Henry C. Griffin

New cold and ultra hot binary and cold ternary spontaneous fission modes for 252Cf and new band structures with gammasphere

Abstract Prompt γ-γ-γ and x-γ-γ coincidence studies following the spontaneous fission of 252Cf were carried out first at Oak Ridge then at Gammasphere first with 36 and later with 72 Ge and two x-ray detectors and a long x-ray-γ coincidence experiment at Idaho. Many new cases of correlated pairs in cold (zero neutron emission) binary fission are observed and for the first time the heavier correlated pairs are identified in ternary fission where the third partners are α, 6He (or α2n), 10Be and, tentatively, 14C. Theoretical calculations were carried out of the relative yields of cold binary and ternary fission. There is reasonable agreement between the relative theoretical and experimental yields. New level structures and isotopes include new octupole deformations, identical bands and other structures. Stable octupole deformation is now observed in N=86, 140Xe, 142Ba and 144Ba and 143Ba, 148Ba and to higher spin in 144Ba. The 142–146Ba data provide the first evidence for the predicted disappearance of stable octupole deformation at high spins from band crossings. Identical yrast bands are observed with widely different neutron and proton numbers in 98,100Sr, 108,110Ru, 112,116Pd, 144,146Ba, 152,154,156Nd, 156Sm, 160Gd and a new type of shifted identical bands in 156,158,160Sm as well as the first identical octupole bands in 142,144Ba. Other new level structures are found. Yields and neutron multiplicities were measured directly for SrNd, ZrCe, MoBa, RuXe, and PdTe correlated pairs. A new ultra hot fission mode was discovered going via only 108Mo144Ba, 107Mo145Ba, and/or 106Mo146Ba pairs where one or more of 44,145,146Ba are hyperdeformed at scission with 3:1 axis ratio.

Production of Co-60 sources for high-accuracy efficiency calibrations of gamma-ray spectrometers.

Activity determination by gamma-ray spectrometry is a valuable aid which is widely used where radioactive sources are applied. For the construction of an efficiency curve vs. energy in a standard geometry, the accuracy is limited not only by the uncertainty of peak area determination and the knowledge of the relevant emission probabilities but also by the uncertainties of the activity values applied to efficiency calibration with standard sources. Recently, a method to determine a relative efficiency function using selected radionuclides with gamma cascades of well known emission probabilities has been developed which yields very accurate efficiency values. Such a curve has to be converted into an absolute efficiency curve by calibration of the detector system with at least one source of very well known activity. Especially for this purpose, a set of Co-60 gamma-ray spectrometer sources was produced at the PTB. The activity values (10-45 kBq) were measured by the 4pi beta-gamma coincidence technique with a standard uncertainty of less than 0.1%. Production and measurement of these sources are described in the present paper. Special care was taken to include all contributions to the standard uncertainty of the activity value when establishing the uncertainty budget for the activity of each of these sources. The activity ratio of two of these sources, as obtained by the absolute measurements, was checked by independent gamma-ray counting at two other laboratories, where the precision achieved was less than 0.2%. The procedure described is considered to be a step towards more accurately determined efficiency functions in gamma-ray spectrometry.

Systematic modeling study of channel waveguide fabrication by thermal silver ion exchange.

A systematic study of thermal silver ion exchange used for the fabrication of optical channel waveguides is reported in a single-alkali glass. The diffusion equilibrium and diffusion dynamics are experimentally studied, and the concentration-dependent diffusion coefficients are determined. The relationship between the fabrication conditions, i.e., time, temperature, and melt concentration, and the induced waveguide refractive index profile is established. It is demonstrated that the diffusion equation can be solved, without use of any free parameters, to predict the refractive index profiles of both planar and channel waveguides. A 1.6 cm diameter integrated optic ring resonator, with a propagation loss of 0.1 dB/cm, is fabricated in a glass by thermal silver ion exchange. The induced refractive index profile is related to the optical characteristics of the functional device.

