On Thu, 1 Aug 2013, yyc2011_at_mail.ustc.edu.cn wrote:
> I read your last email carefully.I have three questions to ask you.
I will try to answer your questions, but I must insist that you should read
carefully the manual. All is explained there, and especially it is clearly
said when you must use LOW-MAT (Note 3) and when you shouldn't (Note 2).
> The first question,In your view,If these are the materials I want, LOW-MAT
> is not needed.
> It is not an error to have a LOW-MAT.Am I right?
I have already told you that! In my previous message I said:
"It is not an error to have a LOW-MAT, but because it is not necessary, it
is easy to make a mistake (see the warning in Note 2) )"
Then, please listen, and don't do it IF IT IS NOT NECESSARY. The proof that
this is good advice is the fact that you did it AND YOU DID IT WRONG (see
below my answer to your third question). So, the warning in Note 2) was
justified! People tend to use LOW-MAT when it is not necessary, and tend to use
it wrongly. And so did you.
MOST OF THE TIME LOW-MAT IS NOT NECESSARY
-----------------------------------------
It is necessary only in special cases:
1) the same name (e.g. CARBON) pointing to non-default cross sections (e.g. at
temperatures different from the normal one, or for a material with a special
molecular binding, e.g. graphite)
2) names pointing to cross sections identified by a different name (e.g.
DIAMOND using the same cross sections as CARBON).
> The second question,"It is needed, instead, if I need one of those who are
> not first."What do you mean?
> If I need the first CARBON?C Free gas natural Carbon 296K?and the second
> ALUMINUM? 27Al Aluminium 27 87K?,
> I think,according your view,for this time,low-mat is needed.Right?
* If you want the name CARBON to mean "Free gas natural Carbon 296K", you DON'T
NEED LOW-MAT, because that is the first CARBON in the list
* If you want the name CARBON to mean "Free gas natural Carbon 87K', you NEED
LOW-MAT, because it is the second in the list
* And you NEED it if you want the name CARBON to mean "Free gas natural Carbon
4K" (third on the list) or "Free gas natural Carbon 430K" (fourth on the list)
or "Graphite bound nat. Carbon 296K" (fifth on the list)
* And if you have a two carbon materials, both at 296K, but with different
properties, for instance different electron production cut-offs, you can
call one CARBON, and the other one another name, for instance MYCARBON:
you don't need a LOW-MAT for the first one, because it is the first on the
list, but you need one for the second, to tell the program that its
neutron cross sections are the same as those of the first.
> The third question," You put it there, however,and you made a mistake!
> LOW-MAT CARBON 13. 27. 296. ALUMINUM
> which would mean: "Use for Carbon the cross sections of Aluminum"!!!!!!!!!"
> which is obviously meaningless.
> I don't understand what you said "Use for Carbon the cross sections of
> Aluminum,which is obviously meaningless".
> Could you explain this in detail?
How can I explain that???? That command means: for the material with the name in
WHAT(1), which is "CARBON", use the neutron cross sections identified by
WHAT(2), WHAT(3), WHAT(4) and the name "ALUMINUM". Do you think it makes
sense to use the aluminum cross sections for carbon?
That is the meaning of LOW-MAT: to tell the program which cross sections are to
be used for a given material.
In most cases it is obvious and LOW-MAT is not needed: "use for a material
the cross sections with the same name as the material and at room temperature".
In some (rare) cases you want to say: "use cross sections with a name different
from the name of the material" or "use cross sections with the same name but at
a different temperature", or "use cross sections with the same name but for
a material with different molecular binding" etc.
Alberto
Received on Thu Aug 01 2013 - 19:32:03 CEST
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