PING: A phoswich instrument for dose rate measurements on board a stratospheric balloon

The interaction of primary cosmic rays with the constituents of the Earth's atmosphere leads to a complex radiation field which consists of charged and neutral particles. For the determination of dose rates up to 30 km a stratospheric balloon flight has been performed near Berlin. The instrument used for this flight is the active radiation detector PING (Phoswich Instrument for Neutrons and Gammas). The instrument has been developed to determine the intensity of neutrons and gammas. The detector is composed of two scintillators, a plastic scintillator BC412 and the inorganic scintillator CsI(Na), optically coupled to each other and to a photomultiplier tube. BC412 is hydrogen rich and thus very sensitive to neutrons while CsI(Na) has a high cross section for gamma radiation due to its high Z. In the balloon flight the dose induced by neutrons, gamma rays and charged particles was measured since the instrument is also sensitive to charged particles. By applying pulse shape analysis it was possible to separate the dose caused by neutrons. A description of the concept of PING as well as calibration measurements and first results of the balloon flight are presented.