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