Neutron Angular Distributions Research Articles

Investigation of [formula omitted] nuclear reaction in a cyclotron accelerator as a neutron source

Using cyclotron accelerator (at Cyclotron Dept. in Karaj) the radioisotope 201Tl is produced through the Tl ( p,3n ) 81 201 Pb 82 201 → Ec, β + Tl 81 201 reaction. The main objective of this paper is to calculate the intensity, energy spectrum and angular distribution of the neutrons produced from the above reactions. The reason is that, if the neutron characteristics are reasonable enough then at the same time that 201Pb (and subsequently 201Tl) is produced, the above nuclear reaction can be considered as a neutron source, which in turn can be applied for different purposes. Of course depends on the application, the neutrons must be collimated and thermalized (if thermal neutron is needed for example for neutron activation analysis). Besides, the knowledge about the characteristics of the emitted neutrons can help us to predict the activity of the concrete walls and equipments in the target room. And also it is possible to design shielding for these sorts of neutron sources. In this paper the intensity, energy spectrum and angular distribution of neutrons produced from the above mentioned reaction is investigated. In our investigation the thickness of thallium layer assumed to be 70 μm coated on copper sub-layer. The target (thallium) was bombarded by protons with energy 28.5 MeV and 200 μA current. By using the computational code SRIM2000 the average proton energy at different points of the traveling path was calculated and then by using computational code ALICE91 and reaction rate equation, the neutron intensity from the Tl ( p,3n ) 81 203 Pb 82 201 reaction was determined to be 1.26 × 10 13 n/s. With the same method, the neutron intensity produced from the copper sub-layer i.e. from 63Cu + p → 63Zn + n nuclear reaction was calculated to be 9.19 × 10 12 n/s. As a result, the total neutron intensity from thallium target and its copper sublayer was determined to be 2.179 × 10 13 n/s, which is comparable with some conventional neutron sources such as Am–Be neutron source, and is high enough to be applied for different purposes. Our calculations also showed that the neutron energy spectrum from thallium target and its copper sub-layer has a peak around 1 MeV region. The angular distribution of produced neutrons, has its maximum value at angle 0–2.5° and decreases slowly as the angle of neutron emission increases, and its minimum value occurs at backward direction, i.e. 177.5–180°. It means that the produced neutrons, are mostly emitted in the forward direction.

A Proton Recoil Telescope for Neutron Spectroscopy

The N2P research program funded by the INFN committee for Experimental Nuclear Physics (CSNIII) has among his goals the construction of a Proton Recoil Telescope (PRT), a detector to measure neutron energy spectra. The interest in such a detector is primarily related to the SPES project for rare beams production at the Laboratori Nazionali di Legnaro. For the SPES project it is, in fact, of fundamental importance to have reliable information about energy spectra and yield for neutrons produced by d or p projectiles on thick light targets to model the ‘‘conversion target’’ in which the p or d are converted in neutrons. These neutrons, in a second stage, will induce the Uranium fission in the ‘‘production target’’. The fission products are subsequently extracted, selected and re-accelerated to produce the exotic beam. The neutron spectra and angular distribution are important parameters to define the final production of fission fragments. In addition, this detector can be used to measure neutron spectra in the field of cancer therapy (this topic is nowadays of particular interest to INFN, for the National Centre for Hadron therapy (CNAO) in Pavia) and space applications.

Nuclear-level densities around Z = 50 from neutron evaporation spectra in (p, n) reactions

Neutron excitation functions, spectra, and angular distributions in the (p, n) reactions on the isotopes 116Sn, 118Sn, 122Sn, and 124Sn were measured in the proton-energy range 7–11 MeV. The measurements were performed by the time-of-flight method with the aid of a fast-neutron spectrometer at the EGP-15 pulsed tandem accelerator of the Institute of Physics and Power Engineering (Obninsk). A high resolution (about 0.6 ns/m) and a high stability of the time-of-flight spectrometer made it possible to identify reliably low-lying levels along with the continuous section of the neutron spectra. The data obtained in this way were analyzed on the basis of the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations were performed with the aid of the precise Hauser-Feshbach formalism of statistical theory. The nuclear-level densities in the isotopes 116Sb, 118Sb, 122Sb, and 124Sb were determined, along with their energy dependences and model parameters. In the excitation-energy range 0–2 MeV, the energy dependence of the nuclear-level densities exhibits a structure that is associated with the shell inhomogeneities of the spectrum of single-particle states near filled shells. The isotopic dependence of the nuclear-level density is discovered and explained. It is also shown that the data obtained here for the nuclear-level density differ markedly from the predictions of model systematics of nuclear-level densities.

