Decay Scheme Research Articles

Systematics of log [formula omitted] values for [formula omitted]−, and EC/[formula omitted]＋ transitions

This work is an update of the 1998 publication by Singh et al. [1] and reviews the logft values for all the known β-decay branches (β−, β＋/EC). Furthermore, an update of all Q-values (from AME2020 [2]), as well as a recalculation of all the logft values (through BetaShape code [3,4]) has been conducted using relevant data in the ENSDF database, as well as in newer literature. Only those cases have been considered in this review, where the beta transitions occur between levels of firm single spin assignments (86% of the transitions), and with probable single spin assignments (14% of the transitions), but with firm parity assignments for all the transitions. Weak β branches of <1% intensity in complex decay schemes have generally been omitted. Out of a total of 26318 β transitions extracted from the ENSDF database and current literature, data for only 4038 β transitions survived the filtering criteria in the present review. The logft values in β decay, spanning about 21 orders of magnitude, have been classified into allowed and forbidden categories according to the classification scheme of Konopinski [5]. All logft values have been deduced using the BetaShape code with new developments presented in this study. A very few number of logft values for very low-energy beta transitions (<5keV) survived the cut criteria and are briefly discussed in terms of atomic overlap corrections. Also tabulated and briefly discussed are seven superallowed cases with ΔT = 0, Tz(parent) = −2, while a known case for 28S to 28P has been omitted as reliable EC/β＋feeding to the analog state in 28P cannot be assigned due to lack of adequate experimental and detailed data for this decay. Centroid, width, minimum and maximum values for each category have been deduced. Uncertainties have been estimated and are also given. For literature coverage in the present review, see discussion in text.

Nuclear Data Sheets for A=245

Available information pertaining to the nuclear structure of ground and excited states for all known nuclei with mass numbers A=245 have been compiled and evaluated. The adopted level and decay schemes, as well as the detailed nuclear properties and configuration assignments based on experimental data, are presented for these nuclides. When there are insufficient data, expected values from systematics of nuclear properties and/or theoretical calculations are utilized. Unexpected or discrepant experimental results are also noted. Since the last evaluation, new rotational bands in 245Pu have been observed to high spin from transfer reaction 244Pu(209Bi, 208Biγ) by 2014Ho16. While in 245Am, the 249Bk α decay measurements by 2013Ah03 added a new rotational band based on π3/2[521] configuration. The 245Pu β− decay scheme is basically what was proposed in the late 60's and 47 γ rays have still not been placed. In 245Cm, precise alpha energies and intensities were measured by 2015Ah03 in 249Cf α decay. Their reported alpha energies of the main α group were about 2 keV lower than in the previous evaluation. The spin and parity of the g.s. of 245Es is still ambiguous as more detailed information on the decay is needed. With the production of 249No via fusion evaporation reaction by groups in Dubna and GSI, it's alpha decay was studied and some properties of the daughter 245Fm were published and included in this evalaution. Information on the other nuclides is scarce and not much has been investigated since the last evaluation. A summary and compilation of the discovery of the various nuclides in this mass region is given in: 2013Fr02 (245Pu, 245Am, 245Cm, 245Bk, 245Cf), 2011Me01 (245Es), and 2013Th02 (245Md, 245Fm).

Nuclear Data Sheets for A=251

The experimental reaction and decay studies producing nuclei in the A=251 mass chain have been reviewed. Data on elements from uranium (Z=92) to nobelium (Z=102) are included, and level and decay schemes are presented for these nuclides. This work supersedes the previous evaluation for this mass chain (2013Br09).

