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BELL SYSTEM TECHNICAL JOURNAL 



with enough oxygen to oxidize a complete atomic layer of caesium, 

 the selective maximum disappeared at both ends of the cathode and 

 only reappeared as a slight indication in Fig. 11 after prolonged 

 heating at 75° C. On baking for five minutes at 200° C. the selective 

 response reappeared prominently with a maximum at 7,330 A. but 

 with a loss in response at 9,000 A. and 10,000 A. sufficient to involve 

 a decrease in integral sensitivity as shown in Table 2. Further baking 



300 



100 



8000 

 WAVELENGTH IN A 



10000 



Fig. 10 — Relative spectral response to equal energy for cell B, position 1. 



involved a further rise in the maximum and a considerable increase in 

 response at 9,000 A. 



In cells C and D, Figs. 12 and 13, which were treated with large 

 amounts of oxygen, the response fell to very low values, rising only 

 slightly on baking at 75° C. But on baking at 200° C. the selective 

 maximum reappeared but at a longer wave-length than in the initial 

 state, and the spectral response at 10,000 A. was higher than it was 

 at the beginning. 



J 



