Γ-ray Multiplicity Research Articles

Prompt-fission observable and fission yield calculations for actinides by TALYS

The nuclear reaction code TALYS adopts the Hauser-Feshbach statistical decay theory, to de-excite fission fragments. This involves for instance the evaporation of prompt fission neutrons and γ-rays. TALYS incorporates databases of primary fission fragment distribution which consists of primary fission fragment yield and data for excitation energy distribution of fission fragments. We conducted a sensitivity study on three parameters in TALYS and fitted them in order to reproduce experimental and evaluated data, in thermal neutron-induced fission of 235U. Moreover, we demonstrate a large-scale calculation of average prompt neutron and γ-ray multiplicities for 243 selected actinide isotopes.

A novel active collimator for compton-suppressed clover HPGe detector and its role in a hybrid gamma detector array

A new active collimator (AC) detector has been designed as a replacement of the heavy metal collimator for the Compton-suppressed clover High Purity Germanium (HPGe) detector, aiming to enhance the performance of the 4π hybrid gamma detector array for nuclear spectroscopy experiments. This replacement promises enhanced functionality and efficiency in detecting gamma radiation within the detector array. By utilizing ACs in combination with Compton-suppressed clover HPGe and LaBr3(Ce) detectors, a highly effective setup can be established for a γ-ray multiplicity filter for angular momentum selection in heavy ion collision reactions. This configuration offers notable advantages when studying weak band structures that undergo decay through high-cut multiplicity γ-ray events. Moreover, by summing the energy deposited in all detectors, the hybrid array can also be effectively utilized for calorimetric applications in specific measurements. We have designed and characterized an AC with a Compton-suppressed clover HPGe detector. Significantly, when using the AC configuration with the 60Co source, the absorption of γ-rays in AC and the peak-to-total ratio in clover HPGe were found to be similar to that obtained with the standard design incorporating the heavy metal configuration. The advantages of employing the AC for higher multiplicity events were demonstrated through GEANT4 simulations. The simulations were conducted for the entire array, and the potential benefits are thoroughly discussed, highlighting the improved performance achievable with the AC configuration.

Instrumentation for correlated prompt [formula omitted] emission studies in coincidence with fission fragments

Recent theoretical and experimental results have brought renewed interest and focus on the topic of fission fragment angular momentum. Measurements of neutrons and γ rays in coincidence with fission fragments remain the most valuable tool in the exploration of fission physics. To achieve these scientific goals, we have developed a system that combines a state-of-the-art fission fragment detector and n−γ radiation detectors. A new twin Frisch-gridded ionization chamber has been designed and constructed for use with a spontaneous fission source and an array of forty trans-stilbene organic scintillators (FS-3) at Argonne National Laboratory. The new ionization chamber design we present in this work aims at minimizing particle attenuation in the chamber walls, and provides a compact apparatus that can be fit inside existing experimental systems. The ionization chamber is capable of measuring fission fragment masses and kinetic energies, whereas the FS-3 provides neutron and γ-ray multiplicities and spectra. The details of both detector assemblies are presented along with the first experimental results of this setup. Planned event-by-event analysis and future experiments are briefly discussed.

Neutron and gamma multiplicities calculated in the consistent framework of the Hauser-Feshbach Monte Carlo code FIFRELIN

Monte-Carlo simulations to calculate the number of prompt particles emitted during fission were performed using the Fifrelin code and compared to recent experimental data. We show that we are able to reproduce both the neutron and γ-ray multiplicity distributions as a function of the pre-neutron mass of the fission fragments using a single consistent set of parameters. This result was made possible by using an energy-dependent spin cut-off model, driving the initial total angular momentum of the fission fragments, together with microscopic level densities from the HFB plus combinatorial method. We also discuss, how the initial excitation-energy sharing shapes the TKE-dependent γ-ray multiplicity.

