Kenton Moody

Octupole deformation in 142,143Ba and 144Ce: new band structures in neutron-rich Ba-isotopes

Abstract New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

Decay properties of heavy mendelevium isotopes

Abstract We investigated the nuclear properties of several mendelevium isotopes produced in the reactions of heavy ions with 245Esg. We measured the alpha particles, spontaneous fissions (SF), and photons emitted by counting samples resulting from chemical and/or mass separations. The 256Md half-life is (78.1 ± 1.8) min; it decays primarily by electron capture (EC), but also by alpha emission (11 ± 3)% of the time. The 256Md ground state has J ⩽ 2 (probably Jπ = 1−), and a mass excess of (87.611 ± 0.053) MeV. The 257Md half-life is (5.523 ± 0.050) h; it decays primarily by EC, but also by alpha emission (15.2 ± 2.6)% of the time and by SF less than 1% of the time. The 256Md mass excess is (88.989 ± 0.003) MeV. The 258Mdg (Jπ = 8−) half-life is (51.50 ± 0.29) d. It decays by alpha emission; the sum of SF, EC, and β− decay branches is less than 3 × 10−3 %. The alpha decay of 258Mdg populates 254Esm (0.60 ± 0.08)% of the time. The 256Mdg mass excess is (91.691 ± 0.007) MeV. The half-life of J π = 1 − 258 Md m is (57.0 ± 0.9) min. It decays by EC; the branch for decay by alpha emission is less than 1.2%. The sum of SF and β− decay branches is less than 30%. The half-life of 259Md is (1.60 ± 0.06) h; it decays primarily by SF. The alpha decay branch of 259Md is less than 1.3%. From the 259Md half-life we calculated a SF hindrance factor associated with the 7 2 − [514] proton configuration of 3.6 × 106. From our data we proposed partial level schemes for 252Es, 253Es, and 254Es.

Observation of enhanced nuclear stability near the 162 neutron shell

In bombardments of {sup 248}Cm with {sup 22}Ne the authors discovered two new isotopes, {sup 265}106 and {sup 266}106, by establishing genetic links between {alpha} decays of the 106 nuclides and SF or {alpha} decays of the daughter (grand-daughter) nuclides. For {sup 266}106 they measured E{sub {alpha}}=8.62{+-}0.06 MeV followed by the SF decay of {sup 262}104 for which they measured a half-life value of 1.2{sup +1.0}{sub {minus}0.5} s. For {sup 265}106 they measured E{sub {alpha}}=8.82{+-}0.06 MeV. They estimated {alpha} half-lives of 10-30 s for {sup 266}106 and 2-30 s for {sup 265}106 with SF branches of {approximately}50% or less. The decay properties of {sup 266}106 indicate a large enhancement in the SF stability of this N=160 nuclide and confirm the existence of the predicted neutron-deformed shell N=162.

Forensic Analyses of Suspect Illicit Nuclear Material

A small metal sample, alleged to be a substance that could substitute for highly enriched uranium in a nuclear weapon, was subjected to qualitative and quantitative forensic analyses using methods of materials science, radioisotopic chemistry, inorganic chemistry, and organic chemistry. The specimen was determined to be moderately pure Sc, likely derived from a uranium refining operation. Although no fissionable species or weaponization signatures were detected, the sample did exhibit some unusual properties. These anomalies included lanthanide fractionation, with concentrations of Dy, Ho, and Er elevated by factors greater than 100 over normal levels, and the presence of long, odd-chain fatty acids.

Nuclear forensic analysis of uranium oxide powders interdicted in Victoria, Australia

Abstract Nuclear forensic analysis was conducted on two uranium samples confiscated during a police investigation in Victoria, Australia. The first sample, designated NSR-F-270409-1, was a depleted uranium powder of moderate purity (∼u20091000u2009μg/g total elemental impurities). The chemical form of the uranium was a compound similar to K2(UO2)3O4u2009·u20094H2O. While aliquoting NSR-F-270409-1 for analysis, the body and head of a Tineid moth was discovered in the sample. The second sample, designated NSR-F-270409-2, was also a depleted uranium powder. It was of reasonably high purity (∼u2009380u2009μg/g total elemental impurities). The chemical form of the uranium was primarily UO3u2009·u20092H2O, with minor phases of U3O8 and UO2. While aliquoting NSR-F-270409-2 for analysis, a metal staple of unknown origin was discovered in the sample. The presence of 236U and 232U in both samples indicates that the uranium feed stocks for these samples experienced a neutron flux at some point in their history. The reactor burn-up calculated from the isotopic composition of the uranium is consistent with that of spent fuel from natural uranium (NU) fueled Pu production. These nuclear forensic conclusions allow us to categorically exclude Australia as the origin of the material and greatly reduce the number of candidate sources.

