Calibration of different plastic track detectors using accelerated heavy ions

Measurements of the dependence of track etch rate on the energy-loss of different ions have been presented. In this method, ₁₈ ⁴⁰ Ar, ₁₀ ²² Ne, ₈ ¹⁶ O and ₆ ¹² C-ions of different energies are used as energetic heavy ions for track formation in the detectors. The bulk etch rate and track etch rate are measured for different temperatures and hence the activation energies are determined. The variation ofV =V _t /V _b along the trajectory of the track has been shown for different temperatures. The maximum etched track length is compared with the theoretical range as well as with the range reported earlier. The experimental results indicate the absence of a well-defined threshold in the plastics studied.     

Use of the temperature peak model for the description of track formation in semiconductor crystals irradiated by fast heavy ions

An attempt to apply the temperature peak model to describe the formation of defects and tracks in semiconductor crystals is made for the first time. The temperature dependences of model parameters, such as specific heat, thermal conductivity, and electron-phonon coupling coefficient are obtained. Agreement between the theoretical results and experimental data for InP and Ge crystals irradiated by ultrafast heavy ions indicates the adequacy of the model, with which one can evaluate the temperature of the local area near the ion trajectory, as well as the diameters of the molten region and experimentally observed track region. The diameter of the cylindrical molten region that forms along the path of 250-MeV Xe⁺ ions in InP is predicted to be 20 nm, and the measured cross-sectional diameters of the tracks fall into the range 7–15 nm.     

Nanoisland nucleation in thermal spike regions on the material surface irradiated by swift heavy ions

The energy that is lost by swift heavy ions (SHIs) in a material highly excites its electronic subsystem, while the ion subsystem initially remains almost unperturbed. Subsequent energy transfer from the excited electrons to target atoms may cause a short-term local temperature rise (thermal spike), which, in turn, may induce phase transitions in the nanodimensional region near the ion trajectory. The possibility of nanoisland nucleation within such spikes on the material surface exposed to SHIs is studied. Presumably, the nanoislands appear when the characteristic nucleation time is shorter than the time of spike region cooling. It is shown that the maximal nucleation rate may be observed at a distance of the center of the spike. This may result in the annular distribution of the islands around the SHI trajectory.     

Dielectric response of makrofol-KG polycarbonate irradiated with 145 MeV Ne6+ and 100 MeV Si8+ ions

The passage of heavy ions in a track detector polymeric material produces lattice deformations. These deformations may be in the form of latent tracks or may vanish by self annealing in time. Heavy ion irradiation produces modifications in polymers in their relevant electrical, chemical and optical properties in the form of rearrangement of bonding, cross-linking, chain scission, formation of carbon rich clusters and changes in dielectric properties etc. Modification depends on the ion, its energy and fluence and the polymeric material. In the present work, a study of the dielectric response of pristine and heavy ion irradiated Makrofol-KG polycarbonate is carried out. 40 μm thick Makrofol-KG polycarbonate films were irradiated to various fluences with Si⁸⁺ ions of 100 MeV energy from Pelletron at Inter University Accelerator Centre (IUAC), New Delhi and Ne⁶⁺ ions of 145 MeV from Variable Energy Cyclotron Centre, Kolkata. On irradiation with heavy ions dielectric constant (ɛ′) decreases with frequency where ɛ′ increases with fluence for both the ions. Variation of loss factor (tan δ) with frequency for pristine and irradiated with Si ions reveals that tan δ increases as the frequency increases. Tan δ also increases with fluence. While Ne irradiated samples tan δ shows slight variation with frequency as well as with fluence. Tan δ has positive values indicating the dominance of inductive behavior.      