Precision measurement of 65Zn electron-capture decays with the KDK coincidence setup

65Zn is a common calibration source, moreover used as a radioactive tracer in medical and biological studies. In many cases, γ-spectroscopy is a preferred method of 65Zn standardization, which relies directly on the branching ratio of Jπ(65Zn) = 5/2− → Jπ(65Cu) = 5/2− via electron capture (EC*). We measure the relative intensity of this branch to that proceeding directly to the ground state (EC0) using a novel coincidence technique, finding IEC0/IEC* = 0.9684 ± 0.0018. Re-evaluating the decay scheme of 65Zn by adopting the commonly evaluated branching ratio of Iβ+ = 1.4271(7)% we obtain IEC* = (50.08 ± 0.06)%, and IEC0 = (48.50 ± 0.06)%. The associated 1115 keV gamma intensity agrees with the previously reported NNDC value, and is now accessible with a factor of ∼2 increase in precision. Our re-evaluation removes reliance on the deduction of this gamma intensity from numerous measurements, some of which disagree and depend directly on total activity determination. The KDK experimental technique provides a new avenue for verification or updates to the decay scheme of 65Zn, and is applicable to other isotopes.

VADER: A novel decay station for actinide spectroscopy

A research programme focused on the study of the nuclear structure of actinide isotopes has recently been implemented at the IGISOL facility, University of Jyväskylä. Within this scope, a new decay station named VADER (Versatile Actinides DEcay spectRoscopy setup) has been developed and commissioned. The system consists of a compact array of silicon detectors, a liquid-nitrogen-cooled silicon lithium (Si(Li)) detector and three broad energy germanium detectors (BEGe), placed around a thin implantation carbon foil. The combined use of different detectors allows the measurement of α particles, conversion electrons and de-excitation γ rays in coincidence, enabling a full reconstruction of nuclear decay schemes. The measurement of basic nuclear decay observables provides a picture of the nuclear shell evolution in neutron-deficient actinides, and highlights the possible emergence of reflection-asymmetric shapes in the region.

True coincidence summing corrections in HPGe detectors

The true coincidence effect is studied in two High Purity Germanium (HPGe) detectors for a variety of isotopes, source geometries and source to detector configurations, via computational tools based on Monte–Carlo simulations. Τhe upgraded patch of MCNP code MCNP–CP and the 2018 version of PENELOPE, which take into account the decay scheme of each cascade emitter, are used to calculate the Full Energy Peak Efficiency (FEPE) for the corresponding gamma-ray energies. The true coincidence correction (TCC) factor is calculated as the ratio of the FEPE derived for each nuclide taking into consideration the true coincidence effect, to the FEPE estimated without considering the phenomenon. In all cases, a satisfactory agreement is observed between the TCC factors calculated using MCNP–CP and PENELOPE 2018. Moreover, the results of the calculations are compared against experimentally derived efficiency values. The correction factors obtained using the TrueCoinc software are applied on experimentally determined FEPE curves, based on measurements performed using reference sources, and consequently the corrected data are compared against the simulations for the "non-coincidence" case. The results of this work contribute to the validation of the computational tools and codes used to study the true coincidence effect and determine the corresponding correction factors, providing useful data for gamma–spectrometry studies of cascade emitters.

Activity determination of 56Mn using extended TDCR-Čerenkov method

The accuracy of activity determination for activated nuclide 56Mn is the key to the manganese bath method applying to the characterization of radionuclide neutron source. As an alternative to the 4π(Č)-γ method, TDCR-Čerenkov method could also be applied to the measurement of 56Mn in the manganese bath device, if the existing calculation model is extended. There are two difficulties when the existing TDCR-Čerenkov method is applied to the activity determination of 56Mn. One is that the efficiency computation of gamma transitions, and the other is the interference contributed by Čerenkov photons emitted in the photomultiplier windows induced by Compton scattering. In this study, the above two difficulties are solved by extending the calculation model. For efficiency computation, the decay scheme of 56Mn is taken into account in the calculation of efficiency. Among them, the efficiency of gamma transition is calculated from the simulated secondary electronic spectra. In addition, Čerenkov photons emitted in photomultiplier windows are corrected by additional light proof experiment and improved calculation model. The results derived from this extended method are in good agreement with other standardization technique.

