Hi James,
> I tried using the lambias card with a reduction factor of 0.001 but still had
> nothing, so I then used 1.E-6 which gave some results (of the order 1.E-11
> fissions per beam particle). Is this number realistic?
you can find out the answer by yourself! The probability of fission per cm
(so-called macroscopic fission cross section) is given by the product
sigma x Av x rho / A
where sigma is the fission cross section in cm^2, Av is Avogadro's number,
rho is the density in g/cm^3 and A is the atomic weight.
If you look up the fission cross section on ENDF, for example on the
nndc website
http://www.nndc.bnl.gov/, you see that of course it depends on
energy (I don't know what is the average energy of your neutrons) but is
of the order of 1.E-4 b = 1.E-28 cm^2
Av is about 6.E23
rho is = 19
A = 238
1.E-28 x 6.E23 x 19 / 238 = 5.E-6
The probability of fission in a 50 nm (5.E-6 cm) layer is = 5.E-6 x 5.E-6 =
5.E-12
Enhancing the probability with LAM-BIAS by a factor 1.E6 gives you a
probability of 5.E-6. Therefore, if you run a million neutrons, you have
a chance to get about 5 fissions (close to what you call "some results").
You can play with the above numbers as you like...
> Also, would a BXDRAW routine to look at flux across a region would still be
> usable in the presence of LAMBIAS?
Yes, provided you take into account the weights of the neutrons crossing
the boundary, which are likely to be of the order of 1.E-6.
Alberto
From: James Ryan <james.ryan-4_at_postgrad.manchester.ac.uk>
Date: Tue, 3 Jun 2014 13:04:58 +0000
Thanks for the quick response Alberto,
I tried using the lambias card with a reduction factor of 0.001 but still had
nothing, so I then used 1.E-6 which gave some results (of the order 1.E-11
fissions per beam particle). Is this number realistic?
Also, would a BXDRAW routine to look at flux across a region would still be
usable in the presence of LAMBIAS?
James Ryan
Nuclear FiRST DTC
University of Manchester
james.ryan-4_at_postgrad.manchester.ac.uk
+447890 486 709
Received on Tue Jun 17 2014 - 12:18:01 CEST