Γ-ray Spectroscopic Techniques Research Articles

Ground-state β-feeding determination using total-absorption spectrometers

The determination of the β intensity probability between the ground states of parent and daughter nuclei has traditionally been a difficult task with standard γ-spectroscopy approaches due to the lack of the associated γ emission. In the last years, the total absorption γ-ray spectroscopy technique has successfully proven its ability to deal with this problem by means of different procedures. This article discusses the potential of these methods, and a new approach for segmented total-absorption γ-ray spectrometers is also introduced. An overview of applications is presented based on past, present, and future β-decay experiments.

Conceptual design and simulated performance of the Barrel part of gamma array for the experimental terminal at HFRS of HIAF

The Barrel of γ array, consisting of 640 CsI(Tl) crystals and covering a polar angle range from 36.4° to 135.6°, has been designed for the experimental terminals at High energy FRagment Separator of High-Intensity heavy-ion Accelerator Facility in Huizhou. Together with the existing Endcap, consisting of 1024 CsI(Tl) crystals and covering a polar angle from 15.6° to 36.4°, at the External Target Facility in Lanzhou to form a new γ array, it is expected to meet the experimental requirements for in-beam γ-ray spectroscopy technique. A Monte Carlo code based on Geant4 was implemented to study the performance of the new γ array. Taking into account the Doppler correction and the intrinsic energy resolution of the detector, the energy resolution is 5.4% (FWHM) for the Endcap and 9.8% (FWHM) for the Barrel when the energy of the emitted γ-ray is 1 MeV in the Center-of-Mass frame with the beam energy of 500 MeV/u (beam velocity β = 0.759). The full-space photopeak efficiency is greater than 40% when the energy of the emitted γ-ray is less than 5 MeV in the Center-of-Mass frame and the beam energy is less than 700 MeV/u (β = 0.821). Such performance can satisfy most of the physics requirements for in-beam γ-ray spectroscopy experiments.

Cs2ZrCl6 scintillation properties studied using γ-ray spectroscopy and Compton coincidence technique

The scintillation properties of cesium-zirconium hexachloride (Cs2ZrCl6) were investigated by γ-ray spectrometry and the Compton Coincidence Technique. The tested cylindrical sample had 20 mm diameter and 12 mm height. The crystal shows a high light output of 40 900 photons per MeV as measured by a spectroscopy type photomultiplier with 20 μs pulse integration time under γ-ray excitation at room temperature. A small deviation from linear response as a function of energy deposited in γ-ray absorption or Compton scattering processes, combined with a high light yield, results in good energy resolution equal to 4.3 % at 662 keV and 2.3 % at 2.6 MeV. Due to long lasting scintillation decay the sample properties were studied at different shaping time constants in an analogue spectroscopy chain or using different integration time gates when employing a digital analyzer.

Measurement of uranium in phosphate fertilizers for groundwater contamination employing X-ray and γ-ray spectroscopic techniques

Measurement of uranium in phosphate fertilizers for groundwater contamination employing X-ray and γ-ray spectroscopic techniques

Development of the Multi-Cubic [formula omitted]-ray spectrometer and its performance under intense 137Cs and 60Co radiation fields

The number of nuclear facilities being decommissioned has been increasing worldwide, in particular following the accident of the Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Station in 2011. Large amounts of radioactive wastes and spent nuclear fuels are stored in these facilities. Furthermore, advanced radiation therapies such as proton therapy, ion therapy, and boron neutron capture therapy using charged-particle accelerators have become popular, but charged-particle accelerators generate radiators during operation. In these nuclear and radiation facilities, proper management of radioactive materials is required until the end of the deactivation, cleanup, or disposal. Then, γ-ray spectroscopy techniques have been useful tools because they can obtain significant information on radioisotopes. Besides, space information of radioisotopes is also important, and γ-ray imaging is also required. However, intense radiation fields are located at these facilities, causing γ-ray spectroscopy and imaging difficultly. A γ-ray spectrometer with four segmentations using small-volume CeBr3 scintillators with a dimension of 5×5×5 mm3 was developed. The four scintillators were coupled to a multi-anode photomultiplier tube specific to intense radiation fields by individual supplied voltages to the last three stages. We performed the γ-ray exposure to the spectrometer under 137Cs and60Co radiation fields at the National Institute of Advanced Industrial Science and Technology in Japan. Under the 137Cs radiation field, the relative energy resolution at 1375 mSv/h was 9.2 ± 0.05%, 8.0 ± 0.08%, 8.0 ± 0.03%, and 9.0 ± 0.04% for the four channels, respectively. As the dose rate increased, significant spectral downward shifts were observed for the four channels under the 137Cs and60Co radiation fields because of the space charge effects in the photomultiplier tube. However, the Multi-Cubic sensor could provide the total throughput rate for the four channels of greater than 6 Mcps (Mcps: 106 counts per second), which increases the detection efficiency under intense radiation fields.

