This value is 1 when {HEAD ~ the cross section} of the particle is {TAIL ~ a perfect circle} 
is
This value is 1 when { HEAD ~ the cross section } of the particle is { TAIL ~ a perfect circle }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL