def SelectSpecies(Species):
    """
    convert various alternatives to standard species name: electron or proton
    """
    if Species.lower() in ('e','e-','electron','beta'):
        Species = 'electron'
    elif Species.lower() in ('p','p+','h+','proton','h','hydrogen'):
        Species = 'proton'
    else:
        raise Exception('Unknown Species: %s ' % str(Species))
        
    return Species