NUSTAR2025

Decay spectroscopy of heavy nuclei at RIBF

Anabel Morales (IFIC, CSIC-UV and RIKEN) On behalf of the BRIKEN and DTAS collaborations

NUSTAR Week 2025

Prague, 2nd October 2025

Motivation

NUSTAR Week 2025 Prague, 2nd October 2025

Motivation

N=126

Terra Incognita

r process

Nuclear properties of interest for the r process

Shell evolution & deformation

Isomers & astromers

NUSTAR Week 2025 Prague, 2nd October 2025

Strength of closed shells

SENIORITY: number of neutrons or protons not paired to J=0. Good quantum number for semi-magic nuclei

[J.J. Resler et al., PRC 69, 034317 (2004)]

NUSTAR Week 2025 Prague, 2nd October 2025

Isomers in the 2νg9/2 shell

[ N. Al-Dahan et al., PRC 80, 061302(R) (2009) ]

[ A. Gottardo et al., PLB 725, 292 (2013) ]

[ A. Gottardo et al., PRL 109, 162502 (2012) ]

NUSTAR Week 2025 Prague, 2nd October 2025

Isomers in the 2νg9/2 shell

[ A. Gottardo et al., PRC 99, 054326 (2019) ]

[ N. Al-Dahan et al., PRC 80, 061302(R) (2009) ]

[ B.M.S. Amro et al., PRC 95, 014330 (2017) ]

NUSTAR Week 2025 Prague, 2nd October 2025

In-flight decay spectroscopy

BRIKEN

TATAKI-Pro

BigRIPS

F11

238U @ 345 AMeV

Steps for measuring the β decay of in-flight fragmentation residues:

1. Production. Relativistic fragmentation in inverse kinematics
2. Identification. Magnetic spectrometer
3. Decay setup. Ion, β, Ɣ, and neutron detectors​

NUSTAR Week 2025 Prague, 2nd October 2025

Decay spectroscopy at RIBF

Systematic measurements of isomeric decays, β half-lives, β strengths and P1n across N=126

More 20 new half-lives More than 60 new P1n More than 50 new P2n

Data for more than 70 nuclei still to be published...

DTAS

NP2112-RIBF208. Shell evolution beyond 208Pb: Isomer and β-decay spectroscopy of neutron-rich Ir toPo isotopes

BRIKEN

NP1712-RIBF158. β-decay spectroscopy in the vicinity of the N=126 closed shell

NUSTAR Week 2025 Prague, 2nd October 2025

Si telescope

BIGRIPS separator

BigRIPS & Xe MUSIC: Particle ID

NEW Xe MUSIC

Relativistic beam

NEW diamond detectors

NUSTAR Week 2025 Prague, 2nd October 2025

BIGRIPS separator

213Tl

215Tl

First N=126 experiment BRIKEN (2021)

BigRIPS & Xe MUSIC: Particle ID

A/Q

NEW Xe MUSIC

Relativistic beam

NEW diamond detectors

Experimental Nuclear Physics with HIAF Huizhou, 3-5 September 2025

The BRIKEN Decay setup

β-decay information extracted from time and position correlations

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NUSTAR Week 2025 Prague, 2nd October 2025

β-decay half-lives at BRIKEN

β decay of Pb isotopes

218Pb decay

217Pb decay

217Pb RIBF

217Pb GSI

218Pb RIBF

218Pb GSI

T1/2 = 7.6(10) s

T1/2 = 15(7) s

T1/2 = 18(3) s

T1/2 = 20(5) s

[ R. Caballero-Folch et al., PRL 95, 064322 (2017) ]

[ L. Sexton, PhD thesis. U. Edimburgh (2024) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

Isomer spectroscopy at BRIKEN

213Tl

New isomeric decay!

[ A. Gottardo et al., PRC 99, 054326 (2019) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

215Tl

2 new isomeric decays!

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NUSTAR Week 2025 Prague, 2nd October 2025

213Tl

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

215Tl

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

Interpretation of level schemes

Large-scale shell-model calculations

• Truncation for 215Tl:
• Max. 2 neutrons from high-spin to low-spin orbitals

[ Menglan Liu & Cenxi Yuan, PRC 106, 044314 (2022) ]

SM1

• SPEs: 207Tl and 209Pb
• TBME: Kuo-Herling and VMU+LS
• Eff. charges: eν = 0.8 & eπ = 1.8
• 7 orbitals above N = 126
• 5 orbitals below Z = 82

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NUSTAR Week 2025 Prague, 2nd October 2025

Interpretation of level schemes

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

Trend of 11/2- states in 207-215Tl

SM1 cannot reproduce the trend of Jπ=(11/2-) states originating from the 0πh11/2 proton-hole excitation as neutrons fill in the 1νg9/2 orbital

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

Trend of 11/2- states in 207-215Tl

SM2

Reduce the 0πh11/2 – 1νg9/2 monopole matrix elements by ~60%

ESPE = SPE + n·Vm

First observation of shell evolution beyond N=126

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

210,212Hg

New isomeric decay!