On the use of [formula omitted]/n correlations in multiplicity counting in small samples

The use of liquid scintillation detectors provides the possibility to acquire information about both γ-rays and neutrons. The capability of plutonium detection via γ/n coincidences in liquid scintillation detectors is well demonstrated in the literature, and it is also acknowledged that correlated γ/n detection can offer better sensitivity and signal to noise ratio compared to neutron–neutron for some applications. In this paper we perform an assessment of the use of γ/n coincidence counting in small samples, what may have use in the context of nuclear safeguards. We formulate the expected number of γ/n coincidences and calculate the average and covariance of γ-ray and neutron multiplicities for 238Pu, 240Pu, 242Pu and 252Cf. The multiplicative coefficients for the 240Pu effective mass equation was then calculated using γ/n coincidences, and Monte Carlo simulations performed in order to model the detection of neutrons and γ-rays inside liquid scintillation detectors.We conclude that γ/n coincidence counting still has potential capabilities when the objective is the detection of plutonium, but its use for plutonium effective mass quantification is limited compared to n/n coincidence counting. Nevertheless, the method could still be applicable for the purpose of plutonium mass quantification by using a calibration curve that is specific to a sample’s mass and size.

Experimental information on mass- and TKE-dependence of the prompt fission γ-ray multiplicity

Prompt γ rays from the spontaneous fission of 252Cf were measured with cerium-doped LaBr3 detectors. The average prompt fission γ-ray multiplicity, Mγ, was determined as a function of fragment mass number (A) and total kinetic energy (TKE). High-statistics data, obtained from three detectors of different size at different angles relative to the fission chamber, confirms unequivocally a saw-tooth like shape of the γ multiplicity as a function of fragment mass, in contrast to previously published data. In addition, the TKE-dependence of Mγ was determined experimentally and compared with recent data.

High resolution gamma-ray spectroscopy of fast-neutron induced fission

Experiments to perform precision spectroscopy of fast neutron induced fission were carried out during the ν-Ball experimental campaign at the ALTO facility of IJC Laboratory Orsay. Low energy fission of 232Th(n,f), 238U(n,f) and spontaneous fission of 252Cf were studied using this hybrid highresolution spectrometer and calorimeter. New observables such as γ-ray multiplicity distributions correlated with specific fission fragments are presented and discussed. A new method using fast-timing techniques to detect prompt fission neutrons in coincidence with prompt fission γ-rays is described.

Using γ rays to disentangle fusion-fission and quasifission near the Coulomb barrier: A test of principle in the fusion-fission and quasielastic channels

The overlap in the mass symmetric region of the reaction products from fusion-fission and quasifission complicates the assignment of symmetric events to complete fusion on the basis of the mass distribution alone. Additional observables, besides mass distribution, should be used. The approach proposed here relies on the fact that fusion-fission and quasifission are characterized by different timescales. Within this framework, we performed a detailed study to find out how timescales can be probed via angular momentum transfer as measured via γ-ray multiplicities. The proof of principle was carried out by measuring the γ rays in coincidence with fusion-fission and quasielastic binary fragments in the reaction S32 + Au197 at beam energy near the Coulomb barrier. The experiment was performed at the Accelerateur Lineaire Tandem a Orsay (ALTO) facility at the Institut De Physique Nucleaire (IPN) in Orsay (France) using a detection setup consisting of ORGAM (ORsay GAMma) and PARIS (Photon Array Radioactive Ion Stable beams) γ-detectors arrays coupled with the CORSET (CORrelation SETup) time-of-flight spectrometer. Results of the sensitivity of this method to distinguish reaction channels with different dynamics are discussed.

A Search for Cosmic Neutrino and Gamma-Ray Emitting Transients in 7.3 yr of ANTARES and Fermi LAT Data

