Gamma Coincidence Measurements Research Articles

MiniPANDA device for alpha–gamma coincidence measurements

MiniPANDA is a detector system for alpha–gamma coincidence measurements for environmental monitoring samples under atmospheric pressure. It is designed to enhance traditional gamma spectrometry with coincidence techniques and list mode data workflow. The performance of the detector is evaluated using a microscopic 238Pu particle sample and an air radioactivity surveillance sample with traces of artificial nuclides. Significant improvement of sensitivity, a factor of 2.6–3.0, for alpha-particle emitting nuclides was achieved under normal measurement times, while maintaining the ability to perform traditional gamma spectrometry. The capability for alpha spectrometry is demonstrated by determining the activities of alpha-particle emitting nuclides from a sample containing 226Ra progeny.

Evaluation of a semiconductor-based atmospheric radioxenon detection system

Abstract A prototype radioxenon detection system for beta–gamma coincidence measurements has been designed using a PIPSBox and a pair of coplanar CdZnTe (CZT) detectors. Coincidence events are identified in real-time using a Field-Programmable Gate Array (FPGA). The measurement of 131m Xe and studies on electron backscatter and memory effect in the PIPSBox have been presented previously; this paper details the measurement of 133∕133m Xe, 135Xe, and background. Absolute efficiencies were determined, regions of interest were defined, and Minimum Detectable Concentrations (MDC) for all four radioxenon isotopes were calculated. When neglecting interferences between the radioxenons, the prototype system has an estimated MDC of 0.61 ± 0.15 mBq/m3 for 133Xe when using gas processing parameters associated with Xenon International, satisfying the CTBTO requirement for sensitivity of ≤ 1 mBq/m3 for 133Xe. Simulation suggests that by increasing number of CZT detectors used by a factor of 16, the MDCs of the system can be improved by a factor of 2-3. The design shows great promise for future improvement and expansion due to its exceptional energy resolution, high background rejection rate, room temperature operation, minimal memory effect, and simple readout electronics.

Gamma–gamma coincidence in neutron activation analysis

Neutron activation analysis is a useful analytical technique for the determination of many nuclides. However, the resulting gamma-ray spectra frequently have overlapping photopeaks, necessitating complicated peak de-convolution techniques to perform an accurate measurement. This work investigates the viability of gamma–gamma coincidence measurements of neutron activation analysis samples for the determination of 76As, 160Tb, and 169Yb to improve peak de-convolution and significantly lower the background. It is shown that these nuclides can be better determined using gamma–gamma coincidence measurements as opposed to single detector measurements. Comparisons are shown between the single channel and coincidence-gated spectra to demonstrate the de-convolution improvements achieved with coincidence gating. Additionally, a quality assurance protocol has been developed using 226Ra and 152Eu to ascertain that the coincidence electronics are set up properly. This protocol quantitatively demonstrates the capability of this system to discriminate between true coincidence and noncoincident events.

Using gamma–gamma coincidence measurements to validate Monte Carlo generated detector response functions

Monte Carlo simulation of gamma-ray transport for the purpose of performing elemental analysis of bulk samples requires the tracking of gamma rays in the sample and also in the detector(s) used. Detector response functions (DRF’s) are an efficient and accurate variance reduction technique that greatly decreases the simulation time by substituting the tracking of gamma rays inside the detector by predefined single energy gamma-ray spectra. These spectra correspond to the average response of the detector for incident gamma rays.DRF’s are generated by Monte Carlo methods and are benchmarked with experimental data. In this work, prompt gamma–gamma coincidence measurements are presented as a way to validate DRF’s for high-energy gamma rays.

Complete spectroscopy of the 162Dy nucleus

States in 162Dy have been populated by ( n , γ ) , ( n , e − ) , and ( α , 2 n ) reactions in order to characterize a complete set of low K bands below 2 MeV. The ( n , γ ) and ( n , e − ) measurements were made using high precision curved crystal and β − spectrometers. Gamma–gamma coincidence and DCO measurements were made following the ( α , 2 n ) reaction using an array of Compton-suppressed Ge detectors. Using all these data and employing the Ritz combination principle, a level scheme was developed which represents one of the most complete and extensive spectra of levels available for comparison with nuclear models. The observed positive and negative parity bands are discussed in terms of collective quadrupole and octupole vibrational excitations as well as 2 quasi-particle excitations.

Decay of proton-rich nuclei between 39Ti and 49Ni

Decay studies of very neutron-deficient nuclei ranging from 39Ti to 49Ni have been performed during a projectile fragmentation experiment at the GANIL/LISE3 separator. For all nuclei studied in this work, 39,40Ti, 42,43Cr, 46Mn, 45,46,47Fe and 49Ni, half-lives and decay spectra have been measured. In a few cases, gamma coincidence measurements helped to successfully identify the initial and final states of transitions. In these cases, partial decay scheme are proposed. For the most exotic isotopes, 39Ti, 42Cr, 45Fe and 49Ni, which are candidates for two-proton radioactivity from the ground state, no clear evidence of this process is seen in our spectra and we conclude rather on a delayed particle decay.

