High-resolution Gamma-ray Spectrometer Research Articles

Gamma-ray observations of Co-56 in SN 1987A

During observations of SN 1987A 286 days after the supernova explosion using a JPL high-resolution gamma-ray spectrometer, a line feature was found in the net supernova spectrum at an energy of 1240.8 + or - 1.7 keV, with an intrinsic width of 8.2 + or - 3.4 keV FWHM, and a net flux of 0.0021 + or - 0.0007 photons/sq cm per s. This feature is interpreted as the 1238 keV line from the decay of Co-56 in the supernova remnant. The blueshift and intrinsic broadening of the 1238 keV line are consistent with models incorporating mixing of the radioactive cobalt in the expanding eject.

On some response characteristics of high-resolution gamma-ray spectrometers at high count rates

It has been recognized that the intensity of a high-energy peak in a gamma-ray spectrum measured by means of a multichannel pulse height analyzer, coupled to a Wilkinson type analog-to-digital converter (ADC) and through the necessary electronics to a Ge(Li) detector, is a function of the threshold of the lower level discriminator (LLD) in the ADC. The LLD effect has been observed for several conventional analyzers and various total count rates up to 6·104 cps. The results of the measurements carried out both in the live time mode and in the clock time mode are presented and the systematic errors which can be introduced by the LLD effect are discussed.

The gamma-ray spectrum of the Galactic center region

The Galactic center region was observed with the HEAO 3 High Resolution Gamma-Ray Spectrometer during the fall of 1979 and the spring of 1980. Between these epochs there was observed (1) a statistically significant decrease in the high-energy (511 keV to about 3 MeV) luminosity, (2) a decrease in the positron annihilation line intensity, reported previousy, and (3) a low positronium annihilation fraction f = 0.38 + or 0.19 during the fall of 1979. If positrons are generated by photon-photon collisions of high-energy photons, then the absence of a detected flux above 511 keV in the spring of 1980 may indicate a time delay between positron production and annihilation. 26 references.

In situ calibration of a high-resolution gamma-ray borehole sonde for assaying uranium-bearing sandstone deposits

A method is presented for assaying radioactive sandstone deposits in situ by using a high-resolution borehole gamma-ray spectrometer. Gamma-ray photopeaks from the same spectrum acquired to analyze a sample are used to characterize gamma-ray attenuation properties, from which a calibration function is determined. Assay results are independent of differences between properties of field samples and those of laboratory or test-hole standards generally used to calibrate a borehole sonde. This assaying technique is also independent of the state of radioactive disequilibrium that usually exists in nature among members of the natural-decay chains.

Analysis of nickel ores by radiative neutron capture

The possibilities were studied of the analytical application of high energy primary gamma rays from the radiative capture of slow neutrons (the NCGA-HE method) to a rapid nondestructive determination of technologically important elements (Ni, Cr, Fe, Si) in large volumes of nickel ores. Neutron source was a241Am−Be (10 Ci) isotopic source, prompt gamma radiation was detected by high resolution gamma-ray spectrometer. Detection limit for nickel was 0.2% for chromium 0.25%.

Crystal growth and applications of mercuric iodide

This paper reports recent progress in the use of HgI2 in high energy resolution X-ray and gamma ray spectrometers which operate at room temperature, and reviews the present state of the art of HgI2 technology. Purification of starting materials, methods of crystal growth, detector fabrication, and characterization methods used for HgI2 are described, and some applications of HgI2 detectors to various device systems are given.

