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