Γ-ray Intensities Research Articles

Computational analysis of the dose rates at JSI TRIGA reactor irradiation facilities

The JSI TRIGA Mark II, IJS research reactor is equipped with numerous irradiation positions, where samples can be irradiated by neutrons and γ-rays. Irradiation position selection is based on its properties, such as physical size and accessibility, as well as neutron and γ-ray spectra, flux and dose intensities. This paper presents an overview on the neutron and γ-ray fluxes, spectra and dose intensities calculations using Monte Carlo MCNP software and ENDF/B-VII.0 nuclear data libraries.The dose-rates are presented in terms of ambient dose equivalents, air kerma, and silicon dose equivalent. At full reactor power the neutron ambient dose equivalent ranges from 5.5×103Svh−1 to 6×106Svh−1, silicon dose equivalent from 6×102Gy/hsi to 3×105Gy/hsi, and neutron air kerma from 4.3×103Gyh−1 to 2×105Gyh−1. Ratio of fast (1MeV<E) vs. thermal neutrons (E<0.625eV) ranges from 1.5 to 8.4×10−2,γ ray ambient dose equivalent at full reactor power from 3.4×103Svh−1 to 3.6×105Svh−1 and γ air kerma range 3.1×103Gyh−1 to 2.9×105Gyh−1.

Strongly coupled rotational band in Mg33

Author(s): Richard, AL; Crawford, HL; Fallon, P; Macchiavelli, AO; Bader, VM; Bazin, D; Bowry, M; Campbell, CM; Carpenter, MP; Clark, RM; Cromaz, M; Gade, A; Ideguchi, E; Iwasaki, H; Jones, MD; Langer, C; Lee, IY; Loelius, C; Lunderberg, E; Morse, C; Rissanen, J; Salathe, M; Smalley, D; Stroberg, SR; Weisshaar, D; Whitmore, K; Wiens, A; Williams, SJ; Wimmer, K; Yamamato, T | Abstract: The island of inversion at N≈20 for the neon, sodium, and magnesium isotopes has long been an area of interest both experimentally and theoretically due to the subtle competition between 0p-0h and np-nh configurations leading to deformed shapes. However, the presence of rotational band structures, which are fingerprints of deformed shapes, have only recently been observed in this region. In this work, we report on a measurement of the low-lying level structure of Mg33 populated by a two-stage projectile fragmentation reaction and studied with the Gamma Ray Energy Tracking In-Beam Nuclear Array (GRETINA). The experimental level energies, ground-state magnetic moment, intrinsic quadrupole moment, and γ-ray intensities show good agreement with the strong-coupling limit of a rotational model.

Quantifying lithium in the solid electrolyte interphase layer and beyond using Lithium- Nuclear Reaction Analysis technique

Accurate knowledge of lithium content within the solid electrolyte interphase (SEI) layer and anode would significantly enhance the current understanding of the lithium ion battery (LIB) degradation mechanisms, enabling knowledge-based improvements in the technology. For the first time, we have demonstrated the capabilities of highly selective Lithium Nuclear Reaction Analysis (Li-NRA) as a non-destructive depth profiling technique for quantifying Li within the SEI and anode without accurate knowledge of the composition, which is unavailable with other depth profiling techniques. The Li-NRA technique detects the gamma radiation resulting from a nuclear reaction at characteristic resonance energy between an incident high-energy proton and Li. The intensity of γ-ray is directly proportional to the Li content, and the energy of the incident proton is increased stepwise to depth profile the sample. We performed Li-NRA on the carbonaceous negative electrodes of commercial LIB coin cells at varying states of charge (SOC) and states of health (SOH) conditions. We used three simple models for the composition of SEI and anode material to show concurrence between theoretical and experimental value for Li content at varying SOC conditions, estimated the average SEI layer thickness, and correlated the residual Li content within the SOH samples with electrochemical data.

Study of fission fragment de-excitation by gamma-ray spectrometry with the EXILL experiment

A large array of Ge detectors installed at ILL, around a 235 U target irradiated with cold neutrons, (EXILL) allowed measurement of prompt gamma-ray cascades occurring in fission fragments with an unambiguous determination of fragments. Here we present preliminary results of a systematic comparison between experimental γ-ray intensities and those obtained from the Monte-Carlo simulation code FIFRELIN, which is dedicated to the de-excitation of fission fragments. Major γ-ray intensities in the 142 Ba and 92 Kr fission products, extracted from EXILL data, were compared to FIFRELIN, as well as to reported values (when available) obtained with EUROGAM2 in the spontaneous fission of 248 Cm. The evolution of γ-ray intensities in 92 Kr versus the complementary partner in fission (i.e. versus the total number of evaporated neutrons by the fission pair) was then extracted and compared to FIFRELIN.

