PIONIC 2p LEVEL WIDTHS IN LIGHT NUCLEI

This paper provides an extension of previous work [l] on the pionic 2p-1s yields for nuclei flom N to Na in two directions. We report here on measurements of the 2p-1s yields for the lighter nuclei Be, FOB, natB and C, and from these data we deduce the natural 2p level widths r(2p) due to pion absorption by comparison with the 2p-1s X-ray transition rate WX. In ref. 1, WX was calculated on a purely electromagnetic basis. Now we take into account the effect of the strong r-nucleus interaction on Wx. We give here also the correspondingly modified values for the nuclei dealt with in ref. 1. The measurements were performed at the CERN 600 MeV Synchrocyclotron using a scintillation counter telescope with coincidence counters-l, 2.3 in front of the target and a veto counter 4 behind the target [2]. The majority of the spectra were measured with a windowless Ge detector of volume 0.8 cm2 X x 1.0 cm. Its energy resolution was 0.8 keV at 70 keV. The Be and natB targets were of cylindrical shape with a diameter of 9 cm and a thickness of 2 g,‘cm2. The IOB powder was contained in a rectangular box (8 X 6 cm2) with a thickness of 0.6 g/cm2. of 5.4 g/cm2. The C target was a graphite sheet