Engineering topics
Publications and source records attributed to Ormes, J. F..
Results from a Monte Carlo simulation of gamma-ray production under astrophysical conditions indicate that it is possible to produce gamma-ray spectra as hard as that of 2CG013+00 reported by COS-B using a monoenergetic beam of cosmic rays hitting a thin target material. It is suggested that the low mass X-ray binary GX13+1 might provide such a mechanism to produce the observed gamma-rays from the region.
Results are reported from the Low Energy Antiproton Experiment (LEAP), a balloon-borne instrument which was flown in August, 1987. No evidence of antiproton fluxes is found in the kinetic energy range of 120 MeV to 360 MeV, at the top of the atmosphere. The 90-percent is found confidence upper limit on the antiproton/proton ratio in this energy range is 3.5 x 10 to the -5th. In particular, this new experiment places an upper limit on the flux almost an order of magnitude below the reported flux of Buffington et al. (1981).
The flux of albedo antiprotons in the 100-1000 MeV kinetic energy range produced by the cosmic ray primaries in the atmosphere is calculated. It is shown that this is not a significant background to measurements of the low energy anti-proton cosmic ray flux.
A measurement of the spectral index of Galactic cosmic ray (GCR) iron has been performed using the High Energy Gas Cerenkov Spectrometer. The spectral index of GCR iron, in the energy range 60 to 200 GeV/n, has been determined to be 2.56 + or - 0.11. This result indicates that the source spectrum of GCR iron is similar to that of other primary GCR nuclei, as expected in the standard leaky box model.
Monte Carlo simulations of the gamma-ray emission from hypothetical cosmic-ray sources are performed. Sources which might correspond to acceleration by supernova shocks in 'average' interstellar conditions and deep within giant molecular clouds are considered. The consequences of dropping the common assumption that the cosmic-ray spectrum at the sources is the same as that observed at earth are examined. Spectral effects which can be related to the depth of the material shroud and the population of accelerated particles are explored using these simulations and are described. The results are compared with the COS B catalog of gamma-ray sources, and the implications for the underlying particle populations and source mechanisms are discussed.
Recent experimental observations and results are discussed. It was found that the approximately 50 antiprotons collected in balloon experiments to date have generated considerable theoretical interest. Clearly, confirmatory experiments and measurements over an extended energy range are required before definite conclusions are drawn. Antiproton measurements have a bearing on astrophysical problems ranging from cosmic ray propagation to issues of cosmological import. The next generation of balloon experiments and the Particle Astrophysics Magnet Facility being discussed for operation on NASA's space station should provide data and insights of highest interest.
If cosmic rays are accelerated by strong shocks, then cosmic ray sources should be characterized by spectra, dN/dE alpha E exp -(2.0-2.2), reflecting the strength of those shocks. This is expected from the 'standard leaky box' model of cosmic ray propagation in which the source spectra are harder than the observed spectra because higher energy particles have shorter residence times in the galactic magnetic fields. Furthermore, data on cosmic ray nucleons suggest that these sources might be surrounded by material. If the latter is true, such sources should be observable in gamma rays at energies beyond 1 GeV where the angular resolution of gamma-ray telescopes is optimized and the background is significantly reduced. For identified sources, the source location accuracy can be shown to improve with increasing energy in spite of the decreasing statistics, as long as the gamma-ray spectrum is harder than dN/dE alpha E exp -gamma. A Monte Carlo model is used to predict the photon spectra which would be expected from cosmic ray sources under varying assumptions about the strength of the shocks in the acceleration region.
Planning for and design tradeoff studies related to the particle astrophysics magnet spectrometer known as Astromag are presented. This facility is being planned for the Space Station Freedom and address questions regarding the origin and acceleration of cosmic rays, explore the synthesis of elements by making detailed measurements of cosmic ray isotopic composition, and search for evidence of antimatter and other cosmologically significant particles. This work was supported by an international study team which includes particle physicists and cosmic ray physicists.
This paper describes a superconducting magnet system which is the heart of a particle astrophysics facility to be mounted on a portion of the proposed NASA space station. This facility will complete the studies done by the electromagnetic observatories now under development and construction by NASA. The paper outlines the selection process of the type of magnet to be used to analyze the energy and momentum of charged particles from deep space. The ASTROMAG superconducting magnet must meet all the criteria for a shuttle launch and landing, and it must meet safety standards for use in or near a manned environment such as the space station. The magnet facility must have a particle gathering aperture of at least 1 square meter steradian and the facility should be capable of resolving heavy nuclei with a total energy of 10 Tev or more.