Comparison of Ramsauer and Optical Model Neutron Angular Distributions

In a recent paper it has been shown that the nuclear Ramsauer model does not do well in representing details of the angular distribution of neutron elastic scattering for incident energies of <60 MeV for 208Pb. In this paper, we show that the default angular bin dispersion most widely used in Monte Carlo transport codes is such that the observed differences in angular shapes are on too fine of a scale to affect transport calculations. The effect of increasing the number of Monte Carlo angle bins is studied to determine the dispersion necessary for calculations to be sensitive to the observed discrepancies in angular distributions. We also show that transport calculations are sensitive to differences in the elastic-scattering cross section given by recent fits of 208Pb data compared with older fits.

Angular distribution of neutrons from heavy ion induced reactions in thick targets

Angular distribution of neutron emission from different heavy ion projectiles of energy up to 10A MeV incident on various thick targets have been analyzed with the help of existing models and empirical relations. Owing to the complexity of heavy ion induced reactions, it becomes difficult to obtain any empirical relation for neutron angular distribution involving parameters like projectile energy as well as target and projectile masses. An exponential function of the emission angle has been found to satisfy the relation approximately involving these parameters. The calculated results using our proposed exponential relation are compared with experimental data showing reasonably good agreement. This empirical expression provides an easy, quick and fairly reliable tool to calculate angular distributions of emitted neutrons from heavy ion induced reactions in thick targets, which are required for various applications.

Comparison doses of secondary neutron with the heavy ions in a 75-mev/n heavy ion beam

The angular distributions for neutrons of energy >6 MeV that are induced by 75 MeV/n 12C6+ and 16O8+ ions were measured with the activation method of Al threshold detectors at the radiobiological terminal of HIRFL. The data were obtained by a high-purity Ge(HpGe) detector. The results show that the neutron angular distributions produced by heavy ion beams are strongly peaked in the forward direction and decreased exponentially with angles in experimental area. The experimental conditions for these measurements were similar to those for biological experiments, so the results should be representative of neutrons produced by heavy ions during the biological experiments and tumour therapy. Comparing with the neutron doses produced by the heavy ion beam, the heavy ion dose is the main factor in biological effects and tumour therapy response, so the contribution of neutron dose can be neglected.

Systematics and empirical expressions for neutron emission from thick targets inα-induced reactions

The effect of two initial exciton (particle-hole) configurations, namely 4p0h and 5p1h, on the angular distribution of neutron emission from $\ensuremath{\alpha}$-induced reactions on various thick targets have been analyzed. In the angular distribution of emitted neutrons the relative contribution of the 4p0h configuration is found to vary as the cosine of the angle of emission. Using such dependence, empirical expressions are developed for the total neutron yield, energy spectra, and angular distribution of neutrons in $\ensuremath{\alpha}$-induced reactions in the 25\char21{}200-MeV energy range. These expressions are based on empirical fits to the hybrid model calculations of neutron emission from target elements in the mass range $^{9}\mathrm{Be}$ to $^{209}\mathrm{Bi}$. The results of these calculations are compared with experimental data showing fairly good agreement. The empirical expressions provide a simple, fast, and reliable tool for calculating neutron emission essentially required for radiation shield design and other applications.

The Role of Fast Neutron-Induced Photon Production Data in the Search for Oil

The sensitivity of coupled neutron-photon transport simulations to the underlying nuclear data is studied for oil well logging applications using the Monte Carlo radiation transport code MCNP4C. Results obtained with the JEF-2.2, ENDF/B-VI.5, and JENDL-3.2 data libraries reveal large discrepancies, confirming immediately the importance of well-established nuclear data. In order to refine this conclusion, the impact of several nuclides is determined by varying their neutron and photon total cross sections. As a next step, neutron cross sections and photon production cross sections are modified per reaction channel to identify the most important nuclear reactions playing a role in C/O logging. The influence of neutron and photon angular distributions is studied as well. The outcome of this analysis is a list of nuclear reactions that have a significant impact on borehole logging tool simulations in different environments and, therefore, would deserve much attention in the construction of a new library for oil well logging.

Measurements of fast ions and neutrons emitted from PF-1000 plasma focus device

The paper presents the results of recent experiments performed within the PF-1000 facility. The main aim of these studies was to determine the neutron emission characteristics, which could enable an approximate settlement of the problem of the neutron emission mechanism. The total neutron yield and angular distribution anisotropy were measured with four silver-activation counters placed at different angles to the electrode axis. The neutron energy spectra were determined by means of an 85m upstream positioned scintillation probe. Fast ion beams were investigated with solid-state nuclear track detectors (SSNTD) of the CR-39 type covered with Al-foil filters and placed at a semicircular support around the PF-1000 electrode outlet.

