Harry R. Bowman

A study of the low-energy transitions arising from the prompt de-excitation of fission fragments

Abstract A four-dimensional experiment has been performed in which the energies of coincident complementary fragment pairs, internal conversion electrons, and K X-rays emitted as a result of the spontaneous fission of 252 Cf were recorded event by event using a multiparameter analyser. The fission fragment energies were used for mass identification and the X-ray energies supplied precise atomic number identification. The analysis of the conversion electron spectra has resulted in the assignment of numerous transitions to new isotopes, the determination of many transition half-lives, and the procurement of limited information concerning multipolarities. It was concluded, based on the X-ray and conversion electron data, that most of the large number of observed low-energy transitions associated with heavy fragments are attributable to odd-mass or doubly odd nuclei and that surprisingly little contribution to the low-energy spectra is associated with doubly even nuclei in the rare-earth region. Low-energy transitions in doubly even nuclei were found to be more prevalent among the light fragments. Data are presented supporting the assignment of a high intensity 241 keV transition as the 2 + to 0 + transition in 110 Ru. An examination of this transition in terms of the energy predicted on the basis of rotational behaviour and with regard to the systematics of neighboring doubly even Ru isotopes reveals evidence which strongly suggests that 110 Ru belongs to a new region of stable deformation.

Correlation of the Rockland ash bed, a 400,000-year-old stratigraphic marker in northern California and western Nevada, and implications for middle Pleistocene paleogeography of central California

Abstract Outcrops of an ash bed at several localities in northern California and western Nevada belong to a single air-fall ash layer, the informally named Rockland ash bed, dated at about 400,000 yr B.P. The informal Rockland pumice tuff breccia, a thick, coarse, compound tephra deposit southwest of Lassen Peak in northeastern California, is the near-source equivalent of the Rockland ash bed. Relations between initial thickness of the Rockland ash bed and distances to eruptive source suggest that the eruption was at least as great as that of the Mazama ash from Crater Lake, Oregon. Identification of the Rockland tephra allows temporal correlation of associated middle Pleistocene strata of diverse facies in separate depositional basins. Specifically, marine, littoral, estuarine, and fluvial strata of the Hookton and type Merced formations correlate with fluvial strata of the Santa Clara Formation and unnamed alluvium of Willits Valley and the Hollister area, in northwestern and west-central California, and with lacustrine beds of Mohawk Valley, fluvial deposits of the Red Bluff Formation of the eastern Sacramento Valley, and fluvial and glaciofluvial deposits of Fales Hot Spring, Carson City, and Washoe Valley areas in northeastern California and western Nevada. Stratigraphic relations of the Rockland ash bed and older tephra layers in the Great Valley and near San Francisco suggest that the southern Great Valley emerged above sea level about 2 my ago, that its southerly outlet to the ocean was closed sometime after about 2 my ago, and that drainage from the Great Valley to the ocean was established near the present, northerly outlet in the vicinity of San Francisco Bay about 0.6 my ago.

Application of High-Resolution Semiconductor Detectors in X-ray Emission Spectrography

Solid-state devices developed primarily for nuclear gamma spectroscopy have many potential uses in x-ray analysis.

Chemical and isotopic constraints on the origin of low-silica latite and andesite from the Andes of central Peru

Low-silica latite highly enriched in large-ion-lithophile elements and moderately potassic low-Si andesite were erupted in central Peru during late Cenozoic time. FeO*/MgO ratios of 0.93 to 1.25 at 53 wt percent SiO/sub 2/ indicate a definitely calcalkalic character. The combination of low FeO*/MgO ratios, low SiO/sub 2/, and high Cr, Co, and Ni with large-ion-lithophile and light rare-earth elements makes it very unlikely that the parent magmas were produced by high-pressure partial melting of subducted ocean-floor basalt (eclogite). The data are more compatible with small degrees of partial melting of ultramafic material or mixtures of basalt and ultramafic mantle. The initial melts probably contained 52 to 53 percent SiO/sub 2/ and had a content of large-ion-lithophile elements nearly as high as that of the rocks. /sup 87/Sr//sup 86/Sr ratios of from 0.7042 to 0.7051 and low to very low Rb/Sr ratios indicate an isotopically variable source region that, at least in part, had earlier been depleted in Rb relative to Sr.

