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Miller, D.

Publications and source records attributed to Miller, D..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Impact of Modular Total Absorption Spectrometer measurements of β decay of fission products on the decay heat and reactor ν ¯ e flux calculation

Here, we report the results of a β-decay study of fission products 86 Br, 89 Kr, 89 Rb, 90 gs Rb, 90m Rb, 90 Kr, 92 Rb, 139 Xe, and 142 Cs performed with the Modular Total Absorption Spectrometer (MTAS) and on-line mass-separated ion beams. These radioactivities were assessed by the Nuclear Energy Agency as having high priority for decay heat analysis during a nuclear fuel cycle. We observe a substantial increase in β feeding to high excited states in all daughter isotopes in comparison to earlier data. This increases the average γ-ray energy emitted by the decay of fission fragments during the first 10 000 s after fission of 235 U and 239 Pu by approximately 2% and 1%, respectively, improving agreement between results of calculations and direct observations. New MTAS results reduce the reference reactor ¯ν e flux used to analyze reactor ¯ν e interaction with detector matter. The reduction determined by the ab initio method for the four nuclear fuel components, 235 U, 238 U, 239 Pu, and 241 Pu, amounts to 0.976, 0.986, 0.983, and 0.984, respectively.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Experimental study of the β decay of the very neutron-rich nucleus Ge 85

The β -decay properties of the very neutron-rich nucleus 85 Ge, produced in the proton-induced fission of 238 U, were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The level scheme of 33 85 As 52 populated in 85 Geβ γ decay was reconstructed and compared to shell-model calculations. The investigation of the systematics of low-energy levels in N =52 isotones together with shell-model analysis allowed us to provide an estimate of the low-energy structure of the more exotic N =52 isotone 81 Cu.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Investigation of negative-parity states in Dy 156 : Search for evidence of tetrahedral symmetry

An experiment populating low/medium-spin states in 156 Dy was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the 148 Nd ( 12 C , 4 n ) reaction and the Gammasphere array was utilized to detect the emitted γ rays. B ( E 2 ) / B ( E 1 ) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. In addition, several other negative-parity structures were observed to higher spin and two new sequences were established.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Crystal accumulation in the Hanford Waste Treatment Plant high level waste melter: Summary of FY2016 experiements

Five experiments were completed with the full-scale, room temperature Hanford Waste Treatment and Immobilization Plant (WTP) high-level waste (HLW) melter riser test system to observe particle flow and settling in support of a crystal tolerant approach to melter operation. A prototypic pour rate was maintained based on the volumetric flow rate. Accumulation of particles was observed at the bottom of the riser and along the bottom of the throat after each experiment. Measurements of the accumulated layer thicknesses showed that the settled particles at the bottom of the riser did not vary in thickness during pouring cycles or idle periods. Some of the settled particles at the bottom of the throat were re-suspended during subsequent pouring cycles, and settled back to approximately the same thickness after each idle period. The cause of the consistency of the accumulated layer thicknesses is not year clear, but was hypothesized to be related to particle flow back to the feed tank. Additional experiments reinforced the observation of particle flow along a considerable portion of the throat during idle periods. Limitations of the system are noted in this report and may be addressed via future modifications. Follow-on experiments will be designed to evaluate the impact of pouring rate on particle re-suspension, the influence of feed tank agitation on particle accumulation, and the effect of changes in air lance positioning on the accumulation and re-suspension of particles at the bottom of the riser. A method for sampling the accumulated particles will be developed to support particle size distribution analyses. Thicker accumulated layers will be intentionally formed via direct addition of particles to select areas of the system to better understand the ability to continue pouring and re-suspend particles. Results from the room temperature system will be correlated with observations and data from the Research Scale Melter (RSM) at Pacific Northwest National Laboratory, and coordinated with modeling efforts underway at Idaho National Laboratory.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Modular total absorption spectrometer

The design and performance of the Modular Total Absorption Spectrometer built and commissioned at the Oak Ridge National Laboratory is presented here. The active volume of the detector is approximately one ton of NaI(Tl), which results in very high full γ energy peak efficiency of 71% at 6 MeV and nearly flat efficiency of around 81.5% for low energy γ-rays between 300 keV and 1 MeV. In addition to the high peak efficiency, the modular construction of the detector permits the use of a γ-coincidence technique in data analysis as well as β-delayed neutron observation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

β -decay study of Kr 94

β decay of neutron-rich nuclide 94 Kr was reinvestigated by means of a high resolution on-line mass separator and β – γ spectroscopy. In total 22 γ-ray transitions were assigned to the decay of 94 Kr, and a new isomeric state was identified. The new information allows us to build detailed levels systematics in a chain of odd-odd rubidium isotopes and draw conclusions on nuclear structure for some of the observed states. Furthermore, the discussed level structure affects the evolution of β-decay half-lives for neutron-rich selenium, krypton, and strontium isotopes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

