7Be Reaction Research Articles

Near threshold 7Li(p,n) 7Be reaction as neutron source for BNCT

7Li(p,n)7Be is an endothermic reaction and working near its threshold (1.88MeV) has the advantage of neutron spectra with maximum energies of about 100keV, considerably lower than at higher beam energies, or than using other neutron-producing reactions or as for the uranium fission spectrum, relevant for BNCT based on nuclear reactors. With this primary energy it is much easier to obtain the energies needed for treating deep seated tumors by BNCT (about 10keV). This work studies bombarding energies up to 2.05MeV, different beam incidence angles and the effect of the undesirable gamma production via the 7Li(p,γp’) 7Li reaction.

Constraining big bang lithium production with recent solar neutrino data

The 3He({\alpha},{\gamma})7Be reaction affects not only the production of 7Li in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from the Sun. This double role is exploited here to constrain the former by the latter. A number of recent experiments on 3He({\alpha},{\gamma})7Be provide precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However, there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and below. This problem can be alleviated, based on precisely calibrated 7Be and 8B neutrino fluxes from the Sun that are now available, assuming the neutrino flavour oscillation framework to be correct. These fluxes and the standard solar model are used here to determine the 3He(alpha,gamma)7Be astrophysical S-factor at the solar Gamow peak, S(23+6-5 keV) = 0.548+/-0.054 keVb. This new data point is then included in a re-evaluation of the 3He({\alpha},{\gamma})7Be S-factor at Big Bang energies, following an approach recently developed for this reaction in the context of solar fusion studies. The re-evaluated S-factor curve is then used to re-determine the 3He({\alpha},{\gamma})7Be thermonuclear reaction rate at Big Bang energies. The predicted primordial lithium abundance is 7Li/H = 5.0e-10, far higher than the Spite plateau.

Broad energy range neutron spectroscopy using a liquid scintillator and a proportional counter: Application to a neutron spectrum similar to that from an improvised nuclear device

A novel neutron irradiation facility at the Radiological Research Accelerator Facility (RARAF) has been developed to mimic the neutron radiation from an Improvised Nuclear Device (IND) at relevant distances (e.g. 1.5km) from the epicenter. The neutron spectrum of this IND-like neutron irradiator was designed according to estimations of the Hiroshima neutron spectrum at 1.5km. It is significantly different from a standard reactor fission spectrum, because the spectrum changes as the neutrons are transported through air, and it is dominated by neutron energies from 100keV up to 9MeV. To verify such wide energy range neutron spectrum, detailed here is the development of a combined spectroscopy system. Both a liquid scintillator detector and a gas proportional counter were used for the recoil spectra measurements, with the individual response functions estimated from a series of Monte Carlo simulations. These normalized individual response functions were formed into a single response matrix for the unfolding process. Several accelerator-based quasi-monoenergetic neutron source spectra were measured and unfolded to test this spectroscopy system. These reference neutrons were produced from two reactions: T(p,n)3He and D(d,n)3He, generating neutron energies in the range between 0.2 and 8MeV. The unfolded quasi-monoenergetic neutron spectra indicated that the detection system can provide good neutron spectroscopy results in this energy range. A broad-energy neutron spectrum from the 9Be(d,n) reaction using a 5MeV deuteron beam, measured at 60 degrees to the incident beam was measured and unfolded with the evaluated response matrix. The unfolded broad neutron spectrum is comparable with published time-of-flight results. Finally, the pair of detectors were used to measure the neutron spectrum generated at the RARAF IND-like neutron facility and a comparison is made to the neutron spectrum of Hiroshima.

