CASTER: a scintillator-based black hole finder probe

Abstract

The primary scientific mission of the Black Hole Finder Probe (BHFP), part of the NASA Beyond Einstein program, is to survey the local Universe for black holes over a wide range of mass and accretion rate. One approach to such a survey is a hard X-ray coded-aperture imaging mission operating in the 10-600 keV energy band, a spectral range that is considered to be especially useful in the detection of black hole sources. The development of new inorganic scintillator materials provides improved performance (for example, with regards to energy resolution and timing) that is well suited to the BHFP science requirements. Detection planes formed with these materials coupled with a new generation of readout devices represent a major advancement in the performance capabilities of scintillator-based gamma cameras. Here, we discuss the Coded Aperture Survey Telescope for Energetic Radiation (CASTER), a concept that represents a BHFP based on the use of the latest scintillator technology.

Scintillation detectors for x-rays

“…Phosphors containing hafnium are worth mentioning as they can constitute host materials of high density, but with practically no background radioactivity resulting in higher background noise, which is inevitably present in the Lucontaining compounds due to the natural abundance of 176 Lu radioisotope. An interest appeared recently in the case of SrHfO 3 host, which was doped by Ce 3+ or Tm 3+ [67][68][69],…”

“…It is worth mentioning that despite the attractiveness of Lu-based scintillators, their widespread applications might be limited by high cost of Lu 2 O 3 and demanding technology, but also by the increased background due to the 2.59% natural abundance of 176 Lu radioactive isotope (half-life 3.78 × 10 10 years), which results in about 300 background countsper-second per each cm 3 of the material. Such a problem can be encountered also with other elements, for instance Rb (27.8% of 87 Rb, half-life 4.75 × 10 10 years), K (0.0117% of 40 K, half-life 1.277 × 10 9 years) or to a lesser extent with La (0.0902% of 138 La, half-life 1.04 × 10 11 years).…”

“…Another mission considered for the future is the 'black hole finder probe', a large field of view, hard x-ray telescope. As one possible choice for the detectors the new scintillators LaBr 3 :Ce or LaCl 3 :Ce are under study due to their unique energy resolution capability [176]. A crucial condition for all scintillation materials to be used in such applications is an extremely low spontaneous background coming from radioactive isotope contamination due to the very low level of registered signals.…”

CASTER: a concept for a Black Hole Finder Probe based on the use of new scintillator technologies

“…We will refer to our design concept as the Coded Aperture Survey Telescope for Energetic Radiation (CASTER). 5 CASTER is designed to employ several new experimental techniques using standard detector technologies, such as inorganic scintillators, wavelength-shifting fibers and Send correspondence to: Mark.McConnell@unh.edu photomultiplier tubes (PMTs), all of which have laboratory and space flight heritage. The development of a new inorganic scintillator material, lanthanum bromide (LaBr 3 ), provides improved performance that is well suited to the BHFP science requirements.…”