Measurement Of Fission Cross Section Research Articles

Cross section measurement for the 232Th(n, f ) reaction in the 4.50−5.40 MeV region using a time projection chamber* *This study was financially Supported by the National Natural Science Foundation of China (12075008), the Key Laboratory of Nuclear Data foundation (6142A08200103), the Basic and Applied Basic Research Foundation of Guangdong Province, China (2021B1515120027), and the State Key Laboratory of Nuclear

Accurate cross sections of neutron induced fission reactions are required in the design of advanced nuclear systems and the development of fission theory. Time projection chambers (TPCs), with their track reconstruction and particle identification capabilities, are considered the best detectors for high-precision fission cross section measurements. The TPC developed by the back-streaming white neutron source (Back-n) team of the China Spallation Neutron Source (CSNS) was used as the fission fragment detector in measurements. In this study, the cross sections of the 232Th(n, f) reaction at five neutron energies in the 4.50−5.40 MeV region were measured. The fission fragments and α particles were well identified using our TPC, which led to a higher detection efficiency of the fission fragments and smaller uncertainty of the measured cross sections. Ours is the first measurement of the 232Th(n, f) reaction using a TPC for the detection of fission fragments. With uncertainties less than 5%, our cross sections are consistent with the data in different evaluation libraries, including JENDL-4.0, ROSFOND-2010, CENDL-3.2, ENDF/B-VIII.0, and BROND-3.1, whose uncertainties can be reduced after future improvement of the measurement.

Measurement of the neutron-induced fission cross section of $$^{243}$$Am relative to $$^{235}$$U in the neutron energy range of 0.3–500 MeV and its analysis

Measurement of the neutron-induced fission cross section of $$^{243}$$Am relative to $$^{235}$$U in the neutron energy range of 0.3–500 MeV and its analysis

Fission cross-section measurements for the 238U(n,f)97m+gNb, 238U(n,f)133gTe and 238U(n,f)130gSb reactions induced by D-T neutrons

In this study, we conducted measurements of the independent fission cross-sections of 238U(n, f)97m+gNb, 238U(n, f)133gTe reactions and the cumulative cross section of 238U(n, f)130gSb reactions induced by neutron at energies around 14 MeV, i.e., 14.1 ± 0.3, 14.5 ± 0.3 and 14.7 ± 0.3 MeV. The measurement results were obtained by the neutron activation method in combination with off-line γ-ray spectrometry techniques. The neutron flux was monitored on line by the accompanying α-particle from T(d, n)4He reaction, and the neutron energies were determined by the cross-section ratio of 90Zr(n, 2n)8+gZr to 93Nb(n, 2n)92mNb reactions. The independent fission cross-sections of the fission reactions were obtained by subtracting the influence of precursor nuclei or excited states. The obtained results are as follows: for 238U(n, f)97m+gNb, the independent cross sections are 1.0 ± 0.89, 0.98 ± 0.85 and 0.78 ± 0.70 mb at the specified neutron energy points. For 238U(n, f)133gTe, the independent fission cross-sections are 26.8 ± 2.8, 27.7 ± 2.9 and 20.5 ± 2.3 mb, respectively, at the same neutron energy points. As for 238U(n, f)130gSb, the obtained cumulative fission cross-sections are 5.35 ± 0.58, 5.05 ± 0.53 and 4.03 ± 0.44 mb, respectively, at the specified neutron energy points.

Experimental setup of the 239Pu neutron capture and fission cross-section measurements at n_TOF, CERN

The experimental setup of the new measurement of 239Pu fission and capture cross-section in the n_TOF time-of-flight facility at CERN is presented. The measurement aims to address the needs and demands of nuclear data users. The experiment incorporates an innovative fast Fission Fragment Detector and the n_TOF Total Absorption Calorimeter, enabling the implementation of the fission tagging technique. Preliminary results exhibit the robust performance of the detector systems, along with the high quality of the new 239Pu samples. These samples were exclusively produced for this measurement by the European Commission’s Joint Research Centre in Geel.

The n_TOF facility at CERN

The neutron Time-of-Flight facility (n_TOF) is an innovative facility operative since 2001 at CERN, with three experimental areas. In this paper the n_TOF facility will be described, together with the upgrade of the facility during the Long Shutdown 2 at CERN. The main features of the detectors used for capture fission cross section measurements will be presented with perspectives for the future measurements.

