Re: Score neutron from 16O(p,xn) reaction

From: Francesco Cerutti <>
Date: Thu, 13 Nov 2008 14:09:55 +0100

Dear Chenyen,

> I want to score the product neutron angle distribution with respect to
> the beam direction, compare with ICRU63.
> If I consider single longitudinal z (plane xy), then the azimuthal
> angle is the angle distribution of the product neutron with respect to
> the beam direction.
> Sorry, I had difficulty comprehend this.

with the cylindrical mesh of USRBIN any point of the halfplane xz with
positive x is identified by phi=0 (being phi the azimuthal angle used with
the cylindrical mesh). On the other hand, only the x axis direction
corresponds to a zero polar angle with respect to the x axis itself
(other directions lying on the plane xz are identified by different polar
Thus USRYIELD is the good scoring choice, furthermore allowing to
discriminate as a function of energy (as you need).

> In LAM-BIAS card, I'm interested in 16O(p,n) reaction, is it correct that I set
> what(4) for proton and what(5) for neutron.
> I had a few runs that I need to increase the statistics,
> Is there any value that I should take into consideration for biasing
> the inelastic hadronic interaction length , like figure of merit(FOM)
> in code MCNP or the range of 20MeV in water(1.9mm)

You need to bias only proton inelastic interactions (with that choice for
WHAT(4-5) you ask for biasing of the inelastic interactions undergone by
the eight particle types going from proton (1) to neutron (8)). The
reduction factor in WHAT(2) has to be set comparing the inelastic
scattering length of beam protons in water (printed in the .out file) and
the lenght of your target (after one scattering length - assuming it
as constant along the energy range of interest - about 63% of the beam
particles underwent an inelastic reaction). Obviously this way you bias,
in addition to p+O reactions relevant for neutron production, also p+H



Francesco Cerutti
CH-1211 Geneva 23
tel. ++41 22 7678962
fax ++41 22 7668854
Received on Fri Nov 14 2008 - 09:26:17 CET

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