Download presentation

Presentation is loading. Please wait.

Published byKolby Newitt Modified over 2 years ago

1
Cluster states around 16 O studied with the shell model Yutaka Utsuno Advanced Science Research Center, Japan Atomic energy Agency ―Collaborator― S. Chiba (JAEA)

2
Introduction Excited states around 16 O – Plenty of -cluster or multiparticle-multihole states Famous example: 0 + 2 of 16 O located at 6.05 MeV Associated with a rotational band (cf. -gas state) Still very difficult to describe with ab initio calculations Still difficult to describe with microscopic models

3
Previous shell-model studies Haxton and Johnson (HJ) – Up to full 4hw states – Shell gap is determined so as to reproduce the intruder states. Warburton, Brown and Millener (WBM) – Model space similar to HJ – WBT interaction – In order to reproduce the intruder states, the N=Z=8 shell gap must be narrowed by ~3 MeV from that of the original interaction. Can this be justified? → Scope of the present work Effect of 6hw and more? W.C. Haxton and C. Johnson, Phys. Rev. Lett. 65, 1325 (1990). 16 O 6hw?

4
Effect of configurations beyond 4p-4h Configurations beyond 4p-4h does not account for the lowering. Any other effect? 0 + of 16 O with PSDWBT (in full p-sd shell) Only ~1 MeV

5
Single-particle energy vs. observables Usual procedure (Koopmans theorem): SPEs are identified with the energies of the “single-particle states” for 17 O and “single-hole states” of 15 O measured from the 16 O energy. – Correct in the independent-particle limit – N=Z=8 gap: S n ( 16 O)-S n ( 17 O) – Correlation energy may change S n ’s but not always does: if the gain in the correlation energy is common, it is cancelled in the expression of separation energy. Taken from A. Bohr and B.R. Mottelson, Nuclear Structure vol. 1 S n ( 16 O) S n ( 17 O)

6
Cross-shell correlation energy Cross-shell correlation energy: the energy gained by incorporating the p to sd shell excitation – the same as the usual correlation energy in 15,16,17 O – Peaked at 16 O: 9.4 MeV for 16 O, 8.4 MeV for 17 O, and for 7.2 MeV 15 O – The 1/2 - in 15 O has an especially small correlation energy. – The “experimental shell gap” S n ( 16 O)- S n ( 17 O) increases by 3.2 MeV. Need for renormalization of SPE

7
What makes the corr. energy of 16 O largest? excitation 16 O 15 O 17 O pn 0065.973.168.3 1123.920.122.8 022.91.42.5 202.93.33.0 Component of the wave function (%) blocked orbit p 1/2 p 3/2 p 1/2 p 3/2 16 O 17 O sd PSDWBT interaction

8
Renormalization of SPE Energies of 17 O(5/2 +, 1/2 +, 3/2 + ), 15 O(1/2 -, 3/2 - ), 20 Ne(0 + ) and 12 C(0 + ) relative to 16 O(0 + ) are fitted to experiment including correlation energy. Seven parameters, SPE’s and overall two-body strengths of p-shell and sd- shell int., are adjusted. A much narrower gap is obtained.

9
Systematics of the 0 + states Comparison with the calculation a.No excitation across the N=Z=8 gap b.Full p-sd calc. with the original gap c.Full p-sd calc. with the reduced gap so as to reproduce the separation energy including correlation – Missing states are reproduced.

10
Breaking of the closure Probability of the closure in the ground state of 16 O: only 45% – decreased from PSDWBT value 66% due to the narrower shell gap – Is this reasonable? M1 excitation: a good observable to probe the closed shell – No M1 excitations are allowed if 16 O were a complete closure. 0p-0h state and 2p-2h cannot be connected with a one-body operator. ExperimentCalculation Ex. (MeV)B(M1)↑n-thTEx. (MeV)B(M1)↑ 16.220.225(30)4116.400.076 17.140.348(51)7117.460.352 18.80.129(30)13118.900.208 Exp.) K.A. Snover et al., Phys. Rev. C 27, 1837 (1983). The calculation also predicts that there are many unobserved 1 + states.

11
The case of a j-j closure 56 Ni Correlation energy is the smallest at the core. Difference from the L-S closure: parity – Odd-particle excitation is allowed. – Deformation (in 52 Fe)

12
Summary Cluster (or multiparticle-multihole) states around 16 O are investigated with the full p-sd shell-model calculation. Correlation energy is peaked at 16 O, which works to decrease the bare shell gap from the “observed” shell gap. As a result, excited states are pulled down to a right position. Large core breaking associated with the narrow gap is supported by strong M1 excitations from the ground state. Perspectives: 40 Ca – impossible to perform a conventional shell-model calculation with a 10 15 m-scheme dimension – use of the Monte Carlo shell model: see Shimizu’s seminar tomorrow for recent progress

13
Selected levels of 16 O Rotational band (positive parity) and 1p-1h are well reproduced. Exp.Calc.

14
Energy levels of 17 O Exp. Calc. 5p-4h state

Similar presentations

OK

Recent shell-model results for exotic nuclei Yutaka Utsuno Advanced Science Research Center, Japan Atomic Energy Agency Center for Nuclear Study, University.

Recent shell-model results for exotic nuclei Yutaka Utsuno Advanced Science Research Center, Japan Atomic Energy Agency Center for Nuclear Study, University.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Oled flexible display ppt online Ppt on road accidents yesterday Ppt on hydroelectric power plant Shared value creating ppt on ipad Ppt on natural resources management Ppt on seven segment display circuit Ppt on census 2001 people Mp ppt online counselling 2012 By appt only Ppt on zener diode operation