Photonuclear Reaction Cross Sections Research Articles

Photonuclear experiments: from the bremsstrahlung to the Compton backward scattering photons

The features of the methods for obtaining the information on photonuclear reaction cross sections using the beams of bremsstrahlung and quasimonoenergetic photons from the annihilation in flight of relativistic positrons with which such the absolute majority of such kind data was obtained in the nucleus excitation energy up to ∼40 MeV are discussed. It was shown that significant disagreements between the results of such experiments in cross sections absolute values and shapes are due to both methods definite shortcomings which to a certain extent can be overcome by using the beams of the photons from the processes of Compton backward scattering.

Methodology for measuring photonuclear reaction cross sections with an electron accelerator based on Bayesian analysis

Accurate measurements of photonuclear reaction cross sections are crucial for a number of applications, including radiation shielding design, absorbed dose calculations, reactor physics and engineering, nuclear safeguard and inspection, astrophysics, and nuclear medicine. Primarily motivated by the study of the production of selected radionuclides with high-energy photon beams (mainly 225Ac, 47Sc, and 67Cu), we have established a methodology for the measurement of photonuclear reaction cross sections with the microtron accelerator available at the Swiss Federal Institute of Metrology (METAS). The proposed methodology is based on the measurement of the produced activity with a High Purity Germanium (HPGe) spectrometer and on the knowledge of the photon fluence spectrum through Monte Carlo simulations. The data analysis is performed by applying a Bayesian fitting procedure to the experimental data and by assuming a functional trend of the cross section, in our case a Breit-Wigner function. We validated the entire methodology by measuring a well-established photonuclear cross section, namely the 197Au(γ, n)196Au reaction. The results are consistent with those reported in the literature.

Status of experimental photonuclear results

Absolute majority of data on photonuclear reaction cross sections was obtained in experiments using bremsstrahlung and quasimonoenergetic photons produced at annihilation in flight of relativistic positrons. There are significant disagreements both in absolute value and shape between the results of experiments of both types. So, the pronounced structural features are clearly observed in the cross sections obtained using bremsstrahlung but those are practically absent in the cross sections obtained on the beams of annihilation photons. The disagreements in absolute values are definitely systematic: they are directly dependent on the data retrieval method and significantly exceed the statistical errors achieved in experiments. There are also the significant disagreements between the data obtained in experiments of the same type. In combined systematic investigations of many data on various photonuclear (primarily, photoneutron) reaction, both total and partial, cross sections the possible reasons for disagreements between the results of photonuclear experiments were found out, the status of those experiments and methods of accounting and elimination of observed disagreements are discussed.

Evaluations of uncertainties in simulations of propagation of ultrahigh-energy cosmic-ray nuclei derived from microscopic nuclear models

Photodisintegration is a main energy loss process for ultrahigh-energy cosmic-ray (UHECR) nuclei in intergalactic space. Therefore, it is crucial to understand systematic uncertainty in photodisintegration when simulating the propagation of UHECR nuclei. In this work, we calculated the cross sections using the random phase approximation (RPA) of density functional theory (DFT), a microscopic nuclear model. We calculated the E1 strength of 29 nuclei using three different density functionals. We obtained the cross sections of photonuclear reactions, including photodisintegration, with the E1 strength. Then, we implemented the cross sections in the cosmic-ray propagation code CRPropa. We found that assuming certain astrophysical parameter values, the difference between UHECR energy spectrum predictions using the RPA calculation and the default photodisintegration model in CRPropa can be more than the statistical uncertainty of the spectrum. We also found that the differences between the RPA calculations and CRPropa default in certain astrophysical parameters obtained by a combined fit of UHECR energy spectrum and composition data assuming a phenomenological model of UHECR sources can be more than the uncertainty of the data.

