Selective X-ray generation by heavy ions (Part 2) measurement of the concentration distribution of ion-implanted antimony in silicon by the use of selective heavy ion X-ray excitation

This investigation demonstrates how the total, concentration distribution of antimony, previously implanted into silicon at 100 keV, may be elucidated without recourse to the usual radioactive isotope techniques. It uses the fact that 100 keV Kr⁺ ions can preferentially excite characteristic X-rays from antimony, even in the presence of a huge excess of silicon. The resultant high sensitivity for the detection of antimony in silicon is accompanied by the fact that the X-rays arise predominantly from less than one hundred Angstroms below the surface of the specimen. Thus bombardment by 100 keV Kr⁺ íons is used ín conjunction with an anodic stripping technique (which removes 169±20 Å at a time) to obtain the antimony distribution profile in silicon. Consideration is also given to the possibility of obtaining the implanted antimony range distribution by using 100 keV Kr⁺ ions to detect the antimony and simultaneously remove silicon by sputtering.     

X-ray emission spectroscopy—part I

Summary of Part I: The detection of X-rays by photographic recording, ionization chambers, proportional counters, scintillation counters, and semiconductor detectors is discussed. The extraordinary improvement in resolution achieved by semiconductor detectors resulted in a new powerful analytical method: detection of characteristic X-rays. Sample excitation, by X-rays, by charged particles produced by accelerators and by radioactive sources, is discussed. Charged particle induced X-ray emission is described within B framework of simple theoretical models. Experimental data on yields of X-rays produced by proton and heavy ion bombardment of different targets are summarized. The cross sections for the production of X-rays in ion-atom collisions are large. This allows the detection of elements present in very small amounts within the target, as well as the measurement of the charge of particles using beam foil spectroscopy.

Part II of this article will describe some applications of X-ray emission spectroscopy in industry, water and air pollution, and in the study of the importance of trace elements in biology and medicine. Sensitivity, background problems, target preparation and data reduction for X-ray emission spectroscopy will be discussed.     

Characteristic X-ray production by heavy ion bombardment as a technique for the examination of solid surfaces

Over the past few years, intense effort has been expended on studying the physical processes responsible for the production of characteristic X-rays during heavy ion/atom collisions. It is considered timely at this stage to assess one of the applications of this work, viz., the use of heavy ions to detect elements at or near to surfaces. It emerges that one of the advantages of the technique is its ability to detect light elements with high sensitivity and to examine the depth distribution of implanted elements. As an example of its application, evidence is presented for the detection of sulphur on the surfaces of copper, nickel and stainless steel.     

On the formation of heavy ion latent tracks in polymeric detectors

Three kinds of polymeric track detectors have been examined by ESR spectroscopy following heavy ion or energetic electron bombardment: (1) Typical nuclear track detectors: makrofol, kapton, terphane; (2) Polymers whose radiolysis under γ-rays or electron beams is well established: PMMA, PE, PP; (3) Polymers in which etchable tracks have not so far been observed e.g. teflon. The influence on the various ESR spectra of the radiation dose, of annealing or chemical etching treatments leads us to suggest that existence of heavy ion latent tracks might be correlated with the formation of “carbon-like” radicals such as produced in polymer pyrolysis.     

Effective stopping of relativistic composite heavy ions colliding with atoms

A nonperturbative theory of energy loss by relativistic composite heavy highly charged ions colliding with atoms is developed. A simple formula for effective stopping is derived. By composite ions, we mean partially ionized atoms of heavy elements consisting of the ion core and several bound electrons that incompletely neutralize the ion core charge. Such ions, which have, as a rule, a high charge (for example, partly stripped uranium atoms), are used in many experiments performed with modern heavy ion accelerators.     