Dependence of neutron yield on the deuterium filling pressure in a plasma focus device

A Mather-type plasma focus device (32 µF, 4 kJ), called Hanyang University Plasma Focus device, is developed as a prototype device for the irradiation test of neutrons for electric probes and cables to be used in Korea Superconducting Tokamak Advanced Research with pure deuterium gas. The six different lengths of electrode are used in order to see the dependence of neutron yield on the deuterium filling pressure at given system conditions such as capacitance, currents and inductance, after optimizing the focusing condition in terms of electrode length versus filling pressure. The relationship between the pressure and electrode length is to be fitted well by the snow-plow model. The neutron fluence and angular distribution are measured at the angles of 0°, 25°, 60° and 90° by locating the bubble neutron dosimeter at a distance 30 cm from the inner electrode head at each electrode length. The anisotropic factor tends to increase with pressure and the total neutron yield is strongly dependent on the isotropic emission. The maximum neutron yield is estimated to be about 1.6 × 108 (n/shot) at a pressure of 3.4 Torr.

Characterization of Li7(p,n)7Be neutron yields from laser produced ion beams for fast neutron radiography

Investigations of 7Li (p,n) 4Be reactions using Cu and CH primary and LiF secondary targets were performed using the VULCAN laser [C.N. Danson et al., J. Mod. Opt. 45, 1653 (1997)] with intensities up to 3×1019 W cm−2. The neutron yield was measured using CR-39 plastic track detector and the yield was up to 3×108 sr−1 for CH primary targets and up to 2×108 sr−1 for Cu primary targets. The angular distribution of neutrons was measured at various angles and revealed a relatively anisotropic neutron distribution over 180° that was greater than the error of measurement. It may be possible to exploit such reactions on high repetition, table-top lasers for neutron radiography.

Light particle emission inCl35+Mg24fusion reactions at high excitation energy and angular momentum

In-plane and out-of-plane correlations of light charged particles and neutrons emitted in the $^{35}\mathrm{Cl}\phantom{\rule{0.3em}{0ex}}(260\phantom{\rule{0.3em}{0ex}}\text{MeV})+^{24}\mathrm{Mg}$ complete fusion reaction have been measured to investigate deformation and angular momentum effects upon the decay of $^{59}\mathrm{Cu}$ compound nucleus. An array of $21\phantom{\rule{0.3em}{0ex}}{\text{BaF}}_{2}$ crystals has been used to identify the light charged particles $(Z\ensuremath{\leqslant}4)$ and neutrons emitted in coincidence with heavy fragments $(Z\ensuremath{\geqslant}5)$ detected in six ionization chamber telescopes. Coincident energy spectra and angular distributions of neutrons, protons, and $\ensuremath{\alpha}$-particles have been described by the statistical-model calculations with nuclear level densities tuned to take account of deformation effects in the emitters. This spin-dependent approach suggests the onset of large nuclear deformation in $^{59}\mathrm{Cu}$ at high spin. This conclusion is consistent with the recent observation of a superdeformed band in the $^{59}\mathrm{Cu}$ nucleus.

Neutron angular distribution in a plasma focus obtained using nuclear track detectors.

The dense plasma focus (DPF) is a coaxial plasma gun in which a high-density, high-temperature plasma is obtained in a focused column for a few nanoseconds. When the filling gas is deuterium, neutrons can be obtained from fusion reactions. These are partially due to a beam of deuterons which are accelerated against the background hot plasma by large electric fields originating from plasma instabilities. Due to a beam-target effect, the angular distribution of the neutron emission is anisotropic, peaked in the forward direction along the axis of the gun. The purpose of this work is to illustrate the use of CR-39 nuclear track detectors as a diagnostic tool in the determination of the time-integrated neutron angular distribution. For the case studied in this work, neutron emission is found to have a 70% contribution from isotropic radiation and a 30% contribution from anisotropic radiation.

Preliminary neutron experiments with the PF-1000 plasma-focus facility

The paper reports on first neutron-emission experiments carried out with the modernized PF-1000 facility. Current sheath dynamics was investigated by means of high-speed cameras. Based on smear pictures, which were taken through a narrow radial slit, the compression velocity was determined. The total neutron yield and angular distribution anisotropy were measured with four silver-activation counters placed at different angles to the electrode axis. It was found that for each initial D/sub 2/-filling pressure value, with an increase in the charging voltage (V/sub 0/), the neutron yield increases to some maximum and with further increase in V/sub 0/ the neutron emission decreases. The highest neutron yield registered so far has been 2/spl middot/10/sup 11/ per shot. The neutron emission anisotropy seems to be lower than that registered in other plasma-focus experiments. The neutron energy spectra, which were measured by means of a scintillating probe in the upstream direction, have been shifted toward lower energy (2.2-2.3 MeV).

