[fluka-discuss]: Why single scattering is extremely demanding in CPU time?

From: <yyc2011_at_mail.ustc.edu.cn>
Date: Fri, 29 Nov 2013 11:28:25 +0800 (CST)

Dear Fluka Experts,
  When I use MULSOPT card, setting WHAT(6)> 1000.0 with SDUM = GLOBAL, GLOBHAD or GLOBEMF, replaces systematically multiple
scattering with single scattering everywhere. This choice is generally extremely demanding in CPU time.(1)But why? In other words,what causes the long computing time?(2)But,When I deal with the same problem with mutiple scattering,the computing time is greatly reduced. So,Are there any differences between single scattering and multiple scattering in the codes?And what are the differences?
  Thanks for any suggestions.Thanks for your time.

Best Regards
Chen Yuan


> -----Original E-mail-----
> From: "Giuseppe Battistoni" <giuseppe.battistoni_at_mi.infn.it>
> Sent Time: 2013-11-25 22:56:18
> To: yyc2011_at_mail.ustc.edu.cn
> Cc: fluka-discuss_at_fluka.org
> Subject: Re: [fluka-discuss]: some questions about charged particle transport
>
> Dear Chen Yuan
> you are asking something very difficult to be summarized by e-mail:
> you have to refer to text books on the argument.
> From your questions it seems that you have to
> improve your background knowledge in the studies of
> interaction of radiation with matter: this is essential for
> any user of general purpose Monte Carlo codes as FLUKA.
>
> If I may give and advice, I strongly suggest to use always multiple scattering
> for all standard problems of realistic detectors and situation. Avoid single scattering
> which is to be considered only something exceptional for very very thin layers.
> (by the way, it's very CPU time consuming).
>
> For your study on Moli¨¨re's Theory of Multiple Scattering
> let me also advice a historical paper by H. Bethe in Phys. Rev. 89, 1256¨C1266 (1953)
>
> Best regards
> Giuseppe Battistoni
>
> On 11/25/2013 11:54 AM, yyc2011_at_mail.ustc.edu.cn wrote:
> > Dear Giuseppe,
> >
> > First,Thanks for your reply.But,I still have some questions.
> > (1)I wil study the paper so as to solve the problem.
> > (2)In the Fluka course,you refer to the validity conditions of Moliere theory more than once. But, what are the validity conditions of Moliere theory? Could you tell me in detail?
> >
> > Any multiple scattering therory applies when in a given step you have several coulomb scattering.Several is a qualitative word. In practice, as a rule of thumb, you may be safe if you expect many tens of scatterings.
> >
> > So,According to your view,when refer to scattering,I can only estimate scattering numbers to determine whether it is appropriate to use the mutiple scattering.And in general,how could you estimate scattering numbers?
> > (3)We advice single scattering only when you have thickness of materials so small that the above conditions risks to be not respected.A couple of practical examples:
> > - layers of nuclear photographic emulsions.where you aim to measure charged tracks with few micron accuracy
> > - very thin layers of silicon trackers (order of 100 micron or less)
> >
> > According to your idea,There are no specific conditions to tell me when should I use single scattering.I must judge whether I should use single sattering as specific questions change.
> >
> > I don't know whether my understanding are right.Wish to receive from you.
> >
> > Best regards
> > Chen Yuan
> >
> >
> >
> >> -----Original E-mail-----
> >> From: "Giuseppe Battistoni" <giuseppe.battistoni_at_mi.infn.it>
> >> Sent Time: 2013-11-25 16:59:43
> >> To: yyc2011_at_mail.ustc.edu.cn, fluka-discuss_at_fluka.org
> >> Cc:
> >> Subject: Re: [fluka-discuss]: some questions about charged particle transport
> >>
> >> Dear Chen Yuan
> >>>
> >>> When I learn charged particle transport,There are a few problems I cannot understand.The questions are as followings.
> >>> (1)The Fluka course said "Accurate PLC (not the average value but sampled from a distribution), giving a complete independence from step size",I cannot understand this sentence at all. What kind of the distribution is? Could you give me a simple interpretations?
> >>
> >> I advice to study the paper (quoted in FLUKA references):
> >> A. Ferrari et al., Nucl. Instr. Meth. in Phys. Res. B71, 412-426 (1992)
> >> and references therein
> >>
> >>> (2)In the Fluka course,you refer to the validity conditions of Moliere theory more
> >> than once. But, what are the validity conditions of Moliere theory? Could you tell me in detail?
> >>
> >> Any multiple scattering therory applies when in a given step you have several coulomb scattering.
> >> Several is a qualitative word. In practice, as a rule of thumb, you may be safe
> >> if you expect many tens of scatterings.
> >>
> >>> (3)In the Fluka course,you mentioned "full single scattering are used to handle very low energy electron problems and very thin layers problems. But,how much low is the electron energy? How much thin are the layers?
> >>> In a word,I want to know when I should use mutiple scattering and when I should use the full single scattering.
> >>> I'm looking forward to receive from you.Thanks for your time.Thanks for your reply.
> >>
> >> We advice single scattering only when you have thickness of materials so small that the above
> >> conditions risks to be not respected.
> >> A couple of practical examples:
> >> - layers of nuclear photographic emulsions.
> >> where you aim to measure charged tracks with few micron accuracy
> >> - very thin layers of silicon trackers (order of 100 micron or less)
> >>
> >> Best regards
> >> Giuseppe Battistoni
> >>
> >> --
> >> INFN Milano
> >> via Celoria 16, 20133 Milano, Italy
> >> tel: +39 02 50317307
> >> fax: +39 02 50317617
> >>
Received on Fri Nov 29 2013 - 07:46:49 CET

This archive was generated by hypermail 2.3.0 : Fri Nov 29 2013 - 07:46:53 CET