Utilization of different radionuclides for high-energy extended efficiency calibration of a HPGe for improved determination of calcium and sulfur using k0-INAA

The present study reports on the performance of three reactor-produced radionuclides (24Na, 56Mn, and 72Ga) and one accelerator-produced radionuclide (56Co) for extending the full-energy peak efficiency calibration of a coaxial HPGe detector up to ~ 3100 keV at different detector to source distances. The differences between the efficiency curves obtained with and without the use of high-energy gamma emitters radionuclides have a considerable impact on the accuracy of the Na, Ca, and S determination by the k0-INAA as evidenced by analysis results of reference materials. The results revealed that 24Na is the most suitable radionuclide for high-energy efficiency calibration due to its reasonable availability, low production cost, simple decay scheme, and well-defined decay properties.

Complete β -decay patterns of Cs142,Ba142, and La142 determined using total absorption spectroscopy

Background: The β decays of fission products produced in nuclear fuel are important for nuclear energy applications and fundamental science of reactor antineutrinos. In particular, nuclear reactor safety is related to the decay modes of radioactive neutron-rich nuclei, primarily via the emission of γ rays, neutrons, and electrons. Additionally nuclear reactors are the most powerful man-made source of antineutrinos emitted during the β decay of fission products. These antineutrinos are used to inspect fundamental properties of leptons as well as informing reactor operation. However, the majority of data on complex decays of fission products collected in the evaluated nuclear data repositories like Evaluated Nuclear Structure Data File (ENSDF) and Evaluated Nuclear Data Files (ENDF) are based on low-efficiency and often incomplete measurements resulting in questionable reference reactor antineutrino flux predictions, see the analysis by [Nichols, J. Nucl. Sci. Technol. 52, 17 (2015)]. Various assessments like the one done under the auspices of the [Yoshida et al., Assessment of Fission Product Decay Data for Decay Heat Calculations: A report by the Working Party on International Evaluation Co-operation of the Nuclear Energy Agency Nuclear Science Committee (Nuclear Energy Agency, Organization for Economic Co-operation and Development, Paris, France, 2007), Vol. 25], as well as by [Sonzogni, Johnson, and McCutchan, Phys. Rev. C 91, 011301(R) (2015)] and [Dwyer and Langford, Phys. Rev. Lett. 114, 012502 (2015)], list the A=142 isobars with high cumulative fission yield among the important nuclei where data for reactor decay heat and/or antineutrino production should be verified and/or improved. Purpose: Our goal is to improve the quality of β-decay measurements and evaluate the impact of modified decay schemes on reactor decay heat and antineutrino energy spectra, for fission products along the A=142 isobaric chain. This work is an in depth follow-up on [Rasco et al., Phys. Rev. Lett. 117, 092501 (2016)]. which presented briefly the impact of the corrected decay scheme of 142Cs. Here, we extend the data to full isobaric decay chain including the daughter nuclei, 142Ba and 142La, and present more details on the 142Cs results. Method: The decays of neutron-rich isobars of mass A=142 produced by means of proton-induced fission of U238 were measured using the Modular Total Absorption Spectrometer (MTAS) array on-line at the mass separator and Tandem accelerator at Oak Ridge National Laboratory. Results: The β-decay schemes for 142Cs and 142La were modified with respect to the nuclear data repositories. A small β-delayed neutron branching ratio for 142Cs emitter was remeasured as 0.10−3+5 %. Improved precision on the measured half-lives is reported. Small corrections to the low-energy decay of 142Ba are made. The β-decay patterns for 142La and 142Cs are presented. The decay heat release and cross section for the detection of reactor antineutrinos are deduced and compared to earlier results. Conclusions: The β-feeding pattern for 142Cs having decay energy value Qβ of over 7 MeV was substantially modified with respect to the current ENSDF entry. Smaller changes were encountered for 142La, but since this A=142 isobar also has a large cumulative yield in fission, the changes influence both decay heat and the antineutrino spectra. The previously known β intensities for 142Ba decay (Qβ value of 2.2 MeV) were verified and slightly modified. Overall, increased decay heat values and lower flux of antineutrinos interacting with matter are presented.12 MoreReceived 13 October 2022Accepted 14 February 2023DOI:https://doi.org/10.1103/PhysRevC.107.034303©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayFissionLifetimes & widthsNuclear reactorsNuclear structure & decaysProperties90 ≤ A ≤ 149TechniquesSpectrometers & spectroscopic techniquesNuclear Physics

