Fission Of 235U Research Articles

Energy Dependence of the Most Stable Nuclei Production in Proton-Induced 238U and 232Th Fission

Using the available experimental data, production cross sections of the most stable nuclei have been calculated for the proton-induced fission of 238U and 232Th at 12, 20, 35, 50, 96 MeV in case of 238U and at 8, 9.3, 12, 19.55, 32.2, 44.7, 53 MeV for 232Th. The analysis has been carried out for the fission fragment mass ranges corresponding to N/Z ratios in the ranges 1.33 ± 0.09 and 1.32 ± 0.08 for 238U and 232Th respectively. Results have been compared with the ones generated indirectly by employing GEF nuclear reaction code, version 2017/1.1. From the production cross sections point of view, for the same energy, 232Th is found to be a better target than 238U for producing nuclei A around the symmetric mass peak, while 238U comes out to be a better one than 232Th for producing the fission fragments around the asymmetric peaks of the mass distribution.

Lifetimes and shape-coexisting states of Zr99

Lifetimes of intermediate-spin states in two rotational bands of 99Zr have been measured. These states were populated following the neutron-induced fission of 235U at the PF1B beamline of the Institut Laue-Langevin, Grenoble, during the EXILL-FATIMA campaign. The nucleus 99Zr59 exhibits shape coexistence and lies precisely on the border of an abrupt change in ground-state deformation when going from N=58 to N=60, making its study interesting for understanding the mechanisms involved in the rapid onset of deformation here. The B(E2) values extracted for decays in the ν3/2[541] band allow quadrupole deformations of β2=0.34(1) and 0.26(3) to be determined for the 821.6- and 1236.6-keV members, whereas β2=0.32(3) was found for the 850.5-keV member of the ν3/2[411]band. Some of the excited states known in 99Zr have been reasonably described with interacting boson-fermion model (IBFM) calculations. Type-II shell evolution is proposed to play a major role in modifying single-particle energies in 99Zr.

The science case of the FRS Ion Catcher for FAIR Phase-0

The FRS Ion Catcher at GSI enables precision experiments with thermalized projectile and fission fragments. At the same time it serves as a test facility for the Low-Energy Branch of the Super-FRS at FAIR. The FRS Ion Catcher has been commissioned and its performance has been characterized in five experiments with 238U and 124Xe projectile and fission fragments produced at energies in the range from 300 to 1000 MeV/u. High and almost element-independent efficiencies for the thermalization of short-lived nuclides produced at relativistic energies have been obtained. High-accuracy mass measurements of more than 30 projectile and fission fragments have been performed with a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) at mass resolving powers of up to 410,000, with production cross sections down to the microbarn-level, and at rates down to a few ions per hour. The versatility of the MR-TOF-MS for isomer research has been demonstrated by the measurement of various isomers, determination of excitation energies and the production of a pure isomeric beam. Recently, several instrumental upgrades have been implemented at the FRS Ion Catcher. New experiments will be carried out during FAIR Phase-0 at GSI, including direct mass measurements of neutron-deficient nuclides below 100Sn and neutron-rich nuclides below 208Pb, measurement of β-delayed neutron emission probabilities and reaction studies with multi-nucleon transfer.

Rapid concentration and isotopic measurements of ultra-trace 235U fission products with comparison to an ORIGEN isotope depletion model

This article presents the application of an automated online separation–direct analysis method, RAPID (Rapid Analysis of Post-Irradiation Debris), for the simultaneous measurement of both radioactive and stable fission isotopes from an irradiated highly-enriched uranium target. Developed for the measurement of the concentration and isotopic composition of over 40 elements down to the femtogram level, the RAPID method possesses the sensitivity, stability, and precision required to achieve accurate, low-level analyses of elements of non-natural origin. The isotopic compositions and concentrations of key fission elements cesium, strontium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, and samarium have been measured repeatedly over a six-week period. The validity of these measurements was confirmed using ORIGEN (Oak Ridge Isotope GENeration), an isotope depletion and decay modeling software, to within 1–3%.

