pyne/pyne — pull request #311 by elliottbiondo (2014-02-14 00:14:42+00:00)
Title: Fixed errors in alara module functions.

Discovered while writing iterative burnup script:
1) Materials cannot be assigned to zones. Only mixtures can be assigned to zones.
2) "number_density" is, unsurprisingly the keyword to output number density, not "constituent".