7Be Reaction Research Articles

Energy-broadened proton beam for production of quasi-stellar neutrons from the 7Li(p,n)7Be reaction

Production of quasi-stellar neutrons by the 7Li(p,n)7Be reaction has been used for measuring s-process cross sections and efforts to upgrade the proton beam intensity with RF linear accelerators are presently ongoing. We investigated the effect of an energy-broadened proton beam, as is expected for a RF linear accelerator, on the produced 25-keV quasi-Maxwellian neutron spectrum and compared it to that of a Van de Graaff accelerator with well-defined proton energy. Neutron spectrum measurements from 0° to 80° were carried out with a pulsed proton beam at the IRMM Van de Graaff accelerator using time-of-flight techniques, both with a narrow energy spread (σ≈1.5 keV) proton beam and with an energy-broadened beam (σ≈20 keV) obtained by straggling through a Au-foil degrader. In the latter case, the neutron spectrum is closer to the Maxwellian flux distribution in the high neutron energy region.

197Au(n, γ) - towards a new standard for energies relevant to stellar nucleosynthesis

Two experiments were performed to resolve a discrepancy of the 197Au(n, γ) cross section between the IAEA standard evaluation and the reference cross section for astrophysical experiments in the lower keV energy region. We measured the 197Au(n, γ) reaction by means of the time-of-flight technique with n_TOF at CERN and extracted the cross section in the unresolved resonance region between 5-400 keV with an overall uncertainty from 3.9-6.7% for a resolution of 20 bins per energy decade. Additionally, we remeasured the neutron spectrum of the 7Li(p, n)7Be reaction with Ep = 1912 keV, which was used as a neutron source for determining the astrophysical reference cross section. The n_TOF data are already fully analyzed and published. The results are in good agreement with the ENDF standard evaluation, but uncertainties don't allow to draw definite conclusions. The analysis of the neutron spectrum of 7Li(p, n)7Be is underway, preliminary results will be reported here.

Astrophysical S factor for the 4He(3He,γ)7Be reaction at medium energies

The astrophysical S factor for the 4He(3He,γ)7Be direct capture reaction plays a major role in the context of solar neutrino flux and primordial 7Li abundances that demand accurate information on the reaction. We report here our recent cross section measurements using the activation method in the region of ECM = 900-2800 keV, that aim to shed light on the discrepancies in the existing data and lead to a more accurate extrapolation of the S factor.

Microscopic calculation of the 3He(α,γ)7Be reaction rate using realistic interactions

The cross sections for the 3He(α,γ)7Be and the 3H(α,γ)7Li radiative capture reactions are calculated in the fully microscopic Fermionic Molecular Dynamics approach using a realistic effective interaction obtained in the Unitary Correlation Operator Method. The model space is divided in an external region where bound and scattering states are described by antisymmetrized products of 4He and 3He/3H ground states and an internal region where additional many-body wave functions obtained by variation after parity and angular momentum projection enlarge the Hilbert space. These additional configurations, representing polarized cluster configurations, are necessary for a successful description of the bound and scattering states. The calculated S-factor for the 3He(α,γ)7Be reaction is in good agreement with recent experimental data both in absolute normalization and energy dependence. In case of the isospin mirror reaction 3H(α,γ)7Li the calculated S-factor is larger than the experimental data by about 15%. Dipole matrix elements are analyzed in terms of overlap functions calculated from the A-body wave functions.

Cross section measurements of the 3He(α, γ)7Be reaction using DRAGON at TRIUMF

We present our initial efforts with the DRAGON separator at TRIUMF facility towards obtaining the energy dependence of the astrophysical S-factor for 3He(α, γ)7Be reaction in the energy range of Ecm = 2 to 3 MeV that was recommended by the recent evaluations. A comparison between the existing data and our new complementary Madrid data, together with the recent theoretical calculations, is also given in the context of our ongoing work.

Measurement of 232Th(n,σ)233Th, 98Mo(n,σ)99Mo, 186W(n,σ)187W, 115In(n,σ 116m1In, and 92Mo(n,p 92mNb Cross Sections in the Energy Range of 1.6 to 3.7 MeV

