Behavior of intruder based states in light Bi and Tl isotopes: The study of [sup 187]Bi α decay

Abstract

Intruder state excitation energies in odd-mass nuclei just outside a closed proton shell plotted versus neutron number generally exhibit parabola-shaped curves with minima near neutron mid-shells. The Bi isotopes, however, do not seem to follow this trend. Recent experiments performed at Argonne National Laboratory have identified the previously unobserved Is7Bi ground state (h9/2) to lS3Tl ground state si12 a transition. Its energy when combined with those of two earlier known transitions, namely Is7Bi (h9/2) + 183mTl (h9/2) and 1s7mBi (~1 1 2 ) -+ 1s3Tl(s~/2), establishes the excitation energies of the 183mTl and 187mBi to be 620(20) keV and I lO(20) keV, respectively, This value for 187mBi is 80 keV lower than the excitation energy of the same intruder level in Is9Bi. Implications of this result with respect to intruder-state systematics are discussed.