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: Absolute vs relative neutron counting.
Date: Aug 04, 10:23 am
Poster: Richard Hull

On Aug 04, 10:23 am, Richard Hull wrote:

More info. from more reading and discussions with an NRL radiation metrologist.

What I am trying to do is make "absolute" neutron counts from the fusor. It turns out that this is the most difficult neutron measurement to make with accuracy. In low flux neutron fields, it becomes even more difficult. I was told, and have read, that absolute measurments with normal counters to within 10% are considered superb efforts.

Most normal measurements are relative neutron measurments in performance tests, etc. Accuracies of less than 1% error with a given instrument are relatively easy to make.

It turns out that it is almost impossible to arrive at a stable absolute efficiency of a neutron detector due to the nature of neutron interactions with matter both inside and outside of the device, altered conditions of measurment from calibration conditions, etc It is just something we have to live with.

So, once again we must take all absolute measurements of neutron output from our fusors with a +/- 10% window as a virtual given.

This oddly enough is just about the difference in instrument spread within the 3 different BF3 units I observed. Yet, all are capable of relative accuracies of a very high order. Hmmmm.....

As an old engineer I would hate to note that the bridge I am working on is absolutely within 10% of being the proper specified length based on work done with a ruler which is only approximately calibrated, while in the same breath proudly announcing all the individual pieces of the bridge are relatively measured against one another to 0.1% precision.

But, of course, neutron counting ain't bridge work.

Richard Hull