2n Reaction Research Articles

Accelerator characterization of the new ion beam facility at MTA Atomki in Debrecen, Hungary

In this work we present the 2 MV Tandetron accelerator manufactured by High Voltage Engineering Europa (HVEE), that was installed at MTA Atomki in Debrecen, Hungary in 2015. Furthermore, we report on the first performance test of the whole facility including the calibration of the terminal voltage using accurately known resonance energies of the 27Al(p,γ)28Si and 13C(p,γ)14N reactions, as well as neutron threshold energies of the 7Li(p,n)7Be and 13C(p,n)13N reactions. The accurate energy calibration of the generating voltmeter (GVM), the good energy stability of the accelerator as well as the low energy spread of the ion beam suited the requirements of nuclear astrophysics, resonance PIGE depth profiling and the nanoprobe beamline. We have investigated whether the terminal voltage reading depends on the insulating gas pressure, and how much the stripper gas pressure modifies the beam energy.

The Study of (n, 2n) Reaction Cross Sections for Ce and Nd Isotopes up to 20 MeV

Neutron cross section calculations for 136Ce(n, 2n)135Ce, 138Ce(n, 2n)137Ce, 140Ce(n, 2n)139Ce, 142Ce(n, 2n)141Ce, 142Nd(n, 2n)141Nd, 144Nd(n, 2n)143Nd, 146Nd(n, 2n)145Nd, 148Nd(n, 2n)147Nd, and 150Nd(n, 2n)149Nd were done in the incident energy range from 10 to 20 MeV. The calculations were performed using three codes TALYS-1.6 for two-component Exciton model, EMPIRE-3.2 Malta for Exciton model, and ALICE/ASH for the Geometry-Dependent Hybrid (GDH) model. The results of model calculations were compared with the available experimental data and also with the evaluated data in the TENDL-2015 (based on the modified TALYS code), ENDF/B-VII.1 libraries. The calculated cross section data were compared with the available experimental data obtained from EXFOR and also compared with semiempirical formulas around 14–15 MeV. The results of model calculation were found to be in good agreement with the experimental data given in literature and semiempirical data around 14–15MeV.

Photonuclear reactions triggered by lightning discharge.

Lightning and thunderclouds are natural particle accelerators. Avalanches of relativistic runaway electrons, which develop in electric fields within thunderclouds, emit bremsstrahlung γ-rays. These γ-rays have been detected by ground-based observatories, by airborne detectors and as terrestrial γ-ray flashes from space. The energy of the γ-rays is sufficiently high that they can trigger atmospheric photonuclear reactions that produce neutrons and eventually positrons via β+ decay of the unstable radioactive isotopes, most notably 13N, which is generated via 14N + γ → 13N + n, where γ denotes a photon and n a neutron. However, this reaction has hitherto not been observed conclusively, despite increasing observational evidence of neutrons and positrons that are presumably derived from such reactions. Here we report ground-based observations of neutron and positron signals after lightning. During a thunderstorm on 6 February 2017 in Japan, a γ-ray flash with a duration of less than one millisecond was detected at our monitoring sites 0.5-1.7 kilometres away from the lightning. The subsequent γ-ray afterglow subsided quickly, with an exponential decay constant of 40-60 milliseconds, and was followed by prolonged line emission at about 0.511 megaelectronvolts, which lasted for a minute. The observed decay timescale and spectral cutoff at about 10 megaelectronvolts of the γ-ray afterglow are well explained by de-excitation γ-rays from nuclei excited by neutron capture. The centre energy of the prolonged line emission corresponds to electron-positron annihilation, providing conclusive evidence of positrons being produced after the lightning.

