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Firestone, R. B.

Publications and source records attributed to Firestone, R. B..

16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

pyEGAF: Modernization of the EGAF database

One of the most comprehensive resources for thermal neutron-capture data is the Evaluated Gamma-ray Activation File (EGAF), containing data from prompt gamma activation analysis measurements carried out at the Budapest Research Reactor for 245 isotopes. Although these valuable datasets have been freely available for many years, the outdated and cryptic adopted format makes it difficult to utilize the data and it is not generally suitable for modern computational technologies. Furthermore, to help overcome these challenges, we have converted the datasets into an open standard JSON format. Additionally, we have developed a Python implementation of an open-source software package, pyEGAF, designed to interact with the JSON data structures for general purpose access, manipulation, and rapid assessment of the capture-gamma data in EGAF.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Radiative-capture cross sections for the La 139 ( n , γ ) reaction using thermal neutrons and structural properties of La 140

A set of prompt partial γ-ray production cross sections from thermal neutron capture were measured for the La 139 ( n , γ ) reaction using a guided beam of subthermal (thermal and cold) neutrons incident on a nat La 2 O 3 target at the Prompt Gamma Activation Analysis facility of the Budapest Research Reactor. Absolute La 140 cross sections were determined relative to the well-known comparator 35 Cl(n,γ) cross sections from the irradiation of a stoichiometric nat LaCl 3 sample. Here, the total cross section for radiative thermal neutron capture on La 139 from the sum of experimentally measured cross sections observed to directly feed the La 140 ground state was determined to be $σ$ $^{expt}_{0}$ = 8.58 (50) b.

139La(n, γ), E=thermal and cold↗
DOE OSTI2016

γ-ray decay from neutron-bound and unbound states in 95 Mo and a novel technique for spin determination

The emission of γ rays from neutron-bound and neutron-unbound states in 95 Mo, populated in the 94 Mo(d,p) reaction, has been investigated. Charged particles and γ radiation were detected with arrays of annular silicon and Clover-type high-purity Germanium detectors, respectively. Utilizing p-γ and p-γ-γ coincidences, the 95 Mo level scheme was greatly enhanced with 102 new transitions and 43 new states. It agrees well with shell model calculations for excitation energies below ≈2 MeV. From p-γ coincidence data, a new method for the determination of spins of discrete levels is proposed. The method exploits the suppression of high-angular momentum neutron emission from levels with high spins populated in the (d,p) reaction above the neutron separation energy. As a result, spins for almost all 95 Mo levels below 2 MeV (and for a few levels above) have been determined with this method.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Determination of the effective sample thickness via radiative capture

Our procedure for determining the effective thickness of non-uniform irregular-shaped samples via radiative capture is described. In this technique, partial γ-ray production cross sections of a compound nucleus produced in a neutron-capture reaction are measured using Prompt Gamma Activation Analysis and compared to their corresponding standardized absolute values. For the low-energy transitions, the measured cross sections are lower than their standard values due to significant photoelectric absorption of the γ rays within the bulk-sample volume itself. Using standard theoretical techniques, the amount of γ-ray self absorption and neutron self shielding can then be calculated by iteratively varying the sample thickness until the observed cross sections converge with the known standards. The overall attenuation provides a measure of the effective sample thickness illuminated by the neutron beam. This procedure is illustrated through radiative neutron capture using powdered oxide samples comprising enriched 186 W and 182 W from which their tungsten-equivalent effective thicknesses are deduced to be 0.077(3) mm and 0.042(8) mm, respectively.

(n, γ) radiative capture↗
DOE OSTI2015

Radiative thermal neutron-capture cross sections for the 180 W($n,\gamma$) reaction and determination of the neutron-separation energy

Prompt thermal neutron-capture partial $\gamma$-ray production cross sections were measured for the first time for the 180 W($n; \gamma$) reaction using a cold guided-neutron beam at the Budapest Research Reactor. Absolute 181 W $\gamma$-ray cross sections were internally standardized using well-known comparator $\gamma$-ray cross sections belonging to the other tungsten isotopes present in the 11.35%-enriched 180 W sample. Transitions were assigned to levels in 181 W based largely upon information available in the literature. The total radiative thermal neutron-capture cross section $\sigma$0 was determined from the sum of direct prompt $\gamma$-ray cross sections populating the ground state and a modeled contribution accounting for ground-state feeding from the quasi continuum. In this work, we find $\sigma$0 = 21.67(77) b. A new measurement of the cross section for the 5/2 - metastable isomer at 365.6 keV, $\sigma_{5/2-}(^{181}W^m; 14.6 \mu$s) = 19.96(55) b, is also determined. Additionally, primary $\gamma$ rays, observed for the first time in the 180 W($n,\gamma$) reaction, provide the most precise determination for the 181 W neutron-separation energy, $S_n$ = 6669.02(16) keV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Nuclear Data Sheets for A = 21