Measurement of the prompt neutron spectrum from thermal-neutron-induced fission in U-235 using the recoil proton method

A measurement of the 235U prompt fission neutron spectrum (PFNS) by the recoil proton method was performed at the Institute of Nuclear Physics and Chemistry, China. Details of the method, which include the calculation and validation of the response matrix, are presented. The PFNS for 235U in the energy range 1–12 MeV, induced by thermal neutrons, was obtained. The measured spectrum in the low-energy region was in good agreement with previous work and the ENDF/B-VII library, except for minor differences. In the high-energy region, however, the relative height of the measured spectrum was greater, and an analysis of the experiment indicated uncertainties of 13% at 10 MeV and 24% at 12 MeV. Experimental results showed that the recoil proton method could be used to measure prompt fission neutron spectra. Some directions for future work are included.

Behavior of the average prompt neutron multiplicity as a function of post-neutron fragment mass in correlation with the pre-neutron fragment mass distribution in thermal neutron induced fission of 235U and 233U

Abstract A Monte Carlo simulation is performed in order to correlate the average prompt neutron multiplicity as a function of post- and pre-neutron fragment mass ( n - ( m ) and ν - ( A ) , respectively). This is applied for 235,233U(nth,f). The input of the simulation consists of quantities related to pre-neutron fragments, i.e. the mass yield Y ( A ) , the average kinetic energy E - ( A ) , its standard deviation σ E ( A ) and a function ν - s ( A ) (composed by three jointed segments) which approximates the sawtooth shape of the experimental prompt neutron multiplicity ν - ( A ) . The ratio of neighboring mass yields R A = Y ( A + 1 ) / Y ( A ) is introduced. It is found that n - ν - s ( n - > ν - s ) approximately in the same ranges of A where R 1 ( R > 1 ) . The average prompt neutron multiplicity as a function of fragment mass N - μ measured by using the 2 E method is also simulated. Its behaviour is similar to the one mentioned above.

Investigation of the chance structure of the fission cross section of 238U by neutrons in energy range from 14 to 18 Mev using the delayed neutrons

In the present work, delayed neutrons are used for the investigation of the chance structure of the fission cross section. For this, time parameters of delayed neutron precursors emitted from the fission of 238U by neutrons with the energies from 14 to 18 MeV have been measured. The T(d,n) reaction was used as a neutron source. The experimental data have been processed to account the effect of degradation of detector counting rate in high intensity neutron flux and the effect of concomitant neutron source D(d,n) caused by implanted deuterium ions in neutron target. The data obtained based on the time parameters of delayed neutron precursors have been used in the analysis of the chance structure of the fission cross section of the 238U.

A novel concept for a molten salt reactor moderated by heavy water

The Heavy Water moderated Molten Salt Reactor (HW-MSR) is a novel concept of a thermal heterogeneous nuclear reactor and pursues for Thorium-Uranium (Th-U) breeding. It adopts heavy water rather than graphite as moderator while employs the same liquid fuel of molten salt reactor (MSR). Thus this new concept inherits the positive properties of MSR (feasible for online reprocessing) and heavy water reactor (high neutron moderating ratio). Furthermore it can address the problems of depleted graphite management and positive temperature coefficient due to neutron spectral shift propitious to 233U fission existed in Molten Salt Breeding Reactor (MSBR). HW-MSR consists of the primary loop system, intermediate cooling loop, energy conversion system, external cooling system and online reprocessing system. Since there is a huge temperature difference between molten salt (higher than 600 °C) and heavy water (lower than 100 °C to keep high density) in the core, effectively preventing the heat transfer between them is one main challenge. To address this problem, a thermal insulator made of Yttria Stabilized Zirconia (YSZ) is applied and analyzed. The calculation results show that both the fuel salt and moderator outlet temperature across the core can satisfy the design requirements. Similar to a traditional MSR, the HW-MSR also implements an online reprocessing system which can online extract and recycle useful fuel during operation, providing a feasible approach for Th-U fuel cycle. In addition, because of the outstanding neutron performance of heavy water moderator, a small initial 233U loading mass is required for HW-MSR, and its breeding ratio can achieve 1.073, corresponding to a doubling time of 12 years at the reprocessing cycle of 10 days. Compared with traditional light water reactor (LWR) whose transuranium (TRU) production is 69 kg/GWy, HW-MSR produces only 0.51 kg/GWy. This much lower radiotoxicity of nuclear waste in the HW-MSR would significantly enhance the sustainability of nuclear energy.

