[ 93 ] 



No. 11. 

 ON THE DETONATING ACTION OF a PAETICLES. 



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

 Chief Scientific Officer, Eoyal Dublin Society. 



[Read November 28. Printed December 7, 1922.] 



It has recently been shown' that a particles are capable of causing the detonation 

 of iodide of nitrogen. This observation suggests two questions of some inr.erest, 

 the first being concerned with the very small probability of explosion— only one 

 detonation occurring on the average per 10' to 10* a particles, and the second with 

 the possibility of danger arising from a similar effect with detonators and 

 explosives in common use. This suggestion has already been put forward by the 

 writer,^ but all the evidence recorded below appears to be of a reassuring nature. 



Taking first the consideration of the manner in which detonation occurs, it is 

 obvious that mere ionisation of a molecule of the iodide is incapable of bringing it 

 about, as in that case the first a particle striking the material would cause an 

 explosion. Two possible explanations of the very small probability effect suggest 

 themselves. Detonation may be caused by the combined effect of two or more 

 a particles passing in rapid succession through the same very small region, and 

 thus raising the local temperature to the detonation point. On this hypothesis 

 the chance of an explosion occurring in a given time should be proportional at 

 least to the square, and probably to a higher power, of the concentration of a 

 particles. If, on the other hand, a single « particle is capable of causing detona- 

 tion, probably by collision with an atomic nucleus, the chance of explosion should 

 be directly proportional to the concentration, and the average number of particles 

 per explosion should be independent of the concentration. 



Several series of observations on this point have been carried out, sets of 

 specimen patches of iodide on filter-paper being prepared, and detonated by 

 placing a small wire loop coated with EaC in the vicinity. The time in 

 seconds (t) that elapsed before detonation was noted. The number (to) of a 

 particles striking the patch per second was estimated from the known activity of 

 the source (obtained by 7-ray test and the law of decay) and the geometrical 

 conditions, allowance being made for small differences in the areas of the test 



1 G. H. Henderson, Nature, June 10, 1922. ^ jSTature, July 29, 1922. 



SCIENT. PEOC. K.D.S., VOL. XVII, NO. 11. ^ 