Measurement of cross section for the 232Th(n, f) reaction using a time projection chamber

Accurate cross sections of neutron induced fission reactions are needed in the development of nuclear science and technology. The time projection chamber (TPC) is viewed as the potential detector to improve the measurement accuracy of the fission cross sections based on its track reconstruction and particle identification capabilities. The TPC developed by the back-streaming white neutron source (Back-n) team of China Spallation Neutron Source (CSNS) was introduced to verify its ability in measuring the cross section of fission reaction. Using our TPC, and based on the mono-energetic neutron source at Peking University and 232Th/238U samples, we have measured the cross section of the 232Th(n, f) reaction at 5.0 MeV. The fission events have been well distinguished from the background alpha events. The present cross section is consistent with the evaluation data from different libraries, which indicates that the fission cross section measurement using our TPC is feasible. By reducing the distance between the two fission samples, the large uncertainty of the present result will be reduced in future experiments.

A detector system for `absolute' measurements of fission cross sections at n_TOF in the energy range below 200 MeV

A new measurement of the 235U(n,f) cross section was performed at the neutron time-of-flight facility n_TOF at CERN. The experiment focused on neutron energies from 20 MeV to several hundred MeV, and was normalized to neutron scattering on hydrogen. This is a measurement first of its kind at this facility, in an energy range that was until now not often explored, so the detector development phase was crucial for its success. Two detectors are presented, a parallel plate fission chamber (PPFC) and a recoil proton telescope (RPT), both dedicated to perform measurements in the incident neutron energy range from 30 MeV to 200 MeV. The experiment was designed to minimize statistical uncertainties in the allocated run time. Several efforts were made to ensure that the systematic effects were understood and under control. The results show that the detectors are suited for measurements at n_TOF above 30 MeV, and indicate the path for possible future lines of development.

Determination of the number of 235U target nuclei in the irregular target using a fission time projection chamber

Based on multiple measurements of ionization loss, the Time Projection Chamber (TPC) combines strong tracking ability with particle identification ability in a large momentum range, which is an important advantage of TPC detection technology over traditional ionization measurement technology. According to these two characteristics of TPC, applying it to the measurement of fission cross-section can greatly improve the measurement accuracy. During the measurement of the fission cross-section, the number of target nuclei is required to be accurately measured. So this paper introduces a method for measuring the number of 235U target nuclei using a fission TPC system. The measurement result agrees with the reference value, and relative error is around 1 %.

Progress in measurements of fission cross sections and total cross sections at CSNS Back-n white neutron source

The neutron-induced cross sections are of great significance for the design of nuclear devices and advanced reactors for the nuclear energy production. At CSNS Back-n white neutron source, new measurements of the fission cross sections and total cross sections are performed with two sets of Day-one spectrometers based on the multi-cell fast fission ionization chamber (FIC). The neutron-induced 236,238U fission cross sections relative to 235U from the fission threshold energy to 200 MeV were measured by using the TOF method and the Fast Ionization Chamber Spectrometer for Fission Cross Section Measurement (FIXM) in the single/double bunch mode of Back-n. The experimental uncertainties are analyzed in detail, and the results from the two modes are consistent. The measured 236,238U/235U fission cross section ratios are compared with previous experiments and evaluations. The 236,238U(n,f) cross sections are obtained based on the standard 235U fission cross section. The neutron total cross sections of carbon and aluminum in the energy region from 1 eV to 20 MeV have been measured by using the TOF method and transmission method based on the Neutron Total Cross Section Spectrometer (NTOX) in the double bunch mode. The total cross section results after unfolding are in good agreement with the previous measurements as well as the broadening of the ENDF/B-Ⅷ.0 evaluation with Gaussian function within the experimental uncertainty. The present results provide the experimental data for further measurements, relevant evaluations and the design of nuclear system.

Fission cross-section measurement for [formula omitted] and [formula omitted] in [formula omitted] reaction induced by 14MeV D-T neutrons

In this work, the independent fission cross-sections of U(n,f)238Xe135g and U(n,f)238Xe135m reactions induced by neutrons with the energies of 14.1 MeV, 14.5 MeV, and 14.7 MeV were measured by activation methods. The neutrons from T(d,n)He4 were used in the experiments and their energies were determined by the ratio of Zr(n,2n)90Zr89 and Nb(n,2n)93Nb92m reaction cross-sections. Aluminum films were chosen as reference samples to measure the neutron fluence relative to the cross section of the Al(n,α)27Na24 reaction. The effect of self-absorption, geometry, and cascade coincidence were also considered during the data analysis. Besides, the increase in the daughter nuclide yield due to the decay of the parent nuclides in the same decay chain was deducted. As a result, the independent fission cross-sections of the U(n,f)238Xe135g reaction are 2.54 ± 0.14 mb, 3.05 ± 0.19 mb and 2.94 ± 0.19 mb, while the cross-sections of U(n,f)238Xe135m reaction are 2.11 ± 0.16 mb, 2.47 ± 0.18 mb and 2.34 ± 0.21 mb for 14.1 MeV, 14.5 MeV and 14.7 MeV neutrons, respectively. This work provides experimental data for the database of nuclear fission reactions.

