A Straw Based HLNCC Multiplicity Counter with Improved FOM in Same Form

Previous modeling studies have shown that boron - coated straw (BCS) detectors can successfully replace 3 He tubes in small to medium size coincidence counters, such as the commercially available High Level Neutron Coincidence Counter (HLNCC - II). Unlike most other replacement technologies, BCS detectors share many strong features of 3 He tubes, including extraordinary gamma discrimination, hig h reliability and robust operation under environmental extremes. Moreover, they are free of ageing components, such as photomultiplier tubes and light transmitting fibers or guides. BCS detectors have already been employed with success in many different co nfigurations for neutron detection in defense and homeland security applications as well as for neutron imaging. We have constructed a BCS - based counter that replicates the exact envelope dimensions of the HLNCC - II. The counter employs 804 round straws, 4. 6 mm in diameter and 60 cm long, uniformly distributed insid e a moderator with a pitch of 9 . 75 m m, and a 10 B 4 C coating thickness of 2.0 µ m. The figure - of - merit ( FOM ) calculated as e 2 / t , where e is the detection efficiency, and t is the neutron die - away tim e, is measured to be 8. 0 (%) 2 / µ s, 13 % over the target FOM of 7.1 (%) 2 / µ s of a commercial 3 He - based counter.