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 Post subject: cross section data
PostPosted: Mon Nov 29, 2010 3:04 pm 
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Hello.. It is not very clear to me the actual meaning of the cross section options "kopt" for fragmentation (Zi,Ai)->(Zf,Af).
That's what I have understood (for the relevant kopts):
-kopt=1 : use Webber93 algorithm as is (wnew.f)
-kopt=2 : use TS00 algorithm as is (yeldx.f)
-kopt=11: pick-up data from file isotope_cs.dat, then use Webber to make fits on these data. If Webber fails, then use TS.
-kopt=12: pick-up data from file eval_iso.dat and make linear interpolation to given energy.
Is that correct?
What's the difference between isotope_cs.dat and eval_iso.dat? Is the latter a compilation of real measured data? Or is it just the output of some other numerical algorithm (which?)? What do you mean with "evaluated cross sections"?
Are these cross sections data for ISM-protons only? How do you handle ISM-helium targets? Why kopt=12 is preferrable to kopt=11?


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 Post subject: Re: cross section data
PostPosted: Tue Nov 30, 2010 4:29 pm 
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Here is a detailed explanation of what the options do (taken from comments in 'nuc_package.cc'):

------------------------------------------
kopt =0 - uses best alghorithm described in comments below (not recommended);
=1 - forces to use Webber'93 code (no renormalization etc.);
=2 - forces to use TS00 code (no renormalization etc.);
=3 - forces to use a const cross section fitted to the data.
=10- forces to use Webber'93 code (renormalized if data exists);
=11- forces to use cross section fit if exists (otherwise equiv. 10);
=12- forces to use a numerical table if exists (otherwise equiv. 11);
=20- forces to use TS00 code (renormalized if data exists).
=21- forces to use cross section fit if exists (otherwise equiv. 20).
=22- forces to use a numerical table if exists (otherwise equiv. 21);
The best values recommended are kopt = 12, 22 (12 is preferrable).
------------------------------------------

If you use one of the recommended values, cross_section_option=12 or 22, then the algorithm goes as follows:

1) If eval_iso.dat contains the requested channel, use it. This file contains:
a) calculated cross sections, mainly by a code by Mashnik and others, for important channels where data are in disagreement with Webber's or ST formulae;
b) measured cross sections interpolated by eye, where enough data points were available.

2) If the above failed, fall back to kopt=11 (or 21) and use data from p_cs_fits.dat. This file contains fits to experimental cross sections, compiled by Igor Moskalenko individually for each channel, where enough data were available.

3) If the above failed, fall back to kopt=1 (or 2) to fits by Webber (1) or Silberberg and Tsao (2), renormalized according to experimental data points from isotope_cs.dat.

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Andrey Vladimirov
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 Post subject: Re: cross section data
PostPosted: Wed Dec 01, 2010 7:21 am 
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Thank you.
So the recommended option gives the priority to numerical tables (Mashnik/CEM2k) rather than measured data, right?
As far as I know, all these tables and data are for proton targets; cross sections for He targets are given throu the scaling function He_to_H_CS(projectile, fragment, energy), right? Where does it come from? From Webber? Is that an energy-dependent scaling function?


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 Post subject: Re: cross section data
PostPosted: Wed Dec 01, 2010 11:08 am 
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The basic information on kopt is from the Explanatory Supplement, but is very basic.
We should put more details since this is obviously central to GALPROP.

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 Post subject: Re: cross section data
PostPosted: Wed Dec 01, 2010 11:13 am 
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You are correct, the recommended option gives priority to numerical tables in eval_cs.dat. Those are compiled from calculations of Mashnik/SEM2k _and_ from data, where enough data points were available to draw a point-to-point approximation by eye. Only some special channels went into eval_cs.dat, those believed to be important for CR propagation, for which available data was in clear contradiction with Webber/ST formulae, or for which there was no data.

I will answer about helium targets shortly.

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 Post subject: Re: cross section data
PostPosted: Thu Dec 02, 2010 8:13 am 
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Only special channels? It seems to me that the vast majority of CS channels is taken from eval_cs.dat (using kopt=12 mode).
Surely almost all of CNO(p,X)LiBeB. Am I wrong?


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 Post subject: Re: cross section data
PostPosted: Mon Dec 06, 2010 3:28 pm 
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Nicola,

I don't know what number or fraction of channels are in eval_cs.dat,
but whatever is there was chosen manually based on the available data
(either if the data contradicted the formulae of Webber or TS, and then results of a calculation were used,
or, if there were enough data, the cross section was approximated with an interpolation).

