Energy Neutron Beam Research Articles

Activation cross section of the (n,2n) reaction on Hf isotopes

Cross sections of the 174Hf(n,2n)173Hf and 176Hf(n,2n)175Hf reactions have been experimentally determined relative to the 27Al(n,α)24Na reference reaction at incident neutron energies of 15.3 and 17.1 MeV by means of the activation technique. The irradiations were carried out at the 5 MV tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" with monoenergetic neutron beams provided via the 3H(d,n)4He reaction, using a new Ti-tritiated target of 373 GBq activity. In the determination of the 176Hf(n,2n)175Hf reaction cross section the contamination of the 174Hf(n,γ)175Hf and 177Hf(n,3n)175Hf reactions has been taken into account. Moreover, the neutron beam energy has been studied by means of Monte Carlo simulation codes and the neutron flux has been determined via the 27Al(n,α)24Na reference reaction.

CONY - Computer code for Neutron Yield calculations: The 7Li(p,n)7Be and 3H(d,n)4He reactions.

The neutron beam facility at NCSR “Demokritos” is driven by a 5.5 MV tandem T11/25 Van De Graff accelerator that provides continuous, high intensity ion beams. Depending on the neutron production reaction, different energy regions of neutron beams are available. Neutron fields with well defined energies are produced by means of nuclear reactions such as: 7Li(p,n)7Be, 3H(p,n)3He, 2H(d,n)3He and 3H(d,n)4He, delivering neutrons up to the energy of ~28 MeV. In order to fully characterize the neutron beam at NCSR “Demokritos”, in the framework of the present work, the CONY C++ computer code has been developed. The implementation of the code for the 7Li(p,n)7Be and 3H(d,n)4He reactions is discussed. The method of calculation of differential neutron yields by thin and thick targets is described. Specifically, for the reaction 7Li(p,n)7Be the mathematical singularity at near threshold energies is discussed along with the method that was used as to overcome this issue. Finally, the results of the code including the double differential neutron yields, the neutron beam energy distribution at the sample position and the total neutron yields have been compared with experimental data as well as with the results of the NeuSDesc software (JRC-IRMM: Neutron Source Description).

Optimum neutron energy simulation in treatment of head and neck cancer at different depths in the BNCT method

Introduction: Recently head and neck cancer has pay attention to many researchers. Its therapeutic methods include surgery, chemotherapy, radiotherapy and Boron neutron capture therapy (BNCT). BNCT is better than conventional radiotherapy because it targets the tumor cell. This method involves two steps of infusion of stable 10B and then neutron radiation with a suitable intensity and energy. The BNCT in combination with boronphenylalanine (BPA) and borocaptate sodium (BSH) that was make using the epithermal neutron. BSH and PBA are used as 10B carriers. Epithermal neutrons reach to thermal transiting through tissues of the body. When 10B absorbed thermal neutrons, the α and 7Li particles produced in the 10B (n, α) 7Li reaction are of high linear energy. Transfer radiation have a short range of one cell diameter. Materials and Methods: Monte Carlo simulations were performed with MCNPX2.6 and RO31 MIRD phantom. The neutron source was employed the surface disk with 10 diameters and the range of energy was considered from 1ev-10Kev. The results of neutron and gamma dose at various depths was calculated using tally F4 and F6 in MCNPX2.6 code. Results: Relative Dose was obtained at various depths based on energy changes for gamma, fast and thermal neutron. The results of this study have shown increases of optimum energy as the tumor get deeper respect to the skin. In addition, an analytical relation was proposed for energy optimization with the position of the tumor. Conclusion: The optimum neutron energy dependence was investigated for neck tumor in different depths. These results provide useful information to the physicians to choice best optimum energy neutron beam in BNCT method.

The (n,2n) reaction for the lightest stable erbium isotope Er162 from reaction threshold up to 19 MeV

The $^{162}\mathrm{Er}(n,2n)^{161}\mathrm{Er}$ reaction cross section (${E}_{th}=9.26\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$) was measured at six incident neutron beam energies by means of the activation technique. Two energy regions were covered in the present work: the near-threshold energies between 10.7 and 11.3 MeV, as well as the higher energies from 17.1 up to 19.0 MeV. In this way, the energy range from the reaction threshold up to 19 MeV was experimentally mapped, considering also the existing experimental information around 14 MeV. The quasi-monoenergetic neutron beam at near-threshold energies was produced via the $^{2}\mathrm{H}(d,n)^{3}\mathrm{He}$ reaction, while the higher neutron beam energies were achieved by using the $^{3}\mathrm{H}(d,n)^{4}\mathrm{He}$ reaction. The primary deuteron beam was delivered in both cases by the 5.5 MV Tandem Van de Graaff accelerator of NSCR ``Demokritos.'' Statistical model calculations were performed and compared with all the available experimental data.

Concept of Small-Angle Diffractometer in Classical Configuration at the Cold Moderator of the IBR-2 Reactor

The possible concepts whereby a time-of-flight small-angle diffractometer optimized for a neutron moderator operating in the cold (at 30 K) and thermal (at 300 K) modes can be implemented at the IBR-2 reactor are studied on the basis of numerical calculations. Under cold conditions, the peak of the neutronbeam energy spectrum is shifted toward low energies (long wavelengths). This extends the sensitivity range of the instrument with respect to the sizes of the objects under study (1–100 nm and higher). A classical scheme enabling the separation of thermal/cold neutrons (E ~10–3–10–2 eV) from the background (formed mainly by fast neutrons), which is based on bent neutron-optical devices, is discussed. Due to restrictions imposed by the geometry of the beamline within which the instrument is planned to be located, a configuration with a short multichannel mirror device for beam bending (beam bender) is preferable. Simulation and optimization of the proposed small-angle instrument is carried out taking into account the real beamline geometry and the available space in the experimental reactor hall. A comparison of the setup has been made with the facility based on the curved neutron guide and the facility with direct view of the moderator.

Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using an alpha–gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478 keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024%. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058%. We discuss the principle of the alpha–gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.

Study of low energy neutron beam formation based on GEANT4 simulations

The possibility of obtaining thermal/epithermal energy neutron beams using external protons from cyclotron C18/18 is studied based on GEANT4 simulations. This study will be the basis of the Beam Shaped Assembly (BSA) development for future Boron Neutron Capture Therapy (BNCT). Proton induced reactions on 9Be target are considered as a neutron source, and dependence of neutron yield on target thickness is investigated. The problem of reducing the ratio of gamma to neutron yields by inserting a lead sheet after the beryllium target is studied as well. By GEANT4 modeling the optimal thicknesses of 9Be target and lead absorber are determined and the design characteristics of beam shaping assembly, including the materials and thicknesses of reflector and moderator are considered.

Production mechanisms of leptons, photons, and hadrons and their possible feedback close to lightning leaders.

It has been discussed that lightning flashes emit high‐energy electrons, positrons, photons, and neutrons with single energies of several tens of MeV. In the first part of this paper we study the absorption of neutron beams in the atmosphere. We initiate neutron beams of initial energies of 350 keV, 10 MeV, and 20 MeV at source altitudes of 4 km and 16 km upward and downward and see that in all these cases neutrons reach ground altitudes and that the cross‐section areas extend to several km2. We estimate that for terrestrial gamma‐ray flashes approximately between 10 and 2000 neutrons per ms and m2 are possibly detectable at ground, at 6 km, or at 500 km altitude. In the second part of the paper we discuss a feedback model involving the generation and motion of electrons, positrons, neutrons, protons, and photons close to the vicinity of lightning leaders. In contrast to other feedback models, we do not consider large‐scale thundercloud fields but enhanced fields of lightning leaders. We launch different photon and electron beams upward at 4 km altitude. We present the spatial and energy distribution of leptons, hadrons, and photons after different times and see that leptons, hadrons, and photons with energies of at least 40 MeV are produced. Because of their high rest mass hadrons are measurable on a longer time scale than leptons and photons. The feedback mechanism together with the field enhancement by lightning leaders yields particle energies even above 40 MeV measurable at satellite altitudes.