In situ liquid water visualization in polymer electrolyte membrane fuel cells with high resolution synchrotron x-ray radiography

In this work, we investigated the dominating properties of the porous materials that impact water dynamics in a polymer electrolyte membrane fuel cell (PEMFC). Visualizations of liquid water in an operating PEMFC were performed at the Canadian Light Source. A miniature fuel cell was specifically designed for X-ray imaging investigations, and an in-house image processing algorithm based on the Beer-Lambert law was developed to extract quantities of liquid water thicknesses (cm) from raw X-ray radiographs. The X-ray attenuation coefficient of water at 24 keV was measured with a calibration device to ensure accurate measurements of the liquid water thicknesses. From this experiment, the through plane distribution of the liquid water in the fuel cell was obtained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

CUORE-0 detector: design, construction and operation

The CUORE experiment will search for neutrinoless double-beta decay of 130 Te with an array of 988 TeO 2 bolometers arranged in 19 towers. CUORE-0, the first tower assembled according to the CUORE procedures, was built and commissioned at Laboratori Nazionali del Gran Sasso, and took data from March 2013 to March 2015. In this study we describe the design, construction and operation of the CUORE-0 experiment, with an emphasis on the improvements made over a predecessor experiment, Cuoricino. Finally, in particular, we demonstrate with CUORE-0 data that the design goals of CUORE are within reach.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

β and β – n decay of the neutron-rich Ge 84 nucleus

In this study, the β-decay properties of the very neutron-rich 84 Ge nucleus were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Several new γ-transitions and levels were added to its decay scheme and the order of the two lowest-lying levels in the daughter 84 As was corrected. For the first time γ radiation following β-delayed neutron emission was observed. The shell-model calculations and apparent β transition intensities were used to guide the spin assignment to the 84 As levels, in particular for the low-energy part of the level scheme. The new spin-parity (2 – ) proposed for the ground state of 84 As is supported also by the systematics of N = 51 isotones.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Review of even element super-heavy nuclei and search for element 120

The reaction 54Cr$ + $248Cm was investigated at the velocity filter SHIP at GSI, Darmstadt, with the intention to study production and decay properties of isotopes of element 120. Three correlated signals were measured, which occurred within a period of 279ms. The heights of the signals correspond with the expectations for a decay sequence starting with an isotope of element 120. However, a complete decay chain cannot be established, since a signal from the implantation of the evaporation residue cannot be identified unambiguously. Measured properties of the event chain are discussed in detail. The result is compared with theoretical predictions. Previously measured decay properties of even element super-heavy nuclei were compiled in order to find arguments for an assignment from the systematics of experimental data. In the course of this review, a few tentatively assigned data could be corrected. New interpretations are given for results which could not be assigned definitely in previous studies. The discussion revealed that the cross-section for production of element 120 could be high enough so that a successful experiment seems possible with presently available techniques. However, a continuation of the experiment at SHIP for a necessary confirmation of the results obtained in a relatively short irradiation of five weeks is not possible at GSI presently. Furthermore, we decided to publish the results of the measurement and of the review as they exist now. In the summary and outlook section we also present concepts for the continuation of research in the field of super-heavy nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Remarks on the fission barriers of super-heavy nuclei

Shell-correction energies of super-heavy nuclei are approximated by using QαQα values of measured decay chains. Five decay chains were analyzed, which start at the isotopes 285 Fl, 294 118, 291 Lv, 292 Lv and 293 Lv. The data are compared with predictions of macroscopic-microscopic models. Fission barriers are estimated that can be used to eliminate uncertainties in partial fission half-lives and in calculations of evaporation-residue cross-sections. In that calculations, fission probability of the compound nucleus is a major factor contributing to the total cross-section. The data also provide constraints on the cross-sections of capture and quasi-fission in the entrance channel of the fusion reaction. Here, arguments are presented that fusion reactions for synthesis of isotopes of elements 118 and 120 may have higher cross-sections than assumed so far.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2016

Reexamining Gamow-Teller decays near Ni 78

Decays of neutron-rich nuclei 82,83 Zn and 82,83 Ga produced in proton-induced fission of 238 U were studied at the Holifield Radioactive Ion Beam Facility using on-line mass separation and β–γ spectroscopy techniques. New γ-ray transitions were identified and level schemes, which include states at high excitation energies in the range between 3–7 MeV were constructed. These high-energy levels were identified to be populated through allowed Gamow-Teller β transitions, and their structure was interpreted with new shell-model calculations. Furthermore, a β-delayed neutron branching ratio of 69±7% was deduced for 82 Zn and revised β-decay half-life values of 82 Zn [155(17)(20) ms] and 83 Zn [122(28) ms] were determined.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