Comparison between calculation and measured data on secondary neutron energy spectra by heavy ion reactions from different thick targets

Measured neutron energy fluences from high-energy heavy ion reactions through targets several centimeters to several hundred centimeters thick were compared with calculations made using the recently developed general-purpose particle and heavy ion transport code system (PHITS). It was confirmed that the PHITS represented neutron production by heavy ion reactions and neutron transport in thick shielding with good overall accuracy.     

Structural properties of swift heavy ion beam irradiated Fe/Si bilayers

The Fe/Si multilayers were prepared by electron beam evaporation in a cryo-pumped vacuum deposition system. Ag⁺ and Au⁺ ions of 100 MeV at two different fluencies such as 1 × 10¹² ions/cm² and 1 × 10¹³ ions/cm² at a pressure of 10^− 7 torr were used to irradiate the Fe/Si samples. The irradiated samples were analyzed by High-Resolution XRD and it reveals that the irradiated films are having polycrystalline nature and it confirms the formation of the β-FeSi₂. The structural parameters such as crystallite size (D), strain (ε) and dislocation density (δ) have been evaluated from the XRD spectrum. The role of the substrates and the influence of swift heavy ions on the formation of β-FeSi₂ have been discussed in this paper.     

Investigation of fragment doses produced by heavy ions in tissue-like material

In this paper, the distribution of fragments produced by 55 MeV/n ??Ar1?? ions in tissue-equivalent material is reported as a function angles relative to the incident particle direction. The relative fragment doses at different angles and the total dose due to the primary beam have been estimated. The results show that the fragments produced by primary beam were concentrated at very small angles, so the fraction of particle fluence diverging from the primary beam was very small. Even though the diverging fluence is a small fraction of the total, it should still be taken into account because biological systems are very sensitive to low doses of heavy ion irradiation.     

Structural and electrical properties of swift heavy ion beam irradiated Co/Si interface

Synthesis of swift heavy ion induced metal silicide is a new advancement in materials science research. We have investigated the mixing at Co/Si interface by swift heavy ion beam induced irradiation in the electronic stopping power regime. Irradiations were undertaken at room temperature using 120 MeV Au ions at the Co/Si interface for investigation of ion beam mixing at various doses: 8 × 10¹², 5 × 10¹³ and 1 × 10¹⁴ cm⁻². Formation of different phases of cobalt silicide is identified by the grazing incidence X-ray diffraction (GIXRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation.I–V characteristics at Co/Si interface were undertaken to understand the irradiation effect on conduction mechanism at the interface.     

Structural and electrical properties of swift heavy ion beam irradiated Fe/Si interface

The present work deals with the mixing of iron and silicon by swift heavy ions in high-energy range. The thin film was deposited on a n-Si (111) substrate at 10⁻⁶ torr and at room temperature. Irradiations were undertaken at room temperature using 120 MeV Au⁺⁹ ions at the Fe/Si interface to investigate ion beam mixing at various doses: 5 × 10¹² and 5 × 10¹³ ions/cm². Formation of different phases of iron silicide has been investigated by X-ray diffraction (XRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation. I-V measurements for both pristine and irradiated samples have been carried out at room temperature, series resistance and barrier heights for both as deposited and irradiated samples were extracted. The barrier height was found to vary from 0·73–0·54 eV. The series resistance varied from 102·04–38·61 kΩ.     

A novel approach to the measurement of the neutron multiplicity associated with reverse kinematics heavy ion reactions

A new fast neutron high multiplicity detector is proposed based on the measurement of the total light yielded by the neutrons in a plastic scintillator. Its performance is simulated by Monte Carlo methods and compared to existing neutron multiplicity detectors. A cost effective design for reverse kinematics heavy ion reactions is presented and connected problems discussed.     

Formation of high-mass cluster ions from compound semiconductors using time-of-flight secondary ion mass spectrometry with cluster primary ions

The detection of high-mass, nonstoichiometric, GaxAsy and InxPy secondary ion clusters using time-of-flight secondary ion mass spectrometry is reported for the first time. The GaxAsy and InxPy clusters are detected in both positive and negative ion spectra and extend to masses of at least 6000 dalton (Da). Consecutive clusters differ by the addition of one gallium (indium) atom. This leads to nonstoichiometric clusters at high mass (i.e., Ga15As3 at 1270 Da) which are metastable above a critical mass. The relative secondary ion yields of high-mass GaxAsy clusters detected using several primary ion sources (Cs+, Bi+, Bi3+, Bi32+, Bi52+, C60+, and C602+) are compared. The relative secondary ion yield of high-mass GaxAsy clusters is significantly enhanced by the use of cluster primary ions and the best relative secondary ion yield is obtained using Bi3+ primary ions. An application of the high-mass GaxAsy clusters is presented, in which these clusters are utilized to distinguish between contaminant levels of Ga and bulk GaAs structure in a depth profile of a MnAs/GaAs heterojunction. These results illustrate improved analysis of inorganic materials using cluster primary ions and break the paradigm of stoichiometric secondary cluster ion formation for SIMS of inorganic compounds.     

