R-3 Repository :: Browsing by Author "Haymes, Robert C."

Browsing by Author "Haymes, Robert C."

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A measurement of hard X and gamma radiation from Sco X-1
(1971) Twieg, Donald Baker; Haymes, Robert C.
Sco X-1 is the brightest extrasolar X-ray source in the sky. Additional knowledge of its output in the hard X-ray and gamma-ray regions could be particularly valuable in judging the validity of hypotheses intended to explain its unusual emission characteristics. On November 26, 1969, a balloon-borne scintillation detector was launched from Parana, Argentina to measure the output of Sco X-1 above 110 keV. Despite complications caused by a partial battery failure and a solar X-ray flare, a flux above 75 keV was measured. The instrument and experimental procedures are discussed briefly, and the reduction procedures and calculated fluxes are presented and discussed. Because of a possible solar contribution, the measured fluxes are interpreted as upper limits, but the results appear to verify the existence of a previously observed possibly non-thermal flux component departing at about /10 keV from the softer thermal component. Observations of Sco X-1 in the X-ray, visual, infrared, and microwave regions are reviewed. Derived source parameters and proposed models for the source are discussed in an appendix. No hypothesis has thus far been completely successful in explaining the many unusual characteristics of the electromagnetic emission of Sco X-1, but the close-binary hypothesis may be the most satisfactory.
An observation of the spectrum of Sco X-1 above 50 KeV
(1972) Prichard, Howard Milton; Haymes, Robert C.
On November 25, 1970, an observation of the hard X-ray spectrum of the object "Sco X-l" was made by a balloon-borne scintillation detector launched from Parana, Argentina. The information obtained from this flight includes the first data on the shape of the spectrum at energies above 50 KeV. The directional detector consisted of a Nal (Tl) central crystal collimated by a guard crystal of the same material connected in anti-coincidence with the central crystal. An on-board 128 channel analyzer was adjusted to cover the incident photon energy range of 30 to 930 KeV; the analyzed pulses, together with engineering data, were radio-telemetered from the balloon at 128,000 feet to the ground. Alternate tenminute observations of the source and background were made for approximately two hours. Channel-by-channel residuals were obtained by subtracting the time-normalized and averaged count rate of two successive background segments from that of the intervening source segment. After correction for atmospheric and instrumental signal attenuation, and for detector efficiency, these residuals were taken to be a measurement of the flux due to Sco X-l incident at the top of the atmosphere. The resulting spectrum is inconsistent with a single-component thermal bremsstrahlung emission mechanism. In the range 50-350 KeV, a flux distribution more consistent with synchrotron radiation is observed, as a power law of spectral index 1.8 provides a good fit to the data. From 350 to 930 KeV, 2-sigma upper limits are obtained that are well above the expected levels due to the above synchrotron mechanism. No evidence of line emission is seen. Possible implications of this measurement are discussed in the light of previous observations.
Atmospheric gamma radiation
(1969) Glenn, Stephen W; Haymes, Robert C.
During the summer of 1967, a series of balloon flights with a directional gamma-ray detector were made. The detector is collimated to a half-angle of about 12° and measurements are made over gamma-ray energies between 30-570 keV. The energy range is divided into 128 channels. Detailed knowledge of the instrument response allows the actual incident spectrum to be unfolded. The altitude dependence of the gamma-ray count rate is well fit by curves of the form f = A ± Be-p/D where p is the pressure and the plus or minus sign is used for pressures below or above the maximum count rate altitude of about 75 mb. The spectra at different altitudes are presented. The spectrum of the gamma radiation high in the atmosphere (3.5 mb) is analyzed in detail and appears to be proportional to the ionizing radiation which varies as a function of geomagnetic latitude. A small zenith angle dependence may have been observed. The -500 keV feature which has been observed previously appears to be at 490 keV. The results of this experiment indicate that any contribution from a possible 511 keV annihilation energy line must be very small compared to the peak at 490 keV. Line features due to neutrons are present in the spectrum and appear to be of expected magnitude. During one of the flights, the sun was in the field of view and an observed increase may be attributed to enhanced solar emission of gamma radiation. The increase appeared to remain constant for at least twenty minutes and the spectrum of the increase at the top of the atmo- sphere is fit by the curve f(E) = 43.1 E-(1.75 ± .05) photons/cm2-sec (where E is in keV).