It may be difficult to identify the sources of some data from comments in eval_cs.dat,
but much of it came from a large collection published by Springer
(A. Iljinov et al., 'Production of radionuclides at intermediate energies')
and adopted for numerical applications in the NUCLEX code.
We are preparing a new publication to revise our data on isotopic production cross sections,
and all the necessary references will be there.

Regarding specifically the cross sections of Li, Be and B production, take a look at
http://adsabs.harvard.edu/abs/2003ICRC....4.1969M
and other papers listed at
http://galprop.stanford.edu/publication ... _processes

The reference for He_to_H_CS function is given in the source file He_to_H_CS.cc, and I am copying and pasting the comment in the source code below:
Code:
//    REFERENCES:                                                                                                                 
// Ferrando P. et al. 1988, PRC 37, 1490                                                                                         
//    MODIFICATIONS OF THE ORIGINAL SCHEME:                                                                                       
// - AMU,DELTA are found from linear extrapolation for E1<E(1);                                                                   
// - for linear inter-/extra-polation of DELTA the log scale in E is applied;                                                     
// - FZI is found from linear inter-/extra-polation on log scale in Z.                                                           


Andrey

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 Post subject: Re: cross section data
PostPosted: Fri Mar 18, 2011 7:32 am 
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Thank you.
And sorry... I have two more questions about the deuteron (2H) production in Galprop.
In addition to spallation from heavier CR progenitor (4He, CNO...), I expect that many 2H come from by proton induced reactions (lighter progenitor!), like p+p->2H+pion.
Are these p-p contributions included in Galprop?
Is the kinetic energy/nucleon assumed to be conserved is such reactions?


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 Post subject: Re: cross section data
PostPosted: Fri Mar 18, 2011 10:14 am 
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Edit: here is a better way to put it.

The nuclear reaction network of GALPROP is designed to work only above 100 MeV per nucleon. There are two reasons for that. First, below 100 Mev/nuc, nuclear reactions are governed by other mechanisms than higher energy reactions (e.g., nuclear resonances are important at low energies), and existing cross section fits (e.g., Tsao & Silberberg's or Webber's) are not designed to reproduce the shapes of these low energy cross sections. The second reason for limiting the applicability of isotopic calculations in GALPROP to >100 MeV/nuc is the fact that any observations of Galactic CRs spectra at these energies we may have are severely modulated by the Sun's magnetic field.

The reaction of deuterium formation that you mentioned must have a significant cross section only way below 100 MeV, just like most other nucleon attachment reactions. This channel is not included in GALPROP's reaction network, but even if it was, the lack of other low energy cross sections in the code make predictions of GALPROP regarding isotopic abundances below 100 MeV/nuc unreliable.

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 Post subject: Re: cross section data
PostPosted: Fri Mar 18, 2011 11:38 pm 
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thanks for the questions, it is important to document all this, unfortunately it is not done in the Explanatory Supplement,
and it is certainly obscure.

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 Post subject: Re: cross section data
PostPosted: Sat Mar 19, 2011 7:38 pm 
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Thank you.
I have noted a tendency of Galprop in underestimating the deuteron production.
And I have noted that the channel p+p->d+pi is already in the code, but it is actually used to give the pion yield only.
So I think it could require little work extending it for the deuteron yield too... (also isotope data are below ~GeV/n at present).


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 Post subject: Re: cross section data
PostPosted: Sat Mar 19, 2011 11:51 pm 
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could you add this under BUGS in the galprop main page?
so that it gets remembered (just a one-liner and a link to here : the discussion can continue in this cosmic-ray forum)

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 Post subject: Re: cross section data
PostPosted: Sun Mar 20, 2011 11:56 am 
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Thanks! I re-assigned the bug to me, and I will add the channel to the updated nuclear reaction database I am working on (to be released in the next version of GALPROP).

Nicola, if I remember correctly, you have the source code of GALPROP. You can easily add this channel into your version by editing the file eval_iso_cs.dat. Just add a few lines to the beginning of the file with several cross section data points, and the code will interpolate between them to calculate the cross section. Don't forget to update the number of lines in the file in the line with the words "array dimensions".

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 Post subject: Re: cross section data
PostPosted: Sun Mar 20, 2011 5:02 pm 
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Yes, but actually I use v54 via Webrun only. The way you propose (to tabulate cross sections into the .dat file) seems good and quick, I think it will work for p+p->2H+pi (if N_iterations=2). By default this approach would give the 2H at the same energy/nucleon of their parent p, right? In case, I wouldn't bet such approximation is fine for p+p reactions. Maybe it can be adjusted using some inelasticity factor...


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