RE: piont-wise cross section

From: Mary Chin <mary.chin_at_cern.ch>
Date: Wed, 22 Feb 2012 13:23:21 +0100

Hi,

I hope this brings a happy and overdue close to the thread:

The (0.432610 MeV. 0.83524 mb) peak quoted by Mary is rightly a (n,g)
peak. This is a peak on the (n,g) cross section but not the peak on the
(n,tot) cross section. The elastic peak is instead (0.435 MeV, 16.55415
b).

There was a confusion for those who weren't following the broken thread.
My post was in response to both the subjects "piont-wise cross section"
and "low energy neutron cross section", both on exactly the same
unresolved issue. The discussion was about the energy range from 0.5 to
1.0 MeV on ENDF cross sections, and about unexplained peaks (20 keV, 70
keV ...) in the pulse height spectrum:

[10 Jan]
> The interaction between low
> energy neutron and oxygen or carbon material is mainly elastic

[10 Jan]
>> it is not true what you say, The total cross section shows large peaks
>> due to inelastic reactions above 0.5 MeV, for both carbon and oxygen.

[10 Feb]
> The large peaks still couldn't be found below 1MeV neutron. But, there
> are several peaks above 2MeV due to the elastic scattering, not due
> to the inelastic scattering which would happen above 4.8MeV.

The (0.432610 MeV. 0.83524 mb) (n,g) peak was cited to support Weihua's
argument that between 0.5 and 1.0 MeV, besides the elastic dominance no
traces of 'large peaks due to inelastic reactions for both carbon and
oxygen' could be found, the only non-elastic peak that could be found AT
ALL was the tiny little 0.83524 mb (n,g) peak.

Beyond 1 MeV, however, both carbon and oxygen of course exhibit sharp
inelastic peaks but that was out of range of the query.

As echoed by Francesco and here I echo again: the peaks on the pulse
height spectrum are recoil kinematics and have nothing to do with the
disputed absent/present inelastic/elastic/capture cross sections from
ENDF.

:) mary

> -----Original Message-----
> From: owner-fluka-discuss_at_mi.infn.it [mailto:owner-fluka-
> discuss_at_mi.infn.it] On Behalf Of Francesco Cerutti
> Sent: 21 February 2012 18:03
> To: Mary Chin; Vasilis Vlachoudis; Alfredo Ferrari; Alberto Fasso
> Cc: FLUKA discussion
> Subject: Re: piont-wise cross section
>
>
> Hi
>
> I would like to take the liberty to make some remarks in order to
> prevent possible misunderstandings
>
> - peak in the pulse height spectrum (energy deposition spectrum). As
> Mary pointed out, this comes from neutrons undergoing just one elastic
> scattering event in the detector and is actually an artefact due to the
> unique kerma value for the given energy. Further scattering events (in
> a larger cavity) would smooth out the spectrum.
> Therefore, such a peak is not related to possible peaks in the total
> cross section as a function of the neutron energy.
>
> - considering now the latter, this naturally displays (elastic and
> inelastic) peaks both for carbon and oxygen. The one mentioned by Mary
> at ~430keV in oxygen, actually is elastic: at that energy capture is
> several orders of magnitude lower.
>
> - still it's highly appreciated the effort of sending to the list clean
> input files, free from unrelevant cards, to collaborate in speeding up
> the diagnosis process
>
> Hope this helps
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. ++41 22 7678962
> fax ++41 22 7668854
Received on Thu Feb 23 2012 - 11:14:14 CET

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