122 Dr. Russell and Mr. Chadwick on the y Rays of 



An investigation of the y-radiation of a quantity of radium 

 at its minimum a-ray activity has therefore been carried 

 out by us. 



A radium solution, from which the radium D, E, and F 

 had been completely removed some days previously, con- 

 taining about five milligrammes of radium bromide, was 

 heated on a water-bath for six hours, the amount of solution 

 being kept constant by adding water. We experienced some 

 difficulty in keeping the radium in solution, and had to add 

 some HC1 to prevent the radium from being precipitated. 

 Every twenty minutes a little air was bubbled through the 

 solution to remove any emanation not otherwise expelled. 

 After about six hours' boiling the solution was evaporated to 

 dryness as rapidly as possible, first on a water-bath and later 

 at a temperature of about 200°. The evaporating dish con- 

 taining the radium was then placed at a distance of 10 cm. 

 from the side of the electroscope between the pole-pieces of 

 the magnet. Measurements of the 0- and the y-ray activity 

 were made through various thicknesses of aluminium until 

 the growth of radium B and C interfered with the measure- 

 ments. Several successful experiments were made, and it 

 was found that the activity of the radium was reduced to 

 about the same amount each time. The #-ray activity of 

 the radium immediately after evaporation was nearly 250 div. 

 per min._, and the y-ray activity 4 div. per min. Although 

 measurements of the rise of the activity of the preparation 

 showed that little or no radium B or radium C was present 

 initially, yet absorption measurements of the /3-radiation 

 indicated the presence of a hard radiation in addition to 

 the soft. The amount of this hard radiation was about 

 10 div. per min., and it had an absorption coefficient of about 

 20 (cm.) -1 in aluminium. We had hoped that absorption 

 measurements of the /5-radiation would afford a test of the 

 purity of the radium, but the presence of these penetrating 

 /3-rays prevented this. 



Some results will now be given which show that the 

 y-radiation measured by us was due to radium, and not to 

 its products. In one experiment the /3-rays through a thick- 

 ness of 0*057 cm. aluminium varied from 9'4 to 21*5 during 

 the course of an experiment, the y-rays in the same time and 

 through the same thickness varied only from 2*8 to 3*5. In 

 another experiment the /3-rays increased from 10 to 17 

 through the same thickness of aluminium as above, while 

 the y-rays increased only from 3*4 to 3*6. Even if the hard 

 /3-rays had been due to radium C the y-rays could not be 

 due to it, and had radium C been present there would have 

 been an initial decay. 