Determination of Photonuclear Reaction Cross-Sections on Stable P-shell Nuclei by Using Deep Neural Networks

Determination of Photonuclear Reaction Cross-Sections on Stable P-shell Nuclei by Using Deep Neural Networks

Resonance nucleon scattering amplitude in the photonuclear reaction

The cross section of the photonuclear reaction in the nucleon-resonance region is calculated to search the resonance-nucleon scattering amplitude in the nucleus. It is assumed that the resonance R is produced and decayed in the elementary photon-nucleon (γN) reaction in the nucleus as γN→R→γN. The resonance interacts with the nucleons while propagating through the nucleus. Therefore, the calculated photonuclear reaction cross section is compared with the data to extract the resonance-nucleon scattering parameters in the nucleus.

The application of the unfolding technique for determination of photo-nuclear reaction cross-section with an example on the $$^{115}$$In($$\gamma $$,$$\gamma ^{\prime }$$)$$^{115m}$$In reaction

The application of the unfolding technique for determination of photo-nuclear reaction cross-section with an example on the $$^{115}$$In($$\gamma $$,$$\gamma ^{\prime }$$)$$^{115m}$$In reaction

Experimental programme with high-brilliance gamma beams at ELI-NP

The emerging experimental program with brilliant gamma beams at the Extreme Light Infrastructure – Nuclear Physics (ELI-NP) facility is presented with emphasis on the day-one experiments which are under preparation. Experiments at ELI-NP will cover nuclear resonance fluorescence (NRF) measurements, studies of large-amplitude motions in nuclei, photo-fission and photonuclear reactions of astrophysics interest, and measurements of photonuclear reaction cross-sections. The physics cases of the flagship experiments at ELI-NP and the performance of the related instruments, which are under construction for their realization, are discussed.

Estimations of Cross-Sections for Photonuclear Reaction on Calcium Isotopes by Artificial Neural Networks

The nuclear reaction induced by photon is one of the important tools in the investigation of atomic nuclei. In the reaction, a target material is bombarded by photons with high-energies in the range of gamma-ray energy range. In the bombarding process, the photons can statistically be absorbed by a nucleus in the target material. Then the excited nucleus can decay by emitting proton, neutron, alpha and light particles or photons. By performing photonuclear reaction on the target, it can be easily investigated low-lying excited states of the nuclei. In the present work, (γ, n) photonuclear reaction cross-sections on different calcium isotopes have been estimated by using artificial neural network method. The method is a mathematical model that mimics the brain functionality of the creatures. The correlation coefficient values of the method for both training and test phases being 0.99 indicate that the method is very suitable for this purpose.

Status of JENDL

Recent progress and future plan of the JENDL project are summarized. Two special purpose files were released recently. One is Photo-nuclear Data File 2016 (JENDL/PD-2016) which contains the data of photo-nuclear reaction cross sections covering a wide area of the nuclear chart. The other one is the JENDL Activation Cross Section File for Nuclear Decommissioning 2017 (JENDL/AD-2017) which provides production cross sections of radioactive nuclei by neutrons. A special purpose file JENDL/ImPACT-2018 dedicated to transmutation of long-lived fission products will be released in 2019. Regarding the general-purpose file, we are preparing to release the next version, which would be made available by 2022 as JENDL-5. Evaluation efforts on nuclides across wide range of nuclei form light to heavy have being made. The first test version JENDL-5α1 was created in 2018. The evaluated data will be updated on the basis of benchmark tests on reactor criticalities and neutron shieldings.

ACTIVATION OF 93Nb NUCLEI ON THE LINAC LUE-40 OF RDC “ACCELERATOR” AND DETERMINATION OF PHOTONUCLEAR REACTION CROSS-SECTIONS

The bremsstrahlung spectra of medium-energy electrons (30…100 МeV) were calculated in GEANT4. Cross-sections for photonuclear reactions were calculated in TALYS1.9. A convolution over the energy of the cross-sections of one- and many-particle reactions with the bremsstrahlung flux density was performed. The numerical values of the yield of 93Nb(γ,xn)93-xNb reactions, the activity of irradiated 93Nb targets, and the average reaction cross-sections were obtained. The differences of the bremsstrahlung spectra from electrons with close initial energies were calculated. The shape of the difference spectra was analyzed. The contributions of the quanta of the low-energy part of the difference spectrum and the quasi-monochromatic peak of the difference spectrum to the total activity of the targets were compared. An approach for correction of the experimental cross-sections of photo-nuclear reactions using the method of "bremsstrahlung spectra difference" was considered.

