0.284

The Lattice constant is a=(2*atomic radius)/sqrt(3)

if a=0.142 then radius = (sqrt(3)*a)/2

or r = (1.73*0.142)/2

= 0.123 nm

so the Diameter is 2r or 0.246 nm

if a=0.142 then radius = (sqrt(3)*a)/2

or r = (1.73*0.142)/2

= 0.123 nm

so the Diameter is 2r or 0.246 nm