[ 45 J 



No. 



SOME FURTHER NOTES ON THE DISTEIBUTION OF ACTIVITY IN 



EADIUM THERAPY. 



By H. H. POOLE, M.A, Sc.D., 

 Chief Scientific Officer, Eoyal Dublin Society. 



[Read Mav 23. Printed June 21, 1922.] 



An account has recently been given [Sc. Proc. R. Dub. Soc. n.s. xvi, 35, 1922] of 

 some determinations of the total activity due to the j3 and .y rays from an 

 emanation tube with various screens. These results were combined with the 

 geometrical law of distance, and in this way, on certain assumptions, the activity 

 to be expected at various depths in the flesh was calculated for a tube enclosed in 

 a serum needle, and also for several arrangements of surface applicators. At 

 the discussion which followed the reading of the paper it was suggested that 

 additional figures were desirable, so as to represent the activity at various points 

 in the neighbourhood of one or more emanation tubes. Further calculations have 

 accordingly been made, the method already given for a single tube being extended 

 to points off the "equatorial plane" of the tube \ji.e., the plane perpendicular to 

 the axis of the tube at its middle point], and the effect of the use of multiple 

 tubes worked out for a couple of typical cases. 



The results are shown in Tables 1 to 4, the corresponding conditions being 

 given with the respective tables. In order to simplify the printing of the tables, 

 the unit adopted has been changed. In every case the figure in the table may be 

 taken to represent the action per millicurie hour of total dose, the action due to a 

 dose of one millicurie hour concentrated at a point at a distance of one centimetre, 

 without any screening except that due to the glass wall of the tube, being taken 

 as 1000. The unit previously employed referred to a distance of one millimetre, 

 and so was a hundred times as great as the new unit. On the other hand, the old 

 figures referred to the activity of ten millicuries, or the total action produced by 

 ten millicurie hours, so that figures in the new tables are ten times as great as the 

 corresponding figures in the old. For example, the figure for the action on the 

 surface of a serum needle is 6,200 in Table 1, and 620 in the table on p. 475 of 

 the previous paper. 



Objection might be taken to the unit adopted, inasmuch as the screening 

 action of the wall of an emanation tube must vary greatly. The unit, however, 

 really refers to one particular tube which was used as a standard. Taking the 

 "bare" activity of this tube as 1,000, the activity at the same distance through 

 rS mm. of brass was lO'O. The action through this thickness of brass, which 

 stops all the j3 rays, is sensibly hidependent of the thickness of the tube, and is 



SCIENT. PROC. R.D.S., VOL, XVII. NO. 5, I 



