Eur. Phys. J. A (2007) 32: 25-29
https://doi.org/10.1140/epja/i2007-10363-0

Regular Article - Nuclear Structure and Reactions

On the unusual properties of the 282 keV state in ¹³⁵Sb

¹ Institute of Experimental Physics, Warsaw University, Hoża 69, PL 00-681, Warsaw, Poland
² Institute for Structure and Nuclear Astrophysics, University of Notre Dame, 46616, Notre Dame, IN, USA
³ Department of Nuclear and Particle Physics, Uppsala University, SE-751 21, Uppsala, Sweden
⁴ Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University, 48824, East Lansing, MI, USA
⁵ Dipartimento di Scienze Fisiche, Università di Napoli Federico II and Istituto Nazionale di Fisica Nucleare, Napoli, Italy
⁶ Institute Laue-Langevin, F-38042, Grenoble Cedex 9, France
⁷ Department of Physics and Astronomy, University of Manchester, Brunswick Street, M13 9PL, UK
⁸ INFN Laboratori Nazionali di Legnaro, Legnaro, Italy
⁹ K.U. Leuven, IKS, Celestijnenlaan 200 D, 3001, Leuven, Belgium

^* e-mail: korgul@fuw.edu.pl

Received: 28 February 2007
Accepted: 5 April 2007
Published online: 30 April 2007

Abstract

Recently the first excited state in ¹³⁵Sb has been observed at the unexpectedly low excitation energy of only 282keV and interpreted as mainly d _5/2 proton coupled to the ¹³⁴Sn core. Based on theoretical considerations it was suggested that its low excitation energy is related to a relative shift of the proton d _5/2 and g _7/2 orbits induced by the neutron excess. We have measured the lifetime of the 282keV state by the advanced time-delayed βγγ(t) method. The measured half-life, T _1/2 = 6.1(4)ns, yields exceptionally low limits of B(M1;5/2₁ ⁺→7/2₁ ⁺)≤3.0×10^-4 μ ² _N and B(E2;5/2₁ ⁺→7/2₁ ⁺)≤54e ² fm ⁴. These strongly hindered M1 and slow E2 transition rates are similar to those for the transition de-populating the first excited state at 405keV in ²¹¹Bi. Results of shell model calculations with realistic interactions are presented. The M1 decay rate was found to be extremely sensistive both to the wave function and to the M1 effective operator.