Azimuthal dependence of the atmospheric gamma-ray background
(1975) Shelton, David Harold; Haymes, Robert C.
On May 15, 1973 a balloon borne gamma-ray detector belonging to Rice University was launched from Palestine, Texas. From 19:4 CDT to 21:25 CDT the atmospheric gamma ray background was observed from 56 KeV to 12.4 MeV in energy. The directional detector was pointed at a constant zenith angle of 13.4° and viewed the atmospheric background at all values of azimuth angle. The experiment was carried out at altitudes of roughly 3.5 gm/cm2 residual atmosphere. The detector consisted of a central crystal of Nal(Tl) which was actively collimated by a shield of the same material. The instrument had a beam width of 15° full width half maximum. Results are consistent with an observed sinusoidal perturbation of the average background count rate between 56 KeV and 375 KeV of the form R = B[1 + (.188 ± .33)sin(Az - (12° ± 22°))] where R is the photon count rate, B is the average photon count rate, and Az is the azimuth angle at which the instrument was pointed. No similar behavior was observed at other energies.
Computer simulation of the Rice University gamma ray telescope
(1988) Sen, Bhaswar; Haymes, Robert C.
Calculations have been made of the new Rice University gamma ray astronomical telescope, over the energy interval 0.1 MeV-5.0MeV. A computer program, ACCEPT, was used and simulations performed on the Rice University's AS-9000 mainframe. For gamma ray fluxes at 3.5 g cm$\sp{-2}$ atmospheric depth over Palestine, Texas, efficiency curves for the principal detector have been obtained. Energy deposition profiles have been calculated and compared to previous simulations and observations. The study shows the simulation code ACCEPT to be more machine dependent than previously believed.
Design and calibration of an automatically oriented balloon-borne gamma-ray telescope
(1967) Craddock, Wade Lafayette; Haymes, Robert C.
Two alternatives have been suggested to explain the approximately exponential decrease in the light output of Type I supernovae. The Californium 254 hypothesis [Burbidge et al., 1957; Hoyle and Fowler, 1960] is that the exponential decay in light intensity is due to the nuclear energy released by the spontaneous fission of Cf254; no efficient mechanism for converting fission energy into visible light was presented. A second hypothesis [Hoyle et al., 1964] is based on the damping of an assumed relativistic oscillation in gravitating masses. Theoretically it has not been possible to specify either radioactivity or gravitation as the sole energy source of the initial light output. The detector system described here will provide a means of experimentally verifying or refuting the Cf254 hypothesis; however, this thesis will not resolve this controversy. Assuming the Cf-hypothesis to be valid and Type I supernovae to be the site of r-process nucleosynthesis, the gamma-ray line spectrum from radioactive decay of trans-bismuth nuclei can be calculated for any time in the history of a Type I supernovae. These calculations have been carried out for the Crab Nebula [Clayton and Craddock, 1965] and the resulting spectrum was used as the design criterion for the detector discussed here. This spectrum sets the requirement that the detector must be able to detect line fluxes of the order of 1 x 10-4 to 1 x 10-5 photons cm 2 sec-1 above a background [Arnold et al., 1962; Metzger et al., 1964] given approximately by dN/dE = 1.2 x 10 -5 E6 -7/4 photons cm 2 sec-1 kev-1 sterad-1 , where E6 is the photon energy in Mev. For photons in the energy range of 30-450 kev, a detector with an energy resolution of approximately 20 kev and a viewing angle of 0.1 sterad or less will give an observable signal. A sodium iodide (thallium activated) scintillator four inches in diameter and two inches thick is used as the detector. The signal from this crystal from photons with energies between 30 and 455 kev is analyzed by a 128 channel pulse height analyzer. Collimation is obtained by a mixture of shielding and anticoincidence techniques. The detector is recessed eight inches into the end of a cylinder of NaI(T1) nine and one half inches in diameter by twelve inches long. Additional collimation is provided by the use of three toroidal shaped plastic scintillators. The detector and the surrounding scintillators are optically decoupled and their signals are connected in anticoincidence. These scintillators reduce the effective half angle of the detector to one and one half to two degrees 3 x 10-3 sterad). A thin plastic scintillator is used to reject charged particles within this viewing angle. This instrument, along with its associated orientation system, is capable of observing the predicted gamma-ray spectrum from the Crab Nebula at altitudes of approximately 130,000 feet. Experimental data are given to demonstrate the capabilities of the system.