Nuclear Structure and Decay Data for A=71 Isobars

Experimental nuclear spectroscopic data are evaluated for 12 known nuclides of mass number=71 (Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Kr). Detailed compiled and evaluated information is presented for each reaction and decay experiment. The β−n decay of 72Co to 71Ni is included in this work, while for β−n decay of 71Co to 70Ni, consult Nuclear Data Sheets for A=70 (2016Gu11) or the ENSDF database for 70Ni. Combining all the available data, recommended values are provided for energies, spins and parities, and half-lives of levels, with energies, branching ratios and multipolarities of γ radiations, and characteristics of β and α radiations in radioactive decays. Excited-states have not yet been identified in 71Mn, 71Fe, and 71Kr, with the ground-state half-life remaining unknown only for 71Mn; data for excited states in 71Co and 71Ni are very limited; 71Ga, 71Ge and 71As are the most extensively studied nuclides via various reactions and decays, followed by 71Cu, 71Zn, 71Se, and 71Br, however, except for 71Ge, the decay schemes of all other nuclides are considered as incomplete due to a large gap between the decay Q-value and the highest observed level. This work supersedes earlier evaluations of A=71 by 2011Ab01.

Determination of positron emission intensity in the decay of 86gY

The β+- emitting radionuclide 86gY (t1/2 = 14.7 h) forms a matched-pair with the β--emitting therapeutic radionuclide 90Y (t1/2 = 2.7 d) for theranostic application in medicine. Precise knowledge of the positron emission probability of the PET nuclide is very important, which was rather uncertain for 86gY until recently. In this work, an 86gY source of high radionuclidic purity was prepared and the positron emission intensity per 100 decay of the parent (hereafter “positron emission intensity”) was determined by measuring the 511 keV annihilation γ-ray using high-resolution HPGe detector. The total source activity was obtained from known γ-ray emission probabilities. The electron capture (EC) intensity was also determined as an additional check by measuring the Kα and Kβ X-rays of energies 14.1 and 15.8 keV, respectively, using a low energy HPGe detector. From those measurements, normalized values of 27.2 ± 2.0% for β+ -emission and 72.8 ± 2.0% for EC were deduced. These results are in excellent agreement with values recently reported in the literature based on a detailed decay scheme study.

Nuclear Data Sheets for A=242

Detailed level schemes, decay schemes, band structure, and the experimental data on which they are based are presented for all nuclei with mass number A=242. The experimental data are evaluated and adopted values are given for level and radiation properties. For references on theory refer to the NSR file at the web site given below under Cutoff Date:. This evaluation replaces the A=242 publication by Y. A. Akovali in Nuclear Data Sheets 96, 177 (2002) (2002Ak06).

