Low-energy Gamma-ray Detector Research Articles

A compact fast low energy gamma ray detector insensitive to high magnetic field

One step of the IRFU GBAR project aims at producing a dense low temperature positronium gaz. In order to characterize the positronium cloud we have tested a detector able to measure gamma energies in the 511 keV domain or lower, which is compact, fast, and insensitive to high magnetic fields. It uses the PreLude 420 scintillating crystal from Saint Gobain and large area Hamamatsu avalanche photodiodes. The performances of the system are presented. It could be used for other purposes.

Study of silicon PIN diode responses to low energy gamma-rays

Low energy gamma-ray detectors play an important role in diagnosis in nuclear medicine, in detection of gamma-ray bursts for gravitational wave research and in detection of underground nuclear tests. The silicon positive-intrinsic-negative (PIN) diode detector is useful for detection of low energy gamma radiation without using a scintillator because it generates a high signal in a small active volume, has a fast response time and has good intrinsic energy resolution. We measured the detector responses, energy resolutions and signal-to-noise ratios for various gamma energies by using manufactured silicon PIN diode and photodiodes. Radioactive gamma sources, 241Am, 133Ba, and 57Co, providing gamma-rays with energies between 14.4 keV and 136.5 keV are used for the measurements. The energy resolution and the signal-to-noise ratio for 14.4 keV gamma-ray are measured to be 17.1 % and 12.8 for a 500 μm thick silicon diode. The energy resolutions measured at the FWHM for 59.5 keV and 122.1 keV gamma-rays by using the silicon diode are better by up to two times compared to those obtained using the NaI:Tl or the BGO scintillator with a photomultiplier tube. The dependence of detection speeds of the signals on the diode’s thickness is also measured.

Measurement of peak and total efficiencies of low-energy gamma-ray detectors with sources emitting photons in cascade

A method for measurement of peak and total efficiencies for point sources measured on low-energy gamma-ray detectors is presented. The efficiencies are measured with radionuclides emitting gamma-rays in a two-step cascade or in a crossover transition. One of the photons emitted in the cascade must have an energy which is much lower than the other in order to attain stronger attenuation as compared to the higher energy photon. The method is illustrated by measurements of the efficiencies with 179Ta and 57Co.

All-sky X-ray and Gamma-ray Astronomy Monitor (AXGAM)

A wide field-of-view, arcsecond imaging, high energy resolution X-ray and low energy gamma ray detector is proposed for a future space mission. It is specifically designed to detect and find counterparts at other wavelengths for /spl gamma/-ray bursts (GRBs). Detection of GRBs requires wide field-of-view (/spl pi/ to 2/spl pi/ field-of-view) and high sensitivity. This will be achieved by using high quantum efficiency CdZnTe pixel detectors with a low energy threshold (few keV) to observe the larger flux levels at lower energies, and large effective area (625 to 1000 cm) per coded aperture imaging module. Counterpart searches can only be done with ultra-high angular resolution detectors (10 to 30 FWHM) which gives 1 to 5 position determination especially for strong GRBs. A few arcsecond size error box is expected to contain at most one object observed at another wavelength. This will be achieved by using ultra-high spatial resolution pixel detectors (50/spl times/50 to 100/spl times/100 /spl mu/m) and a similar resolution coded aperture to achieve the required angular resolution. The low energy range may provide important new information on GRBs and the high energy resolution is expected to help in the observation and identification of emission and absorption lines in the GRB spectrum. The effective energy range is planned to be 2 to 200 keV which is exceptionally wide for such a detector. The major scientific goals of the proposed mission in addition to continuously monitoring GRBs, is to observe AGN, transient phenomena, isolated and binary pulsars, and solar flares. A space-deployed AXGAM detector is expected to observe a few hundred GRBs per year.

Procedure for the determination of 210Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry

A procedure is described for the determination of 210Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry of the 46.5 keV gamma ray of 210Pb. The procedure involves microwave dissolution, removal of interfering Fe by extraction with thiocyanate in isobutyl methyl ketone and extraction of Pb as the diethyldithiocarbamate (DDTC) complex into CHCl3. After evaporation of the CHCl3, the DDTC complex is decomposed and Pb is precipitated as PbCrO4. The chemical yield is determined gravimetrically and the precipitate is counted on a low-energy gamma-ray detector. Experiments proved the linearity between the 210Pb counting result for PbCrO4 masses in the range 15–100 mg. For materials with levels of approximately 500 Bq kg–1, 10 g of material are processed and the PbCrO4 preparate is counted for 24 h. Materials with a 210Pb content lower than 75 Bq kg–1 demand larger sample masses and/or longer counting times. The limit of determination is 75 Bq kg–1. A relative standard deviation of 2.5–5.0% at the 500 Bq kg–1 level for replicate 210Pb determinations in phosphate ore and gypsum was achieved. An inaccuracy of the method of less than 10% was derived from results for selected materials, that were also analysed by direct gamma-ray spectrometry.

High-energy solar capabilities of approved space missions

Several instruments on approved space missions will provide coverage of energetic solar flare activity during the next solar maximum. However, only Japan's SOLAR-A is dedicated to observations of solar activity. These planned experiments will provide significant improvements in detection sensitivity for gamma rays and neutrons, generally using similar detection techniques to those employed previously. Improvements in the temporal resolution of energetic flare phenomena will also be realized, but with generally sporadic solar coverage. Important capabilities critically required for advancing our understanding of the solar flare phenomenon, such as dedicated high-resolution gamma-ray spectroscopy, imaging hard X-ray and low-energy gamma-ray detectors, polarimeters, and dedicated high-efficiency neutron detectors, are not included on any of the approved missions.