Γ-ray Decay Research Articles

Delayed gamma-ray spectroscopy combined with active neutron interrogation for nuclear security and safeguards

For the purpose of nuclear security and safeguards, an active neutron interrogation non-destructive assay technique, Delayed Gamma-ray Spectroscopy (DGS), is under development. The technique of DGS uses the detection of decay γ rays from fission products to determine ratios of fissile nuclides in a sample. A proper evaluation of such γ-ray spectra requires integration of nuclear data such as fission cross-sections, fission yields, half-lives, decay-chain patterns, and decay γ-ray yields. Preliminary DGS experiments with the Pulsed Neutron Interrogation Test Assembly, named PUNITA, of the European Commissions’ Joint Research Center have been performed. Signals of delayed γ ray from nuclear materials were successfully observed.

Neutron single-particle strengths at N=40 , 42: Neutron knockout from Ni68,70 ground and isomeric states

The distribution of single-particle strength in 67,69Ni was characterized with one-neutron knockout reactions from intermediate-energy 68,70Ni secondary beams, selectively populating neutron-hole configurations at N = 39 and 41, respectively. The spectroscopic strengths deduced from the measured partial cross sections to the individual final states, as tagged by their γ-ray decays, are used to identify and quantify neutron configurations in the wave functions. While 69Ni compares well to shell-model predictions, the results for 67Ni challenge the validity of current effective shell-model Hamiltonians by revealing discrepancies that cannot be explained so far. These results suggest that our understanding of the low-lying states in the neutron-rich, semi-magic Ni isotopes may be incomplete and requires further investigation on both the experimental and theoretical sides.

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.

Electromagnetic properties of neutron-rich nuclei adjacent to the Z = 50 shell closure

Low-lying high-spin yrast states in the exotic odd–odd isotopes 124–128Sb (Z=51) and 118–128In (Z=49), studied for the first time, show a striking difference in their observed γ-ray decay. With a single valence proton particle/hole occupying the g7/2/g9/2 spin-orbit partners, dominant electric quadrupole transitions occur in Sb as opposed to magnetic dipole transitions in In. The observed properties are explained on the basis of general principles of symmetry and with large-scale shell-model calculations, and reveal novel aspects of the competition between the neutron–proton interaction and the like-nucleon pairing interaction.

Improving γ-ray energy resolution, non-proportionality, and decay time of NaI:Tl+ with Sr2+ and Ca2+ co-doping

Commercially available thallium activated sodium iodide scintillators are typically characterized by a γ-ray energy resolution of 6.5% at 662 keV and a scintillation decay time constant of 230 ns. Energy resolution, non-proportionality, and scintillation decay time are improved when the crystal is co-doped with alkaline earth metals (Sr2+ and Ca2+). The energy resolution of NaI:Tl+ is improved to 5.3%, and the decay time is simultaneously reduced to 170 ns with Sr2+ and Ca2+ co-doping. The improvement in energy resolution, non-proportionality, and decay time are likely due to the suppression of the slow scintillation processes in NaI:Tl+.

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.

New Millisecond Isomer Lifetime Measurements at LANSCE

New half-life measurements have been made of the millisecond isomers 71mGe, 114m2In, 208mBi, 88m1Y, 88m2Y, and 75mAs populated in neutron-induced reactions. These measurements were made using the unique time structure of the LANSCE/WNR neutron source, by observing the γ-ray decays of the isomers during the time between the LANSCE proton macropulses. Two different LANSCE proton beam time structures were used. The GEANIE array of HPGe detectors was used to detect the γ-ray decays.

