Ian F. Bubb

Detection efficiency of time-of-flight energy elastic recoil detection analysis systems

Abstract The detection efficiency of recoils with masses ranging from H up to Nb at energies from 0.05 to 1 MeV per nucleon has been investigated for Time-of-Flight Energy Elastic Recoil Detection (ToF-E ERD) systems. It is observed that the detection efficiency for the ToF-E detector telescope depends on the stopping power in the carbon foils, which in turn relies upon the recoil mass and energy. Furthermore, the limits of this behaviour depend on the setting of the discriminator thresholds. The detection efficiency of a time detector could be fitted to a universal curve that can be described by a simple empirical formula as a function of recoil electronic stopping power in the carbon foil. This formula can be used to predict the detection efficiency by recoil energy for N, O and other elements, for which it may not be easy to prepare suitable reference samples containing only that element.

Multivariate analysis method for energy calibration and improved mass assignment in recoil spectrometry

Abstract Heavy ion recoil spectrometry is rapidly becoming a well established analysis method, but the associated data analysis processing is still not well developed. The pronounced nonlinear response of silicon detectors for heavy ions leads to serious limitation and complication in mass gating, which is the principal factor in obtaining energy spectra with minimal cross talk between elements. To overcome the above limitation, a simple empirical formula with an associated multiple regression method is proposed for the absolute energy calibration of the time of flight-energy dispersive detector telescope used in recoil spectrometry. A radical improvement in mass assignment was realized, which allows a more accurate and improved depth profiling with the important feature of making the data processing much easier.

Transit dose of an Ir-192 high dose rate brachytherapy stepping source

Clinical dosimetry for high dose rate (HDR) brachytherapy with a single stepping source generally neglects the transit dose. This study investigates the effects of the transit dose in the target volume of an HDR brachytherapy stepping source. A video method was used to analyse the entrance, exit and the interdwell transit speed of the source for different path lengths and step sizes ranging from 2.5 mm to 995 mm. The transit speed was found to vary with the step size and path length. For the travelled distances of 2.5, 5.0, 10.0, 230 and 995 mm, the average transit speeds were 54, 72, 233, 385 and 467 mm s(-1) respectively. The results also show that the manufacturer has attempted to compensate for the effects of interdwell transit dose by reducing the actual dwell time of the source. A well-type chamber was used to determine the dose differences between two sets of measurements, one being the stationary dose only and the other being the sum of stationary and transit doses. Single catheters of active lengths of 20 and 40 mm, different dwell times of 0.5, 1, 2 and 5 s and different step sizes of 2.5, 5 and 10 mm were used in the measurements with the well-type chamber. Most of the measured dose differences between stationary and stationary plus interdwell source movement were within 2%. The additional dose due to the source transit can be as high as 24.9% for the case of 0.5 s dwell time, 10 mm step size and 20 mm active length. The dose difference is mainly due to the entrance and exit source movement but not the interdwell movement.

Recoil spectrometry : ion accelerator based elemental characterisation of surface layers

Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)35C1,81Br or127I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications.

INTERFACIAL REACTION STUDIES OF CR, NI, TI, AND PT METALLIZATION ON INP

Interfacial reactions between (100) InP and thin films of the transition metals Cr, Ni, Pt, and Ti have been studied. A thin layer of metal was deposited onto the InP substrates using e‐beam evaporation and parts of the samples were then subjected to heat treatment in vacuum for 30 min at several temperatures up to 500 °C. Separate characterizations of the metal, In, and P depth distributions were carried out using mass and energy dispersive recoil spectrometry. The different crystalline phases observed were determined using x‐ray diffraction. The near‐noble metals (Ni, Pt) formed ternary phases, while Ti and Cr formed phosphides. The phases formed were generally stable up to 500 °C with the major exception being Pt where the ternary phase decomposed to form PtIn2, PtP2, and Pt3In7.

Empirical characterisation of mass distribution broadening in ToF-E recoil spectrometry

Abstract The mass broadening function in mass and energy dispersive recoil spectrometry using a detector telescope for time-of-flight and energy determination, has been characterised for a number of isotopes in the range A = 12 to 197. The broadening was well described by a Gaussian function where the standard deviation is given by the empirical equation: θ A ( E, A ) = C 1 + C 2 A 3/2 E − 1 + C 3 A 2 E − 2/3 + C 4 AE 1/2

The effects of large angle plural scattering on heavy ion elastic recoil detection analysis

Heavy ion elastic recoil detection analysis (HIERDA) is becoming widely used to study a range of problems in materials science, however there is no standard methodology for the analysis of HIERDA spectra. Major impediments are the effects of multiple and plural scattering which are very significant, even for quite thin (∼100 nm) layers of very heavy elements. To examine the effects of multiple scattering a fast FORTRAN version of TRIM has been adapted to simulate the spectrum of backscattered and recoiled ions reaching the detector. The results of the simulations are compared with experimental measurements on well characterised samples including thin Au layers and pure elements beyond the single scattering critical angle performed using ToF-E HIERDA at Lucas Heights and show good agreement except in the long tails.

Recoil spectrometry of thin film reactions in the Pd/InP system

Interfacial reactions between (100) InP and Pd were investigated as part of a systematic study aimed at investigating the stability of planar nonalloyed metallizations to InP. A 50‐nm‐thick Pd film was deposited on an InP substrate, and parts of it were subsequently thermally treated for 30 min at temperatures varying from 100 to 500 °C in steps of 50 °C. Separate characterizations of the Pd, In, and P depth distributions were obtained using mass and energy dispersive recoil spectrometry. The different phases were determined using x‐ray diffraction, and scanning electron microscopy was used to study the surface topography. It is assumed that the interaction starts in the as‐deposited sample, and definite formation of a ternary phase with the suggested composition Pd5In2P2 starts at an annealing temperature of 100 °C. At 250 °C all Pd is chemically reacted. Preferential outdiffusion of P leads to a loss of P from the surface at 500 °C, and the only phase observed in the x‐ray diffraction spectrum from the ...

Mass and energy dispersive recoil spectrometry of SixGe1−x grown by electron beam evaporation

Abstract Mass and energy dispersive recoil spectrometry employing 77 MeV 127 I ions from the recently commissioned ANTARES (FN Tandem) accelerator facility at Lucas Heights have been used to examine the isotopic composition of samples of Si x Ge 1− x grown by Electron Beam Evaporation (EBE) at the Australian National University. Analysis of RBS spectra using yield simulations indicated the presence of an unobserved element. Oxygen was considered a likely contaminant for incorporation into the Si x Ge 1− x layer by a reaction between Ge and residual oxygen in the EBE system. Determination of oxygen concentration and distribution is not normally possible with RBS but may be inferred from yield simulations using the code RUMP. Recoil spectrometry has shown the presence of oxygen in the Si x Ge 1− x layer at lower concentrations than inferred from RBS and has enabled the determination of energy spectra for individual elements.

Measurement of carbon contamination in barium strontium titanate films

Abstract Ferroelectric films are being developed for use in DRAMs. The films are often manufactured using spin-on techniques making contamination with residual carbon inevitable. The concentration of carbon is rarely known and its effect not understood. This paper describes the analysis of barium strontium titanate (BST) films for carbon content using both Mass and Energy Dispersive Recoil Spectrometry (RS) with 77 MeV 127 I ions and Nuclear Reaction Analysis (NRA) using the 12 ( 3 He,p 0 ) 14 N reaction.