Nuclear Inst. and Methods in Physics Research, B (v.267, #1)

NIMB Editorial for 2009 by Mark Breese; Lynn Rehn; Christina Trautmann; Ian Vickridge (1-2).

The total mass attenuation coefficients (μm ), for Cr, Fe, Ni and Fe x Ni1− x (x  = 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 and 0.2), Fe x Cr y Ni1−( x + y ) (x  = 0.7, y  = 0.1; x  = 0.5, y  = 0.2; x  = 0.4, y  = 0.3; x  = 0.3, y  = 0.3; x  = 0.2, y  = 0.2 and x  = 0.1, y  = 0.2) and Ni x Cr1− x (x  = 0.8, 0.6, 0.5, 0.4 and 0.2) alloys were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The samples were irradiated with 10 mCi Cd-109 and 100 mCi Am-241 radioactive point source using transmission arrangement. The γ- and X-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections (σt and σe ), effective atomic and electron numbers (Zeff and Neff ) were determined experimentally and theoretically using the obtained mass attenuation coefficients for investigated 3d alloys. The theoretical mass attenuation coefficients of each alloy were estimated using mixture rule. The experimental values were compared with the calculated values for all samples.
Keywords: Mass attenuation coefficients; Effective atomic and electron number; Alloy; 3d Transition metal;

For the purpose of treating the difference in stopping power between condensed and gaseous substances, we first discuss our method of statistical analysis of published experimental data. We distinguish between a positive effect where the difference between mass stopping powers Ssolid Sgas is positive and a negative effect where the opposite holds true. Experimentally, the positive effect has been found so far with heavy ions at high energy, and the negative effect with light ions at low energy. The positive effect is due to the difference in ionic charges and can be described by the CasP program by Grande and Schiwietz. An apparent persistence of the positive effect down to low energy is found to be mainly an artifact inherent in the stopping table of ICRU Report 73. The negative effect can be described by a difference in mean ionization potentials between gases and condensed matter. It is large for metals, much smaller for compounds. It should be possible to see both effects in one projectile – target combination.
Keywords: Energy loss of ions; Gas–solid difference of stopping power; Statistical analysis of data; Ionic charge;

Charged particle induced reactions can be used to monitor in real time the wear of mechanical structures such as internal combustion engines and turbines. Charged particle induced reactions with suitable properties also can be used for monitoring the actual parameters of bombarding particle beams. One of these reactions is the natFe(d,x)57Co process. The available experimental data in the literature are well established around and above the maximum of the excitation function, however only a little, scattered data are available in the threshold energy region of the reaction. In this work we measured the excitation functions of relevant processes resulting in 55,56,57,58Co, 59Fe and 52,54Mn induced by deuteron beams on natural iron in the energy range from threshold up to 10 MeV. The new experimental data collected are used to determine with high confidence recommended values for the missing low energy part of the investigated excitation functions.
Keywords: Natural iron target; Deuteron irradiation; Cyclotron; Excitation function; Cross section; Cobalt-57 radioisotope; Thin layer activation; Monitor reaction;

Excitation functions of the proton-induced nuclear reactions on natSn up to 40 MeV by Mayeen Uddin Khandaker; Kwangsoo Kim; Kyung-Sook Kim; Manwoo Lee; Young Seok Lee; Guinyun Kim; Young-Sik Cho; Young-Ouk Lee (23-31).
We have measured the production cross-sections of the residual radionuclides for proton-induced reactions on natural tin by using a stacked-foil activation technique in the energy range from threshold energy to 40 MeV at the MC-50 cyclotron of the Korea Institute of Radiological and Medical Sciences. The results were compared with the earlier reported experimental data and theoretical calculations based on the TALYS and the ALICE-IPPE codes. The present results are in general good agreement with the available literature data and calculated results by using the computer codes TALYS and ALICE-IPPE. The thick target integral yields were also deduced from the measured excitation functions of the produced radionuclides.
Keywords: p+natSn; 40 MeV proton beam; Stacked-foil activation technique; Excitation functions; Integral yields;

Double-electron excitation processes of helium atoms by proton and antiproton impact have been theoretically investigated using the four-body formalism of boundary corrected continuum intermediate state (BCCIS-4B) approximation in the energy range of 50–500 keV. In this formalism, the presence of the projectile in the exit channels is described by distorting the final bound state wave functions with coulomb waves (associated with the projectile–electron interactions). The results are in good agreement with the other theoretical and experimental results. Reasonably better agreements have been found in the intermediate and high energy regions. Contributions to the cross section of the different magnetic sub-shells are also analysed.
Keywords: Ion–atom collision; Double excitation; Cross section;

