On Jul 3, 2009, at 5:16 PM, Michael Foster wrote:
I'm afraid I haven't been following the discussion of Kowalski's
work and don't know why he needs the 6u material or if it has to be
polyester.
Kowalski and others use (typically 6 micron) Mylar to isolate the
cathode from the CR-39, in order to eliminate scratching and chemical
attack as candidates for etching track formers. Mylar absorbs about 1
MeV per 25 microns for heavy particles, so thin is better than thick
for the isolation purpose. The original SPAWAR experiments were
though to be detecting alphas and another class (about 1 MeV I think)
of lighter particles, possibly deuterons or protons. In addition, the
back side of the CR-39 was found to have tracks "inside", found there
by repeated or long term etching, and this was interpreted as
possible evidence for neutrons. Contaminated NaOH etching baths could
provide an alternative explanation, so careful controls and changing
of the bath is required. Also, triple tracks in the CR-39 was
interpreted by SPAWAR as possible evidence for high energy neutrons
characteristic of D-T reactions.
I think it is interesting that Mylar itself can be etched by NaOH
bath to make tracks visible just like polycarbonate, or even to make
the Mylar porous by opening up the tracks into pores by extended
etching. See:
http://www.ias.ac.in/matersci/bmsoct2004/417.pdf
Polyester is probably not too good as a CR-39 replacement for SPAWAR
type experiments, but it is more resistant to etching (thus probably
PdCl etching as well) than polycarbonate and it sure is cheap:
http://tinyurl.com/6s7d4o
Mylar might be good as a neutron moderator and for detecting only the
very energetic particles from neutron activation when used with a
boron back (dry) side, possibly sandwiched between the Mylar and CR-39.
It might be interesting to develop an etching protocol for Mylar
using radioactive sources. It would take some careful control work
first to get the etching procedure down and to see if anything of use
is feasible. Just a thought.
Anyway, 6 micron makes a very effective and thin chemical barrier, as
proven by control experiments. It is one possible candidate for Layer
4 of "AN EDGE-ON-GRID CO-DEPOSITION METOD:" I posted in the "Do it
backwards: added 1997-style, science-based Vortex" thread earlier.
It would be nice if I could spell.
I use roughly 9 tons of 12.5u polyester (Mylar) film per day, so I
have a lot of it around. I also use a lot of 9u film of this type.
I rarely run 6u film, but probably have a stray roll of it and some
4u capacitor grade film as well. These rolls will typically be
1.1m wide and 10 or 15km long. If Mr. Kowalski can't get the film
he needs elsewhere, I'll have someone search my warehouse to see if
I can come with what he needs.
I thought it was pretty funny about the measurement bias. When you
have been working with these films as long as I have, you can just
sort of rub the stuff between your fingers and identify the
thickness. Virtually all of my employees can do this, so it isn't a
unique talent. Not very scientific, but apparently more accurate
than an ordinary micrometer with an unpracticed operator.
M.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
