Photoneutron Reactions Research Articles

Photonuclear partial reaction cross sections: Systematic uncertainties and reliability

The well-known significant systematic disagreements between cross sections of partial photoneutron reactions (γ,1n) and (γ, 2n) obtained in various experiments majority of which have been carried out at Livermore (USA) and Saclay (France) were analyzed using the objective physical criteria of data reliability. It was found that experimental data for more than 50 nuclei from 51V to 209Bi in general do not meet those criteria and therefore are more or less unreliable. The experimental-theoretical method based on the Combined PhotoNuclear Reaction Model (CPNRM) was used to evaluate partial reaction cross sections that meet the reliability criteria. It was shown using the analysis in detail of differences between evaluated and experimental cross sections that the major sources of large systematic uncertainties in obtained cross sections are certain shortcomings of experimental neutron multiplicity sorting method have been used for indirect separation of partial reactions. It was shown that the newly evaluated cross sections of partial photoneutron reactions differ significantly (at least noticeably) from the ones obtained using the method of neutron multiplicity sorting but agree with experimental data obtained by alternative methods used for reliable direct separation of partial reactions. The consolidated review of many problems with partial photoneutron reaction experimental data reliability and some ways to solve ones are presented.

Reliability of Cross Sections of the Photoneutron Reactions on 51V and 59Co Nuclei in the Bremsstrahlung Beam Experiments

Reliability of Cross Sections of the Photoneutron Reactions on 51V and 59Co Nuclei in the Bremsstrahlung Beam Experiments

Evaluation of 180mTa formation cross-sections in photoneutron reactions

Determining the relative production cross-sections of the short-lived (ground) and long- lived (metastable) states of 180Ta is integral in nuclear physics research. However, direct measurement of these cross-sections is challenging. In this study, we proposed a method for estimating the total flux-weighted average formation cross-section of 180m+gTa based on GEANT4 modeling to evaluate the short-lived (ground) and long-lived (metastable) states of 180Ta. A Ta target was irradiated by a bremsstrahlung photon beam (maximum electron energy: 20 MeV) obtained from the linear electron accelerator LUE-75 at the A.I. Alikhanyan National Science Laboratory (AANL), Armenia. The experiment was performed using the activation technique, and the proposed GEANT4 simulation-based method was employed to evaluate the flux-weighted average formation cross-section of 180mTa. In addition, the isomeric cross-section ratio for the 180m,gTa isomeric pair was calculated. The theoretical results obtained using the TALYS 1.96 and EMPIRE 3.2 codes were consistent with the experimental ones. To the best of the authors’ knowledge, this paper reports the estimated flux-weighted average formation cross-section of 180mTa and isomer ratio for the 180m,gTa isomeric pair, induced by the irradiation of a bremsstrahlung beam with an end-point energy of 20 MeV, for the first time. This study opens new avenues for determining the relative production cross-sections of the ground and metastable states of 180Ta, which is widely studied as a natural isomeric target in various fields, including nuclear transformation reactions, fission dynamics, etc.

Reliability of 51V partial photoneutron reaction cross sections obtained using bremsstrahlung

Reliability of 51V partial photoneutron reaction cross sections obtained using bremsstrahlung

Study of the isomeric yield ratio in the photoneutron reaction of natural holmium induced by laser-accelerated electron beams

Introduction: An accurate knowledge of the isomeric yield ratio (IR) induced by the photonuclear reaction is crucial to study the nuclear structure and reaction mechanisms. 165Ho is a good candidate for the investigation of the IR since the Ho target has a natural abundance of 100% and the residual nuclide has a good decay property.Methods: In this study, the photoneutron production of 164m, gHo induced by laser-accelerated electron beams is investigated experimentally. The γ-ray spectra of activated Ho foils are off-line detected. Since the direct transitions from the 164mHo are not successfully observed, we propose to extract the IRs of the 164m, gHo using only the photopeak counts from the ground-state decay.Results: The production yields of 164m, gHo are extracted to be (0.45 ± 0.10) × 106 and (1.48 ± 0.14) × 106 per laser shot, respectively. The resulting IR is obtained to be 0.30 ± 0.08 at the effective γ-ray energy of 12.65 MeV.Discussion: The present data, available experimental data, and TALYS calculations are then compared to examine the role of the excitation energy. It is found that besides the giant dipole resonance, the excitation energy effect also plays a key role in the determination of the IRs.

Cross Sections of Partial Photoneutron Reactions on $${}^{59}$$Co in Experiments with Bremsstrahlung

Cross Sections of Partial Photoneutron Reactions on $${}^{59}$$Co in Experiments with Bremsstrahlung

Similarity and distinctions of <sup>58, 60</sup>Ni photodisintegration processes

Reliability of (γ, 1n) and (γ, 2n) reactions cross sections for 58, 60Ni obtained in experiments carried out on the beams of bremsstrahlung and quasimonoenergetic annihilation photons was investigated using objective physical criteria. It was found that data of the first type experiment do not satisfy those criteria and definitely are not reliable. At the same time there are serious doubts in reliability of the data obtained in the second type experiment. New partial photoneutron reaction cross sections on 58, 60Ni satisfying physical criteria of data reliability were used for analysis of characteristics of both isotope photodisintegration processes. It was obtained that for neighboring (differ in two neutrons) isotopes because of various type systematic uncertainties there are significant disagreements between evaluated and experimental cross sections of various reactions which for isotopes 58Ni and 60Ni are of significant different character. It was shown that the reasons are not only the differences in energy thresholds and absolute values of cross sections of the (γ, 1n), (γ, 1n1p) and (γ, 2n) reactions on 58Ni and 60Ni but significant differences in specific features of neighboring isotopes shell structure also.

