Short-pulse, high-brightness X-ray production with the PLEIADES Thomson-scattering source

PLEIADES is a compact, tunable, high-brightness, ultra-short-pulse, Thomson-scattering X-ray source. Picosecond pulses of hard X-rays (10–200 keV) are created by colliding an ultra-relativistic (20–100 MeV), picosecond-duration electron beam with a high-intensity, sub-picosecond, 800-nm laser pulse. Initial operation of this source has produced 78-keV X-rays with 10⁶ photons per pulse using a 57-MeV, 0.3-nC, 50-m rms width electron beam and a 180-mJ, 15-m rms width laser pulse. The angular distribution, energy, and energy spectrum of the source are found to agree well with theory and simulations. Source optimization is expected to increase X-ray output to between 10⁷ and 10⁸ photons per pulse with a peak brightness approaching 10²⁰ photons/s/0.1% bandwidth/mm²/mrad². PACS 41.50.+h; 07.85.Fv; 41.75.Ht; 42.62.-b     

Plasma in open magnetic trap injected from independent UHF source

The properties of plasma injected into the open magnetic trap of uniform field from an independent UHF source have been investigated. It is established that a rather quiescent plasma with control density within the range of 2×10⁸–2×10¹² cm^–3 and temperature 2–3 eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it is not practically changed with the variation of neutral gas pressure and reaches the maximum value 4×10^–3 s at magnetic field strength in the trap equal 1600 Oe. Besides, the experimental data are analyzed on the basis of balance equations.     

Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.     

Polarization measurements in high energy elastic scattering of pions,kaons, protons and antiprotons on protons and comparison with regge phenomenology

The polarization parameterP has been measured for elastic scattering on polarized protons, of ^–, K^– and ¯p at 40 GeV/c and of ⁺, K⁺ and p at 45 GeV/c. Four-momentum transfer ranges from –0·08 to –1·8 (GeV/c)² for ^–p, and from –0·08 to about –1sd0(GeV/c)² for p, ⁺, K^± and ¯p.The angular distribution of the polarization in ^–p exhibits the well known non sense double zero att=–0·6 (GeV/c)². The K^–p and ¯pp results are compatible with exchange degeneracy for ¦t¦_r <0·5 (GeV/c)². The energy dependence of the polarizationP(t) in ^–p and in K⁺p above 10 GeV/c incident momentum is compatible with interference between Pomeron and Regge poles. On the contrary, the polarization in pp elastic scattering decreases faster than ordinary Regge model predictions. This result can be explained by interference between non flip and flip amplitudes of the Pomeron, leading to negative values for the polarization.Presented by A.de Lesquen at the Symposium on Hadron-Hadron Scattering at High Energies, Liblice, Czechoslovakia, June 16–21, 1975.     

Light Source with a Thermoionic Cathode

A light source with a thermoionic cathode has been investigated in helium at atmospheric pressure; the spectral radiance of the light source in the range 200–800 nm and the cathode temperature (3510 K) have been determined. Its employment as a light source in absorption spectroscopy for determination of the concentration of triplet and singlet metastable helium atoms in an atmospheric-pressure glow discharge has been demonstrated. The total concentration of metastable atoms was 3.5·10¹³ cm^–3.     

Microplasticity of silicon crystals

The low-frequency (1 Hz) internal friction (Q^–1) method was used to study the microplasticity of silicon whisker crystals grown by the method of chemical gas-transport reactions in a closed ampoule. A study was made of p-type crystals with the growth axis 111, 1–60 in diameter, working length 1–3 mm, both in the original state and after plastic ( 1%) deformtion by torsion. The temperature and amplitude dependences of Q^–1 were studied in 5·10^–5 torr vacuum. The amplitude of alternating vibrations was within the range 10^–5–10^–3 and the axial stresses were 10⁶–10⁷ N/m². The experimental results led to the conclusion that the microplasticity of undeformed silicon whiskers was due to heterogeneous nucleation of dislocations in stress concentration regions near surface defects, assisted by thermal fluctuations. In deformed whiskers the microplasticity was attributed to the nucleation and motion along dislocations of single and double thermal kinks in accordance with the Seeger model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 88–93, May, 1980.     