Systematic studies of scintillation detector with timing resolution of 10 ps for heavy ion beam

We have tested Time-Of-Flight detectors consisting of several combinations of scintillators and photomultiplier tubes for the identification of produced heavy ion beam. Timing resolution of 6.8 ps (RMS) is achieved with energy deposited of 150–160 MeV in the plastic scintillator, where ⁴⁰Ar beam is used as a primary beam at the total energies of 3.8 GeV. Our systematic studies suggest the importance of maximizing the number of photoelectrons, where the timing resolution seems to be scaled by the pulse height according to the characteristic function of the photomultiplier tube. In addition, scintillator with faster timing property seems to be also essential for better timing resolution.     

Simulation of material sputtering with a focused ion beam

The evolution of the surface of a sample under the action of a focused ion beam (FIB) has been simulated using the level set method in the framework of a model that takes into account the redeposition of atoms primarily sputtered by the incident ions. In order to improve quantitative agreement between the results of simulation and experimental data, special experiments have been performed so as to refine the FIB shape and the model of secondary sputtering of the redeposited material. Using the example of rectangular cavities, it is shown that the proposed approach ensures high-precision simulation of a surface relief formed under the effect of an FIB.

     

Large area multiwire chamber ΔE-E telescope for (n, Z) studies in a continuous energy neutron beam

Multiwire chambers have been constructed for detecting reaction products created in a continuous energy neutron beam ranging from 15 to 50 MeV. The charged reaction products are identified by large area plastic detectors using the ΔE-E technique.     

Expanding the library of secondary ions that distinguish lignin and polysaccharides in time-of-flight secondary ion mass spectrometry analysis of wood

Extracted pine (Pinus spp.) wood and the holocellulose and cellulose fractions of pine were analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The main sources of variation among wood constituents were elucidated by principal component analysis (PCA). Peaks characteristic of lignin or polysaccharides were identified through the combination of high mass resolution analyses of pine fractions and high lateral resolution image analyses distinguishing the lignin-rich middle lamella from the secondary cell wall layers in solid wood cross-sections. A collection of peaks was compiled which (1) extends the library of characteristic lignin and polysaccharide secondary ions in wood, (2) can be applied to both high and nominal mass resolution spectra, and (3) is free from peaks that contraindicate between wood components. The removal of additional peaks to avoid mass interferences with common contaminants was also successful. Many of the characteristic peaks were high-intensity fingerprint ions below m/z 100, which provided for rapid analysis of the lignin and polysaccharide biopolymers in woody samples. The analysis also identified important mass interferences with previously reported wood ions.     

Systematic analysis of neutron yields from thick targets bombarded by heavy ions and protons with moving source model

A simple phenomenological analysis using the moving source model has been performed on the neutron energy spectra produced by bombarding thick targets with high energy heavy ions which have been systematically measured at the Heavy-Ion Medical Accelerator (HIMAC) facility (located in Chiba, Japan) of the National Institute of Radiological Sciences (NIRS). For the bombardment of both heavy ions and protons in the energy region of 100–500 MeV per nucleon, the moving source model incorporating the knock-on process could be generally successful in reproducing the measured neutron spectra within a factor of two margin of accuracy. This phenomenological analytical equation is expressed having several parameters as functions of atomic number Z_p, mass number A_p, energy per nucleon E_p for projectile, and atomic number Z_T, mass number A_T for target. By inputting these basic data for projectile and target into this equation we can easily estimate the secondary neutron energy spectra at an emission angle of 0–90° for bombardment with heavy ions and protons in the aforementioned energy region. This method will be quite useful to estimate the neutron source term in the neutron shielding design of high energy proton and heavy ion accelerators.     

Measurement of ion beam profiles in a superconducting linac with a laser wire

A laser wire ion beam profile monitor system has been developed at the Spallation Neutron Source accelerator complex. The laser wire system uses a single laser source to measure the horizontal and vertical profiles of a pulsed hydrogen ion (H(-)) beam along a 230 m long superconducting linac, which accelerates H(-) from 200 MeV to 1 GeV. In this paper, we describe the laser optics requirement for the system, the performance of the profile measurement, and the effects of laser parameters on the measurement reliability. The result provides a practical guideline for the development of a large-scale, operational, laser-based diagnostics in accelerator facilities.     

