flux and isotope production information using MCNPX, a multi-cell transmutation analysis based n CINDER90, the generation of decay gamma source terms, and the gamma transport analyses of the decay gammas arriving at residual dose rates again using MCNPX. . Due to the complexity of the geometry of the lower segment, transport analyses for the residual dose rate require elaborate work for the source terms definition.
Neutronics Analysis for ITER Diagnostic Generic Upper Port Plug
This paper presents new results of neutronics analysis performed for the updated design of the ITER Diagnostic Generic Upper Port Plug (DGUPP). Such analysis is performed regularly during the development of the ITER Ports design. Neutronics analysis is an important step in support of the development of ITER components irradiated by 14 MeV neutrons generated in D-T fusion thermonuclear reactions. The neutrons are born in the ITER tokamak plasma chamber and then impinge on the surrounding blanket and port plugs, after that they diffuse through shielding material of vacuum vessel components or could stream through the diagnostic channels and assembly gaps far away from plasma up to the bio-shield and in a small amount beyond it. While ITER machine is in operation it is inaccessible, after the shut-down it is planned to provide personnel access to the Upper Port Inter-Space Structure (UP ISS) behind the Port Plug via the corridors. Neutrons activate the ITER materials and those radioactive materials emit decay gammas during the shut-down causing a Shut-Down Dose Rate (SDDR) field distributed all around the activated materials. Decay gammas could also stream through the void channels. That emphasizes the need for calculation of decay gamma transport in evaluations of SDDR, which is reflected in the use of transport - activation interface code described in Section of Computational Modelling. The assessment of radiation environment (fluxes and SDDR) at DGUPP was focused on the port back-side area of UP ISS, where personnel access is planned along the ISS maintenance corridors. Minimization of SDDR at the front part of the ISS maintenance corridors was the target value for optimization of the DGUPP shielding and analysis of related neutronics effects. Following the dose ALARA (As Low As Reasonably Achievable) principle, every possibility to reduce SDDR should be investigated, emphasizing the importance of this analysis. The challenges of such analysis are inextricably connected with the engineering complexity of the ITER machine, with integration of many diagnostics systems having channels and gaps inside the ITER ports. Those gaps result in radiation streaming and negatively affect the shielding performance of the port plugs. The computational complication is caused by the need to model precisely the ITER geometry and then to run deep penetrating radiation transport in the substantially heterogenic toroidal geometry of ITER large-size tokamak, with 30 m height and diameter of its bio-shield. The whole mass of Upper Port Plug (UPP) could be up to 25 tons and it must be very precisely positioned inside the port opening in blanket and Vacuum Vessel. Facing the engineering challenges for the assembly of DGUPP, there were proposed two Project Change Requests (PCRs) No. 439 and 709 concerning the design updates of UPP/blanket interface and its remote handling.
Titanium Material Comparison for Second Target Station Moderators
Two titanium alloys, Ti 15-3-3-3 and Grade 5 Ti, have been analyzed for their neutronic differences after being exposed to neutron fluxes from a 5-year operational period in the Second Target Station (STS)moderators. There are several differences in the original composition of the two alloys where Ti 15-3-3-3contains Cr and Sn and Grade 5 Ti does not. The differences in original composition propagate through the analysis to yield discrepancies in decay power density and decay gamma intensity density of more than a factor of 3.5 at some times during operation. Immediately after the 5-year operational period, Ti 15-3-3-3has a factor of 3.59 higher intensity of high-energy decay gammas than Grade 5 Ti, and Ti 15-3-3-3 also has a factor of 3.53 higher decay power than Grade 5 Ti. After 1 year of shutdown, Ti 15-3-3-3 has a 48% higher intensity of high-energy decay gammas and a 86% greater decay power density when compared with Grade 5 Ti. The quantities-of-interest in this report are per unit volume and the overall volume of titanium should be considered when making engineering judgment on final titanium alloy selection.