快重离子辐照聚酰亚胺潜径迹的电子能损效应

快重离子辐照聚合物材料时，由于密集电离激发在其路径上产生几纳米直径的潜径迹，径迹形貌受离子种类、离子能量等多种因素的影响.为了研究电子能损对径迹形成所起的作用，利用1.158GeV 的Fe⁵⁶离子和 1.755GeV Xe¹³⁶离子在室温真空环境下辐照叠层聚酰亚胺(PI)薄膜，结合傅里叶转换红外光谱(FTIR)分析技术对辐照引起的化学变化进行了测量.聚酰亚胺官能团的降解及炔基的生成是离子辐照聚合物的主要特征，在注量1×10¹¹到6×10¹²/cm²范围及较宽的电子能损(dE/dX)_e范围 (Fe⁵⁶ 离子：2.2 到 5.2 keV/nm， Xe¹³⁶ 离子：8.6 到 11.3 keV/nm)对官能团的断键率及炔基生成率进行了研究. 红外结果显示在实验涉及的能损范围都有炔基生成，应用径迹饱和模型对实验结果进行拟合，不同能损下的平均损伤径迹半径及炔基生成径迹半径被得到，通过热峰模型对实验结果拟合，给出了离子在聚酰亚胺中产生潜径迹的能损阈值，实验给出的径迹形貌的电子能损效应曲线与热峰模型预言走势基本一致. 关键词： 离子辐照 潜径迹 红外光谱 热峰模型     

Thermal annealing of heavy ion tracks in muscovite mica

Abstract

Thermal annealing of latent tracks caused by the passage of heavy ions, viz. Pb²⁰⁸ (13.8 MeV/n) and Ni⁵⁸ (15.37 MeV/n), in muscovite mica is investigated. The activation energy for track annealing, determined using different annealing models, is compared. The effect of thermal annealing on size and energy resolution of heavy ions in mica, based on the track etch rate and track length reduction, is discussed.     

Single-sheet identification method of heavy charged particles using solid state nuclear track detectors

The theoretical and experimental investigations of the penetration of charged particles in matter played a very important role in the development of modern physics. Solid state nuclear track detectors have become one of the most important tools for many branches of science and technology. An attempt has been made to examine the suitability of the single-sheet particle identification technique in CR-39 and CN-85 polycarbonate by plotting track cone length vs. residual range for different heavy ions in these detectors. So, the maximum etchable ranges of heavy ions such as ⁹³Nb, ⁸⁶Kr and ⁴He in CR-39 and ⁴He and ¹³²Xe in CN-85 polycarbonate have been determined. The ranges of these ions in these detectors have also been computed theoretically using the Henke-Benton program. A reasonably good agreement has been observed between the experimentally and theoretically computed values.      

High Energy Charged Particle Registration in CR-39 Polycarbonated Detector

Track etch rate characteristics of CR-39 plastic detector exposed to ²⁸Si ions of 670 MeV energy have been investigated. Experimental results were obtained in terms of frequency distribution of the track diameter, track density and bulk etching rate. A dependence of the mean track diameter on energy was found. The application of the radiation effect of heavy ions on CR-39 in the field of radiation detection and dosimetry are discussed. Results indicated that it is possible to produce etchable tracks of ²⁸Si in this energy range in CR-39. We also report the etching characteristics of these tracks in the CR-39 detector.     

Different shapes of tracks in phlogopite, biotite and soda lime glass

Etched track opening geometries in Biotite, Phlogopite and soda-lime glass irradiated with swift heavy ions [¹⁹⁷Au(11.64 MeV/n), ¹³⁶Xe(11.56 MeV/n), ⁵⁸Ni(11.56 MeV/n)] at different angle of incidence have been studied using appropriate chemical etching technique. Different geometries (Hexagonal, irregular polygon, triangular in case of Biotite and Phlogopite, and circular & elliptical in case of soda lime glass detector) of heavy ion tracks are reported in the present investigations using optical microscope. The different shapes of these heavy ions track geometries are found to be related with various target-projectile parameters (viz: type of projectiles, energy, stopping power, angle of incidence of the projectile, density of defects and its reactivity with etchant, etching conditions and chemical structure of the detectors). The dependence of different shapes of heavy ion tracks in isotropic and anisotropic medium on the variation of radiation damage densities along the ion trajectories have also been discussed in the present paper.      

Dynamics of ionization mechanisms in relativistic collisions involving heavy and highly-charged ions

The dynamics of mechanisms associated with the ionization of inner-shell electrons in relativistic collisions involving heavy and highly-charged ions is investigated within a nonperturbative approach formulated explicitly in the time domain. The theoretical treatment is based on the exact numerical solution of the time dependent Dirac equation for two Coulomb centers on a lattice in momentum space. We present results for ionization in encounters between 100 MeV/u Au⁷⁹⁺ projectile ions impinging on a hydrogen-like uranium target. By directly visualizing the collision dynamics we identify a new ionization mechanism in which electrons are emitted from the internuclear region preferentially in the transverse direction with respect to the projectile trajectory. A striking characteristic of this ionization mechanism is that the velocity of the electron is higher than the projectile velocity. Received 26 June 2001 and Received in final form 27 November 2001     

The role of collective inertias in heavy ion fusion

The role of collective inertias in determining the fusion excitation function for heavy ions is investigated. We use a generalized trajectory calculation which allows for a fully dynamical treatment of collective deformations. It is shown that for high bombarding energies, the cross section is sensitive to the choice of collective inertias. For comparison with experiment we chose the symmetric system ⁴⁰Ca+⁴⁰Ca.     