The states of Cygnus X-1

view Abstract Citations (50) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The states of Cygnus X-1. Ling, J. C. ; Mahoney, W. A. ; Wheaton, W. A. ; Jacobson, A. S. ; Kaluzienski, L. Abstract HEAO 3 High Resolution Gamma-Ray Spectrometer observations of Cygnus X-1 in the 48-300 keV range, along with correlated 3-6 keV Ariel 5 data, have led to the identification of a new state for this object with low flux in both the soft and hard X-ray regions. This is followed by a slow increase in the hard X-ray flux to the normal low state of the source, characterized by a low intensity soft X-ray emission and a high intensity hard X-ray emission. The new 'superlow' state is interpreted in terms of the Compton model, where the X-ray emission arises from the scattering of low energy photons and one-billion K hot electrons. The superlow state may be seen as one extreme of a continuum of low state behavior, given that Compton cooling should begin to quench the hot electrons at higher soft X-ray fluxes, giving rise to the softer X-ray spectrum and to the anticorrelation in changes in the soft and hard X-ray fluxes. Publication: The Astrophysical Journal Pub Date: December 1983 DOI: 10.1086/161534 Bibcode: 1983ApJ...275..307L Keywords: Cygnus Constellation; Gamma Ray Astronomy; X Ray Sources; Compton Effect; Heao 3; X Ray Spectra; Astrophysics full text sources ADS | data products SIMBAD (1)

In situ capture gamma-ray analysis of coal in an oversize borehole

In situ capture gamma-ray analysis in a coal seam using a high resolution gamma-ray spectrometer in a close-fitting borehole has been reported previously. In order to check the accuracy of the method under adverse conditions, similar measurements were made by means of a small-diameter sonde in an oversize borehole in the Pittsburgh seam, Greene County, Pennsylvania. The hole was 5 times the diameter of the sonde, a ratio that substantially increased the contribution of water (hydrogen) to the total spectral count and reduced the size of the sample measured by the detector. The total natural count, the 40K,count, and the intensities of capture gamma rays from Si, Ca, H, and Al were determined as a function of depth above, through, and below the coal seam. From these logs, the depth and width of the coal seam and its partings were determined. Spectra were accumulated in the seam for 1 h periods by using neutron sources of different strengths. From the spectra obtained by means of several 252Cf neutron sources of different sizes, the ultimate elemental analysis and ash content were determined. The results were not as good as those obtained previously in a close-fitting borehole. However, the results did improve with successively larger source-to-detector distances, i.e.,as the count contribution due to hydrogen in the water decreased. It was concluded that in situ borehole analyses should be made in relatively close-fitting boreholes.

Computer simulation study of multiple germanium gamma-ray sensor arrays

Design studies of large high resolution gamma-ray spectrometer systems employing multiple sensors are greatly facilitated by the use of computer simulation techniques. A study has been made by interfacing a detector geometry code with the EGS-3 version of the Stanford Linear Accelerator Center Monte-Carlo Code which has been modified to run on our VAX computer. The detector responses have been simulated for input photons with energies between 0.1 and 10 MeV. Examples are given to illustrate the performance of complex sensor arrays with different configurations of the anticoincidence system. Of particular interest is a design composed of an array of 7 detector elements each consisting of a thin planar Ge (1 cm thick) detector mounted in front of and in tandem with a large coaxial Ge detector.

Gamma-ray and optical observations of the 1979 November 8 solar flare

The solar flare on 1979 November 8 11h 21m 28s UT was observed by the Tel Aviv telescope of the Big Bear Solar Observatory and the High Resolution Gamma-Ray Spectrometer on the High Energy Astronomy Observatory HEAO 3. Photographs in alpha hydrogen show the development of the flare and a subsequent Moreton wave. Although the flare was not detected with the high spectral resolution germanium detectors, the HEAO C-1 CsI shield detected a statistically significant signal above 80 keV, from 420 to 585 keV, and above 3.8 MeV. The temporal structure of microwave, optical, X-ray, and gamma-ray emission is consistent to within about 1 s with a simultaneous flare response at all energies. There is no evidence for either second-stage acceleration of charged particles (Bai and Ramaty, 1979) or a delay between gamma-ray and X-ray continuum emission due to energy-dependent electron energy loss times (Bai and Ramaty).