Detection of nuclear gamma radiation from Centaurus A
(1976) Hall, Richard Dale; Haymes, Robert C.
Centaurus A (NGC 5128) was observed in the low-energy gamma-ray region (.33 MeV-12.25 MeV) on 1974 April 2 U.T. by a balloon-borne detector. The detector is an actively collimated scintillation counter with a sensitive area of 182 cm^ and a 13° FWHM (.4 steradians) field-of-view. The instrumental field-of-view encompassed the entire extent of the Cen A radio lobes without contamination from other dis¬ crete X-ray sources. The detector was launched from Rio Cuarto, Argentina, and the observations were made at an atmospheric depth of 4 gm/cm . To measure the background flux the detector was periodically rotated ^18° in azimuth from the Cen A orientation. To derive the source spectrum the background fluxes were subtracted from the fluxes observed when the detector was pointed towards Cen A. The residual flux was then cor¬ rected for instrumental effects and atmospheric absorption. Pointing difficulties during the experiment required incorporation of off-axis attenuation correction factors. Occasional, random telemetry-saturating count rates were observed. These anomalous counts are probably due to impact of high-energy particles on the detector. To avoid distortion by these counts, they were deleted from the data. Statistical anomalies in the data required a variance analysis of the data and modifications of the data reduction. The anomalies were isolated to the breakdown of the statistical methods used when working with few counts per channel. The computed Cen A spectrum shows a ten-fold increase since 1971 in hard X-ray flux. The best fit to the intensified continuum detected in the 1974 observation is (.86 +_ .17)E[keV] 1*9+.4 photons-cm ^-sec ^-keV^. Gamma-ray spectral lines were also detected. These are the first nuclear lines detected from what is apparently an extragalactic source. The lines are at 1.6 MeV and 4.5 MeV. The 1.6 MeV line is 3.3a above the continuum and is 24.51 FWHM broadened. The 4.5 MeV line is also 3.3o above the continuum but is not broadened. The lines are most likely from nuclear deexcitation of 24Mg*(1.37 MeV), 2Ne*(1.63 MeV), and Si*(1.78 MeV) for the broad 1.6 MeV feature and deexcitation of ^2C*(4.43 MeV) for the 4.5 MeV line. No positron annihilation line (.511 MeV) was detected. The nuclear lines may be due to low-energy cosmic rays interacting with interstellar gas in Cen A, from nucleosynthesis in the galaxy NGC 5128, or, possibly, from line-of-sight contamination by low-energy cosmic rays within our Galaxy.
Gamma ray observations of black hole candidates nova Ophiuchus 1993 and nova Velorum 1993
(1997) Moss, Michael Jamieson; Haymes, Robert C.
