AFM and electronic transport studies of swift heavy ion irradiated Mn/p-Si bilayer structure

Mn/p-Si structures have been realised by electron beam evaporation of manganese on etched and cleaned p-Si wafers. Bilayer structures have been irradiated by swift heavy ions (of 100 MeV Fe⁷⁺ having a fluence of 1 × 10¹³ ions/cm²). The electronic transport features across the bilayer of the structure (i.e. I–V characteristics across the Mn/p-Si interface) show a significant increase of current (by two orders of magnitude) for the irradiated ones as compared to un-irradiated ones. I–V characteristics across the interface has also been recorded in presence of in-plane (i.e., along the plane of the interface) magnetic field which show a significant magnetic field sensitivity for the irradiated ones. The surface morphological studies from AFM show a granular structure with open face having micro-particles in it, prior to the irradiation and round shaped embedded granular structure after the irradiation. XRD data show the formation of manganese silicide (Mn₅Si₂). The results are understood in the realm of interfacial intermixing which is tailored by the swift heavy ion irradiation.     

Ionizing particles may create shockwaves

To find a model that describes the gas diffusion on irradiated polymers (Makrofol KG polycarbonate) the diffusion constants have been measured with argon as diffusion gas. The polymers were irradiated with uranium, gold and lead ions of about 10 MeV/u and ion fluences between 1×10¹⁰ and 4×10¹¹ ions/cm². The ion irradiated probes show two quite different dependencies of the diffusion constant on the ion energy loss. These effects are strongly related to the fluence of the irradiation. In case of low ion fluences, the diffusion constant is up to 8 times higher than that of pristine material. In the probes with high ion fluences we observe a decrease of diffusion constant to half the value of the pristine material. To understand the dependence of the diffusion constant on ion fluences we apply a model of compacting. This model describes the compacting ability of shockwaves arising from latent tracks. A track formation model is suggested. When an ion penetrates the foil it creates shockwaves around its path. These shockwaves put compacting forces on earlier created latent tracks in the same foil.     

Modification of optical, chemical and structural response of CR-39 polymer by 50 MeV lithium ion irradiation

CR-39 polymer samples were irradiated with 50 MeV lithium ion beam; the fluence was varied in the range 10¹¹–10¹³ ionscm⁻². Irradiation effects were studied using UV–visible, FTIR spectroscopic and X-ray diffraction techniques. The observation of the recorded spectra shows that the detector is sensitive to swift ions irradiation and its UV absorption is influenced by the stopping power (dE/dx)_e. The FTIR spectra does not show any considerable changes due to the irradiation indicating that the detector is chemically stable. No appreciable change in the diffraction pattern of CR-39 polymer after irradiation upto the fluence level of 10¹³ ionscm⁻² is observed, showing its structural stability also.     

Cathode spot energy transfer simulated by a focused laser beam

Minimum conditions for the formation of surface craters by laser irradiation were studied experimentally and theoretically for various metals. The critical power density for crater formation within 20 ns was about 10¹¹ W/m². It is therefore concluded that crater formation by ion bombardment requires an ion current density on the order of 10¹⁰ A/m²     

Multiplicity and angular distributions of charged particles in interactions of Fe in emulsion at 2.5A GeV/c

Data are presented on multiplicity and angular distributions of charged secondary particles from inelastic interactions of ⁵⁶Fe in emulsion at 2.5A GeV/c. Comparisons with data, at nearby the same incident momentum per nucleon from p-A, ¹⁴N-A, ¹⁶O-A and ⁴⁰Ar-A collisions are performed in order to trace the dependence on projectile and target mass. Furthermore, the ⁵⁶Fe data are compared with the results from a cascade-evaporation model. This comparison shows some significant deviations between the model and the data which are not observed for light ion induced collisions.     

