Capture Reaction Cross Sections Research Articles

Candidate-nuclei for observation of a bound dineutron. Part II: The (n,2n + n) and (γ,2n) nuclear reactions

This is a second part of a survey for stable isotopes in the mass range 90 < A < 210, to find candidates showing the bound dineutron nuclear reaction output channel after irradiation with neutrons or photons. To this end, the neutron capture reaction cross sections were calculated in the (0 - 30) MeV energy range with the TALYS-2.0 code for nuclei in the outgoing channel, which are expected to host bound dineutrons. This study was performed to find appropriate candidates to observe bound dineutron decay meeting the criteria based on the (n, γ) resonance cross section analysis. This study opens up a new direction in dineutron research with the (n, n2+n) and (γ, n2) nuclear reactions.

Measurement of spectral averaged cross sections of capture reactions in the LR-0 reference neutron field

Nuclear data evaluations are periodically updated to render state of the art of knowledge, and the independent validation experiments are still of interest of the community. Current work describes validation of selected capture reactions used for monitoring of thermal neutrons in mixed fields, as well as reactions responsible for activation of components exposed to neutron flux. The validation was performed also for reaction 50Cr (n,γ), which is very important reaction directly affecting criticality safety, because chromium is essential component of stainless steel used as structural component of the core baffle closely adjoining to nuclear fuel. Described experiments were performed in reference neutron field of the LR-0 reactor. The activation rate was derived by gamma spectrometry using well-characterized HPGe detector. It was found that the capture cross sections for the dosimetry reactions 23Na (n,γ), 58Fe (n,γ), and 59Co (n,γ) agreed well within 10 % with calculations in thermal and epithermal region, but larger discrepancy was found for the isotopes of tin.

Candidate-nuclei for observation of a bound dineutron. Part I: The (n,2n) nuclear reaction

Current research has been performed for the stable isotopes within the 90 < A < 210 mass range in order to select properly those of them to be irradiated with neutrons for observation of a bound dineutron in the output channel. To this end, the neutron capture reaction cross sections were calculated in the (0 - 30) MeV energy range with the TALYS-1.96 code. That was performed in accordance with the purpose of this study to meet the criteria based on the (n, γ) resonance cross section analysis to find the appropriate candidates to be used for the possible future experimental confirmation of the formation of the dineutron in the (n,n2) nuclear reaction channel.

Continuum random-phase approximation for (n,γ) reactions on neutron-rich nuclei: Collective effects and resonances

We formulate a microscopic theory to calculate cross section of the radiative neutron capture reaction on neutron-rich nuclei using the continuum random-phase approximation (cRPA) to the time-dependent density functional theory (TDDFT). With an intention of applying to the $r$ process, for which the statistical reaction model may not be appropriate, we describe the transition between a initial state of incident neutron and a final state of the $\ensuremath{\gamma}$ decay by means of a single many-body framework of the cRPA-TDDFT. With the cRPA approach, it is possible to describe various excitation modes present in the $(n,\ensuremath{\gamma})$ reaction, including soft dipole excitation, the giant resonances, as well as noncollective excitations and the single-particle resonances. Furthermore, it enables us to describe the $(n,\ensuremath{\gamma})$ reaction where the the final states of the $\ensuremath{\gamma}$ transition are low-lying surface vibrational states. We demonstrate the theory by performing numerical calculation for the reaction $^{139}\mathrm{Sn}(n,\ensuremath{\gamma})^{140}\mathrm{Sn}$. We discuss various new features which are beyond the single-particle model: the presence of narrow and wide resonances originating from noncollective and collective excitations and roles of low-lying quadrupole and octupole vibrational states.

Determination of asymptotic normalization coefficients for the channel $$^{16}$$O$$\rightarrow \alpha +^{12}$$C: excited state $$^{16}$$O($$0^+; 6.05$$ MeV)