Absolute intensities of the γ-ray emissions originating from the electron capture decay of 153Gd

153 Gd has widespread use, in non-destructive testing, as a line source in SPECT imaging and has been recently proposed as an in-vitro interstitial rotating shield brachytherapy (I-RSBT) source. In this work, the six most intense emissions in the de-excitation of the daughter nucleus 153 Eu have been measured, with an improved accuracy and precision to γ-ray emission intensities reported previously, via two characterised HPGe spectrometers. A specific absolute activity of 512.5 (25) kBq g−1 was determined using the 4π (LS)-γ digital coincidence counting technique. This absolute activity was used to determine an absolute intensity for the 97.4 keV γ-ray emission of 30.15 (20) per 100 decays. The reported absolute emission intensity of this transition in this work has a relative difference of 4% from the currently recommended value.

Neutron capture cross sections of 70Zn and the decay of 71mZn

Radiative neutron capture was studied in the 70Zn(n,γ)71m,gZn reaction in order to determine the thermal neutron capture cross sections for the reactions. The resonance integrals were also measured to facilitate corrections for the epithermal neutron component. In addition, cross sections for the 64Zn(n,γ)65Zn and 68Zn(n,γ)69mZn reactions were determined. Through high-resolution γ-ray spectrometry in the 71mZn decay, a new set of γ-ray energies and intensities was obtained of roughly an order of magnitude greater precision than the previous set, and several transitions new to the decay scheme are proposed. The implications for the properties of the levels of 71Ga are discussed. More precise values of the decay half-lives for 69mZn, 71gZn, and 71mZn have been determined.

Isotropic diffuse and extragalactic γ-ray background: emission from extragalactic sources vs dark matter annihilating particles

The isotropic diffuse γ-ray background (IGRB) has been detected by various experiments and recently the Fermi-LAT Collaboration has precisely measured its spectrum in a wide energy range. The origin of the IGRB is still unclear and we show in this paper the significative improvements that have been done, thanks to the new Fermi-LAT catalogs, to solve this mystery. We demonstrate that the γ-ray intensity and spectrum of the IGRB is fully consistent with the unresolved emission from extragalactic point sources, namely Active Galactic Nuclei and Star Forming Galaxies. We show also that the IGRB can be employed to derive sever constraints for the γ-ray emission from diffuse processes such as annihilation of Dark Matter (DM) particles. Our method is able to provide low bounds for the thermal annihilation cross section for a wide range of DM masses.

Thermal neutron capture cross sections forO16,17,18andH2

Author(s): Firestone, RB; Revay, Z | Abstract: Thermal neutron capture γ-ray spectra for O16,17,18 and H2 have been measured with guided cold neutron beams from the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) reactor and the Budapest Research Reactor (BRR) on natural and O17,18 enriched D2O targets. Complete neutron capture γ-ray decay schemes for the O16,17,18(n,γ) reactions were measured. Absolute transition probabilities were determined for each reaction by a least-squares fit of the γ-ray intensities to the decay schemes after accounting for the contribution from internal conversion. The transition probability for the 870.76-keV γ ray from O16(n,γ) was measured as Pγ(871)=96.6 ±0.5% and the thermal neutron cross section for this γ ray was determined as 0.164±0.003 mb by internal standardization with multiple targets containing oxygen and stoichiometric quantities of hydrogen, nitrogen, and carbon whose γ-ray cross sections were previously standardized. The γ-ray cross sections for the O17,18(n,γ) and H2(n,γ) reactions were then determined relative to the 870.76-keV γ-ray cross section after accounting for the isotopic abundances in the targets. We determined the following total radiative thermal neutron cross sections for each isotope from the γ-ray cross sections and transition probabilities; σ0(O16)=0.170±0.003 mb; σ0(O17)=0.67±0.07 mb; σ0(O18)=0.141±0.006 mb; and σ0(H2)=0.489±0.006 mb.