New Geant4 cross section models for PIXE simulation by H. Ben Abdelouahed; S. Incerti; A. Mantero (37-44).
We have implemented in the Geant4 simulation toolkit a set of new ionisation cross sections for the simulation of particle induced X-ray emission (PIXE), based upon theoretical and semi-empirical models. The set provides a model based on the so-called ECPSSR theory for the computation of K-shell ionisation cross sections for proton and alpha particle impact. A second model is based upon semi-empirical expressions proposed by Orlic for the calculation of L i -subshells ionisation cross sections for proton impact. Our developments are compared to ionisation cross sections already existing in the Geant4 toolkit and to experimental data.
Keywords: Geant4 simulation toolkit; PIXE; Ionisation cross sections; ECPSSR;

Electron inelastic mean free paths in biological matter based on dielectric theory and local-field corrections by D. Emfietzoglou; I. Kyriakou; I. Abril; R. Garcia-Molina; I.D. Petsalakis; H. Nikjoo; A. Pathak (45-52).
The inelastic mean free path (IMFP) of electrons with energies up to a few keV is calculated from the dielectric electron-gas theory for densities corresponding to those of biological matter. The effect of the many-body local-field correction on the Lindhard dielectric response function is examined using some of the available analytical approximations to its static limit. We have tested the performance of several Hubbard-type local-field corrections along with the formula proposed by Corradini and co-workers [M. Corradini, R. Del Sole, G. Onida, M. Palumno, Phys. Rev. B 57 (1998) 14569] which is extensively used in connection with the exchange-correlation kernel of time-dependent density functional theory. It is shown that the Lindhard dielectric function provides reasonable estimates of electron IMFPs below about 50 eV, where the majority of semi-empirical dielectric calculations based on the extended-optical-data methodology fail. The use of LFC results in a sizeable reduction of the IMFP which, at low energies, may reach ∼20%.
Keywords: Inelastic mean free path; Dielectric theory; Local-field corrections; Biological materials; Water;

Modelling swift heavy ion irradiation in iron by A.M. Rutherford; D.M. Duffy (53-57).
Swift heavy ions moving in metals lose most of their energy to inelastic scattering of electrons. The energy deposited in the electronic system is transferred into the atomic system via electron–ion interactions and can lead to melting and creation of new damage and also annealing of pre-existing atomic defects. Using a combination of molecular dynamics and a consistent treatment of electron energy transfer and transport we have modelled experiments performed in Fe to investigate the annealing effect and damage creation under electronic excitations. We observe both annealing and new damage creation at low and high electronic stopping, respectively. Rapid separation of interstitial atoms and vacant lattice sites is seen due to efficient transport via replacement collision sequences. Our results suggest that the role of electronic excitation can be significant in modeling of the behaviour of metals under swift heavy ion irradiation and attempts to modify metals via ion implantation.
Keywords: Radiation damage; Defects; Ion beam mixing; Defect annealing; Electronic excitation;

Formation of Au nanoparticles in sapphire by using Ar ion implantation and thermal annealing by L.H. Zhou; C.H. Zhang; Y.T. Yang; B.S. Li; L.Q. Zhang; Y.C. Fu; H.H. Zhang (58-62).
In this paper, we present results of the synthesis of gold nanoclusters in sapphire, using Ar ion implantation and annealing in air. Unlike the conventional method of Au implantation followed by thermal annealing, Au was deposited on the surface of m- and a- cut sapphire single crystal samples including those pre-implanted with Ar ions. Au atoms were brought into the substrate by subsequent implantation of Ar ions to form Au nanoparticles. Samples were finally annealed stepwisely in air at temperatures ranging from 400 to 800 °C and then studied using UV–vis absorption spectrometry, transmission electron microscopy and Rutherford backscattered spectrometry. Evidence of the formation Au nanoparticles in the sapphire can be obtained from the characteristic surface plasmon resonance (SPR) absorption band in the optical absorption spectra or directly from the transmission electron microscopy. The results of optical absorption spectra indicate that the specimen orientations and pre-implantation also influence the size and the volume fraction of Au nanoparticles formed. Theoretical calculations using Maxwell–Garnett effective medium theory supply a good interpretation of the optical absorption results.
Keywords: Sapphire; Annealing; Ion implantation; Au nanoparticle; Optical absorption; Surface plasmon resonance;

