Are different isotopes of the same element share the same

From: Alberto Fasso' <fasso_at_SLAC.Stanford.EDU>
Date: Thu, 7 Apr 2011 12:33:47 -0700 (PDT)

neutron cross section data in FLUKA/FLAIR?


in the FLUKA low-energy neutron cross section library, some cross
sections are
available for single isotopes, others only for the natural composition
of the
element. If there is only the natural composition, you can get average cross
sections for the element, but there is no way to distinguish an isotope from
For hydrogen, there are cross sections for H-1 and H-2 separately (and also
for the natural composition). Same thing for Lithium.
For gadolinium, only natural composition is available.
You CANNOT distinguish between gadolinium-155 and gadolinium-157.

> To speak more specifically,I want to simulate a neutron source coming into
> a region stuffed respectively by Gd-155 and Gd-157.I want to see the photon
> deposition by energy.As these two isotopes have different neutron cross
> sections,the results should be different.I have used the LOW-MAT card,only
> to find that the library contains cross-sections for the natural gadolinium,
> at two different temperatures,but not for gadolinium isotopes, while
> cross-sections for isotopes of Hydrogen and Lithium,for example,are contained.
> I'm not sure whether the cross-sections for the natural gadolinium contained
> in the library are derived from all the isotopes of gadolinium,according to
> their natural storage.If so,can I extract them?
> So how can I associate the isotopes of gadolininium (that I create in MATERIAL
> card)
> with the neutron cross sections of the GD isotopes respectively?

Of course the cross-sections for the natural gadolinium are derived from
all the
stable isotopes of gadolinium ("natural" means "with the same isotopic
that Gd has in nature". But you CANNOT "extract" them. You CANNOT
"associate the
isotopes of gadolininium (that you create in MATERIAL card) with the
neutron cross
sections of the GD isotopes respectively".



On Thu, 7 Apr 2011, wrote:

> Dear Vasilis,
> What if the meterial that I create is not H-2,but other isotopes,
> gadolinium-155 and gadolinium-157,for example,so how to associate
> these 2 isotopes with the neutron cross section,as the library only
> contains the natural gadolinium-neutron cross section, but not gadolinium
> (155 or 157)-neutron cross section?
> ----- =E5=8E=9F=E5=A7=8B=E9=82=AE=E4=BB=B6 -----
> From: "Vasilis Vlachoudis"<>
> To:,
> Subject: RE
> Options Z: 1, Am: 2.0079, A: 2, rho: 0.0000821(or what ever gas density you need)
> The most important is to specify the Z and A
> then you can create your heavy water using the DEUTERIU material
> Cheers
> Vasilis
> ________________________________________
> From: []
> Sent: 16 March 2011 06:21
> To:
> Subject: how to add isotope in material
> Dear all,
> In FLAIR,how to add isotope.For example,what can I do to add DEUTERON(gas)
> and heavy water?It seems to have not enough information in the manual.
> Best regards,
> Danny

Alberto Fasso`
SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
Phone: (1 650) 926 4762   Fax: (1 650) 926 3569
Received on Thu Apr 07 2011 - 22:36:23 CEST

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