Wm. C. McHarris

Coincidence-anticoincidence gamma-ray spectroscopy with a NaI(TI) split annulus and a Ge(Li) detector☆

Abstract A versatile gamma-ray spectrometer system consisting of a Ge(Li) detector surrounded by a large (20.3 cm × 20.3 cm) split NaI(Tl) annulus is described, and experimental results are presented as examples of its use in a number of coincidence and anticoincidence experiments. The annulus as a whole was used as an anti-Compton spectrometer and was found to reduce the Compton backgrounds in the Ge(Li) detector considerably. When the optically-isolated halves of the annulus were used separately, the system was found to be very efficient for triple-coincidence experiments and as a pair spectrometer. As the latter, it yielded double-escape spectra having essentially no underlying backgrounds, even when used with complex gamma-ray emitters such as 56Co. It was also very effective in determining relative β+ feedings to various levels in the decay of position emitters. When the system was used as a coincidence spectrometer with narrow gates set on the pulses from the annulus, the Compton backgrounds of coincident gamma-rays detected in the Ge(Li) detector were reduced significantly.

The decay schemes of 56Co and 56Mn and their use as calibration standards

Abstract The gamma rays accompanying the beta decays of 56 Co and 56 Mn have been studied using Ge(Li) and NaI(Ti) detectors in singles and in coincidence experiments. Excited states in 56 Fe are placed at 846.6±0.5, 2084.8±0.7, 2657.6±0.8, 2960.1±0.8, 3123.7±1.2, 3369.9±0.7, 3445.0±0.7, 3856.2±11.2, 4049.7±0.7, 4101.0±0.7, 4120.7±0.7, 4298.3±0.7 and 4394.2±2.1 KeV. The usefulness of the 56 Co decay as a gamma-ray energy and relative intensity standard is indicated.

Fast-Fourier-transform spectral enhancement techniques for γ-ray spectroscopy

Abstract The application of a discrete, fast-Fourier-transformation algorithm to multiply-gated γ-ray spectra enhances low intensity components, removes high-frequency noise, and increases the signal-to-background ratio. This method is preferable to a three-point smoothing technique for low- and medium-intensity peaks.

InSb as a γ-ray detector

Abstract The III-V semiconductor InSb has the potential for being a superior γ-ray detector, with a possible improvement over Ge by the factors: resolution, 2 ×; peak-to-Compton ratio, 12 ×; efficiency (per mole), 9 ×. Recent availability of “intrinsic” InSb, coupled with pulse-height discrimination techniques to overcome geometrical dependence on charge collection, makes it feasible to investigate the practicality of this material for producing detectors. We discuss its advantages and disadvantages.

The states of 117Sn

Abstract Gamma rays emitted in the decay of 2.8 h 117 Sb have been investigated with 2.5 to 45 cm 3 Ge(Li) detectors. Gamma rays of energies (and relative intensities) 158.5 (99.6), 553.2 (0.07), 846.2 (0.04), 861.7 (0.29), 1004.5 (0.22), 1020.6 (0.09), 1021.0 (0.10), 1287.6 (0.026), 1339.5 (0.009), 1420.1 (0.016), 1446.4 (0.051) and 1578.0 (0.018) keV have been observed. On the basis of energy sums, relative intensities and two-dimensional Ge(Li)-Ge(Li) coincidence experiments, states are placed in 117 Sn at 0 ( 1 2 + ), 158.5 ( 3 2 + ), 711.7 ( 7 2 + ), 1004.5 ( 3 2 + ), 1020.2 ( 5 2 + ), 1179 ( 5 2 + ), 1446.4 ( 3 2 + , 5 2 + ), 1498.0 ( 5 2 + , 3 2 + ) and 1578.3 keV ( 5 2 + , 3 2 + ). The spin assignments and limits have been made on the basis of log ƒt values and relative photon intensities from 117 Sb decay, which were aided in some cases by 117 In decay, and also by information gleaned from nuclear reaction data. The structures of the states are discussed in terms of current nuclear models, and the behavior of these states is followed as a function of neutron number.