The cross section functions for neutron induced reactions with Rhenium in the energy range 13.0–19.5 MeV

The technique for measuring neutron activation cross-sections using wide energy neutron beams (NAXSUN) was recently developed at JRC-Geel . This method is based on the detection of the gamma activity induced by the activation of the samples in different but overlapping neutron fields and following an unfolding procedure. In the present work, measurements of the cross-section functions by the NAXSUN technique for the (n,a), (n,2n), (n,p) and (n,3n) reactions on rhenium isotopes 185 Re and 187 Re were performed. The results are the first experimental data for the mentioned reaction cross-sections in the energy range 13.0–19.5 MeV. The obtained data are of interest for possible applications of Re in nuclear technology and medicine.

Analysis of the relationship between neutron dose and Cerenkov photons under neutron irradiation through Monte Carlo method

To theoretically explore the feasibility of neutron dose characterized by Cerenkov photons, the relationship between Cerenkov photons and neutron dose in a water phantom was quantified using the Monte Carlo toolkit Geant4. Results showed that the ratio of the neutron dose deposited by secondary electrons above Cerenkov threshold energy to the total neutron dose is approximately a constant for monoenergetic neutrons from 0.01 eV to 100 eV. With the initial neutron beam energy from 0.01 eV to 100 eV, the number of Cerenkov photons has a good correlation with the total neutron dose along the central axis of the water phantom. The changes of neutron energy spectrum and mechanism analysis also explored at different depths. And the ratio of total neutron dose to the intensity of Cerenkov photons is independent of neutron energy for neutrons from 0.01 eV to 100 eV. These findings indicate that Cerenkov radiation also has potential in the application of neutron dose measurement in some specific fields.

Experimental verification of a method to create a variable energy neutron beam from a monoenergetic, isotropic source using neutron elastic scatter and time of flight

An experiment was performed to determine the neutron energy of near-monoergetic deuterium–deuterium (D–D) neutrons that elastically scatter in a hydrogenous target. The experiment used two liquid scintillators to perform time of flight (TOF) measurements to determine neutron energy, with the start detector also serving as the scatter target. The stop detector was placed 1.0m away and at scatter angles of π/6, π/4, and π/3rad, and 1.5m at a scatter angle of π/4rad. When discrete 1ns increments were implemented, the TOF peaks had estimated errors between −21.2 and 3.6% relative to their expected locations. Full widths at half-maximum (FWHM) ranged between 9.6 and 20.9ns, or approximately 0.56–0.66MeV. Monte Carlo simulations were also conducted that approximated the experimental setup and had both D–D and deuterium–tritium (DT) neutrons. The simulated results had errors between −17.2 and 0.0% relative to their expected TOF peaks when 1ns increments were applied. The largest D–D and D–T FWHMs were 26.7 and 13.7ns, or approximately 0.85 and 4.98MeV, respectively. These values, however, can be reduced through manipulation of the dimensions of the system components. The results encourage further study of the neutron elastic scatter TOF system with particular interest in application to active neutron interrogation to search for conventional explosives.

Autophagic flux in glioblastoma cells

To establish metabolic context for radiation sensitivity by measuring autophagic flux in two different glioblastoma (GBM) cell lines. Clonogenic survival curve analysis of U87 or U251 cells exposed to γ radiation, fast neutrons, a mixed energy neutron beam (METNB) or Auger electrons from a gadolinium neutron capture (GdNC) reaction suggested other factors, beyond a defective DNA damage response, contribute to cell death of U251 cells. Altered tumor metabolism (autophagy) was hypothesized as a factor in U251 cells’ clonogenic response. Each of the four different radiation modalities induced an increase in the number of autophagosomes in both U87 and U251 cells. Changes in the number of autophagosomes can be explained by either induction of autophagy or alterations in autophagic flux so autophagic flux was assayed by p62 immunoblotting or in engineered GBM cells that stably express an autophagy marker protein, LC3B-eGFP-mCherry. Perturbations in later stages of autophagy in U251 cells corresponded with radiation sensitivity of U251 cells irradiated with 10 Gy γ rays. Establishment of altered autophagic flux is a useful biomarker for metabolic stress and provided metabolic context for radiation sensitization to 10 Gy γ rays. These results provide strong evidence for the usefulness of managing tumor cell metabolism as a tool for the enhancement of radiation therapy.