Results of spectral analysis and time series analysis of the transient source x-ray nova Velorum 1993 (GRS 1009-45) and x-ray nova Ophicuhus 1993 (GRS 1716-249) are presented. These data were accumulated using the OSSE (Oriented Scintillation Spectrometer Experiment) low-energy gamma ray telescope on the Compton Gamma Ray Observatory. Spectral observations of the two x-ray novae showed the presence of gamma ray emission to greater than 100 keV, which is thought to be a signature of a binary system with an accreting black hole. Observations of GRS 1009-45 shows that it was in a gamma-ray soft state during the one-day OSSE observation, which occurred during the exponential decay phase of the outburst. The spectrum of GRS 2716-249 acquired during the plateau stage of outburst indicated a hard state, while spectra acquired during the sawtooth outbursts suggest that a hard to soft transition occurs as the decay progresses. The 40-200 keV pre-outburst luminosity of GRS 1716-249 is shown to be two orders of magnitude less than that estimated during the plateau-stage observation. The only significant power density spectrum was that acquired for GRS 1716-249 during the plateau stage of outburst. It is consistent with the sum of two QPO peaks at 0.128 and 0.32 Hz and a red noise ($\nu\sp{-1}$) component. This power spectrum is consistent with other black hole candidate power spectra for which the source is in the low state. Power spectra for GRS 1009-45 and GRS 1716-249 during the peak of a sawtooth outburst are also presented. They are consistent with band-limited white noise. Corresponding autocorrelations are shown for all observations.
High-energy X-radiation from M-87
(1968) Fishman, Gerald Jay; Haymes, Robert C.
M-87 (NGC 4486), a radio galaxy in the Virgo cluster, exhibits several unusual features which prompted a search for high energy X-radiation from it. Soft X-rays have been detected from the galaxy implying an X-ray luminosity of 10 to the 43rd ergs/sec. The X-ray datum, the optical emission from an unusual jet extending from the nucleus of the galaxy and the radio core emission can all be fitted to a single power-law spectrum characterized by a spectral index of -0.80. Polarization of the optical radiation from the jet indicates that the synchrotron mechanism is probably operative there. A balloon-borne experiment was performed in August, 1967 in an attempt to observe a high energy extrapolation of the radiation from M-87. The detector system is similar to that used previously by the Gamma-Ray Astronomy Group at Rice University. The central detector is a sodium iodide scintillator crystal (thallium activated) 5 cm thick with a sensitive area of 75 cm2 . An on-board 128 channel pulse-height analyzer responds to photons in the energy range from 27 keV to 555 keV, so that the differential energy spectrum may be measured. A large crystal surrounding the central crystal acts as an active collimator to produce a half-intensity, half-angle field of view of 12°. The detector mounting is of an equatorial type and uses the geomagnetic field as an azimuth reference. Data were obtained from the Virgo region, centered on M-87, for 63 minutes and from sky background regions for 84 minutes. A flux at the top of the earth's atmosphere of 8.2 ± 3.5 x 10 to the -3 photons - cm -2 - sec -1 was detected from the Virgo region in the energy range from 40 keV to 107 keV. Low upper limits were measured for energies greater than 107 keV and for the 511 keV annihilation line. Due to the large field of view of the detector, the source of the observed radiation could not unambiguously be determined although it is shown that the most probable source is M-87. The present measurement is consistent with a high energy extrapolation of the radio core source in M-87, although there is great need for a confirmation of this high energy X-ray source with a detector of increased angular resolution.
Low and medium energy gamma radiation from the Crab Nebula
(1975) Chambliss, Joe Preston; Haymes, Robert C.
The Crab Nebula was observed for 58 minutes in the .6 to 12 MeV energy range in the first successful flight of Gammascope VI. A continuum of radiation in the .6 to .6 MeV energy range was detected. Upper limits for the 1 to 12 MeV energy range were established. The sensitivity of the detector was established for the range of .6 to 12 MeV by comparison with other experiments. The data for this energy range is more detailed than that of previous experiments covering portions of this energy range. The emission of the Earth's atmosphere in the 1-12 MeV range combined with leakage of radiation in this range by the detector produced poor statistics in the 1 to 1-12 MeV energy range. A possible spectral feature is noticed in the 1 keV energy range. This possible feature is a weak peak of no more than one standard deviation above a curve fit of the data but is consistent with the "bump" at that energy in the spectrum of Peterson etal. (1968). The synchotron mechanism Is supported by the experiment's low energy data. A map of the source of background Is presented indicating that three minor sources of X-rays were 1n or near the field of view during background measurements. It is not thought that these faint sources caused significant contamination of the Crab data. The higher energy data could be accounted for by a source of MeV photons that could correspond to one of these three sources. Such a source is thought highly unlikely because it would imply that the source emitts predominantly from nuclear reactions and thus would be different from any previously known astrophysical objects. However, the most likely explanation of the poor statistics in evidence in the 1-12 MeV energy range is seen to be leakage of the detector to such high energy photons combined with the dominance of the Earth's atmosphere as an emitter of 1-12 MeV energy photons over celestial sources. The 1-12 MeV data is better fit by an extrapolation of lower energy data rather than the decreased spectral index appropriate to Baker et. al. (1973). A power law of the form [equation] was found to best fit the data of this experiment.
