Reply To: General thought on old coal mines.

[vansig]

exit beam alphas should be roughly from 600 to 2900 keV, which is *not* relativistic.

at the upper end of this, 2900 keV = 4.646e-13 joule, mass ~ 4u = 6.64e-27 kg
and kinetic energy, E_k = .5 m v² so

v = sqrt( 2 E_k / m) = sqrt ( 2 x 4.646e-13 / 6.64e-27 ) = .04 c

the bulk of them are probably closer to 600 keV = 9.613e-14 joule,
v = sqrt ( 2 x 9.613e-14 / 6.64e-27 ) = 0.018 c

*after* extracting 80% of their energy with the capture coil, they’ll still be traveling at 2400 km/s, which is 42x the relative momentum of any given particle in the compressed airstream at mach-24. but even a small number of collisions with any air particles will change that, in the same way as shooting a break at a pool table slows the cue ball.

by the way, for each 5 MW anode, i estimate ~ 10^17 alphas in a pulse, 1000 pulses/sec.

for a 400 MW engine, that’s 8 x 10^21 alphas exiting each second. (about 53 mg)

in other news, industrial physicist has a good article by Dean Andreadis, showing scramjet engine design
http://www.aip.org/tip/INPHFA/vol-10/iss-4/p24.pdf