A Thorium Reactor Antineutrino Spectrum Analysis

Antineutrino monitoring of nuclear reactors for nonproliferation applications traditionally asses the plutonium inventory. When applied to thorium reactors the diversion 233U, bred through neutron capture on 232Th, becomes the material of interest. In the absence of experimental data, the antineutrino emission from the fission of 233U is estimated ab initio from known beta energy endpoints and fission yields for 233U. Using the derived antineutrino spectrum and rate evolution, the antineutrino emission under normal conditions and an anomalous scenario was compared to determine the time necessary to detect diversion of a significant quantity of 233U.

Scission point model for the mass distribution of ternary fission

A modified scission point model is adopted to study the mass distribution of thermal neutron induced binary and ternary fission of 235U. The scission configuration and the most favourable fragment deformation is identified through an energy balance criterion where the macroscopic part due to liquid drop and the microscopic part due to shell correction together with the deformation dependent interaction potential are used. The available energy for each channel together with fragment deformation is used to evaluate nuclear level densities in the Fermi gas model. Since the model is found to give the expected double humped mass distribution for binary fission of 236U, this is then applied for the ternary fission of the same nuclei with fixed third fragment. Two different third fragments with two cases of collinear arrangement were studied with the model. The obtained ternary mass distribution was then compared with the calculated binary mass distribution. In all the cases, the influence of shell effects is found to be prominent with one of the fragments associated with the Sn nucleus. The closed shell nuclei possess maximum yield in both binary and ternary mass distribution.

ВРЕМЕННАЯ ЗАВИСИМОСТЬ АКТИВНОСТИ ЗАПАЗДЫВАЮЩИХ НЕЙТРОНОВ И ГРУППОВЫЕ ПАРАМЕТРЫ В 6- И 8-ГРУППОВОМ ПРЕДСТАВЛЕНИИ ПРИ ДЕЛЕНИИ 235U, 238U И 239Pu ТЕПЛОВЫМИ И БЫСТРЫМИ НЕЙТРОНАМИ

In the present work the digital data on decay curves of delayed neutron intensity, measured for the fission of 235U, 238U and 239Pu by thermal and fast neutrons, is presented. The estimation of time parameters of delayed neutrons in 6 and 8 groups representation have been made on the base of individual experimental series using iterative least squares technique. It have been shown, that uncertainties of the parameters estimation in the 8 group representation, obtained on the basis of the experimental data are comparable with the uncertainties of the 6-group representation. The experimental data measured in the wide range of the time after the end of irradiation - (0,1-700 s) are of significant interest for intercomparison and validation of the different mathematical methods and programs, used for the processing of the decay curves of delayed neutron intensity, and also for analysis of the experimental data in the process of formulating of the evaluated data on relative abundances and half-lives of the delayed neutron precursors for the wide range of the fissioning nuclides.