Nuclear Data Sheets for A = 227

The evaluated spectroscopic data are presented for ten known nuclides of mass 227 (Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np). For 227Po, 227At, 227Rn, 227Pa, 227U and 227Np nuclei, only the ground-state information is available. Their decay characteristics are mostly unknown. Levels in 227Fr are known only from the decay of 227Rn to 227Fr. This decay scheme at present cannot be normalized to deduce γ intensities per 100 decays due to lack of knowledge about multipolarities of many low-energy transitions. The levels in 227Ra, 227Ac and 227Th are known from several decays and reactions, including particle-transfer data for 227Ra and 227Ac. The decay scheme of 227Ra to 227Ac was last studied in 1971 using small Ge detectors. Improved γ-ray intensity data need to be obtained with a better γ-detection system. The datasets for 227Ac have undergone extensive revisions, including detailed data for 231Pa α decay from 1986BaYK report, and single-proton transfer data from 1986MaYU thesis. High-spin (J>13/2 or so) structures are known only for 227Th. Level lifetime data are quite scarce for all the nuclides in this mass chain, thus limiting the knowledge of reduced transition probabilities.Band structures for 227Fr, 227Ra, 227Ac and 227Th are known in detail, together with evidence of weak octupole deformation and consequent parity-doublet structures.This evaluation was carried out as part of a joint IAEA-ICTP workshop for Nuclear Structure and Decay Data, organized and hosted by the IAEA, Vienna and ICTP, Trieste, March 24–28, 2014. The evaluation work was coordinated by B. Singh (McMaster). This work supersedes previous A=227 evaluation (2001Br31) published by E. Browne which covered literature before May 2001.

On the iteration of coincidence summing correction for determination of gamma-ray intensities

In order to determine the γ-ray emission intensities of nuclei far from the β-stability line with HPGe detectors under large solid-angle geometry, coincidence summing corrections should be performed, even if full energy peak efficiencies of detectors are accurately measured with standard sources. Because the summing effects depend on decay schemes and emission intensities, the correction needs to be iterated several times starting from the initial values of intensities obtained directly from the measured peak counts of γ-rays. Considering 134Cs, 154Eu and 56Co as typical examples, we discuss the number of iterations of summing correction required for self-consistency with respect to the total efficiencies of the detectors.

Determination of absolute photon emission intensities of 210Pb

Photon emission intensities of 210Pb have been determined using sources prepared from a standard solution, whose activity was measured by liquid scintillation counting. The absolute γ-ray and X-ray emission intensity was measured by conventional γ-ray spectrometry. Complementary measurements of the L X-ray spectrum were performed using a cryogenic detector, characterized by very high energy resolution and constant detection efficiency. As a result, precise emission intensities of the individual X-ray lines were obtained taking into account the presence of satellite lines.

Structure of 207Pb populated in 208Pb + 208Pb deep-inelastic collisions

The yrast structure of 207Pb above the 13=2+ isomeric state has been investigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Argonne National Laboratory. New and previously observed transitions were measured using the Gammasphere detector array. The level scheme of 207Pb is presented up to ∼ 6 MeV, built using coincidence and γ-ray intensity analyses. Spin and parity assignments of states were made, based on angular distributions and comparisons to shell model calculations.

Validating (d,pγ) as a Surrogate for Neutron Capture

The r-process is responsible for creating roughly half of the elements heavier than iron. It has recently become understood that the rates at which neutron capture reactions proceed at late times in the r-process may dramatically affect the final abundance pattern. However, direct measurements of neutron capture reaction rates on exotic nuclei are exceptionally difficult, necessitating the development of indirect approaches such as the surrogate technique. The (d,pγ) reaction at low energies was identified as a promising surrogate for the (n,γ) reaction, as both reactions share many characteristics. We report on a program to validate (d,pγ) as a surrogate for (n,γ) using 95Mo as a target. The experimental campaign includes direct measurements of the γ-ray intensities from the decay of excited states populated in the 95Mo(n,γ) and 95Mo(d,pγ) reactions.

Structure of $^{207}$Pb Populated in $^{208}$Pb + $^{208}$Pb Deep-inelastic Collisions

The yrast structure of 207Pb above the 13/2+ isomeric state has been investigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Argonne National Laboratory. New and previously observed transitions were measured using the Gammasphere detector array. The level scheme of 207Pb is presented up to ~ 6 MeV, built using coincidence and γ-ray intensity analyses. In addition, the spin and parity assignments of states were made, based on angular distributions and comparisons to shell model calculations.

The Effect of Gamma Irradiation on the Structural Properties of Porous Silicon

Porous silicon layers (PSi) were prepared from p-type silicon wafer by using electrochemical cell with etching time 20 min, current 30 mA and fixed electrolyte solution HF:C2H5OH (1:4). The effect of increase of γ-ray intensity (50Gy and 100Gy) on the structural properties of porous silicon has been studied using SEM, AFM, XRD and Raman spectrum. The SEM images before irradiation shows high density and randomly distributed of pores that cover all of the surface which have different size and spherical shape. After irradiation by 50Gy, the pores seems more obvious, discriminate and larger diameters. The initial elementary pores on the PSi surface decrease with the increasing of radiation intensity to 100Gy, as a result of formation of new pores with in the initial layer of Psi. The AFM images show that the roughness of the samples increase with irradiation. XRD spectrum before irradiation did not show clearly any featured peaks while the spectra after irradiation show the presence of different peaks but the most important distinctive was peaks at ( 2θ = 28.12) which give indication that the structure is cubic. An extremely symmetric band shape were recognized from Raman spectra of the samples after and before irradiation.