Gamma–gamma coincidence measurements following inelastic neutron scattering

Gamma-gamma coincidences following the inelastic scattering of accelerator-produced monoenergetic neutrons have been experimentally observed. A coincidence system consisting of a neutron collimator and three HPGe γ-ray detectors, is shown to provide important information on the isotopic identification and placement of γ rays. The development and use of the system is described, and initial results are presented.

Octupole instability and E1 transitions in 222Ra and in the neighbouring even isotopes of radium

Isotopes of francium have been produced via a spallation reaction of thorium carbide and separated in the ISOCELE facility. The very weak beta branch (0.35%) of 220Fr decay and the beta decay of 222Fr leading to the levels of 220Ra and 222Ra, respectively, have been studied by means of gamma -ray singles and beta -gated gamma - gamma coincidence measurements. A strong evidence has been obtained for the 1- state in 220Ra at 412.9 keV and 15 new levels have been added to the eight excited states known previously in 222Ra. The 3- to 2+ E1 transition in the latter nucleus has been found to be remarkably enhanced compared with analogous transitions in the heavier radium isotopes. This enhancement together with the low energy of the 1- state reflects octupole instability of 222Ra. The essentially higher energy of the 1- state in 220Ra suggests that the latter nucleus already lies at the border of the octupole instability region. In contradiction to experimental indications the theory places 220Ra inside this region. For 222Ra it predicts a Q1 value not far from the authors' experimental result but fails to reproduce Q1, changes in 224,226,228Ra nuclei.

New 233U levels fed in the 233Pa β-decay

The beta -decay of radiochemically separated 233Pa sources has been reinvestigated using planar and coaxial HPGe detectors: the energies and intensities of 23 gamma -photons were determined in this work, eight of them are reported for the first time; the placement of the main gamma -lines was confirmed by gamma - gamma coincidence measurements. A 233U revised level scheme exhibits eleven excited states, of which three are newly proposed at energies 320.90, 380.30 and 455.96 keV, respectively interpreted as the Ipi =5/2- member of the 5/2- (752) rotational band, the Ipi =7/2+ member of the 3/2+ (631) band and the 5/2+ member of the 1/2+ (631) band. The Ipi =5/2- level at 301.99 keV, observed in Coulomb excitation experiments, is also fed in 233Pa beta -decay.

The development of a detection system for TDPAC studies of 75Se

A fast-slow timing system employing a pair of barium fluoride scintillation counters for gamma—gamma coincidence measurements is currently being developed to enable the binding of 75Se to the protein glutathione peroxidase to be studied using the time differential perturbed angular correlation (TDPAC) technique. Consideration has been given to the need to optimise the system time resolution whilst maintaining reasonable energy resolution. Factors such as scintillator quality, surface treatment, voltage divider design and time pick-off are discussed. The improvements in time resolution realised by making certain changes to the original system are reported.

An improved description of 182W

New experimental results from the beta - decay of 182Ta to 182W are reported, based on gamma singles and gamma - gamma coincidence measurements. A new decay scheme for 182W is built up, from which several previously reported transitions and five energy levels are removed while five transitions and two new energy levels are added. Energy levels are supported by an IBM-1 calculation in which the SU(3) Hamiltonian is modified by a small pairing interaction.

The158Tb decay and the possibility of determining neutrino mass

High-precision direct gamma -ray and K X- gamma coincidence measurements have been performed in the electron-capture decay of 158Tb. A revised level scheme of 158Gd is proposed, with high-precision energies and intensities. The Q value determined for this decay using K capture to the high-lying levels in 158Gd shows that a K capture to the 1187 keV level is excluded. In addition the authors' K X- gamma coincidence measurements do not show any such event with an upper limit of 2*10-5 (90% CL).

K-electron capture decay of158Tb: a disappointment for the neutrino mass 'balance' experiment

High-precision K x- gamma coincidence measurements have been performed in the electron-capture decay of 158Tb in order to measure the K-capture probability to the high-lying levels in 158Gd. Results show that the Q-value of this decay does not allow an ultra-low-energy capture decay to the 1187 keV level as predicted previously. In addition, the K x- gamma coincidence measurements do not show any such event within the statistical errors.

High-spin states in 157,158Er and 158,159Tm.