Microstructural changes in β–Cu–Zn–Al due to SHI irradiation by E. Zelaya; A. Tolley; G. Schumacher (63-68).
The effects of irradiation with swift heavy ions on L21 long range ordered β phase Cu–Zn–Al single crystals with surface orientation close to (0 0 1)β were investigated. The resulting change in structure and microstructure were characterized by transmission electron microscopy. A phase transformation to a close-packed phase, loops and cavities were observed and characterized after the irradiation process. The origin and the stability of the microstructural changes due to irradiation are discussed.
Keywords: Ion radiation effects; Radiation effects on metals and alloys; Transmission electron microscopy; Microscopic defects; Shape memory alloys;

Heavy ion beam micromachining on LiNbO3 by F. Nesprías; M. Venturino; M.E. Debray; J. Davidson; M. Davidson; A.J. Kreiner; D. Minsky; M. Fischer; A. Lamagna (69-73).
In this work 3D micromachining of x-cut lithium niobate crystals was performed using the high energy heavy ion microbeam (HIM) at the Tandar Laboratory, Buenos Aires. The samples were machined using 35Cl beams at 70 MeV bombarding energy combined with wet etching with hydrofluoric acid solutions at room temperature. As the ion beam penetrates the sample, it induces lattice damage increasing dramatically the local etching rate of the material. This technique was applied to the fabrication of 3D waveguides with long control electrodes. The resulting structures indicate that well defined contours with nearly vertical sidewalls can be made. The results also show that with fluences of only 5 × 1012  ions/cm2, this technique is suitable for the fabrication of different shapes of LiNbO3 control-waveguides that can be used in different optical devices and matched with the existing optical fibers.
Keywords: Direct write; Swift heavy ions; Lithium niobate; Wave guides;

Ab initio study electronic structures of LiYF4 crystal containing interstitial oxygen atoms by Jigang Yin; Qiren Zhang; Tingyu Liu; Xiaofeng Guo; Min Song; Xien Wang; Haiyan Zhang (74-78).
The positions of the interstitial oxygen atoms in LiYF4 crystal are simulated by computer technologies. It is found that the total energy of cluster is low when interstitial oxygen atoms exist around the Li+ ion. Basing on the computer results, the electronic structures of perfect LiYF4 and the LiYF4 containing interstitial oxygen atoms with the lattice structure optimized are studied within the framework of the density functional theory. By analyzing the calculated results it can be concluded that an interstitial oxygen atom could combine with formal lattice fluorine ions forming molecular ions, which cause the 260 nm absorption band.
Keywords: LiYF4 crystal; Lattice relaxation; Interstitial oxygen atoms; ABINIT; Absorption band;

Gallium nitride (GaN) epilayers have been grown by chloride vapour phase epitaxy (Cl-VPE) technique and the grown GaN layers were irradiated with 100 MeV Ni ions at the fluences of 5 × 1012 and 2 × 1013  ions/cm2. The pristine and 100 MeV Ni ions irradiated GaN samples were characterized using X-ray diffraction (XRD), UV-visible transmittance spectrum, photoluminescence (PL) and atomic force microscopy (AFM) analysis. XRD results indicate the presence of gallium oxide phases after Ni ion irradiation, increase in the FWHM and decrease in the intensity of the GaN (0 0 0 2) peak with increasing ion fluences. The UV-visible transmittance spectrum and PL measurements show decrease in the band gap value after irradiation. AFM images show the nanocluster formation upon irradiation and the roughness value of GaN increases with increasing ion fluences.
Keywords: GaN; Ion irradiation; X-ray diffraction; AFM; Photoluminescence; UV-visible optical transmission spectrum;

Experimental study on heavy ion single event effects in SOI SRAMs by Li Yonghong; He Chaohui; Zhao Fazhan; Guo Tianlei; Liu Gang; Han Zhengsheng; Liu Jie; Guo Gang (83-86).
Silicon-on-insulator (SOI) technologies have been developed for radiation-hardened military and space applications. The use of SOI has been motivated by the full dielectric isolation of individual transistors, which prevents latch-up. The sensitive region for charge collection in SOI technologies is much smaller than for bulk-silicon devices potentially making SOI devices much harder to single event upset (SEU). In this study, 64 kB SOI SRAMs were exposed to different heavy ions, such as Cu, Br, I, Kr. Experimental results show that the heavy ion SEU threshold linear energy transfer (LET) in the 64 kB SOI SRAMs is about 71.8 MeV cm2/mg. Accorded to the experimental results, the single event upset rate (SEUR) in space orbits were calculated and they are at the order of 10−13 upset/(day bit).
Keywords: SOI SRAM; Single event upset; Single event upset rate;

