7Be Reaction Research Articles

Analysis of the 3He(α,γ)7Be and 3H(α,γ)7Li astrophysical direct capture reactions in a modified potential-model approach

Astrophysical S factors and reaction rates of the direct radiative capture processes He3(α,γ)7Be and H3(α,γ)7Li, as well as the primordial abundance of the Li7 element, are estimated in the framework of a modified two-body potential model. It is shown that suitable modification of phase-equivalent α−3He potentials in the d waves can improve the description of the astrophysical S factor for the direct He3(α,γ)7Be radiative capture reaction at energies above 0.5 MeV. An estimated Li/H7 abundance ratio of (4.89±0.18)×10−10 is in very good agreement with the recent measurement of (5.0±0.3)×10−10 by the LUNA collaboration.

Underground experimental study finds no evidence of low-energy resonance in theLi6(p,γ)Be7reaction

Underground experimental study finds no evidence of low-energy resonance in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>Li</mml:mi><mml:mprescripts/><mml:none/><mml:mn>6</mml:mn></mml:mmultiscripts><mml:mo>(</mml:mo><mml:mi>p</mml:mi><mml:mo>,</mml:mo><mml:mi>γ</mml:mi><mml:mo>)</mml:mo><mml:mmultiscripts><mml:mi>Be</mml:mi><mml:mprescripts/><mml:none/><mml:mn>7</mml:mn></mml:mmultiscripts></mml:mrow></mml:math>reaction

A bi-tapered and air-gapped beam shaping assembly used for AB-BNCT

The 7Li(p,n)7Be reaction, which leads to a soft neutron field, is often chosen as the neutron producing reaction used for accelerator-based boron neutron capture therapy (AB-BNCT). This study aims to design a compact beam shaping assembly (BSA) and auxiliary system for a 7Li(p,n)7Be reaction-based neutron source and to evaluate the relationship between the BSA design and the consequent neutron beam quality for further optimization.In this study, five types of moderator shapes for the BSA model were designed. Both the in-air and in-phantom figures of merit were considered to evaluate the performance of the BSA designs. It was found that the BSA with a bi-tapered and air-gapped design could generate a high-intensity epithermal neutron beam, which could be used to treat deep-seated brain tumors within a reasonable time.

The Study of the 6Li(p,γ)7Be Reaction at LUNA

The 6Li(p,γ)7Be reaction is mainly involved in two astrophysical scenarios: the primordial nucleosynthesis and 6Li consumption in pre-main and main sequence stars. A recent measurement of 6Li(p,γ)7Be reaction S-factor reported a resonance-like structure at Ecm = 195 keV, which has not been confirmed neither by other direct measurements nor by theoretical calculations.A new experiment was performed at the Laboratory for Underground Nuclear Astrophysics (LUNA). The extremely low background environment allowed to measure the 6Li(p,γ)7Be cross section down to low energies with unprecedented sensitivity leading to clarify the existence of the claimed resonance. Details on the experimental setup and the preliminary results of the ongoing analysis are reported in this work.

Investigation of the 7Li(p,n) neutron fields at high energies

The neutron activation method has been proven to be a well-suited tool for the investigation of neutron capture cross sections relevant for the main component of the s-process. Neutrons produced via the 7Li(p,n)7Be reaction at a proton energy of Ep = 1912 keV can be used to recreate a quasi-stellar neutron energy distribution mimicking the astrophysical s-process scenario at kBT = 25keV. For the weak s-process, which takes place in massive stars at temperatures between kBT = 25 keV and kBT = 90 keV, the activation method has not yet been successful in recreating quasi-stellar neutron spectra. However, simulations show that the activation method can be improved in order to recreate a quasi-stellar neutron spectrum at different energies by linear combination of different neutron spectra. In order to verify these simulations the neutron fields of the reaction have to be measured at different proton energies.

