Fission Cross Sections Research Articles

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.

Cross-Evaluation of the PU-MET-FAST criticality benchmark experiments in ICSBEP handbook (by the end of 2022)

Criticality experiments play an important role in the fields of criticality safety, neutron transport program validation and nuclear data validation. ICSBEP handbook collects about 5000 criticality benchmark experiments. Most of the criticality benchmark experiments in ICSBEP handbook are retrospective evaluation experiments, they are evaluated long after the experiments and their evaluations may be based on inaccurate or incomplete data. When these experiments are used in nuclear data validations and cross section adjustments, contradictions between some criticality benchmark experiments have been found. Therefore, it is necessary to analyze whether these retrospective evaluation criticality benchmark experiments are applicable in the fields of nuclear data validations (including cross section adjustments) and validations of nuclear system design. To solve this problem, we have developed cross-evaluation method of criticality benchmark experiments, which could evaluate the biases of criticality benchmark experiments from the point of statistics. In this article, we used this method to cross-evaluate the PU-MET-FAST criticality benchmark experiments in ICSBEP handbook. The results indicate that there are many contradictions between the retrospective evaluation experiments in the PU-MET-FAST category. Because of the limited number of experiments in this category, the number of experiments that are similar to each other after cluster analysis is small, which reduces the effectiveness of the cross-evaluation. There are only 1 or 2 experiments in some clusters. Even if there are contradictions in these clusters, it is impossible to judge which experiment has a higher quality. Based on these results, it is recommended to do new PU-MET-FAST criticality benchmark experiments to resolve contradictions between these retrospective evaluation experiments and to help validate the nuclear data more effectively.

Measurement of fast neutron spectrum in the radial channel of VR-1 research reactor

Having knowledge of the spectrum of fast neutrons in the irradiation position of a reactor plays an important role in many experimental settings. If well described, it can be used as a reference neutron field for validating and testing measuring devices or detectors. This paper compares model calculations with measurements of the neutron spectrum in the research reactor VR-1. The fast neutron spectrum was measured in the radial channel of VR-1 reactor using a stilbene scintillation detector and the NGA-01 measuring device. The NGA-01 is a two-parameter spectrometric system for neutron and gamma radiation fields. The calculations were performed in a critical mode of the MCNP6 code using ENDF/B-VII.1 nuclear data library. Generally, a good agreement was achieved. However, a slight discrepancy in the neutron spectrum between the calculated and measured values was found in the 2–3 MeV region. In other regions, the differences between calculated and experimental values are comparable with uncertainties. Since the detector is distanced from the core, the neutron beam can be assumed parallel and therefore possible issues with stilbene anisotropy are eliminated. Thus, this experiment can be used for validation of a reactor leakage spectrum and nuclear cross sections in the energy region above 6 MeV, which is of interest for the nuclear data section of International Atomic Energy Agency.

Classification of events from [formula omitted]-induced reactions in the MUSIC detector via statistical and ML methods

The Multi-Sampling Ionization Chamber (MUSIC) detector is typically used to measure nuclear reaction cross sections relevant for nuclear astrophysics, fusion studies, and other applications. From the MUSIC data produced in one experiment scientists carefully extract an order of 103 events of interest from about 109 total events, where each event can be represented by an 18-dimensional vector. However, the standard data classification process is based on expert-driven, manually intensive data analysis techniques that require several months to identify patterns and classify the relevant events from the collected data. To address this issue, we present a method for the classification of events originating from specific α-induced reactions by combining statistical and machine learning methods that require significantly less input from the domain scientist, relative to the standard technique. We applied the new method to two experimental data sets and compared our results with those obtained using traditional methods. With few exceptions, the new method yields results such that the percent change with respect to results obtained with traditional methods are within ±20%. With the present method, which is the first of its kind for the MUSIC data, we have established the foundation for the automated extraction of physical events of interest from experiments using the MUSIC detector.

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 %.

