High Energy Gamma Emission Research Articles

Very high energy gamma astronomy at the South Pole

Abstract The Air Cherenkov Technique (ACT) is a very important tool to extend our present knowledge on very high energy (VHE) gamma emission from compact astrophysical sources. To overcome the intrinsic limitations of this technique, we are testing the possibility of installing an ACT Telescope at the South Pole. This site is ideal for several reasons: The long polar night permits almost continuous ovservation of a source (up to 400 hours per month and 1700 hours per year). The circumpolarity of the sky simplifies data analysis. The region of the sky is particularly rich in candidate sources. To test the effectiveness of the site, we installed a prototype telescope in the austral summer of 1989–1990. The prototype started to operate in May 1990.

High-energy gamma emission in heavy-ion collisions at 9-14 MeV/nucleon.

We have measured the cross sections for high-energy photon production in $^{12,13}\mathrm{C}$${+}^{92,100}$Mo reactions at incident beam energies of 9--14 MeV/nucleon. The bombarding energy dependence, angular distribution, and projectile-target mass dependence of the photon yields at high energy, ${\mathit{E}}_{\ensuremath{\gamma}}$\ensuremath{\ge}30 MeV, have been examined. Our measurements are consistent with production of these photons via nucleon-nucleon bremsstrahlung, the production mechanism dominant in heavy-ion collisions for E/A\ensuremath{\ge}20 MeV/nucleon.

Gamma densitometry for the measurement of skeletal density

A method is described for the measurement of the density of calcium carbonate materials from the attenuation of a narrow, collimated beam of gamma photons. For the measurement of density for slices, approximately 0.5 to 1.0 cm thick, from the skeletons of reef building corals, the optimum beam energy is 30–34 keV; and measurement is practical from approximately 22 to 100 keV. The potential utilities of five commercially available isotopic sources (109Cd,125I,253Gd,210Pb and241Am) are evaluated. Methods and results are presented for gamma densitometry using210Pb and241Am. The210Pb point source had its principal gamma emission at 46.5 keV. Bremsstrahlung and high energy (800 keV) gamma emissions associated with the210Pb decay grand-daughter were detected, and procedures were developed to accommodate the contribution of these emissions to the overall count rate. The attenuation of count rate by aluminium and aragonite absorbers closely followed simple theoretical considerations provided that narrow energy window settings were used at the radiation monitor. These theoretical considerations take account of the density of the material absorbing the radiation, and hence the density could be determined from the attenuation of the gamma beam. Increased accuracy was achieved by the use of241Am and high speed counting equipment.241Am has its principal gamma emission at 59.6 keV. The attenuation of this gamma beam follows simple theoretical considerations for targets with mass thicknesses from 0 to 6 g cm-2. Aragonite from the shell of a giant clam was found to have slightly different properties in the absorption of gamma photons to aragonite from a coral skeleton. The differences were small but statistically significant.

A primate model for the study of the interaction of 111In-labeled baboon platelets with Dacron arterial prostheses.

This paper presents early experience with a primate model for the noninvasive study of the interaction of circulating platelets with healing arterial prostheses. These experiments demonstrate that baboon platelets can be isolated and labeled with 111Indium with high efficiency using a sterile technique. Platelets subjected to this process have a linear life span similar to that of 51Chromium-labeled baboon platelets. The high energy gamma emission of 111Indium oxine allows for external scanning using a standard gamma camera. The small quantity of 111Indium-labeled platelets in the region of the graft can be discriminated from the surrounding blood vessel and quantitated by gamma camera imaging and computer analysis. There was a significant increase in the platelet deposition on prosthetic surfaces observed 5--48 hours after graft implantation and injection of 111Indium-labeled autologous platelets.

Measurement of absorbed dose by the third space satellite vehicle

GAMMA-400 is an international project of a high apogee orbital astrophysical observatory for studying the characteristics of high-energy gamma-emission, electrons/positrons and light nuclei fluxes. The energy range for γ-rays and electrons/positrons registration in the main aperture is from ∼0.1 GeV to ∼3.0 TeV. Also, this aperture allows high energy light nuclei fluxes characteristics investigation. Moreover, special aperture configuration allows registering of gamma-quanta, electrons (positrons) and light nuclei from the lateral directions too.The spacecraft GAMMA-400 orbit will be located in the Earth's magnetosphere and will pass front shock wave from magnetosphere interaction with the solar wind, turbulent-transition region, magnetopause and so on. During the satellite's movement through various Earth's magnetosphere regions its anticoincidence detectors will register high intensity fluxes of low energy charged particles captured by the magnetic field. The working area sections of GAMMA-400 detector systems used as anticoincidence shield are about 1 m2 each. The high intensity low energy charged particles flux influence on anticoincidence detectors should be taken into account during particle identification.This article presents a comparison between Earth's magnetosphere theoretical model according to SPENVIIS package and real data measured by detectors onboard THEMIS series satellites. The differences between these two datasets indicate that the calculated data are not sufficient to make short time predictions of variations of magnetic induction in the outer magnetosphere. A special trigger marker flag will be produced by GAMMA-400 counting and triggers signals formation system accordingly to the data of two onboard magnetometers. This flag's presence leads to special algorithms execution start, putting the plastic detectors into a dedicated working mode taking into account possible high count rates of external detector layers.