Calculation of astrophysical S-factor and reaction rate in 12C(p, γ)13N reaction

The 12C(p, γ)13N reaction is the first process in the CNO cycle. Also it is a source of low-energy solar neutrinos in various neutrino experiments. Therefore, it is of high interest to gain data of the astrophysical S-factor in low energies. By applying Faddeev’s method, we calculated wave functions for the bound state of 13N. Then the cross sections for resonance and non-resonance were calculated through using Breit–Wigner and direct capture cross section formulae, respectively. After that, we calculated the total S-factor and compared it with previous experimental data, revealing a good agreement altogether. Then, we extrapolated the S-factor in zero energy and the result was 1.32 ± 0.19 (keV.b). In the end, we calculated reaction rate and compared it with NACRE data.

Studying the energy stability of a vacuum-insulated tandem accelerator using γ-resonance reactions

Experiments on the detection of γ rays generated in the 13C(p, γ)14N reaction at the Novosibirsk vacuum-insulated tandem accelerator were carried out. Owing to the updated detection system, it was possible to measure the energy spread of beam protons and develop a method for long-term stabilization of the slow drift of the beam energy. The measured energy spread was 1.20 ± 0.15 keV, which was only 0.07% of the total beam energy. This makes the tandem accelerator developed by the vacuum-insulated Budker Institute of Nuclear Physics an attractive tool for solving various research and applied problems.

The total cross sections of the 11B(α,n)14N and the 10B(α,n)13N reactions between 2 and 6 MeV

There is considerable interest in potential aneutronic fusion reactors. One possible reaction is 11B(p,α)2α. However, the emitted alpha particles are energetic enough to generate neutrons by interacting with boron inside the reactor through the 11B(α,n)14N and 10B(α,n)13N reactions. To aid in evaluating neutron production within this potential aneutronic reactor, the total cross sections were measured for the 11B(α,n)14N reaction between 2 and 6 MeV and for the 10B(α,n)13N reaction between 2 and 4.8 MeV. The results are presented and compared with previously reported results.

Study of the 15N(p,n)15O reaction as a monoenergetic neutron source for the measurement of differential scattering cross sections

The 15N(p,n) reaction is a promising candidate for the production of monoenergetic neutrons with energies of up to 5.7 MeV at the facilities where the T(p,n)3He reaction cannot be used. The characteristic properties of this reaction were studied focusing on its suitability as a source of monoenergetic neutrons for the measurement of differential scattering cross sections in the neutron energy range of 2 MeV to 5 MeV . For this purpose differential and integral cross sections were measured and the choice of optimum target conditions was investigated. The reaction has already been used successfully to measure of elastic and inelastic neutron scattering cross sections for natPb in the energy range from 2 MeV to 4 MeV and for 209Bi and 181Ta at 4 MeV .

The impact of the revised17O(p,α)14N reaction rate on17O stellar abundances and yields

Context. Material processed by the CNO cycle in stellar interiors is enriched in 17O. When mixing processes from the stellar surface reach these layers, as occurs when stars become red giants and undergo the first dredge up, the abundance of 17O increases. Such an occurrence explains the drop of the 16O/17O observed in RGB stars with mass larger than 1.5 M_\solar. As a consequence, the interstellar medium is continuously polluted by the wind of evolved stars enriched in 17O . Aims. Recently, the Laboratory for Underground Nuclear Astrophysics (LUNA) collaboration released an improved rate of the 17O(p,alpha)14N reaction. In this paper we discuss the impact that the revised rate has on the 16O/17O ratio at the stellar surface and on 17O stellar yields. Methods. We computed stellar models of initial mass between 1 and 20 M_\solar and compared the results obtained by adopting the revised rate of the 17O(p,alpha)14N to those obtained using previous rates. Results. The post-first dredge up 16O/17O ratios are about 20% larger than previously obtained. Negligible variations are found in the case of the second and the third dredge up. In spite of the larger 17O(p,alpha)14N rate, we confirm previous claims that an extra-mixing process on the red giant branch, commonly invoked to explain the low carbon isotopic ratio observed in bright low-mass giant stars, marginally affects the 16O/17O ratio. Possible effects on AGB extra-mixing episodes are also discussed. As a whole, a substantial reduction of 17O stellar yields is found. In particular, the net yield of stars with mass ranging between 2 and 20 M_\solar is 15 to 40% smaller than previously estimated. Conclusions. The revision of the 17O(p,alpha)14N rate has a major impact on the interpretation of the 16O/17O observed in evolved giants, in stardust grains and on the 17O stellar yields.