Radiation effects on ohmic and Schottky contacts based on 4H and 6H-SiC by Kübra Çınar; Cevdet Coşkun; Emre Gür; Şakir Aydoğan (87-90).
A systematic study of Ni based ohmic and Schottky contacts (SCs) onto the n-4H-SiC and n-6H-SiC under relatively low-dose (1 × 1012  e  cm−2) and high-energy (6, 12, 15 MeV) electron irradiation (HEEI) has been introduced. Lower specific contact resistivity has been reached for Ni based ohmic contact structures on both 4H and 6H-SiC after each electron irradiation. This finding has been explained by the displacement damage produced by the collision of electrons with atoms of Ni contact material. It has been observed that the HEEI caused to increase in the ideality factors of both SCs indicating deviation from thermionic emission theory in current transport mechanism. While the Schottky barrier height (SBH) for Ni/4H-SiC SC remains nearly constant, an increase has been observed for the Ni/6H-SiC SC. Donor concentrations for both diodes have decreased with increasing electron energy probably due to the trapping effect of the irradiation induced defect(s).
Keywords: Ohmic contact; Schottky diode; Electron irradiation; 4H-SiC; 6H-SiC;

The highly swelling Poly (acrylamide/maleic acid/gelatin) P(AAm/MA/G) hydrogels were prepared by gamma-irradiation at low dose rate (0.94 kGy/h) and moderate dose rate (3.84 kGy/h). The hydrogels were confirmed by FTIR. The effect of copolymer composition, dose and dose rate on the swelling behaviour was discussed. Increasing of MA content and G in the initial mixture leads to an increase in the amount of MA and G in the gel system and decrease in the gelation %. The swelling behaviours of the hydrogel prepared at moderate dose rate increased with increasing MA mole content in the gel system but, there is no systematic dependence of swelling on MA content was observed for the hydrogels obtained at low dose rate. Pore structure of the hydrogels was monitored by using scanning electron microscopy. Thermogravimetric analysis (TGA) and the rate of the thermal decomposition of P(AAm/MA/G) hydrogels has been evaluated to give a better understanding of the thermal stability of polymers, The X-ray data of P(AAm/MA/G) hydrogels was discussed to investigate some features namely the degree of ordering and crystallite size.
Keywords: Poly acrylamide; Maleic acid; Gelatin; Swelling; Hydrogel; Thermal analysis;

A 3 MeV He2+ beam was used to irradiate C8 (a flocculant-producing bacteria) with a fluence ranging from 1011 to 1013  ions/cm2. The effects on the survival ratio, TTC-dehydrogenase activity, flocculating activity and RAPD analysis are reported. The survival ratio curve caused by irradiation is proved to be “saddle-shaped”. Eleven mutants were obtained, all of which had a significant change in dehydrogenase activity and most showed a positive change in flocculating activity. RAPD measurements were used to analyse the DNA of mutants with a flocculating activity over 80%, which indicated that all their DNA had been changed by irradiation.
Keywords: Ion irradiation; Bioflocculant; Dehydrogenase; Survival ratio; Heavy ions; RAPD;

Hydrocarbon proton-conductive membranes prepared by radiation-grafting of styrenesulfonate onto aromatic polyamide films by Dengrong Li; Jinhua Chen; Maolin Zhai; Masaharu Asano; Yasunari Maekawa; Hiroyuki Oku; Masaru Yoshida (103-107).
Novel method for preparing aromatic hydrocarbon proton-conductive membranes without sulfonation and membrane casting process is achieved by radiation-grafting of sodium styrenesulfonate to an aromatic polyamide, poly(m-xylylene adipamide) (Nylon-MXD6) films and subsequent ion-exchange. The styrenesulfonate was easily grafted into the Nylon-MXD6 films from an oxygen-free dimethyl sulfoxide (DMSO) solution at 60 °C. As a result, the resulted styrenesulfonic acid-grafted Nylon-MXD6 films, namely proton-conductive membrane, with high ion-exchange capacity up to 1.63 mmol/g, can be obtained. The membrane was transparent and highly hydrophilic. The proton conductivity, water uptake and methanol permeability of the proton-conductive membranes were investigated with respect to their use in fuel cells. The high proton conductivity reached 0.083 S/cm, comparable to Nafion. Furthermore, the methanol permeability was significantly lower than that of the Nafion membrane. Therefore, the Nylon-MXD6-based proton-conductive membrane is a more promising material for the direct methanol fuel cells (DMFCs).
Keywords: Radiation-grafting; Proton-conductive membranes; Direct methanol fuel cell (DMFC); Aromatic polyamide; Styrenesulfonate;

