Search for two-phonon octupole excitations in 146 Gd Energy Postgraduate Conference 2013 University of Zululand/ University of the Western Cape Nontobeko Khumalo

 Introduction & Literature Review  Experimental Techniques and Equipment  Preliminary Results  References  Acknowledgements Outline

147 Tb 146 Gd 144 Eu 144 Gd 145 Gd 149 Dy 148 Dy 146 Tb 148 Tb 147 Gd 143 Eu 145 Eu 140 Pm 143 Sm 142 Sm 146 Eu 148 Gd 144 Sm 141 Sm 142 Eu 142 Pm 145 Sm 143 Pm 141 Pm 142 Nd 140 Nd 141 Nd 149 Tb 150 Dy 147 Eu 143 Nd 144 Pm 146 Sm Z Introduction & Literature Review N stable nuclei

ћћ 2ћ2ћ 3ћ3ћ ,2,4 + 0,2,3,4,6 + E –3– 0,2,4,6 + E3 Quadrupole Vibration Octupole Vibration Introduction & Literature Review

 Single-particle Energies (MeV)  146 Gd has the features of a doubly closed shell nucleus.  It is accesible by low momentum transfer fusion-evaporation reactions.  146 Gd is the only doubly even nucleus besides 208 Pb with a 3 - first excited state (lowest in energy).  Expectation to observe the 3 -  3 - double octupole. S.W.Yates et al.. Z. Phys. A324 (1986) 417 Introduction & Literature Review

381.7 keV gate KeV E1 E KeV KeV E KeV E2 324 KeV 7 - E KeV E KeV 146Gd keV Introduction & Literature Review Caballero L. et al., (2010). Phys. Rev. C 81,

AFRODITE with nine standard clover detectors and each clover is composed of 4 crystal elements. (at iThemba LABS)  γ - γ coincidence experiment with the 144 Sm (α, 2n) 146 Gd fusion-evaporation reaction at an energy of 26.3 MeV  144 Sm target of 3 mg/cm2 thickness was bombarded with α particles.  This reaction is the most suitable stable- beam combination to study non-yrast states in 146 Gd.  Maximum frequency of ~50 KHz coincidence rate using the new digital- electronics system.  Gamma rays were detected using the AFRODITE array composed of nine standard clovers with BGO shields. Experimental Techniques & Equipment

 Gamma-ray energy spectrum showing the total projection for the γ - γ coincidence matrix.  The data collected have ~ 1.85×10 9 γ - γ coincidences for the total projection with a time prompt condition.  Best time coincidence condition (100 ns gives the best peak/total) Preliminary Results

DISCUSSION AND CONCLUSION  This was the first ever experiment at iThemba LABS performed with the digital electronics and there was an improvement by a factor of ~x10 coincidence rate.  So far there is no evidence for two-phonon octupole vibrations.  The next step will be to set the limits for these extremely weak transitions.

References 1. Bohr A. and Mottelson B.R.(1998). Nuclear Structure, Vol 2. Caballero L. et al., (2010). Phys. Rev. C 81, Yates S.W. et al., (1986). Z. Phys. A 324, Caballero L. (2010), PhD Thesis Acknowledgements  Thank God for everything!  My supervisors, Prof J.N Orce and Dr S.S Ntshangase.  iThemba LABS.  Special thanks to Tshepo Dinoko, Jayson Easton, Dr P. Jones, Siyabonga Majola and Vincent Kheswa  NRF and the MANUS/MATSCI programme. References & Acknowledgements