Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Study of β-delayed proton emitters in the region from Zn to Kr
T. Goigoux,∗1 P. Ascher,∗1 B. Blank,∗1 M. Gerbaux,∗1 J. Giovinazzo,∗1 S. Grévy,∗1 T. Kurtukian Nieto,∗1C. Magron,∗1 J. Agramunt,∗2 A. Algora,∗2∗3 V. Guadilla,∗2 A. Montaner-Piza,∗2 A. I. Morales,∗2S. E. A. Orrigo,∗2 B. Rubio,∗2 D. S. Ahn,∗4 P. Doornenbal,∗4 N. Fukuda,∗4 N. Inabe,∗4 G. G. Kiss,∗4 T. Kubo,∗4S. Kubono,∗4 S. Nishimura,∗4 H. Sakurai,∗4 ,∗5 Y. Shimizu,∗4 C. Sidong,∗4 P.-A. Söderström,∗4 T. Sumikama,∗4H. Suzuki,∗4 H. Takeda,∗4 P. Vi,∗4 J. Wu,∗4 Y. Fujita,∗6∗7 M. Tanaka,∗6 W. Gelletly,∗2∗8 P. Aguilera,∗9F. Molina,∗9 F. Diel,∗10 D. Lubos,∗11 G. de Angelis,∗12 D. Napoli,∗12 C. Borcea,∗13 A. Boso,∗14 R. B. Cakirli,∗15
E. Ganioglu,∗15 J. Chiba,∗16 D. Nishimura,∗16 H. Oikawa,∗16 Y. Takei,∗16 S. Yagi,∗16 K. Wimmer,∗3G. de France,∗17 S. Go,∗18 and B. A. Brown∗19Counts / 20 keVCounts / keV

Nucleus Proton branching ratio (%) Half-life (ms)57
Zn81(2)44.8(4)61Ge86(2)39.1(4)65Se
88(2)33.2(6)68
Kr
90(10)
20(4)69Kr
95+530(2)−6Table 1. Measured proton branching ratios and half-lives.

Studies of nuclei far from stability can provide excellent tests of the validity of nuclear structure models.
They are also of interest in relation to astrophysicalprocesses such as the rp-process (rapid-proton capture)for proton-rich nuclei. They decay via direct proton,
β-delayed proton (βp) or γ emission.
The production of very exotic proton-rich nuclei wasachieved at RIBF by 78 Kr projectile fragmentation ona Be target. This reaction was used for the ﬁrst time
during the 78 Kr campaign in 2015, allowing the observation of new isotopes1) and 2p radioactivity2) . After
selection and identiﬁcation by BigRIPS and the ZD
spectrometer, the nuclei were implanted in the three
WAS3ABi DSSSDs to measure β particles and protons, surrounded by the EURICA γ-ray array3) .
A DSSSD allows implantation-decay position andtime correlations, strongly reducing the background in
the spectra. However, a lot of random correlations remain. Background can be removed using two energy
spectra: one from implantation-decay correlations in apositive time window and another in a negative one of
the same width. Because the background time distribution is uniform, the background is removed when thesecond spectrum is subtracted from the ﬁrst one. The
proton branching ratios were determined comparing
the number of events above 1 MeV with the number of
implants happening in the same pixel. β particles havean average energy loss of 400 keV, their contribution
can therefore be neglected above 1 MeV. The half-lives
were determined from time spectra considering our ex-1500

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Eγ(keV)

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Energy (keV)

Fig. 1. Charged-particle spectrum for 65 Se decay after
background subtraction. The inset shows the γ-ray
spectrum in coincidence with the 2.6 MeV proton peak.
The 901.7-keV peak conﬁrms the feeding of the 2+ →0+ transition in 64 Ge and the scheme proposed by ref.4) .

perimental branching ratios and the β-detection eﬃciency for the daughter contributions. This eﬃciency
was estimated from known β emitters.
The high statistics of the experiment gave more accurate values for βp emitters (cf. Table 1) as comparedto the literature values. New measurements of 65 Se(see Fig. 1) and 69 Kr were made, relevant for the rpprocess because of their proton-unbound β daughters
65
As and 69 Br4) . New values for 61 Ge and 57 Zn allow
a comparison with existing ones5) . 68 Kr was measured
for the ﬁrst time.

∗1CEN Bordeaux GradignanIFIC, CSIC-Universidad de Valencia∗3 Atomki, Debrecen∗4 RIKEN Nishina Center∗5 Department of Physics, University of Tokyo∗6 Department of Physics, Osaka University∗7 Research Center for Nuclear Physics, Osaka University∗8 Department of Physics, University of Surrey∗9 Comisı́on Chilena de Energia Nuclear∗10 Institute of Nuclear Physics, University of Cologne∗11 Physik Department E12, Technische Universität München∗12 Laboratori Nazionali di Legnaro dell’ INFN
∗13 IFIN-HH∗14 INFN Sezione di Padova and Dipartimento di Fisica∗15 Department of Physics, Istanbul University∗16 Department of Physics, Tokyo University of Science∗17 Grand Accélérateur National d’Ions Lourds, Caen
∗18 Dept. of Physics and Astronomy, University of Tennessee∗19 Department of Physics and Astronomy, and NSCL, MSU∗2References
1) B. Blank et al., Phys. Rev. C 93, 061301(R) (2016).
2) T. Goigoux et al., Phys. Rev. Lett. 117, 162501 (2016).
3) P.-A. Söderström et al., Nucl. Instrum. Methods Phys.
Res. Sect. B 317, 649 (2013).
4) A. M. Rogers et al., Phys. Rev. C 84, 051306(R) (2011).
5) B. Blank et al., Eur. Phys. J. A 31, 267 (2007).

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