Search for two-phonon octupole excitations in 146Gd

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

147Tb

146Gd

144Eu

144Gd 145Gd

149Dy148Dy

146Tb 148Tb

147Gd

143Eu 145Eu

140Pm

143Sm142Sm

146Eu

148Gd

144Sm141Sm

142Eu

142Pm

145Sm

143Pm141Pm

142Nd140Nd 141Nd

149Tb

150Dy

147Eu

143Nd

144Pm

146Sm

8280 81 8379 84

64

60

61

66

65

62

63

Z

Introduction & Literature Review

N

stable nuclei

ћ

2ћ

3ћ

0 0+

2+

0,2,4+

0,2,3,4,6+

E2

E2

E2

0+

3–

0,2,4,6+

E3

E3

QuadrupoleVibration

OctupoleVibration

Introduction & Literature Review

82

64

50

126

82

50

-5

-10

0

-15

Single-particle Energies (MeV) 146Gd has the features of a

doubly closed shell nucleus.

It is accesible by low momentum transfer fusion-evaporation reactions.

146Gd is the only doubly even nucleus besides 208Pb 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

502.6 KeVE1

E31905.8 KeV

0+

3 -

5 -

1579 KeVE3

1078 KeVE2

324 KeV7 - E2

6+826.7 KeVE1

3484 KeV

146Gd

381.7 keV

Introduction & Literature Review

Caballero L. et al., (2010). Phys. Rev. C

81, 031301

AFRODITE with nine standard clover detectors and each clover is composed of 4 crystal elements. (at iThemba LABS)

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 .

Experimental Techniques & Equipment

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)

Preliminary Results

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, 0313013. Yates S.W. et al., (1986). Z. Phys. A 324, 4174. 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