Isospin non-conserving interactions studied through triplet energy differences. David Jenkins

Transcription

1 Isospin non-conserving interactions studied through triplet energy differences David Jenkins

2 evena odda!2!1012!5/2!3/2!1/21/23/25/2 Isobaric Spin (Isospin) In the absence of Coulomb interactions between the protons, a perfectly charge-symmetric and chargeindependent nuclear T excitedstates force would result in the binding energies of all these isobaric analogue nuclei being identical; that is, they would be structurally identical. forbiddenstates protonrich N=Z N=Z neutronrich ( ) 2 T z = N Z projec;on forbiddenstates 5/2 3/2 1/2 isospin 2 1 0

3 For T=1 triplets: MED J = E J,T z = 1 E J,T z =+1. Mirror energy differences are isovector and sensitive to: single-particle Coulomb shifts, electromagnetic spin-orbit interaction, changes of shape/radius of nuclei TED J = E J,T z = 1 + E J,T z =+1 2E J,T z =0. Isotensor energy differences reflecting differences between nn, pp and pn force. Not sensitive to one-body terms but only two-body i.e. sensitive to Coulomb multipole and isospin-nonconserving forces 3

4 Shapes of N=Z nuclei Very Prolate Oblate Triaxial Very, very sensitive to underlying quantum structure The original phenomonological M-M theory, (Microscopic Macroscopic) was very sound. P. Moller and J.R. Nix. At. Nuc. Data Tables, 26 (1981) 1965 S. Aberg. Phys Scr. 25 (1982) 23 W. Nazarewicz. Nucl. Phys A435 (1985) 397. R. Bengtsson. Conf on the structure in the zirconium region, 1988 {Classic Potential Energy Surface calculations. BUT The whole concept of isolated shapes is naive: there are multiple shapes with lots of mixing, as the barriers between shapes are not high.

5 Recoil-decay tagging 5

6 Recoil-beta tagging 6

7 RDT Instrumentation at JYFL GREAT Focal plane spectrometer RITU Gas-filled recoil separator Transmission JUROGAM TDR Total Data Readout Triggerless data acquisition system with 10 ns time stamping 7

8 Test case: 74 Rb 8

9 Proof-of-principle nat Ca ( 36 Ar, pn) 74 Rb E beam = 103 MeV τ ½ ( 74 Rb) = 65 ms β + endpoint ~ 10 MeV σ ~ 10 µb 9

10 74 Rb 10

11 Crossing the line of N=Z 11

12 UoY Designed to suppress events associated with cp evapora3on channels. Consists of x 20 mm CsI crystals (Hamamatsu) divided into 6 flanges (8 x 2 crystals in each flange). Signal chain: Mesytech preamplifiers -> GObox -> Lyrtech ADCs. Measured detec3on efficiency for 1 charged par3cle is RITU LISA chamber JurogamII

13 66 Se P. Ruotsalainen et al., Phys. Rev. C 83, (2013) 13

14 Counts / kev Counts / kev Counts / kev Sr 74 Sr kev 74 Rb kev 74 Rb kev 74 Sr kev E γ (kev) (a) (b) (c) Counts / 2 kev (a) (b) (c) ( 70 Br) 70 Kr 964 ( 70 Br) Energy (kev) 1069 ( 70 Br)

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16 Conclusions New techniques developed to study structure of nuclei beyond the line of N=Z: - Beta-tagging - - Charged particle veto Highly-pixellated silicon detectors Results obtained on excited states of N=Z-2 nuclei: 66 Se, 70 Kr and 74 Sr TED extracted and compared with shell model calculations TED appear to need additional isospin-nonconserving component to reproduce them as earlier shown in f7/2 shell TED can be reproduced using 100 kev INC term irrespective of orbitals involved e.g. fp for 66 Se and g9/2 for 74 Rb What is the origin of this INC component in terms of nuclear force?

17 Acknowledgements York, JYFL RITU-GAMMA group P. Ruotsalainen - 66 Se D. Debenham - 70 Kr J. Henderson - 74 Sr