RE: How do i improve statistics (produce more neutrons)

From: Lawrence Mhatiwa <lawrencemhatiwa_at_hotmail.com>
Date: Fri, 4 Sep 2009 09:09:10 +000

Dear Alberto and all Fluka users

Thanks Alberto .I think i forgot to mention that i am supposed to compare
also the Neutron to photon dose at the isocenter of the Linac.So if i use
energy cut offs of 7MeV for photons and 10MeV for neutron i have a filling
that my comparison will not truly represent neutron/photon dose at the
isocenter on the actual LINAC.

For now iam going to increase the baising of the photon hadronic interaction
length from the present 0.02 to 0.01

Please help

Lawrence Mhatiwa

Medical Physics Department
University Of Free State
South Africa

> Date: Thu=2C 3 Sep 2009 10:07:55 -0700
> From: fasso_at_SLAC.Stanford.EDU
> To: fluka-discuss_at_fluka.org
> CC: lawrencemhatiwa_at_hotmail.com
> Subject: Re: How do i improve statistics (produce more neutrons)
>
> Dear Lawrence
>
> first of all you should set a much higher cutoff for electrons and
> photons. In your present input=2C the cutoff is set at 1 MeV TOTAL energy
> for electrons (i.e. about 500 keV kinetic energy) and 10 keV for
> photons. The lowest neutron production threshold in the materials
> you are using is a little higher than 7 MeV: therefore tracking particles
> below that energy is a complete waste of time. I suggest that you set
> the photon cutoff at 7 MeV and the electron cutoff a bit higher (10 MeV).
>
> That should already improve the efficiency a lot.
> If you find that it is not sufficient=2C you can increase the biasing of
> the photon hadronic interaction length (WHAT(2) of LAM-BIAS) from the
> present 0.02 to 0.01. But not much more=2C I think.
>
> Best regards
>
> Alberto
>
>
> On Thu=2C 3 Sep 2009=2C Lawrence Mhatiwa wrote:
>
> > --_64ce674f-922d-4c25-9d79-0ff7a6eadf85_
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> > boundary=3D"_91c33713-57ec-4927-9629-c276ca06bd77_"
> >
> > --_91c33713-57ec-4927-9629-c276ca06bd77_
> > Content-Type: text/plain=3B charset=3D"iso-8859-1"
> > Content-Transfer-Encoding: quoted-printable
> >
> >
> > Dear Fluka Users
> >
> > I am characterising photoneutrons produced by a 15MeV Linear Accelerato=
r. I
> > am using USRTRACK to score neutron fluence spectra at various locations
> > inside and outside the Bunker as shown in my input file.I can score neu=
trons
> > at these locations but my problem is that iam running 5.8 Billlion(20 M=
il/cycle)
> > histories and it takes one week to finish 4 cycles but there is no impr=
ovement
> > on the statistics of the spectra scored on locations outside the bunker=
.
> >
> > Could someone please help me on how I can improve (generate more neutro=
ns)
> > on the statistics of my scores in a reasonably shorter time.I have atta=
ched
> > my input and project files to this mail. Also attached is the log-log n=
eutron
> > fluence spectrum behind the door outside the bunker=3D2C you can seee t=
hat
> > the statistics is still very poor.
> >
> > Please help
> >
> > Lawrence Mhatiwa
> >
> > Medical Physics Department
> > University Of Free State
Received on Fri Sep 04 2009 - 12:27:49 CEST

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