Barium Chloride on the Bench

Hélène - the electroscope has been sitting on the bench since the eighth of March, and I am writing to tell you what it has finally done, because you will want the number and not the story.

I prepared the sample on the eighth, a fraction of a gram of the barium chloride fraction, the one that had already shown four times the activity of uranium in the ionization chamber. The reading that afternoon was steady: the leaf fell in nineteen seconds. I measured it again on the tenth, the twelfth, the fifteenth. Nineteen seconds. Nineteen seconds. I began to doubt the apparatus and checked it against the standard quartz piezo-electric sample, which gave the same value it has given since December. The instrument was not drifting. The sample was not changing.

What I did not understand until this week is that the sample was changing, but at a rate I could not see against the noise of the first measurement. The leaf falls in nineteen seconds because the radiation is intense enough to strip the air in the chamber almost as fast as the electroscope can recharge it. The change I was looking for - the slow appearance of a daughter product, the gradual ingrowth of something new - was buried under the intensity of the parent.

So I took a smaller quantity. One-twentieth of the sample, sealed in the same lead-lined box, and I have measured it every morning since the twenty-second. The leaf now falls in four minutes and twelve seconds. On the first of April it fell in four minutes and forty seconds. On the fifteenth, five minutes and six seconds. The activity is increasing. Slowly. The parent is decaying into something that ionizes more strongly than the parent itself.

I have not isolated the daughter. I have not named it. I have only the curve, drawn in pencil on the back of the ionization-chamber ledger, and the fact that the curve rises.

The sample was sealed on the eighth of March. Today is the twenty-ninth of April. The leaf falls in five minutes and twenty-two seconds.