The Advanced X-ray Astrophysics Facility (AXAF) contains two focal-plane science instrumentsthe microchannel-plate High-Resolution Camera (H1tC) and the AXAF CC1D Imaging Spectrometer (ACTS). Each of these instruments provides two low-internal-background detectors, one for imaging and the other for reading out AXAF's ol)jective transmission gratings. Taking maximum advantage of the low internal background of these instruments requires shielding against external electromagnetic and particle radiation. To optimize tlie shielding itlfii weight constraints, we peiformeci extensive numerical simulations of the photon transport and of the partidc tl'ansl)ort ail activation within the AXAF. \Ve discuss the simulations and report the results of the shielding study.With the adopted shielding design, the paiticle-iiiducecl background and the x-ray-induced background are each comparable to or less than the anticipated internal background of AXAF's imaging detectors (HRC and ACTS). Thus, the predicted total non-imaged background is very low -less than 0.2 counts arcsec2 day1 for the HII.C and even lower for the ACTS! In view of AXAF's half-aicsec angular resolution, this low background has negligible effect upon point-source detection, for reasonable observation durations. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx SPIE Vol. 2518 /109 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx SPIE Vol. 2518 / 115 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
We have been developing and testing a scintillating fiber detector (SFD) for use as a fast neutron sensor which can discriminate against neutrons entering at angles non-parallel to the fiber axis ("directionality"). The detector/convertor component is a fiber bundle constructed of plastic scintillating fibers each measuring 10 cm long and either 0.3 mm or 0.5 mm in diameter. Extensive Monte Carlo simulations were made to optimize the bundle response to a range of fast neutron energies and to intense fluxes of high-energy gamma-rays. The bundle is coupled to a set of gamma-ray insensitive electro-optic intensifiers whose output is viewed by a CCD camera directly coupled to the intensifiers. Two types of CCD cameras were utilized: 1) a standard, interline RS-170 camera with electronic shuttering and 2) a high-speed (up to 850 frame/sec), field-transfer camera. Measurements of the neutron detection efficiency and directionality were made using 14 MeV neutrons, and the response to gamma-rays was performed using intense fluxes from radioisotopic sources (up to 20 R/hr). Recently, the detector was constructed and tested using a large 10 cm by 10 cm square fiber bundle coupled to a 10 cm diameter GEN I intensifier tube. We present a description of the current detector system and report the results of experimental tests.
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