Measurement of neutron-induced fission cross sections of 232Th from 1 to 300 MeV at CSNS Back-n

232Th/233U fuel cycle is an alternate candidate for future nuclear energy. Neutron-induced fission cross section of 232Th is one of the important nuclear data if using thorium as the fuel in the future. 232Th(n, f) cross sections from 1 to 300 MeV were measured at China Spallation Neutron Source (CSNS) Back-streaming neutron facility (Back-n) relative to 235U(n, f) and n-p scattering. A fast ionization chamber for fission cross section measurement (FIXM) and a proton recoil telescope (PRT) were used to perform the measurement. The neutron energy in this measurement reaches up to 300 MeV which is supposed to be the highest among the current Experimental Nuclear Reaction Data (EXFOR) library. It stands as the only experimental data in the region of 200-300 MeV in EXFOR as well. The experimental and evaluated data of 232Th(n, f) cross section above 60 MeV are scarce, the measurement data of this work will be valuable references for future evaluation in high energy. For the data below 60 MeV, most of our data are more consistent with ENDF/B-VIII.0, excepting in the region of 1-2 MeV where our data are more in favor of CENDL-3.2.

Simulation and data analysis of a fission time projection chamber based on Monte Carlo method

In this study, we use Monte Carlo method to conduct simulation research on a time projection chamber (TPC) which used for fission cross-section measurement. Based on Garfield, SRIM, COMSOL and other platforms and software, we explore the physical process during its actual operation, and analyze the simulation data. We carry out α particle track measurement experiments with U-235 ultra-thin target, and the measured results are in good agreement with the simulation results. This paper focuses on the simulation and reconstruction of particle tracks at different emission angles, and introduces the concept of ballistic deficit to correct the experimental measurement results. The corrected 2D distribution of particle track length and energy is closer to the theoretical model than the uncorrected distribution.

Detector set up for the measurements of the neutron-induced fission cross section of 235U relative to n-p scattering up to 150 MeV at CERN-n_TOF

A new measurement of the 235U(n,f) fission cross section was carried out at n_TOF. The experiment covered the neutron energy range from 10 MeV up to 500 MeV, and it used the 1H(n,n) cross section as normalization for the neutron fluence measurement. In this contribution, the measurements and the characterization of the detectors covering the incident energy range up to 150 MeV are discussed.

Measurement of neutron-induced fission cross sections of 235U and 238U relative to n-p scattering at CSNS Back-n facility

235U and 238U are very important isotopes in the nuclear energy system. Their neutron-induced fission cross sections have been measured intensively and evaluated as standard up to 200 MeV. However, as a matter of fact, the experimental data in the high-energy region are scarce. This work reports the measurement of 235, 238U(n, f) cross sections relative to n-p scattering performed at the China Spallation Neutron Source (CSNS) back-streaming neutron facility (Back-n). Preliminary results of 235, 238U(n, f) cross sections from 10 to 66 MeV are obtained, which are generally following the shape of the IAEA standard. However, significant discrepancies are observed at some given energies, which will be further studied.

Neutron induced fission cross section measurements of $$^{240}$$Pu and $$^{242}$$Pu relative to the neutron–proton scattering cross section at 2.5 and 14.8 MeV

Neutron induced fission cross section measurements of $$^{240}$$Pu and $$^{242}$$Pu relative to the neutron–proton scattering cross section at 2.5 and 14.8 MeV

6Li(n,t)α reaction event-identification for the 235U(n,f)/6Li(n,t) cross section ratio measurement in the NIFFTE fissionTPC

While nuclear data play an important role in nuclear physics applications, it has become important to have a better understanding of the data and try to minimize the uncertainties. In particular, there is a need for precision neutron-induced fission cross section measurements on fissile nuclei. Neutron-induced fission cross sections are typically measured as ratios, with a well-known standard in the denominator. While the 235U(n,f) reaction is a well measured standard, some light particle reactions are also well-known and their use as reference can provide information to remove shared systematic uncertainties that are present in an actinide-only ratio. A recent measurement of the 235U(n,f) reaction using as a reference the standard 6Li(n,t) reaction, was conducted at the Los Alamos Neutron Science Center using the NIFFTE collaboration’s fission time projection chamber (fissionTPC). The fissionTPC is a 2×2π charged particle tracker designed for measuring neutron-induced fission. Detailed 3D track reconstruction of the reaction products enables evaluation of systematic effects and corresponding uncertainties which are less directly accessible by other measurement techniques. This work focuses on the analysis for the event identification of the 6Li(n,t)α reaction in the fissionTPC.