Contribution of secondary particles to the dose in 12C radiotherapy and other heavy ion beams

The results of experimental studies performed in a radiotherapy (12)C ion beam with a nominal energy of 500 MeV/amu and in (16)O and (56)Fe ion beams with a nominal energy of 1 GeV/amu have been described. Linear energy transfer (LET) spectra have been established by means of an LET spectrometer based on a chemically etched track detector, and the measured results were also compared with theoretical calculations obtained using the program Stopping and Range of Ions in Matter (SRIM). It was observed that with increasing depth in a beam, the LET spectra are shifted towards higher values of LET; one can also observe an important widening of the spectra along the range, as well as an increasing amount of nuclear reaction products and/or of fragments in the spectra. The relative contribution of these secondary particles to the total absorbed dose was assessed.     

Patterned ion beam implantation of Co ions into a SiO2 thin film via ordered nanoporous alumina masks

Spatially patterned ion beam implantation of 190 keV Co(+) ions into a SiO(2) thin film on a Si substrate has been achieved by using nanoporous anodic aluminum oxide with a pore diameter of 125 nm as a mask. The successful synthesis of periodic embedded Co regions using pattern transfer is demonstrated for the first time using cross-sectional (scanning) transmission electron microscopy (TEM) in combination with analytical TEM. Implanted Co regions are found at the correct relative lateral periodicity given by the mask and at a depth of about 120 nm.     

GEANT4 used for neutron beam design of a neutron imaging facility at TRIGA reactor in Morocco

Neutron imaging has a broad scope of applications and has played a pivotal role in visualizing and quantifying hydrogenous masses in metallic matrices. The field continues to expand into new applications with the installation of new neutron imaging facilities.In this scope, a neutron imaging facility for computed tomography and real-time neutron radiography is currently being developed around 2.0MW TRIGA MARK-II reactor at Maamora Nuclear Research Center in Morocco (Reuscher et al., 1990 [1]; de Menezes et al., 2003 [2]; Deinert et al., 2005 [3]).The neutron imaging facility consists of neutron collimator, real-time neutron imaging system and imaging process systems. In order to reduce the gamma-ray content in the neutron beam, the tangential channel was selected. For power of 250 kW, the corresponding thermal neutron flux measured at the inlet of the tangential channel is around 3×10¹¹ ncm²/s.This facility will be based on a conical neutron collimator with two circular diaphragms with diameters of 4 and 2 cm corresponding to L/D-ratio of 165 and 325, respectively. These diaphragms' sizes allow reaching a compromise between good flux and efficient L/D-ratio. Convergent-divergent collimator geometry has been adopted.The beam line consists of a gamma filter, fast neutrons filter, neutron moderator, neutron and gamma shutters, biological shielding around the collimator and several stages of neutron collimator. Monte Carlo calculations by a fully 3D numerical code GEANT4 were used to design the neutron beam line (http://www.info.cern.ch/asd/geant4/geant4.html[4]).To enhance the neutron thermal beam in terms of quality, several materials, mainly bismuth (Bi) and sapphire (Al₂O₃) were examined as gamma and neutron filters respectively. The GEANT4 simulations showed that the gamma and epithermal and fast neutron could be filtered using the bismuth (Bi) and sapphire (Al₂O₃) filters, respectively.To get a good cadmium ratio, GEANT 4 simulations were used to define the design of the moderator in the inlet of the radiation channel. A graphite block of 22 cm thickness seems to be the optimal neutron moderator.The results showed that the combination of 5 cm of bismuth with 5 cm of sapphire permits the filtration of gamma-rays, epithermal neutrons as well as fast neutrons in a considerable way without affecting the neutron thermal flux.     

Dynamics of plasma and ion flux in a vacuum neutron tube

Results of the numerical simulation of the formation of the ion beam in the accelerating gap of a vacuum neutron tube are presented. Calculations are performed with the KARAT code in a two-dimensional nonstationary formulation for plasma formed in arc discharge and inflowing into an accelerating gap with the given time dependences of parameters (density, expansion velocity). The small duration of the vacuum arc leads to a considerable change of parameters of inflowing plasma during the accelerating pulse. Two geometries are considered: the conventional and sectioned diode, in which the total voltage is divided between the anode, intermediate electrode, and cathode.