Question on results interpretation

Dear Beatrice,

your expectation to find more or less energy deposited in various materials
depending on their hydrogen content is very naive.
Hydrogen does not shield neutrons in the same way that lead shields photons.
Neutrons are first slowed down and then absorbed. And the energy deposited by
these processes depends on the thickness of the material: you cannot expect
the .out file to give you any useful information about this.
To evaluate neutron attenuation, you must not score energy deposition in the
shield, but neutron fluence (or dose equivalent) behind the shield.
In addition, you have not specified what is the energy of the protons.
Depending on the proton energy, you will not get only fission neutrons, but also
neutrons of higher energy which are not shielded at all by hydrogen (usually,
iron is the best shield for neutrons with energies larger than 20 MeV).

Alberto

> From: beatrice pomaro <pomaro_at_dic.unipd.it>
> Date: Thu, 29 Sep 2011 15:58:41 +0200
> Dear Fluka experts,
> I need a help in the interpretation of the results of the xxx.out file.
> The geometry is a concrete room around a UC2 target. Near the point
> of coordinates (400, 500, 370) a small portion of the concrete
> shielding is created at a mesoscale: aggregates and paste. Fission
> reactions are produced by collisions of protons on the target.
> I provide you the two .out files of the problem in which two
> different compositions have been considered for the aggregates in the
> cement paste (quarzitic in one and limestone in the other) and a file
> with usrbin results in terms of energy deposition.
> I expected to see a lower amount of deposited energy out from the
> aggregate, i.e. in the cement paste, where a certain amount of
> hydrogen is present, supposed to shield against neutrons; but this is
> not; on the contrary, comparing deposited energy in quartz aggregates
> and limestone aggregates a lower amount is found for the latter,
> which contains more hydrogen, as expected.
> May the contradictory results depend on the density of aggregates
> (higher than for the cement paste)?
> Am I missing informations from the .out files?
> Thank you,
> any help would be appreciated,
> Kind regards,
> Beatrice
Received on Thu Oct 06 2011 - 09:30:32 CEST