R-Matrix Analysis of Reactions with Excitation of the 10B Compound Nucleus at Energies of 6.5–19.5 MeV

An R-matrix analysis is performed for experimental data on 9Be(p,p0)9Be, 9Be(p,p1)9Be* (1.670 MeV), 9Be(p,p2)9Be* (2.430 MeV), 9Be(p,n0)9B, 9Be(p,d0)8Be, 9Be(p,α0)6Li, 9Be(p,α2)6Li* (3.5618 MeV), and 7Li(3He,p0)9Be reactions at 6.5–19.5 MeV excitation energies of 10B compound nucleus. Experimental data on differential and integral cross sections of the 9Be(p,α2)6Li* (3.5618 MeV, Jπ = 0+) reaction at proton energy Ep = 2.3–4.5 MeV are included in the analysis, along with data on differential cross sections of the 9Be(p,n0)9B reaction at angle 0° in the Ep = 2.2–3.5 MeV energy range. New 10B levels are determined and characteristics of states detected earlier are improved.

Study of the 7Be(α,γ)11C reaction with DRAGON for vp–process nucleosynthesis

The production of the p–nuclei is one of the unsolved puzzles in nuclear astrophysics. A possible mechanism is the nucleosynthesis in the neutrino–driven winds of core–collapse supernovae (νp–process), but it carries uncertainties, mostly in the supernova dynamics and the nuclear physics input. The pp-chain breakout reaction 7Be(α,γ)11C, which occurs prior to the supernova explosion, was identified as an important link which can influence the nuclear flow of the z/p-process and the final abundances of the p-nuclei. Nevertheless, its reaction rate is poorly known over the relevant energy range (T=1.5-3 GK). To improve the 7Be(α,γ)11C rate for vp-process nucleosynthesis temperatures, the first measurement of the strengths of two important resonances with unknown strength was recently performed at TRIUMF. A radioactive 7Be beam (t1/2 = 53.24 d) beam and the DRAGON recoil separator were used. The experimental details and preliminary results for the resonance strengths will be discussed.

In situ study of the blistering effect of copper with a thin lithium layer on the neutron yield in the 7Li(p,n)7Be reaction

A vacuum insulated tandem accelerator was used to study the effect of blistering on the neutron yield under 2-MeV proton bombardment of lithium target. The target is a thin lithium layer evaporated onto an efficiently cooled copper substrate. Targets with lithium thickness from 1 to 84 µm were irradiated by protons up to fluence of 6.3 1020 cm−2 which was significantly greater than the blistering threshold. The state of the targets surface was observed using long-distance microscope, video camera, infrared camera. The neutron dose was measured by dosimeters, the neutron flux density was measured by neutron detector. After irradiation, the targets were analyzed on Raman spectrometer, single crystal diffractometer, electron microscope, scanning profilometer, scanning electron microscope, atomic emission spectrometer. The article describes the experiment, presents the results obtained and notes their significance in the enhancement of a target for the neutron source used in boron neutron capture therapy.

Production cross-sections of Mo-isotopes induced by fast neutrons based on the 9Be(p, n) reaction

We measured the flux-weighted average cross-sections of the 100Mo(n, 2n)99Mo and 92Mo(n, 3n)90Mo reactions with the average neutron energies between 14.0- and 31.8-MeV by using an activation and off-line γ-ray spectrometric technique. The fast neutrons were generated based on the 9Be(p, n) reaction with the proton energies of 25-, 35- and 45-MeV from the MC-50 Cyclotron at the Korea Institute of Radiological and Medical Sciences (KIRAMS). The neutron flux was measured by using the 27Al(n, α)24Na monitor reaction, whereas the neutron spectra were simulated by using the MCNPX 2.6.0 code. The theoretical cross-sections of the 100Mo(n, 2n)99Mo and 92Mo(n, xn)91.90,89Mo reactions as a function of mono-energetic neutron were calculated by using the TALYS-1.9 code. The present results for the 100Mo(n, 2n)99Mo and 92Mo(n, 3n)90Mo reactions are compared with the calculated neutron flux-weighted average values based on the literature data and theoretical cross-sections as a function of mono-energetic neutron energy, and show a good agreement.

