ZoitsehriftforPhysik A Z. Phys.A - Atomic Nuclei 335,25-29 (1990) Atomic Nuclei Springer-Verlag 1990 Electron Capture Probabilities in ~ M.V.S. Chandrasekhar Rao 1, G. Sree Krishna Murty 1, K. Radha Krishna 1, S. Bhuloka Reddy i, G. Satyanarayana l, C.V. Raghavaiah 1, D.L. Sastry 1, and S.N. Chintalapudi 2 Swami Jnanananda Laboratories for Nuclear Research, Andhra University, Visakhapatna.rn, India 2 Variable Energy Cyclotron Centre, Calcutta, India Received August 10, 1989 The K-electron capture probabilities for the 1/2---*3/2- and 1/2---* 1/2 + transitions in the decay of a~ were measured for the first time using the sum coincidence method. The experimental PK values were estimated to be 0.824+0.042 and 0.851+0.046 for the allowed and first-forbidden beta transitions, respectively in agreement with the theory. The PL experimental values to these two levels were also computed using the experimental PL/PK values reported by earlier authors. These results are also found to be consistent with the theoretical PL values. PACS: 23.40.Hc; 27.60. +j 1. Introduction In recent years the availability of heavy ion machines, high resolution solid state detectors and sophisticated data acquisition systems have facilitated the produc- tion of neutron deficient isotopes and the study of nuclear structure upto high spins. The K-electron capture probability and EC/fl + ratios in these nuclei are being experimentally investigated and compared with the theoretical values. Schulz et al. [1] have mea- sured the PL/P K ratios concerning the 1/2- --+ 3/2- and 1/2-~ 1/2 + electron capture decay transitions in 1~ The present work concerns a measurement of the K-electron capture probability characterising al- lowed 1/2---* 3/2- and non-unique first forbidden 1/2---* 1/2 +, fl+ transitions in the decay of neutron deficient ~~ isotope employing the sum coinci- dence method. The decay of 1~ is well studied in on-line as well as off-line modes [24]. The decay scheme [5] of the l~ of present interest is shown in Fig. 1. The transitions studied in this work are indi- cated by thick lines. The sum coincidence method proposed by Dasmahapatra and Mukherjee [6] and used by other authors [7-9] is followed in the present measurements. The intensity in the sum peak is due to 1) the summing of X-rays followed by electron capture decay and the cascade v-ray and 2) the sum- ming of the same v-ray and the X-rays due to internal conversion of the following cascade v-rays. For the determination of the K-electron capture probability (PK), the theoretical expression used by Behrens and Janecke [10] was used. The PL experimental values are deduced from the knowledge of Ph/Pr and PK ex- perimental values. 2. Experimentation and Results The present experiments were carried out at the Swa- mi Jnanananda Laboratories for Nuclear Research, Andhra University, Visakhapatnam, India. The 1~ isotope was produced by irradiating l~ target of thickness 12 mg/cm 2 with s-particles at a bombarding energy of 30 MeV and a beam current of 500 nA via the reaction l~ 2n)l~ at Variable Energy Cyclotron Centre, Calcutta, India. Besides 1~ some other short lived isotopes like l~ l~ l~ ~~ l~ and l~ with half-lives of the order of minutes and another isotope l~ with Tx/2=8.5 d were produced through side channels.