Re: Fwd: [fluka2010] Results check

From: Alberto Fasso' <fasso_at_slac.stanford.edu>
Date: Mon, 6 Dec 2010 11:10:37 -0800 (PST)

Dear Beatrice,

Joachim has done a good job to answer your N questions. Next time, I
suggest
that you limit the number of questions per single mail: not all people
have the
patience to answer all the questions, and you risk to get no answer at
all, or
that some of the questions will be ignored.
And indeed, despite all Joachim's good will, this is what has happened.
I will pick up a few questions that have escaped Joachim's attention,
and that show some confusion in your physical concepts.

> If I need
> deposition on an unit area (per cm2) should I multiply for which length?

What do you mean by "deposition on an unit area (per cm2)"?
Energy can be deposited only in a volume, not on an area.

> For the same graph if I want to convert GeV/(cm3
> s) into C/s I need to divide by 6,27*10**9
> (from MeV to W) to divide by concrete density
> (2,33g/cm3) and concrete conductivity (0,949
> J/(g C)) and to multiply by 1,87*10**15 p/s.

1) 1/6.27*10**9 is (approximately) the conversion factor from GeV
     to J, not from MeV to W. (Actually it should be 1/6.24*10**9).
2) what you call concrete conductivity is actually called its
     specific heat
3) I don't know where you got the value 0.949 J/(g C) for the
     concrete specific heat. Wikipedia (under the entry "Heat capacity")
     gives for it 0.880 J/(g C).
4) if you divide GeV/(cm3 s) by GeV/J, by g/cm3 and by J/(g C),
     you get C/s: it is already "per second", so there is no sense
multiplying
     it by p/s. That, unless the starting quantity is GeV/cm3, and not
     GeV/(cm3 s) as you have written.

> This way I obtain 1,35 C/s. If I consider the
> target will work 5000hours per year I get 2E7C.
> Is it possible to have such a thermal incre
> from ambient temperature due to radiation?

No, it is not possible. You are assuming that all the heat will
be absorbed and none at all will be radiated away: this is not what
happens in real life. And even if there was no heat dissipation
(that is, if the concrete was perfectly insulated - a very
unlikely occurrence indeed), at some temperature (probably
a few thousand degrees) the concrete would decompose and melt
and its temperature would not increase anymore.
2E7C is more than the temperature at the center of the Sun!
Did you really expect it could be obtained on Earth by
proton irradiation?

Alberto
Received on Mon Dec 06 2010 - 23:31:34 CET

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