Status of low-energy accelerator-based BNCT worldwide and in Argentina

Existing and active low-energy Accelerator-Based BNCT programs worldwide will be reviewed and compared. In particular, the program in Argentina will be discussed which consists of the development of an Electro-Static-Quadrupole (ESQ) Accelerator-Based treatment facility. The facility is conceived to operate with the deuteron-induced reactions 9Be(d,n)10B and 13C(d,n)14N at 1.45 MeV deuteron energy, as neutron sources. Neutron production target development status is specified. The present status of the construction of the new accelerator development laboratory and future BNCT centre is shown.

Neutron yields of Be-9(p,xn) reactions and beam characterization for accelerator-based boron neutron capture therapy facility using MCNP6, PHITS, and GEANT4 simulation results

Neutron yields from 9Be(p,xn) reactions with a 2-cm thick beryllium target bombarded by proton beams of 5, 6, 7, 8, 9, and 10 MeV were investigated. Neutron beam characteristics through a pilot design of beam shaping assembly were calculated by using MCNP6, PHITS, and GEANT4. The neutron yield with a 10 MeV beam by MCNP6 was 7.7 times larger than values by the other codes, but close to the experimental data. The neutron spectrum and directionality were different among the codes. These differences could stem from different cross-section libraries and models used in the codes. The epithermal flux at the beam irradiation port by MCNP6 was 1.4 × 109 cm−2 s−1 for a proton current of 8 mA hitting the target. The ratio of thermal and epithermal flux was less than 0.01 and the forward directionality was 0.78. However, we suggest a new criterion regarding a ratio of fast and epithermal flux.

Astrophysical S-factor for the 3He(α,γ)7Be reaction via the asymptotic normalization coefficient (ANC) method

The detection of the neutrinos produced in the p−p chain and in the CNO cycle can be used to test the Standard Solar Model. The 3He(α,γ)7Be reaction is the first reaction of the 2nd and 3rd branch of the p−p chain, therefore, the uncertainty of its cross section sensitively influences the prediction of the 7Be and 8B neutrino fluxes. Despite its importance and the large number of experimental and theoretical works devoted to this reaction, the knowledge on the reaction cross section at energies characterizing the core of the Sun (15 keV - 30 keV) is limited and further experimental efforts are needed to reach the desired (≈ 3%) accuracy. The precise knowledge on the external capture contribution to the 3He(α,γ)7Be reaction cross section is crucial for the theoretical description of the reaction mechanism. In the present work the indirect measurement of this external capture contribution using the Asymptotic Normalization Coefficient (ANC) technique is reported. To extract the ANC, the angular distributions of deuterons emitted in the 6Li(3He,d)7Be α-transfer reaction were measured with high precision at EH3e = 3.0 MeV and EH3e = 5.0 MeV. The ANCs were then extracted from comparison of DWBA calculations to the measured data and the zero energy astrophysical S-factor for 3He(α,γ)7Be reaction was found to be 0.534 ± 0.025 keVb.

Study of charged particle activation analysis (II): Determination of boron concentration in human blood samples

Boron Neutron Capture Therapy (BNCT) is a radiotherapy for the treatment of intractable cancer. In BNCT precise determination of 10B concentration in whole blood sample before neutron irradiation of the patient, as well as accurate neutron dosimetry, is crucial for control of the neutron irradiation time. For this purpose ICP-AES and neutron induced prompt γ-ray analysis are generally used. In Ibaraki Neutron Medical Research Center (iNMRC), an intense proton beam will be accelerated up to 8 MeV, which can also be used for Charged Particle Activation Analysis (CPAA). Thus, in this study, we apply the CPAA utilizing the proton beam to non-destructive and accurate determination of 10B concentration in whole blood sample.A CPAA experiment is performed by utilizing an 8 MeV proton beam from the tandem accelerator of Nuclear Science Research Institute in Japan Atomic Energy Agency. The 478 keV γ-ray of 7Be produced by the 10B(p, α)7Be reaction is used to quantify the 10B in human blood. The 478 keV γ-ray intensity is normalized by the intensities of the 847 keV and 1238 keV γ-rays of 56Co originating from Fe in blood. The normalization methods were found to be linear in the range of 3.27 μg 10B/g to 322 μg 10B/g with correlation coefficients of better than 0.9999.

