CONTEMPORARY ADVANCES IN PHYSICS 



141 



mass, and the disintegrations observed at any voltage might have been 

 produced by particles of any energy up to the maximum correspond- 

 ing to the voltage. It comes from the Berkeley school, the data being 

 procured chiefly by Henderson.^^ It refers only to fragments of ranges 

 superior to 5.32 cm., a grave limitation, accepted in order to make sure 

 that none of the primary protons could get into the detector (a Geiger 

 counter). From 400,000 volts onward, the curve of Fig. 17 conforms 



OL 500 



100 200 300 400 500 600 700 800 900 1000 1100 1200 



ENERGY IN ELECTRON-KILO VOLTS 



Fig. 17 — Disintegration-function of lithium measured with a thick layer of lithium 



fluoride. (Henderson) 



to a simple and somewhat surprising assumption : viz. the assumption 



that a proton of energy superior to 400,000 is neither more nor less 



efficient in disintegrating lithium than a proton of only 400,000 



electron-volts, and that the whole of the rise in the curve from this 



voltage onwards is entirely due to the fact that the faster the proton, 



the farther it dives into the target and the more chances it has to 



^ The curve also fits the data of Cockcroft and Walton within the uncertainty of 

 experiment, due regard being had to the difference in the values of the solid angle 

 (letter from Dr. Henderson). In their work the screen between target and detector 

 had an air-equivalent of 3 cm. (letter from Dr. Cockroft). The curve of Fig. 8 

 shows that this had the same effect as Henderson's 5.32 cm. 



