The gamma-ray burst monitor on board the SAX satellite

Summary The anticoincidence lateral shields of the high-energy ((15÷200) keV) detector PDS aboard the SAX satellite will be used to detect celestial gamma-ray bursts. As a gamma-ray burst monitor (GRBM), the shields have a 5σ sensitivity in the (60÷600) keV nominal energy band about 10⁻⁶ erg/cm², and a capability of determining the burst location to an accuracy of a few tenths of degree to several degrees, depending on burst direction and strength. The GRBM will be mainly devoted to study the burst time profile with a time resolution down to 0.5 ms. Its expected performances are evaluated by means of Monte Carlo simulations. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

The LAPEX experiment for observation of the supernova SN 1987A in hard X-rays

Summary The LAPEX payload is described in the configuration that will be launched to observe the supernova SN 1987A. The balloon flight will be performed from Alice Springs (Australia) in April 1989 as a part of a NASA balloon campaign. The experiment will allow simultaneous observations of source and background in order to minimize systematic errors due to background variations. The limiting flux sensitivity of the instrument in the (20÷200) keV energy band is 4·10⁻⁶ ph/(cm²s keV) or ∼2.5 mCrab for a 10⁴ s observation of SN 1987A. The presence of a⁵⁷Co emission line in the SN 1987A photon spectrum could be detected down to an intensity level of ∼8·10⁻⁵ photons/cm²s as at 99.7% confidence level. The high resolution of the event timing (<0.1 ms) will make it possible to detect millisecond pulsations with amplitudes down to ∼4% of the expected average flux from SN 1987A in the (20÷60) keV band. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Corrosion behavior of low energy,high temperature nitrogen ion-implanted AISI 304 stainless steel

This work presents the results of a low-energy nitrogen ion implantation of AISI 304 type stainless steel (SS) at a moderate temperature of about 500°C. The nitrogen ions are extracted from a Kauffman-type ion source at an energy of 30 keV, and ion current density of 100 μA cm⁻². Nitrogen ion concentration of 6 × 10¹⁷, 8 × 10¹⁷ and 10¹⁸ ions cm⁻², were selected for our study. The X-ray diffraction results show the formation of CrN polycrystalline phase after nitrogen bombardment and a change of crystallinity due to the change in nitrogen ion concentration. The secondary ion mass spectrometry (SIMS) results show the formation of CrN phases too. Corrosion test has shown that corrosion resistance is enhanced by increasing nitrogen ion concentration.      

Measuring of spatio-temporal characteristics Z-pinch from deuterated polyethylene

On the S-300 installation at currents up to 2 MA with rise time 100 ns, the investigation of the formation process of high-temperature plasma in fast Z-pinch was carried out. The central part of the loads was made from agar-agar and represented a deuterated polyethylene cylinder with small density 50 and 75 mg/sm³ and 1–2 mm diameter. On the ICT images, obtained in optical and soft X-ray range of a spectrum with 3–5 ns exposition, it is visible that on the axis of the polyethylene cylinder at the current`s rise time a cord is formed and it is separated into bright formations. They were observed on a background of a luminous area which occupied the initial neck volume. On time-integrated pinhole pictures obtained in SXR range (E > 1–4 keV), hot points with minimal size of 50 microns were registered. From the chronograms results, obtained by means of the optical high-speed-streak camera mount along the neck axis with time resolution < 1 ns, it follows that luminous formations arise sequentially during the different time moments (in 10–30 ns). Occurrence of luminous formations was accompanied by X-ray radiation occurrence with energy E > 1 keV with short duration of 2–4 ns. Simultaneously with X-ray radiation neutrons with the maximal yield of 4.5×10⁹ were registered. The average energy measured in 4 directions under angles with an axis of: 0^○ (above the anode), 90^○, 180^○ (under the cathode) and 270^○, were accordingly: 2.4±0.2, 2.5±0.1, 2.5±0.1, 2.5±0.1 MeV.     

