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: Neutron detection, 5" scintillator on a 2" PMT?
Date: Sep 28, 8:19 pm
Poster: Jim Lux

On Sep 28, 8:19 pm, Jim Lux 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)