A tip formed at the apex of said {HEAD ~ end} conical portion has a radius of curvature of {TAIL ~ about 500 Å} 
A tip formed at the apex of said { HEAD ~ end } conical portion has a radius of curvature of { TAIL ~ about 500 Å }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL