A study of gadolinium isotopes around N = 90 utilizing particle-gamma coincidences

• Main Author: Ross, Timothy J.
• Published: University of Surrey 2012
• Subjects: 621.4837
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582858

Particle-γ coincidence data can be used as a strong tool for studying low energy nuclear structure. The STARS-LIBERACE array at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory was used to study gadolinium isotopes straddling the N = 90 shape change region. A 25 Me V proton beam was impinged upon 154Gd and 158Gd targets. The gadolinium isotopes 152,153,154,156,157,158Gd were studied following the (p,p'), (p,d) and (p,t) neutron transfer reactions. The primary focus of this work is to study the structure of and identify single- neutron quasi-particle states in the odd N Gd nuclei following the (p, d) reactions. Nu- merous new levels are observed in both 153Gd and 157 Gd and multiple new, rays have been observed and associated with these and other previously known levels. A large excitation energy gap between approximately 500 keV and 1500 keV is observed in the level schemes of both nuclei where very few states are populated. This gap appears to demonstrate the persisting influence of the N = 64 spherical sub-shell closure to inter- mediate deformations. It is striking that such an effect is apparent when probed from so far above (i.e. ~ 30 neutrons away). The secondary focus of this work is upon the angular momentum transferred to the statistical continuum region of these nuclei via different light ion transfer reactions, i.e. between approximately 2 Me V and the neutron separation energy. The angular momen- tum transferred via (p,d) and (p,t) reactions populating 157 Gd and 156Gd respectively was measured using two independent techniques. The first technique involves studying the ,-ray decay path within the residual nucleus, the second technique involves measur- ing the angular distribution of the light ions following the reaction. The two techniques are in good agreement and appear to verify each other. The measured angular momen- tum transferred via the (p,t) reaction is measured to be a distribution centered around ΔL = 4 - 5 h. The angular momentum transferred via the (p,d) reaction is slightly lower and is closer to ΔL = 4 h.