| Screens employed. | Thickness. M.m. | Current observed. |
|---|---|---|
| Aluminium | 0·01 | 17·9 |
| Brass | 0·005 | |
| Brass | 0·005 | 6·7 |
| Aluminium | 0·01 | |
| Aluminium | 0·01 | 150 |
| Tin | 0·005 | |
| Tin | 0·005 | 125 |
| Aluminium | 0·01 | |
| Tin | 0·005 | 13·9 |
| Brass | 0·005 | |
| Brass | 0·005 | 4·4 |
| Tin | 0·005 |
The results obtained prove that the radiation is modified in passing through a solid screen. This conclusion accords with the experiments in which, of two similar superposed metallic screens, the first is less absorbent than the second. From this it is probable that the transforming action of a screen increases with the distance of the screen from the source. This fact has not been verified, and the nature of the transformation has not been studied in detail.
I repeated the same experiments with a very active salt of radium; the result was negative. I only observed insignificant variations in the intensity of the radiation transmitted with interchange of the order of the screens. The following systems of screens were experimented with:—
| Aluminium, thickness | 0·55 m.m. |
| Aluminium, thickness | 0·55 m.m. |
| Aluminium, thickness | 0·55 m.m. |
| Aluminium, thickness | 1·07 m.m. |
| Aluminium, thickness | 0·55 m.m. |
| Aluminium, thickness | 1·07 m.m. |
| Aluminium, thickness | 0·15 m.m. |
| Aluminium, thickness | 0·15 m.m. |
| Aluminium, thickness | 0·15 m.m. |
| Platinum, thickness | 0·01 m.m. |
| Lead, thickness | 0·1 m.m. |
| Tin, thickness | 0·005 m.m. |
| Copper, thickness | 0·05 m.m. |
| Brass, thickness | 0·005 m.m. |
| Brass, thickness | 0·005 m.m. |
| Platinum, thickness | 0·01 m.m. |
| Zinc, thickness | 0·05 m.m. |
| Lead, thickness | 0·1 m.m. |
The system lead-aluminium was slightly more opaque than the system aluminium-lead, but the difference was not great.
Thus, I was unable to discover an appreciable transformation of the rays of radium. However, in various radiographic experiments, M. Becquerel observed very intense effects due to scattered or secondary rays, emitted by solid screens which received radium rays. Lead seemed to be the most active substance in this respect.
Ionising Action of Radium Rays on Insulating Liquids.
M. Curie has pointed out that radium rays and Röntgen rays act upon liquid dielectrics as upon air, imparting to them a certain electrical conductivity. The experiment was carried out in the following manner (Fig. 9):—
The experimental liquid is placed in a metal vessel, C D E F, into which a thin copper tube, A B, is plunged; these two pieces of metal serve as electrodes. The outer vessel is maintained at a known potential, by means of a battery of small accumulators, one pole of which is connected to earth. The tube, A B, is connected to the electrometer. When a current traverses the liquid the electrometer is kept at zero by means of a quartz electrical piezometer, which gives the strength of the current. The copper tube, M N M′ N′, connected to earth, serves as a guard tube, preventing the passage of the current through the air. A bulb containing the radium-barium salt may be placed at the bottom of the tube, A B; the rays act on the liquid after having penetrated the glass of the bulb and the sides of the metal tube. The radium may also be allowed to act by placing the bulb beneath the side, D E.
In working with Röntgen rays the course of the rays is through side D E.