developing into the interference fringe by means of a berek 39 s compensator u03b1 is the diameter of the filament and u03bb is the wavelength of the sodium d rays the crystal size l is a value obtained in accordance with the following p scherrer 39 s equation which represents the size of a crystal in a direction approximately at right angles to the fiber axis equ3 wherein b is a 010 diffraction peak width in radian unit when the diffraction intensity is it iam 2 in which it is a diffraction intensity at 010 peak position and iam is a meridional x ray diffraction intensity at a bragg 39 s reflection angle of 2 u03b8 17 7 u00b0 the term 34 shrinkage of the fibers in boiling water 34 is defined as 34 percent decrease in length of material when exposed to elevated temperatures for a period of time and under 0 05 g p d tension 34 in the present invention the percent thermal shrinkage is measured in a boiling water bath of 100 u00b0 c for a period of 30 minutes the shrinkage of the fiber is determined in accordance with the following formula equ4 wherein l 1 is original length of fiber and throughout the present specification.