Low-energy gamma radiation from Cen. X-4
(1972) Johnson, Wiley Neil, 1945-; Haymes, Robert C.
In July of 1969 a new X-ray source was detected in the southern sky near the constellation Centaurus. This source, identified as Centaurus X-4, displayed a variable intensity in the energy range 3 to 12 keV which at its maximum was more than twice as great as that from Sco X-l, the brightest discrete extrasolar X-ray source in the sky. A balloon-borne gamma-ray detector was launched from Parana, Argentina, on November 26, 1969, in an effort to measure the high-energy spectrum from this transient X-ray source. Due to partial failure of the instrument midway through the flight, the full sensitivity of the actively collimated Nal(Tl) detector was not achieved. This complication, coupled with the apparent time variation of the source, allowed only upper limits to be placed on the high-energy flux from this object in the range 80 keV to 2 MeV. As a result of this flight, the first high-altitude balloon research from Argentina, comparisons of Cen X-4 with other nova-like X-ray sources may be made. In addition, useful information on the response of actively collimated scintillation detectors to gamma radiation under varied conditions may he determined. The atmospheric gamma-ray background over Argentina, as well as the facilities avail able in Parana, proved to be ideal for southern hemisphere balloon research. In 1970 and 1971 two more successful expeditions to Argentina were made which produced valuable new data on various southern hemisphere celestial X-ray objects.
Lunar neutron simulation
(1969) Voss, John Mark; Haymes, Robert C.
Cosmic rays interacting with the surface nuclei of the moon produce neutrons, some of which emerge from the surface. This emergent albedo will depend strongly on the composition of the surface, especially concentrations of hydrogen. A measurement of the ratio of the slow to fast neutron counting rates will serve as an index of the hydrogen content in the lunar surface. A feasibility study is made on the effect on the slow and fast neutron counting rates due to increases in water content. A lunar neutron simulator, consisting of neutron detectors and a fast neutron source, measures the effect of water concentration using a basaltic material with a sane mixture used for comparison. Data obtained using a 0.3% water content in basalt indicate an increase of about 4% over the 0.2% water content level in the slow neutron counting rates. The fast counting rates were not measurably changed by this increase in water content. We conclude that the experiment as proposed is sufficiently sensitive to detect a variation in water concentration of 0.1% (by weight).
Measurement of the perseus cluster gamma-ray spectrum
(1976) Walraven, David; Haymes, Robert C.
On May 15, 1973 a balloon-borne gamma-ray telescope belonging to the Rice University Gamma-Ray Astronomy Group was launched from Palestine, Texas. Both source and background segment counting rates were measured over the 56 keV to 12.4 MeV energy range from 118 CDT to 1313 CDT. In each of the source segments, the detector was pointed at the Seyfert galaxy NGC 1275 in the Perseus cluster. However the entire cluster was within the field of view of the detector during the observations of this galaxy. The experiment was carried out at altitudes corresponding to a residual atmospheric depth of approximately 4 gm/cm. The detector consisted of a central crystal of Nal (Tl) which was actively collimated by a shield of the same material. The instrument had a beam width of 13° full width half maximum. The results obtained show that NGC 1275 in particular and the Perseus cluster in general do not constitute a detectable gamma-ray source. A series of upper limits to the flux in the 56 keV to 12.4 MeV energy range was computed.
