A search for α-decay of high spin isomers in rare earth nuclei using a decay-in-flight technique

The technique employed for these experimental investigations made use of a specially designed trajectory detector to observe α-decay directly from the reaction products which recoiled from a thin target. Studies have been performed to optimize this decay-in-flight method for the observation of charged particle decay of short lived systems having small production cross sections. The results of these studies are reported.

Analytical procedures developed for reduction of the decay-inflight data are discussed which yielded information about the particle types detected, the energies of these particles, the trajectories followed, and the positions of parent nuclei at the time the detected particles were emitted. Kinematic and solid angle corrections are considered which permitted correction for Doppler broadening effects and allowed estimates to be made with regard to the lifetime and production cross section of the parent state.

The experimental method and the associated analytical procedures were verified by study of α-decay following the reaction ²⁰⁸Pb(¹⁶0,p6n)²¹⁷Ac. The results obtained were in agreement with those reported by others. Detailed investigation of the background radiations associated with decay-in-flight measurements permitted determination of the limits of detection sensitivity.

No system studied in the search for yrast trap α-decay showed activity significantly above background in the 6 - 16 MeV energy range. Alpha-decay cross section limits were placed for 14 of the predicted reaction products in which high spin isomers are known with lifetimes in the range studied. These upper limits ranged from ~ 3 - 200 µ b. Comparison to theoretical total cross sections allowed α-branching ratio estimates to be made.