An Improved Particle Identifier for Studies of Low-Yield Nuclear Reactions

Studies of low-yield nuclear reactions such as (He3, He6) or (He4, He8) require definite identification of about one interesting particle in the presence of 106 to 107 reaction product particles. Conventional ¿E-E identifier systems are of limited value in these experiments as a small fraction of the abundant reaction particles produce ¿E signals which deviate considerably from their normal value. The resulting false identification signals cause a general background in the identifier output spectrum which interferes with the peak due to interesting particles. In the improved identifier two ¿E detectors are employed; each time a particle passes through the counter telescope two identifications are made, each using one of the ¿E signals. If they do not agree with each other within prescribed limits (due to one of the ¿E signals deviating from normal) the event is completely rejected. Fast coincidence and pile-up rejector techniques are used to reduce the effects of chance coincidences between unrelated detector signals and a fourth counter is used to reject high energy particles which pass completely through the telescope. Details of the instrument and its performance in several experiments are given, and the general problems in this type of work are also discussed.