Disentangling decaying isomers and searching for signatures of collective excitations in β decay

In this contribution we summarize the recent study of the β decay of neutron-rich nuclei with isomeric states close in energy to the ground states. The disentanglement of each pair of β-decaying states was achieved by applying different strategies and using the purification capabilities of the JYFLTRAP double Penning trap system at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. The Total Absorption γ-ray Spectroscopy technique was employed to determine the β intensity probabilities populating the excited states in the daughter nuclei. Previously undetected β intensity was found and we have already evaluated the impact of part of these results on reactor summation calculations. The possibility to populate states associated with the Pygmy Dipole Resonance in the β decay of 96gsY has also been investigated thanks to the sensitivity of our technique to high-lying strength in the daughter nuclei.

Shape-coexistence Studies in the Ni Isotopic Chain by Using the Selectivity of Different Reaction Mechanisms

We report on the investigation of the shape coexistence phenomenon in the Ni isotopic chain, from A = 62 to A = 66, by using γ-ray spectroscopy techniques and different reaction mechanisms, such as sub-Coulomb barrier transfer reactions and thermal-neutron capture. Our aim is to understand, from the microscopic point of view, the appearance of nuclear deformation in Ni isotopes at low excitation energy. A series of experiments was performed at the Tandem Accelerator Laboratory in Bucharest, at ALTO IPN-Orsay and at the ILL reactor in Grenoble. Various mean-field theoretical approaches, as well as recent state-of-the-art Monte Carlo Shell Model (MCSM) calculations, predict in 66Ni a deep secondary prolate minimum in the nuclear potential energy surface at spin zero, resulting in a hindered electromagnetic decay towards the spherical ground state (i.e., with an E2 transition probability less than 1 W.u.). This has been confirmed in the first experiment performed in Bucharest. Less pronounced prolate minima, at higher excitation energies, are also expected in lighter neutron-rich Ni isotopes, from state-of-the-art Monte Carlo Shell Model (MCSM) calculations. Preliminary results are discussed for 62Ni and 64Ni, in comparison with theory predictions.

High spin states of 195Hg

High spin states in 195Hg, populated using the 150Nd(48 Ca,3n) reaction, were investigated by γ-ray spectroscopic techniques. Two backbendings are observed in the yrast band considered to be caused by the alignment of a pair of i13/2 and p3/2 neutrons respectively. The strong backbending behaviour observed in the negative parity side band is consistent with the alignment of a pair of i13/2 neutrons. The similarity with the corresponding backbendings in the neighbouring isotopes is impressive.

Large Impact of the Decay of Niobium Isomers on the Reactor ν[over ¯]_{e} Summation Calculations.

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The β-intensity distributions of ^{100gs,100m}Nb and ^{102gs,102m}Nb β decays have been determined using the total absorption γ-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the β decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.