SPES and the neutron facilities at Laboratori Nazionali di Legnaro

The SPES Radioactive Ion Beam (RIB) facility, now in the construction phase at INFN-LNL, has the aim to provide high-intensity and high-quality beams of neutron-rich nuclei for nuclear physics research as well as to develop an interdisciplinary research center based on the cyclotron proton beam. The SPES system is based on a dual-exit high-current cyclotron, with tunable proton beam energy 35-70MeV and 0.20-0.75mA. The first exit is used as proton driver to supply an ISOL system with an UCx Direct Target able to sustain a power of 10kW. The expected fission rate in the target is of the order of \( 10^{13}\) fissions per second. The exotic isotopes will be re-accelerated by the ALPI superconducting LINAC at energies of 10 A MeV and higher, for masses around \( A=130\) amu, with an expected beam intensity of \( 10^7\) - \( 10^9\) pps. The second exit will be used for applied physics: radioisotope production for medicine and neutrons for material studies. Fast neutron spectra will be produced by the proton beam interaction with a conversion target. A production rate in excess of \( 10^{14}\) n/s can be achieved: this opens up the prospect of a high-flux neutron irradiation facility (NEPIR) to produce both discrete and continuous energy neutrons. A direct proton beam line is also envisaged. NEPIR and the direct proton line would dramatically increase the wide range of irradiation facilities presently available at LNL. We also present LENOS, a proposed project dedicated to accurate neutron cross-sections measurements using intense, well-characterized, broad energy neutron beams. Other activities already in operation at LNL are briefly reviewed: the SIRAD facility for proton and heavy-ion irradiation at the TANDEM-ALPI accelerator and the BELINA test facility at CN van de Graaff accelerator.

Neutron-neutron quasifree scattering inndbreakup at 10 MeV

The neutron-deuteron (nd ) breakup reaction provides a rich environment for testing theoretical models of the neutron-neutron (nn ) interaction. Current theoretical predictions based on rigorous ab-initio calculations agree well with most experimental data for this system, but there remain a few notable discrepancies. The cross section for nn quasifree (QFS) scattering is one such anomaly. Two recent experiments reported cross sections for this particular nd breakup configuration that exceed theoretical calculations by almost 20% at incident neutron energies of 26 and 25 MeV [1, 2]. The theoretical values can be brought into agreement with these results by increasing the strength of the 1 S0 nn potential matrix element by roughly 10%. However, this modification of the nn effective range parameter and/or the 1 S0 scattering length causes substantial charge-symmetry breaking in the nucleon-nucleon force and suggests the possibility of a weakly bound di-neutron state [3].We are conducting new measurements of the cross section for nn QFS in nd breakup. The measurements are performed at incident neutron beam energies below 20 MeV. The neutron beam is produced via the 2 H(d , n )3 He reaction. The target is a deuterated plastic cylinder. Our measurements utilize time-of-flight techniques with a pulsed neutron beam and detection of the two emitted neutrons in coincidence. A description of our initial measurements at 10 MeV for a single scattering angle will be presented along with preliminary results. Also, plans for measurements at other energies with broad angular coverage will be discussed.

GEANT4 simulations of the n_TOF spallation source and their benchmarking

Neutron production and transport in the spallation target of the n_TOF facility at CERN has been simulated with GEANT4. The results obtained with different models of high-energy nucleon-nucleus interaction have been compared with the measured characteristics of the neutron beam, in particular the flux and its dependence on neutron energy, measured in the first experimental area. The best agreement at present, within 20% for the absolute value of the flux, and within few percent for the energy dependence in the whole energy range from thermal to 1 GeV, is obtained with the INCL++ model coupled with the GEANT4 native de-excitation model. All other available models overestimate by a larger factor, of up to 70%, the n_TOF neutron flux. The simulations are also able to accurately reproduce the neutron beam energy resolution function, which is essentially determined by the moderation time inside the target/moderator assembly. The results here reported provide confidence on the use of GEANT4 for simulations of spallation neutron sources.