Partial photoneutron reaction cross sections in experiments with bremsstrahlung

The analysis of reliability of experimental partial photoneutron reaction cross sections of the reactions (γ, 1n) and (γ, 2n) obtained in experiments on the beams of bremsstrahlung was carried our using the objective physical criteria. In this type of experiments partial reaction cross sections were obtained using the procedure of neutron yield cross section σ(γ, xn) corrections calculated on the base of statistical theory. It was found out that in the cases of 59Co, 58,60Ni, 112, 114, 119Sn reaction cross sections obtained using that procedure do not satisfy the physical criteria of data reliability and therefore are not reliable. At the same time in the cases of 127I, 165Ho и 181Ta one has not any doubts in the data obtained reliability.

Cross Sections of Partial Photoneutron Reactions in Experiments on Beams of Bremsstrahlung

Cross Sections of Partial Photoneutron Reactions in Experiments on Beams of Bremsstrahlung

A portable and monoenergetic 24 keV neutron source based on 124Sb-9Be photoneutrons and an iron filter

A portable monoenergetic 24 keV neutron source based on the 124Sb-9Be photoneutron reaction and an iron filter has been constructed and characterized. The coincidence of the neutron energy from SbBe and the low interaction cross-section with iron (mean free path up to 29 cm) makes pure iron specially suited to shield against gamma rays from 124Sb decays while letting through the neutrons. To increase the 124Sb activity and thus the neutron flux, a >1 GBq 124Sb source was produced by irradiating a natural Sb metal pellet with a high flux of thermal neutrons in a nuclear reactor. The design of the source shielding structure makes for easy transportation and deployment. A hydrogen gas proportional counter is used to characterize the neutrons emitted by the source and a NaI detector is used for gamma background characterization. At the exit opening of the neutron beam, the characterization determined the neutron flux in the energy range 20–25 keV to be 6.00±0.30 neutrons per cm2 per second and the total gamma flux to be 245±8 gammas per cm2 per second (numbers scaled to 1 GBq activity of the 124Sb source). A liquid scintillator detector is demonstrated to be sensitive to neutrons with incident kinetic energies from 8 to 17 keV, so it can be paired with the source as a backing detector for neutron scattering calibration experiments. This photoneutron source provides a good tool for in-situ low energy nuclear recoil calibration for dark matter experiments and coherent elastic neutrino-nucleus scattering experiments.

Cross sections of partial photoneutron reactions: the problems with reliability and new data

The (𝛾, 1𝑛), (𝛾, 2𝑛) and (𝛾, 3𝑛) reactions cross sections the majority of which were obtained using beams of quasimonoenergetic annihilation photons were discussed. The significant systematic uncertainties of the experimental results far exceeding the achieved statistical accuracy were considered. The results of experiments for about 50 nuclei from 51V to 209Bi were analyzed using objective physical criteria of data reliability. It was shown that in many cases the systematic uncertainties of experimental cross sections were significant and data do not satisfy physical criteria. The experimental theoretical method for evaluation of cross sections satisfying those criteria was described. The systematic uncertainties of several types due to shortcomings of the method of photoneutron multiplicity sorting used in experiments and specific features of neutron detectors used. The new evaluated reliable cross sections of the partial reactions and total photoneutron reaction (𝛾, 1𝑛)+(𝛾, 2𝑛)+(𝛾, 3𝑛) were presented.

Borosilicate glass media for neutron sensing

This work using a borosilicate glass medium seeks to detect photoneutrons generated by a medical linear accelerator. The studies involved an Elekta Infiniti accelerator located in the Oncology Centre, Medical City, Riyadh, the neutrons resulting from interactions at above-threshold therapeutic photon energies. The borosilicate detectors were produced from microscope glass slides of nominal thickness 1.0 mm, the latter made into square segments of area 0.6 × 0.6 cm2, a size capable of being accommodated within the planchette of the thermoluminescent (TLD) Reader (Harshaw 600). With some 4% boron in the coverslip glass and the abundance of 10B being 19.8%, thermalised neutrons 10B(n,α)7Li interactions offer a cross-section that can achieve a value as large as 3837 b. Apart from interactions in boron, of additional note is that 2H(γ,n)1H and 9Be(γ,n)8Be are two further photoneutron reactions, giving rise to particularly low threshold energies at 2.226 and 1.666 MeV, respectively. The presence of natural carbon in the present borosilicate samples has been measured to be 1.3%. Accordingly, with the abundance of 13C in natural carbon being 1.109% this would appear to be of very little interest herein. Moreover, compositional measurements made on the borosilicate coverslip glass indicates 9.40 Na. The induced activity in the glass falls to some 25% 30 h post-irradiation, a delay time beyond which readout can subsequently be conducted.