4th-Order-SENS: A Software Module for Efficient and Exact 4th-Order Sensitivity Analysis of Neutron Transport

This work presents a software module called 4th-Order-SENS, which enables the efficient computation of exactly obtained expressions for all sensitivities, up to and including the 4th order, of a functional of the particle flux (e.g., the leakage of particles out of a body) with respect to nuclear parameters (total, scattering, and fission cross sections; nu, chi, sources; and number densities) for systems modeled by the neutron transport equation. The 4th-Order-SENS module implements the nth-Order Comprehensive Adjoint Sensitivity Analysis Methodology for Linear Systems (nth-CASAM-L), which is the only practically implementable methodology for obtaining the exact expressions of arbitrarily high-order sensitivities of model responses to model parameters, for response-coupled forward/adjoint large-scale linear systems. In addition to presenting the equations that are solved to obtain the 1st-order through 4th-order sensitivities, this work also describes the components of the module 4th-Order-SENS, including the user interface, input file, output files, and several independent code verification capabilities using symmetries and/or finite-difference formulas. The 4th-Order-SENS module is written in Python and Fortran and runs on Linux platforms. Several illustrative applications involving fixed-source problems in one-dimensional spherical and slab geometries are also presented.

Dosimetric effects of inserted non-radioactive elements in a tumor area in proton therapy

Introduction: Various prompt gamma (PG) ray-based techniques have been proposed to monitor the proton range during treatment, but the poor PG statistics produced entangle their clinical application. Recently, we developed a Monte Carlo (MC) simulation model for the enhancement of PG production based on the nuclear cross section of protons with the material transversed, via inserting the non-radioactive elements 19F, 17O, and 127I in a hypothetical tumor area. This work aimed to study the dose distribution changes caused by the addition of specific % weight fractions of PG enhancers in a water medium using MC simulations.Methods: Our MC model was created using the TOPAS MC package and retaining identical geometries, mixture compositions, and incident proton energies (75, 100, and 200 MeV, respectively) previously tested for the PG statistics enhancement. The total dose deposition in water and in mixture compositions that have been found to maximally increase the PG production was scored and evaluated based on the important dosimetric metrics R90, Bragg peak (BP) width, and full width at half maximum (FWHM). Furthermore, the spatial correlation of PG emissions relative to BPs was also studied and compared on the basis of the BP decrease at R90.Results and Discussion: There is no significant change in total dose deposition except for 127I. However, dose curve shifts in R90 toward shallower depth, followed by steeper BP and reduced FWHM, were observed in all cases. The percentage changes vary with incident proton energies and mixture compositions. The addition of the stable elements had no effect on the PG spatial emission. The dosimetric study reveals that the addition of the tested stable elements did not change the dose distribution and did not alter the dose deposited by secondary particles. Since their addition increases the electron density of the medium, the shift of BP to shallower depths is linked with the mixture composition changes. Furthermore, a steeper BP value is observed that could be beneficial for OAR avoidance. Since this theoretical study of using 19F, 17O, and 127I as PG enhancers is promising from a dosimetric point of view, experimental studies are necessary to determine their clinical application feasibility.

Sensitivity and uncertainty analysis of effective multiplication factor of KRITZ-1 benchmark using ENDF/B-VIII.0 and JEFF3-3 nuclear data libraries

Sensitivity and uncertainty analysis have been performed to estimate the uncertainty in the effective neutron multiplication factor, keff, of the KRITZ-1 benchmark and to identify which nuclear reactions and isotopes of interest could be significantly influencing it. First, the adjoint-weighted perturbation method using the KSEN card of the MCNP6 code is applied to compute the sensitivity vectors for 235U, 238U, 1H, 16O, and 10B isotopes with the JEFF-3.3 and ENDF/B-VIII.0 nuclear data libraries. Then, the sensitivity vectors and covariance matrices were combined to calculate the uncertainty in keff due to uncertainties in nuclear data. The 44 group covariance matrices have been processed with the NJOY21 system.It was found that the uncertainty in keff is mostly due to uncertainties on ν‾p , fission cross section of 235U, the capture cross section of the two isotopes 238U and 1H in the aforementioned data libraries

Phenomenological Description and Parameterization of Nucleon-Induced Fission Cross Sections of Heavy Nuclei in Intermediate and High Energy Region

Phenomenological Description and Parameterization of Nucleon-Induced Fission Cross Sections of Heavy Nuclei in Intermediate and High Energy Region

Empirical formula for (n, f) reaction cross sections of Uranium isotopes at 1–20 MeV neutrons