Multi-kilohertz,ultrafast hard X-ray <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="BoldItalic">α</Emphasis></Subscript> source

We report on the performance of a femtosecond laser-based hard X-ray K_α source operating up to 10 kHz repetition rate. Using chromium- or iron-containing tapes, spectrally narrow band K_α1 and K_α2 radiation at about 5.4 and 6.4 keV is generated. Employing up to 1 mJ pulse energy in the fundamental more than 10⁹ K_α photons s^-1 are generated in 4π steradian. PACS 07.58.Fv; 52.38.Ph; 52.50.Jm     

Pac studies of neutron irradiated Li2HfO3

The influence of defects, created in the reaction⁶Li (n,α)³H on the perturbed angular correlation (PAC) of 133–482 keV cascade of¹⁸¹Ta in Li HfO₃ has been studied. Two different types of defects were identified. Its concentration remains constant during the isochronal annealing up to 300°C. 10 min annealing at 350°C leads to its disappearing.     

Femtosecond hard X-ray plasma sources with a kilohertz repetition rate

Laser-driven plasma sources of femtosecond hard X-ray pulses have found widespread application in ultrafast X-ray diffraction. The recent development of plasma sources working at kilohertz repetition rates has allowed for diffraction experiments with strongly improved sensitivity, now revealing subtle fully reversible changes of the geometry of crystal lattices. We provide a brief review of this development and present a novel plasma source with an optimized mechanical and optical design, providing a high flux of several 10¹⁰ photons/s at the Cu-Kα energy of 8.04 keV and a pulse duration of ≤300 fs. First experiments, including the generation of Debye–Scherrer diffraction patterns from Si powder, demonstrate the high performance of this source.     

Balloon program for hard-X-ray astronomy

Summary An observation program of X-ray sources in the (20÷200) keV energy band by means of a balloon-borne NaI(Tl) seintillator array was undertaken in 1980. Three balloon flights have been performed and 10 X-ray rources observed, some more than once. We present details of this balloon program and results obtained from the analysis of the Crab observation performed in October 1980. Paper presented at the 2° Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–June 1984.     

Table-top kHz hard X-ray source with ultrashort pulse duration for time-resolved X-ray diffraction

The interaction of ultrashort laser pulses with solid state targets is studied concerning the production of short X-ray pulses with photon energies up to about 10 keV. The influence of various parameters such as pulse energy, repetition rate of the laser system, focusing conditions, the application of prepulses, and the chirp of the laser pulses on the efficiency of this highly nonlinear process is examined. In order to increase the X-ray flux, the laser pulse energy is increased by a 2nd multipass amplifier from 750 μJ to 5 mJ. By applying up to 4 mJ of the pulse energy a X-ray flux of 4×10¹⁰ Fe K _α photons/s or 2.75×10¹⁰ Cu K _α photons/s are generated. The energy conversion efficiency is therefore calculated to η _Fe≈1.4×10⁻⁵ and η _Cu≈1.0×10⁻⁵. The X-ray source size is determined to 15×25 μm². By focusing the produced X-rays using a toroidally bent crystal a quasi-monochromatic X-ray point source with a diameter of 56 μm×70μm is produced containing ≈10⁴ Fe K _α1 photons/s which permits the investigation of lattice dynamics on a picosecond or even sub-picosecond time scale. The lattice movement of a GaAs(111) crystal is shown as a typical application.     

Fluence dependant formation of <Emphasis Type="Italic">β</Emphasis>-SiC by ion implantation and thermal annealing

The β-SiC nanocrystals were synthesized by the implantation of carbon ions (C⁻) into silicon followed by high-temperature annealing. The carbon fluences of 1×10¹⁷, 2×10¹⁷, 5×10¹⁷, and 8×10¹⁷ atoms/cm² were implanted at an ion energy of 65 keV. It was observed that the average size of β-SiC crystals decreased and the amount of β-SiC crystals increased with the increase in the implanted fluences when the samples were annealed at 1100 °C for 1 h. However, it was observed that the amount of β-SiC linearly increased with the implanted fluences up to 5×10¹⁷ atoms/cm². Above this fluence the amount of β-SiC appears to saturate. The Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, and X-ray diffraction (XRD) techniques were used to characterize the samples.     

