Stanley G. Prussin

Photopeak method for the computer analysis of gamma-ray spectra from semiconductor detectors

Abstract A method is presented for computer analysis of γ-ray spectra from semiconductor detector systems. We describe a mathematical formalism for the representation of photopeaks and the continua in their vicinity which is applicable to analysis of spectra measured under widely varying conditions. With this formalism the line shape is defined for each peak in the spectrum. The region of data about a single peak or multiple peaks is then fitted with the shape functions and a function representing the background continuum. The line-shape calculations and the fitting are performed by using a least-squares procedure with an iterative gradient minimization method with variable metric. For an automatic analysis an algorithm is developed to search the raw data for statistically significant peaks. The method has been incorporated into a general-purpose Fortran computer program. In addition to searching and fitting single and multiple peaks, the code performs the energy, efficiency, and line-shape calibrations and makes complete statistical and calibration-error estimates. For establishing the goodness of fit for each peak the output also includes numerical and graphical representation of the fit. Optionally, an on-line cathode-ray- tube display system may be used to assure the completeness of the results even with very complex spectra. The code has been used with a variety of spectra from Ge(Li) detectors of varying resolution and active volume. The performance is evaluated with test cases and by comparing the results of complete computer and careful hand analysis of 177m Lu and 72 As spectra. Applications to spectroscopic measurements and routine data analysis are discussed.

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.

Investigation of beta strength functions by neutron and gamma-ray spectroscopy

Abstract Neutron spectra from the decay of the β− delayed neutron precursors 55.6 sec 87Br, 24.5 sec 137I, 2.05 sec 85As and 1.71 sec 135Sb have been studied with high resolution 3He ionization chambers. By γ-ray measurements, the partial neutron emission probabilities to excited states in 84Se and 134Te have been determined independently. For the neutron-emitter nuclei 87Kr and 137Xe, from which neutron decay proceeds only to the ground states of the final nuclei, 86Kr and 136Xe, unique information on the shape of the β− strength function Sβ(E) is obtained. For the emitter nuclei 85Se and 135Te, correlations between neutron transition energies and differences in level energies in 84Se and 134Te, have defined some levels in 85Se and 135Te which are strongly fed by β− decay. It is shown that the experimental shape of the β− strength function cannot be explained by the widely used assumptions Sβ(E) = const or Sβ(E) ∼ ϱ(E) or by the “gross theory” of β-decay, but that it is the result of structures in the low-energy tail of the Gamow-Teller giant resonance (GTGR) expected from general nuclear structure considerations.

Delayed-neutron spectroscopy with 3He spectrometers

Abstract The characteristics of a 3 He ionization chamber for high-resolution spectroscopy of β-delayed neutrons have been examined. The detector response function is given in the energy range 0.019–2.77 MeV. A considerably improved energy resolution has been achieved by minimizing effects due to pulse summing, detection of scattered neutrons, and microphonics, and is most evident in the low-energy part of the spectra.

Direct Measurement of Osteolysis in Man

Precise, direct measurement of bone calcium release (v(o-)) has been accomplished using a continuous tracer administration (CTA) technique. Dietary calcium (96.97% (40)Ca) is replaced by (40)Ca (99.991% (40)Ca) and blood levels of the naturally occuring isotope (48)Ca are monitored by neutron activation analysis as a function of time. (48)Ca abundance falls as this isotope is excreted and only partially replaced by release from bone. After a suitable period, an asymptotic abundance of (48)Ca in serum, E, is approached which is the fraction of the turnover rate of the rapidly exchangeable calcium pools coming from the skeleton (E = v(o-)/v(t)). E is determined with a standard error of 2%, providing a precise, sensitive index of v(o-). 13 studies in three normal men and one postmenopausal woman receiving maintenance estrogen show large intersubject variations in parameters of calcium metabolism using both CTA and pulse tracer administration (PTA) plus balance techniques. Induced hypercalcemia results in a prolonged decrease in v(o-). Glucocorticoid therapy initially and consistently induces a marked hypercalciuria while effects on most other parameters of calcium kinetics are variable. In two men E fell when testosterone was added to glucocorticoid treatment, consistent with the known antiosteolytic effect of androgens, despite the short period of study.

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.

A low-lying 2− state in 236U

Abstract A low-lying KIπ = 22− state of 236U, first characterized in measurements of 240Pu alpha decay, has been more thoroughly studied through the electron-capture decay of 236Np. The energy of the state is 687.70 ± 0.10 keV, its half-life is 4.4 ± 0.6 nsec, and it decays by M2 and E1 transitions to members of the ground state band. It is populated with an intensity of 1.5 ± 0.3% in the decay of 236Np, and (2.1 ± 0.4) × 10−5% in the decay of 240Pu, in the latter case presumably via an alpha transition to the unobserved spin-3 member of the band. Besides having the lowest energy of any known 2− state in an even nucleus, the state is characterized by fast M2 transitions and highly hindered El transitions.

Measurement of single 14 MeV neutron bursts with 100 ps time resolution

We have constructed a detector using neutron‐damaged GaAs and used it to measure subnanosecond 14 MeV neutron bursts from laser‐driven deuterium‐tritium filled microspheres. The detector’s very fast response (measured to be 60 ps full width at half‐maximum) is due to the phenomenon of radiation‐induced conductivity. The absolute sensitivity of the detector has been measured and is in excellent agreement with Monte Carlo calculations. We have also verified that the dectector is linear with neutron flux over two orders of magnitude.

Delayed neutrons and high-energy γ-rays from decay of 87Br

Abstract Delayed neutrons and high-energy γ-rays following decay of 87Br have been studied to characterize the β-decay to and the decay of neutron unbound levels in 87Kr. The principal part of the neutron spectrum appears due to some 20–30 individual transitions and for seven of these, decay by γ-ray emission has been demonstrated. The β-strength function derived from these data and the decay scheme at lower energies is dominated by a broad resonance located near the neutron binding energy which can be identified with the main strength of a single-particle transition. The fluctuations in the reduced β-transition probabilities are found to be in accord with the Porter-Thomas distribution and the observed level density just above the neutron binding energy is consistent with the Gilbert and Cameron prediction after accounting for fluctuation in the β-decay transition probabilities.

Precipitation of crystalline neptunium dioxide from near-neutral aqueous solution

Abstract We report experimental evidence that crystalline neptunium dioxide, NpO2(cr), will precipitate from near-neutral aqueous solutions that initially contain NpO2+(aq), even under mildly oxidizing conditions. Observed decreases in aqueous Np concentrations with time are balanced by corresponding decreases in pH and accompanied by formation of high-purity crystals of NpO2. The crystalline NpO2 was characterized by X-ray powder diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, and scanning electron microscopy (SEM). Thermodynamic data in the literature suggest that NpO2(cr) is possibly the stable solid phase in aqueous systems containing dissolved NpO2+(aq); however, the precipitation of NpO2(cr) from solutions containing initially NpO2+(aq) had not been observed experimentally until now, possibly because of slow reaction kinetics. Our experiments were conducted at 200°C in order to overcome slow reduction reactions and/or precipitation kinetics. Because long time scales may render slow reaction kinetics irrelevant, thermodynamically stable NpO2(cr) may keep dissolved Np concentrations well below the relatively high Np concentrations (10-3 M) associated with meta-stable Np(V) solids observed in previous laboratory experiments. Projects investigating the suitability of sites for an underground repository for high-level nuclear waste disposal may not need be so concerned with high dose rates due to migration of Np over long times, because these may not apply to repository-relevant time scales over which NpO2(cr) is likely to be stable.