ISSN:0094-243X    

DOI:10.1063/1.40892

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Future observations of cosmic sources of gamma‐ray lines will require instruments with sensitivities of the order of 10−6photons/cm2‐s. To achieve this sensitivity, external background can be reduced by placing the Ge detector array inside a thick active shield, but the internal background produced by beta decay in the detector must be rejected by the Ge detector itself. In a colloboration between the High Energy Astrophysics Group at JPL and the Semiconductor Spectrometer Team at Lawrence Berkeley Laboratory (LBL), externally segmented coaxial detectors have been fabricated by dividing the outer electrode into five segments. The segmented detector is operated in a multi‐segment mode to reject internal beta activity by requiring that events interact in two or more segments of the detector to be recorded. In this way, approximately 90% of the beta decays can be rejected, while the efficiency for detecting gamma rays remains high. To verify the operation of the first externally segmented detector, the full‐energy‐peak (FEP) efficiency was measured in this multi‐segment mode as a function of the incident gamma‐ray energy and of the discriminator threshold of the segments. To evaluate the the beta rejection efficiency, the detector was irradiated with neutrons to produce75Ge (t1/2=82.78 min) from neutron capture by74Ge(36.5% of natural Ge) in the detector itself.The beta activation spectra of the detector were then recorded by self counting in a series of measurements. Calculations with the Monte Carlo code ACCEPT were made of the gamma‐ray FEP efficiency and of the beta rejection efficiency of the segmented detector. Thre was good agreement with the laboratory measurements, indicating that the code can be applied with confidence to model the response of more complicated detector configurations and environments.

ISSN:0094-243X    

DOI:10.1063/1.40893

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The encapulation of germanium detectors has been a long sought after goal. We have begun to develop encapsulation technology that should significantly improve the viability of germanium gamma‐ray detectors for a number of important applications. A specialized vacuum chamber has been constructed in which the detector and the encapsulating module are processed in high vacuum. Very high vacuum conductance is achieved within the valveless encapsulating module. The detector module is then sealed without breaking the chamber vacuum. The details of the vacuum chamber, valveless module, processing, and sealing method are presented in the paper.

ISSN:0094-243X    

DOI:10.1063/1.40954

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The dominant background source for germanium gamma ray detector spectrometers used for some astrophysics observations is internal &bgr; decay. Externally segmented germanium gamma ray coaxial detectors can identify &bgr; decay by localizing the event. Energetic gamma rays interact in the germanium detector by multiple Compton interactions while &bgr; decay is a local process. In order to recognize the difference between gamma rays and &bgr; decay events the external electrode (outside of detector) is electrically partitioned. The instrumentation of these external segments and the consequence with respect to the spectrometer energy signal is examined.

ISSN:0094-243X    

DOI:10.1063/1.40894

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Electronic instrumentation used in conjunction with germanium gamma‐ray detectors for astrophysics observations must be tested under conditions similar to those encountered during actual operations. Simulation of cosmic‐rays, gamma‐ray bursts and solar flares is necessary to validate the performance of the entire spectroscopy chain. A random charge pulser used in conjunction with other diagnostic pulsers, and the techniques developed to verify the performance with and without a germanium gamma‐ray detector are described.

ISSN:0094-243X    

DOI:10.1063/1.40895

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A new coded aperture detector design approach is discussed, whereby square element coded aperture unit patterns are a mosaiced onto a circular detector with a view to maximising the are occupied by the unit pattern, and hence the size of the field of view. The results for these optimum patterns are presented for all URA and MURA unit patterns of orderv<400.

ISSN:0094-243X    

DOI:10.1063/1.40896

出版商:AIP    

年代:1991

数据来源: AIP