X射线探测器的脉冲标定技术

利用强流电子束技术产生通量密度为10¹⁸—10¹⁹X-ray photon/sr·s的脉冲CuKX射线源,标定PIN型硅二极管半导体探测器对X光子的脉冲灵敏度。用绝对X射线监测器——P10气体脉冲电离室作为脉冲X射线通量密度的标准。脉冲电荷自动测量仪由微处理机进行程序控制,并予以实时校准。该电离室测量通量密度的精度为±5％,适用的能通量率范围可达4×10^-9—2×10²W/cm²,适用的光子能量范围为1.5—10keV,标定探测器的精度为±7.0％,并发现PIN型硅二极管的脉冲灵敏度比稳态X射线束标定的灵敏度高30％左右。 关键词：     

Hard X-ray photoelectron spectroscopy from 5-14.5 keV

Photoemission spectroscopy at high energies can be used to probe bulk electronic states. We used a specially designed high-voltage retarding lens and a commercial Perkin-Elmer PHI 10-360 hemispherical electron analyzer to investigate the core and valence band region of Au, YBa₂Cu₃O_7−δ and highly oriented pyrolytic graphite samples with hard X-rays in the energy range 5-14.5 keV. The overall instrumental resolution obtained at 8 keV was 218 meV. The photo ionization cross-sections for Au 5d and 6s excitations were determined experimentally. In comparison with published calculations for atomic cross-sections neglecting corrections for angular anisotropy, the values we find are twice as large for the 5d and an order of magnitude larger for the 6s (conduction band) level. Our results demonstrate the feasibility of bulk sensitive valence band spectroscopy with high resolution at high brilliance X-ray sources such as the ESRF. The measured cross-sections provide important input for improving current theoretical models.     

Fast electron energy deposition in aluminium foils: Resistive vs. drag heating

The high current electron beam losses have been studied experimentally with 0.7 J, 40 fs, 6 10¹⁹ Wcm^-2 laser pulses interacting with Al foils of thicknesses 10-200 μm. The fast electron beam characteristics and the foil temperature were measured by recording the intensity of the electromagnetic emission from the foils rear side at two different wavelengths in the optical domain, ≈407 nm (the second harmonic of the laser light) and ≈500 nm. The experimentally observed fast electron distribution contains two components: one relativistic tail made of very energetic (T _h ^tail ≈ 10 MeV) and highly collimated (7° ± 3°) electrons, carrying a small amount of energy (less than 1% of the laser energy), and another, the bulk of the accelerated electrons, containing lower-energy (T _h ^bulk=500 ± 100 keV) more divergent electrons (35 ± 5°), which transports about 35% of the laser energy. The relativistic component manifests itself by the coherent 2ω₀ emission due to the modulation of the electron density in the interaction zone. The bulk component induces a strong target heating producing measurable yields of thermal emission from the foils rear side. Our data and modeling demonstrate two mechanisms of fast electron energy deposition: resistive heating due to the neutralizing return current and collisions of fast electrons with plasma electrons. The resistive mechanism is more important at shallow target depths, representing an heating rate of 100 eV per Joule of laser energy at 15 μm. Beyond that depth, because of the beam divergence, the incident current goes under 10¹² Acm^-2 and the collisional heating becomes more important than the resistive heating. The heating rate is of only 1.5 eV per Joule at 50 μm depth.     

Electron microscopy studies of void swelling and annealing of voids in aluminium irradiated with aluminium ions

Abstract

MgO single crystals implanted with Au⁺ ions (180 keV, 6 10¹⁶-10¹⁷ ions cm^?2) and annealed at temperatures between 25°C and 1100°C, have been analysed—by optical spectrophotometry—by Rutherford back-scattering (to confirm the effective presence and to study the distribution profile of Au atoms), and by TEM and X-ray diffraction (to identify the phases precipitated by thermal treatment).

Thermal annealing between 550°C and 1100°C produced an optical absorption band located between 565 nm and 600 nm. This band can be attributed to a fee Au precipitate with diameter varying from 50 to 200 Å. Larger metallic colloids 1000 Å are in simple orientation with the matrix.

Annealing at temperatures higher than 500°C produces a supplementary optical absorption located at 425 nm. This band can be attributed to Au plasma resonance.

After annealing for 15 min at 1100°C, a new phase is detected by X-ray diffraction and TEM and identified as Au₃Mg alloy with hexagonal structure.     

