. The American journal of roentgenology, radium therapy and nuclear medicine . Fig. 15 The distribution curve is appreciablyflattened by the use of the filters. On going,for example, from 350° to 3200 the intensityfalls off with no filter per cent, with of copper per cent and with 1 copper there is no measurable change. At the back of the target the intensityreaches a maximum at a point close to1800 where it should be a maximum fromgeometrical considerations. The maximum intensity from the backof the target with no filter is per centof the maximum from the front of th
. The American journal of roentgenology, radium therapy and nuclear medicine . Fig. 15 The distribution curve is appreciablyflattened by the use of the filters. On going,for example, from 350° to 3200 the intensityfalls off with no filter per cent, with of copper per cent and with 1 copper there is no measurable change. At the back of the target the intensityreaches a maximum at a point close to1800 where it should be a maximum fromgeometrical considerations. The maximum intensity from the backof the target with no filter is per centof the maximum from the front of thetarget; with mm. of copper filter it per cent and with 1 mm. of copperfilter it is per cent. The average pene-trating power of the radiations comingfrom the back of the target is then seen. >oo > hc mp Fig. 16 vertical axis, are given in Table xxvnand plotted in Figure 15. The significance of the numbers of thefirst column of the table will be made clearby reference to the direction diagram ofFigure 15. The other columns have thesame significance as the correspondingcolumns of the preceding table. From 70 to no degrees there is a gapwhich cannot be filled in, owing to thepresence of the cathode structure. r> From the values of -r it is seen that theA rays are least penetrating in a direction normal to the face of the target and that the penetrating power increases on both sides of this direction as glancing incidence is approached. High Voltage AT-Ray Work 97 It will be noted that, with no filter, theintensity maximum in this plane liesabout 10 degrees away from the centralbeam towards the heel of the target and,with mm. and mm. of copper filter,about 20° from the central beam. The direction of maximum intensityappears then to make an acute
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