High resolution148Nd(3He,nγ) two proton stripping reaction and the structure of the 02+state in150Sm

1 , O. Shirinda 3 , P. Abstract. The challenge of achieving high resolution in binary reactions involving an outgoing high energy neutron is solved by detecting the γ-ray decay of populated excited states in an array of escape suppressed HPGe detectors in coincidence with fast neutrons detected in a wall of scintillator detectors 2m down beam of the target. The selectivity of the arrangement is of the order of 1 in 1000. The time-of-flight difference is sufficient to separate fast neutrons from direct reactions from a large background of statistical neutrons from fusion-evaporation reactions. Our interest is in the wavefunction of the 02 + state at 740 keV in the N=88 nucleus 150 Sm which, with the 02 + state in 100 Ru, are the only two excited states observed in 2β2ν double β-decay.

Determination of 232Th(n, γ) reaction rate induced by D-T neutrons in one-dimensional alternate depleted uranium/polyethylene shells

A series of neutron integral fundamental researches of thorium nuclear data in set-ups containing thorium samples is carried out. One-dimensional alternate depleted uranium/polyethylene shells containing thorium samples are constructed by referring to the conceptual design of fusion-fission hybrid reactor, where a D-T neutron source driven by accelerator is used to simulate the fusion core of the reactor. 232Th (n, γ ) reaction rates in samples located at different positions in the shells are measured in 5% uncertainty by using activated thorium sample decay γ-ray off-line measurement technique. The results show that the moderation of polyethylene to 14.1 MeV neutron will efficiently increase the capture rate of thorium, and the depleted uranium is also conducible to this increase obviously. The comparison between our measured data and the results available from mainstream nuclear data bank shows that the calculation results from ENDF/B-VI.6 and JENDL-3.3 are around 6% higher than the experimental results, while the newer ENDF/B-VII.0 will achieve better results, around 4% higher than the experimental results. We recommend the ENDF/B-VII.0 to be used in one-dimensional alternate depleted uranium/polyethylene shells related conceptual design when calculating the 232Th (n, γ) reaction rate.

Thorium capture ratio determination through γ-ray off-line method

To determine the thorium capture ratio and thorium-uranium conversion ratio in the thorium cladding of the fusion-fission reactor model, a new approach, activated thorium sample decay γ -ray off-line measurement, is introduced in this paper. This method is based on the measurement of the 311.98 keV characteristic decay γ-ray emitted by 233Pa which is produced through decay of 233Th, the capture product of 232Th. Then some reverse mathematic approach is brought in and finally the 232Th (n, γ ) 233Th reaction ratio is determined, with an uncertainty of 6% in the test experiment (233Th/232Th under the order of magnitude 10-17). In the paper, we introduce the detail of the approach including the background, principle and the result of a simple test experiment which shows that this approach can work well in thorium capture ratio determination. Compared with prompt γ-ray method and mass spectrometer method, this decay γ-ray off-line method has many advantages in determining the thorium capture ratio and thorium-uranium conversion ratio in the thorium cladding. It is also promising in the measurement of other relevant parameters.

Vela Jr.：超新星喷发团块与超新星遗骸的互动

重迭在船帆座超新星遗骸(Vela supernova remnant)视线上的ROSAT X射线源RX J0852.0-4622，或称Vela Jr.，因其在1.3千电子伏的波段上呈现圆壳外观和检测出44Ti的γ射线衰变线，所以被认为是新发现的年轻超新星遗骸。然而，观测证据指出Vela Jr.应属于船帆座超新星遗骸的一部份而非独立的物体。二维气体动力学模拟显示，超新星快速的高密度喷发气体物(子弹)可以影响遗骸的外围，产生类似于Vela Jr.的圆环结构。估计Vela Jr.的能量为 The ROSAT source RX J0852.0-4622, or Vela Jr., superposed on the Vela supernova remnant, has been identified as a separate young supernova remnant based on its shell-like appearance in X-ray > 1.3 keV and on its detection as a source of the 44Ti γ-ray decay line. However, a re-examination of the observational facts suggests that Vela Jr. should be part of the Vela remnant. We suggest that the shell X-ray feature is produced by a fast ejecta clump (bullet) from the Vela supernova that deposited its kinetic energy in the supernova remnant shell. The estimated energy < 0.3 × 1049 erg could be supplied by a <~0.1M⊙ clump moving at1700 km/s. Two-dimensional gas dynamic simulations show that a circular appearance can be produced in the supernova shell under proper conditions. We suggest that the nickel bubble effect is responsible for producing such heavy ejecta clumps in supernovae. There may be other similar X-ray features at a lower brightness level and there may be emission from heavy element ejecta in the object.