Neutron-induced reaction cross sections for the reaction 232Th(n, σ)233Th have been measured at neutron energies of 1.6 ± 0.03 MeV, 2.2 ± 0.03 MeV, 3.0 ± 0.03 MeV, and 3.7 ± 0.03 MeV. We have also measured cross sections for the reactions 98Mo(n, σ)99Mo, 186W(n, σ)187W, 115In(n, σ)116m1In, and 92Mo(n, p)92mNb at a neutron energy of 3.2 ± 0.03 MeV. The 7Li(p, n)7Be reaction was used as the neutron source with the proton beam from the 14-MV Pelletron accelerator, Mumbai, and the standard off-line gamma counting method was followed for activation measurement. The present measurements supplement the existing data and provide new data in the neutron energy range where no results are available. While the cross-section values for the 98Mo(n, σ)99Mo and 186W(n, σ)187W reactions are reported for the first time, the data for 92Mo(n, p)92mNb exists with a large discrepancy between the two available data sets. For the 115In(n, σ)116m1In reaction, our measurement at 3.2 MeV is an additional data point where there exists significant disagreement among the data measured by different groups. The measurements are performed relative to the 115In(n, n′)115mIn and 197 Au(n, σ)198 Au cross sections of International Reactor Dosimetry File 2002. Detailed theoretical calculations using the statistical model code EMPIRE-II (latest version EMPIRE-2.19) have been performed. Good agreement with the present data along with the existing data set has been obtained by suitable adjustment of the level density parameter for all the systems. The experimental and theoretical results have been compared with the recent evaluations of ENDF/B-VII.0, JENDL-4.0, and JEFF-3.1.

Indirect determination of Li via 74Ge(n,γ)75mGe activation reaction induced by neutrons from 7Li(p,n)7Be reaction

An indirect method to determine Li by 74Ge(n,γ)75mGe activation reaction induced in a high purity Ge (detector) crystal by neutrons from the 7Li(p,n)7Be reaction in a typical particle-induced γ-ray emission (PIGE) spectroscopy experimental set-up is described. Performed with proton beams of energies in excess of 1.88MeV, the threshold energy (Eth) of the 7Li(p,n)7Be reaction, the determination involves the activity measurement of 75mGe isotope that has a half-life of 47.7s and decays with the emission of 139keV γ-rays. Rapidity, selectivity and sensitivity down to ppm levels are the attractive features of the method. It is a suitable alternative to 7Li(p,p′γ)7Li reaction based PIGE technique in the analyses of matrices that contain light elements such as Be, B, F, Na and Al in significant proportions. Interferences can arise from elements, for example V and Ti, that have Eth⩽1.88MeV for (p,n) reaction. In the case of elements such as Cu, Mo which have with Eth>1.88MeV, the incident proton beam energy can be judiciously selected to avoid or minimize an interference. The method, under optimized irradiation conditions, does not entail a risk of neutron stimulated degradation of the performance of the detector. Besides analytical purposes, the measurement of the 75mGe activity can serve as a powerful tool to monitor even low (∼25n/cm2s) thermal neutron fluxes.

The 11B(p,α)8Be → α + α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV

Measurements of the absolute cross section and angular distributions for the \(^{11} \hbox{B}(p,\alpha)^{8}{\text{Be}}\rightarrow\alpha+\alpha\) and the 11B(α,α)11B reactions have been performed from 0.15 to 3.8 MeV for the 11B(p,α) study and from 2 to 5.4 MeV for the 11B(α,α) reaction. The absolute cross sections are presented in terms of the total number of α-particles detected in order to avoid uncertainties due to ambiguities in the number of alpha particles emitted in the reaction at a particular energy. The angular distributions of the 11B(p,α)8Be(2+) reaction were fit to a Legendre polynomial expansion and the coefficients are presented. Finally, the 11B(α,α)11B data were fit in terms of phase shifts (ignoring the spin of the target), providing a convenient representation of the elastic cross section data between 2 and 5.4 MeV.

Calibration of a Bonner sphere spectrometer in quasi-monoenergetic neutron fields of 244 and 387 MeV

This paper describes the results of calibration measurements for a Bonner sphere spectrometer (BSS) with 3He proportional counter performed in quasi-monoenergetic neutron fields at the Research Center for Nuclear Physics (RCNP) at the University of Osaka, Japan. Using 246 MeV and 389 MeV proton beams, neutron fields with nominal peak energies of 244 MeV and 387 MeV were generated via 7Li(p,n)7Be reactions. At high energies, the neutron spectra were measured by means of the time-of-flight (TOF) method. The low-energy part of the neutron spectra were determined by BSS measurements down to thermal energies using the MSANDB unfolding code and three different sets of response functions. These were obtained by means of Monte Carlo (MC) calculations including various codes and intra-nuclear cascade (INC) models. Unfolded BSS fluence rates were additionally confirmed by GEANT4 calculations. For calibration of the BSS, measured count rates were corrected for low-energy contributions and compared with count rates calculated using TOF data and various response functions. In addition, measured response values were compared with mono-energetic response calculations, and best agreement was found with GEANT4 results using the Bertini INC model.

