Subject: antimatter and mass

Hello!! 

 In chemistry we have recently learnt about positron emission. 
My chemistry teacher is unsure of whether antimatter paticles have a 
negative or positive mass.  Could you help me out?  If The mass is 
positive, then why, when you consider the individual proton breaking 
down into a neutron and a positron in the breakdown of Na-22 to Ne-22, 
does the reaction seems to ignore the law of conservation of mass?? 
and if the mass is negative, just what is negative mass??

Also, through-out my quest to try to understand antimatter, I've read 
about vacum flucuations in which tiny particles of matter and 
antimatter come into being and anniliate each other.  I just wanted to 
check, were these particles formed from gamma rays (into which they go 
when they anniliate each other) and if so what caused these gamma rays 
to suddenly become matter?  

Thank-you very much for all your help!

Koa

Re: antimatter and mass