This article describes how to calculate neutron-induced fission reaction cross sections using a proposed empirical formula and the EMPIRE 3.2.3 and TALYS 1.95 computer codes for Uranium isotopes up to the third fission plateau. In this study, the excitation functions of 232U (n, f), 233U (n, f), 234U (n, f), 235U (n, f), 236U (n, f), 237U (n, f) and 238U (n, f) nuclear reactions were calculated at 1–20 MeV neutron energies. The results were contrasted to measured values from the Experimental Nuclear Reaction Data (EXFOR) as well as the evaluated data from Evaluated Nuclear Data File (ENDF) such as (EAF-2010, JEFF-3.3, ENDF/B-VIII.0 and TENDL-2019). Overall, the calculated, experimental, and evaluated fission cross-sections are in concordance.

A deep-learning representation of multi-group cross sections in lattice calculations

To compute few-group nodal cross sections, lattice codes must first generate multi-group cross sections using continuous energy cross-section libraries for each material in each fuel cell. Since the processing cost is significant, we propose representing the multi-group cross sections during lattice calculations using a pre-trained deep-learning-based model. The model utilizes a combination of Principal Component Analysis (PCA) and fully connected Neural Networks (NN). The model is specifically designed to manage extensive multi-group cross-section data sets, which contain data for several dozen nuclides and encompass more than 50 energy groups. Our testing of the trained model on a PWR assembly with a realistic boron letdown curve revealed an average relative error of around 0.1% for both fission and total macroscopic cross sections. The average time required for the model to generate the cross sections was approximately 0.01% of the time needed to execute the cross-section processing module.

Investigations on Coulomb fission time scales and cross sections in inverse kinematics

In inverse kinematics, we explored Coulomb fission cross-sections and time scales. Heavier projectiles such as 238U, 132Xe, and 208Pb on lighter targets such as 16O 26Mg, 27Al, 32S, 35Cl, 40,48Ca, 45Sc, 48,50Ti, 56,58Fe, 64Ni, 89Y, 30Si and 65Zn were looked into. The photofission cross-sections and the number of equivalent photons impinge on the target nuclei are important parameters in cross-section assessment. The anticipated cross-sections increases with increase in atomic number of target nuclei. We also explored the time scale of projectile nuclei at various transition levels. The estimated time scales accord well with the available experimental value, which is in the order of picoseconds. In addition, we predicted time scales of 165Ho nuclei in the transition state from 19/2+→15/2+ to 29/2+→25/2+ for which experimental time scales are not available in literature. As a result, Coulomb fission is one of the causes that has severely hampered in the formation of compound nuclei. Prediction of time scales, in particular, would aid in understanding the structure of various energy levels.

Research on Emerging Medical radionuclides from the X-sections (REMIX): The Accelerator-based Production of 47Sc, 149Tb, 152Tb, 155Tb and 161Tb

The REMIX project is focused on the cyclotron-based production of 47Sc, 149Tb, 152Tb, 155Tb and 161Tb radionuclides, whose decay characteristics make them suitable for medical applications. This work will outline the main results achieved withing the REMIX collaboration, that is organized in the following Work Packages (WP): WP1. Target manufacturing (49Ti, 50Ti and 155Gd2O3) and characterization; WP2. Nuclear cross section (XS) measurements with 49Ti and 50Ti targets for 47Sc production; WP3. Nuclear XS measurements with natDy, 159Tb and natEu targets for xxTb production; WP4. Nuclear XS modeling for 47Sc and 155Tb production; WP5. Dosimetric calculations for 47Sc- and xxTb-labelled radiopharmaceuticals; WP6. 155Tb Thick Target Yield (TTY) measurements; WP7. Apparatus design and realization for irradiation tests with the LARAMED beamline. Since the LARAMED bunkers and ancillary laboratories are currently under completion at the INFN-LNL, the nuclear XS experiments are carried out in collaboration with the GIP ARRONAX facility (Saint-Herblain, France) and the Thick Target Yield (TTY) measurements are performed at the Sacro Cuore Don Calabria hospital (SCDCh, Negrar, Verona, Italy).