Detection system of the COMBAS fragment separator

The (ΔE1, ΔE2, E) multidetector telescope has been developed and tested. The telescope is a compact combination of two 32-strip silicon ΔE1-, ΔE2-detectors and a scintillation E-detector, which is a 3 × 3 array of CsI(Tl) crystals. A timing signal can be obtained from any of the Si detectors for time-of-flight (TOF) measurements. Single-channel and 32-channel charge-sensitive preamplifiers have been developed and manufactured for the multidetector module to serve the ΔE- and E-detectors with high efficiency and sensitivity. Reaction products obtained in the 40Ar (35 MeV/nucleon) + 9Be reaction have been unambiguously identified in the experiment by mass number A and atomic number Z.

Evaluation of A-dependence of cross-sections for light charged particle production in proton induced reactions at intermediate energies

Abstract Proton-, deuteron-, triton-, 3He, and α-particle production cross-sections were evaluated for proton induced reactions for 278 stable target nuclei with an atomic number from 3 to 83 for a number of incident proton energies from 62 to 1200 MeV using available experimental data and results of model calculations. Data obtained can be used for the evaluation of gas production cross-sections and gas production rates in reactions induced by intermediate energy protons. An example of the use of the data is given for 9Be(p,x) reactions.

A high-power liquid-lithium target (LiLiT) for neutron production

A high-power liquid-lithium target (LiLiT) was built and commissioned with a 1.2 mA, 1.91 MeV (2.3 kW) proton beam from the SARAF (Soreq Applied Research Accelerator Facility, Israel). The lithium film acts both as a neutron-producing target via the 7Li(p,n)7Be reaction with a yield of ~ 2 × 1010 n/s/mA and as a power beam dump. The neutron source is suited for the study of neutron capture reactions on nuclides (stable or radioactive) of low abundance for nuclear astrophysics and to the needs of boron neutron capture therapy (BNCT).

New method to evaluate the 7Li(p, n)7Be reaction near threshold

In this work a complete description of the 7Li(p,n)7Be reaction near threshold is given using center-of-mass and relative coordinates. It is shown that this standard approach, not used before in this context, leads to a simple mathematical representation which gives easy access to all relevant quantities in the reaction and allows a precise numerical implementation. It also allows in a simple way to include proton beam-energy spread affects. The method, implemented as a C++ code, was validated both with numerical and experimental data finding a good agreement. This tool is also used here to analyze scattered published measurements such as (p,n) cross sections, differential and total neutron yields for thick targets. Using these data we derive a consistent set of parameters to evaluate neutron production near threshold. Sensitivity of the results to data uncertainty and the possibility of incorporating new measurements are also discussed.

A theoretical analysis of the 6He + 9Be reaction: phenomenological and double folding model approximations

We investigate the elastic scattering data of the 6He + 9Be reaction by using the phenomenological and double folding model potentials within the framework of the optical model. In the phenomenological calculations, we use the optical model parameters existed in literature to explain 6He + 9Be reaction. The real potentials in double folding calculations are obtained by using two different density distributions of 6He nucleus. For both the phenomenological and double folding model calculations, the imaginary potentials have the shape of the Woods-Saxon volume. We compare the phenomenological model results with the double folding model ones as well as the experimental data. We present that the folding model results are in better agreement with the experimental data than the phenomenological results for the 6He + 9Be reaction.

Measurement of the High Energy Neutron Flux on the Surface of the Natural Uranium Target Assembly QUINTA Irradiated by Deuterons of 4 and 8 GeV Energy

Experiments with the natural uranium target assembly “QUINTA” exposed to 4 and 8GeV deuteron beams of the Nuclotron accelerator at the Joint Institute for Nuclear Research (Dubna) are analyzed. The reaction rates of 27Al(n,y1)24Na, 27Al(n,y2)22Na and 27Al(n,y3)7Be reactions with effective threshold energies of 5, 27, and 119 MeV were measured at both 4GeV and 8GeV deuteron beam energies. The average neutron fluxes between the effective threshold energies and the effective ends of the neutron spectra (which are 800 or 1000 MeV for 4 or 8GeV deuterons) were determined. The evidence for the intensity shift of the neutron spectra to higher neutron energies with the increase of the deuteron energy from 4GeV to 8GeV was found from the ratios of the average neutron fluxes. The reaction rates and the average neutron fluxes were calculated with the MCNPX 2.7 code.