Two separate Li ionic motions observed by Li and B NMR in xLi2S + (1 − x)B2S3 glassy fast ionic conductors

Studies of ion dynamics in the highly conductive glassy fast ionic conductor (FIC) xLi₂S + (1 − x)B₂S₃ (x = 0.65 and 0.70) were made with NMR nuclear spin lattice relaxation (NSLR) R₁(ω, T) of both mobile ⁷Li and immobile ¹¹B ions, and ⁷Li NMR line narrowing δν(T). The possible dependence of ion dynamics on the short range order structures (SRO) and the distribution of activation energies (DAE) in this highly conductive FIC was investigated. Two Gaussian DAE were employed to fit ⁷Li NSLR data, where each Gaussian DAE was correlated to a separate ¹¹B NSLR in a BS₃ and in a BS₄ group. The long range diffusion of Li ions among BS₃ groups and a seemingly localized ionic hopping motion around BS₄ group is suggested as a microscopic model for the ion dynamics in thioborate glasses, namely a ‘two channel relaxation’.     

TL and PTTL in natural fluorite previously irradiated with gamma rays and heavy ions

The effect of annealing temperature on the phototransfer thermoluminescence (PTTL) signal was studied to determine the appropriate annealing temperature for treating the natural powder before irradiation. The temperatures used to anneal virgin natural fluorite samples (only natural dose without giving the samples any artificial doses) were 150, 250, 350, 450, 550, 650 and 750°C for a duration of 1 h in each case. The results show that the PTTL response did not change for anneal temperatures up to 450°C, but at higher temperatures the signal decreased rapidly. The height of the 90°C peak decreased by two orders of magnitude as the anneal temperature increased from 450 to 750°C, whilst the height of the 180°C peak decreased by three orders of magnitude between the same two annealing temperatures. In order to investigate the effect of previous gamma rays and heavy ion irradiation on thermoluminescence (TL) and PTTL signals, powdered samples of natural fluorite from Cornwall, England, were annealed at 500°C and then irradiated (at GSI, Darmstadt, Germany) with ¹⁶¹Dy ions of energy 13 Mev/n; the range of fluences used was from 10⁴ to 10¹² ion cm⁻². Identical samples were given gamma doses in the range 1 Gy to 2.6 × 10⁴ Gy in order to compare the effects of gamma rays and heavy ions. The sensitivities of TL and PTTL were studied by giving the samples a gamma test dose of 1 Gy after annealing the samples at 500°C for 30 min in order to eliminate the TL resulting from previous gamma or heavy ion irradiation.     

Structural modification in swift heavy ion irradiated muscovite mica

Two-layer monoclinic(2 M) muscovite mica sheets with a thickness of 12 μm are irradiated with Sn ions at room temperature with electronic energy loss( dE/dx)_e of 14.7 keV/nm. The ion fluence is varied between 1×10~(11) and1×10~(13) ions/cm~2. Structural transition in irradiated mica is investigated by x-ray diffraction(XRD). The main diffraction peaks shift to the high angles, and the inter-planar distance decreases due to swift heavy ion(SHI) irradiation. Dehydration takes place in mica during SHI irradiation and mica with one-layer monoclinic(1 M) structure is thought to be generated in 2 M mica after SHI irradiation. In addition, micro stress and damage cross section in irradiated mica are analyzed according to XRD data. High resolution transmission electron microscopy(HRTEM) is used on the irradiated mica to obtain the detailed information about the latent tracks and structural modifications directly. The latent track in mica presents an amorphous zone surrounded by strain contrast shell, which is associated with the residual stress in irradiated mica.     

快重离子辐照对非晶态SiO2薄膜光致发光谱的影响

用湿氧化法在单晶硅表面生长了非晶态SiO2薄膜,再用高能Pb和Xe离子对薄膜进行辐照,最后用荧光光谱分析了辐照参数(剂量、电子能损值)与发光特性改变的相关性.研究发现,快重离子辐照能显著影响薄膜的发光特性,进一步分析显示,辐照导致了SiO2薄膜内O-Si-O缺陷、缺氧缺陷和非桥式氧空位缺陷的产生,且缺氧缺陷和非桥式氧空...     