Production and isolation of homologs of flerovium and element 115 at the Lawrence Livermore National Laboratory Center for Accelerator Mass Spectrometry

New procedures have been developed to isolate no-carrier-added (NCA) radionuclides of the homologs and pseudo-homologs of flerovium (Hg, Sn) and element 115 (Sb), produced by 12–15xa0MeV proton irradiation of foil stacks with the tandem Van-de-Graaff accelerator at the Lawrence Livermore National Laboratory Center for Accelerator Mass Spectrometry (CAMS) facility. The separation of 113Sn from natIn foil was performed with anion-exchange chromatography from hydrochloric and nitric acid matrices. A cation-exchange chromatography method based on hydrochloric and mixed hydrochloric/hydroiodic acids was used to separate 124Sb from natSn foil. A procedure using Eichrom TEVA resin was developed to separate 197Hg from Au foil. These results demonstrate the suitability of using the CAMS facility to produce NCA radioisotopes for studies of transactinide homologs.

Note: Radiochemical measurement of fuel and ablator areal densities in cryogenic implosions at the National Ignition Facility

A new radiochemical method for determining deuterium-tritium (DT) fuel and plastic ablator (CH) areal densities (ρR) in high-convergence, cryogenic inertial confinement fusion implosions at the National Ignition Facility is described. It is based on measuring the (198)Au/(196)Au activation ratio using the collected post-shot debris of the Au hohlraum. The Au ratio combined with the independently measured neutron down scatter ratio uniquely determines the areal densities ρR(DT) and ρR(CH) during burn in the context of a simple 1-dimensional capsule model. The results show larger than expected ρR(CH) values, hinting at the presence of cold fuel-ablator mix.

Synthesis of Superheavy Elements

The Island of Stability of spherical superheavy nuclides exists at the extreme limit of the Chart of the Nuclides, beyond regions of nuclear stability associated with deformed nuclear shapes. In this chapter, the reactions that are used to synthesize these transactinide nuclides are discussed. Particular emphasis is placed on the production of nuclides with decay properties that are conducive to a radiochemical measurement. The cold- and hot-fusion reactions that lead to the formation of evaporation residues are discussed, as are the physical techniques that have been used in production experiments. Recent results from 48Ca-induced fusion reactions are included. Speculative methods of producing the more neutron-rich nuclides that populate the approaches to the center of the Island of Stability are also presented.

Nuclear science research with dynamic high energy density plasmas at NIF

Nuclear reaction measurements are performed at the National Ignition Facility in a high energy density plasma environment by adding target materials to the outside of the hohlraum thermo-mechanical package on an indirect-drive exploding pusher shot. Materials are activated with 14.1-MeV neutrons and the post-shot debris is collected via the Solid Radiochemistry diagnostic, which consists of metal discs fielded 50 cm from target chamber center. The discs are removed post-shot and analyzed via radiation counting and mass spectrometry. Results from a shot using Nd and Tm foils as targets are presented, which indicate enhanced collection of the debris in the line of sight of a given collector. The capsule performance was not diminished due to the extra material. This provides a platform for future measurements of nuclear reaction data through the use of experimental packages mounted external to the hohlraum.

First fission yield measurements at the National Ignition Facility: 14-MeV neutron fission of 238U

The use of the Solid Radiochemistry diagnostic platform at the National Ignition Facility (NIF) has allowed the development and implementation of the Target Option Activation Device assembly for fielding materials of interest inside the NIF chamber during high yield neutron shots. Preliminary studies with ultra-depleted uranium have allowed for the measurements of fission yields of 238U. Radiochemical procedures were utilized for the separation of fission and reaction products from the target material to provide higher sensitivity measurements. Cumulative fission mass-yields for 32 different isobars, 72xa0≤xa0Axa0≤xa0153, were measured from experiments fielded on two separate NIF shots.