Re: your mail

Hi Lior,

I had a lot of fun with your problem: it is the first time I hear about a
beam of D+ ! Do you have one :-) ?

The D+ has a mean life of 1.040E-12 s and a mass of 1869.62 MeV (Rev. of=20
Particle Physics).
You can read in the FLUKA output that the corresponding momentum is 388.772=
=20
MeV/c. Divided by the mass, it gives you a velocity of 0.208 the speed of l=
ight
(let's neglect any relativistic corrections, must be small in this case).
That gives a velocity of 6.23E+9 cm/s.
You start your beam 2 cm upstream of the target. The time it takes for the
D+ to reach the target is 3.32E-10 s, which is equal to 320 mean lives.
So, no D+ hits the target, they all decay before. You can easily check it b=
y=20
putting BEAMPART in your SCORE command: no star is produced in the target b=
y
the primary particles. You can also find confirmation looking at the
statistics at the end of output (Number of particles decayed per beam parti=
cle:
1.0000E+00 for D+).

Now, the target is hit by all the decay products (there are 171 possible=20
branches listed in the Rev. of Particle Physics). They will have many diffe=
rent
energies, but don't forget that all the mass of the D+ is available (nearly
2 GeV!). No wonder that some of the decay products have enough energy=20
to produce 400 MeV neutrons.

Alberto

At 40 MeV, if I calculate correctly, the velocity of the D+ is

On Wed, 14 Jan 2009, Lior Cahana wrote:

> Good morning Fluka experts,
> We have been trying to simulate a pencil beam D+ source hitting a natural=
 Li target and count the emitted neutrons according to their energy.
> The D+ energy is 40 MeV and the Q value for the reaction is ~15MeV howeve=
r we receive neutrons with energy up to ~400MeV.
> We attach the input, what are we doing wrong?
> wE would like to see how many neutrons in each energy bin reached the b1-=
b4 structures, are we doing it right?
> Thank you and have a great day
> Lior Cahana
>

--=20
Alberto Fass=F2
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
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Received on Fri Jan 16 2009 - 09:16:16 CET