928 



Mr. D. C. II. Florance on 



relation between thickness of radiator x the density, and the 

 amount of radiation passing through as measured by the 

 electroscope in scale-divisions per minute. It will be noticed 

 that the curve for carbon falls between those for iron and 

 lead. Thi- i< unexpected, but it may he due to the fact that 

 the radiation has to pass through the >ide of an electroscope 

 6 mm. thick, which would out out the radiations emitted 

 from different radiators in a varying degree. The second 

 group of curves shows the effect of placing 6*24 mm. of lead 

 against the electroscope. The initial drop is not so great in 

 this case. For equal weights per unit area the amount of 

 radiation passing through varies for different substances. 

 A comparison in the following table is made of the quan- 

 - passing through different radiators which give the same 

 iicient of absorption when examined by lead. 



Radiator. 



D ... 



Iron 



: 



Thicl 

 10 cm. 



12 cm. 

 •25 om. 



er iip.ii area 

 mi gra. 



Quantity 



14 

 17 

 26 



X. 

 •G5 

 •63 



•Go 



11-7 

 28 



A greater amount of the primary radiation passes through 

 the lead than through the carbon, vet the absorption co- 



efficient is the same in both cases. There is no difficulty in 

 explaining this it' we assume that the y-rays of radium are 

 heterogeneous. For the sake of clearness consider the y-rays 



divided into a hard and a soft group. Probably the soft 

 group is in excess of the hard group. The results of expe- 

 riments in the second part of this paper show that there 

 is more scattering in a substance like carbon than in lead. 

 The relative amount of scattering and of absorption of the 

 two groups will most likely vary according to the material 

 of the radiator. It is well known that lead cuts out a 

 soft radiation much more rapidly than does a similar weight 

 of iron. Therefore, when the primary radiation strikes the 

 lead radiator, the softer portion will be cut out much more 

 in proportion to the harder than in the case of the carbon 

 radiator. If a radiator produces a scattering of the primary 

 radiation, then the sorting out process will be simply a 

 difference in degree for the two groups by different radiators. 

 There is no need to suppose there has been a change in type 

 of the primary radiation. 



