From: Matthew Worcester (mworcest@hep.uchicago.edu)
Date: Fri Apr 22 2005 - 16:57:52 CDT
Matt,
I may not be able to phone in, but I do have a few things to report:
1. G4 is up and running. Everything looks good and I think we will may it
easily, but see below. We can put it into your CVS repository whenever
you wish.
2. The way we have planned things is not going to work out exactly as
planned, I think it will work out better than planned. Here's why: our
idea was that I would give you a flux function containing neutrons at the
vessel and veto information which you would then read in to ReactorFSim.
The problem is that we expect one unvetoed neutron per day. G4 generats
events at about 2 Hz and we need to sample over 20 m^2. At 450 MWE, the
rate over 20 m^2 is 3.2 Hz, so to get one neutron to put into
ReactorG4Sim, I need to run G4 for a day and a half.
In addition, you do not yet have a way to propagating a 100 MeV neutron
and taking into account n-p scattering at these energies. Maybe by now
you do, which is fine. In any event, what we can do, which is much
easier, is this: attached is a file of neutrons generated at (0,0,-3.5m)
with cos_thete=(0,1). The neutron energy is flat over 0.1-1000 MeV and
the polar angle distubution is flat over (0,1). I thien let G4 propogate
them through the mineral oil and flag the proton scatterings. This way,
you only need worry about the what happens with the proton (Birke's law)
and neutron after it hits the proton. You run all these events through
ReactorFSim, but be sure to keep track of the initial neutron position and
energy: if you know that, then I can use G4 to give you weights for each
and we're done.
There are some points: the way G4 moves a neutron through any sort of
scattering is to destroy the initial state neutron and create a final
state neutron. I just write everything into the event record:
The first 9001 energy is the initial neutron
9004 is the scattered proton
The 9001 record just before a scattered proton gives you the neutron
momentum vector before the scattering; you work out the neutron momentum
vector after.
This should be easy. I've attached a file of 500 events; you tell me and
I can give you as many as you want.
Best,
Peter
Peter Fisher Office 617-253-8561
Professor of Physics Fax 617-253-4100
44-118 MIT email fisherp@mit.edu
Cambridge, MA, 02139
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