Very proton rich nuclei with N≈82 - I. In-beam γ spectroscopy; seniority isomerism in¹⁵⁰Er

Postaccelerated⁵⁸Ni and⁶⁰Ni beams from the Munich MP tandem have been used to study the compound reactions⁵⁸Ni→⁹³Nb,⁹²Mo,⁹⁴Mo and⁶⁰Ni→⁹²Mo. The final nuclei¹⁴⁸Er,¹⁵⁰Er and¹⁴⁷Ho have been investigated with in-beam γ-spectroscopic methods, such as excitation functions, γγ coincidences, bunched-beam and pulsed-beam techniques. Level schemes of¹⁴⁸Er,¹⁵⁰Er and¹⁴⁷Ho have been established with the following level energies, spins, parities and half-lives:¹⁴⁸Er: 646.6 keV 2⁺; 1,524.0(4⁺); 2,254.3(5^-); 2,526.9(6⁺); 2,537.3(7^-), 2,706.0(7^-, 8^-); 2,784.4(8⁺); 2,915.5(10⁺) 13±3 μs¹⁵⁰Er: 1,578.9 keV 2⁺; 1,786.4 3^-; 2,261.2(5^-); 2,634.1(7^-); 2,734.3(8⁺); 2,798.3(10⁺) 2.7±0.2 us; 4,001.9; 4,491.8; 4,886.0; 5,222.7¹⁴⁷Ho: 765.4; 1,737.2; 2,355; 2,656.6 The level scheme of¹⁵⁰Er has been discussed in the framework of the seniority scheme. Perfect agreement with the experiment has been found for the predictions of this scheme for the half-lives of 10⁺ states in N=82 isotones. This is the first nuclear region where the predictions of the seniority scheme have been observed without strong perturbation.