Converter optimization for photonuclear production of Mo-99

We used Monte Carlo simulations to study optimal configuration of bremsstrahlung converter for photonuclear production of 99Mo. To account for details of bremsstrahlung photons production and energy dependency of photonuclear reaction cross section we introduced a new metric – the effective bremsstrahlung efficiency criterion. Monte Carlo simulations using PHITS transport code showed that converter optimization using this criterion allows to achieve 2–2.8% increase in 99Mo production in a thick radioisotope producing target.

Highlights of the day-one experimental program at the gamma-beam system of ELI-NP

The emerging experimental program with brilliant gamma beams at the Extreme Light Infrastructure - Nuclear Physics facility (ELI-NP) is presented with emphasis on the prepared day-one experiments. Ex- periments at ELI-NP will cover nuclear resonance fluorescence measurements, studies of large-amplitude motions in nuclei, photo-fission and photonuclear reactions of astrophysics interest, and measurements of photonuclear reaction cross sections. The physics cases of the flagship experiments at ELI-NP and the performance of the related instruments, which are under construction for their realization, are discussed.

Indirect measurement of bremsstrahlung photons and photoneutrons cross sections of 204Pb and Sb isotopes compared with TALYS simulations

A massive sliced Pb-target was irradiated by 20 MeV electrons and the bremsstrahlung photons produced plus the photoneutrons are applied to measure Pb204(γ,n) and Pb204(n,n′) reactions cross section. The radioactivity induced inside the Pb-target slices was measured using γ-spectrometry. Incidentally, the Sb121(γ,n) and (n,γ) besides the Sb123(γ,n) nuclear reactions were also measured, since Sb is added in lead alloys to increase their rigidity. A detailed geometry of the Pb-target has been simulated using the GEANT4 code and the initial photons and neutrons fluence at the entrance of the Pb-target was calculated. The average cross sections of photonuclear reactions on 204Pb and Sb isotopes as well neutrons inelastic reaction on 204Pb and capture on 121Sb were determined. Theoretical cross sections using the TALYS code have been simulated for all isotopes. An agreement between the experimental and simulated results appears while useful conclusions are presented regarding the nuclear parameters used in the simulations after comparison to experimental data.

Experiments with brilliant gamma beams at ELI-NP: A glimpse in the future

The emerging experimental program with brilliant gamma beams at the Extreme Light Infrastructure – Nuclear Physics facility (ELI-NP), which is under construction in Magurele, Romania is presented with emphasis on the prepared day-one experiments. Experiments at ELI-NP will cover nuclear resonance fluorescence (NRF) measurements, studies of large-amplitude motions in nuclei, photofission and photonuclear reactions of astrophysics interest, and measurements of photonuclear reaction cross sections. The physics cases of the flagship experiments at ELI-NP are discussed, as well as the related instruments which are under construction for their realization.

Physical criteria for the reliability of data on the photodisintegration of the 89Y nucleus

Experimental photonuclear reaction cross sections obtained in experiments using quasimonoenergetic annihilation, monoenergetic tagged photons, and bremsstrahlung γ-radiation are analyzed using physical criteria for the reliability of data on the 89Y nucleus. It is found that the reliability of data on the cross sections of partial reactions (γ, 1n) and (γ, 2n), obtained by means of photoneutron multiplicity sorting, is highly doubtful. Reliable cross sections of reactions (γ, 1n) and (γ, 2n) are obtained using the experimental–theoretical method (ETM) for evaluating using both experimental cross sections of neutron yield reaction σexp(γ, xn) that are free of neutron multiplicity problems, and theoretically calculated F i theor ratios of the cross sections of definite (i) partial reactions to cross section σtheor(γ, xn). It is shown that the evaluated cross sections differ noticeably from the experimental data.