Neutron anisotropy and X-ray production of the FN-II dense plasma focus device

The FN-II Dense Plasma Focus is a small (< 5kJ ) Mather type device, where the dependence of neutron yield and its anisotropy, in terms of deuterium filling pressure, and the neutron emission angular distribution have been studied. Two diferent electrode configurations have been tested, showing that their geometry plays an important role both on neutron yield and anisotropy. Time integrated anisotropy has been measured with silver activation counters, on a shot to shot basis. CR-39 nuclear track detectors are used to determine the angular distribution of neutrons, averaged over tens of shots, showing that an isotropic pedestal accounts for 70% of the emission, while the anisotropy component accounts for the remaining 30%. The neutron yield shows a tendency to increase with anisotropy, as well as with the emission of hard X-rays observed on-axis. Scintillator- photomultiplier detectors show a slight Doppler shift in the neutron energy at backward angles, supporting the beam-target mechanism. Additional information has been obtained from time inte- grated X-ray diagnostics, which include filtered multi-pin-hole cameras.

Coulomb-nuclear coupling and interference effects in the breakup of halo nuclei

Nuclear and Coulomb breakup of halo nuclei have been treated often as incoherent processes and structure information have been extracted from their study. The aim of this paper is to clarify whether interference effects and Coulomb-nuclear couplings are important and how they could modify the simple picture previously used. We calculate the neutron angular and energy distributions by using first order perturbation theory for the Coulomb amplitude and an eikonal approach for the nuclear breakup. This allows for a simple physical interpretation of the results which are mostly analytical. Our formalism includes the effect of the nuclear distortion of the neutron wave function on the Coulomb amplitude. This leads to a Coulomb-nuclear coupling term derived here for the first time which gives a small contribution for light targets but is of the same order of magnitude as nuclear breakup for heavy targets. The overall interference is constructive for light to medium targets and destructive for heavy targets. Thus it appears that Coulomb breakup experiments need to be analyzed with more accurate models than those used so far.

Coulomb versus nuclear break-up of 11Be halo nucleus in a nonperturbative framework

The 11Be break-up is calculated at 41 MeV per nucleon incident energy on different targets using a nonperturbative time-dependent quantum calculation. The evolution of the neutron halo wave function shows an emission of neutron at large angles for grazing impact parameters and at forward angles for large impact parameters. The neutron angular distribution is deduced for the different targets and compared to experimental data. We emphasize the diversity of diffraction mechanisms, in particular we discuss the interplay of the nuclear effects such as the towing mode and the Coulomb break-up. A good agreement is found with experimental data.

Double-differential cross sections for the neutron production from heavy-ion reactions at energiesE/A=290–600MeV

We have measured the double-differential cross sections for neutron production from C, Ne, and Ar projectiles at $E/A=290--600\mathrm{MeV}$ on C, Cu, and Pb targets. Neutron energies were measured at laboratory angles between 5\ifmmode^\circ\else\textdegree\fi{} and 80\ifmmode^\circ\else\textdegree\fi{}. The measured neutron spectra have three components. At forward angles, a prominent peak originating from the projectile-fragmentation process was observed. The velocity of neutrons corresponding to the peak was about the same as that of the projectile. In addition to the peak, two components of Maxwellian-shape distributions corresponding to the preequilibrium and equilibrium processes were observed. By fitting with a moving-source model having three components, the neutron spectra were fairly well described. The parameters obtained for each component are consistent with a picture of the projectile fragmentation, preequilibrium, and equilibrium processes. By integrating the fitted functions with respect to the neutron energies and solid angles, the angular distributions and total cross sections for the neutron production were determined. The neutron spectra, angular distributions, and total cross sections were compared with those calculated by the quantum molecular dynamics and heavy-ion codes. We found that neither of the codes could reproduce the measured cross sections for all combinations of the projectiles and targets.

NODAL TRANSPORT METHODS FOR XYZ AND HEXAGONAL-Z GEOMETRY

A new 3-D nodal SNtransport method has been developed for Cartesian and hexagonal geometries. In the present method, the neutron angular distributions of intra-node fluxes and transverse-leakage are represented using the SNquadrature set, and the spatial distribution of neutron source is approximated by a quadratic polynomial expansion. Several considerations in numerical procedures to achieve stable convergence are also mentioned. Some numerical results are represented to show the validity of the method.

Analysis of the Karlsruhe Neutron Transmission experiment using MCNP with various beryllium nuclear data

Analysis of the Karlsruhe neutron transmission experiment has been performed using the three-dimensional Monte Carlo code MCNP version 4B in order to investigate the accuracy of various beryllium nuclear data. The EFF-1 reproduced best with the measured total neutron multiplications among five files. Significant discrepancies between calculated and measured leakage spectra, however, were observed in some energy windows for all beryllium nuclear data, which were due to the difference of the secondary energy and angular distribution of neutrons emitted through the 9Be(n, 2n) reaction among various beryllium nuclear data.