γ-ray spectroscopy of one-proton knockout from45Cl

The role of proton shell effects in the structure of the N=28 isotones 45Cl and 44S has been studied via one-proton knockout from 45Cl. We compare measured γ-ray intensities, inclusive and partial knockout cross sections, and the inclusive momentum distribution of outgoing 44S particles with shell-model and reaction-theory predictions. The strong population in this reaction of the recently identified 41+ state in 44S, identified through its subsequent γ-ray decay energy, makes a compelling case for a Jπ=3/2+ ground state in 45Cl.

Crystal growth and scintillation properties of Er-doped Lu 3Al 5O 12 single crystals

Er-doped Lu 3Al 5O 12 (Er:LuAG) single crystalline scintillators with different Er concentrations of 0.1, 0.5, 1, and 3% were grown by the micro-pulling-down (μ-PD) method. The grown crystals were composed of single-phase material, as demonstrated by powder X-ray diffraction (XRD). The radioluminescence spectra measured under 241Am α-ray excitation indicated host emission at approximately 350 nm and Er 3+ 4f–4f emissions. According to the pulse height spectra recorded under γ-ray irradiation, the 0.5% Er:LuAG exhibited the highest peak channel among the samples. The γ-ray excited decay time profiles were well fitted by the two-component exponential approximation (0.8 μs and 6–10 μs).

Nuclear Data Sheets for A = 35

The experimental data are evaluated for known nuclides of mass number A=35 (Na,Mg,Al,Si,P,S,Cl,Ar,K, Ca). Detailed evaluated level properties and related information are presented, including adopted values of level and γ-ray energies, decay data (energies, intensities and placement of radiations), and other spectroscopic data. This work supersedes earlier full evaluations of A=35 published by 1990En08 (also 1998En04 update) and 1978En02. No excited states are known in 35Na, 35Mg, 35Ca. No γ rays are known in 35K. Experimental data for 35Al and 35Si are limited and their radioactive decay schemes seem incomplete in view of large Q values and known excitations much below than allowed by Q values. The 35S, 35Cl and 35Ar nuclides remain as the most extensively studied from many different reactions and decays.

Nuclear Data Sheets for A = 44

The experimental data are evaluated for known nuclides of mass number A=44 (Si,P,S,Cl,Ar,K,Ca,Sc,Ti,V, Cr,Mn). Detailed evaluated level properties and related information are presented, including adopted values of level and γ-ray energies, decay data (energies, intensities and placement of radiations), and other spectroscopic data. This work supersedes earlier full evaluations of A=44 published by 1999Ca45 and 1990En08 (also 1998En04 update). No excited states are known in 44Si, 44P, 44Cr, 44Mn. Only one excited state is known in 44V and its Isobaric Analog State (IAS) has been observed but with the level energy not known. Information for 44S, 44Cl and 44Ar is limited and their radioactive decay schemes seem incomplete in view of large Q values and known excitations much below than allowed by Q values. The 44Ca, 44Sc and 44Ti nuclides remain as the most extensively studied from many different reactions and decays.