A novel BNCT irradiation system with an on-line monitor using 7Li(P,N)7Be near threshold neutrons

Abstract A neutron irradiation system for boron neutron capture therapy using accelerators with an online dose monitoring system was studied for the possible practical implementation of hospital-based BNCT. For this purpose the neutrons produced by the near threshold 7Li(p,n)7Be reaction, i.e. an incident proton energy of around 1.90 MeV, have suitable properties. Such as the maximum energy below 100 keV and mostly forward-directed. A good candidate material to shield gamma rays from the Li-target was Lead and the suitable boron-dose enhancer was polyethylene. The optimum physical dimensions and configuration of the irradiation system was determined using the concept of treatbale protocol depth as figures of merit. For the online monitor system, the single photon emission computed tomography using prompt gamma-ray was studied to provide an ideal dose estimation system. A neutron producing target system with a liquid lithium jet flow of about 30 m/s at a thickness of 1 mm and a cross-sectional area of 50 mm × 50 mm is proposed.

Excited states of 12C above the alpha-decay threshold

The excitation energy spectrum of 12C is important for both structural and astrophysical reasons; here we present evidence for a new state in 12C. The two reactions 12C(4He,4He+4He+4He)4He and 9Be(4He,4He+4He+4He)n were measured using an array of four double sided strip detectors. Excited states in 12C were reconstructed filtered by the condition that the alpha-decay proceeded via the 8Be ground-state. In both measurements evidence was found for a new state at 13.3(0.2) MeV with a width 1.7(0.2) MeV. Angular correlation measurements from the 12C(4He,4He+4He+4He)4He reaction indicates that the state may have J π = 4+.

Measurement of Energy-angular Neutron Distribution for 7Li, 9Be(p,xn) Reaction at EP = 70 MeV and 11 MeV

Measurement of Energy-angular Neutron Distribution for 7Li, 9Be(p,xn) Reaction at EP = 70 MeV and 11 MeV

Neutrons do not produce a bystander effect in zebrafish irradiated in vivo

Purpose: Neutron irradiations at the McMaster Tandetron Accelerator were performed to study direct and bystander effects of neutrons in a live organism.Methods: The neutrons were produced through 7Li(p,n)7Be reaction. Although the gamma contamination of the neutron beam cannot be completely eliminated, it was designed to be as low as possible and remain below a threshold already established for bystander effects. Microdosimetric methods using a tissue-equivalent proportional counter have been used to measure the neutron and gamma doses for the cell irradiation. Previous data for a cell line exposed in vitro suggested that neutrons did not produce bystander effects at doses below 300 mGy. The current experiments sought to confirm this using a live whole organism (zebrafish) where tissue samples harvested 2 h after exposure were examined for direct evidence of apoptosis and tested for secretion of bystander factors using an established bioassay. Fish were either exposed directly to the beam or were allowed to swim with or in water previously occupied by irradiated fish.Results: Using the zebrafish model it was found that there was significant direct cell death seen both by apoptosis scores and clonogenic assay when the neutron dose was approximately 100 mGy. An equivalent dose of gamma rays produced a more toxic effect. It was further found that neutrons did not induce a bystander effect in fish receiving signals from irradiated fish.Conclusion: The results confirm in vitro experiments which suggest neutrons do not induce bystander signaling. In fact they may suppress gamma induced signaling suggesting a possible intriguing new and as yet unclear mechanism.

Comparison of asymptotic normalization coefficients for 10B → 9B + n and 10B → 9Be + p configurations obtained from 10B(d,t)9B and 10B(d,3He)9Be reactions

The differential cross sections of the 10B(d,t)9B and 10B(d,3He)9Be reactions at E d = 25 MeV were measured to obtain the ratio of asymptotic normalization coefficients for the bound states of the last neutron and the last proton in the symmetric nucleus 10B. The obtained ratio is shown to be in agreement with the theoretical value.

The 7Li(18O, 16N)9Be reaction and optical potential of 16N + 9Be versus 16O + 9Be

Abstract Angular distributions for the 7Li(18O, 16N)9Be reaction at an energy of E lab ( O 18 ) = 114 MeV for the ground and excited states of 9Be and 16N were measured. The data were analyzed within the coupled-reaction-channels method for one- and two-step transfers of nucleons and clusters. The 7Li + 18O optical potential fitted to the 7Li + 18O elastic and inelastic scattering data was used in the reaction calculations. The needed spectroscopic amplitudes for transferred nucleons and clusters were calculated within the translational-invariant shell model. The 9Be + 16N potential parameters were deduced by fitting 7Li(18O, 16N)9Be reaction data for ground and excited states of 9Be and 16N. The reaction is dominated by deuteron transfer. The 9Be + 16N potential is compared with the 9Be + 16O potential deduced by fitting previously reported 9Be + 16O elastic scattering data at energies E c.m. = 5.4 – 100.9 MeV and found to be less strongly absorbing.

