. The Becquerel rays and the properties of radium. tive source. Thearrangement employed is indicated diagrammatically no. and Kleeman-s apparatus. -C OO ^^® radio-active surface R is of small size. m IlSr. uLi. A narrow cone of a-rays from it is defined . „ by the metal stop f. This cone falls per- Ihe radio-active SUriaCe, pendicularly on the ionisation chamber, consisting of a narrow space between two of smaU area, is placed ^ri^raTJ^t Xto eAtf^Thehorizontally. A metal dia- iXt *^ °^ ° phragm over it confines the rays employed in the experiment to a narrow amount of ionisa
. The Becquerel rays and the properties of radium. tive source. Thearrangement employed is indicated diagrammatically no. and Kleeman-s apparatus. -C OO ^^® radio-active surface R is of small size. m IlSr. uLi. A narrow cone of a-rays from it is defined . „ by the metal stop f. This cone falls per- Ihe radio-active SUriaCe, pendicularly on the ionisation chamber, consisting of a narrow space between two of smaU area, is placed ^ri^raTJ^t Xto eAtf^Thehorizontally. A metal dia- iXt *^ °^ ° phragm over it confines the rays employed in the experiment to a narrow amount of ionisation produced at any cross-section of this cone can be measured between twolarge flat metal electrodes close together, the lower ofwhich is made of wire gauze, to let the rays electrodes are fixed at a given distance apart,but can be moved up and down together, so as to varytheir distance from the radio-active surface. The thinstratum between these electrodes is called the ionisa-tion chamber. At a distance, the radiation is of. 102 THE BECQUEREL EAYS course enfeebled by lateral spreading out of the coneof rays. Since, however, the ionisation chamber isbroad enough to intercept the whole cone at anydistance used, there should be no difference from thiscause in the amount of ionisation at various distances. When, however, the ionisation chamber is far fromthe radio-active surface, the a-rays have had to passthrough a long distance in air, and their velocity isaccordingly much reduced. It was in order to tracethe effect of this reduction of velocity on the ionisationat any point that these experiments were made. It was found that at a definite distance from theradio-active substance, ionisation abruptly ceased. At all distances less than this the ionisation wasnearly the same, though, strangely enough, on movingoutwards, it was found to increase a little just beforestopping altogether. To bring these results outclearly, it is necessary to use a very thin layer
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectradiati, bookyear1906