POSITRON ANNIHILATION RADIATION FROM THE GALACTIC CENTER REGION*

Measurements of 0.511 MeV radiation from the vicinity of the galactic center performed by the high resolution gamma ray spectrometer aboard the HEAO 3 spacecraft are discussed. The spectrometer is described and an exploded view of it exhibited, and scans in the 50-244 keV region as well as 0.511 MeV are shown. The intensity from the Crab nebula remained constant while that of the Cygnus source increased considerably, and there was a decrease in the radiation from the vicinity of the galactic center. The flux emanating from the center implies an annihilation rate of 10 to the 43rd per second. The apparent time variation and the spatial extent observed tend to limit the source to a single object and the annihilation region to a size less than about one light year.

An in-Situ Neutron Activation Analysis System for Assaying Metal Ores

The topic of this paper is a method of in-situ neutron activation using high resolution gamma ray spectroscopy and a californium 252 neutron source. The paper is divided into three parts: a description of the authors' high resolution gamma ray spectrometer probe, results to date using a Cf-252 source and applications made possible by a small accelerator. The basic tool of measurement is the PGT probe - a high resolution gamma ray spectrometer that incorporates an intrinsic germanium detector and a computerized multichannel analyzer. The system is capable of operating at data rates as high as 100,000 counts per second and can record 4000-channel gamma ray spectra in-situ. The probe is 2.5 inches diameter and 12 feet long. All data are transmitted digitally over standard 4-H-O armored cable to a computer-based logging system. Complete analysis can be performed on site.

The HEAO 3 gamma-ray spectrometer

The Third High Energy Astronomy Observatory (HEAO 3), successfully launched into low earth orbit on 20 September 1979, carries a large high resolution gamma-ray spectrometer designed for cosmic nuclear spectroscopy. This Gamma-Ray Spectrometer (the HEAO C-1 experiment) consists of a cluster of four coaxial high purity germanium detectors, each with a volume of approximately 100 cm 3. Surrounding the germanium detectors is a 6.6 cm thick CsI shield operating in active anticoincidence with the central detectors and defining a field of view of about 30° fwhm. An initial energy resolution of 3 keV fwhm at 1.46 MeV was achieved for each detector. All valid events in the germanium detectors are individually analyzed by an 8192 channel pulse area analyzer and transmitted at a maximum rate of 15.6 events/s for each detector. During a 6 month mission, the experiment will perform a complete sky survey for narrow cosmic gamma-ray line emission to the sensitivity level of about 10 −4 photons/cm 2 s over an operating energy range of 0.05–10 MeV.

A possible line feature at 73 keV from the Crab Nebula

Evidence is reported for a possible line feature at 73 keV from the Crab Nebula. The experiment was conducted with a balloon-borne high-resolution gamma-ray spectrometer on June 10, 1974, over Palestine, Texas. The intensity and the width of the line derived from the fitting of these data are approximately 0.0038 photon per (sq cm-sec) and less than 4.9 keV FWHM, respectively. The line is superposed on a power-law continuum of 11.2 E to the -2.16 photons per (sq cm-keV) in the energy range from 53 to 300 keV, which is consistent with other measurements of the Crab Nebula spectrum.

Measurement of 0.511-Mev gamma rays with a balloon-borne Ge(Li) spectrometer

A collimated high-resolution gamma ray spectrometer was flown on a balloon over Palestine, Texas, on June 10, 1974, to obtain measurements of the terrestrial and extraterrestrial 0.511-MeV gamma rays. The spectrometer consists of four 40-cu-cm Ge(Li) crystals operating in the energy range 0.06-10 MeV; this cluster of detectors is surrounded by a CsI(Na) anticoincidence shield. This system is used primarily to allow measurements of the two escape peaks associated with high-energy gamma ray lines. It also allows a measurement of the background component of the 0.511-MeV flux produced by beta(+) decays in materials inside the CsI(Na) shield. It is shown that the measurements of the atmospheric fluxes are consistent with earlier results after allowance is made for an additional component of the background due to beta(+) decays produced by neutron- and proton-initiated interactions with materials in and near the detector. Results of the extraterrestrial flux require an extensive detailed analysis of the time-varying background because of activation buildup and balloon spatial drifts.

