R. Stephen White

X‐Ray Spectra from Dense Plasma Focus Devices

X‐ray spectra with energies up to 350 keV are reported for two paraboloidal plasma focus devices, the Mark I and Mark III device. Low energy x rays with energies between 5.46 and 29.2 keV were measured with Ross filters. Both time resolved and time integrated spectra were obtained. The higher energy x rays from 60 to 350 keV were measured with K‐5 nuclear emulsions. The energies of the individual electrons produced by the photoelectric effect and by Compton scattering in the nuclear emulsion were measured and the x‐ray spectra were deduced. The x‐ray spectra from each device can be represented by the function (dN/dE)Eu2009=u2009AE−m. In the Mark I device, Au2009=u2009(0.85u2009±u20090.28)u2009×u2009108 ergs (keV)1.5 and mu2009=u2009(2.5u2009±u20090.8); in the Mark III device, Au2009=u2009(3.8u2009±u20091.0)u2009×u2009108 ergs (keV)1.5 and mu2009=u2009(2.5u2009±u20091.0), where E is the photon energy in kiloelectron volts. Both spectra are similar in shape, but the x‐ray intensity from Mark III, with four times the bank energy, is greater. The x rays appear to be produced by thick target brem...

A promising large area VHE gamma ray detector with excellent hadron rejection capability

Abstract A new large area VHE gamma ray detector for detecting atmospheric Cerenkov light from very high energy celestial gamma rays is proposed. It will be constructed by converting Solar One, a 10 MW Solar Thermal Central Receiver Pilot Plant at Barstow, California, which uses the solar tower technology with heliostats as light collectors. Solar energy research at this facility has recently been terminated. The detector will cover an area of at least 200 m diameter, which is only about 5% of the total area available at Solar One, so that a significant fraction of the Cerenkov light pool is detected. Each heliostat will focus the Cerenkov light onto a photomultiplier tube (PMT) selected to match the optical quality of the heliostat. Its active reflecting surface is 71,000 m2, which is about 375 times larger than the largest VHE gamma ray atmospheric Cerenkov detector, the twin 11 m dia. collectors at Sandia Labs, Albuquerque1. It is expected to have the lowest energy threshold (≥10 GeV) for atmospheric Cerenkov observations. This will enhance counting rates significantly and bridge the gap between HE and VHE gamma ray astronomy with some overlapping. It will also have excellent inherent hadron rejection. One hundred million dollars worth of installation is already constructed and ready to use. The rest of the detector can be built for a small fraction,

Double Scatter Telescope for Medium Energy Gamma Ray Astronomy from a Satellite

A large area (1 m2) medium energy (1-30 MeV) telescope for gamma ray astronomy is discussed. This telescope utilizes the double scattering of gamma rays between two scintillator arrays with directionial discrimination by means of time-of-flight. The first and second arrays consist of a series of plastic and NaI(Tl) scintillators, respectively, in the shape of long (1 m) linear elements viewed by photomultiplier tubes at both ends. The lateral position of the interaction in the plastic is determined by timing and in the NaI(Tl) by pulse height. Neutron-induced background is eliminated by using a pulse shape discrimination plastic scintillator. At 6 MeV, the telescope has an area-efficiency factor of 300 cm2, an energy resolution of 8% (FWHM), an angular resolution of 3° (HWHM) and a sensitivity of 5 × 10-6 ¿/cm2sec for line emission. Discrete sources can be located to 0.5°.

Neutron and proton interaction backgrounds in compton-telescopes used for gamma-ray astronomy

Gamma-ray background counting rates encountered in astronomy observations are calculated for a double Compton scatter telescope. Backgrounds not eliminated by the usual growth curve could be produced by albedo neutrons and/or cosmic ray protons interacting with the carbon and/or hydrogen of the detector. They are the albedo neutron-carbon interaction gamma-rays, cosmic ray proton interaction delayed gamma rays and the moderated albedo neutron-proton photocapture gamma rays. It is decisive to know the contribution of these backgrounds, because they must be subtracted before the cosmic diffuse flux can be determined. Estimates of the neutron induced background events in a Compton telescope show that they might contribute a considerable fraction of the counting rate. In the near future the calculations will be checked with a calibrated neutron beam.