Comparative study of precise measurements of natural radionuclides and radiation dose using in-situ and laboratory \u03b3-ray spectroscopy techniques

In this study, in-situ and laboratory γ-ray spectroscopy techniques were compared to evaluate the activity concentration of natural radionuclides in soil. The activity concentrations of 238U (226Ra), 232Th, and 40K in the soil in 11 sites were simultaneously measured with in-situ portable HPGe and the NaI(Tl) detectors. In parallel, 55 soil samples collected from these sites were analyzed with a laboratory γ-ray spectroscopy technique (HPGe). A strong correlation was observed between the in-situ and laboratory HPGe techniques with a linear correlation coefficient (R2) of 0.99 for 226Ra and 232Th and 0.975 for 40K, respectively. The in-situ HPGe technique shows a strong correlation with the NaI(Tl) detector. γ-Rays cps of 226Ra, 232Th, and 40K of the NaI (Tl) detector were then converted to specific activities (Bq kg−1 unit) in soil using the empirical formulas obtained in this study. The absorbed dose rate in air at 1 m height above ground due to these radionuclides was calculated using the Beck’s formula and the results were compared with measured values obtained with an high pressure ionization chamber. The results of the calculated and measured dose rate show a strong correlation of R2 = 0.96. The reliability and precision of analytical spectroscopy techniques of radioactivity and radiation dose were confirmed in this work.

FaNGaS: A new instrument for [formula omitted] reaction measurements at FRM II

The FaNGaS instrument was set up at the research reactor FRM II, Garching. It performs measurements of (n,n′γ) reactions based on the γ-ray spectroscopy technique within the fission neutrons energy region. The optimization studies of the experimental setup were carried out using MCNP simulations. A full characterization of the detector system and the neutron beam is presented. The determination of the neutron energy spectrum was done using the foil activation method. An average neutron energy of about 2MeV and a neutron flux of 108cm−2·s−1 were measured.

Natural Radioactivity Assessment of Kaolin and Gibbsite Rock Materials in Sinai, Egypt

The activity concentrations of 238U, 232Th, and 40K in the kaolin and gibbsite samples collected from various localities of Sinai, Egypt have been measured using the γ-ray spectroscopy technique. For each sample, various characterizing quantities such as Raeq, Hex, Hin, and Iγ values are calculated. All the values lie within the worldwide range. the dose rates of the most samples varies from 48.07 to 88.27 with average 46.21 which are agreement with the recommended limits (18-93 nGy h-1) except two samples are high called T.3.2 in EL Tih I location (201.04 nGy h-1 ) and M6 in Mussaba Salama ( 98.33 nGy h-1). The Chemical and mineralogy analysis show that the uranium concentration ranges from 2 to 18 PPm which are agreement with the recommended limits except M1 sample equals 44 PPm.and Fe2O3% ranges from 0.45 to 4.20 except one sample called T.3.2 equals 15.7% and AL2O3 ranges from 11.7 to 37.2 %. So it is desirable to used in industrial, where Kaolin and gibbsite is host several economic metal values. Which used in many important industries such as; paper industry, ceramics, refractory bricks, white cement, textiles, Rubber, medical industries, and special types of plastics.

Band structures in 99Rh

Excited states in the 99Rh nucleus were populated using the fusion-evaporation reaction 75As(28Si,2p2n) at and the de-excitations were investigated through in-beam γ-ray spectroscopic techniques using the INGA spectrometer consisting of 18 clover detectors. The observed band structures are discussed in the framework of tilted axis cranking shell-model calculations. Level structures at low energies are identified as resulting from the rotational bands based on the and configurations. The = 1 coupled bands are observed at higher excitation energies and have been interpreted as based on the , and configurations. Calculations based on cranked Nilsson–Strutinsky (CNS) formalism have been performed to interpret the favoured states with = (41/2−, 43/2−) and (51/2−, 53/2−) as maximal spin aligned states built on the valence space configuration combined with the fully-aligned configuration and the configuration with one anti-aligned proton, respectively.

Excited states above the proton threshold in 26Si

The level scheme above the proton threshold in 26Si is crucial for evaluating the 25Al(p, γ)26Si stellar reaction, which is important for understanding the astrophysical origin of the long-lived cosmic radioactivity 26Al(T 1/2 = 7.17 × 105 y) in the Galaxy. The excited states in 26Si have been studied using an in-beam γ-ray spectroscopy technique with the 24Mg(3He, nγ)26Si reaction. γ-rays with energies up to 4.6 MeV emitted from excited states in 26Si have been measured using large volume HPGe detectors. The spin-parity of one of the most important states reported recently at 5890.0keV has been assigned as 0+ by γ-γ angular correlation measurements in this work.