Multiple electromagnetic excitation with relativistic heavy ions

The multiple electromagnetic excitation with fast projectiles (heavy ions) is studied theoretically in the sudden approximation. Of special interest is the excitation of rotational states coupled to giant (dipole) vibrations. Closed form expressions are obtained for the excitation of a rigid rotor. The strong pulse of high energy equivalent photons in relativistic heavy ion collisions opens up new possibilities for nuclear structure studies, not possible e.g. with electron scattering or nuclear Raman scattering. It is also pointed out that the “Brink-hypothesis” can be investigated in a new way by means of multiple electromagnetic excitation with relativistic heavy ions of low lying states coupled to the giant dipole mode.     

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.     

Cross sections of inelastic processes in collisions between relativistic structured heavy ions and atoms

A nonperturbative method is developed for the calculation of cross sections of inelastic processes in collisions between structured high-charge heavy ions moving at relativistic velocities and atoms. By structure ions are meant partly stripped ions consisting of an ion nucleus and a number of bound electrons which partly compensate the core charge and form the electron “coat” of the ion. The single ionization cross section of hydrogen atom and single and double ionization cross sections of helium atom are calculated. It is demonstrated that the inclusion of the extent of ion charge may bring about a marked variation of the respective cross sections compared to ionization by point ions of the same charge and energy.     

Quasimolecular K X-ray excitation by bombardment of Ge atoms with Ge ions

By bombardment of Ge targets with ⁷⁴₃₂Ge⁵⁺ of 81 MeV, a continuous X-ray intensity distribution has been obtained, which ranges up to the K X-ray energies of ₆₄Gd. The shape of the spectra, corrected for the detector efficiency, confirms the assumption that this continuum is caused by K X-rays of Z = 64 quasimolecules, which are transiently formed during the adiabatic heavy-ion collision. The yield of quasimolecular radiation was determined to be about 4 x 10⁻⁵ X-rays per beam K-vacancy.     

Interferences of molecular X-rays in heavy ion collisions

The possibility of coherence effects in molecular orbital X-rays emitted during multiple heavy ion collisions in a crystal target is investigated. That X-ray energy region is found, where in spite of the thermal vibrations of the target atoms interferences have to be expected. The dynamical theory for the molecular orbital evolution is used. The 70 MeV Ni — Ni collisions are treated as an example. An experiment for checking the coherent photon emission in multiple molecular scattering processes is suggested, which in turn can eventually be used to measure the ratio of e.g. triple to binary collision.     

不同离子激发Au靶的多电离效应

重离子与固体表面相互作用时,会引起靶原子内壳层的电离,相应空穴退激过程中发射的X射线对研究重离子与固体表面的相互作用有着重要意义,可为相关研究提供基础数据.目前,在K和L壳层电离方面做了一些工作,而M壳层的研究较少,本文依托兰州重离子加速器国家实验室320 kV高电荷态离子综合研究平台,测量了不同能量的H~+, Ar~(8+), Ar~(12+), Kr~(13+)和Eu~(20+)离子与Au表面作用产生的特征X射线谱及其能移,计算了X射线的产额比值.结果表明:重离子引起了靶原子内壳层的多电离,多电离效应使Au的MX射线有不同程度的能移;多电离程度取决于入射离子能量、离子的原子序数和其外壳层的空穴数量.     

Nanoprecipitation resulting from the decomposition of supersaturated solid solutions in the tracks of swift heavy ions

The electron subsystem of a material is strongly excited when swift heavy ions pass through the material. The subsequent relaxation of this excitation results in considerable short-term (<10⁻⁹ s) heating of the material in the nanometer vicinity of the projectile trajectory. Nanoprecipitation stimulated by such thermal spikes in supersaturated solid solutions is studied. Nanoprecipitates are shown to form when the temperature in the track reaches a point where the characteristic time of precipitation becomes shorter than the time of cooling of the track. The region of most efficient precipitation may be offset from the track axis. The initial cylindrical nonuniformity of the spatial density of nucleating clusters may cause the formation of nanodimensional tubular heterostructures extended along the trajectory of the heavy ions. The parameters of the system that are the most favorable to the tubular mode of precipitation are found.     

Transfer reactions with heavy ions

A simple model is derived for angular distributions in heavy ion transfer reactions which takes into account the dynamic as well as the quantal dispersion of the wave packet.     

