Irradiation Effects on GIMM

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Irradiation Effects on GIMM
Lance L Snead
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I need to know the fluence and irradiation
temperatures for an accurate assessment of GIMM
performance. However, I will assume the
following. - fast neutron fluence of about 1E24
n/m2, - a thermal fluence of about 1E25 n/m2,
- and a nominal temperature of 200C - uniform
gamma heating Given this input, my primary
concern is swelling and thermal conductivity.
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SiC as a Substrate
SiC is now used as a highly polished substrate
for mirror applications. Typically, CVD SiC
material is used. The cost tends to be fairly
high for the base material, especially for large
pieces. The polishing is straightforward.
For the application conditions assumes, SiC is
one of the worst behaving materials as far as
dimensional stability and conductivity reduction.
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Assumption
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Alternatives?
An possible alternative material, which
contains 4 protons, is also used in space mirror
applications. - Al coating has been
demonstrated for mirrors and an
alloy with aluminum is commercially available. -
2/3 density than SiC - nominally the same
cost as CVD SiC mirror - thermal conductivity
will be unchanged - swelling will be less than
0.01. Silicon nitride - should be easily
polished and plated, though hasnt
been used as a mirror to my knowledge. -
better performance under irradiation.