Spectroscopy of 7He in stopped pion absorption

Formation of the 7He heavy isotope was studied in the reactions of stopped pion absorption by light nuclei 9Be, 10,11B and 12,14C. Measurements were performed using the two-arm multilayer semiconductor spectrometer. Contrary to the results of other studies, we observed several narrow highly excited states (Ex > 16 MeV) of 7He. From the analysis of the continuous excitation spectrum in reactions 9Be(π−, d)X and 11B(π−, dd)X it was obtained first indication that the 4He+3n structure is not present in the ground state of 7He.

Astrophysical S(E) for the 9Be(p, d)8Be and 9Be(p, α)6Li Reactions by Direct Measurement

Abstract The p–9Be reactions play a key role in accurate prediction of the primordial abundance of beryllium, and its abundance can be used to exquisitely probe the nucleosynthesis and mixing mechanism of stars. In the present work, astrophysical S(E) factors of the 9Be(p, d)8Be and 9Be(p, α)6Li reactions have been obtained from the thick-target yield Yield(E i) for proton energies from 18 to 100 keV. A full R-matrix analysis was performed to fit both the 9Be(p, α)6Li and 9Be(p, d)8Be reactions simultaneously. The resulting astrophysical S(E) factors agree well with direct measurements, leading to S(0) = 17.3 ± 2.1 and 13.9 ± 1.8 MeV·b for the 9Be(p, α)6Li and 9Be(p, d)8Be reactions, respectively. However, the obtained screening potential (U s = 512 ± 77 eV) is lower than results of previous work (900 ± 50 and 806 eV), and all of them are larger than the adiabatic limit of 264 eV. The reaction rates were also calculated in the temperature range (0.01–1) ⨯ 109 K, which improves on the precision of the standard database NACRE and NACRE II.

Anomalous Radioisotope Production for 68ZnO Using Polyethylene by Accelerator Neutrons

We measured the yields of radionuclides after neutron irradiation on an enriched 68ZnO sample covered with polyethylene blocks. The neutrons were generated from the 9Be(d,n) reaction by 40 and 50 M...

Systematic study of the response of single crystal diamond neutron detectors at high temperature

For many years artificial diamond detectors have been studied for application in high temperature environments. An open question is whether the performance of such detectors is influenced by the electrical contacts. In the attempt to better understand this point, a systematic study of electrical contacts deposited with different techniques and materials on top of commercial artificial single crystal diamond (SCD) films was performed. In this paper we report on the results obtained using three types of electric contacts produced both using metal and not metal layers: a) double Schottky, b) double ohmic; c) Schottky-ohmic contacts. The detectors were studied under 14 MeV neutron irradiation, and were operated in pulse mode. The pulse height spectra (PHS) produced by the 14 MeV neutrons were recorded as a function of temperature and the detector behaviour was studied by analysing the variation of the peak produced in the PHS by the 12C(n,α)9Be reaction induced by 14 MeV neutrons in carbon. The maximum operational temperature limit of the tested detectors was found to be around 230̂C and it resulted to be slightly dependent, within ±10̂C, upon the type of the electrical contact. It turned out that, together with the type of the electrical contact, other parameters such as the intrinsic diamond properties and the film thickness have to be considered to understand the response of the detector at high temperature.