Optical emission measurements during beam plasma interactions
(1985) Mantjoukis, George A.; Haymes, Robert C.; Bernstein, William; Wolf, Richard A.; Freeman, John W.
3914 A light intensity profiles were measured with a geometrically scanning photometer during interations of an energetic electron beam with a weakly ionized plasma. Mass spectrometric measurements indicated N^ to be the dominant neutral constituent. The experiments were carried in the very large SESL vacuum facility at the Johnson Space Center which allowed an interaction length of ~ 2 m. Variable current (1-7 ma) and variable energy (5-16 V) beams were injected over a large pitch angle range ( to ~75°) for several applied magnetic field strengths (.89, 1.52, and 2.22 Gauss) over the pressure range .6-3. x 1“® Torr to allow study of the light intensity dependence on the experiment parameters. The photometer measurements were made at a fixed axial position (midway between the electron gun and the collector); overall measurements of the complete beam emission patterns (total light) were made with several low light level TV cameras. The measured 3914 Â intensity profile gives the radial distribution of the relative ionization rate while its integral gives the (relative) total ionization rate independent of geometry. The following important results were obtained 1) At low beam currents (1^ < Ic, the beam current required for BPD ignition) the relative light intensity and beam geometric configuration were consistent with single particle behavior. 2) For I], > Ic (BPD) the geometry of the illuminated region changes drastically and the 3914 total intensity increases by factors of 1-3 indicating the presence of new ionization sources (suprathermal electrons). (a) For beam injection parallel to the magnetic field (zero pitch angle), the radial width (FWHM) of the illuminated region is approximately twice the maximum (anti-node) width for preBPD conditions; it scales approximately as 1/B and E1/2. (b) For non-zero pitch angle injection, the full width of the illuminated region is approximately equal to the diameter of the single particle helix; at large pitch angle injection, the BPD shows significant limb brightening indicating a somewhat hollow configuation. Significant ionization outside the helical dimensions is not observed. (c) For all conditions the total 3914 light intensity during BPD can be fitted to the parabolic relationship QT ~ K Ic1/2 (Ib - Ic)1/2 Thus the total ionization rate increases nonlinearly with I (the nominal power supply return current) and remains proportional to the square root of the threshold current during BPD although I|j » Ic. The consistency of this scaling over the large injection pitch angle range implies that the important plasma processes are Independent of injection pitch angle. (d) The maximum efficiency of energy transfer from the beam to the plasma (as measured by the total ionization rate) occurs when I|j 2 Ic. Typical estimates of this maximum efficiency range from 3-12Z for the 2 meter path length.
The beam-plasma discharge revisited (a new theoretical model)
(1983) Llobet Ribeiro, Xavier (b. 1963); Bernstein, William; Haymes, Robert C.; Michel, F. Curtis
Many features related to the ignition of the Beam-Plasma Discharge can be explained with the requirement of a critical density, which in case of a self-made plasma translates into a critical current. However, other characteristics indicate that this requirement which arises from the geometry, is a necessary but not sufficient condition. In this thesis it is shown that a second requirement must exist, also taking the form of a minimum current. With these two constraints most of the ignition-related features can be explained. A preliminary analysis of the discharge showing how the second requirement arises is presented.
The design and development of Prometheus 1: Rice University's coded aperture faint object gamma ray telescope
(1988) Fitch, John E.; Haymes, Robert C.