Sensitivity and uncertainty analysis on the first core criticality of the RSG GAS multipurpose research reactor

The results of criticality, sensitivity and uncertainty (S/U) analyses on the 1st core criticality of the Indonesian 30 MWth Multipurpose Reactor RSG GAS (MPR-30) using the recent nuclear data libraries (ENDF/B-VII.1 and JENDL-4.0) and analytical tools available at present (Whisper-1.1) are presented. Two groups of criticality benchmark cases have been carefully selected from the experiments conducted during the first criticality approach and control rod calibrations. The C/E values of k (effective neutron multiplication factor) for the worst case is found around 1.005. Large negative sensitivities are found in (n,γ) reaction of H-1, U-235, Al-27, U-238, and Be-9 while large positive sensitivities are found in U-235 (total nu and fission), H-1 (elastic), Be-9 (free gas, elastic) and H-1 S(α,β) (lwtr.20t, inelastic). The energy dependency of the sensitivities is also presented and discussed in detail. From the S/U analysis, it is found that the uncertainties of k due to the nuclear data are about 0.6%, which are comparable to the [C/E−1] values. k Differences in the sensitivities amongst the two nuclear data libraries are also identified, and recommendation for improving the nuclear data library is given.

Rapid measurements of 235U fission product isotope ratios using an online, high-pressure ion chromatography inductively coupled plasma mass spectrometry protocol with comparison to isotopic depletion models

An automated online separation–direct analysis method, RAPID (rapid analysis of post-irradiation debris), has been developed for the measurement of the concentration and isotopic composition of over 40 elements down to the low-picogram level. Here we discuss the application of RAPID to irradiated highly-enriched uranium, demonstrating that it has the sensitivity required to achieve precise, low-level analyses of non-natural isotopes, even in the presence of a bulk uranium matrix. Isotopic ratios have been successfully measured at the low-picogram level, and the accuracy of these ratios was confirmed using an isotopic depletion and decay modeling software to within 1–2%.

Parameter optimization and uncertainty analysis of [formula omitted] for spontaneous fission

In this paper we report on an effort to determine an optimal parameter set for the complete event fission model FREYA to reproduce spontaneous fission of 252Cf(sf), 244Cm(sf), 238Pu(sf), 240Pu(sf), 242Pu(sf), and 238U(sf). Earlier studies have partially optimized the event-by-event fission model FREYA with respect to the available experimental data using brute force computational techniques. We have confirmed and expanded these results using a least-squares minimization based on the simulated annealing approach. We have also developed a more complete statistical picture of this optimization, consisting of a full correlation matrix for the parameters utilized by FREYA. The newly improved parameter values themselves, along with this correlation matrix, have led to a more well-developed physical picture of the fission process.

Prompt Fission Neutron Investigation in 235U(nth,f) and 252Cf(sf) Reactions

The prompt neutron emission in thermal neutron induced fission of 235U and spontaneous fission of 252Cf was investigated by using digital signal electronics. The goal was to check a new revised data analysis software with fission fragment (FF) kinetic energy corrections after prompt fission neutron (PFN) emission. The revised software was used to reanalyze old data measured in EC-JRC-IRMM, where 252Cf(sf) reaction was investigated. Both measurements were done using similar twin Frisch grid ionization chamber for fission fragment detection with equivalent NE213 fast neutron detector. About 0.5*106 FF with PFN coincidences have been analyzed in both measurements. The fission fragment kinetic energy, mass and angular distribution were investigated along with prompt neutron time of flight and pulse shape analysis using a six channel synchronous waveform digitizer (WFD) with sampling frequency of 250 MHz and 12 bit resolution in the 235U(nth,f) reaction. Similar WFD with sampling frequency of 100 MHz was used for PFN investigation in 252Cf(sf) reaction. These two experiments were considered as a reference for further investigations with a new setup composed of position sensitive ionization chamber to detect FF and an array of 32 liquid scintillators recently constructed in Dubna to detect neutrons.

