3027. Instrument for vacuum ultraviolet fluorescence lifetime measurements

Classified abstracts 3026-3035 intense focused electron beam, was examined to study the electron absorption mechanism for a I-MeV electron beam with a current density of 1 MA/cm-'. The VUV emission was observed with aluminium cathode x-ray diodes operated with and without I,:2-ttm aluminium filters and a near-normal incidence grating spectrograph. The data obtained arc consistent with classical electron deposition and indicate an anode surface temperature of a few eV with the peak temperature occurring at the time of impedance collapse. D J Johnson et al, J Appl Phrs 48 (3), 1977, 1058-1060. 12 3026. A low-pressure cloud chamber to study the spatial distribution of ionizations. (GB) To further the understanding of the biological eft'eels of radiation a knowledge of the spatial distribution of ionizations in small volumes is required. A cloud chamber capable of resolving the droplets formed on indiviudal ions in the tracks of low-energy electrons has been constructed. It is made to high-vacuum specifications and contains a mixture of permanent gases and vapours, unsaturated before expansion, at a total pressure of 10 kPa. Condensation efficiencies close to 100 °/ /o are obtained without significant background from condensation on uncharged particles and molecular aggregates. This paper describes the chamber, associated equipment and method of operation and discusses the performance of the system. Photographs of the droplets produced from the interaction of low-energy x-rays in the chamber gas for various omdes of operation are presented. The mean energy loss per ion pair (14/ ) for electrons produced by the interaction of AI x-rays in the chamber gas (8130 Pa H.,, 700 Pa C.,HsOH, 690 Pa H_,O, 400 Pa He, 70 Pa air) has been measured as 29.8 I 0 . 7 eV per ion pair compared with a calculated value of 29.6 ±0.4 eV per ion pair. The measurement and analysis of the spatial distribution of droplets will be presented elsewhere. D C Hedges and M Marshall, J Phys E." Scient Instrum, 10 (4), 1977, 342-350. 12 3027. Instrument for vacuum ultraviolet fluorescence lifetime measurements. (USA) An instrument is described for measuring fluorescence lifetimes, fluorescence excitation spectra, and relative fluorescence quantum yields by photon counting in the vacuum ultraviolet. The temporal resolution is satisfactory down to lifetimes of 200 psec, and the sensitivity permits measurements on totally absorbing samples with quantum yields as low as I0-'*. The nanosecond H: flash lamp is a satisfactory source for these measurements with a useful range from 120 to 400 nm. (Canada) R L Lyke and W R Ware, Rev Sci Ins/rum, 48 (3), 1977, 320-326. 12 3028. Gas phase electrochromism studies in the vacuum ultraviolet. (USA) An instrument and technique have been developed for the measurement of medium-resolution electrochromism spectra of gas phase samples in the ultraviolet spectral region from 300.0 to 165.0 nm. The primary result of studies utilizing this method is the difference in dipole moment between the ground state and an excited state of a molecule. The electrochromism spectrum of aniline is presented for the B2+--At 0r*-~-~) transition at 293.84 nm. The absolute value of the change in dipole moment for this transition is tl.254-0.301 D, which compares favourably with the value of 10.92±0.10I D reported from Stark field studies of a high-resolution spectrum. The primary advantage of the technique is that it allows the determination of dipole moment changes associated with excited states, even when resolved rotational structure cannot be obtained. G C Causley et al, Rev Sci Instrum, 48 (3), 1977, 264-267. 12 3029. Medium pressure diffusion plasma column in a coaxial cold cathode discharge. (USA) A quiet homogeneous cylindrical plasma column is produced by using a coaxial diffusion discharge tube at medium pressure (0.1-10 torr) with a cold cathode dc discharge. The basic characteristics of this plasma are checked by an electrostatic probe. By varying the gas pressure and input power, electron densities can be obtained from 106 to 10 tx cm -3, and electron temperatures from 0.1 to a few eV. Using this plasma source, the advantage to the probe experiment is shown, and the possibility for time-independent measurements of the volume recombination coefficient is suggested. (Japan) S-L Chen and M Kamitsuma, Rev Sci Instrum, 48 (3), 1977, 261-263.

