At 10:05 AM 11/3/2009, Michel Jullian wrote:
> Interesting, but .... remember, I want to watch the cathode with a
> microscope.
Precisely, a thin Mylar window --which costs you close to zero (maybe
even slightly negative if implemented as suggested above since you're
saving on the cell bottom!)-- is just the thing for that, and for IR
imaging too as the presently discussed SPAWAR hot spot work shows.
Actually, I just purchased a roll of 6 micron mylar. Whether I want
to do a windowed cell or not -- I just don't see the need for it if
I'm mainly looking for neutrons -- somebody else will, and I expect
to have laser-cut cells available as well.
The back of the cathode does seem to be the place to watch closely,
whether in terms of light or particle emissions!
No, I don't think so. I am, by the way, going to be watching the
back, but I'd rather watch the front, I only expect to see the
effects side-on, or, if I'm lucky, at a certain depth in the deposit,
which might be visible against the CR-39. That CR-39 may be damaged,
as would just about anything. I still expect to be able to see
through it, for the most part. Mylar would present the same problem.
Here is what I expect to find with neutrons: they are emitted in all
directions, and the only way to tell where they came from will be to
infer distance to source from intensity; I'll have a range of
distances to the source of my detector layer (which is the interface
between two sheets of CR-39) of a minimum of 250 microns (from the
surface of the CR-39 to the cathode in contact with it) (but it's
another 250 microns to the other side of the wire), to about an inch,
or over 25 mm, to the other side of the cell), with all distances in
between, or even greater distances to the top of the cell (or lower
angle between the incident neutrons and the detector surface, we
might get some interesting views of protons making a groove instead of a pit.)
Don't you think it will be interesting to compare a CR-39 detector
stack in contact with the anode to one in contact with the cathode?
If the source of the neutrons is the cathode, as we expect, there
should be a difference in tracks per inch of two orders of magnitude
between the two detector stacks. And now that I think of it, I'd like
to put another detector stack in there. Edge on between the cathode
and anode. I.e., the normal incidence will be level with the surface,
and the distance will vary from maybe 500 microns to the full inch. I
need to get some information. I've been thinking that the cathode
wire would be horizontal, toward the bottom of the cell, which allows
a lower depth of D20. Expensive stuff, and it will evaporate to some
degree, this will be an open cell to start.
(Explanation of detector stack for those who have not been following
this: instead of just having one sheet of CR-39, I'd use two (or
more). The two sides would be registered to each other, probably with
drilled holes, and they would be held in contact, it's just been
suggested that they be heat-bonded at the edges, I don't know if that
would work, but I'll play with the material. I also have a glue
coming that is, I believe, simply a solvent for the plastic, so it
shouldn't add complicating chemicals to the electrolyte. So knock-on
protons generated in the first piece, if generated close enough to
the surface, would exit the surface and cause damage in the next
sheet. Then, if I only count tracks that appear on both sheets, in
register (or close enough), I have eliminated pre-assembly
background! Allowing me, I hope, to use commercial makrolon CR-39,
which is much cheaper, so I can make stacks and stacks....)
mmm... I can also do the same thing with LR-115, which have a 100
micron polyester (mylar) base, and I could put a stack inside the
cell, if the edges are sealed to prevent contact between the
electrolyte and the cellulose acetate detector layer.... Interesting
use of LR-115, I'd think. Neutron detector. Insensitive to alphas and
other charged particles at low energy, they'd have to be awfully fast
to make it through 100 microns of mylar. Easy to read, you can see
the pits with the naked eye, apparently (10 micron holes in the red
cellulose acetate layer).
I wonder if there is a way to get plain cellulose acetate film, red,
6 microns. Roll your own. Might need to be thicker, it would be
awfully fragile.
