Efficiency

The photopeak gamma-ray efficiency depends acutely on the geometry employed. TIARA is designed to be able to use the most close-packed of all the Exogam geometries, called the ``gamma-cube''. The photopeak efficiencies for several different geometries are included in Table 1. The different shield configurations depend on whether the side shields on the detectors are used, or not. The maximum value (at 662 keV) is 28% absolute photopeak efficiency.

 

Table 1: Properties of the EXOGAM gamma-ray array in selected geometries using just the 90 degree detectors (adapted from the project definition document). The efficiency and resolution are quoted for 662 keV and the resolution is for a source velocity of 0.075c. The quoted efficiency is for the true absolute photopeak detection efficiency. Cube-A numbers (%,keV) are scaled from Cube-B results.

	Suppression	Target	Photopeak	Energy
Geometry	shield	distance	efficiency	resolution
	configuration	(mm)	(%)	(keV)
Gamma-Cube	A	50.3	28	15.5
Cube	B	68.3	15	11.4
8 detectors	A	114.1	14	7.6