Abstract We analyze 7.3 yr of ANTARES high-energy neutrino and Fermi Large Area Telescope (LAT) γ-ray data in search of cosmic neutrino + γ-ray (ν+γ) transient sources or source populations. Our analysis has the potential to detect either individual ν+γ transient sources (durations s), if they exhibit sufficient γ-ray or neutrino multiplicity, or a statistical excess of ν+γ transients of individually lower multiplicities. Individual high γ-ray multiplicity events could be produced, for example, by a single ANTARES neutrino in coincidence with a LAT-detected γ-ray burst. Treating ANTARES track and cascade event types separately, we establish detection thresholds by Monte Carlo scrambling of the neutrino data, and determine our analysis sensitivity by signal injection against these scrambled data sets. We find our analysis is sensitive to ν+γ transient populations responsible for >5% of the observed gamma-coincident neutrinos in the track data at 90% confidence. Applying our analysis to the unscrambled data reveals no individual ν+γ events of high significance; two ANTARES track + Fermi γ-ray events are identified that exceed a once per decade false alarm rate threshold (p = 17%). No evidence for subthreshold ν+γ source populations is found among the track (p = 39%) or cascade (p = 60%) events. Exploring a possible correlation of high-energy neutrino directions with Fermi γ-ray sky brightness identified in previous work yields no added support for this correlation. While TXS 0506+056, a blazar and variable (nontransient) Fermi γ-ray source, has recently been identified as the first source of high-energy neutrinos, the challenges in reconciling observations of the Fermi γ-ray sky, the IceCube high-energy cosmic neutrinos, and ultrahigh-energy cosmic rays using only blazars suggest a significant contribution by other source populations. Searches for transient sources of high-energy neutrinos thus remain interesting, with the potential for either neutrino clustering or multimessenger coincidence searches to lead to discovery of the first ν+γ transients.

Fission dynamics in systems of intermediate fissility

It is well accepted that fission is a slow process dominated by nuclear viscosity. This is demonstrated by experimental observations, mainly based on measurements of fission fragment TKE, pre-scission light particles and GDR γ-ray multiplicities, energy spectra. The fission time-scale, as well as the nature of energy dissipation during the process and its dependence on the nuclear shape and temperature are the main aspects which have often been addressed. In spite of the extensive work, there are still many open questions on the dynamics of the fission process, mainly due to the lack of constraints on the models and to the different probes used. Intermediate fissily systems are particularly suited for this study as they present comparable cross sections in the fusion-fission and fusion-evaporation channels, allowing to measure observables in both channels, and therefore to further constrain the models. Furthermore, the path from equilibrium to saddle configuration is expected to dominate with respect to saddle-to-scission one, reducing the complexity of the physical process to be studied. We present here an in depth review of a study performed on the nucleus 132Ce, which shows the limits of the statistical model in accounting for an extended set of observables. We further present the analysis of the same data with a 3D Langevin dynamical approach which proves to be capable of reproducing the values of the whole set of observables. Our analysis reinforce the fact that extended data sets are essential to achieve reliable simulations to address the open questions on fission dynamics and strongly suggest the use of setups of high efficiency.

Study of giant dipole resonance in hot rotating light mass nucleus 31P

An exclusive systematic study of the giant dipole resonance (GDR) parameters has been performed in very light mass nucleus P31 in the temperature range of ∼0.8–2.1MeV and average angular momentum of ∼11–16ħ. The high-energy γ rays from the decay of the GDR, evaporated neutrons and γ-ray multiplicities have been measured. The angular distribution of high-energy γ rays has also been measured at Ebeam=42MeV. The GDR parameters, nuclear level density parameter and nuclear temperature were precisely determined by simultaneous statistical model analysis of high-energy γ ray and evaporated neutron spectra. It is observed that the measured width remains roughly constant up to a temperature of ∼1.6MeV. Moreover, the thermal pairing plays no role in describing the GDR width in this open-shell light nucleus at the above-mentioned temperatures and angular momenta. The present measurements provide an excellent platform to extend the applicability of the existing theoretical models down to the very light mass nuclei.

Total prompt γ-ray emission in fission

The total prompt γ-ray energy distributions were measured for the neutron-induced fission of 235U, 239,241Pu at incident neutron energy of 0.025 eV–100 keV, and the spontaneous fission of 252Cf using the Detector for Advanced Neutron Capture Experiments (DANCE) array in coincidence with the detection of fission fragments by a parallel-plate avalanche counter. Corrections were made to the measured distribution by unfolding the two-dimension spectrum of total prompt γ-ray energy vs multiplicity using a simulated DANCE response matrix. A summary of this work is presented with the emphasis on the comparison of total prompt fission γ-ray energy between our results and previous ones. The mean values of the total prompt γ-ray energy ⟨Eγ,tot⟩, determined from the unfolded distributions, are ∼20% higher than those derived from measurements using single γ-ray detector for all the fissile nuclei studied.