Elemental and isotopic geochemistry of nonhydrated quartz latite glasses from the Eureka Valley Tuff, east-central California

The Eureka Valley Tuff, erupted from the late Miocene Little Walker volcanic center, east-central California, includes two major ash-flow sheets: the more voluminous, widespread, and more silicic Tollhouse Flat Member and the overlying By-Day Member. Nonhydrated quartz latitic glasses from the Tollhouse Flat and By-Day Members have, respectively, 65.5 and 63.3 wt percent SiO 2 and are extremely rich in large-ion lithophile elements. The K 2 O contents and K/Rb ratios are 5.3 wt percent and 195 for the Tollhouse Flat glass and 5.5 wt percent and 190 for glasses from the By-Day Member. FeO*/MgO (FeO* = total Fe as FeO) ratios are transitional between values characteristic of basaltic and calc-alkalic suites. Initial 87 Sr/ 86 Sr ratios of 0.7054 to 0.7055 are consistent with the pattern of northwestward decrease in 87 Sr/ 86 Sr observed for Mesozoic plutonic and Cenozoic volcanic rocks in the western Great Basin and Sierra Nevada provinces. The glasses are higher in Rb than are Mesozoic granitic rocks of the Sierra Nevada batholith that have comparable Sr contents and initial 87 Sr/ 86 Sr ratios. Pb isotopic compositions fall at the upper end of arrays found for upper Cenozoic calc-alkalic rocks from the Cascade Mountains and nearly on trends found for rocks of the Sierra Nevada batholith. The moderately high FeO*/MgO ratios, very low Co, Cr, and Ni contents, high Ba/Sr and K/Sr ratios, and approximately 25 percent negative Eu anomalies demonstrate that the glasses are the products of appreciable crystal fractionation. This in turn strongly suggests that the Eureka Valley Tuff was derived from a hypersthene-normative or only slightly quartz-normative parent magma. A model is outlined in which a potassic mafic parent magma was produced by a moderate degree of partial melting of diapirically upwelling, undepleted ultramafic mantle material followed by zone refining of upwelling mantle and other material within the asthenosphere and lithosphere. Extensive fractional crystallization and crystal separation subsequently enriched the melt further in large-ion lithophile elements. The evidence for appreciable plagioclase separation demonstrates that much fractionation took place well within the Earth9s crust. The Tollhouse Flat and By-Day Members were erupted from discrete — although closely related — bodies of magma. Lower water and halogen contents of the By-Day magma may have prevented the intratelluric crystallization of biotite and thereby allowed the magmatic liquid to become richer in K and Rb than that of the more highly fractionated Tollhouse Flat Member.

Magnetic Steering Device for Electron Coincidence Experiments

The highly convergent fringing field produced by a 100 kVA C‐magnet has been used to guide electrons emitted at a source around a 90° arc to a Si(Li) detector. This source‐detector configuration is often desirable because it enables the electron detector to be effectively shielded from other radiations emitted at the source. The electron motion in this device consists of a superposition of a trochoidal motion and a vertical oscillation through the magnet symmetry plane. The high detection efficiency of the system (∼5%) makes it particularly well suited for applications in electron coincidence experiments. Utilization of the device in a study of internal conversion in coincidence with fission is described, and several other applications are suggested.

THE PROMPT GAMMA RAY, PROMPT ELECTRON AND PROMPT X-RAY SPECTRA ASSOCIATED WITH FISSION FRAGMENTS OF SECIFIC MASS

Author(s): Bowman, Harry R.; Thompson, Stanley G.; Watson, Rand L.; Kapoor, S.S.; Rasmussen, John O.

Internal Conversion Electrons from Primary Fission Fragments

Publisher Summary This chapter discusses a multidimensional pulse-height analyzer in which successive pulse heights or time delays from various detectors are recorded as successive binary numbers on magnetic tape via a 256-channel analog to digital converter. The magnetic tape with the primary three-dimensional information may be sorted event by event on the IBM 7094 computer. Various programs of the computer permit the spectrum in one dimension to be displayed in association with any combination of pulse heights in the other two dimensions. The study of spontaneous fission is concerned with gamma-ray spectroscopy. Nuclear spectroscopic information on the energy levels is gained in the region of nuclei near the double magic Sn132. As a result of the experiments described in the chapter, many completely resolved gamma rays in the energy region up to approximately 500 keV have been seen and the expected Doppler shifts have been observed for those gamma rays, which are emitted in less than a nanosecond—the approximate flight time from fission source to detector.