Fermi-LAT γ-ray anisotropy and intensity explained by unresolved radio-loud active galactic nuclei

Radio-loud active galactic nuclei (AGN) are expected to contribute substantially to both the intensity and anisotropy of the isotropic γ-ray background (IGRB). In turn, the measured properties of the IGRB can be used to constrain the characteristics of proposed contributing source classes. We consider individual subclasses of radio-loud AGN, including low-, intermediate-, and high-synchrotron-peaked BL Lacertae objects, flat-spectrum radio quasars, and misaligned AGN. Using updated models of the γ-ray luminosity functions of these populations, we evaluate the energy-dependent contribution of each source class to the intensity and anisotropy of the IGRB. We find that collectively radio-loud AGN can account for the entirety of the IGRB intensity and anisotropy as measured by the Fermi Large Area Telescope (LAT). Misaligned AGN provide the bulk of the measured intensity but a negligible contribution to the anisotropy, while high-synchrotron-peaked BL Lacertae objects provide the dominant contribution to the anisotropy. In anticipation of upcoming measurements with the Fermi-LAT and the forthcoming Cherenkov Telescope Array, we predict the anisotropy in the broader energy range that will be accessible to future observations.

Simulating γ–γ coincidences of β-delayed γ-rays from fission product nuclei

Analyzing radiation from material that has undergone neutron induced fission is important for fields such as nuclear forensics, reactor physics, and nonproliferation monitoring. The γ-ray spectroscopy of fission products is a major part of the characterization of a material׳s fissile inventory and the energy of incident neutrons inducing fission.Cumulative yields and γ-ray intensities from nuclear databases are inputs into a GEANT4 simulation to create expected γ-ray spectra from irradiated 235U. The simulations include not only isotropically emitted γ-rays but also γ–γ cascades from certain fission products, emitted with their appropriate angular correlations. Here γ singles spectra as well as γ–γ coincidence spectra are simulated in detectors at both 90° and 180° pairings.The ability of these GEANT4 Monte Carlo simulations to duplicate experimental data is explored in this work. These simulations demonstrate potential in exploiting angular correlations of γ–γ cascades in fission product decays to determine isotopic content. Analyzing experimental and simulated γ–γ coincidence spectra as opposed to singles spectra should improve the ability to identify fission product nuclei since such spectra are cleaner and contain more resolved peaks when compared to γ singles spectra.

EC decay of 244Bk

Berkelium isotopes have been produced in 11B-induced reaction on 238U. The EC decay of 244Bk → 244Cm has been studied by carrying out the single and coincidence measurements of the γ-rays emitted during the de-excitation of the 244Cm levels. Radiochemical separations have been carried out to minimize the contribution from the fission products and target. The new half-life of 244Bk is obtained as 5.02 ± 0.03 h, which is close to the theoretically calculated value. The relative intensities of the decay γ-rays have been re-evaluated. Based on the coincidence measurements, a tentative partial level scheme for 244Bk → 244Cm decay has been proposed.

Correction to the recommended γ-ray emission intensity of the 255.13 keV photons in the decay of 113Sn

The authors provide corrected measured values of the relative γ-ray emission intensity of the 255.13keV photons from the decay of 113Sn. Consequently, new recommended values of the evaluated relative and absolute γ-ray emission intensity of the 255.13keV photons following the decay of 113Sn are proposed.

Investigation of (d,x) nuclear reactions on natural ytterbium up to 24 MeV

Production cross-sections of the natYb(d,x)169,170,171,172,173,174m,174,176m,177gLu and 169,175,177Yb reactions have been measured from a 24-MeV deuteron energy down to their respective thresholds by using a stacked-foil activation technique combined with high resolution γ-ray spectrometry. Our new experimental data extended the experimental database toward the lower energy region for 169Yb, 171Lu, 172Lu, and 176mLu, and the higher region for 174Lu, 176mLu, and 177Yb. An overall good agreement is found with some of the earlier measurements, whereas a partial agreement is obtained with the theoretical data extracted from the TENDL-2013 library. The (d,p) channel contribution underestimated by the TENDL-2013 library is successfully reproduced in the global renormalization by Ignatyuk for the FENDL-3.0 library. The production cross-sections of 175Yb available in the literature were revised based on the latest γ-ray intensity adopted in 2004. Physical thick target yields for the investigated reaction products were also deduced and compared with the directly measured ones in the literature. The derived thick target yields for 173Lu and 174gLu are higher than the directly measured ones by Dmitriev et al. at 22MeV. The deduced yield curves indicate that a low energy (<11MeV) cyclotron and a highly enriched 176Yb target could be used to obtain 177gLu with negligible impurity from 177mLu.