Nuclear Structure and Decay Data for A=231 Isobars

The present evaluation of currently known nine nuclides of A=231: (231Rn, 233Fr, 231Ra, 231Ac, 231Th, 231Pa, 231U, 231Np and 231Pu) represents an update and revision of previous A=231 evaluation by 2013Br04. All the known decay and reaction data are evaluated, with recommended properties given in the Adopted Levels, Gammas datasets, for gamma-ray energies, photon branching ratios, level half-lives, spins, parities, transition probabilities, and configuration assignments. For 231Rn, only an identification of the nuclide has been made without an experimental determination of its half-life. For 231Fr, no excited states are known. About 30 levels in 231Ra up to 1774 keV excitation are known only from β− decay of 231Fr with level half-lives determined for five excited states. For 231Ac, excited states up to 3122 keV are known from β− decay, (t,α), and fragmentary information for high-spin levels from two heavy-ion reaction studies, with lifetimes of excited states measured for five levels. Extensive structure and rotational band information for 231Th is available for a large number of levels up to 1714 keV from β− and α decays, (n,γ) thermal and resonance, single-particle transfer reactions (d,p), (d,t) and (3He,α), with limited data for high-spin levels from one secondary reference, and half-lives available for five excited states. Very detailed structure data are available for 231Pa up to 2139 keV from β−, ε and α decays, (α,t), (d,d′) and high-spin data from heavy-ion Coulomb excitation and (p,2nγ) reaction, with level half-lives known for 34 excited states, mostly deduced by evaluators from transition probabilities determined in Coulomb excitation. Only eight excited states are known in 231U up to 1268 keV from ε and α decays, with no data for half-lives of excited states. For 231Np and 231Pu, only the ground-state is known from α decays, with a tentative level at 324 keV in 231Pu. Measurements of nuclear rms charge radius and isotope shifts for 231Ra have been made by 2018Ly01, and that for rms charge radius for 231Fr by 2014Bu06.235U is a well known nuclide for nuclear structure and reactor applications. There have been a large number of studies of its alpha decay to levels in 231Th, including some recent ones such as 2018Ma03 and 2017Le03, yet evaluators' analysis of the decay scheme suggests that, while α-particle transitions are well established, but several issues still remain about intricacies of gamma-ray and conversion electron spectroscopy which need to be resolved through dedicated experiments for a complete understanding of the decay scheme characteristics, although, this sort of research project would seem a challenging spectroscopic problem. As commented in individual datasets for other decays, important spectral information is lacking for most of the decay schemes, with almost no information available for some of these, resulting in many incomplete decay schemes in A=231 mass chain.

A Highly Efficient Model to Study the Semantics of Salient Object Detection.

CNN-based salient object detection (SOD) methods achieve impressive performance. However, the way semantic information is encoded in them and whether they are category-agnostic is less explored. One major obstacle in studying these questions is the fact that SOD models are built on top of the ImageNet pre-trained backbones which may cause information leakage and feature redundancy. To remedy this, here we first propose an extremely light-weight holistic model tied to the SOD task that can be freed from classification backbones and trained from scratch, and then employ it to study the semantics of SOD models. With the holistic network and representation redundancy reduction by a novel dynamic weight decay scheme, our model has only 100K parameters, ∼ 0.2% of parameters of large models, and performs on par with SOTA on popular SOD benchmarks. Using CSNet, we find that a) SOD and classification methods use different mechanisms, b) SOD models are category insensitive, c) ImageNet pre-training is not necessary for SOD training, and d) SOD models require far fewer parameters than the classification models. The source code is publicly available at https://mmcheng.net/sod100k/.

Nuclear Structure and Decay Data for A=149 Isobars

Experimental nuclear structure and decay data are evaluated for all the 17 known nuclides of mass 149 (Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb). Detailed compiled and evaluated spectroscopic information is presented for each reaction and decay dataset, and recommended values are provided for level properties, α, β and γ radiations, and other spectroscopic parameters, based on an evaluation of all the available experimental data for A=149 isobaric nuclides. Although large amounts of nuclear spectroscopic data are available for nuclides of A=149, yet large gaps in knowledge exist, as described below. For the lowest atomic number nuclide 149Xe, only the isotopic identification has been made, with no data for its ground-state half-life. For 149Cs, 149Tm and 149Yb information is available for only the respective ground states. For 149Ba, 149La and 149Er, limited data exist for excited states. Many of the decay schemes of radioactive nuclei of A=149 are considered as incomplete, either due to large energy differences between the highest observed excited states in daughter nuclides and the respective Q-values, or due to the lack of confirmed γ-ray data, as listed below: 149Cs → 149Ba, 149Ba → 149La, 149La → 149Ce, 149Ce → 149Pr, 149Pr → 149Nd, 149Tb(4.17 min) → 149Gd, 149Ho(21.0 s and 56 s) → 149Dy, 149Er(4 s and 9.6 s) → 149Ho, and 149Tm → 149Er. No data exist for the decay of 149Yb to 149Tm. Data for half-lives of the excited states in this mass chain are generally lacking as given below by the number of excited levels of known half-life / approximate number of known levels in a nuclide: 2/17 for 149Ba, 0/18 for 149La, 3/53 for 149Ce, 3/44 for 149Pr, 17/110 for 149Nd, 9/90 for 149Pm, 10/210 for 149Sm, 2/125 for 149Eu, 6/270 for 149Gd, 5/200 for 149Tb, 3/80 for 149Dy, 3/90 for 149Ho, and 3/14 for 149Er. This work supersedes earlier evaluations of A=149 nuclides published by 2004Si16, 1994Si18, 1985Sz01 and 1976Ho17.

