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: Long Counter
Date: Aug 02, 9:33 am
Poster: Richard Hull

On Aug 02, 9:33 am, Richard Hull wrote:

I just picked up a nice He3 neutron proportional counter tube. Fill pressure is 340cm (3400 torr or ~4.5 atmospheres!). According to some of the texts I have consulted, this makes a better fast neut counter and the BF3 tube (almost an order of magnitude improvement). Still, like the BF3 tube it detects thermals better due to its 4300 barn cross section for the sensitive reaction.

I had a nice chat about this with an Eberline engineer. Their new SWENDI-II neutron head vastly outperforms there venerable world standard NPD rem ball above 1MEV, and it uses a high pressure He3 tube in PE moderator.

The unit I have is most suitable for a long counter of sorts. It is 1.25" in diameter and 23" long. I'll have to get a length of PE solid rod stock about 6" in diameter to make up the device.

Calibration will be another matter, although I have a friend who can cal it at a local nuclear medicine facility.

I'll also have to make up the electronics. the preamp is the key item and I will probably use a circuit I have from an old NIM module.

I have about 12 projects in mid stream now and Fusor IV has taken a distant back seat. As I am struggling to get the most accurate neutron data possible with near zero error, the neutron measurement issue and getting as far above the noise floor as possible is an issue of the first order. I have several BF3 counters and the BC-720 proton recoil system. The agreement between the Bf3 units is only +/- 15% and between the proton recoil system and the BF3's only +/-20%! Not the warm and fuzzy feeling I was looking for.

Some of my contacts in nuclear metrology sort of laugh at my quest for precision as most of them are in health physics and not research and order of magnitude accuracy is all that is required. I can see where a lot of guys measuring neutrons in research are really just manipulating numbers and doing statistics on the neutron measurements. Few specify error in the measurements.

The age old regime of taking measurements for long enough periods over many passes and cooking the data down to a close approximation seems to be the modus operandi.

Richard Hull