Sputtering of solids by heavy ions and temperature effects in electronic and lattice subsystems

The results of sputtering coefficient measurements for pure metals, alloys, amorphous alloys, semiconductors, and highly oriented pyrolytic graphite under irradiation by high energy ions are considered. The possible mechanisms of strong sputtering of materials with high defect concentrations are discussed. The three-dimensional thermal spike model (“hot ion track”) with the temperature dependence of thermodynamic parameters (specific heat thermal conductivity) is formulated for single-layer mono-and polycrystals and multilayer systems (materials). The results of a numerical solution to the introduced system of partial differential equations are considered for the lattice and electronic subsystem temperatures around and along the fast heavy ion trajectory as a function of the time t, as well as radial r and longitudinal z coordinates, taking into account possible phase transitions such as melting and evaporation. The results obtained are discussed.     

Study of intermixing and Zr-silicide formation using swift heavy ion irradiation

Swift heavy ion (SHI) beam induced irradiation is an established technique for investigating structural modifications in thin films depending on the S _e sensitivity of material. Intermixing due to 120 MeV Au ion irradiation at different fluences from 10¹² to 10¹⁴ ions/cm² has been reported as a function of ion fluence in a-Si/Zr/a-Si thin films on Si substrate. The samples are characterized before (pristine) and after irradiation using Grazing Incident X-ray Diffraction (GIXRD) and Rutherford Backscattering Spectroscopy (RBS), which confirm the formation of ZrSi at thin film interface. It is suggested that mixing is mainly due to electronic energy loss since the energy transferred from high energy ions seems to create a transient molten zone along the ion track. It is found that the interface mixing increases linearly with the increase in ion fluence. The mixing effect explained in the framework of Thermal spike model. The irradiation effect on the surface roughness of the system is measured using Atomic Force Microscopy (AFM) technique. The current conduction mechanism and Schottky barrier height are also calculated by taking I–V curves across the Metal/Si junction.     

Identification of the Xe beam at the JINR NUCLOTRON-M by the track length measurement method

Xe ions accelerated for the first time at the Nuclotron-M were identified. The dependence of the track length of ions in a substance on their energy was used to solve this problem. The measurements were carried out at the Nuclotron-M upon the acceleration of ¹²⁴Xe⁴²⁺ ions. The detecting part was located on the beam ejection and consisted of ΔE and E detectors. The experimental and simulation data using the GEANT program are presented.     

A modified REL track formation model and its application to registration of 1 GeV/n Au and U ions in polycarbonate

Identification of heavy ions recorded in track detectors requires the knowledge of the physical processes which take place in each of the three steps involved in ion registration: (i) energy deposition by the incident particle in the detector; (ii) track formation; and (iii) the identification method itself. The amount of energy deposited by the incident particle per unit path length (dE/dx) is usually calculated by means of the Bethe–Bloch formula, which is described in terms of the so-called close and distant collisions. The REL track formation model excludes the contribution of close collisions when calculating the fraction of dE/dx leading to track formation. The identification method relates REL to a measurable signal S in the detector, so that S=g(REL)^h where g and h are parameters to be obtained from calibration. In this work, we present a modified REL model in which the energy deposited by close collisions may contribute partially to track formation. This contribution is accounted for by means of a new coefficient κ, introduced in the modified REL expression, which can take values between 0 and 1. We estimate the value of κ from measurements of tracks originated in polycarbonate detectors by incident Au and U ions of energy from accelerator. The results are consistent with a small contribution (κ0.3) of close collisions.     