Occupational radiation exposure assessment during the management of [68Ga]Ga-DOTA-TOC

BackgroundSince it was first approved in Europe in 2016, the gallium-68 (68Ga) radiopharmaceutical [68Ga]Ga-DOTA-TOC has been widely used for imaging of somatostatin receptor (SSTR) positive tumours using positron emission tomography–computed tomography (PET/CT). Significant patient benefits have been reported, so its use is rapidly increasing. However, few studies have been published regarding occupational doses to nuclear medicine personnel handling this radiopharmaceutical, despite its manual usage at low distances from the skin and the beta-emission decay scheme, which may result in an increased absorbed dose to their hands. In this context, this study aims to analyse the occupational exposure during the administration of [68Ga]Ga-DOTA-TOC for PET/CT imaging. For this purpose, extremity, eye lens and whole-body dosimetry in terms of Hp(0.07), Hp(3) and Hp(10), respectively, was conducted on six workers with both thermoluminescent dosimeters, and personal electronic dosimeters.ResultsThe non-dominant hand is more exposed to radiation than the dominant hand, with the thumb and the index fingertip being the most exposed sites on this hand. Qualitative analysis showed that when no shielding is used during injection, doses increase significantly more in the dominant than in the non-dominant hand, so the use of shielding is strongly recommended. While wrist dosimeters may significantly underestimate doses to the hands, placing a ring dosimeter at the base of the ring or middle finger of the non-dominant hand may give a valuable estimation of maximum doses to the hands if at least a correction factor of 5 is applied. Personal equivalent doses for the eyes did not result in measurable values (i.e., above the lowest detection limit) for almost all workers. The extrapolated annual dose estimations showed that there is compliance with the annual dose limits during management of [68Ga]Ga-DOTA-TOC for diagnostics with PET in the hospital included in this study.ConclusionsImaging with [68Ga]Ga-DOTA-TOC is a safe process for the workers performing the administration of the radiopharmaceutical, including intravenous injection to the patient and the pre- and post-activity control, as it is highly unlikely that annual dose limits will be exceeded if good working practices and shielding are used.

Alternative routes for 64Cu production using an 18 MeV medical cyclotron in view of theranostic applications

Radiometals play a fundamental role in the development of personalized nuclear medicine. In particular, copper radioisotopes are attracting increasing interest since they offer a varying range of decay modes and half-lives and can be used for imaging (60Cu, 61Cu, 62Cu and 64Cu) and targeted radionuclide therapy (64Cu and 67Cu), providing two of the most promising true theranostic pairs, namely 61Cu/67Cu and 64Cu/67Cu. Currently, the most widely used in clinical applications is 64Cu, which has a unique decay scheme featuring β+-, β−-decay and electron capture. These characteristics allow its exploitation in both diagnostic and therapeutic fields. However, although 64Cu has extensively been investigated in academic research and preclinical settings, it is still scarcely used in routine clinical practice due to its insufficient availability at an affordable price. In fact, the most commonly used production method involves proton irradiation of enriched 64Ni, which has a very low isotopic abundance and is therefore extremely expensive. In this paper, we report on the study of two alternative production routes, namely the 65Cu(p,pn)64Cu and 67Zn(p, α)64Cu reactions, which enable low and high 64Cu specific activities, respectively. To optimize the 64Cu production, while minimizing the mass of copper used as a target in the first case, or the co-production of other copper radioisotopes in the second case, an accurate knowledge of the production cross sections is of paramount importance. For this reason, the involved nuclear reaction cross sections were measured at the Bern medical cyclotron laboratory by irradiating enriched 65CuO and enriched 67ZnO targets. On the basis of the obtained results, the production yield and purity were calculated to assess the optimal irradiation conditions. Several production tests were performed to confirm these findings.