The Kα and Kβ X-ray spectra of Al,Ti, Cr,Fe and Ni induced by 84 MeV nitrogen ions

The K X-rays from the target elements due to N-ion bombardment are measured with a crystal spectrometer. Some aspects owing to high incident energy are discussed. The Kα satellite, Kα hypersatellite and Kβ satellite peak spacings are obtained.     

Energy spectra of light ions backscattered from random solids

A scheme for the calculation of energy spectra of ions backscatterred from random solids is proposed for the energy region where multiple collisions dominate. Calculations are performed for light ion bombardment of heavy targets, which is a case of special interest for the plasma-well interaction in fusion reactors. Examples of spectra obtained for protons incident on a Cu target are presented. A maximum in the spectra is found in accordance with measurements. The position of the maximum seems to vary slowly with the initial ion energy.     

Absolute photon yield from silicon surface under electron and ion irradiation

The characteristics of the optical radiation accompanying the bombardment of silicon surface by electrons and medium-energy ions have been studied. The continuous radiation observed in this case is related to interband electronic transitions. The characteristic radiation (which is present in both cases), in the case of ion bombardment, is emitted by silicon atoms sputtered in the excited state and scattered helium ions; in the case of electron bombardment, this radiation is emitted by desorbed excited atoms and residual atmosphere molecules, which cover the silicon surface under study.     

Status of bubble detectors for high-energy heavy ions

Five types of bubble detectors (T-15, T-34, T-12, T-24 and T-14) of large volume and different sensitivities were developed in the China Institute of Atomic Energy for the purpose of heavy ion research. Calibrations were carried out with beams of high-energy protons, He, C, Si, Ar, Fe, Kr and Xe, at accelerators in the energy region 150–650 MeV/u. The bubble detectors were demonstrated to be a family of detectors for recording tracks of high-energy heavy ions with atomic numbers from Z=1 (proton) to all the numbers in the whole periodic table of elements. The threshold levels of the detectors differ from each other with values 0.05±0.01 (T-15), 1.62±0.05 (T-34), 1.68±0.03 (T-12), 2.24±0.06 (T-24) and 6.04±0.80 (T-14) MeVmg⁻¹ cm², respectively, which are about the same or even lower than the levels of plastic track detectors for recording heavy ions. The distinguishing features of bubble detectors are high sensitivity, active recording, real-time display, volume registration and background discriminating capacities. Bubble detectors are a new type of high sensitivity detectors and are very promising for detection of heavy ions, neutrons and exotic particles.     

Combined field ion microscopy and transmission electron microscopy of heavy ion damage in tungsten

Abstract

A field ion microscopy (FIM) and transmission electron microscopy (TEM) investigation of radiation damage in tungsten after heavy ion bombardment has been carried out. Field ion specimens of tungsten were irradiated with 180–230 keV Xe⁺ ions. The irradiation doses were varied between 4 × 10¹¹ and 4 × 10¹² ions/cm². The irradiated specimens were examined in FIM. Experiments combining both TEM and FIM were performed in order to compare the results obtainable by these two methods. The distribution of defects visible by TEM was inhomogeneous. The influence of the imaging field in FIM on the defects visible in TEM is discussed.     

Process in high energy heavy ion acceleration

A review of processes that occur in high energy heavy ion acceleration by synchrotrons and colliders and that are essential for the accelerator performance is presented. Interactions of ions with the residual gas molecules/atoms and with stripping foils that deliberately intercept the ion trajectories are described in details. These interactions limit both the beam intensity and the beam quality. The processes of electron loss and capture lie at the root of heavy ion charge exchange injection. The review pays special attention to the ion induced vacuum pressure instability which is one of the main factors limiting the beam intensity. The intrabeam scattering phenomena which restricts the average luminosity of ion colliders is discussed. Some processes in nuclear interactions of ultra-relativistic heavy ions that could be dangerous for the performance of ion colliders are represented in the last chapter. The text was submitted by the author in English.