High-spin states in /sup 157,158/Er and /sup 158,159/Tm have been studied via the /sup 122/Sn(/sup 40/Ar,5,4n) and /sup 141/Pr(/sup 22/Ne,5,4n) reactions, respectively, using in-beam gamma-ray spectroscopy techniques which included gamma - gamma coincidence, angular correlation, angular distribution, excitation function, and multiplicity measurements. The favored ( pi =+, alpha =+1/2) /b i//sub 13/2/ neutron band in /sup 157/Er has been established up to the 53/2/sup +/ level ( h omega =0.417 MeV), and the favored ( pi =-, alpha =-1/2) and unfavored ( pi =-, alpha =+/sup 1///sub 2/)/b h//sub 11/2 / proton bands in /sup 159/Tm, up to the 59/2/sup -/ ( h omega =0.454 MeV) and 61/2/sup -/( h omega =0.480 MeV) levels, respectively, i.e. well above the range of rotational frequency h omega where a second backbending has been observed in the neighboring even-even nuclei. In /sup 158/Er, the yrast levels have been observed up to 38/sup +/, and in /sup 158/Tm, up to 25/sup -/. The favored /b i//sub 13/2/ band of the odd-/b N/ nucleus /sup 157/Er displays a strong upbending at h omega =0.40 MeV, whereas, in the two branches of the /b h/ /sub 11/2/ yrast band of the odd-/b Z/ nucleus /sup 159/Tm, no alignment effect has been observed between h omega =0.27 and 0.48 MeV. The experimental results have been analyzed in the framework of the cranked shell model. On the basis of blocking arguments and cranked shell model calculations, the obtained results show that the second backbending in the yrast band of even-even nuclei near /b A/=158 is due to an /b h//sub 11/2/ proton alignment. The signature splitting of the intrinsic excitation energies (Routhians) and aligned angular momenta in /sup 159/Tm has been reproduced in cranked shell model calculations by introducing a triaxial deformation. The observed steep rise of the /b B/(/b M/ 1)//b Q//sub 0/ /sup 2/ values in the favored and unfavored bands of /sup 159/Tm are consistent with an increase of |/b g//sub K/-/b g//sub R/| at the firsts backbending due to the alignment of a neutron pair around h omega =0.27 MeV. The evolution of the kinematical and dynamical moments of inertia at very high rotational frequencies ( h omega >0.50 MeV) yields information on the nuclear pairing correlations in this frequency range.

Spectroscopy of gamma rays from the decay of202,204Au

202Au and 204Au were produced through the reactions 202Hg(n,p)202Au and 204Hg(n,p)204Au. The half-lives were determined to be 28.8+or-1.9 s and 39.8+or-0.9 s, respectively. Gamma-ray spectroscopy and gamma - gamma coincidence measurements using Ge and Ge-Ge(Li) detectors have revealed the presence of three new gamma transitions accompanying the decay of 202Au and 11 new transitions accompanying the decay of 204Au. The energy of the second excited state in 204Hg has been established as 1128.30+or-0.16 keV. Inconsistencies regarding the proposed existence of a 4.0+or-1.0 s activity in 204Au are discussed.

Decay scheme and lifetimes of excited levels in50Ti

Excited levels in 50Ti have been populated by means of the 49Ti(d,p)50Ti reaction at 6 MeV. A consistent decay scheme up to an excitation energy of 6.7 MeV has been established by means of p- gamma coincidence measurements. Lifetimes or lifetimes limits for 14 levels have been measured by the Doppler-shift attenuation method.

Gamma-ray spectroscopy on87Sr and the energy-B(E2) rule

In-beam gamma -ray measurements following the reaction 84Kr( alpha ,n gamma )87Sr have been undertaken. The level scheme has been established with gamma - gamma coincidence measurements. Mean lifetimes for several levels were obtained with the DSA method. New spin-parity assignments have been made for a number of levels from angular distribution and linear polarisation measurements. The mod g92/-1)(X) mod 88Sr(21+)) quintuplet is discussed in terms of a new energy-B(E2) rule.

A comprehensive study of the γ-ray spectroscopy of43Ca

The reaction 40Ar( alpha ,n gamma )43Ca was used to populate the levels in 43Ca at bombarding energies between 5.5 and 19 MeV, gamma - gamma coincidence measurements at Ealpha =8.5, 15 and 16 MeV being used to establish the decay scheme of 53 levels. Several new levels and new decays of levels with high angular momentum were established. The Doppler-shift attenuation method was used with solid Ar targets to deduce the mean lifetimes for most of these levels. A Ge(Li)-Na(Tl) escape-suppressed spectrometer and a three-Ge(Li) Compton polarimeter were used to measure the angular distribution and linear polarisation of gamma rays at alpha bombarding energies of 7.0, 14.5 and 17 MeV.

Experimental evidence for low-lying intruder states in54Mn

High-spin states in 54Mn were populated in the 52Cr( alpha ,pn gamma ) reaction. Using angular distribution, linear polarisation and gamma - gamma coincidence measurements, the following unambiguous spin and parity assignments were obtained: Ex, Jpi ; 1073 keV, 6+; 1784 keV, 7+; 1925 keV, 7+; 2857 keV, 8+; and 3244, (9)+. In addition a new level was observed at an excitation energy of 3939 keV. The experimental data show evidence for low-lying intruder states as predicted by a recent shell-model calculation.

Study of151Eu levels via the (p,2nγ) reaction

Gamma rays from levels in 151Eu have been studied following the 152Sm (p,2n) reaction. A level scheme based on excitation functions, on angular distributions and on prompt and delayed gamma - gamma coincidence measurements is proposed and compared with findings by other authors. Some transitions observed lead to levels not previously compared with findings by other authors. Some transitions observed lead to levels not previously identified in gamma -ray work. The experimental results are compared with the predictions of the rigid rotor-plus-particle model including Coriolis coupling. Negative-parity states are described in terms of the interacting-boson model.