At 01:56 AM 12/8/2012, Axil Axil wrote:
IMHO, Beryllium does not need to be reformed in
any way no matter what its original shape. It is
a neutron moderator; most neutrons will pass
right through it. But some will be slowed if the beryllium is very thick.
The problem is that I have an Am-241 source which
is a sheet of metal (steel?) with a circular
ridge welded onto it. The Am-241 is in the well
formed by the ridge. So if I place the beryllium
on top of the ridge, it will be elevated from the
source by ... okay, damn it! I'll go find the durn thing and measure it.
By some total miracle, I found the source in only a minute.
The well is about 0.7 mm deep.
It is about 2.3 mm diameter.
The range of Am-241 alphas. 5.5 MeV, in air, is about 4 cm.
Might not be a problem at all.
Let's see: 1 Ci = 3.7 × 104 disintegrations per
second = 2.22 × 10^6 disintegrations per minute.
about half of these, if I understand the
situation correctly, will be absorbed by the Be
if it's sitting on top of the well. From
Wikipedia, "a representative alpha-beryllium
neutron source can be expected to produce
approximately 30 neutrons for every one million alpha particles."
So, roughly, I'd expect rougly 33 neutrons per
minute. I'd think they might be anisotropic,
heading in more or less the same direction as the
original alphas. Then I need to look at how many of these would be detected.
Using a bunch of detectors, I could look for anisotropy.... LR-115 is cheap.
I can detect fast neutrons through proton
knock-on, that's an advertised usage for LR-115,
and I have a boron-t10 converter screen which I
can use to detect slow neutrons. Hey, this is
cool: Am-241 -> alpha -> (Be9, alpha, C12, n) ->
(B10, n, alpha). The key will be finding alphas
on the other side of the Be ingot, and only with
a B10 screen. Aside from that, just using direct
neutrons, how many triple tracks will I find?
Turns out they are really easy to spot, the
alphas hit the LR-115 like a brick, they make
really clear tracks, and three radiating from a
point stands out clearly. Proton tracks are more
subtle. And that's part of what I want to test.
So, now, how do I get a real proton source? My
guess is that, realistically, if I want to
calibrate my LR-115 for proton detection, I'll
need to find someone willing to expose the
material. Much easier, I'd think, to move a few
tiny pieces of plastic film to a source, like a
linear accelerator, than to move the source to the film....