Photoneutron reaction cross sections from various experiments – analysis and evaluation using physical criteria of data reliability

The majority of photonuclear reaction cross sections important for many fields of science and technology and various data files (EXFOR, RIPL, ENDF, etc.) supported by the IAEA were obtained in experiments using quasimonoenergetic annihilation photons. There are well–known systematic discrepancies between the partial photoneutron reactions (γ, 1n), (γ, 2n), (γ, 3n). For analysis of the data reliability the objective physical criteria were proposed. It was found out that the experimental data for many nuclei are not reliable because of large systematic uncertainties of the neutron multiplicity sorting method used. The experimentally–theoretical method was proposed for evaluating the reaction cross sections data satisfying the reliability criteria. The partial and total reaction cross sections were evaluated for many nuclei. In many cases evaluated data differ noticeably from both the experimental data and the data evaluated before for the IAEA Photonuclear Data Library. Therefore it became evident that the IAEA Library needs to be revised and updated.

Electromagnetic processes in silver isotopes

Peculiarities of electromagnetic interactions in silver isotopes are considered. Excited states of Ag isotopes are studied as a function of the mass number A = 95–117. Low-lying excited states reveal clear features that are specific for rotational spectra for the energies E < 4–5 MeV. In the energy domain above the nucleon separation threshold of 5–10 MeV, single-particle excited states overlap and produce a continuous spectrum. For energies E = 10–35 MeV, excitation of giant dipole resonance plays the most important role in Ag isotopes. Experimental data on the cross sections of photonuclear reactions in Ag isotopes are analyzed.

Optimization of a photoneutron source based on 10 MeV electron beam using Geant4 Monte Carlo code

Geant4 Monte Carlo code has been used to conceive and optimize a simple and compact neutron source based on a 10MeV electron beam impinging on a tungsten target adjoined to a beryllium target. For this purpose, a precise photonuclear reaction cross-section model issued from the International Atomic Energy Agency (IAEA) database was linked to Geant4 to accurately simulate the interaction of low energy bremsstrahlung photons with beryllium material. A benchmark test showed that a good agreement was achieved when comparing the emitted neutron flux spectra predicted by Geant4 and Fluka codes for a beryllium cylinder bombarded with a 5MeV photon beam. The source optimization was achieved through a two stage Monte Carlo simulation. In the first stage, the distributions of the seven phase space coordinates of the bremsstrahlung photons at the boundaries of the tungsten target were determined. In the second stage events corresponding to photons emitted according to these distributions were tracked. A neutron yield of 4.8×1010neutrons/mA/s was obtained at 20cm from the beryllium target. A thermal neutron yield of 1.5×109neutrons/mA/s was obtained after introducing a spherical shell of polyethylene as a neutron moderator.

Calculation of photo-nuclear reaction cross sections for16O

Because of the high thermal expansion coefficient of uranium, the fuel used in nuclear power plants is usually in the form of UO2 which has ceramic structure and small thermal expansion coefficient. UO2 include one uranium atom and two oxygen atoms. After fission progress, total energy values of emitted gamma are about 14 MeV. This gamma energy may cause transmutation of 16 O isotopes. Transmutation of 16 O isotopes changes physical properties of nuclear fuel. Due to above explanations, it is very important to calculate photo-nuclear reaction cross sections of 16 O. In this study; for (γ,p), (γ,np), (γ,n) and (γ,2n) reactions of 16 O, photo-nuclear reaction cross-sections were calculated using different models for pre-equilibrium and equilibrium effects. Taking incident gamma energy values up to 40 MeV, Hybrid and Cascade Exciton Models were used for pre-equilibrium calculations and Weisskopf-Ewing (Equilibrium) Model was used for equilibrium model calculations. Calculation results were compared with experimental and theoretical data. While experimental results were obtained from EXFOR, TENDL-2013, JENDL/PD-2004 and ENDF/B VII.1 data base were used to get theoretical results.