Can baryonic dark matter be solid hydrogen

Some requirements are discussed for solid hydrogen formation in cold dark dense clouds in galaxies. If temperatures in the clouds are near the microwave background temperature of 2.7 K and molecular hydrogen densities are 3×105 cm−3 or higher, as suggested by recent observations, it may be possible for solid hydrogen objects to form. Comet size hydrogen solids could build from molecular hydrogen condensation on grains and by collisions. Heated primarily by cosmic rays, objects with 100 km radii could last billions of years. The larger objects may be detectable, in the future, by sensitive gravitational lensing or eclipsing observations. Other possibilities are discussed for future detection of the cold dark dense molecular hydrogen regions. In our model, helium is added along with the hydrogen to preserve the primordial helium to hydrogen mass ratio,Yp, of the standard model. In the hot regions of the universe the solid hydrogen objects sublime and melt so our model predictsYp=0.250, the same as other baryonic dark matter models with identical values of ω=0.1,Ho=50 and η=6.8×10−10. This value cannot be ruled out at present because of the large systematic uncertainties in the observed value of 0.232. In the cold dark regions where solid hydrogen objects exist, we predict thatYp will be greater than 0.250. Observations are not yet sensitive enough to measure this ratio.Some requirements are discussed for solid hydrogen formation in cold dark dense clouds in galaxies. If temperatures in the clouds are near the microwave background temperature of 2.7 K and molecular hydrogen densities are 3×105 cm−3 or higher, as suggested by recent observations, it may be possible for solid hydrogen objects to form. Comet size hydrogen solids could build from molecular hydrogen condensation on grains and by collisions. Heated primarily by cosmic rays, objects with 100 km radii could last billions of years. The larger objects may be detectable, in the future, by sensitive gravitational lensing or eclipsing observations. Other possibilities are discussed for future detection of the cold dark dense molecular hydrogen regions. In our model, helium is added along with the hydrogen to preserve the primordial helium to hydrogen mass ratio,Ynn pn , of the standard model. In the hot regions of the universe the solid hydrogen objects sublime and melt so our model predictsYnn pn =0.250, the same as other baryonic dark matter models with identical values of ω=0.1,Hnn on =50 and η=6.8×10−10. This value cannot be ruled out at present because of the large systematic uncertainties in the observed value of 0.232. In the cold dark regions where solid hydrogen objects exist, we predict thatYnn pn will be greater than 0.250. Observations are not yet sensitive enough to measure this ratio.

Tracking and imaging gamma-ray experiment (TIGRE) for 300-keV to 100-MeV gamma-ray astronomy

The Tracking and Imaging Gamma-Ray Experiment (TIGRE) uses multilayers of silicon strip detectors both as a gamma-ray converter and to track Compton recoil electrons and positron-electron pairs. The silicon strip detectors also measure the energy losses of these particles. For Compton events, the direction and energy of the Compton scattered gamma ray are measured with arrays of small CsI(TI)-photodiode detectors so that an unique direction and energy can be found for each incident gamma ray. The incident photon direction for pair events is found from the initial pair particle directions. TIGRE is the first Compton telescope with a direct imaging capability. With a large (pi) -steradian field-of-view, it is sensitive to gamma rays from 0.3 to 100 MeV with a typical energy resolution of 3% (FWHM) and a 1-(sigma) angular resolution of 40 arc-minutes at 2 MeV. A small balloon prototype instrument is being constructed that has a high absolute detection efficiency of 8% over the full energy range and a sensitivity of 10 milliCrabs for an exposure of 500,000 s. TIGREs innovative design also uses the polarization dependence of the Klein-Nishina formula for gamma-ray source polarization measurements. The telescope will be described in detail and new results from measurements at 0.5 MeV and Monte Carlo calculations from 1 to 100 MeV will be presented.

Some requirements of a colliding comet source of gamma ray bursts

Colliding comets in the Solar System may be an important source of gamma ray bursts. The spherical gamma ray comet cloud required by the results of the Venera Satellites (Mazets and Golenetskii, 1987) and the BATSE detector on the Compton Satellite (Meeganet al., 1992a, b) is neither the Oort Cloud nor the Kuiper Belt. To satisfy observations ofN(>Pmax) vsPmax for the maximum gamma ray fluxes,Pmax > 10−5 erg cm−2 s−1 (about 30 bursts yr−1), the comet density,n, should increase asn ∼a1 from about 40 to 100 AU wherea is the comet heliocentric distance. The turnover above 100 AU requiresn ∼a−1/2 to 200 AU to fit the Venera results andn ∼a1/4 to 400 AU to fit the BATSE data. Then the masses of comets in the 3 regions are from: 40–100 AU, about 9 earth masses,mE; 100–200 AU about 25mE; and 100–400 AU, about 900mE. The flux of 10−5 erg cm−2 s−1 corresponds to a luminosity at 100 AU of 3 × 1026 erg s−1. Two colliding spherical comets at a distance of 100 AU, each with nucleus of radiusR of 5 km, density of 0.5 g cm−3 and Keplerian velocity 3 km s−1 have a combined kinetic energy of 3 × 1028 erg, a factor of about 100 greater than required by the burst maximum fluxes that last for one second. Betatron acceleration in the compressed magnetic fields between the colliding comets could accelerate electrons to energies sufficient to produce the observed high energy gamma rays. Many of the additional observed features of gamma ray bursts can be explained by the solar comet collision source.

Propagation of plasma beams across the magnetic field

1407_62Beams of charge- and current-neutralized plasma will cross a transverse-magnetic field by a combination of collective-plasma processes. These processes were studied for a high-to-low beta ((beta) equalsV plasma energy density/magnetic field energy density) hydrogen-plasma beam injected into a vacuum transverse magnetic field with nominal parameters: (Tau) i approximately equals 1 eV, (Tau) e approximately equals 5 eV, n 14 cm-3, vi 6 cm/s, tpulse < 70 microsecond(s) , (Beta) z (Rho (i)) (Rho (i)), where a is the beam radius, x is the downstream distance, and (Rho (i)) is the ion gyroradius. A brief state of initial diamagnetic propagation is observed, followed by a rapid transition to

Comptel science module III neutron calibration and simulation

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[Comment on “Teaching evolution, the Kansas School Board of Education, and the democratization of science”] The causes of anti‐science views

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