Excited states in 133 Sn were investigated through the β decay of 133 In at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for 133 In, allowing us to study separately, and in detail, the β-decay branch of 133 In J π = (9/2 +) ground state and its J π = (1/2 −) isomer.

There is sparse direct experimental evidence that atomic nuclei can exhibit stable 'pear' shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole (E3) matrix elements have been determined for transitions in 222,228 Ra nuclei using the method of sub-barrier, multi-step Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of E3 matrix elements for different nuclear transitions is explained by describing 222 Ra as pear-shaped with stable octupole deformation, while 228 Ra behaves like an octupole vibrator.

Published version Kirsebom, O. S.; Hukkanen, M.; Kankainen, A.; Trzaska, W. H.; Strömberg, D. F.; Martínez-Pinedo, G.; Andersen, K.; Bodewits, E.; Brown, B. A.; Canete, L.; Cederkäll, J.; Enqvist, T.; Eronen, T.; Fynbo, H. O. U.; Geldhof, S.; de Groote, R., Jenkins, D. G.; Jokinen, A.; Joshi, P.; Khanam, A.; Kostensalo, J.; Kuusiniemi, P.; Langanke, K.; Moore, I.; Munch, M.; Nesterenko, D. A.; Ovejas, J. D.; Penttilä, H.; Pohjalainen, I.; Reponen, M.; Rinta-Antila, S.; Riisager, K.; de Roubin, A.; Schotanus, P.; Srivastava, P. C.; Suhonen, J.; Swartz, J. A.; Tengblad, O.; Vilen, M.; Vínals, S.; Äystö, J. Kirsebom, O. S.; Hukkanen, M.; Kankainen, A.; Trzaska, W. H.; Strömberg, D. F.; Martínez-Pinedo, G.; Andersen, K.; Bodewits, E.; Brown, B. A.; Canete, L.; Cederkäll, J.; Enqvist, T.; Eronen, T. et al. (2019). Measurement of the 2+→0+ ground-state transition in the β decay of 20F.We report the first detection of the second-forbidden, nonunique, 2 + → 0 + , ground-state transition in the β decay of 20 F. A low-energy, mass-separated 20 F + beam produced at the IGISOL facility in Jyväskylä, Finland, was implanted in a thin carbon foil and the β spectrum measured using a magnetic transporter and a plasticscintillator detector. The β-decay branching ratio inferred from the measurement is b β = [0.41 ± 0.08(stat) ± 0.07(sys)] × 10 −5 corresponding to log f t = 10.89(11), making this one of the strongest second-forbidden, nonunique β transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on 20 Ne is now known to within better than 25% at the relevant temperatures and densities.

There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the Standard Model of particle physics. Isotopes of both radon and radium have been identified as candidates for such measurements. Here, we observed the low-lying quantum states in 224Rn and 226Rn by accelerating beams of these radioactive nuclei. We show that radon isotopes undergo octupole vibrations but do not possess static pear-shapes in their ground states. We conclude that radon atoms provide less favourable conditions for the enhancement of a measurable atomic electric-dipole moment.

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