Rice University has been developing a gamma ray telescope to be used for the detection of spectral gamma ray lines from Type I supernovae within one megaparsec in the energy range from 100 keV to 10 MeV. The detector is an actively shielded array of 121 0.5$\sp{\prime\prime}$ x 0.5$\sp{\prime\prime}$ x 2.0$\sp{\prime\prime}$ NaI(Tl) crystals, each optically separated from the remainder of the array independently viewed. Inflight calibration of the 121 individual PMTs will be handled by an on board computer in conjunction with LEDs attached to the crystals. The active shield is constructed of individual blocks viewed separately by one or more photomultiplier tubes acting in anticoincidence with the central detector, providing excellent isolation from non-source gamma ray detections. The telescope uses a coded aperture approach yielding an overall geometrical spatial resolution of 2.6$\sp\circ$ x 2.6$\sp\circ$ FWHM. The energy resolution of the detector is expected to be 12% FWHM at 0.661 MeV. Simulations of the detector/shield assembly yield a projected sensitivity of 1 $\times$ 10$\sp{-4}$ photons cm$\sp{-2}$ sec$\sp{-1}$ for a 3 sigma detection at 1 MeV. (Abstract shortened with permission of author.)
The design of a coded aperture mask for Prometheus I
(1995) Wooten, James Gregory; Haymes, Robert C.
A coded aperture mask has been designed for Prometheus I, a Rice University gamma-ray telescope sensitive to energies ranging from 0.03 MeV to 6.5 MeV. The mask will allow Prometheus I to record images at those energies. If it is successful, these will be the first astronomical MeV gamma ray images ever recorded. To create the mask, first a basic 9 x 7 uniformly redundant array was generated using the m-sequences method described by E. C. Fenimore (1983). A two by two mosaic of that pattern produced the final 18 x 14 array. The mask is passive rather than active; the opaque sections are two inches thick and made of tungsten. The distance from the center of one square to the center of an adjacent one is 5/8 inch, which is equal to the distance from the center of one detector element to a neighboring one. With 128 of the 252 mask elements transparent, the mask will have an open fraction of 50.7%. When it is installed on Prometheus I, the mask will be located 60 inches from the detector, giving the instrument an angular resolution of 28.6 arc minutes. Its fully coded field of view will be 5.4$\sp\circ$ and its partially coded field of view will be 16$\sp\circ$. The first flight of Prometheus I is scheduled for summer 1994.
The design, construction, and performance of a balloon-borne gamma-ray telescope
(1972) Harnden, F. R. (Frank Roderic), 1945-; Haymes, Robert C.
This thesis describes a new balloon-borne system which was designed, constructed, and flown with the purpose of increasing the sensitivity of gamma-ray observations. In an attempt to reduce the background counting rate, the detector employed a previously-untried composite shield of the following materials and depths of materials (in units of gm cm-2): plastic scintillator - 4, LiF epoxy - 2, lead - 43, sodium iodide - 5, and aluminum - 7. Both the plastic and the Nal (Tl) scintillators were used in an active anticoincidence system; the plastic detects charged particles which may initiate cascades in the lead collimator, and the sodium iodide detects low energy photons which emerge from the inner surface of the lead. The LiF epoxy is a slow neutron absorber, and the aluminum was used as the supporting structure. The new telescope system is capable of remaining aloft for ~40 hours and, through radio-control, of observing several celestial objects during a given flight. The detector proved to be a very effective collimator of gamma rays and exhibited a low counting rate at sea level. The high counting rate that was encountered at balloon altitudes, though unexpected, can, however, be explained in terms of Compton and neutron interactions in the central crystal which was composed of CsI (Na).
The gamma-ray background at balloon altitudes
(1977) Djuth, Frank T. (Frank Thomas); Haymes, Robert C.
On April 2, 1974, a balloon-borne observation of the gamma-ray background at 4 mbar pressure was conducted in the energy band .3-12.27 MeV. The measurements were made at a geomagnetic cutoff rigidity of 11.9 GV. Cosmicray-induced activation of the Nal(Tl) detector was discovered to be a major source of the background count rate in the energy region .15-2.5 MeV. The cosmic diffuse gamma radiation makes a sizable contribution to the background count rate in the low energy region .3 - .15 MeV. At these energies lower limits for the diffuse gamma-ray flux were determined. A search of the detector data for evidence of cosmic gamma-ray bursts proved inconclusive. The conclusions drawn from the background study can be utilized in order to design a very low background gammaray detector for celestial observations.

Browsing by Author "Haymes, Robert C."

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