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.

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

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

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.

This result was confirmed by different researchers using various experimental arrangements.

Strict conservation of energy in the elementary process had thus been confirmed also by a negative experiment.

To demonstrate this simultaneity is by no means trivial, because it may for example happen that the product nucleus always forms in an activated state at first.

The material particle nature of primary cosmic radiation has been confirmed, although the processes turned out to be extraordinarily more complicated than we had assumed.

Many applications of the coincidence method will therefore be found in the large field of nuclear physics, and we can say without exaggeration that the method is one of the essential tools of the modern nuclear physicist.

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.