Some Insights into Cluster Structure of <sup>9</sup>Be from <sup>3</sup>He + <sup>9</sup>Be Reaction

The study of inelastic scattering and multi-nucleon transfer reactions was performed by bombarding a 9Be target with a 3He beam at the incident energy of 30 MeV. Angular distributions for 9Be(3He, 3He) 9Be, 9Be (3He, 3He) 8Be, 9Be (3He, 7Be) 5He, 9Be (3He, 6Li) 6Li and 9Be (3He, 7Li) 5Li reaction channels were measured. Experimental angular distributions for the corresponding ground states (g.s.) were analyzed within the framework of the optical model, the coupled-channel approach and the distorted-wave Born approximation. Cross sections for channels leading to unbound 5Heg.s., 5Lig.s. and 8Be systems were obtained from singles measurements where the relationship between the energy and the scattering angle of the observed stable ejectile was constrained by two-body kinematics. Information on the cluster structure of 9Be was obtained from the transfer channels. It was concluded that cluster transfer was an important mechanism in the investigated nuclear reaction channels. In the present work an attempt was made to estimate the relative strengths of the interesting (n + 8Be) and (α + 5He) cluster configurations in 9Be. The contributions of different exit channels have been determined confirming that the (α + 5He) configuration plays an important role. The configuration of 8Be consisting of two bound helium clusters (5He + 6He) is significantly suppressed, whereas the two-body configurations (n + 8Be) and (α + 5He) including unbound 8Be and 5He are found more probable.

Treatment of the Mirror 3H(α, γ) 7Li and 3He(α, γ) 7Be Reactions in the Algebraic Version of the Resonating Group Model

A unified microscopic approach based on the algebraic version of the resonating group model has been realized for description of the radiative capture reactions 3H(α, γ)7Li and 3He(α, γ)7Be, which play an important role for modern nuclear astrophysics. The astrophysical S-factors of the reactions and branching ratios between capture to the ground and first excited states of the 7Li and 7Be nuclei have been calculated. The comparison with the most recent experimental data demonstrates a good agreement.

Microscopic interpretation of the results of new measurements for the 3He(α, γ)7Be reaction

A microscopic approach based on the algebraic version of the resonating group method was implemented by applying it to the radiative capture reaction 3He(α, γ)7Be. The astrophysical S-factor of the reaction and the branching ratio between the capture to the ground and the first excited states of the 7Be nucleus were calculated. A comparison of the theoretical results with the most recent experimental data was performed, and good agreement with these data was found. Advantages of the theoretical approach realized are indicated, and possible ways to refine upon it are outlined.

Ameliorating neutron damage in orthogonal-strip planar germanium detectors

The segmentation of the electrodes of germanium detectors facilitates gamma-ray imaging and tracking. Replacing the traditional n-type lithium drifted contact is a key to finer segmentation. Amorphous-germanium is a promising alternative contact technology, and large, highly segmented detectors have been fabricated. One factor in adopting any new detector technology is its robustness in hostile environments. Therefore, to explore the effects of neutron damage on position sensitive amorphous-contact germanium gamma-ray detectors and investigate methods for mitigation and repair of damage, two detectors were intentionally exposed to a non-uniform neutron fluence of greater than 4(1) ×109n/cm2 produced in the 7Li(p, n)7Be reaction at the UMass Lowell Van-de-Graaff accelerator. Post-irradiation tests were made on the counters by varying the electric field, the charge deposition rate, the operating temperature, and utilizing various annealing cycles in order to ascertain the robustness of their performance after irradiation.