Method to measure composition modifications in polyethylene terephthalate during ion beam irradiation by M. Abdesselam; J.P. Stoquert; S. Chami; M. Djebara; A.C. Chami; M. Siad (108-112).
Matter losses of polyethylene terephthalate (PET, Mylar) films induced by 1600 keV deuteron beams have been investigated in situ simultaneously by nuclear reaction analysis (NRA), deuteron forward elastic scattering (DFES) and hydrogen elastic recoil detection (HERD) in the fluence range from 1 × 1014 to 9 × 1016  cm−2. Volatile degradation products escape from the polymeric film, mostly as hydrogen-, oxygen- and carbon-containing molecules. Appropriate experimental conditions for observing the composition and thickness changes during irradiation are determined. 16O(d,p0)17O, 16O(d,p1)17O and 12C(d,p0)13C nuclear reactions were used to monitor the oxygen and carbon content as a function of deuteron fluence. Hydrogen release was determined simultaneously by H(d,d)H DFES and H(d,H)d HERD. Comparisons between NRA, DFES and HERD measurements show that the polymer carbonizes at high fluences because most of the oxygen and hydrogen depletion has already occured below a fluence of 3 × 1016  cm−2. Release curves for each element are determined. Experimental results are consistent with the bulk molecular recombination (BMR) model.
Keywords: Polyethylene terephthalate; Polymer irradiation; Radiolysis; Forward elastic scattering; Nuclear reaction analysis;

The depth profiles of lattice strain near the interface regions of LaAlO3/Si and the SiO2 interfacial layer/Si were investigated by the ion channeling technique using high-resolution Rutherford backscattering spectroscopy (HRBS). In the case of the LaAlO3/Si stack, horizontal tensile strain in the Si near the interface was clearly observed. However, this strain was relaxed by formation of the interfacial layer through annealing in an oxygen ambient. These results suggest that the strain in Si induced by a dielectric strongly depends on the material in contact with Si.
Keywords: LaAlO3; HRBS; Strain; Interface;

Analysis of elemental maps from glaze to body of ancient Chinese Jun and Ru porcelain by micro-X-ray fluorescence by Lin Cheng; Rongwu Li; Qiuli Pan; Guoxia Li; Weijuan Zhao; Zhiguo Liu (117-120).
The reasons how the middle layer of Ru and Jun porcelain between the glaze and body came into being are still not completely understood. Here, elemental maps from the glaze to the body of pieces of ancient Chinese Ru and Jun porcelain were analyzed by micro-X-ray fluorescence. The results show the middle layer was probably formed by the chemical composition of the glaze turning into glassy states and undergoing complex physical–chemical reactions with the body. However, the middle layer of Jun porcelain was formed by the chemical composition of the glaze turning into glassy states and then infiltrating the body at high temperatures during the firing process.
Keywords: Polycapillary optics; Ancient porcelain; Micro-X-ray fluorescence; Ancient porcelain; Middle layer;

PIXE–PIGE analysis of Carolingian period glass from Slovenia by Ž. Šmit; D. Jezeršek; T. Knific; J. Istenič (121-124).
Glass artifacts excavated from the Late Roman and Carolingian period site at Bašelj Slovenia were analyzed by the combined PIXE–PIGE method using a proton beam in air. The results show that the majority of objects and glass ingots were made of traditional Roman, natron-type glass. Increased titanium and other impurities were found indicating that the glass had been recycled several times. As the composition of the ingots was similar to the other objects, a possibility exists of a secondary glass workshop in the local vicinity. The typologically and stratigraphically dated objects confirm that the Roman glassmaking continued in the area of Eastern Alps well into the 9th century.
Keywords: PIXE; PIGE; Glass; Natron; Late Roman; Carolingian;

