456 
without absorption and practically all, at least 99%, of the ionization is pro- 
duced by the « rays. In the @ ray electroscope the radiation must pass 
through .05 mm. aluminum, which absorbs all the alpha rays and the ioniza- 
tion is produced by the @ rays. In they ray electroscope the radiation must 
pass through 2 mm. of lead, which completely absorbs the « and @ radiation 
leaving they rays to produce the ionization. Thus for very weak radioactive 
bodies the x rays are used, to produce the ionization. 
TABLE 2. 
Uranium RapiumM SERIES. 
| | Absorption Coefficients. 
Half- Transforma-| Range of ~ 
SUBSTANCE. Radiation. value tion Con- rays in ems. 
Period. stant sec. | (15° C.). 6 rays Jj rays 
| |Alum. em~.| Lead em". 
| 
Uranium 1.... a g |5<10*years.| 4°610- 2°50 
Uranium 2.... , z% 2X10*years.} 1110-4 
Uranium X... ae 6,9 24°6 days.| 3°26107 14°4 and 510, 72 
(Uranium Y)..... 6 | 1 5 days.| 5°34X10- 360 
WON: aa es) 7 210% years.| 1°1X1073 | 3 00 | 
RAC 3). re ano = : a, 6 2000 vears.| 1 1107 3°30 200 
Radium Emanation... || og 3 85 days. 12°085 10-5 4°16 
Radium A... gd. | 3 Omin. | 3 85x10 4 75 
Radium B. ... @,y | 26 7min. | 4°33x<10-« 13 and 91 | 4-6 
Radium (). a,@,y | 195 min. | 5°93x10- 6 94 13 and 53 50 
(Radium Cy). 6 14min. | 825x107 13 
Radium b..... ; 6 16 5years. 1°331079 very soft. | 
Radio e. fas. 6 ; 6, y 5 days.) 1 6010-6 43 | very soft. 
Radium F (Polonium).. a 136 days.| 5 901078 Sa 
The substances in parentheses are products not in the direct line of transformation. 
Makower & Geiger’s Practical Measurements in Radioactivity. 
One notes in the radioactive series (Table 2), that the disintegration 
product of radium is emanation, a gas, which gives off an « particle and 
changes into Rad. A. This emanation is a gas and obeys all the gas laws. 
Rad. A has a half value period of three minutes and gives off an « particle 
and changes into Rad. B. Rad. B has a half value period of 26.8 minutes and 
gives off @ andy radiation and changes into Rad. C. Rad. C has a half value 
period of 19.5 minutes, gives off z, @ andy particles and changes into Rad. 
C, and Rad. D. Rad. D has a slow half value period of 16.5 years. This is 
so slow that the ionization produced by this change can be neglected in com- 