The Inclusion of Photofission, Photonuclear, (n, xn), (n, n′xγ), and (n, xγ) Reactions in the Neutron-Gamma Feynman-Alpha Variance-to-Mean Formalism

This paper sets up a formalism that is sufficiently general to describe the effects of photofission, photonuclear, (n, xn), (n, n′xγ), and (n, xγ) reactions on the neutron-gamma Feynman-alpha variance-to-mean ratios. Such a formalism is obtained using the Chapman-Kolmogorov (master) forward equation for the above-mentioned set of nuclear reactions. Thereafter, the issue of estimating reaction intensities for gammas in the master equation is highlighted by the paper. As an example, a quantitative evaluation of reaction intensities is given for a case when (n, γ), photonuclear, and (n, 2n) reactions are relevant for the system. However, an evaluation of the influence of these types of reactions to the values of the Feynman variance-to-mean ratios is not within the scope of this paper. Overall, the results obtained in this paper are intended to give an extended systematic framework for the study of the neutron- and gamma-based nondestructive assay problems in nuclear reactor applications and materials control.

Integral experiments on thorium assemblies with D-T neutron source

To validate nuclear data and code in the neutronics design of a hybrid reactor with thorium, integral experiments in two kinds of benchmark thorium assemblies with a D-T fusion neutron source have been performed. The one kind of 1D assemblies consists of polyethylene and depleted uranium shells. The other kind of 2D assemblies consists of three thorium oxide cylinders. The capture reaction rates, fission reaction rates, and (n, 2n) reaction rates in 232 Th in the assemblies are measured by ThO2 foils. The leakage neutron spectra from the ThO2 cylinders are measured by a liquid scintillation detector. The experimental uncertainties in all the results are analyzed. The measured results are compared to the calculated ones with MCNP code and ENDF/B-VII.0 library data.

A 13C(d,n)-based epithermal neutron source for Boron Neutron Capture Therapy

PurposeBoron Neutron Capture Therapy (BNCT) requires neutron sources suitable for in-hospital siting. Low-energy particle accelerators working in conjunction with a neutron producing reaction are the most appropriate choice for this purpose. One of the possible nuclear reactions is 13C(d,n)14N. The aim of this work is to evaluate the therapeutic capabilities of the neutron beam produced by this reaction, through a 30mA beam of deuterons of 1.45MeV. MethodsA Beam Shaping Assembly design was computationally optimized. Depth dose profiles in a Snyder head phantom were simulated with the MCNP code for a number of BSA configurations. In order to optimize the treatment capabilities, the BSA configuration was determined as the one that allows maximizing both the tumor dose and the penetration depth while keeping doses to healthy tissues under the tolerance limits. ResultsSignificant doses to tumor tissues were achieved up to ∼6cm in depth. Peak doses up to 57Gy-Eq can be delivered in a fractionated scheme of 2 irradiations of approximately 1h each. In a single 1h irradiation, lower but still acceptable doses to tumor are also feasible. ConclusionsTreatment capabilities obtained here are comparable to those achieved with other accelerator-based neutron sources, making of the 13C(d,n)14N reaction a realistic option for producing therapeutic neutron beams through a low-energy particle accelerator.

Capture cross sections of 15N(n, γ)16N at astrophysical energies**Support given by National Natural Science Foundation of China (11447236, 11505002, 11247001) and Foundation of Anhui University of Science and Technology (11130, 12608)

We have reanalyzed reaction cross sections of 16N on a 12C target. The nucleon density distribution of 16N, especially surface density distribution, was extracted using the modified Glauber model. On the basis of dilute surface densities, the 15N(n, γ)16N reaction is discussed within the framework of the direct capture reaction mechanism. The calculations agree quite well with the experimental data.