Effect of electron energy on the accumulation of color centers in reflective coatings based on ZnO

We have made the first studies of the effect of electron energy in the range of tens of keV on the intensity changes of the intrinsic absorption bands of color center point defects (F⁺ and F centers, V _Zn ⁻ , V _Zn ²⁻ , (V _Zn ⁻ — Zn _i ⁰ )-, etc.) and temperature-control coatings (TCC) for space equipment based on it, obtaining an expansion of the integral induced absorption band into components. It was established that the intensity grows in the region 10–100 keV up to an energy of about 15 keV and then it decreases. An explanation is proposed for the behavior seen. It has been established that the free electron concentration increases by a power law with increasing electron acceleration energy. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 85–90, April, 1998.     

A high-pressure parallel-grid gas scintillation proportional counter for high-energy X-ray astronomy

Summary We present preliminary results on a new detector for X-ray astronomy sensitive in the energy range from 3 to 120 keV. The detector can be implemented either as a narrow-field instrument (∼1 degree field of view) or as wide field camera (30×30 degree field of view). This detector with its large area, good energy resolution and background rejection represents a valid option to the present generation of instruments for high-energy X-ray astronomy. Paper presented at the 2° Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.     

Electronic structure at rubrene metal interfaces

Many studies have been done on low energy (1–200 keV) and high dose (10¹⁶–10¹⁷) implantation of Mn in GaAs. This study is an attempt to incorporate Mn ions in GaAs through implantation of 1 MeV Mn⁺¹ ions in semi-insulating GaAs substrates at doses of 3×10¹⁵/cm² and subsequent annealing. This was done to find out if any alloy of Mn–Ga–As, or binary compounds of Mn–Ga or Mn–As form due to annealing of Mn⁺¹ ions implanted in GaAs substrates. High Resolution XRD (HRXRD) performed before annealing shows a possibility of Ga–Mn–As alloy formation, and after annealing at 800°C, except for GaAs main peaks no other phase peaks were detected. Scanning electron microscopy (SEM) shows nanostructures of various dimensions which are thought to be formed due to the defects generated due to implantation. Fourier Transform Infrared (FTIR) study shows the shift in bandgap due to Mn doping. Raman spectroscopy shows the red shift in LO and TO peak positions of GaAs after annealing, which indicates the presence of disorder and damage due to implantation. Resistivity measurement shows a thermally activated semiconductor character of charge conduction with an activation energy of 51 meV and this activation may have occurred through the transitions from impurity band to valence band. Large positive (∼25%) magnetoresistance and a mixture of ferromagnetic and paramagnetic behavior obtained in the magnetization measurement indicate the presence of ferromagnetic MnAs nanoclusters embedded in paramagnetic GaAs:Mn matrix.     

Energy and charge distributions of fast hydrogen ions and atoms reflected from Cu in the case of grazing incidence

The energy and charge distributions of protons and hydrogen atoms reflected from the Cu surface in the case of grazing incidence angles are measured at energies of incident particles (H⁺ and H⁰) of 200 and 250 keV. The charged fractions of reflected particles are analyzed. A weak dependence of the neutral fraction of reflected particles on the scattering angle is discovered for incidence angles of 1°–2° and an energy of scattered particles of 60 keV or less. It is shown that the neutral fraction of reflected particles with an energy of 60–80 keV or more is independent of the scattering angle and is determined by the ratio of the cross sections for the electron capture and loss by ions in the material.     

钴离子注入对二氧化钛晶体的结构和光学性能的影响

采用离子注入法制备了钴离子掺杂的金红石相TiO₂样品;离子注入能量、注量分别为40 keV(1×10¹⁶cm^-2),80 keV(5×10¹⁵,1×10¹⁶,5×10¹⁶,1×10¹⁷cm^-2),120 keV(1×10¹⁶cm^-2). 通过XRD,XPS和UV-Vis等手段对掺杂前后样品的结构和光学性能进行了表征,分析了掺杂元素在金红石TiO₂中的存在形式. XRD测试表明随着注入能量的增加晶体的损伤程度增加. UV-Vis测试表明掺杂后所有样品在可见光区的吸收增强; 并且随着注量的增加,注量为5×10¹⁵cm^-2到5×10¹⁶cm^-2范围内注入样品的光学带隙逐渐变小. 关键词： 钴 二氧化钛 离子注入 掺杂