654

12 3030. X-ray streak camera for observation of tightly pinched relativistic electron beams. (USA) A pinhole camera is coupled with a Pilot-B scimillator and imageintensilied TRW streak camera to study pinched electron beam protiles via observation of anode target bremsstrahhmg. Streak intensification is achieved with an EMI image inlensifier operated at a gain of up lo 10~' which allows optimizing Ihc pinhole configuration so thai resolution is sinmhaneously limited by photon-counting statistics and pinhole geometry. The pinhole used is one-dimensional and is fabricated by inserting uranium shims s~ilh hyperbolic curved edges between two 5-cm-lhick lead blocks. The loss of spatial resolution due to the X-ray transmission through the perimeter of the pinhole is calculated and a streak photograph of a Gamble 1 pinched beam interacting with a brass anode is presented. D J Johnson, Rec Sci hlslrum, 48 (3), 1977, 209-213. 12 3031. Secondary electron emission from 0.5-2.5-MeV protons and deutrons. (USA) Measurement of the secondary electron currents leaving AI, V, Fe. 316 stainless steel, Nb, and Mo foils undergoing 0.5-2.5-MeV proton and deuteron bombardment were made to determine the secondary electron emission ratios for these ions. The measured secondary electron yields were of the order of 1.0, with the deuterons producing generally higher yields than the protons. T A Thornton and J N Anno, J Appl Phvs 48 (4), 1977, 1718-1719. 12 3032. Equilibrium temperatures in a CO, TEA laser. (USA) Equilibrium gas temperatures as high as 600~ 30 K have been observed in the center of a CO, TEA laser discharge by measuring the absorption of a CO_, laser beam following the gain pulse. Uncertainties in the theoretical variation of absorption with temperature were avoided by measuring the absorption coefficient of the gas mix used in the laser in a temperature-controlled oven, up to a temperature of 610 K, so that the observed absorption in the laser discharge could then be directly related to the gas temperature. The temperature decreased from the center of the discharge towards the sides, and was initially constant along the direction of the transverse current. A temperature increase was observed with input energy, while a decrease was observed with pressure, distance between electrodes, and flamess of the electrode profile. A temperature of approximately 450 K was optimum for maximizing the small-signal gain in this system. (Canada) A M Robinson and Y-K Hsieh, J Appl Phrs 48 (4), 1977, 1589-1595. 12 3033. Laser operation by dissociation of metal complexes. II. New transitions in Cd, Fe, Ni, Se, Sn, Te, V, and Zn. (USA) New laser transitions at 15 wavelengths from 1.454 to 14.54 p, have been observed from eight metal atoms. A double-discharge technique has been employed for the production and excitation of metal atoms by dissociation of metal halides, alkyls and carbonyls. The possibility of laser action on the TI(I) 6s'-8p "-Pa~,..3 J,-+6s "-7s'-Sj ~,_ transitions at 6714 and 6550 A. is discussed. M S Chou and T A Cool, J Appl Phys, 48 (4), 1977, 1551-1555. 12 3034. Ultrahigh vacuum investigations on the exoelectron energy distribution of NaF-surfaces. (Germany) NaF single crystal surfaces are cleaned by baking in uhv. Adsorbates, grown after 02 or H20 inlet and monitored by the Auger-signal of oxygen, do not influence the glow curve of the thermally stimulated exoelectron emission but affect the energy distribution. U Brunsmann and A Scharmann, Vakttttm-Tech, 26 (3), 1977, 78-80 (hi German). 12 3035. The theory of the instantaneous triple-probe method for directdisplay of plasma parameters in low-density eollisionless plasmas. (GB) An exact theory taking the ion temperature T= into account is developed for a triple-probe in an orbital-morion-limited collisionless plasma, i.e. when charged particle mean free path>>Debye length>> probe radius. Formulae for determining electron temperature and electron density are given for both spherical and cylindrical probes. Analytical results show that the effect of Tj on measurements of plasma parameters is small when using a cylindrical probe and is negligible when compared to the errors obtained when using a