First prompt in-beam γ-ray spectroscopy of a superheavy element: the 256Rf

Using state-of-the-art γ-ray spectroscopic techniques, the first rotational band of a superheavy element, extending up to a spin of 20 ℏ, was discovered in the nucleus 256Rf. To perform such an experiment at the limits of the present instrumentation, several developments were needed. The most important of these developments was of an intense isotopically enriched 50Ti beam using the MIVOC method. The experimental set-up and subsequent analysis allowed the 256Rf ground-state band to be revealed. The rotational properties of the band are discussed and compared with neighboring transfermium nuclei through the study of their moments of inertia. These data suggest that there is no evidence of a significant deformed shell gap at Z = 104.

Shell-Structure and Pairing Interaction in Superheavy Nuclei: Rotational Properties of theZ=104NucleusRf256

The rotational band structure of the Z=104 nucleus (256)Rf has been observed up to a tentative spin of 20ℏ using state-of-the-art γ-ray spectroscopic techniques. This represents the first such measurement in a superheavy nucleus whose stability is entirely derived from the shell-correction energy. The observed rotational properties are compared to those of neighboring nuclei and it is shown that the kinematic and dynamic moments of inertia are sensitive to the underlying single-particle shell structure and the specific location of high-j orbitals. The moments of inertia therefore provide a sensitive test of shell structure and pairing in superheavy nuclei which is essential to ensure the validity of contemporary nuclear models in this mass region. The data obtained show that there is no deformed shell gap at Z=104, which is predicted in a number of current self-consistent mean-field models.

Band structures and shape coexistence in 187Pt

High-spin states in 187Pt have been studied by means of γ-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy.

Shape isomerism and shape coexistence effects on the Coulomb energy differences in theN=Znucleus66As and neighboringT=1multiplets

Excited states of the N=Z=33 nucleus 66As have been populated in a fusion-evaporation reaction and studied using γ-ray spectroscopic techniques. Special emphasis was put into the search for candidates for the T=1 states. A new 3+ isomer has been observed with a lifetime of 1.1(3) ns. This is believed to be the predicted oblate shape isomer. The excited levels are discussed in terms of the shell model and of the complex excited Vampir approaches. Coulomb energy differences are determined from the comparison of the T=1 states with their analog partners. The unusual behavior of the Coulomb energy differences in the A=70 mass region is explained through different shape components (oblate and prolate) within the members of the same isospin multiplets. This breaking of the isospin symmetry is attributed to the correlations induced by the Coulomb interaction.Received 10 February 2012DOI:https://doi.org/10.1103/PhysRevC.85.034320©2012 American Physical Society

High-j proton alignments in 101Pd

High-spin states in 101Pd have been investigated by means of in-beam γ-ray spectroscopic techniques via the 76Ge(28Si, 3n) reaction at beam energies of 85 and 95 MeV. The previously known d 5/2 and 1/2−[550] bands were extended to higher spins, and the unfavored signature branch of the 1/2−[550] band was built. The band crossings observed experimentally are explained by the alignment of g 9/2 protons. The band properties in 101Pd are compared with those in the neighboring nuclei and are discussed within the framework of the cranked shell model (CSM).

Disappearance of theN=14shell gap in the carbon isotopic chain

The structure of 617−20C nuclei was investigated by means of the in-beam γ-ray spectroscopy technique using fragmentation reactions of radioactive beams. Based on particle-γ and particle-γγ coincidence data, level schemes are constructed for the neutron-rich C17−20 nuclei. The systematics of the first excited 2+ states in the carbon isotopes is extended for the first time to A=20 showing that in contrast to the case of the oxygen isotopes, the N=14 subshell closure disappears. Experimental results are compared with shell-model calculations. Agreement between them is found only if a reduced neutron-neutron effective interaction is used. Implications of this reduced interaction in some properties of weakly bound neutron-rich Carbon are discussed.Received 5 June 2008DOI:https://doi.org/10.1103/PhysRevC.78.034315©2008 American Physical Society