RECOIL EFFECTS FROM p DECAY AND y EMISSION 49 



has a molecular weight of 36,000 and it was hoped that in this large 

 molecule some bonds would not be severed by recoil from S^^ formation 

 and that an appreciable fraction of all the broken bonds would rejoin. 



As a control, cystine was bombarded in another sealed tube in the 

 same aluminum container that held the insulin. The cystine, when 

 purified, had an activity of 170 cpmin per mg compared to 15,500 cpmin 

 per mg of the insulin, thus proving that the large protein held on to its 

 activity as tenaciously as had been hoped. Half-life and absorption 

 measurements show that most of the radioactivity is due to S^^. 



A series of physical and chemical tests was then carried out to see 

 whether the insulin had been badly damaged. The ultraviolet absorp- 

 tion spectrum of the irradiated material appeared unchanged except for 

 a slightly increased background absorption. None of the radioactivity 

 could be removed by dialysis. However, it soon became clear that 

 the material was impure because it was not possible to ciystallize the 

 bombarded insulin, though fibrils could be formed with a recovery of 

 up to 65 per cent of the original nitrogen. The material purified by 

 fibril formation had a specific activity of 19,000 cpmin per mg, higher 

 than the original. As final confirmation, a run on the ultracentrifuge 

 showed that the initial pure compound had returned as a material of 

 mixed molecular weights, so impure that no single peak could be 

 observed in the ultracentrifuge. 



The cystine, which contains all the sulfur in the insulin molecule, 

 should be separable on acid hydrolysis; the cystine from the irradiated 

 insulin brought with it only a small portion of the total radioactivity, 

 thus indicating that many of the sulfur bonds had been broken, with 

 consequent reattachment of the sulfur elsewhere in the molecule. 



The most interesting finding that has emerged from this study is the 

 relatively high biological activity of the degraded molecular mixture. 

 The irradiated material has been found to have 25 per cent of the 

 biological activity of the initial pure insulin. It is apparent that in this 

 respect neutron bombardment serves as a new physical means of protein 

 fractionation, making it possible to convert the molecule into fractions 

 different from those usually obtained by the classical methods of chemical 

 degradation. 



Recoil Effects from Beta Decay and Gamma Emission 



The recoil effects following beta decay are even more complex; not 

 only is a neutrino of small but unknown mass emitted simultaneously 

 with the electron, but also the angular correlation of the direction of 

 emission of the neutrino and the electron is virtually unknown. How- 