A laser infrared source of nanosecond pulses tunable from 1.4 to 22 μm

A reliable source of coherent ns pulses of infrared radiation continuously tunable between 1.4 and 22 m has been designed and built with the aim of developing a time-resolved infrared vibrational spectroscopy for species adsorbed on surfaces. The system is based on a Nd: YAG-laser and dye-laser combination which drive difference mixing processes in a sequence of nonlinear optical crystals (two LiNbO₃, and a CdSe or AgGaS₂). The system operates at MW peak power levels above 2500 cm^–1, at kW power levels from 1000–2500 cm^–1 and at 10–100 W levels down to 450 cm^–1. These power levels are certainly sufficient for spectroscopic purposes, and at shorter wavelengths molecular pumping and applications requiring high-power should be possible. Vibrational spectra of a monolayer of CO adsorbed on Pt in an electrochemical cell have been obtained in an initial application of this source.     

Infrared absorption of silane,ammonia, acetylene and diborane in the range of the CO2 laser emission lines: Measurements and modelling

Absorption spectra of the gases SiH₄, NH₃, C₂H₂ and of SiH₄/Ar and SiH₄/B₂H₆ mixtures have been measured in the spectral range of the CO₂ laser from 9.2 to 10.8 µm. In agreement with literature, silane shows the highest absorption (absorption coefficient = 3.3 × 10^–2 Pa^–1 m^–1). The deviation of the measured absorption behaviour of silane from literature, as far as the pressure dependence is concerned, can be explained by the enhanced spectral energy density in our experiment. This is confirmed by a rate-equation model involving the basic mechanisms of V-V and V-T energy transfer between vibrationally excited silane molecules. In contrast to silane, the absorption coefficient of NH₃ at the 10P(20) laser line is 4.5 × 10^–4 Pa^–1 m^–1 atp = 20 kPa and has its maximum of 4.5 × 10^–3 Pa^–1 m^–1 at the 10R(6) laser line. For C₂H₂ and B₂H₆, is even less ( 2.1 Ò 10^–5 Pa^–1 m^–1 for C₂H₂).     

Particle masses,force constants,and Spin(8)

From a number of qualitative conjectures, the constantsm _e ,c, , and a spin(8) gauge field theory, I derive the following particle masses (quark masses are constituent masses) and force constants: up quark mass=312.7542 MeV; down quark mass=312.7542 MeV; proton mass=938.2626 MeV; neutrino masses (all types)=0; muon mass=104.76 MeV; strange quark mass=523 MeV; charmed quark mass=1989 MeV; tauon mass=1877 MeV; bottom quark mass=5631 MeV; top quark mass=129.5 GeV;W ⁺ mass=80.87 GeV;W ^– mass=80.87 GeV;W ₀ mass=99.04 GeV; fine structure constant= 1/137.036082; weak constant times the proton mass squared M _p ² =0.97×10^–5; color constant=0.6286. From the pion mass in addition, I derive the Planck mass (1–1.6)×10¹⁹ GeV, so that the gravitational constant times the proton mass squared GM _p ² (3.6–8.8)×10^–39.     

Calculation of the carrier-induced refractive index change in InSb

We report a theoretical model for an estimate of carrier-induced changes in the refractive index of InSb at room temperature. The dispersion of n within the photon-energy interval of 0.12–0.24 eV is investigated for nonequilibrium carrier concentrations of 10¹⁵–10¹⁸ cm^–3. An analysis of the influence of the initial carrier density on n is performed. The obtained results can help to develop InSb opto-electronic devices.     