Development and evaluation of the Combined Ion and Neutron Spectrometer (CINS) by C. Zeitlin; R. Maurer; D. Roth; J. Goldsten; M. Grey (125-138).
The Combined Ion and Neutron Spectrometer, CINS, is designed to measure the charged and neutral particles that contribute to the radiation dose and dose equivalent received by humans in spaceflight. As the depth of shielding increases, either onboard a spacecraft or in a surface habitat, the relative contribution of neutrons increases significantly, so that obtaining accurate neutron spectra becomes a critical part of any dosimetric measurements. The spectrometer system consists of high- and medium-energy neutron detectors along with a charged-particle detector telescope based on a standard silicon stack concept. The present version of the design is intended for ground-based use at particle accelerators; future iterations of the design can easily be streamlined to reduce volume, mass, and power consumption to create an instrument package suitable for spaceflight. The detector components have been tested separately using high-energy heavy ion beams at the NASA Space Radiation Laboratory at the Brookhaven National Laboratory and neutron beams at the Radiological Research Accelerator Facility operated by Columbia University. Here, we review the progress made in fabricating the hardware, report the results of several test runs, and discuss the remaining steps necessary to combine the separate components into an integrated system. A custom data acquisition system built for CINS is described in an accompanying article.
Keywords: Galactic cosmic rays; Dosimetry; Heavy ions; Neutrons; Spectrometry;

Data acquisition for the Combined Ion and Neutron Spectrometer (CINS) by M. Grey; J. Goldsten; R. Maurer; D. Roth; C. Zeitlin (139-143).
The CINS (Combined Ion and Neutron Spectrometer) consists of three detector systems: a boron-loaded plastic scintillator for medium energy neutrons, a silicon detector system for high-energy neutrons, and a charged particle stack containing both silicon detectors and scintillators. A readout system built for the charged particle stack is described here. The stack must be able to detect particles over a wide range of charge and energy. It contains 7 detectors, including 4 silicon detectors that each have two output paths. The readout must have a large usable dynamic range and must be able to handle the relatively high event rates that occur when the stack is placed in an accelerator beam. The data acquisition system detects events (that is, compares incoming signals to user-supplied trigger definitions), proceeds to capture waveform data from the preamplifiers, and saves the data to a hard drive. Although only used with the charged particle stack to date, the system can also be used with the other elements of CINS.
Keywords: Galactic cosmic rays; Dosimetry; Heavy ions; Neutrons; Spectrometry;

Since 1960 the potential of obsidian as a chronometer in archaeology has been subjected to several drawbacks and studies. While economical, simple and fast, obsidian hydration dating today is generally unreliable. A novel approach towards obsidian hydration dating, named SIMS-SS, has recently been initiated based on modelling the hydrogen profile acquired by secondary ion mass spectrometry (SIMS), following Fick’s diffusion law, and the rationale of surface saturation (SS) with water molecules. The new nuclear method is presented with significant refinement regarding numerical calculation of age parameters, the suitability criteria of the sampling area and the spectral shape of the concentration dependant H+ profile. A reappraisal is applied to thirteen obsidian specimens from all over the world ranging some 100’s to 30,000 years old. The results reinforce the precision and reliability of the SIMS-SS method, enhancing its wide applicability.
Keywords: Obsidian; SIMS; Diffusion; Hydration; Surface saturation; Dating; Hydrogen profile;

The energy and intensity distributions of multiple backscattering of 1.12 MeV gamma photons emerging from targets of elements and alloys are observed as a function of thickness and atomic number (Z) of the target. The numbers of these multiply backscattered events show an increase with increase in target thickness, and then saturate for a particular thickness of the target called saturation thickness (depth). The saturation thickness decreases with increasing atomic number and varies as e Z . The multiple backscattering, an interfering background noise in Compton profile, has been successfully used to assign the ‘‘effective atomic number’’ to alloys. Monte Carlo calculations also support the present experimental results. The number, energy and dose albedos are also found to be saturating for the same thickness where the numbers of multiply backscattered events saturate.
Keywords: Singly and multiply backscattered events; Saturation thickness; Number; Energy and dose albedos; Effective atomic number;