Angular Distribution of Neutrons Around Thick Beryllium Target of Accelerator-Based 9Be(d, n) Neutron Source

Abstract An experimental work and simulations were carried out to determine the angular distributions of neutrons and yields of the 9Be(d, n) reaction over all angular range (360 deg) on a thick beryllium target as an accelerator-based neutron source at incident-deuteron energy 13.6 MeV. The neutron activation method was used in the experimental part using aluminum and iron foils as detectors to calculate the neutron flux. The Monte Carlo neutral-particles code (MCNP5) was used to demonstrate and simulate the neutron distribution, also to understand and compare with the experimental results. The neutron energy spectrum was computed using the projection angular-momentum coupled evaporation code PACE4 (LISE++) and the spectrum was adopted in MCNP5 code. Two experimental ways were used, one with beryllium target and another one without the beryllium target, to evaluate the neutron flux emitted only by the beryllium target. Typical computational results were presented and are compared with the previous experimental data to evaluate the computing model as well as the characteristics of emitted neutrons produced by the 9Be(d, n) reaction with a thick Be-target. Moreover, the results can be used to optimize the shielding and collimating system for neutron therapy.

Nuclear Data Sheets for A=98

Experimental spectroscopic data on nuclear structure and decay are evaluated for known nuclides of mass 98 (Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In). Detailed evaluation results of individual reactions and decays are presented together with the Adopted values that are recommended for level properties, γ and β radiations, and other spectroscopic information. 98Mo remains as the most extensively studied nuclide via various reactions and decays. Level schemes of Sr, Y, Zr, Tc, and Pd nuclides in this mass chain are also well established to date; while Kr, Rb, Nb, Ag and Cd are amongst the least-studied ones for excited states, with only limited data available for each. On the neutron-rich side, 98Br has been identified in the 9Be(238U,F) reaction, but no spectroscopic data are yet available, while for 98In on the proton-rich side, only the ground state and an isomer are known with half-lives measured but their spin-parities and the absolute level energy of the isomer yet to be determined. While 98Ru and 98Rh have also been extensively studied, large discrepancies exist between the high-spin sections of the proposed level schemes in different measurements, and these need to be clarified and resolved with further experimental investigations to improve the currently-adopted ones, which have been selected from the measurements with higher statistics, considering no other criteria of preference. This work supersedes all the earlier evaluations of A=98 (2003Si07, 1998Si18, 1992Si21, 1983Mu21, 1974Me34).

The Interaction of Neutrons with 7Be at BBN Temperatures: Lack of Standard Nuclear Solution to the “Primordial 7Li Problem”

We report the first measurement of alpha-particles from the interaction of neutrons with 7Be at “temperatures” of Big Bang Nucleosynthesis (BBN). We measured the Maxwellian averaged cross sections (MACS), with neutron beams produced by the LiLiT at the SARAF in Israel (with kT = 49.5 keV hence 0.57 GK). In addition, we measured the cross section of the 7Be(n,p) reaction, which is in excellent agreement with the recent measurement of the n_TOF collaboration, further substantiating our method as a demonstration of “proof of principle”. The cross section for the 7Be(n,ga) and the 7Be(n,a) reaction measured in the “BBN window” is considerably smaller than compiled by Wagoner in 1969 and used today in Big Bang Nucleosynthesis (BBN). We also rule out a hitherto unknown resonance in 8Be at the BBN window, that was conjectured as a possible standard nuclear physics solution to the “Primordial 7Li Problem”. Together with previous results, we deduce a new Wagoner-like Rate for the destruction of 7Be by neutrons which is based on all current measured data. We conclude the lack of a standard nuclear solution to the “Primordial 7Li Problem”. Our upper limit on the cross sections for the high energy alpha-particles is in agreement with recent measurement of the n_TOF collaboration, but it is considerably smaller than the p-wave extrapolation of the Kyoto collaboration. We measured the alpha-particles from the 7Be(n,gi)8Be*(3.03 MeV) reaction, which is considerably larger than a previous s-wave estimate. Hence, in contrast, we conclude s-wave dominance at BBN energies, as would be expected due to the broad (122 keV) low lying 2” state at En = 10 keV.