Measurement of neutron energy spectra and neutron dose rates from 7Li(p,n)7Be reaction induced on thin LiF target

The measurements of neutron energy spectra and neutron dose rates were performed using the KN Van de Graaff accelerator, located at the McMaster University Accelerator Laboratory (MAL). Protons were accelerated on the thin lithium fluoride (LiF) target and produced mono-energetic neutrons which were measured using three different spectrometers: Bonner Sphere Spectrometer (BSS), Nested Neutron Spectrometer (NNS), and Rotational Proton Recoil Spectrometer (ROSPEC). The purpose of this work is (1) measurement and quantification of low energy accelerator neutron fields in terms of neutron fluence and dose, (2) comparison of results obtained by three different instruments, (3) comparison of measurements with Monte Carlo simulations based on theoretical neutron yields from 7Li(p,n)7Be nuclear reaction, and (4) comparison of results obtained using different neutron spectral unfolding methods. The nominal thickness of the LiF target used in the experiment was 50μg/cm2, which corresponds to the linear thickness of 0.19μm and results in approximately 6keV energy loss for the proton energies used in the experiment (2.2, 2.3, 2.4 and 2.5MeV). For each of the proton energies, neutron fluence per incident proton charge was measured and several dosimetric quantities of interest in radiation protection were derived. In addition, theoretical neutron yield calculations together with the results of Monte Carlo (MCNP) modeling of the neutron spectra are reported. Consistent neutron fluence spectra were obtained with three detectors and good agreement was observed between theoretically calculated and measured neutron fluences and derived dosimetric quantities for investigated proton energies at 2.3, 2.4 and 2.5MeV. In the case of 2.2MeV, some plausibly explainable discrepancies were observed.

Study of the [formula omitted] and [formula omitted] reactions for PIGE purposes

Differential cross sections were measured at 8 angles and at proton energies from 2 to 5MeV for the 10B(p,αγ)7Be and 10B(p,p′γ)10B reactions using two thin targets. The γ-rays emitted at Eγ=429 and 718keV respectively, were detected by four HPGe detectors placed on a motorized turntable. The overall systematic uncertainty of the measurements was estimated to be ∼8% while the statistical errors did not exceed 5%. The validity of the obtained cross sections was tested by performing a thick target benchmarking experiment. The results of the present work are compared with existing ones from literature and possible explanations for the observed differences are discussed.

Comparing the response of PSD-capable plastic scintillator to standard liquid scintillator

This work discusses a test campaign to characterize the response of the recently developed plastic scintillator with pulse shape discrimination (PSD) capabilities (EJ-299-33). PSD is a property exhibited by certain types of scintillating material in which incident stimuli (fast neutrons or γ rays) can be separated by exploiting differences in the scintillation light pulse tail. Detector geometries used were: a 10cm×10cm×10cm cube and a 10-cm diameter×10-cm long cylinder. EJ-301 and EJ-309 liquid scintillators with well-known responses were also tested. The work was conducted at the University of Massachusetts Lowell Van De Graaff accelerator. The facility accelerated protons on a thin Li target to yield quasi-monoenergetic neutrons from the 7Li(p,n)7Be reaction (Q-value: –1.644MeV). Collimated fast neutrons were obtained by placing detectors behind a neutron spectrometer. Rotating the spectrometer, and thus changing the neutron energy, allowed us to achieve 0.5–3.2MeV neutrons in 200–300keV steps. Data were acquired through a flash analog-to-digital converter (ADC) capable of performing digital PSD measurements. By using the PSD technique to separate the neutron events from unwanted γ background, we constructed a pulse height spectrum at each energy.Obtaining a relationship of the relative light output versus energy allowed us to construct the response function for the EJ-299-33 and liquid scintillator. The EJ-299-33 response in terms of electron equivalent energy (Ee.e.) vs. proton equivalent energy (Ep.e.), how it compared with the standard xylene-based EJ-301 (or, NE-213/BC-501A equivalent) and EJ-309 liquid scintillator response, and how the EJ-301 and EJ-309 compared, are presented. We find that the EJ-299-33 demonstrated a lower light output by up to 40% for <1.0MeV neutrons; and ranging between a 5–35% reduction for 2.5–3.0MeV neutrons compared to the EJ-301/309, depending on the scintillator and geometry. Monte Carlo modeling techniques were used to investigate how the neutron beam and accelerator background environment affected the detector response. We find relatively good agreement between our results and the modeling; however, the observed response could not be fully accounted for due to events with pulse pile up, thus leading to contamination of the neutron PSD selected events.

