RESUMO
We studied the decay of 189W as produced via the 192Os[n,alpha]189W reaction on a 99.9% isotopically enriched 192Os target. The irradiations were performed at the intense neutron beam facility at Cyclotron Research Center, Université Catholique Louvain-la-Neuve (CRC-UCL) (Belgium), where fast neutrons [En approximately 20 MeV, phi(n) = (4.8 +/- 0.3)10(11) ns(-1) cm(-2)] were generated by stopping 50 MeV deuterons on a thick Be target. The half-life of 189W was determined to be 9.3 +/- 0.3min, compared to 10.8 +/- 0.2min obtained from the 188W[n,gamma]189W reaction. The energies of the two predominant gamma-rays of 189W, 260.4 +/- 1.3 and 421.7 +/- 1.4 keV were in good agreement with that from the [n,gamma] reaction, however, the relative intensities of the two gamma-rays were not consistent. From the [n,gamma] reaction, the relative intensities of the 260 and 421 keV gamma-rays were 97 to 100, whereas from the [n,alpha] reaction the relative intensities were 100 to 77, respectively. Assuming a cross-section ratio of 20 +/- 5 for [n,p3n] to [n,alpha] reactions, a cross-section of 0.5 +/- 0.2 mb was suggested for the 192Os[n,alpha]189W reaction, and the absolute intensity of the 260 keV gamma-ray was estimated to be approximately 50%.