β decay of neutron-rich Cu76 and the structure of Zn76

The $\ensuremath{\beta}$ decay of $^{76}\mathrm{Cu}$ to the levels of $^{76}\mathrm{Zn}$ was studied at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). A purified $^{76}\mathrm{Cu}$ beam was developed and data were recorded for the decay of the $A=76$ decay chain using four high-purity germanium (HPGe) clover detectors at the Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). In this measurement, data on \ensuremath{\gamma}-ray emission following $\ensuremath{\beta}$ decay, including $\ensuremath{\beta}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidences, were collected and $\ensuremath{\gamma}\ensuremath{\gamma}$ spectra were analyzed to identify the statistically significant coincidences. From this analysis, we propose a level scheme for $^{76}\mathrm{Zn}$ which contains a total of 59 energy levels up to 6.0 MeV containing 105 $\ensuremath{\gamma}$ rays. We have identified an additional 53 $\ensuremath{\gamma}$ rays associated with this decay which could not be place in the decay scheme due to insufficient coincidence information or no energy match to identified levels. No $\ensuremath{\gamma}$ rays from states in $^{75}\mathrm{Zn}$ fed in the delayed-neutron branch were observed even though other $\ensuremath{\gamma}$ rays in the $A=75$ decay chain were observed. Spin and parity assignments are proposed for some levels based on comparison to systematics and shell model calculations.

Beta-Ray-Bremsstrahlung Contributions to Short-Lived Delayed Photoneutron Groups in Heavy Water Reactors

Hard bremsstrahlung produced during the deceleration of fission-product beta rays in nuclear fuel is proposed as a source of delayed photoneutrons (PNs) in heavy water reactors. Electron Gamma Shower (EGS5) code simulations of coupled electron-photon transport in seven fuel element geometries immersed in an infinite heavy water medium confirm high-energy beta rays produce sufficient bremsstrahlung yields with photon energies greater than the D(γ,n)1H reaction threshold such that the beta-ray contribution to an isotopic PN yield can be comparable to or greater than yields from hard gamma rays emitted during the isomeric transition of the daughter, especially for some short-lived fission products with high-intensity direct-to-ground-state beta transitions where the beta ray and antineutrino carry away the majority of the Q-value. Some fission products that do not have hard gamma rays in their decay schemes are in fact PN precursors due to the beta-ray-bremsstrahlung contribution. The lack of evaluated nuclear data for many short-lived fission products, data reliability issues of fission products with decay scheme data, cross-section library effects, and possible decay-chain/parent-feeding phenomenon are affecting the accuracy of PN group parameters derived from a small number of legacy experiments. The reanalysis of two legacy PN experiments supports the existence of a very-short-lived direct-delayed neutron group.

Corrections of HPGe detector efficiency curve due to true coincidence summing by program EFFTRAN and by Monte Carlo simulations

Standard reference sources, used for efficiency curve calibration of detector, often contain radionuclides with complex decay schemes (such as 60Co, 88Y, 152Eu …), introducing a potential problem in gamma-ray spectrometry, due to the appearance of coincidence summing of detected photons, in particular at a low source-detector distance. In this paper, a set of Monte Carlo simulations of an identical experimental setup were performed in order to obtain the efficiency curve of coaxial p-type HPGe detector for energy region (0–2) MeV, with the effect of true coincidence summing and without it. Obtained efficiency curves are compared with the experimental curve after applied EFFTRAN corrections. Fairly well agreement (between simulated and experimental curves with EFFTRAN corrections (with a relative deviation of 10%) proved the reliability of EFFTRAN corrections, as well as the possibility of Monte Carlo simulations for efficiency curve determination.