This evaluation of A = 21 has been updated from previous evaluations published in 2004Fi10, 1998En04, 1990En08, and 1978En02. Coverage includes properties of adopted levels and γ-rays, decay-scheme data (energies, intensities and placement of radiations), and cross reference entries. The following tables continue the tradition of showing the systematic relationships between levels in A = 21. Much of the new data in this evaluations were taken directly from the xundl database, compiled under the direction of Balraj Singh, McMaster University. The evaluator is particularly appreciative of the efforts of the xundl compilers.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Failure of the gross theory of beta decay in neutron deficient nuclei

The neutron deficient isotopes 117-121 Xe, 117-124 Cs, and 122-124 Ba were produced by a beam of 28 Si from the LBNL SuperHILAC on a target of nat Mo. The isotopes were mass separated and their beta decay schemes were measured with a Total Absorption Spectrometer (TAS). The beta strengths derived from these data decreased dramatically to levels above ≈1 MeV for the even-even decays; 3–4 MeV for even-Z, odd-N decays; 4–5 MeV for the odd-Z, even-N decays; and 7–8 MeV for the odd-Z, odd-N decays. The decreasing strength to higher excitation energies in the daughters contradicts the predictions of the Gross Theory of Beta Decay. The integrated beta strengths are instead found to be consistent with shell model predictions where the single-particle beta strengths are divided amoung many low-lying levels. The experimental beta strengths determined here have been used calculate the half-lives of 143 neutron deficient nuclei with Z=51–64 to a precision of 20% with respect to the measured values.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

γ decay from the quasicontinuum of 197,198 Au

Here, the average electromagnetic dipole response of levels in the quasicontinuum of 197,198 Au has been measured using ( 3 He, 3 He') and (d,p) reactions. The extracted γ-ray strength functions have been normalized according to three model assumptions for the nuclear spin distribution. An enhancement in the energy region E γ = 3.0–6.5 MeV is observed for both isotopes. The E1 component of such excess of strength is studied in detail for 198 Au and is interpreted as the pygmy dipole resonance with an energy centroid of 5.9(1) MeV and exhausts about 1% of the total integrated strength. The pygmy dipole resonance is shown to have a significant impact on the calculated 197 Au(n,γ) 198 Au cross section.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

TANDEM: a mutual cooperation effort for transactinide nuclear data evaluation and measurement

Here, the need for accurate nuclear reaction data of actinides is well documented and several initiatives from international organizations for improvement have been initiated in the past. This need, particularly in view of method development for non-destructive assay of nuclear waste, has generated a joint effort to use prompt and delayed neutron activation techniques to enhance nuclear capture data of some long lived actinides such as 237 Np, 242 Pu and 241 Am in the frame of a multilateral cooperation. This research initiative is targeted to lay grounds for the development of a non-destructive active neutron interrogation technique to quantify actinides in mixed waste and residues from decommissioning of nuclear installations for safe treatment and storage of such materials.

42 ENGINEERING↗
DOE OSTI2014

Photon strength and the low-energy enhancement

Several measurements in medium mass nuclei have reported a low-energy enhancement in the photon strength function. Although, much effort has been invested in unraveling the mysteries of this effect, its physical origin is still not conclusively understood. Here, a completely model-independent experimental approach to investigate the existence of this enhancement is presented. The experiment was designed to study statistical feeding from the quasi-continuum (below the neutron separation energy) to individual low-lying discrete levels in {sup 95}Mo produced in the (d, p) reaction. A key aspect to successfully study gamma decay from the region of high-level density is the detection and extraction of correlated particle-gamma-gamma events which was accomplished using an array of Clover HPGe detectors and large area annular silicon detectors. The entrance channel excitation energy into the residual nucleus produced in the reaction was inferred from the detected proton energies in the silicon detectors. Gating on gamma-transitions originating from low-lying discrete levels specifies the state fed by statistical gamma-rays. Any particle-gamma-gamma event in combination with specific energy sum requirements ensures a clean and unambiguous determination of the initial and final state of the observed gamma rays. With these requirements the statistical feeding to individual discrete levels is extracted on an event-by-event basis. The results are presented and compared to {sup 95}Mo photon strength function data measured at the University of Oslo.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Photon Strength Function at Low Energies in 95 Mo

A new and model-independent experimental method has been developed to determine the energy dependence of the photon strength function. It is designed to study statistical feeding from the quasi continuum to individual low-lying discrete levels. This new technique is presented and results for 95 Mo are compared to data from the University of Oslo. In particular, questions regarding the existence of the low-energy enhancement in the photon strength function are addressed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