Systematic Distortion Factor and Unrecognized Source of Uncertainties in Nuclear Data Measurements and Evaluations

Each experiment provides new information about the value of some physical quantity. However, not only measured values but also the uncertainties assigned to them are an important part of the results. The metrological guides provide recommendations for the presentation of the uncertainties of the measurement results: statistics and systematic components of the uncertainties should be explained, estimated, and presented separately as the results of the measurements. The experimental set-ups, the models of experiments for the derivation of physical values from primary measured quantities, are the product of human activity, making it a rather subjective field. The Systematic Distortion Factor (SDF) may exist in any experiment. It leads to the bias of the measured value from an unknown “true” value. The SDF appears as a real physical effect if it is not removed with additional measurements or analysis. For a set of measured data with the best evaluated true value, their differences beyond their uncertainties can be explained by the presence of Unrecognized Source of Uncertainties (USU) in these data. We can link the presence of USU in the data with the presence of SDF in the results of measurements. The paper demonstrates the existence of SDF in Prompt Fission Neutron Spectra (PFNS) measurements, measurements of fission cross sections, and measurements of Maxwellian spectrum averaged neutron capture cross sections for astrophysical applications. The paper discusses introducing and accounting for the USU in the data evaluation in cases when SDF cannot be eliminated. As an example, the model case of 238U(n,f)/235U(n,f) cross section ratio evaluation is demonstrated.

Measurement of fission cross sections for 232Th(n,f)[formula omitted] reaction around the neutron energy of 14 MeV

Neutron induced fission cross sections of 232Th(n,f)84Se, 232Th(n,f)84mBr, 232Th(n,f)84gBr reactions were measured based on neutrons from the D-T source. The α-particles emitted from the T(d,n)4He reaction were measured to monitor the neutron flux, while the ratio of 90Zr(n,2n)89Zr to 93Nb(n,2n)92mNb reactions was used to determine the neutron energy. The gamma-ray activity of samples was measured with a well calibrated HPGe-γ detector. In the 232Th(n,f) reaction at the neutron energies of 14.1 ± 0.3, 14.5 ± 0.3 and 14.7 ± 0.1 MeV, the cross sections are 2.74 ± 0.23, 2.75 ± 0.25, and 2.30 ± 0.21 mb for 84mBr, 3.41 ± 0.37, 3.35 ± 0.37, and 3.81 ± 0.42 mb for 84gBr, and roughly 8.79 ± 0.58, 9.36 ± 0.62, and 9.26 ± 0.62 mb for 84Se, respectively.

Fission cross-section measurement for the 238U(n,f)89Rb reaction induced by D-T neutrons

The fission reactions of 238U induced by D-T neutrons were investigated by neutron activation technique and low-background HPGe-γ spectrometer. The half-life was used to identify the possible daughter nuclide. The fission cross-sections of 238U(n,f)89Rb reaction induced at the neutron energy around 14 MeV, i.e., 14.1 ± 0.3, 14.5 ± 0.3 and 14.7 ± 0.3 MeV, were measured precisely. The neutron flux was monitored by accompanying α-particle of the T(d,n)4He reaction and the neutron energies were determined by the cross-section ratio of 90Zr(n,2n)89Zr to 93Nb(n,2n)92mNb reaction. The fission cross-sections of the 238U(n,f)89Rb reaction are 33.2 ± 2.1 mb, 32.2 ± 2.0 mb, and 32.6 ± 2.1 mb, corresponding to the above neutron energy points.

MicroMegas-based detectors for time-of-flight measurements of neutron-induced reactions

MicroMegas detectors are versatile gaseous detectors which are used for ionizing particle detection. A MicroMegas detector consists of two adjacent gas-filled volumes. One volume acts as a drift region with an electric field operating in the ionization chamber regime, the second volume is the amplification region acting as a parallel-plate avalanche counter. The use of the microbulk technique allows the production of thin, radiation resistant, and low-mass detector with a highly variable gain. Such MicroMegas detectors have been developed and used in combination with neutron time-of-flight measurements for in-beam neutron-flux monitoring, fission and light-charged particle reaction cross section measurements, and for neutron-beam imaging. An overview of MicroMegas detectors for neutron detection and neutron reaction cross section measurements and related results and developments will be presented.