The high energy gas Cerenkov Spectrometer (HEGCS) was flown by balloon from Palestine, Texas on September 30, 1983. The instrument maintained an altitude of 118,000 ft (4.7 g/sq cms) for 6 hours. Details of the ongoing data analysis and preliminary results on the Fe spectrum to 10 to the 13th power eV/nucleus are given.
Preliminary results from the High Energy Gas Cerenkov Spectrometer indicate that the sub-iron to iron ratio increases beyond 100 GeV/nucleon. This surprising finding is examined in light of various models for the origin and propagation of galactic cosmic rays.
The techniques to be used in a balloon borne experiment APEX to detect 220 MeV antiprotons are described, paying particular attention to potential sources of background. Event time history is shown to be very effective in eliminating this background. Results of laboratory tests on the timing resolution which may be achieved are presented.
Cerenkov detectors are used to measure the velocity of particles in configurations designed to study the isotopic composition of galactic cosmic rays. The geometrical properties of the detector are outlined. Monte-Carlo simulations of photon propagation in a diffusive detector were undertaken. The scattering properties of diffusively reflecting white paint and of surface treatments for the radiator material were measured. It is found that the absorption of light in the radiator is an important light loss mechanism. The simulations are used to find optimal mapping techniques and data reduction strategies. The application of these techniques are discussed with respect to the large area isotopic composition experiment (ALICE) Cerenkov detector.
A range-energy experiment was built to measure the isotopic composition of galactic cosmic rays. An enrichment of neutron rich isotopes, 22Ne and (25Mg + 26Mg) in particular, when compared to the solar composition is shown. A rich statistics measurement of these and other neutron-rich isotopes in the galactic flux yields information to the source of these particles. A computer simulation of the experiment was used to estimate the instrument resolution. The Cherenkov detector light collection efficiency, was calculated. Absorption of light in the radiator was considered to determine the optimum Cherenkov medium thickness. The experiment will determine the isotopic composition for the elements neon through argon in the energy range 300 to 800 MeV per nucleon.
It is suggested that a ring of HI gas lying in the galactic plane is part of a supershell which formed some 3 x 10 to the 7th power years ago. The consequences of a closed magnetic supershell for cosmic ray propagation are examined and it is concluded that there is no evidence which precludes the production and trapping of cosmic rays in such a region. A consequence of superbubble confinement is that the mean age of cosmic rays would be independent of energy. This can be tested by high energy observations of the isotopic composition of Be.
Experimental measurements are proposed to determine the existence of cosmic antiprotons and to differentiate between various hypothetical origins for them. The balloon-borne experiment proposed by Balasubrahmanyan et al. (1983) for detecting 50-220-MeV antiprotons and measuring their energy distribution is described; the astrophysical significance of antiproton measurements is considered; the antiproton/proton ratios predicted by various cosmic-ray and exotic models are presented graphically; and the performance required of a Space Station superconducting-magnet detector for the 10-1000-GeV range is discussed. It is concluded that an instrument with 0.3-sq m sr geometry could distinguish (at a 5-sigma level) between hypotheses with spectral-exponent separation of 0.1 in observing time about 1 month, assuming a spectral exponent as steep as E to the -3rd.
The scientific aims and design concept of a High-Energy Space Station (HESS) cosmic-ray detector array are discussed. The current state of knowledge on cosmic-ray acceleration and high-energy interactions is briefly reviewed, and the need for observations yielding elemental composition and spectra in the 10-10,000-TeV/nucleon range is demonstrated. It is predicted that 2 yr of observations with a space-borne detector of geometry factor 30 sq m sr would provide adequate data to determine the acceleration mechanism (by comparing the energy level at which the spectra of He nuclei and protons break). A modular HESS array comprising W/scintillator/PM-tube calorimeter modules and Cerenkov charge-sensitive detector modules and weighing about 30 tonnes is described. The array could be assembled on orbit after transport in the Space Shuttle cargo bay, and data could be taken as soon as one or two layers of modules had been attached to the mounting-frame/support-electronics unit.
It is suggested that a ring of HI gas lying in the galactic plane is part of a supershell which formed some 3 x to the 7th power years ago. The consequences of a closed magnetic supershell for cosmic ray propagation are examined and it is concluded that there is no evidence which precludes the production and trapping of cosmic rays in such a region. A consequence of superbubble confinement is that the mean age of cosmic rays would be independent of energy. This can be tested by high energy observations of the isotopic composition of Be.