[ A. Gottardo et al., PLB 725, 292 (2013) ]

210Hg

212Hg

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NUSTAR Week 2025 Prague, 2nd October 2025

210,212Hg

New isomeric decay!

[ A. Gottardo et al., PLB 725, 292 (2013) ]

210Hg

212Hg

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NUSTAR Week 2025 Prague, 2nd October 2025

210,212Hg

SM1

SM1

210Hg:

• New placement of 662-keV transition based on γ-intensity balance and half-life
• Observation of a candidate (8+) → (6+) transition at 98 keV

212Hg:

• Observation of a candidate (2+) → 0+ transition at 632 keV

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NUSTAR Week 2025 Prague, 2nd October 2025

210,212Hg

SM1

SM1

ν1g9/24 (υ=4)

ν1g9/24 (υ=2)

ν1g9/24 (υ=2)

All excitation energies are in good agreement with SM1 calculations

SM1 predicts 4+1 with υ = 2, and 4+2 with υ = 4 ( R64 = 4 )

Ratio R64 = 16(7) from γ-intensity balance indicates Δυ = 2 for the 6⁺ → 4+2 transition

The ratio for exact conservation of seniority ( R64 = 7.6 ) is consistent with the measured value

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NUSTAR Week 2025 Prague, 2nd October 2025

The TATAKI-Pro decay setup

β-decay information extracted from time and position correlations

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NUSTAR Week 2025 Prague, 2nd October 2025

DTAS beyond N=126

Isomer spectroscopy

214Pb

8+ seniority isomer (ENSDF)

t1/2 = 6.05(8) μs

[ A. Gottardo et al., PRL 109, 162502 (2012) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

DTAS beyond N=126

Isomer spectroscopy

214Pb

8+ seniority isomer (ENSDF)

[ A. Gottardo et al., PRL 109, 162502 (2012) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

DTAS beyond N=126

Isomer spectroscopy

214Pb

8+ seniority isomer (ENSDF)

[ A. Gottardo et al., PRL 109, 162502 (2012) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

DTAS beyond N=126

[ J. Wu et al., submitted to PRL ]

Isomer spectroscopy

[ A. Gottardo et al., PLB 725, 292 (2013) ]

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NUSTAR Week 2025 Prague, 2nd October 2025

DTAS beyond N=126

210Hg

Isomer spectroscopy

[ A. Gottardo et al., PLB 725, 292 (2013) ]

[ J. Wu et al., submitted to PRL ]

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NUSTAR Week 2025 Prague, 2nd October 2025

CONCLUDING REMARKS

GSI and RIBF are presently the only facilities where heavy nuclei beyond N=126 can be successfully produced and studied. They are of great interest in nuclear structure and r-process nucleosynthesis

Very rich scientific outputs of BRIKEN N=126 experiment: New isomers in 213,215Tl, and 212Hg First evidence of an evolving orbital beyond N=126 ( πh11/2 ) (2+1) systematics extended up to N=132 in Hg

First DTAS experiment beyond N=126 successfully carried out in November 2024. Large scientific output. Analysis ongoing

Future opportunities: IDATEN - Largest fast-timing array in the world (FATIMA) C2URIE - 4π HPGe array for high-resolution γ-ray spectroscopy (DEGAS)