Double folding analysis of the α+28Si elastic scattering system

Using the double folding model (DFM), we reanalyzed 20 sets of experimental angular distributions for the elastic scattering [Formula: see text]+[Formula: see text]Si system in a wide energy range of [Formula: see text]-particles from 12.7[Formula: see text]MeV to 240[Formula: see text]MeV. We used three effective nucleon–nucleon (NN) interactions that are CDM3Y6, São Paulo Potential (SPP2), and Brazilian Nuclear Potential (BNP) to generate the DF potentials. The data analysis was performed using semi-microscopic (SM) and fully microscopic (FM) methods. In the SM approach, the real part of the optical potential (OP) is created with the DFM, and the Woods–Saxon (WS) potential is considered for the imaginary part of the OP. In the FM approach, the DF potential renormalization factors [Formula: see text] and [Formula: see text] for the real and imaginary parts of the OP were extracted. We investigated the energy dependencies of the [Formula: see text] and [Formula: see text] factors, as well as of nuclear potential volume integrals and reaction cross-sections. We reasonably reproduced the data using [Formula: see text] and [Formula: see text] factors obtained from their energy-dependent functions.

Measurement of the neutron energy response curve of 4H-SiC detector based fission target detection system at the CSNS Back-n white neutron source

The fission target detection system, which is based on U-235(or U-238)fission target and large area 4H-SiC detector, has been developed for pulsed neutron detection. However, calibration of its neutron energy response curve is challenging due to its very low detection efficiency to fast neutrons. In the past, the calibration of the neutron sensitivity for the fission target detection system was limited to using ∼ 14 MeV neutrons generated by the Cockcroft-Walton accelerator. To obtain the response function for the complete range of neutron energies, extrapolation based on neutron fission cross sections was required. In this paper, we present the calibration of its energy response at the China Spallation Neutron Source (CSNS) Back-n beam line using the time of flight method, both with double-bunch and single-bunch mode in end-station 1(with a flight path of ∼ 55 m). The SiC detector with a thin sensitive thickness of 30 μm has lower scattering background than the traditional Si-PIN detector . As a result, the energy response curve of the fission target detection system above 0.26 MeV has been successfully acquired. The spectrum of the double-bunch mode was unfolded using the Bayesian algorithm, and the results indicate that, under conditions of sufficient counts, this method can yield results similar to those obtained from the single-bunch mode. The issue of pulse height defect of SiC detector to fission fragments is discussed. This experiment confirms that our detection system of SiC+fission target has a strong signal-to-noise ratio and anti-interference capability. At the same time, it demonstrates that this device has its own advantages in measuring the energy response of low sensitivity detectors.

Separation of 44mSc/44gSc Nuclear Isomers Based on After-Effects.

44gSc presents a particular interest for application in nuclear medicine for positron emission tomography (PET) due to its favorable nuclear decay properties (t1/2 = 3.97 h, Emax = 1.47 MeV, branching ratio 94.3% β+). Its nuclear isomer 44mSc (t1/2 = 58.61 h) decays by isomeric transition (IT) into 44gSc, accompanied by ≈12% of conversion electron emission, which can cause a partial release of the daughter 44gSc from the chelate complex. A 13 MeV cyclotron at TRIUMF was used to produce both 44mSc and 44gSc via the natCa(p,n)44m,gSc reaction. A 44mSc/44gSc generator was designed by using a Strata C-18E cartridge. After several tested systems, a successful separation method was developed using DOTATOC as a chelator, a Strata C-18E cartridge as a generator column, and an elution solution of 0.1 M NH4-α-HIB. The yield of the generator with the daughter 44gSc release was equal to 9.8 ± 1.0% (or ≈80% per portion of conversion). This result shows the important role of after-effects in the design of radionuclide generators. Nuclear cross-section calculations were applied using the TALYS code to allow for the determination of the most promising alternative routes for 44mSc production, which will enable the development of a full-scale 44mSc/44gSc radionuclide generator based on after-effects.

Evaluation of the production amount of 225Ac and its uncertainty through the 226Ra(n,2n) reaction in the experimental fast reactor Joyo

ABSTRACT 225Ac is a promising nuclide for targeted alpha therapy. At present, the nuclide is mainly extracted from 229Th generators, but its total radioactivity of the world is only 63 GBq/y. Therefore, it is unclear whether this method alone can meet future global medical demand. In this study, we analyzed the production amount of 225Ac and its uncertainty due to the neutron flux and nuclear reaction cross-sections while analyzing the generation process of 225Ac using the experimental fast reactor Joyo operated by the Japan Atomic Energy Agency (JAEA). The analysis showed that irradiating 1 g of 226Ra for 45 d at the core center of Joyo can produce 15.4 ± 6.2 GBq of 225Ac. Therefore, with six irradiations per year (45 d × 6 = 270 d/year), Joyo can produce 55.3 to 129.1 GBq of 225Ac, equivalent to 86 to 200% of the current world supply.