Nuclear spectroscopic studies of 252Es

Abstract The decay scheme of 252Es has been investigated with high-resolution semiconductor detectors in conjunction with coincidence techniques. The half-life of 252Es was measured by following the decay of the α-count rate associated with 252Es decay and was found to be 350±50 d. The electron capture and α-decay branchings were measured to be (22±2)% and (78±6)%, respectively. The EC decay almost entirely populates a level at 969.8 keV in 252Cf with a logft value of 8.9. This state has been identified as the two-neutron state n [613] 7 2 + ; n [620] 1 2 + 3 + . A Kπ = 2− band has been identified at 830.8 keV. A rotational band built on an 804.8 keV level has been interpreted as the γ-vibrational band (Kπ = 2+). On the basis of the observed log ft value, the ground state of 252Es has been given an assignment of {n[613] 7 2 + ; p [521] 3 2 − 5 − . The favored α-transition of 252Es has been found to populate a level at 590 keV in 248Bk. The ground state of 248Bk has been given a spin-parity assignment of 6+ with the twoquasiparticle configuration n [734] 9 2 − ; p [521] 3 2 − .

Nuclear data sheets for A = 101

Abstract The 1961 version of the Nuclear Data Sheets for A = 101 has been revised on the basis of experimental data published prior to September 1 1972. The present evaluation contains information obtained from approximately 70 papers. There are currently nine nuclei known for A = 101. Only the presumed ground states and half-lives have been determined in 101 Zr and 101 Cd. Decay-scheme studies of 101 Zr and 101 Cd have established two levels in 101 Nb and 101 Ng, respectively. The identification of levels in 101 Mo and some subsequent spin and parity assignments depend primarily on recent sub-Coulomb stripping results. The identification of levels in 101 Mo fed by the β -decay of 101 Nb is somewhat uncertian at this time. Nine levels in 101 Pd have been identified from the β -decay study of 101 Ag, but the data are not sufficient to assign spins and parities. e/β + -decay studies of 101 Pd have established approximately 19 levels in 101 Rh and have resulted in some tentative spin and parity assignments. During The course of the compilation, the results of 72Col6 and 72Co17 concerning the β -decay of 101 Mo were communicated to the compilers. This study resulted in the identification of 152 transitions and the placement of approximately 45 levels in 101 Tc. In addition, conversion-electron work resulted in the identification of previously unobserved levels in 101 Tc at 0.009317 and 0.15601 MeV, requiring a reassignment of level energies in 101 Tc. The stable nucleus 101 Ru has been studied via β -decay, γ -decay, and Coulomb excitation. As a result, a number of spin assignments for low-lying states are firm. Some additional gaps and uncertainties remain in the data. The relative intensities of transitions depopulating the same levels in 101 Ru as observed in β -decay, Coulomb-excitation, and γ -decay studies do not agree in some cases. Reaction studies would help to confirm the spins of low-lying states in 101 Tc and 101 Rh and provide additional information on higher spin states in 101 Mo. The existing data on levels in 101 Pd populated by the β -decay of 101 Ag were obtained in early work with semi-conductor detectors and are probably incomplete at this time.

Nuclear data sheets for A = 104

Nuclear structure data available through January 1976 are compiled, and adopted level properties are given. The bulk of the data is presented pictorially for easy comparison. Experimental details, references, and additional comments, where required, are given in the text. All drawings, tables, and comments are reproduced from the computerized Evaluated Nuclear Structure Data File (ENSDF). Any additions or corrections desired by the users should be addressed to the compilers for maintenance and updating of the computer file.

On improving Ge detector energy resolution and peak-to-Compton ratios by pulse-shape discrimination

Abstract The rise-time discrimination of pulses from Ge detectors can be used to improve the spectra on two levels: first, by discriminating against slower-rising pulses, both the energy resolution and peak-to-Compton ratios can be improved significantly, especially for detectors that have suffered neutron damage. Second, by adding a pulse-height correction to compensate for effects of varying rise-time, an improved composite spectrum can be obtained without significant loss in detector efficiency.

Gamma-ray spectroscopy of implanted 7Be and 22Na for tribology studies

Abstract We have developed techniques for implanting 7 Be and/or 22 Na in the surface layer of a sample to be used for tribology studies. Wear of the surface can be studied by following the γ-rays from these activities. We produce the activities with heavy-ion beams ( 14 N and 20 Ne) on C and Al targets, and by choosing the energy of the beam and a suitable set of absorbers we can produce a desired dose-depth profile in the implanted surface. These techniques are independent of the material being studied for wear, so they can be applied to low- Z materials, such as ceramics and plastics. They also produce far less radiation damage to the surface than do conventional activation techniques — a factor of 10 5 between primary beam and implanted secondary beam. And the γ-ray spectra are very clean, making studies possible with NaI(Tl) as well as Ge detectors. Our studies thus far have concentrated on an Si 3 N 4 disc, implanted to a depth of 0.051 cm with 7 Be. Our sensitivity to wear is of the order of 100 nm.