Features of current carrier scattering in epitaxial films

The properties of epitaxial cadmium selenide films obtained by condensation in a vacuum on mica substrates under almost equilibrium conditions are investigated. The temperature dependences of the conductivity and current carrier mobility and concentration are studied. The electron concentration in the films depended on the gas phase composition (coevaporation of CdSe + Se or CdSe + In) and varied between 5·10¹⁰cm^–3 and 3.5·10¹⁸. It is shown that the current carrier scattering mechanism depends on their concentration and production conditions. For n₁ 10¹⁶ cm^–2 (T_S520C),n₂ < 10¹⁵ (T_S=630C), scattering on intercrystallite barriers predominated. For n₁ and n₂ greater than the quantities mentioned, scattering by ionized defects becomes dominant. It is established that the magnitude of the intercrystallite barrier in films with 10¹⁵ < n < 10¹⁶ cm^–3 is comparatively small and does not exceed 4·10^–3 eV, whereupon scattering at the barriers is not explicitly manifest. Concentrations of the ionized centers, magnitudes of the intercrystallite barriers, and ionization energies of the donor levels are determined for films obtained under different conditions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 98–103, September, 1977.     

Chemical structure and internal diffusion within polymer chains in the melt

The single chain dynamics of polydimethylsiloxane in the melt is studied by means of quasielastic neutron scattering. For this polymer the wave vector range 0.03 Å^–1q0.30 Å^–1 covers the regime of universal modes as well as local diffusive processes. A model is described which incorporates the specific chemical structure of the macromolecule and allows to interpret our data in the full wave vector regime. The only parameter which enters the model, the monomer diffusion constantD _m, is found to be (1.2±0.2)·10^–5 cm²s^–1.     

Wide gas-ion beam source based on an arc discharge in a nonuniform magnetic field

The construction of an ion source based on a low-pressure arc with a screened cathode spot is described. The source is ignited by an auxiliary glow discharge in a magnetron electrode system. Ions are extracted from the plasma of the anode part of the arc, generated in a reflective electrode system. The effect of the magnetic induction and the emitter electrode potential on the parameters of the anode plasma was investigated, and the conditions required for generation of a dense uniform plasma, ion emission from which gives beams of ions of nitrogen, argon, oxygen, other gases with cross section 100 cm², current density 10 mA/cm² and nonuniformity of the plasma distribution in the beam cross section 10%, were determined. The formation of wide and converging beams with ion energies up to 50 keV by multiple-aperture ion-optic systems were examined. The source operates in the periodic-pulse mode. The repetition frequency of 1-msec pulses can be regulated from 0 to 50 sec^–1 giving an average beam current of up to 50 mA. It is intended for use in technologies for modification of the surface properties of materials and deposition of thin films. A cold cathode makes possible prolonged operation of the source with chemically active gases.Institute of Electrophysics, Ural Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 3, pp. 66–75, March, 1994.     

On the Possible Mechanisms of Activation Changes of Enzymes under Pulsed Irradiation

Classical radiation biology, radiation treatment of patients, and pulsed radiation chemistry usually deal with weak beams of radiation and operate in terms of dose (D). In this case, only the absolute number of ionizing particles or photons interacting with the object independently of one another is important. In this work, we resume our previous investigations of enzyme activation/inactivation produced by pulsed ionizing radiation from a dense plasma focus (DPF) device at a very short and intense irradiation process, when the concentrations of spurs and blobs are sufficiently dense to allow the micro-volumes to overlap each other. The time interval is small compared with the corresponding biochemical process. It is shown that the irradiation of biological objects for a few nanoseconds by beams of x-ray photons with a low dose (D 10^-6–10^-3 Gy) but at a high dose power (D/10³–10⁵ Gy/s) may be of a collective nature and result in synergetic effects. In particular, it was found that a remarkable activation/inactivation of enzymes (horseradish peroxidase, angiotensin-converting-enzyme) takes place at low doses in these regimes. The results of irradiating the above-mentioned enzymes in vitro with x-rays of nanosecond pulse duration coming from a dense plasma focus are presented here. Neutrons (2.5 MeV, 10³–10⁵ n/cm² and x-ray photons of different energy ranges (7–9 keV and 20–200 keV) together with dose power factors are analyzed as possible reasons for the activation/inactivation of enzymes in various dose ranges. Our results are compared to those of the same experiments conducted with continuous x-ray sources based on a classical x-ray tube and on a ¹³⁷Cs-isotope source (D10^-3–10² Gy).     