Radii of the bound states in 16N from the asymptotic normalization coefficients**Supported by National Natural Science Foundation of China (11505117, 11490560, 11475264, 11321064, 11375269), Natural Science Foundation of Guangdong Province (2015A030310012), 973 program of China (2013CB834406) National key Research and Development Province (2016YFA0400502)

The asymptotic normalization coefficients (ANCs) of the virtual decay 16N → 15N + n are extracted from the 15N(7Li, 6Li)16N reaction populating the ground and first three excited states in 16N. The root-mean-square (rms) radii of the valence neutron in these four low-lying 16N states are then derived by using the ANCs. The probabilities of the valence neutron staying out of the core potentials are found to be 31% ± 8%, 58% ± 12%, 32% ± 8%, and 60% ± 12%. The present results support the conclusion that a one-neutron halo may be formed in the 16N first and third excited states, while the ground and second excited states do not have a one-neutron halo structure. However, the core excitation effect has a strong influence on the one-neutron halo structure of the ground and first excited states in 16N.

Theoretical Cross-Section Calculation of In-111, Tc-99m, Co-57 Radioisotopes Used for Kidney Imaging

Many radioisotopes are used in nuclear medicine diagnostics and therapy. Co-57, In-111 and Tc-99m isotopes are widely used in nuclear medicine and are successfully implemented in renal imaging. In this work, the cross section calculation of the (p, 2n) reaction, which is necessary for production of the nuclei of Co-57, In-111, Tc-99m, were calculated using TALYS 1.6 nuclear reaction code. The calculated cross sections were compared with the experimental data from the EXFOR.

SU‐F‐J‐196: A Prototype System for Portal Imaging for Intensity Modulated Neutron Therapy

Purpose:Fast neutron therapy is offered at the University of Washington Medical Center for treatment of selected cancers. The hardware and control systems of the UW Clinical Neutron Therapy System are undergoing upgrades to enable delivery of IMNT. To clinically implement IMNT, dose verification tools need to be developed. We propose a portal imaging system that relies on the creation of positron emitting isotopes (11C and 15O) through (n, 2n) reactions with a PMMA plate placed below the patient. After field delivery, the plate is retrieved from the vault and imaged using a reader that detects the annihilation photons. The pattern of activity produced in the plate provides information to reconstruct the neutron fluence map that can be compared to fluence maps from Monte Carlo (MCNP) simulations to verify treatment delivery. We have previously performed Monte Carlo simulations of the portal imaging system (GATE simulations) and the beam line (MCNP simulations). In this work, initial measurements using a prototype system are presented.Methods:Custom electronics were developed for BGO detectors read out with photomultiplier tubes (previous generation PET detectors from a CTI ECAT 953 scanner). Two detectors were placed in coincidence, with a detector separation of 2 cm. Custom software was developed to create the crystal look up tables and perform a limited angle planar reconstruction with a stochastic normalization. To test the initial capabilities of the system, PMMA squares were irradiated with neutrons at a depth of 1.5 cm and read out using the prototype system. Doses ranging from 10–200 cGy were delivered.Results:Using the prototype system, dose differences in the therapeutic range could be determined.Conclusion:The prototype portal imaging system is capable of detecting neutron doses as low as 10–50 cGy and shows great promise as a patient QA tool for IMNT.

Tests of a Compton imaging prototype in a monoenergetic 4.44 MeV photon field—a benchmark setup for prompt gamma-ray imaging devices

