On Jun 7, 2007, at 10:44 AM, Jones Beene wrote:
Horace,
It is not possible to get an exposure in a vacuum from degassing
species using the same exposure time as with atmospheric pressure
gas. This is not even a close call. The exposure times are way
too long. The radioactive species gets immediately evacuated.
Do you have a reference for this high initial degassing rate,
followed by a subsequent almost complete degassing turn-off ?
This is a nonsensical model of the process and certainly *not* one
implied by me. Degassing rate from Pd follows a decline curve. It
is not the Pd degassing rate which removes the radioactive species
from the film vicinity, keeps its concentration low, but rather the
vacuum pump.
I would have thought that following a high initial rate (few
seconds) which takes the loading down 10% or so, from the starting
level, that the subsequent rate of degassing would be slow and steady.
Yes it is slow and declining. It depends on the diffusion rate of
the species in the matrix and the pressure differential. But that is
not important to my point. My point is the gas, once out of the Pd,
is quickly removed by the vacuum pump. It can't stick around to
expose the film.
And besides - what kind of beta decay or radioactivity produces
~300 eV electons?
As I said, one from a tritium nucleus having a less than normal
excitation level.
Regards,
Horace Heffner