BRIKEN and DTAS collaborations

Thank you very much for your attention

16-19

12-15

1-2

3-5

6-10

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20-21

22-23

24-26

30-32

28-29

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Misc

RIBF208

r process

CORR

TAGS

BRIKEN

Systematics in Tl & Pb nuclei

SM2

Reduce the 0πh11/2 – 1νg9/2 monopole matrix elements by ~60%

Apply SM1 truncation to all excited states in Tl and Pb with N>126

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

Good reproduction of all excitation energies in both isotopic chains

Systematics in Tl & Pb nuclei

SM2

Reduce the 0πh11/2 – 1νg9/2 monopole matrix elements by ~60%

Apply SM1 truncation to all excited states in Tl and Pb with N>126

Calculate B(E2) & B(E3) transition probabilities

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

NUSTAR Week 2025 Prague, 2nd October 2025

Systematics in Tl & Pb nuclei

SM2

Reduce the 0πh11/2 – 1νg9/2 monopole matrix elements by ~60%

Apply SM1 truncation to all excited states in Tl and Pb with N>126

Calculate B(E2) & B(E3) transition probabilities

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

Disagreement between measured and calculated B(E2) & B(E3) rates

Systematics in Tl & Pb nuclei

SM3

• Reduce the 0πh11/2 – 1νg9/2 monopole matrix elements by ~60%
• Valence space:
• 3 orbitals above N = 126
• 5 orbitals below Z = 82
• 3 orbitals above Z = 82
• Allow for one π-hole excitation across Z=82

Systematics in Tl & Pb nuclei

SM3

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

Good restoration of the B(E2; 17/2+→13/2+) asymmetry at the middle of 1νg9/2

Increase of the B(E3; 11/2-→5/2+) strength

B(E2) systematics in Hg

SM4

• Reduce the 0πh11/2 – 1νg9/2 monopole matrix elements by ~60%
• Valence space:
• 6 orbitals below N = 126
• 7 orbitals above N = 126
• 5 orbitals below Z = 82

• Allow for one ν-hole excitation across N = 126
• Monopole-based truncation scheme: only single-particle configurations with energies smaller than 10 MeV are used

B(E2) systematics in Hg

SM4

SM4

• Reduce the 0πh11/2 – 1νg9/2 monopole matrix elements by ~60%
• Valence space:
• 6 orbitals below N = 126
• 7 orbitals above N = 126
• 5 orbitals below Z = 82

• Allow for one ν-hole excitation across N = 126
• Monopole-based truncation scheme: only single-particle configurations with energies smaller than 10 MeV are used

SM1

Article submitted by J. Wu

DTAS beyond N=126

213Tl

215Tl

Isomer spectroscopy

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

DTAS beyond N=126

Isomer spectroscopy

217Bi

25/2- seniority isomer (ENSDF)

t1/2 = 2.92(4) μs

[ A. Gottardo et al., PRC 90, 034317 (2014) ]

DTAS beyond N=126

Isomer spectroscopy

217Bi

25/2- seniority isomer (ENSDF)

[ A. Gottardo et al., PRC 90, 034317 (2014) ]

DTAS beyond N=126

Isomer spectroscopy

217Bi

25/2- seniority isomer (ENSDF)

[ A. Gottardo et al., PRC 90, 034317 (2014) ]

Monte-Carlo simulated isomer spectra

5000 implanted nuclei of 216Pb

*Courtesy of V. H. Phong

First DTAS measurement beyond N=126 carried out at RIBF in November 2024!

Very high β and γ detection efficiency

Versatile: Simultaneous measurements of β strengths, isomers, nuclear and β lifetimes, decay schemes, and Meitner-Ellis electrons

Successfully commissioned in 2019 @RIBF with AIDA (Decay of 100Sn, Algora / Rubio)

Implantations and decays:

• Time
• Energy
• Pixel (x,y,z)

Performance of ideal stopper:

• High efficiency and pixelation
• Wide dynamic energy range
• Reasonable energy thresholds
• Radiation tolerance
• Linear energy resolution

NP2112-RIBF208

*Courtesy of V. H. Phong

[ T.T. Yeung et al., PRL 133, 072501 (2024) ]

Time correlations:

• Ion-Ɣ correlations (~ms)
• Ion-β correlations (~ms - 100s)
• Ion-MEE correlations (~ms - s)
• Ion-α correlations (~ms - 1000s)
• β-Ɣ correlations (~300ns - 6μs)
• Ɣ-Ɣ correlations (~100ns)

642

662

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552

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(11/2-)

(5/2+)

N=130

(5/2+)

(11/2-)

N=132

(5/2+)

N=134

(5/2+)

N=136

642

662

98

552

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HIAF

Key role of νi11/2 in β decay

Higher occupation of the νi11/2 orbital in the ground states can result in larger GT contribution in their β decay, eventually impacting on the weak interaction rates in the region

RQRPA + QVC predicts the appearance of a low-energy GT state with ~60% contribution from the νi11/2→ πi13/2 transition at N~130 that becomes more fragmented over many single-particle contributions for more exotic nuclei

662

642

552

169

98

222

632

662

642

552

169

98

222

632