Nuclear Data Sheets for A = 33

The experimental data are evaluated for known nuclides of mass number A=33 (Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K). Detailed evaluated level properties and related information are presented, including adopted values of level and γ-ray energies, decay data (energies, intensities and placement of radiations), and other spectroscopic data. This work supersedes earlier full evaluations of A=33 published by 1990En08 (also 1998En04 update) and 1978En02. Experimental studies for the identification of the 33Ne and 33K nuclides have not met with success as yet. Values of S(n) and S(p) from systematics for 33Ne and 33K, respectively suggest that these nuclei are likely to be unstable to particle emission. The radioactive decay schemes of 33Na and 33Al seem incomplete in view of large Q values and known excitations much below than allowed by the Q values. The 33S and 33Cl nuclides remain as the most extensively studied from many different reactions and decays.

Optical and scintillation characteristics of Y2O3 transparent ceramic

Various fundamental characteristics of Y2O3 ceramics, such as optical transmittance, reflectivity, absorption coefficient, refractive index, and dielectric constant, were investigated. Furthermore, in order to evaluate the possible application of this material as γ-ray scintillator, other radiation responses, like the α-ray excited emission spectrum, the γ-ray excited pulse height spectrum, the light yield, the nonproportionality, the energy resolution, and the γ-ray excited scintillation decay curves were obtained. The light yield of Y2O3 ceramics was evaluated in about 1.13 times higher than that of Bi4Ge3O12(BGO):Ce single crystals and was estimated in 9300 photon/MeV. The nonproportionality measurements showed a good proportionality. The scintillation decay curve could be fitted by an exponential function characterized by a fast component of about 34 ns.

Neutron Activation of74Ge and76Ge

The upcoming GERDA and MAJORANA experiments will use germanium crystals, isotopically enriched in 76Ge to search for the neutrinoless double beta decay (0ν2β). The very long half-life of 0ν2β (> 1025 y for 76Ge) requires an extremely low background level. Neutrons induced by cosmic muons can be captured after thermalization by 74Ge or 76Ge, followed by β− -decay of 75Ge and 77Ge respectively. The prompt γ-cascade after neutron capture and the β-decay contribute to the total backround in these experiments. For a good estimation of the background the poorly known cross-sections for the 74Ge(n,γ)75,75mGe reactions were measured using targets, isotopically depleted in 76Ge. Furthermore the prompt γ-rays in 77Ge were measured with isotopically enriched germanium targets. The results of the latter measurement were combined with the results of a dedicated coincidence measurement to reconstruct the prompt γ-ray decay scheme.

β−-delayed spectroscopy of neutron-rich tantalum nuclei: Shape evolution in neutron-rich tungsten isotopes

The low-lying structure of W188,190,192 has been studied following β decays of the neutron-rich mother nuclei Ta188,190,192 produced following the projectile fragmentation of a 1-GeV-per-nucleon Pb208 primary beam on a natural beryllium target at the GSI Fragment Separator. The β-decay half-lives of Ta188, Ta190, and Ta192 have been measured, with γ-ray decays of low-lying states in their respective W daughter nuclei, using heavy-ion β−γ correlations and a position-sensitive silicon detector setup. The data provide information on the low-lying excited states in W188, W190, and W192, which highlight a change in nuclear shape at W190 compared with that of lighter W isotopes. This evolution of ground-state structure along the W isotopic chain is discussed as evidence for a possible proton subshell effect for the A~ 190 region and is consistent with maximization of the γ-softness of the nuclear potential around N~116.11 MoreReceived 18 September 2009DOI:https://doi.org/10.1103/PhysRevC.80.064308©2009 American Physical Society

Evolution of the [formula omitted] shell gap below 132Sn inferred from core excited states in 131In

The γ-ray decay of an excited state in 131In, the one proton hole neighbor of the doubly magic 132Sn has been measured. A high-spin, core-excited isomer with T1/2=630(60) ns was identified following production by both relativistic fragmentation of a 136Xe beam and fission of a 238U beam. This state deexcites by a single γ-ray branch of 3782(2) keV from which direct evidence for the size of the N=82 shell gap is inferred. The results are discussed in comparison to a shell-model calculation including configurations across the closed shells at N=82 and Z=50.