Response of the Li-7-enriched Cs2LiYCl6:Ce (CLYC-7) scintillator to 6–60 MeV neutrons

We discuss a test campaign designed to irradiate the 7Li-enriched Cs2LiYCl6:Ce3+ (CLYC-7) scintillator with 6–60MeV neutrons using the cyclotron located at the Crocker Nuclear Laboratory in Davis, CA. CLYC-7 is a newly developed scintillator that exhibits the ability to make good γ-ray measurements and has the ability to detect and discriminate fast neutrons via pulse shape discrimination (PSD) while functioning as a spectrometer. This allows a single detector to make good measurement of both stimuli simultaneously. The response of this scintillation detector has been investigated below 20MeV [1] but has yet to be explored for energies greater than 20MeV. Understanding the spectral and pulse shape response across a broad energy range is important for any radiation detection instrumentation capable of detecting multiple species. At the highest energies sampled, the CLYC-7 PSD demonstrated not only the standard electron/proton separation expected in a mixed γ/n field but the ability to discriminate locally produced deuterons, tritons and α particles. We show the results from the four different neutron beam energies sampled during the experiment. Lastly, we present the results obtained for relating the light output equivalence between electrons and protons/deuterons.

The new vertical neutron beam line at the CERN n_TOF facility design and outlook on the performance

At the neutron time-of-flight facility n_TOF at CERN a new vertical beam line was constructed in 2014, in order to extend the experimental possibilities at this facility to an even wider range of challenging cross-section measurements of interest in astrophysics, nuclear technology and medical physics. The design of the beam line and the experimental hall was based on FLUKA Monte Carlo simulations, aiming at maximizing the neutron flux, reducing the beam halo and minimizing the background from neutrons interacting with the collimator or back-scattered in the beam dump.The present paper gives an overview on the design of the beam line and the relevant elements and provides an outlook on the expected performance regarding the neutron beam intensity, shape and energy resolution, as well as the neutron and photon backgrounds.

Systematic effects on cross-section data derived from reaction rates at a cold neutron beam

The methodology to derive cross-section data from measurements in a cold neutron beam was studied. Mostly, capture cross-sections at thermal energy are derived relative to a standard cross-section, e.g. the cross-section of the 1H(n,γ), 14N(n,γ), or 197Au(n,γ) reaction, and proportionality between the standard and the measured cross-section, evaluated at different energies in the sub-thermal region, is often assumed. Due to this assumption the derived capture cross-section at thermal energy can be biased by more than 10%. Evidently the bias depends on how much the energy dependence of the cross-section deviates from a direct proportionality with the inverse of the neutron speed. The effect is reduced in case the cross-section is not derived at thermal energy but at an energy close to the average energy of the cold neutron beam. Nevertheless, it is demonstrated that the bias can only be avoided in case the energy dependence of the cross-section is known and proper correction factors are applied. In some cases the results are also biased when the attenuation of the neutron beam within the sample is neglected in the analysis. Some of the cross-section data reported in the literature suffer from such bias effects. Hence, the results have to be corrected using the correction factors presented in this paper.

A method for using neutron elastic scatter to create a variable energy neutron beam from a nearly monoenergetic neutron source

Abstract This work describes preliminary investigation into the design of a compact, portable, variable energy neutron source. The proposed method uses elastic neutron scatter at specific angles to reduce the energy of deuterium–deuterium or deuterium–tritium (D–T) neutrons. The research focuses on D–T Monte Carlo simulations, both in idealized and more realistic scenarios. Systematic uncertainty of the method is also analyzed. The research showed promise, but highlighted the need for discrimination of multiply-scattered neutrons, either through a pulsed generator or associated particle imaging.

Hard light meson production in (anti)proton-hadron collisions and charge-exchange reactions

An extension of the QED “return to resonance” mechanism to light meson emission (π, ρ) in (anti)proton collisions with a hadronic target (nucleon or nucleus) is proposed. The cross section and the multiplicity distributions are calculated. The collinear emission (along the beam direction) of a charged meson may be used to produce high energy (anti)neutron beams. Possible applications at existing and planned facilities are considered.