Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: Neutron detection, 5
Date: Sep 29, 9:42 am
Poster: Mark Harriss

On Sep 29, 9:42 am, Mark Harriss wrote:

>Just a thought.. The cost difference between a 2" disk of BC720 and a 5" disk isn't all that great (about 30-40% more) and the nominal detection area is more than 6 times bigger. What if you were to optically couple the output of the big scintillator to the small tube?
>I recognize that "optically couple" is non trivial, and that it's not just a matter of making a suitable opaque cone shaped housing. The air space between the two will reduce the transmission, because some of the photons will reflect off the surface, for instance. But what about a machined clear plastic cone, lapped and gooped on both ends? Does the refractive index of the BC720 match silicone goo and glass?
>Increasing your detector area, though, helps get the "lower limit of detection" down, as well as improving the statistics on higher neutron rates.
>Or, is it cheaper just to scrounge up a bigger PMT than to fool with machining and lapping a plastic cone (although acrylic is pretty cheap..., and lapping time is nominally free.. many is the waveguide flange I've lapped sitting in front of the TV)