Asymptotic normalization coefficients (ANC) determine the overall normalization of cross sections of peripheral radiative capture reactions. In the present paper, we treat the ANC $C$ for the virtual decay $^{16}$O$(0^+; 6.05$ MeV)$\to \alpha+^{12}$C(g.s.), the known values of which are characterized by a large spread $(0.29-1.65)\times 10^3$ fm$^{-1/2}$. The ANC $C$ is found by analytic continuation in the energy of the $\alpha^{12}$C $s$-wave scattering amplitude, known from the phase-shift analysis of experimental data, to the pole corresponding to the $^{16}$O bound state and lying in the unphysical region of negative energies. To determine $C$, two different methods of analytic continuation are used. In the first method, the scattering data are approximated by the sum of polynomials in energy in the physical region and then extrapolated to the pole. The best way of extrapolation is chosen on the basis of the exactly solvable model. Within the second approach, the ANC $C$ is found by solving the Schr\"odinger equation for the two-body $\alpha^{12}$C potential, the parameters of which are selected from the requirement of the best description of the phase-shift analysis data at a fixed experimental binding energy of $^{16}$O$(0^+; 6.05$ MeV) in the $\alpha+^{12}$C channel. The values of the ANC $C$ obtained within these two methods lie in the interval (886--1139) fm$^{-1/2}$.

^{74}Ge(n,gamma ) cross section below 70 keV measured at n_TOF CERN

Neutron capture reaction cross sections on ^{74}Ge are of importance to determine ^{74}Ge production during the astrophysical slow neutron capture process. We present new resonance data on ^{74}Ge(n,gamma ) reactions below 70 keV neutron energy. We calculate Maxwellian averaged cross sections, combining our data below 70 keV with evaluated cross sections at higher neutron energies. Our stellar cross sections are in agreement with a previous activation measurement performed at Forschungszentrum Karlsruhe by Marganiec et al., once their data has been re-normalised to account for an update in the reference cross section used in that experiment.

R -matrix analysis of elastic scattering, phase shifts, and radiative capture reaction cross sections in the α+α system

The unstable nucleus $^8$Be, with its two $\alpha$-cluster configuration, is the doorway to the formation of heavier $\alpha$-cluster nuclei. Most importantly, its the precursor of the production of $^{12}$C through the Hoyle state, a resonance state of three $\alpha$ clusters, in the helium burning phase of a massive star. The nucleus exhibits a ground state band of rotational states established through $\alpha-\alpha$ scattering experiments. A subsequent precision particle-$\gamma$ coincidence measurement of the electromagnetic transition between the 4$^+\rightarrow$ 2$^+$ excited states also corroborated the evidence for a highly deformed dumb-bell shaped structure of $^8$Be. A simultaneous phenomenological R-matrix analysis of the measured capture reaction cross sections along with the elastic excitation function and phase shift data has been performed. The resulting reduced transition strength of 21.96$\pm$3.86 $e^2 fm^4$ compares well with the estimated experimental value of 21.0$\pm$2.3 e$^2$ fm$^4$. The R-matrix yield of the B($E2$) value is closer to the prediction of cluster model but about 19$\%$ less than the {\it ab initio} result.

Kollektif Etkilerin Nötron Yakalama Reaksiyon Tesir Kesiti Üzerindeki Rolü

The neutron capture reaction is one of the important reactions that provides the determination of the structural properties of the nucleus and detailed information about the capture reaction mechanisms. In this study, cross section values of 89Y(n,g)90Y reaction, which is a neutron capture reaction, were calculated with TALYS computer code up to 10 MeV incident particle energy using different level density models. In the calculations, back-shifted Fermi gas model (BSFGM), constant temperature model (CTM), generalized superfluid model (GSM), and collective semi-classical Fermi gas model (CSCFGM) were preferred. The obtained results were compared with the data taken from the experimental database. In addition, the quality factors of the models were presented in the table. As a result of the calculations, it has been presented that the CSCFGM, which takes the collective effects into account basically, is more successful model to reproduce the experimental data and that the collective effects play a dominant role on the neutron capture reaction cross sections. Therefore, it has been demonstrated that CSCFGM is a model, which can be used for neutron capture reaction analyses in the future.

Preparation and characterization of isotopically pure Mo targets for nuclear science measurements

Isotopically pure molybdenum targets are essential in various nuclear science measurements. For studies of cross sections of capture reactions on molybdenum, uniform targets with areal densities of hundreds of μg/cm2 are desired. Mechanical rolling of enriched metal pieces or vacuum sputtering methods used in previous studies to prepare molybdenum targets are challenging and involve labor- and time-intensive processes. Therefore, reliable and straightforward methods to produce molybdenum targets are crucial. We have developed a new double-step method to produce targets meeting these needs. The first step consists of evaporating isotopically enriched MoO3 onto gold backings. The second step involves the reduction of the oxide layer in a 5% H2-Ar environment to obtain molybdenum targets. X-ray fluorescence (XRF) spectroscopy, X-ray Diffraction (XRD), a scanning electron microscope/focused ion beam milling, and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the targets. These methods show that the targets exhibit a uniform coverage of Mo over the gold backings. However, significant volume shrinkage occurring during the reduction of MoO3 creates a porous Mo layer where the gold diffuses due to the high processing temperatures, resulting in mixed Mo–Au layers.

