Re: about atomic weight

From: Stefan Roesler <sroesler_at_mail.cern.ch>
Date: Wed, 3 Dec 2008 23:01:59 +0100

Hi Hantao Jing,

The parameter defined with MATERIAL/What(2) is 'atomic weight' of an
element (sometimes also called 'relative atomic mass'), fully consistent
with its definition (IUPAC):

    "An atomic weight (relative atomic mass) of an element from a
    specified source is the ratio of the average mass per atom of the
    element to 1/12 of the mass of an atom of 12C."

It is not to be confused with 'atomic mass', defined as the mass of an
atom, which can only be one isotope at a time and is not an
abundance-weighted average.

Please note that 'atomic weight' has by definition nothing to do with the
force exerted on an object in a gravitational field and is only for
historical reasons called 'weight'.

The FLUKA manual uses in a few isolated places 'atomic mass' instead of
'atomic weight' for MATERIAL/What(2) which will be corrected.

Cheers
Stefan

On Wed, 3 Dec 2008, Hantao Jing wrote:

> Dear fluka experts,
> I find one refers to 'atomic weight' but 'atomic mass' for what(2) in
> material card. In fact, the number for what(2) is particle mass in u unit in
> given example. I am confused with concept of 'atomic weight' in fluka because
> I believe that the weight is equal to that of mass multiplied by gravitational
> acceleration, namely, N=mg, usually described in classical mechanics. Can you
> explain the difference with 'atomic weight' and 'atomic mass' in fluka? Thank
> you very much!
>
> Best regards,
> Hantao Jing
> 2008-12-3
>
>

-- 
___________________________________
Stefan Roesler
CERN, SC/RP
CH-1211 Geneva 23
Switzerland
Phone:  +41-22-7679891
Fax:    +41-22-7669639
E-mail: Stefan.Roesler_at_cern.ch
Received on Thu Dec 04 2008 - 09:23:20 CET

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