E. T. Jurney

A revision of the meteorite based cosmic abundance of boron

Abstract Analyses of meteorites for B abundances have shown that many chondrites are contaminated with terrestrial B, producing erroneously high meteoritic abundances of this element. Boron concentrations in freshly prepared interior samples are significantly lower than they are in samples with unknown or unspecified terrestrial histories. An estimate of the cosmic abundance based upon the analyses of 8 interior samples of 2 carbonaceous chondrites and 1 interior sample of each of 8 ordinary chondrites is a factor of 6.7 less than the previous low estimate. Our revised value, 3.0 B/1010H, is in excellent agreement with estimates based on observations of the solar photosphere. There is no longer a need to consider processes that enrich B in carbonaceous chondrites or deplete it in the sun. Relative meteoritic abundances of Li, Be and B are now in general agreement with models of nucleosynthesis of these light elements by galactic cosmic ray induced spallation.

Multielement analysis of major and minor elements by thermal neutron induced capture gamma-ray spectrometry

The utility of prompt gamma-rays from thermal neutron capture for the measurement of nine elements (Si, Al, Fe, Na, K, Ca, Ti, Mg and P) in major and minor abundance has been investigated. National Bureau of Standards (NBS) and United States Geological Survey (USGS) standards were used to demonstrate generally good agreement between experimental measurements and certified values. Usually accuracies and precisions of ±10% were observed.

Gamma-ray spectrum from 204Pb(n, γ)205Pb

Abstract The gamma-ray spectrum following thermal neutron capture by 204 Pb was observed to populate directly 16 levels in 205 Pb. A total of 23 low-energy gamma rays, of which three are doubtful, were observed to depopulate these levels. A decay scheme using the above information is proposed and compared to theoretical predictions. The neutron binding energy for 205 Pb was determined to be 6734.2±1.5 keV, and the neutron capture cross section for 204 Pb was found to be 661±70 mb.

Superallowed 26Alm(β+ + EC)26Mg decay

The reaction energies of 25Mg(n, γ)26Mg and 25Mg(p, γ)26Alm have been measured as Q = 11093.24 6 and 6078.09 8 keV, respectively, which yields Q = 4232.81 10 keV for the 26Alm(β+ + EC)26Mg decay energy. By combining it with the known 26Alm half-life and by applying electromagnetic corrections one obatains Ft = 3073.5 18 s for this superallowed 0+ → 0+ decay, in good agreement with the value for the 14O “standard” 0+ → 0+ decay Ft = 3075.18 16 s, thus resolving a long-standing discrepancy.

Simultaneous determination of nitrogen, carbon, and hydrogen by thermal neutron prompt γ-ray spectrometry

Abstract Thermal neutron prompt γ-ray spectrometry is applied to the determination of nitrogen, carbon, and hydrogen in environmental materials. Useful, simultaneous, nondestructive analyses with 1-g samples can be achieved at concentrations greater than 500 ppm, 10% and 5 ppm, respectively.

Energy levels and configurations in 94Nb

In the high-energy thermal neutron capture gamma-ray spectrum of 94Nb, 83 gamma rays were observed between 4500 keV, and the neutron binding energy determined here to be 7229.5 ± 1.5 keV. A total of 71 low-energy gamma rays was observed from 30 keV to 1500 keV. These and previous data were used to develop a decay scheme. The presence of states arising predominantly from the following configurations is proposed: πg92v(d52)523,πg92v(d52)323, π(p12)−1(g92)02v(d52)523 and, more tentatively, π(p12)−1(g92)02v(d52)923 and πg92v(d52)02S12. Some preliminary assignments of spins and parities to other states have also been attempted. Calculations based on 90Zr and 88Sr cores both agree well with energies, spectroscopic factors and reduced M1 transition probabilities. The generally close agreement between the calculations involving different cores is surprising in view of the considerable differences in the two sets of wave functions. This is probably to be understood in terms of the ability of the effective nucleon-nucleon interaction to absorb the effect of configuration mixing.

Superallowed 42Sc(β+)42Ca decay

Abstract The neutron-separation energy of 42Ca and the proton-separation energy of 42Sc have been measured accurately via the 41Ca(n, γ)42Ca and 41Ca(p, γ)42Sc reaction, respectively. The measured values imply a Q-value of 6425.92 ± 0.19 keV for the total β-decay energy of 42Sc. If the conserved vector-current hypothesis is valid and the electromagnetic corrections are made properly, the ƒt values of superallowed 0+ → 0+ β-decays should all be the same. The ft values for the superallowed 42Sc and 14O decays were found to be equal to better than 13 ± 18 parts in 104, in agreement with the expectations.

Gamma-ray transitions in {sup 206}Pb studied in the {sup 205}Pb({ital n},{gamma}) reaction

A study of the {gamma}-ray spectrum following thermal-neutron capture by {sup 205}Pb has revealed 54 {gamma} rays, which have been incorporated into a level scheme consisting of 22 excited states in {sup 206}Pb. This study was carried out with an {approximately}9 mg lead sample enriched to 78.9{percent} in radioactive {sup 205}Pb. The neutron binding energy of {sup 206}Pb was determined to be 8086.67{plus_minus}0.06 keV, and the thermal-neutron-capture cross section for {sup 206}Pb to be 4.5{plus_minus}0.2 b. The low-lying portion of the level scheme of {sup 206}Pb and the {gamma}-ray branchings of positive-parity states have been compared with shell-model predictions. The overall agreement is excellent for the former and reasonably good for the latter. {copyright} {ital 1996 The American Physical Society.}

Nuclear spectroscopy of90Y

The level structure of90Y has been studied using the91Zr(t,α)90Y and89Y(n,γ)90Y reactions. The proton pickup reaction was studied with 17 MeV tritons and a Q3D spectrometer. In the thermal89Y(n, γ)90Y reactionγ-rays from ≈100 to 6,857 keV were observed. In addition to previously known states and configurations, the ten states of theπ(p 3/2)−1v(d 5/2)1 andπ(f 5/2)−1v(d 5/2)1 configurations are assigned. Also many other new levels are identified from the (n, γ) data. The 0−state of theπ(f 5/2)−1v(d 5/2)1 is assigned at 3,130keV. Finite-range shell model calculations suggest that the tensor force is necessary to reproduce the experimentally observed splittings.

Gamma Spectra from 233U, 235U, and 239Pu During Thermal Neutron Irradiation

The gamma spectra from three fissionable isotopes were measured during neutron irradiation in the thermal column of the Omega West Reactor. The measurements were preceded by a neutron irradiation of at least 20000 s to build up a near-equilibrium concentration of the shorter half-life fission products. The measurements provide the total gamma spectra and do not distinguish between photons emitted following neutron capture, fission, or by fission products. The thermal neutron flux of 6 × 1011 n/cm2s has a 350°K Maxwellian energy distribution.