Study of neutron-induced background and its effect on the search of 0νββ decay in 124Sn

Neutron-induced background has been studied in various components of the TIN.TIN detector, which is under development for the search of Neutrinoless Double Beta Decay in 124Sn. Fast neutron flux ∼106 n cm-2s-1 covering a broad energy range ∼0.1 to ( ∼18 MeV) was generated using 9Be(p,n)9B reaction. In addition, reactions with quasi-monoenergetic neutrons were also studied using 7Li(p,n)7Be reaction. Among the different cryogenic support structures studied, Teflon is found to be preferable compared to Torlon as there is no high energy gamma background Eγ > 1 MeV) . Contribution of neutron-induced reactions in nat, 124Sn from other Sn isotopes (A = 112–122) in the energy region of interest, namely, around the Qββ of 124Sn (E ∼ 2.293 MeV), is also investigated.

Neutron beam optimization based on a 7Li(p,n)7Be reaction for treatment of deep-seated brain tumors by BNCT

Neutron beam optimization for accelerator-based Boron Neutron Capture Therapy (BNCT) is investigated using a 7Li(p,n)7Be reaction. Design and optimization have been carried out for the target, cooling system, moderator, filter, reflector, and collimator to achieve a high flux of epithermal neutron and satisfy the IAEA criteria. Also, the performance of the designed beam in tissue is assessed by using a simulated Snyder head phantom. The results show that the optimization of the collimator and reflector is critical to finding the best neutron beam based on the 7Li(p,n)7Be reaction. Our designed beam has 2.49×109n/cm2s epithermal neutron flux and is suitable for BNCT of deep-seated brain tumors.

Baseline design of a low energy neutron source at ESS-Bilbao

This article briefly describes the basic design of the ESS-Bilbao neutron target station as well as its expected neutronic performance. The baseline engineering design, associated ancillary systems, and plant layout for the facility is now complete. A rotating target composed of twenty beryllium plates has been selected as the best choice in terms of both neutron yield and engineering complexity. It will provide neutron beams with a source term of 1015 n s−1 resulting from the direct 9Be(p, xn) reaction using a 75 mA proton beam at 50 MeV. The design envisages a target station equipped with two fully optimized moderators capable of withstanding a proton-beam power of 112 kW. This design is flexible enough to accommodate future upgrades in final proton energy. The envisaged neutron-beam brightness will enable several applications, including the use of cold and thermal neutrons for condensed matter research as well as fast-neutron irradiation studies. We close by discussing the role that this facility may play once the European Spallation Source becomes operational in Lund, Sweden.

Theoretical Predictions of Excitation Functions of Neutron-Induced Reactions on 6Li, 9Be, 12C and 23Na Nuclei at Low Energies

In the present work, the excitation functions of neutron reactions 6Li(n,p)6He, 9Be(n,α)6He, 12C(n,p)12B, 12C(n,α)9Be, 23Na(n,p)23Ne, 23Na(n,2n)22Na and 23Na(n,α)20F produced by the incident neutrons were studied for the investigation of fusion structural materials. Tel et al. formulae (for sodium isotopes), the codes ALICE–ASH and CEM03.01 (for all nuclei) were employed for the obtaining of cross-sections. In addition, hybrid model and geometry-dependent hybrid model with pre-equilibrium emissions, and Weisskopf Ewing model with the equilibrium emissions, and the cascade-exciton model with cascade interactions were used to calculate the excitations curves. The obtained results and Tendl-2011 library data were compared with the experimental literature values. Finally it is to mention that the cross-section data obtained may be useful for the safety design of future fusion reactors.