Search for two-phonon octupole excitations in 146 Gd

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

2. Outline • Introduction & Literature Review • Experimental Techniques and Equipment • Preliminary Results • References • Acknowledgements

3. Introduction & Literature Review Z 148Dy 149Dy 150Dy 66 149Tb 146Tb 147Tb 148Tb 65 144Gd 145Gd 146Gd 147Gd 148Gd 64 142Eu 143Eu 144Eu 145Eu 146Eu 147Eu 63 62 141Sm 142Sm 143Sm 144Sm 145Sm 146Sm 140Pm 141Pm 142Pm 143Pm 144Pm 61 stable nuclei 140Nd 141Nd 142Nd 143Nd 60 N 79 80 81 82 83 84

4. 3ћ 0,2,3,4,6+ 0,2,4,6+ E2 E3 0,2,4+ 2ћ E2 3– 2+ ћ E3 E2 0 0+ 0+ Introduction & Literature Review Octupole Vibration Quadrupole Vibration

5. 0 -5 -10 -15 Introduction & Literature Review Single-particle Energies (MeV) • 146Gd has the features of a doubly closed shell nucleus. 82 64 126 • 146Gd is the only doubly even nucleus besides 208Pb with a 3- first excited state (lowest in energy). 50 • It is accesible by low momentum transfer fusion-evaporation reactions. 82 • Expectation to observe the 3-3- double octupole. 50   S.W.Yates et al.. Z. Phys. A324 (1986) 417

6. 381.7 keV 502.6 KeV E1 1905.8 KeV E3 Introduction & Literature Review 6+ 3484 KeV 826.7 KeV Caballero L. et al., (2010). Phys. Rev. C 81, 031301 7 - 324 KeV E1 E2 5 - 1078 KeV E2 3 - 381.7 keV gate 1579 KeV E3 0+ 146Gd

7. Experimental Techniques & Equipment • γ - γ coincidence experiment with the 144Sm (α, 2n) 146Gd fusion-evaporation reaction at an energy of 26.3 MeV • 144Sm 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 146Gd. • 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 . • AFRODITE with nine standard clover detectors and each clover is composed of 4 crystal elements. (at iThemba LABS)

8. Preliminary Results • Gamma-ray energy spectrum showing the total projection for the γ - γ coincidence matrix. • The data collected have ~ 1.85×109 γ - γ coincidences for the total projection with a time prompt condition. • Best time coincidence condition (100 ns gives the best peak/total)

9. 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.

10. References & Acknowledgements 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. Thank You ! References 1. Bohr A. and Mottelson B.R.(1998). Nuclear Structure, Vol 2. Caballero L. et al., (2010). Phys. Rev. C 81, 031301 3. Yates S.W. et al., (1986). Z. Phys. A 324, 417 4. Caballero L. (2010), PhD Thesis