Precision laser spectroscopy of highly charged ions

Recently, intense beams of highly charged ions have become available at heavy ion cooler rings. The obstacle for producing these highly interesting candidates is the large binding energy of K-shell electrons in heavy systems in excess of 100 keV. One way to remove these electrons is to strip them off by passing the ion through material. In the cooler ring, the ions are cooled to a well defined velocity. At the SIS/ESR complex it is possible to produce, store, and cool highly charged ions up to bare uranium with intensities exceeding 10⁸ atoms in the ring. This opens the door for precision laser spectroscopy of hydrogenlike-heavy ions, e.g.²⁰⁹Bi⁸²⁺, and allows to examine the interaction of the single electron with the large fields of the heavy nucleus, exceeding any artificially produced electric and magnetic fields by orders of magnitude. In the electron cooler the interaction of electrons and highly charged ions otherwise only present in the hottest plasmas can be studied.     

Mechanism of the direct three-body recombination of atomic ions in a central collision

The detailed dynamics of direct three-body recombination of the Cs⁺ and Br⁻ heavy ions in the presence of the Xe atom as a third body is studied by the quasiclassical trajectory method. A potential energy surface that quantitatively correctly describes the dynamics of the reverse process of ion formation induced by collisions of CsBr with Xe is used. Depending on the impact parameter of the third body, the stabilization of the product molecule proceeds by several different mechanisms. At impact parameters of b _R ≤ 7 au, the stabilization of the nascent molecule is largely controlled the repulsion potential between one of the ions or both the ions and the third body. The energy transferred to the third body does not depend directly on the repulsive potential energy between the ion and the third body. The phase of collision of the ions at the instant of closest approach plays a key role in the process of energy transfer. For collinear collision configurations of the three particles, the ion-Xe shallow potential wells are demonstrated to produce a noticeable effect.     

热峰模型在聚碳酸酯非晶化潜径迹中的应用

为了描述快重离子在聚合物中的潜径迹行为，用不同能量的快重离子 (1158GeVFe5656,1755GeVXe136¹³⁶及2636GeVU238²³⁸) 辐照 叠层半结晶聚碳酸酯膜 (Makrofol KG型)，结合x射线衍射测量技术，在较宽的电子能损 (1 9—171keV/nm)和离子注量（5×1010¹⁰—3×1012¹² cm-2^-2）范围研究了离子在半 关键词： 离子辐照 聚碳酸酯 非晶化 潜径迹     

Methylene blue as a DNA probe for a comparative study of Cd, Pb and Cr ions binding to calf thymus DNA

Methylene blue (MB) was developed as a sensitive DNA probe for a comparative study of Cd²⁺, Pb²⁺ and Cr³⁺ ions binding with calf thymus DNA (ctDNA). The fluorescence intensity of the MB-ctDNA system increased dramatically when heavy metal ions (Cd²⁺, Pb²⁺ and Cr³⁺ ions) were added, which indicated that some of the bound MB molecules were released from the ctDNA base pairs. To compare the binding affinity of these three different heavy metal ions with ctDNA, the relationships between the fluorescence intensity of the MB-ctDNA-M (Metal ions) system and the concentration ratio of [M]/[DNA(p)] were investigated. The results showed that the order of the binding affinity of heavy metal ions with ctDNA had the following sequence: Cr³⁺> Cd²⁺>Pb²⁺. This order was further proved by the effects of heavy metal ions on the number of MB bound to ctDNA, the measurements of binding constants of these heavy metal ions to ctDNA, and the effects of heavy metal ions on the absorption of the MB-ctDNA system. In addition, the interaction mechanisms of Cd²⁺, Pb²⁺ and Cr³⁺ ions with ctDNA were also discussed in detail. These results indicated that their interaction mechanisms are related to the concentration ratios of heavy metal ions to DNA.     

A search for superheavy nuclei tracks in extraterrestrial olivine crystals

A study is made for the search of superheavy nuclei in Marjalahti, Eagle Station and in other pallasite olivines. The olivine crystals are calibrated for heavy ion track lengths by using heavy ion beams from cyclotrons. The calibration for ultra heavy ions which are presently not available with sufficient energy to produce volume tracks in olivine crystals, is based on Katz and Kobetich model of track formation. The length spectrum of volume tracks, revealed by puncturing them with focussed Nd-glass laser beam, is measured and the abundances of different nuclei groups are calculated. Partial annealing has been used at 430°C for 32 hr which eliminates the interfering tracks due to nuclei of atomic numberS ≤ 50. During the scanning 4 cm³ olivine crystals, about 360 long tracks of uranium group as well as two very long tracks have been found. If these tracks belong to superheavy nuclei, the relative abundance of super heavies is found to be 6 × 10⁻¹¹ in galactic cosmic rays.