Neutron capture cross section measurements for &lt;sup&gt;nat&lt;/sup&gt;Lu with different thickness

The C&lt;sub&gt;6&lt;/sub&gt;D&lt;sub&gt;6&lt;/sub&gt; detection system coupling with the pulse height weighting technique is widely used for experimentally measuring the neutron capture cross section. The thickness of sample used in the experiment directly affects the neutron beam time and the reliability of the experimental data. In the present work, we compare the lutetium (Lu) neutron capture reaction cross sections among the samles with different thickness, obtained by the C&lt;sub&gt;6&lt;/sub&gt;D&lt;sub&gt;6&lt;/sub&gt; detection system of the back-streaming white neutron beam line at China spallation Neutron Source (CSNS back-n). The light response of the detection system is simulated with the consideration of the sample thickness by GEANT4 Monte Carlo simulation code. The 4&lt;sup&gt;th&lt;/sup&gt; order polynomial pulse weight functions for different samples are determined by using the above light response function. In the experiment, the high precision capture yield distributions in the resonance energy region are obtained by measuring the longer flight distance and background. The experimental resonance parameters are deduced by analyzing the capture yield distribution with the R-matrix theory. The comparisons of the results of capture yield and the resonance parameters between the two groups show that the resonance curve of 1.06mm &lt;sup&gt;nat&lt;/sup&gt;Lu sample changes due to its thickness effect, and there is a large difference between the experimental resonance parameters and ENDF/B-VIII.0 database. However, the experimental results of 0.207mm &lt;sup&gt;nat&lt;/sup&gt;Lu sample can well accord with the ENDF/B-VIII. 0 data.

First Direct Measurement of an Astrophysical p-Process Reaction Cross Section Using a Radioactive Ion Beam.

We have performed the first direct measurement of the ^{83}Rb(p,γ) radiative capture reaction cross section in inverse kinematics using a radioactive beam of ^{83}Rb at incident energies of 2.4 and 2.7A MeV. The measured cross section at an effective relative kinetic energy of E_{cm}=2.393 MeV, which lies within the relevant energy window for core collapse supernovae, is smaller than the prediction of statistical model calculations. This leads to the abundance of ^{84}Sr produced in the astrophysical p process being higher than previously calculated. Moreover, the discrepancy of the present data with theoretical predictions indicates that further experimental investigation of p-process reactions involving unstable projectiles is clearly warranted.

Neutron-induced mass shift of tin isotopes recognized using inductively coupled plasma mass spectrometry as an isotopic fingerprint on neutron reactions

The phenomenon of isotope shift in response to neutron irradiation was investigated. The high fission-neutron fluence of 1.44×1018 cm−2 from the second Egyptian research reactor (ETRR-2) was used to induce a mass shift in a metallic tin sample. A triple-quadrupole inductively coupled plasma mass spectrometry system was used to analyze the isotope abundances in the mass range from A=111 to A=125. The problem of mass bias due to kinetic fractionation on use of the inductively coupled plasma mass spectrometry system was treated by our calibrating the mass bias with a standard reference tin solution and building a response function. The response function was used to obtain absolute abundances in each mass range instead of isotope ratios. The results show that the mass shifts in the irradiated sample are dependent on the cross section of the neutron capture reaction in the tin isotopes.