Double differential distributions of electron emission in ion–atom and electron–atom collisions using an electron spectrometer by Deepankar Misra; K.V. Thulasiram; W. Fernandes; Aditya H. Kelkar; U. Kadhane; Ajay Kumar; Yeshpal Singh; L. Gulyás; Lokesh C. Tribedi (157-162).
We study electron emission from atoms and molecules in collisions with fast electrons and heavy ions (C6+). The soft collision electrons (SE), two center electron emission (TCEE), the binary encounter (BE) events and the KLL Auger lines along with the elastically scattered peaks (in electron collisions) are studied using a hemispherical electrostatic electron analyzer. The details of the measurements along with description of the spectrometer and data acquisition system are given. The angular distributions of the low energy (few eV) electrons in soft collisions and the binary encounter electrons at keV energies are compared with quantum mechanical models based on the first Born (B1) and the continuum distorted wave-Eikonal initial state approximation (CDW-EIS).
Keywords: Electron spectroscopy; Hemispherical analyzer; Ionization; Ion–atom collision; Electron–atom collision; Electron emission;

An outlook of heavy ion driven plasma research at IMP-Lanzhou by Yongtao Zhao; Guoqing Xiao; Hushan Xu; Hongwei Zhao; Jiawen Xia; Genming Jin; Xinwen Ma; Yong Liu; Zhihu Yang; Pengming Zhang; Yuyu Wang; Deihui Li; Huanyu Zhao; Wenlong Zhan; Zhongfeng Xu; Di Zhao; Fuli Li; Ximeng Chen (163-166).
Since the successful completion of the cooling storage ring (CSR) project in China at the end of 2007, high qualitative heavy ion beams with energy ranging from keV to GeV/u have been available at the Heavy Ion Research Facility at Lanzhou (HIRFL). More than 109 1 GeV/u C6+ particles or 108 235 MeV/u Xe particles can be stored in the CSR main-ring and extracted within hundred nano-seconds during the test running, the beam parameters will be improved in the coming years so that high energy density (HED) conditions could be achieved and investigated there. Recent scientific results from the experiments relevant to plasma research on HIRFL are summarized. Dense plasma research with intense heavy ion beams of CSR is proposed here.
Keywords: Plasma; HED physics; Heavy ion fusion;

We analyzed the energy dependence of electron stopping powers (SPs) calculated for 41 elemental solids from experimental optical data for electron energies between 100 eV and 30 keV. Our analysis was performed with the Hill equation to represent a series of steps in plots of the slopes of Fano plots. The average root-mean-square difference between SPs from fits with an equation derived from the Hill equation and the calculated SPs was 1.0%. The new equation can provide SPs over a wide energy range for Monte Carlo simulations of electron transport with the continuous slowing-down approximation.
Keywords: Electron stopping power; Fano plot; Elemental solids; Energy dependence;

Identification of origin of single aerosol particles using polycapillary X-ray lens by Tianxi Sun; Zhiguo Liu; Guanghua Zhu; Hui Liu; Qing Xu; Yude Li; Guangpu Wang; Hongbo Sun; Ping Luo; Qiuli Pan; Xunliang Ding (171-174).
A micro X-ray fluorescence (Micro-XRF) spectrometer based on a polycapillary focusing X-ray lens (PFXRL) and a laboratory X-ray source was designed to carry out the XRF analysis of single aerosol particles. The minimum detection limit (MDL) of this Micro-XRF spectrometer was 9 ppm for the Fe-Kα. The percentage of the particles of vehicle exhaust among aerosol particles was studied in Beijing, Chinese capital, during the test of odd–even driving restrictions for Beijing 2008 Olympics Games. This Micro-XRF spectrometer had potential applications in the analysis of single aerosol particles.
Keywords: Micro-XRF; Capillary X-ray optics; Single aerosol particle analysis;

Total cross section of solid mesitylene, toluene and a mixture of them at thermal neutron energies by L.A. Rodríguez Palomino; F. Cantargi; J.J. Blostein; J. Dawidowski; J.R. Granada (175-177).
The total neutron cross sections of mesitylene, toluene and a solution 3:2 by volume of mesitylene and toluene were measured at the electron LINAC based pulsed neutron source of Centro Atómico Bariloche. Measurements were performed at 180 K, 120 K and 31.6 K for mesitylene and at 120 K and 31.6 K for toluene and a solution 3:2 by volume of mesitylene and toluene. The systems are potential moderator materials to be considered in the design of a cold neutron source due to their high resistance to radiation and the richness in low-energy excitations of their frequency spectra, that lead to produce an enhanced cold neutron flux.
Keywords: Total cross section measurements; Cryogenic materials; Cold neutron moderators;

Calendar (178-179).