Comprehensive modeling of prompt fission neutrons and γ rays in the spontaneous fission of 252Cf

We present a comprehensive set of calculations performed with the Monte Carlo Hauser-Feshbach code CGMF of the prompt fission neutrons and γ rays emitted in the spontaneous fission of Cf-252. This reaction has been studied in depth over the years and provides an almost perfect test for the assumptions, parameters and output of the CGMF code. Here we present results for prompt neutron observables beyond the ubiquitous average prompt fission neutron spectrum and multiplicity. In particular, we compare CGMF calculations to experimental data on neutron data per fragment mass split, neutron-light fragment and neutron-neutron angular distributions, and on the time dependence of the average prompt γ-ray multiplicity. Finally, we briefly discuss the recent integration of CGMF into the MCNP6.2 transport code.

The performance of the γ-ray tracking array GRETINA for γ-ray spectroscopy with fast beams of rare isotopes

The γ-ray tracking array GRETINA was coupled to the S800 magnetic spectrometer for spectroscopy with fast beams of rare isotopes at the National Superconducting Cyclotron Laboratory on the campus of Michigan State University. We describe the technical details of this powerful setup and report on GRETINA's performance achieved with source and in-beam measurements. The γ-ray multiplicity encountered in experiments with fast beams is usually low, allowing for a simplified and efficient treatment of the data in the γ-ray analysis in terms of Doppler reconstruction and spectral quality. The results reported in this work were obtained from GRETINA consisting of 8 detector modules hosting four high-purity germanium crystals each. Currently, GRETINA consists of 10 detector modules.

Evidence of dynamical dipole excitation in the fusion-evaporation of theCa40+Sm152heavy system

The excitation of the dynamical dipole mode along the fusion path was investigated for the first time in the formation of a heavy compound nucleus in the A∼190 mass region. The compound nucleus was formed at identical conditions of excitation energy and spin from two entrance channels: the charge-asymmetric Ca40+Sm152 and the nearly charge-symmetric Ca48+Sm144 at Elab=11 and 10.1 MeV/nucleon, respectively. High-energy γ rays and light charged particles were measured in coincidence with evaporation residues by means of the MEDEA multidetector array (Laboratori Nazionali del Sud, Italy) coupled to four parallel plate avalanche counters. The charged particle multiplicity spectra and angular distributions were used to pin down the average excitation energy, the average mass, and the average charge of the compound nucleus. The γ-ray multiplicity spectrum and angular distribution related to the nearly charge-symmetric channel were employed to obtain new data on the giant dipole resonance in the compound nucleus. The dynamical dipole mode excitation in the charge-asymmetric channel was evidenced, in a model-independent way, by comparing the γ-ray multiplicity spectra and angular distributions of the two entrance channels with each other. Calculations of the dynamical dipole mode in the Ca40+Sm152 channel, based on a collective bremsstrahlung analysis of the reaction dynamics, are presented. Possible interesting implications in the superheavy-element quest are discussed.2 MoreReceived 19 January 2016DOI:https://doi.org/10.1103/PhysRevC.93.044619©2016 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsLow & intermediate energy heavy-ion reactionsTechniquesNuclear reactionsNuclear Physics

Total promptγ-ray emission in fission

The total prompt γ-ray energy distributions were measured for the neutron-induced fission of 235 U, 239,241 Pu at incident neutron energy of 0.025 eV–100 keV, and the spontaneous fission of 252 Cf using the Detector for Advanced Neutron Capture Experiments (DANCE) array in coincidence with the detection of fission fragments by a parallel-plate avalanche counter. Corrections were made to the measured distribution by unfolding the two-dimension spectrum of total prompt γ-ray energy vs multiplicity using a simulated DANCE response matrix. A summary of this work is presented with the emphasis on the comparison of total prompt fission γ-ray energy between our results and previous ones. The mean values of the total prompt γ-ray energy ⟨Eγ,tot⟩, determined from the unfolded distributions, are ∼20% higher than those derived from measurements using single γ-ray detector for all the fissile nuclei studied.

