Re: y-89(n,2n)y-88

Andrzej,

first I want to warn you that what you want to do is not possible for
primary neutrons with energy < 20 MeV. Below that energy, the cross sections
give only the probability that after a collision you get a neutron in a
certain energy group. That the reaction be (n,n'), (n,2n) or (n,3n) makes a
difference only concerning the neutron weight, but you still get only one
neutron.
Above 20 MeV, however, it is possible. You need to write a user routine
mgdraw, under ENTRY USDRAW. Check that LTRACK .EQ. 210 (i.e. it is a
primary particle) and ICODE .EQ. 101 (inelastic reaction).
If this is the case, do a loop like this:
       ICOUNT = 0
       DO 100 IP = 1, NP
          IF (KPART(IP) .EQ. 8) THEN
             ICOUNT = ICOUNT + 1
          ELSE
             ICOUNT = 0
             GO TO 200
          END IF
  100 CONTINUE
  200 CONTINUE

At this point, the value of ICOUNT tells you if it was (n,2n), (n,3n) etc.
(I made it to be reset to 0 if a particle different from a neutron was emitted:
to avoid counting for instance (n,p2n)).

Of course, it is up to you what to do with this information and to write the
logic for it.

Alberto

On Mon, 6 Jun 2011, Andrzej Wojciechowski wrote:

> Dear Alberto
> Thank you for your fast answer.
> How can I calculated y89(n,2n)y88 reactions using only primary
> neutrons? I would like to calculate the (n,3n), (n,4n) and (n,5n)
> reactions too.
> Kind reagards
> Andrzej
>
> Dnia 03-06-2011, pi? o godzinie 10:36 -0700, Alberto Fasso' pisze:
>> Andrzej,
>>
>> how do you calculate a cross section from RESNUCLEi results? Your result
>> would only be valid if you used an extremely thin target, and in any
> case you
>> have no way to know if the target was thin enough.
>> I suspect that the difference you get with respect to TENDL comes from
> the fact
>> that as energy increases you produces more and more secondary neutrons,
> which
>> can contribute to the reaction you are interested in.
>> In other words, you probably get y89(n,2n)y88 reactions not only due to
> primary
>> neutrons, but also to secondaries: and this is why the "FLUKA cross
> section"
>> appears to be larger.
>>
>> Alberto
>>
>>
>> On Wed, 1 Jun 2011, Andrzej wrote:
>>
>>> Dear FLUKA experts
>>> I would like to calculate the cross section of y89(n,2n)y88 reaction
> using
>>> RESNUCLEi command.(see ny200.inp).
>>> Unfortunately the results are not correctly for beam energy greater than
>>> 70MeV (comparing with TENDL data) (see TENDL-n2n.doc.)
>>> Are TENDL evaluated data reliable?
>>> What is the reeaons? What do I do badly?
>>> Kind regards
>>> Andrzej
>
>
>

-- 
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