Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Study of the superallowed 0+ → 0+ β decay of 70 Br†
A. I. Morales,∗1 A. Algora,∗1,∗2 B. Rubio,∗1 K. Kaneko,∗3 J. Agramunt,∗1 V. Guadilla,∗1 A. Montaner-Pizá,∗1
S. E. A. Orrigo,∗1 G. de Angelis,∗4 D. Napoli,∗4 F. Recchia,∗5 S. Lenzi,∗5 A. Boso,∗5 S. Nishimura,∗6 G. Kiss,∗6
V. H. Phong,∗6 J. Wu,∗6 P.-A. Söderström,∗6 T. Sumikama,∗6 H. Suzuki,∗6 H. Takeda,∗6 D. S. Ahn,∗6H. Baba,∗6 P. Doornebal,∗6 N. Fukuda,∗6 N. Inabe,∗6 T. Isobe,∗6 T. Kubo,∗6 S. Kubono,∗6 H. Sakurai,∗6Y. Shimizu,∗6 C. Sidong,∗6 B. Blank,∗7 P. Ascher,∗7 M. Gerbaux,∗7 T. Goigoux,∗7 J. Giovinazzo,∗7 S. Grévy,∗7
T. Kurtukián Nieto,∗7 C. Magron,∗7 W. Gelletly,∗1,∗8 Zs. Dombrádi,∗7 Y. Fujita,∗9 M. Tanaka,∗9 P. Aguilera,∗10F. Molina,∗10 J. Eberth,∗11 F. Diel,∗11 D. Lubos,∗12 C. Borcea,∗13 E. Ganioglu,∗14 D. Nishimura,∗15
H. Oikawa,∗15 Y. Takei,∗15 S. Yagi,∗15 W. Korten,∗16 G. de France,∗17 P. Davies,∗18 J. Liu,∗19 J. Lee,∗19T. Lokotko,∗19 I. Kojouharov,∗20 N. Kurz,∗20 and H. Shaﬀner∗20
80
half-life [ms]

(a)

78
76

42
14000

15000

16000

17000

80

18000

19000 20000
final range [ms]

(b)
45

78
76
50

100

150200250
β threshold [keV]40

isomeric ratio

half-life [ms]44isomeric ratio

One of the core concepts of the Electroweak Standard Model (ESM) is the unitarity of the CabibboKobayashi-Maskawa (CKM) matrix which describes
the mixing between the three families of quarks. Increasingly high-precision measurements of the CKM
matrix elements are required to set the limits on any
possible physics beyond the ESM. The largest matrix
element, the up-down term Vud , can be extracted fromhigh-precision measurements of half-lives, masses, andbranching ratios of superallowed β transitions between
J π = 0+ , T = 1 analog states starting in N = Z nuclei.1) In this report we provide the most precise halflife measurement for the T = 1 (J π = 0+ ) groundstate of the heavy self-conjugate nucleus 70 Br and theﬁrst estimate of the total branching fraction decaying
through the ﬁrst 2+ state in the daughter nucleus, 70 Se.
The 70 Br nuclei were produced in the fragmentation of a 78 Kr primary beam at 345 MeV/nucleon and38 pnA colliding with a 5-mm thick Be target. After
separation and selection in the BigRIPS separator, thenuclei were implanted in the WAS3ABi active stopper,
surrounded by the EURICA γ-ray spectrometer.2)
Standard delayed-coincidence techniques were applied to study the β decay of 70 Br, including an exhaustive evaluation of the factors that could inﬂuence thehalf-life measurement.3) As an example, Fig. 1 shows

Fig. 1. Measured half-lives for the T = 1 (J π = 0+ ) groundstate (empty triangles) and isomeric ratios for the T = 0(J π = 9+ ) isomer (full dots) in 70 Br as a function of thefitting range (a) and the β threshold (b).

the half-life of the T = 1 (J π = 0+ ) ground state asa function of the ﬁtting range (a) and the β threshold(b). The average half-life deduced is shown as a thickcontinuous line and the total error as dotted-dashedlines. The isomeric ratio of the T = 0 (J π = 9+ )state is also shown for each lifetime ﬁt and, in thickdashed line, the overall deduced value. The resulting
half-lives for the T = 0 (J π = 9+ ) isomer and theT = 1 (J π = 0+ ) ground state, t1/2 = 2157+53−49 msand t1/2 = 78.42 ± 0.51 ms, respectively, are the mostprecise values reported hitherto in the literature.
The branching ratio of the superallowed 0+ → 0+transition, R = 97.94 ± 1.75%, was estimated from the70
measured γ imbalance of the 2+Se, as de1 level inscribed in Ref. 3). This has allowed for a ﬁrst estimateof the Ft value associated with this decay, calling for
a new mass measurement of 70 Br in order to conﬁrm
the Conserved Vector Current hypothesis.1)
The analyses of the 70,71 Kr β and 71 Kr isomer decays
are in progress.

†Condensed from the article in Phys. Rev. C 95, 064327(2017)∗1 IFIC, CSIC-Univ. Valencia∗2 MTA ATOMKI∗3 Department of Physics, Kyushu Sangyo University∗4 INFN-Legnaro∗5 INFN-Padova∗6 RIKEN Nishina Center∗7 CEN Bordeaux-Gradignan∗8 Department of Physics, Surrey University∗9 Osaka University∗10 CCHEN∗11 Institute of Nucl. Physics, Universität zu Köln∗12 Physik Department, Technische Universität München∗13 IFIN-HH, Bucarest∗14 Department of Physics, University of Istanbul∗15 Tokyo Univ. Sci.
∗16 CEA-Saclay∗17 GANIL-Caen∗18 Department of Physics, York University∗19 Department of Physics, University of Hong Kong
∗20 GSI, Germany

References
1) J. C. Hardy, I. S. Towner, Phys. Rev. C 91, 025501(2015).
2) S. Nishimura, Prog. Theor. Exp. Phys. 03C006 (2012).
3) A. I. Morales et al., Phys. Rev. C 95, 064327 (2017).

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