[ROOT] TGeoMixture: how to define with the proportion by number of atoms?

From: Y. Shitov (shitov@cenbg.in2p3.fr)
Date: Wed Oct 13 2004 - 13:59:07 MEST 

Hi, ROOT team,

Is it possible to implement GEANT-3 GSMIXT() NLMAT-like option in
TGeoMixture?

-----------------from GEANT-3 doc----------->
CALL GSMIXT (IMATE,NAMATE,A,Z,DENS,NLMAT,WMAT*)
...
NLMAT -  number of elements in the mixture;
	 > 0 WMAT contains the proportion by weights of each material in
		  the mixture;
	 < 0 WMAT contains the proportion by number of atoms of each kind,
		  the content of WMAT in output is changed to contain the relative
		  weights;
-----------------from GEANT-3 doc----------->

I think it will be suitable to define materials according to its
chemical formulas like:

TGeoElement* O = new TGeoElement ("O","Oxygen",15.9994,8,);
TGeoElement* C = new TGeoElement ("C","Carbon",12.0107,6,);
TGeoElement* H = new TGeoElement ("H","Hydrogen",1.00794,1);

// Mylar wrapper C10H8O4
TGeoMixture *mat4 = new TGeoMixture("MYLAR",3,dmyl);
mat4->SetUniqueID(   4);
mat4->DefineElement(C,-10.);
mat4->DefineElement(H,-8.);
mat4->DefineElement(O,-4.);

Best,
Yuri

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