Unit cell dimensions for polyethylene may be assumed to be as follows: a-0.741 nm, b=0.496 nm, c=0.254 nm, a=ß=y= 90° the wavelength of cuk radiation is 0.1542 nm. 17.1 a flat-plate x-ray diffraction pattern was obtained from an unoriented sample of polyethyl- ene using cukk, radiation. it consisted of three rings of radius 22.2, 36.6 and 19.7 mm. the specimen-to-film distance was 50 mm. calculate the d-spacing of the planes giving rise to these reflections. it is thought that these reflections are from (hk0) type planes. draw a scale diagram of the unit cell of polyethylene projected along the c-axis. measure the spacing of the low-index (hk0) type planes and hence identify the planes giving rise to the observed reflections