Study of short-lived silver isotopes with a laser ion source

The continuum part of the⁶Li (a,a)⁶Li (1.47–2.47 MeV) scattering data at E_a=50 MeV are extracted in two discretized bins. Coupled-channel calculations are carried out coupling the 1⁺ ground state of⁶Li with both the resonant, 3⁺ ₁ state, and two non-resonant continuum states. The discretized continuum of the⁶Li (p,p)⁶Li (1.75–3.25 MeV) scattering data at E_p=65 MeV are also analysed on the same footing. In both the cases the effect of coupling is found to be minimal.     

A thin film source of ultra-cold neutrons

Ultra-cold neutron (UCN) densities have been calculated for a thin film source using realistic phonon spectra of the film material (hydrogen and deuterium). The UCN's build up to a significant density inside a cryogenic container whose walls support the thin films. The UCN's density dependence on the neutron temperature,T _n, was also investigated. It was found that the density reaches a maximum value atT _n20K. A deuterium film at low temperature (5K) andT _n=30 K yields a UCN density 10^–9 ₀ where ₀ is the total flux.Work supported in part by NSF Grant # DMR-8024662     

Optical and Photoelectric Inhomogeneity of CdTe:V Crystals

The optical and photoelectric properties of CdTe:V crystals with the doping impurity concentration N _V = 5·10¹⁸–5·10¹⁹ cm^–3 are investigated and the possibility of their use as a photorefractive material is considered. As is seen from the spectra of optical transmission, the crystals of both types possess high transparency (50–65%), which for CdTe:V specimens with N _V = 5·10¹⁹ cm^–3 decreases sharply and in the range 12–14 m does not exceed 5%, whereas for CdTe:V crystals with vanadium concentration of 5·10¹⁸ cm^–3 such a value of transmission remains unchanged up to 25 m, implying a good optical quality of the latter crystals and their possible application in the spectral range 1.06–1.25 m in modern fiber-optic communication lines.     

Optical bistability in fluorescein dyes

Optical bistability has been observed in highly concentrated fluorescein dye solutions and in thin (1 m) doped polymeric films. At concentrations larger than 10^–5 mole/l dye dimers are formed. For fluorescein dye, the dimer-monomer equilibrium constant is 10⁵ l/mole so that most of the dye species are in the dimer form. At 480 nm the dimer absorption cross section is 10^–18 cm²/molecule, while that for the dye monomer molecule is 7.6×10^–17 cm²/molecule. Upon laser excitation dimers dissociate to form monomers thus providing a highly nonlinear laser induced absorption. This high nonlinear absorption coefficient can be utilized for optically bistable response of the dye system.Optical bistability was observed by placing dye solutions or dye thin films inside a Fabry-Perot resonator and exciting it with 480 nm dye laser pulses of 10 ns duration. The effect is more pronounced in 10^–4 mole/l fluorescein than in 10^–6 mole/l fluorescein in which dimer formation is not that efficient.In disodium fluorescein no significant dimer formation is observed even at 10^–3 mole/l dye concentration. The observed bistability both in solution and in thin films can be explained in terms of recent models for optical bistability in nonlinearly absorbing molecular systems.     

Monte Carlo simulation of spin-aligned atomic hydrogen

The density dependent ground-state properties of spin-aligned atomic hydrogen are studied using the Monte Carlo technique for 32 and 128 atoms in a cube with periodic boundary conditions. The one-particle density matrix, the two-body correlation function, the structure and pairing function have been evaluated and are compared to other recent work. The total number of particles in the condensate is largest at a density 6·10^–3 Å^–3 and amounts to ⁰=2.03·10^–3Å^–3. In addition, the elementary excitation spectrum is discussed in the framework of the Brueckner-Sawada theory. The correct initial slope of the spectrum is obtained from variational results on the structure function. From these results one may tentatively conclude that the roton like part of the spectrum disappears at densities less than 10^–2 Å^–3.     

High rate primary ion beam deposition of a-Si:H films

Hydrogenated amorphous silicon films have been prepared by primary ion beam deposition with a new electrodeless rf ion source. The design of the ion source is described. The composition of the a-Si:H films has been determined by Rutherford backscattering, and the photoconductivity by the constant photocurrent method (CPM). The best a-Si:H films show photoconductivities of 5×10^–5 ( cm)^–1. The deposition rates were between 0.7 and 1.2 nm s^–1.