Magnetic dipole moments near Sn: Measurement on isomeric 11/2 states in odd-A Te and Te by NMR/ON

On-line low temperature nuclear orientation (OLNO) experiments have been performed on the odd-A Te isotopes ¹³¹Te and ¹³³Te using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moments of the isomeric 11/2⁻ states have been measured extending the known data on these states in the Te isotopes up to the neutron shell closure at N = 82. The contribution to the 11/2⁻ magnetic moment in ¹³³Te due to core polarisation is calculated using an RPA shell model as well as corrections to the magnetic dipole operator caused by mesonic exchange currents. The neutron number dependence of the magnetic moments of the 11/2⁻ isomers in heavy Te isotopes is discussed in terms of particle-core coupling model (PCM) calculations.     

Structure and properties of molybdenum implanted with high-flux carbon ion

High purity molybdenum was implanted by C ion in a metal vapour vacuum arc (MEVVA) implanter. The influence of implantation parameters was studied by varying ion fluence and ion current density. The samples were implanted by 45 keV C ion with fluences from 1×10¹⁵ to 1×10¹⁸ ions/cm², respectively. The as-implanted samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and nanoindenter. Different morphologies were observed on the surfaces of the as-implanted samples due to irradiation damage, and clearly related to implantation parameters. XRD spectra confirm formation of β-Mo₂C with ion fluences equal to or larger than 1×10¹⁶ ions/cm², and formation of -Mo₂C with ion fluence of 1×10¹⁸ ions/cm². The maximum nanohardness and maximum modulus of the as-implanted samples increased gradually with increasing ion fluence, and reached the corresponding maximum values with ion fluence of 1×10¹⁸ ions/cm². The experimental results suggest that the structure and properties of the as-implanted Mo samples exhibited strong dependence on implantation parameters.     

The Relation Between K+/π+ Ratio and Secondary Collisions in Ultra-Relativistic Heavy Ion Collisions

Based on the concep, t of the formation time, the contribution of secondary collisions to the change of the K⁺/π⁺ ratio in ultra-relativistic heavy ion collisions is calculated. The result shows that the effect of secondary collisions in the target nucleus is not enough to explain the observed change of the K⁺/π⁺ ratio.     

The response of thermally and optically stimulated luminescence from Al2O3:C to high-energy heavy charged particles

The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al₂O₃ dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelarator at Chiba, Japan. The samples were Al₂O₃ single-crystal chips, of the type usually known as TLD-500, and Luxel^TM dosimeters (Al₂O₃:C powder in plastic) from Landauer Inc. The samples were exposed to ⁴He (150 MeV/u), ¹²C (400 MeV/u), ²⁸Si (490 MeV/u) and ⁵⁶Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/μm in water and doses from 1 to 100 mGy (to water). A ⁹⁰Sr/⁹⁰Y beta source, calibrated against a ⁶⁰Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (η_HCP,γ) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel^TM) and the luminescence method used to define the signal—i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al₂O₃ in the areas of space radiation dosimetry and radiation oncology.     

Reaction filters. Charged-particle multiplicity and linear momentum transfer

The relation between charged-particle multiplicity and linear momentum transfer to heavy reaction residues has been investigated with a 4π charged-particle detector for the reactions ³⁶Ar+²³⁸U at E/A=35 MeV and ¹⁴N+²³⁸U at E/A=50 MeV. The multiplicity of charged particles at backward angles (θ > 35°) incrreases linear momentum transfer while the multiplicity of charged particles in the forward direction is almost independent of the linear momentum transfer.     

Investigations of heavy ion tracks in polyethylene naphthalate films

The heavy ion beam (with fluence 3x10⁸ ion/cm²) from a cyclotron has been used for irradiation of thin polyethylene naphthalate (PEN) films. Latent tracks in these polymeric films have been sensitized by UV radiation and then chemically etched in NaOH solution. The etching process parameters have been controlled by the electroconductivity method. After etching, parameters of samples have been examined by SEM and bubble point methods (Coulter® Porometer II instrument). Results have shown good quality of PEN track membranes with pore sizes in the range: 0.1 – 0.5 μm. The described procedure is known for thin polythylene terephthalate (PET) films. Taking into consideration that PEN films have got better mechanical, thermal, gas barrier as well as better chemical resistance properties in comparison with PET films, the possibility of application of such membranes is much wider.     