Modelling of the reactor cycle cost for thorium-fuelled PWR and environmental aspects of a nuclear fuel cycle

The paper presents the methodology applied to the cost modelling of the uranium-thorium nuclear reactor cycle for PWR reactors as well as brief introduction to the environmental impact of the nuclear fuel cycle. The reactor core contains seed uranium fuel and blanket thorium fuel. In such a cycle, energy is produced in the fission of 235U included in the fresh fuel and in the fission of 233U bread from the fertile 232Th. A modified methodology developed by the OECD Nuclear Energy Agency was used for the reactor cycle cost modelling. The method is based on the levelized lifetime cost methodology for a reactor cycle, which is directly related to the heavy metal mass balance. Contrary to the case of uranium-fuelled nuclear reactors, the cost modelling includes the additional cash flow for thorium fuel. The abundance of thorium in the Earth’s crust is about 3–5 times larger than that of uranium, which suggests its promising potential as a nuclear fuel. However, this needs to be proved economically.

Prompt and Delayed Neutron Emissions and Fission Product Yield Calculations with Hauser-Feshbach Statistical Decay Theory and Summation Calculation Method

We demonstrate the neutron emission and fission product yield calculations using the Hauser–Feshbach Fission Fragment Decay (HF3D) model and β decay. The HF3D model calculates the statistical decay of more than 500 primary fission fragment pairs formed by the neutron induced fission of 235U. In order to calculate the prompt neutron and photon emissions, the primary fission fragment distributions, i.e. mass, charge, excitation energy, spin and parity are deterministically generated and numerically integrated for all fission fragments. The calculated prompt neutron multiplicities, independent fission product yield are fully consistent each other. We combine the β-decay and the summation calculations with the HF3D model calculation to obtain the cumulative fission product yield, decay heat and delayed neutron yield. The calculated fission observables are compared with available experimental data.

Shape transition in the neutron-rich Y nuclei and its evolution across the isotopic chain

The evolution of the deformation across the Y isotopic chain, in the vicinity of N = 60 boundary, has been studied using gamma spectroscopy methods. The nuclei of interest have been produced by neutron induced fission of 235U and 241Pu targets, during two experimental campaigns named EXILL and FIPPS at the Institute Laue-Langevin in Grenoble. The emitted gamma rays have been collected by HPGe and LaBr3 detectors providing the identification of the high-spin levels in the 94Y and 96Y isotopes up to 6 MeV excitation energy, as well as information about the half-lives of the in-band states in the 98Y nucleus. The obtained results shed new light on the onset of deformation in the neutron-rich Y isotopes and, in general, in the A ≈ 100 region.

Probing the nuclear structure in the vicinity of 78Ni

Theoretical and experimental studies of neutron-rich nuclei have shown that the general concept of shell structure is not as robust and universal as earlier thought, but can exhibit significant changes as a function of neutron excess. New magic numbers appear and some other conventional ones disappear mainly because of a different ordering of the single-particle orbitals. In the present contribution, recent experimental studies of neutron-rich Cu isotopes, performed at RIKEN using β decay and one-proton knockout reactions, will be discussed. Neutron-rich nuclei near 78Ni were populated through in-flight fission of 238U on thick 9Be targets in both experiments. In the β-decay study, 75,77Ni nuclei were implanted into the WAS3ABi silicon array, while γ rays from excited states in 75,77Cu emitted after β decay of the implanted ions were detected with the EURICA Ge detector array that was surrounding the active stopper. In a second experiment within the SEASTAR campaign at RIKEN, the same 75,77Cu nuclei were produced in (p,2p) knockout reactions from 76,78Zn beam particles at around 250 MeV/nucleon impinging onto the MINOS liquid hydrogen target. In the latter experiment the DALI2 NaI array was used to detect de-excitation γ rays measured in coincidence with Cu nuclei identified in the Zero Degree Spectrometer. Both studies are complimentary and greatly contribute to our understanding on the nuclear structure in the 78Ni region.

Observation of antineutrinos from 235U fission by the PROSPECT experiment at HFIR

Observation of antineutrinos from 235U fission by the PROSPECT experiment at HFIR