Neutron capture reaction cross section measurement for iodine nucleus with detailed uncertainty quantification

Neutron capture reaction cross section measurement for iodine nucleus with detailed uncertainty quantification

Cross section measurement of neutron capture reaction based on back-streaming white neutron source at China spallation neutron source

The data of neutron capture cross section are very important for the research of nuclear astrophysics, advanced nuclear energy development. Owing to the limitation of neutron source and detector, the experimental data of neutron capture cross section in an energy range of 1 eV–10 keV were almost blank in China. The first Chinese gamma-ray total absorption facility has been constructed in the key laboratory of nuclear data at China institute of atomic energy, which consists of 40 BaF&lt;sub&gt;2&lt;/sub&gt; detector units. The BaF&lt;sub&gt;2&lt;/sub&gt; crystal shell with a thickness of 15 cm and an inner radius of 10 cm covers 95.2% of the solid angle. On-line measurement method of neutron capture reaction cross section is established on the back-streaming white neutron source of China spallation neutron source by using the upgraded facility. The cross section of &lt;sup&gt;197&lt;/sup&gt;Au neutron capture reaction is measured for the first time under the experimental condition of irregular 30 mm neutron beam spot. The measured position of resonance peak is well consistent with the relevant data of ENDF evaluation database, which verifies the reliability of the measurement device and measurement technology, and thus laying the foundation for the acquisition of high precision cross section in future.

A 4π γ-summing method for cross-section measurements of capture reactions

Capture reaction cross sections at energies far below the Coulomb barrier are of major importance for the understanding of stellar nucleosynthesis. Since the cross sections of the majority of these reactions are very small, the use of high efficiency detectors is essential. In this work, a new method for capture reaction cross section measurements based on a large volume 4π NaI detector is presented.

Cross sections of proton capture reactions of Sr isotopes

Cross section measurements of the proton capture reactions of the 86Sr, 87Sr and 88Sr isotopes were carried out at energies Ep=1.4-5 MeV. At Ep &lt;3.5 MeV an array of 4 HPGe detectors with 100% relative efficiency shielded with BGO scintillators for Compton background suppression was used, whereas at Ep &gt;3.5 MeV, the measurements were performed by means of one HPGe detector of 80% relative efficiency. For the 87Sr(p,7)88Y and 88Sr(p,7)89Y reactions total cross sections ranging from 0.5 μο-5 mb were found. The data analysis of the 86Sr(p,7)87Y reaction is in progress. Cross sections have also been calculated by means of the statistical model code MOST. A very good agreement between the experimental data and the theoretical predictions has been found.

Proton capture reactions on 116Sn and 118Sn relevant to the p process

The proton capture reaction cross sections on 116Sn and 118Sn have been determined at astrophysically relevant energies by means of activation, 7-ray angular distribution and angle-integrated 7-flux measurements. The results of the present work together with those obtained in previous measurements are compared to the predictions of the Hauser-Feshbach theory.

High Efficiency Total Absorption Spectrometer HECTOR for capture reaction measurements

Proper understanding of the stellar nucleosynthesis processes requires information on a variety of capture reaction cross sections. Since these cross sections are typically very low, they require efficient measurement techniques. The High Efficiency Total Absorption Spectrometer (HECTOR) was designed to measure capture cross sections relevant for astrophysical processes. HECTOR is a $ \gamma$ -summing detector comprised of 16 separate NaI(Tl) segments. The detector design is presented, as well as a detailed study of the detector's summing efficiency and analysis procedure. The results of the commissioning of HECTOR are presented. The resonance strengths of the well-known resonances in the 27Al $ (\mathrm{p},\gamma)$28Si reaction measured with HECTOR are compared with the literature values.

A simple angle integration method for the determination of capture reaction cross sections

In order to determine the cross section of a reaction by the angular distribution method, it is essential to calculate the angular distributions of all secondary transitions that lead to the ground state. This is achieved by analysing spectra from HPGe detectors at various detection angles, which is a time consuming process. In this work, a simpler angle integration method is presented that allows to determine cross sections of capture reactions by measuring spectra at fewer detection angles.

New Instruments for Nuclear Astrophysics

A major task in experimental nuclear astrophysics is the measurement of cross sections of capture reactions. In the last years, the astrophysics group of NCSR “Demokritos” developed and used a method for conducting this kind of research using a 4π NaI γ-detector. Of great importance in this method is the determination of the efficiency of the detector, which depends on the average multiplicity of the γ-cascade de-exciting the entry state of the produced nucleus. Two new experimental setups have been studied and are in course of installation at the Tandem Laboratory of the Institute of Nuclear and Particle Physics of NCSR “Demokritos”, that will provide the possibility for conducting this kind of experiments inhouse. The first one is a new 14x14 inches NaI detector and the second is the BGO Ball of the GASP setup. These detector setups as well as their potential experimental use will be described in detail.