Isothermal desorption of hydrogen from polycrystalline diamond films

The kinetics of isothermal H₂ desorption from polycrystalline diamond are studied in real time. The surface H coverage (θ_H) is measured by mass analyzing the recoiled H₊ ion signal during the desorption. We find that the H₂ desorption is 1st order in θ_H with an activation energy of 69 ± 6 kcal/mol and a prefactor of 10^{10.5 ± 0.9} s⁻¹. We suggest that formation of a C---C π-bond on the clean surface plays a key role in H₂ desorption from diamond, a view consistent with previous theoretical calculations of H₂ desorption from diamond.     

Degradation of β-Ga_2O_3 Schottky barrier diode under swift heavy ion irradiation

The electrical characteristics and microstructures of β-Ga_2 O_3 Schottky barrier diode(SBD) devices irradiated with swift heavy ions(2096 Me V Ta ions) have been studied. It was found that β-Ga_2 O_3 SBD devices showed the reliability degradation after irradiation, including turn-on voltage Von, on-resistance Ron, ideality factor n, and the reverse leakage current density Jr. In addition, the carrier concentration of the drift layer was decreased significantly and the calculated carrier removal rates were 5 × 10~6–1.3 × 10~7 cm~(-1). Latent tracks induced by swift heavy ions were observed visually in the whole β-Ga_2 O_3 matrix. Furthermore, crystal structure of tracks was amorphized completely. The latent tracks induced by Ta ions bombardments were found to be the reason for the decrease in carrier mobility and carrier concentration. Eventually,these defects caused the degradation of electrical characteristics of the devices. In terms of the carrier removal rates, theβ-Ga_2 O_3 SBD devices were more sensitive to swift heavy ions irradiation than Si C and Ga N devices.     

EPR and ENDOR study of an oxygen-vacancy-associated Ti center in RbTiOPO4 crystals

The dominant Ti³⁺ trapped electron center in flux-grown RbTiOPO₄ (RTP) crystals has been characterized using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR). This center is produced during an X-ray irradiation at room temperature when a Ti⁴⁺ ion traps an electron and becomes a Ti³⁺ ion, and is best studied in the 30–40 K range. The EPR spectrum contains a three-line hyperfine pattern from two nearly equivalent neighboring ³¹P nuclei, along with hyperfine lines from the ⁴⁷Ti and ⁴⁹Ti nuclei. The g matrix, determined from the angular dependence of the EPR spectrum, has principal values of 1.819, 1.889, and 1.947. Hyperfine matrices for four ³¹P nuclei are obtained from the angular dependence of the ENDOR spectrum. The proposed model for this defect is a Ti³⁺ ion adjacent to an oxygen vacancy at an OT position. Analogies are made to a similar Ti³⁺ center in KTiOPO₄ (KTP) crystals.     

SSNTD and radiochemical studies on the transmutation of nuclei using relativistic ions

Extended targets were irradiated for transmutation studies with relativistic heavy ions. For this, a metal core was surrounded by a paraffin moderator. The metal is either copper or lead and it was irradiated with deuterium, alpha, or carbon beams of 1.5 or 3.7 GeV/u at the SYNCHROPHASOTRON, LHE, JINR, Dubna, Russia. During this irradiation copious amounts of secondary neutrons are produced and studied with SSNTD detectors and radiochemical sensors, for example ¹³⁹La (n, γ) ¹⁴⁰La→β⁻. The yield of reaction products allows an estimation of secondary neutron fluxes. The yields of all kinds of reactions produced with deuterium and alpha beams obey to some extent the law of “limiting fragmentation”, i.e. they show little influence on the energy and the kind of incoming particles. However, one observes with 44 GeV ¹²C ions always enhanced nuclear cross-sections induced by secondary particles. This behavior could not be confirmed with theoretical estimations based on the Dubna Cascade Model in its Cascade Evaporation Model version (DCM-CEM). Finally, some results for transmutation studies on ¹²⁷I and Cu will be presented.