The finite range of a proton beam in tissue opens new vistas for the delivery of a highly conformal dose distribution in radiotherapy. However, the actual particle range, and therefore the accurate dose deposition, is sensitive to the tissue composition in the proton path. Range uncertainties, resulting from limited knowledge of this tissue composition or positioning errors, are accounted for in the form of safety margins. Thus, the unverified particle range constrains the principle benefit of proton therapy. Detecting prompt γ-rays, a side product of proton-tissue interaction, aims at an on-line and non-invasive monitoring of the particle range, and therefore towards exploiting the potential of proton therapy. Compton imaging of the spatial prompt γ-ray emission is a promising measurement approach. Prompt γ-rays exhibit emission energies of several MeV. Hence, common radioactive sources cannot provide the energy range a prompt γ-ray imaging device must be designed for. In this work a benchmark measurement-setup for the production of a localized, monoenergetic 4.44 MeV γ-ray source is introduced. At the Tandetron accelerator at the HZDR, the proton-capture resonance reaction 15N(p,α γ4.439)12C is utilized. This reaction provides the same nuclear de-excitation (and γ-ray emission) occurrent as an intense prompt γ-ray line in proton therapy. The emission yield is quantitatively described. A two-stage Compton imaging device, dedicated for prompt γ-ray imaging, is tested at the setup exemplarily. Besides successful imaging tests, the detection efficiency of the prototype at 4.44 MeV is derived from the measured data. Combining this efficiency with the emission yield for prompt γ-rays, the number of valid Compton events, induced by γ-rays in the energy region around 4.44 MeV, is estimated for the prototype being implemented in a therapeutic treatment scenario. As a consequence, the detection efficiency turns out to be a key parameter for prompt γ-rays Compton imaging limiting the applicability of the prototype in its current realization.

Cross sections of the reactions 14N(γ, 2n)12N, 14N(γ, 2p)12B, and 13C(γ, p)12B

Known experimental and model-calculated data, along with independent calculations using the TALYS- and EMPIRE-codes, are compiled for the cross sections of reactions 14N(γ, 2n)12N, 14N(γ, 2p)12B, and 13C(γ, p)12B used in the photonuclear technique under development for the detection of hidden explosives. Indications of a substantial underestimate of model-calculated values, compared to the available measured results, are obtained.

Proton induced gamma-ray production cross sections and thick-target yields for boron, nitrogen and silicon

The excitation functions for the reactions 14N(p,p′γ)14N, 28Si(p,p′γ)28Si and 29Si(p,p′γ)29Si were measured at an angle of 55° by bombarding a thin Si3N4 target with protons in the energy range of 3.6–6.9MeV. The deduced γ-ray production cross section data is compared with available literature data relevant for ion beam analytical work. Thick-target γ-ray yields for boron, nitrogen and silicon were measured at 4.0, 4.5, 5.0, 5.5, 6.0 and 6.5MeV proton energies utilizing thick BN and Si3N4 targets. The measured yield values are put together with available yield data found in the literature. The experimental yield data has been used to cross-check the γ-ray production cross section values by comparing them with calculated thick-target yields deduced from the present and literature experimental excitation curves. All values were found to be in reasonable agreement taking into account the experimental uncertainties.

A Modified activation method for reaction total cross section and yield measurements at low astrophysically relevant energies

The activation method is proposed for collection of the sufficient statistics during the investigation of the nuclear astrophysical reactions at low energies with the short-living residual nuclei formation. The main feature is a multiple cyclical irradiation of a target by an ion beam and measurement of the radioactivity decay curve. The method was tested by the yield measurement of the 12C(p,γ)13N reaction with detecting the annihilation γγ- coincidences from 13N(β+ν)13C decay at the two-arm scintillation spectrometer.

Production and separation of 99mTc from cyclotron irradiated 100/naturalMo targets: a new automated module for separation of 99mTc from molybdenum targets

The direct production of 99mTc through (p, 2n) reaction on natural molybdenum target and enriched 100Mo target was investigated. Separation of technetium radionuclide from the irradiated 100Mo target by a new method using Dowex-1 ion exchange resin as well as by the standard solvent extraction (methyl ethyl ketone) method was studied. An automated computer controlled module was developed based on the Dowex-1 separation methodology. The new chemical separation method recovered more than 80 % of 99mTc from the irradiated target. The recovered pertechnetate had requisite radionuclidic, radiochemical and chemical purity for the preparation of 99mTc-radiopharmaceuticals.