A balloon-borne Ge(Li) spectrometer for gamma-ray astronomy

On June 10, 1974, a new high-resolution gamma ray spectrometer operating in the energy range of 0.05 to 10 MeV was succesfully balloon-flight tested. This system uses four 40 cm 3 Ge(Li) crystals in a single cryostat as prime sensors. A 6.35 cm thick CsI (Na) shield provides background rejection and collimation, defining a solid angle of 0.095 sr. Cooling is provided by a liquid-nitrogen dewar. The system was highly stable with spectral resolution of better than 2.5 keV at 1 MeV for the flight duration. The background total count rate was about 20 counts/s. Numerous lines were observed, most of which originated from secondary neutron interactions in the spectrometer. The sensitivity of the system to line emissions originating in cosmic point sources is 10 −4-10 −3 photons/cm 2 s over the energy range.

A Pulse Area Analyzer (PAA) for High Resolution Gamma Ray Spectroscopy

A different type multichannel analyzer has been designed, built, and tested for the High Spectral Resolution Gamma Ray Spectrometer to be flown on the HEAO spacecraft. This system offers superior dynamic range, energy conversion, and stability for large Ge(Li) detectors. Theoretical and measured results from an 8192 channel analyzer are presented.

A Stable ADC for Use with Ge(Li) Detectors

A new type of ADC is being developed to satisfy the requirements of the HEAO high spectral resolution gamma ray spectrometer. This 13 bit design utilizes a double successive approximation technique that overcomes the usual differential linearity problem. Stability of a few ppm/°C, differential linearity of 2% and integral linearity of 0.05% have been demonstrated.

A Satellite-Borne High Resolution Ge(Li) Gamia-Ray Spectrometer System Part 2: Description of the Electronic, Data Handling and Auxiliary Sensor Systems

The first high-resolution gamma-ray spectrometer system employing Ge(Li) detectors has been designed and successfully flown on an earth-orbiting satellite. The complete scientific payload consists of two large-volume Ge(Li) spectrometers for the measurements of photons in the 40 keV - 2.8 MeV energy range with 4096-channel energy resolution and six auxiliary sensors for measuring the location, intensity and energy spectra of charged-particle backgrounds in earth orbit. To achieve and maintain an overall systems resolution of 3.5-4 keV in photon energy, a low-noise bias power supply and charge sensitive preamplifier-amplifier combination were designed for the germanium detectors. Amplified signals are analyzed in a 4096-channel analyzer of the linear-ramp type, with an integral and differential linearity of ± 0.2 percent and ± 1.0 percent, respectively. Individual pulse-height addresses are sampled at a rate of 1625 addresses/sec and time tagged together with absolute count-rate data by the experiment digital-data-handling system and then stored on magnetic tape recorders. A detailed description of the gamma-ray spectrometer electronic system including the method of collecting and analysis of flight data is given.

A High Stability Pulser and Charge Injection Capacitor for Servostabilization of High Resolution Gamma Ray Spectrometers

This paper discusses the design of a reference pulser and air-dielectric capacitor for use in stabilization of high-resolution gamma-ray spectrometers. Additionally, the adverse effects of coaxial cable series resistance and detector coupling capacitor instability are considered. The reference pulser circuitry is completely transistorized and features a highly-stable dual-transistor pulse generation network. The temperature stability of the pulser output is ? ±5 PPM/°C from 10°C to 50°C. The long-term stability is approximately ±. 02 channels per day. The air-dielectric capacitor is a three-terminal device constructed of Kovar-steel and glass. The rigid glass-metal seal insures long-term stability. The capacitance temperature coefficient from liquid nitrogen to room temperature is approximately + 10 ppM/° C. Data are presented which shows that the series resistance of a coaxial cable will cause significant pulse drift when terminated and essentially no drift if left unterminated. An analysis also indicates that drift in a detector coupling capacitor can produce uncorrectable spectral drift.