Fission time-scale from the measurement of pre-scission light particles and γ-ray multiplicities

An overview of the experimental result on simultaneous measurement of pre-scission neutron, proton, α-particle and GDR γ-ray multiplicities for the reaction 28Si +175Lu at 159 MeV using the BARC–TIFR Pelletron–LINAC accelerator facility is given. The data were analysed using deformation-dependent particle transmission coefficients, binding energies and level densities which are incorporated in the code JOANNE2 to extract fission time-scales and mean deformation of the saddle-to-scission emitter. The neutron, light charged particle and GDR γ-ray multiplicity data could be explained consistently. The emission of neutrons seems to be favoured towards larger deformation as compared to charged particles. The pre-saddle time-scale is deduced as (0–2) × 10−21 s whereas the saddle-to-scission time-scale is (36–39) × 10 −21 s. The total fission time-scale is deduced as (36–41) × 10 −21 s.

Overview of research by the fission group in Trombay

Nuclear fission studies in Trombay began nearly six decades ago, with the commissioning of the APSARA research reactor. Early experimental work was based on mass, kinetic energy distributions, neutron and X-ray emission in thermal neutron fission of 235U, which were carried out with indigenously developed detectors and electronics instrumentation. With the commissioning of CIRUS reactor and the availability of higher neutron flux, advanced experiments were carried out on ternary fission, pre-scission neutron emission, fragment charge distributions, quarternary fission, etc. In the late eighties, heavy-ion beams from the pelletron-based medium energy heavy-ion accelerator were available, which provided a rich variety of possibilities in nuclear fission studies. Pioneering work on fragment angular distributions, fission time-scales, transfer-induced fission, γ-ray multiplicities and mass–energy correlations were carried out, providing important information on the dynamics of the fission process. More recently, work on fission fragment γ-ray spectroscopy has been initiated, to understand the nuclear structure aspects of the neutron-rich fission fragment nuclei. There have also been parallel efforts to carry out theoretical studies in the areas of shell effects, superheavy nuclei, fusion–fission dynamics, fragment angular distributions, etc. to complement the experimental studies. This paper will provide a glimpse of the work carried out by the fission group at Trombay in the above-mentioned topics.

Detector-Response Correction of Two-Dimensionalγ-Ray Spectra from Neutron Capture

The neutron-capture reaction produces a large variety of γ-ray cascades with different γ-ray multiplicities. A measured spectral distribution of these cascades for each γ-ray multiplicity is of importance to applications and studies of γ-ray statistical properties. The DANCE array, a 4π ball of 160 BaF2 detectors, is an ideal tool for measurement of neutron-capture γ-rays. The high granularity of DANCE enables measurements of high-multiplicity γ-ray cascades. The measured two-dimensional spectra (γ-ray energy, γ-ray multiplicity) have to be corrected for the DANCE detector response in order to compare them with predictions of the statistical model or use them in applications. The detector-response correction problem becomes more difficult for a 4π detection system than for a single detector. A trial and error approach and an iterative decomposition of γ-ray multiplets, have been successfully applied to the detector-response correction. Applications of the decomposition methods are discussed for two-dimensional γ-ray spectra measured at DANCE from γ-ray sources and from the 10B(n, γ) and 113Cd(n, γ) reactions.

γ probe of nuclear dissipation

The Langevin model is applied to investigate the roles of excitation energy and system size in the evolution of post-saddle giant dipole resonance (GDR) γ-ray multiplicity (Mγ) with post-saddle friction strength (β). It is demonstrated that Mγ is more sensitive to β at high energy. Furthermore, it is shown that the dependence of γ emission on friction is sensitive to the size of fissioning nuclei, and a large system size significantly increases the sensitivity. Our findings indicate that in experiments, to tightly constrain post-saddle dissipation through the γ probe, it is optimal to produce heavy fissioning systems with high energy.