Cross Sections of Partial Photoneutron Reactions: Problems of Reliability and New Data

Cross Sections of Partial Photoneutron Reactions: Problems of Reliability and New Data

Photoneutron cross section measurements on 208Pb

Photoneutron reactions on 208Pb in the Giant Dipole Resonance (GDR) energy range have been investigated at the γ-ray beam line of the NewSUBARU synchrotron radiation facility in Japan. Making use of quasi-monochromatic laser Compton scattering (LCS) γ-ray beams and of a novel flat-efficiency neutron detection system along with associated neutron-multiplicity sorting method, total and partial (γ,xn) photoneutron cross sections with x = 1 to 4 have been measured for 208Pb in a broad energy range covering the neutron threshold up to 38 MeV.

Photofission and photoneutron cross sections for 238U and 232Th

A specific objective of the recent IAEA Coordinated Research Project on Photonuclear Data and Photon Strength Functions (Code F41032; Duration 2016-2019) has been to measure photonuclear cross-section data where needed, for unexplored nuclei and cases of discrepant existing data. A dedicated experimental campaign has been conducted at the laser Compton-scattering γ-ray source of the NewSUBARU synchrotron radiation facility of SPring8, Japan, where photoneutron reactions for 11 nuclei from 9Be to 209Bi have been investigated in the Giant Dipole Resonance energy region. The measurements followed the development of a flat-effi ciency moderated neutron detection array and the associated neutron-multiplicity sorting techniques. The IAEA CRP campaign has been followed at NewSUBARU by new measurements of photofission and photoneutron reactions on 238U and 232Th in the energy range of 5.87 MeV – 20.14 MeV. The neutron-multiplicity sorting of high-multiplicity fission neutron coincidence events has been performed using a dedicated energy dependent, multiple firing statistical treatment. The photoneutron (γ, xn) and photofission (γ, fxn) reactions have been discriminated by considering a Gaussian distribution of prompt-fission-neutrons (PFN) multiplicities predicted by the evaporation theory. We here provide preliminary experimental (γ, n), (γ, 2n) and (γ, F) cross sections, average energies of PFN and of photoneutrons emitted in (γ, n) and (γ, 2n) reactions, as well as the mean number of PFN per fission act. The new 238U cross sections are compared with recent statistical-model calculations performed with the EMPIRE code on existing data.

A Study of Photoneutron Reactions Using Statistical Analysis

The well-known inputs for determining the reaction cross section are nuclear level density (NLD) and -ray strength functions. In this work, effects of -ray strength functions and NLD models on photoneutron reactions of 76,77,78Se isotopes are analyzed by using the latest version of TALYS computer code. For -ray strength functions, macroscopic and microscopic options which are available in the TALYS, are used in the calculations. Kopecky-Uhl and Brink Axel -ray strength function models as macroscopic options, Hartree-Fock BCS tables, Hartree-Fock Bogolyubov tables and Goriely’s hybrid model as microscopic options are preferred. The statistical analysis is carried out to determine the -ray strength function that reproduces the experimental data quite well. And then, calculations of photoneutron cross section are redone by using the determined -ray strength function via the NLD models. The Constant Temperature Model (CTM), Back Shifted Fermi Gas Model (BSFGM) and Generalized Superfluid Model (GSM) are preferred to use in NLD calculations. The predictions are compared with each other and the available experimental data. EXFOR library is used to take all experimental data.

Reliability of $${}^{{159}}$$Tb Partial Photoneutron Reaction Cross Sections Obtained in Various Experiments

Reliability of $${}^{{159}}$$Tb Partial Photoneutron Reaction Cross Sections Obtained in Various Experiments

New Evaluated Data on Photoneutron Reaction Cross Sections for $${}^{60}$$Ni Nuclei

New Evaluated Data on Photoneutron Reaction Cross Sections for $${}^{60}$$Ni Nuclei

The specific features of photoneutron reactions on 58Ni

The specific features of photoneutron reactions on 58Ni

Investigation of level density and Gama strength function for photoneutron reaction in medical linacs in Beamline

Photoneutron reaction cross-sections of 197Au, 187Re, 186W, 181Ta, 94,95,96,97,98,100Mo isotopes were calculated through the TALYS 1.95 nuclear reaction code. The energy range of the incident photon chosen as 7 MeV–30 MeV corresponded to the range of the giant dipole resonance region, which is also an applicable energy range in radiotherapy for many commercial medical linear accelerators. Calculations were performed using three phenomenological level density models available in code, namely the Constant Temperature Fermi Gas Model, the Back-shifted Fermi Gas Model, and the Generalized Superfluid Model. The most convenient level density model for each reaction was chosen using relative variance calculations. The cross-section calculations were repeated using gamma strength function models, Kopecky-Uhl generalized Lorentzian model, Brink-Axel Lorentzian model, and Goriely's hybrid model and the best level density model was kept constant. The calculated data and the experimental data from the international Experimental Nuclear Reaction Data Library were analysed and compared graphically.