. Radio-activity : an elementary treatise from the standpoint of the disintegration theory . Curie for the investigation of the a-rays of poloniumis shown in Fig. 22. The object of the experiment is tomeasure the ionisation current due to the rays between theplates PP, PP from a polonium preparation at A when thedistance AT was varied. The hole T in the plate PP is THE a, 13 AND y-RA YS. 17 covered with the thinnest possible sheet of aluminium foil (notshown) to prevent the ions formed in CCCC finding their wayinto the space PPPP. When AT is over 4cm. no current passes,,indicating that the ray
. Radio-activity : an elementary treatise from the standpoint of the disintegration theory . Curie for the investigation of the a-rays of poloniumis shown in Fig. 22. The object of the experiment is tomeasure the ionisation current due to the rays between theplates PP, PP from a polonium preparation at A when thedistance AT was varied. The hole T in the plate PP is THE a, 13 AND y-RA YS. 17 covered with the thinnest possible sheet of aluminium foil (notshown) to prevent the ions formed in CCCC finding their wayinto the space PPPP. When AT is over 4cm. no current passes,,indicating that the rays are all absorbed in this thickness of appearance of the rays between the plates is manifested,somewhat suddenly as the distance AT is reduced. If suc-cessive layers of foil are placed over the polonium, the absorp-tion caused by the second layer is greater than that producedby the first. These considerations and the existence of this peculiarity fora-rays generally led Rutherford {Phil. Mag., 1903, VI., 5, p. 177)to regard the a-rays as consisting of projectiles, and to examine. t,\ecK2!3l2Il. Fig. 22. them carefully in the most intense magnetic fields under con-ditions where the slightest deviation could be detected. Hisapparatus is represented in Fig. 23. The radium rays passupwards through a series of very narrow slits placed betweenthe poles of a very powerful electromagnet and emerge insidethe gold-leaf electroscope placed above. A current of hydrogenis kept flowing through the electroscope and the slits in adownward direction, and this serves to prevent the diffusionof any emanation from the radium into the electroscope.* It * The aluminium foil placed above the top of the slits serves the samepurpose as in Mme. Curies apparatus just described. It is excessivelythin and, being porous, offers no obstruction to the passage of thehydrogen. 78 RADIO-ACTIVITY. also greatly reduces the absorption of the a-rays in passingthrough the slits, and so increases the effect t
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectradioac, bookyear1904