Measurement of absolute gamma emission probabilities

Abstract The energies and emission probabilities (intensities) of gamma-rays emitted in radioactive decays of particular nuclides are the most important characteristics by which to quantify mixtures of radionuclides. Often, quantification is limited by uncertainties in measured intensities. A technique was developed to reduce these uncertainties. The method involves obtaining a pure sample of a nuclide using radiochemical techniques, and using appropriate fractions for beta and gamma measurements. The beta emission rates were measured using a liquid scintillation counter, and the gamma emission rates were measured with a high-purity germanium detector. Results were combined to obtain absolute gamma emission probabilities. All sources of uncertainties greater than 0.1% were examined. The method was tested with 38 Cl and 88 Rb.

Optimization of measurement of 63Ni in reactor waste samples using 65Ni as a tracer

Abstract Consistent, clean, and high chemical recovery is important for 63 Ni analysis of low-level radioactive waste samples from nuclear power reactors. These samples generally contain numerous radionuclides in high concentrations which can interfere with nickel measurements. Chemical recovery of approx. 90% can be achieved consistently using an optimized procedure. The use of 65 Ni as a chemical tracer was incorporated into such a procedure to provide sample-specific chemical recovery. eliminating error associated with using the average recovery value of several standards. Methods were also used to correct the contaminants of 55 Fe, 58 Co, and 60 Co should they be present in separated fractions for measurement of 63 Ni activity.

Decay characteristics of 84Se

Abstract The nuclide 84Se has been identified among the fission products of 235U. The selenium fraction was obtained by solvent extraction from HBr into 2,6-dimethyl-4-heptanone. The radiations were studied by β- and γ-ray scintillation spectroscopy, by γ-ray spectroscopy with a Ge(Li) detector, and by coincidence measurements. The decay of 84Se shows a half life of 3·1±0·2 min and involves a single β transition of 1·4±0·05 MeV and a coincident γ ray of 407·7±0·5 keV.

Cold binary and ternary fragmentations in spontaneous fission of252Cf

SummaryThe phenomenon of cold (neutronless) binary and ternary fission in spontaneous fission of252 Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Many correlated pairs for both binary and ternary (4He,10Be) fission were observed in the spontaneous fission of252 Cf. Yields of cold ternary and cold binary fission were extracted. These results are compared with the theoretical calculations using M3Y nucleon-nucleon potential and WKB approximation for barrier penetration.

Antihydrogen: Production and Applications

The formation of antihydrogen (\(\overline H\)) is of interest for a variety of reasons. Properties of the \(\overline H\) such as the electronic energy levels, fine structure, Lamb shift, and hyperfine structure can be measured and compared to the corresponding quantities in hydrogen as tests of CPT invariance. Novel investigations of the interactions of \(\overline H\) with atoms and with gravitation can be undertaken. Finally, applications such as the production of polarized antiprotons or the storage of macroscopic quantities of \(\overline H\) can also be pursued.

Photon emissions observed in the decay of 233Th.

Stock solutions of (233)Th were produced by the (232)Th(n,gamma) reaction and multiple purifications were used to obtain relative intensities of weak transitions. Liquid scintillation counting (absolute disintegration rates) and gamma-ray spectroscopy with HPGe detectors yielded absolute photon intensities. Absolute intensities in % (with statistical uncertainties) of prominent radiations (L and K X-rays; 29, 86, and 459 keV gamma-rays) are 8.23(8), 1.32(10), 2.17(1), 1.843(2), and 0.989(2), respectively. These intensities are more precise and approximately 30% lower than previous results.

Fabrication of 58Co positron sources

Abstract A technique for producing 58 Co positron sources for use in slow positron beams has been developed. The method has been successfully tested at the μCi and mCi level. Scaling up of the technique is under way to consistently produce 1–2 Ci sources from 60 g of irradiated nickel.