Experimental assessment of nuclear cross sections for the production of Tb radioisotopes with a medical cyclotron

155Tb is one of the most interesting radionuclides for theranostic applications. It is suitable for SPECT imaging and it can be used as a true diagnostic partner of the therapeutic 149Tb and 161Tb. Its production by proton irradiation using enriched 155Gd and 156Gd oxide targets is currently being investigated and represents a promising solution. To achieve the level of radionuclidic purity required in the clinical setting, the co-production of Tb impurities has to be minimized. For this purpose, an accurate knowledge of the cross sections of the nuclear reactions involved is of paramount importance. In this paper, we report on the assessment of cross sections of the reactions 154Gd(p,xn)153,154,154m1,154m2Tb, 155Gd(p,xn)154,154m1,154m2,155Tb, 156Gd(p,xn)155,156Tb and 157Gd(p,2n)156Tb derived with a specific data analysis procedure developed by our group. This method allows to disentangle the nuclear contributions from the production cross section by inverting linear systems of equations and it requires the measurement of the cross sections from as many materials as the reactions involved in the production of the radionuclide under study. For this purpose, the experimental data previously measured by our group at the Bern medical cyclotron by irradiating natural Gd2O3, enriched 155Gd2O3 and enriched 156Gd2O3 targets were used. For some of these nuclear reactions, cross sections were assessed for the first time. On the basis of our findings, production yield and purity can be calculated for any kind of isotopic composition of the enriched material.

Cross-section measurement of thulium radioisotopes with an 18 MeV medical PET cyclotron for an optimized 165Er production

165Er is a pure Auger-electron emitter with promising characteristics for therapeutic applications in nuclear medicine. The short penetration path and high Linear Energy Transfer (LET) of the emitted Auger electrons make 165Er particularly suitable for treating small tumor metastases. Several production methods based on the irradiation with charged particles of Er and Ho targets can be found in the literature. In this paper, we report on the study of 165Er indirect production performed via the 166Er(p,2n)165Tm →165Er reaction at the 18 MeV Bern medical cyclotron. Despite the use of highly enriched 166Er2O3 targets, several Tm radioisotopes are produced during the irradiation, making the knowledge of the cross sections involved crucial. For this reason, a precise investigation of the cross sections of the relevant nuclear reactions in the energy range of interest was performed by irradiating Er2O3 targets with different isotopic enrichment levels and using a method based on the inversion of a linear system of equations. For the reactions 164Er(p, γ)165Tm, 166Er(p,n)166Tm, 166Er(p, γ)167Tm, 167Er(p,3n)165Tm, 167Er(p, γ)168Tm, 168Er(p,2n)167Tm and 170Er(p,3n)168Tm, the nuclear cross section was measured for the first time. From the results obtained, the production yield and purity of the parent radioisotope 165Tm were calculated to assess the optimal irradiation conditions. Several production tests with solid targets were performed to confirm these findings.

Strengths and weaknesses of the modal expansion method for perturbations calculations in nuclear reactor physics

Reactor design and uncertainties propagation request repeated execution of neutron diffusion calculations. To address this, one can rely on the Generalized Perturbation Theory which is restricted to single integral values such as reaction rate ratios. To overpass such limitations, the perturbed flux could be calculated with the modal expansion method. The difficulty to calculate more than one eigenvector has limited its use. Hence, modal expansion lacks a clear explanation of its strengths and weaknesses. Using recent advances in eigenvalues solvers, we have successfully applied modal expansion to the 2D-BIBLIS and IAEA-3D benchmarks. Our results are promising for fission and capture cross sections perturbations. Still, modal expansion is faulty for local perturbations or when it concerns the reflector. In terms of computational cost, modal expansion is more efficient than solving the direct problem with a calculation time divided by 8 for a basis of 20 eigenvectors.