Precise measurements of the thick target neutron yields of the 7Li(p,n) reaction

Thick target neutron yield of the 7Li(p,n) 7Be reaction was measured in the proton energy range from 1.95 to 2.3 MeV by determining induced activity of the 7Be. A HPGe detector was used to detect the 478 keV gamma-rays emitted through 7Be decay. A series of irradiations with nominal proton energies of 1.95, 2.0, 2.1, 2.2, and 2.3 MeV were carried out. In an independent experiment, raw neutron spectra were collected by a 3He ion chamber for the same series of proton energies. From the raw neutron spectra, it was noted, that the effective proton energies were lower than the nominal by 50–58 keV. After corrections for the proton energy offsets were applied, the measured neutron yields matched the analytically calculated yields within 20%. Long term stability of neutron yield was tested at two nominal proton energies, 2.1 and 1.95 MeV over an experimental period of one year. The results show that the yield at 2.1 MeV was stable within rmse variation coefficient of 4.7% and remained consistent even when the lithium target was replaced, whereas at 1.95 MeV, the maximum fluctuations reached a factor of 10.

Measurement of the neutron capture cross-section of 232Th using the neutron activation technique

The 238U(n, γ)239U reaction cross-section at average neutron energy of 3.7 ± 0.3 MeV from the 7Li(p, n)7Be reaction has been determined using activation and off-line γ-ray spectrometric technique. The 238U(n, γ)239U and 238U(n, 2n)237U reaction cross-sections at average neutron energy of 9.85 ± 0.38 MeV from the same 7Li(p, n)7Be reaction have been also determined using the above technique. The experimentally determined 238U(n, γ)239U and 238U(n, 2n)237U reaction cross-sections were compared with the evaluated data of ENDF/B-VII, JENDL-4.0, JEFF-3.1 and CENDL-3.1. The experimental values were found to be in general agreement with the evaluated value based on ENDF/B-VII, and JENDL-4.0 but not with the JEFF-3.1 and CENDL-3.1. The present data along with literature data in a wide range of neutron energies were interpreted in terms of competition between different reaction channels including fission. The 238U(n, γ)239U and 238U(n, 2n)237U reaction cross-sections were also calculated theoretically using the TALYS 1.2 computer code and were also found to be in agreement experimental data.

Experimental response functions of a single-crystal diamond detector for 5–20.5 MeV neutrons

A single crystal diamond detector was exposed to quasi mono-energetic neutron fields in the energy range from 5 to 20.5 MeV. Response functions of such a detector were measured for the first time for neutron energies above 14 MeV. The pulse height spectra showed sharp peaks at specific energies. These peaks result from neutron induced charged particle reactions occurring in carbon at different neutron energies. The centroid of the peaks due to the 12C(n,α) 9Be reaction permitted, by means of the reaction Q-values, to point out a good linearity of the detector response versus neutron energy and a good intrinsic energy resolution of about 56 keV at full width at half maximum. The results reveal that single crystal diamond detectors are good candidates as high resolution fast neutron spectrometers for nuclear fusion applications and for systematic studies of beam and target characteristics for neutron-producing reactions.

AB-BNCT beam shaping assembly based on 7Li(p,n)7Be reaction optimization

A numerical optimization of a Beam Shaping Assembly (BSA) for Accelerator Based-Boron Neutron Capture Therapy (AB-BNCT) has been performed. The reaction (7)Li(p,n)(7)Be has been considered using a proton beam on a lithium fluoride target. Proton energy and the dimensions of a simple BSA geometry have been varied to obtain a set of different configurations. The optimal configuration of this set is shown.

Microscopic Calculation of theHe3(α,γ)Be7andH3(α,γ)Li7Capture Cross Sections Using Realistic Interactions

The radiative capture cross sections for the 3He(alpha,gamma)7Be and 3H(alpha,gamma)7Li reactions are calculated in the fully microscopic fermionic molecular dynamics approach using a realistic effective interaction that reproduces the nucleon-nucleon scattering data. At large distances bound and scattering states are described by antisymmetrized products of 4He and 3He/3H ground states. At short distances the many-body Hilbert space is extended with additional many-body wave functions needed to represent polarized clusters and shell-model-like configurations. Properties of the bound states are described well, as are the scattering phase shifts. The calculated S factor for the 3He(alpha,gamma)7Be reaction agrees very well with recent experimental data both in absolute normalization and energy dependence. In case of the 3H(alpha,gamma)7Li reaction the calculated S factor is larger than available experimental data by about 15%.