During this time I had the singular good fortune of being able to discuss the problem constantly with Einstein. Some experiments done at Einstein's suggestion yielded no decisively new result.

Film consumption however was so enormous that our laboratory with the film strips strung up for drying sometimes resembled an industrial laundry.

Shortly afterwards (1930) I discovered, with H. Becker, the gamma rays that are generated on bombarding not only boron, but also other elements, with alpha rays.

Direction coupling between the various radiations generated in a nuclear reaction both with one another and with the initiating radiation can also be detected and measured by coincidences; this provides valuable information about the structure of the atomic nuclei.

During conversion, the newly formed nucleus is not always immediately in the ground state, but is at times in one of the possible activated states.

I used a circuit employing a multiple-grid coincidence valve as early as 1929.

Rossi was the first to describe another system working with valves in parallel; it has the advantage that it can easily be extended to coincidences between more than two events, and is therefore predominantly used today.

In this case, the particle formed has correspondingly less energy, whereas the product nucleus passes into the ground state with emission of the quantity of energy saved as gamma radiation.

Our arrangement therefore consisted of two needle counters, past the common front wall of which, without touching it, swept a beam of X-rays.