RE: definition of liquid hydrogen?

Brandon,

I had a look at your input files.
The definition of liquid hydrogen at 4 K in input file testb.inp is correct.

Alberto

On Mon, 14 May 2012, REDDELL, BRANDON D. (JSC-EV511) wrote:

> Alberto,
> I appreciate your response, but I'm not sure if you are confirming my
> questions or not. Do you agree if my input files (in particular, the set up of
> my liquid hydrogen cards) are correct? I am going to find out how these other
> LH2 dose calculations were validated (if at all!).
>
> Brandon
>
> -----Original Message-----
> From: Alberto Fasso' [mailto:fasso_at_slac.stanford.edu]
> Sent: Monday, May 14, 2012 11:05 AM
> To: fluka-discuss_at_fluka.org
> Cc: REDDELL, BRANDON D. (JSC-EV511)
> Subject: RE: definition of liquid hydrogen?
>
> Dear Brandon,
>
> you say that "it is well known that liquid hydrogen shielding drastically
> lowers dose". That is true for doses of neutrons with energies higher than a few
> tens of MeV, but not for neutrons of much higher energy.
> For a typical shield of a high energy proton accelerator, the best shielding
> configuration consists of a layer of high-Z (high atomic number) material, such
> as steel, followed by a low-Z shield with high hydrogen content - most often
> concrete. This scheme takes advantage of high inelastic cross sections such as (n,xn) or
> (n,n') in high-Z materials to reduce the neutron energy effectively. The lower
> energy neutrons generated in this process are then best attenuated by moderation
> and absorption down to thermal energies in hydrogenous material.
>
> Of course, I realize that a steel shield would be difficult to set up in space.
> But don't be surprised that neutrons from 1 GeV spallation are only partially
> shielded by pure hydrogen.
>
> Alberto
>
> On Fri, 11 May 2012, REDDELL, BRANDON D. (JSC-EV511) wrote:
>
>> Thank you for the help with the H2 definition in FLUKA. The problem I am still
>> having is that it is well known that liquid hydrogen shielding drastically
>> lowers dose. In the case that I am running, I am only seeing an ~18% reduction
>> from what aluminum shielding provides. I've attached the two cases. Both cases
>> have approximately the same shielding mass (~55 g/cm2). Whether I run a
>> spectrum of protons (like the GCR protons) or mono-energetic beam of around 1
>> GeV, I get similar results. Other data shows that the reduction should be ~90%
>> or so. Is there something wrong with either my input file or the definition of
>> the material still? If, these input files are correct, then the secondary
>> particles that FLUKA generates contribute 4-5x more than the beam particles
>> (at this shielding thickness)..which suggests the effectiveness of the liquid
>> hydrogen shielding isn't as great as thought to be.
>>
>> Brandon
>

-- 
Alberto Fasso`
SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
Phone: (1 650) 926 4762   Fax: (1 650) 926 3569
fasso_at_slac.stanford.edu