Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

New isotope search conducted concurrently with BRIKEN campaign
Y. Shimizu,∗1 N. Fukuda,∗1 K. P. Rykaczewski,∗2 R. K. Grzywacz,∗3 J. L. Tain,∗4 I. Dillmann,∗5
S. Nishimura,∗1 H. Takeda,∗1 H. Suzuki,∗1 D. S. Ahn,∗1 N. Inabe,∗1 K. Yoshida,∗1 H. Ueno,∗1 N. T. Brewer,∗2
B. C. Rasco,∗2 D. W. Stracener,∗2 and J. M. Allmond∗2 for the BRIKEN collaboration
In order to measure new β-delayed neutron emission
properties for near doubly magic nucleus 78 Ni using theworld-largest array of 3 He counters BRIKEN,1) the experiment was performed at the RIKEN Nishina Center
RI Beam Factory (RIBF). The nuclei of interst were
produced by the in-flight fission of a 345 MeV/nucleon
238
U beam colliding with a 3.87-mm-thick Be target.
The primary beam intensity was 56.6 particle nA onaverage. Fission fragments were separated and identified using the superconducting in-flight separator BigRIPS.2) In order to separate and purify the RI beams,
two wedge-shaped energy degraders were placed at theF1 and F5 dispersive foci. The typical counting rate
at the F3 and F7 achromatic foci were 545.4 Hz and102.4 Hz, respectively. Table 1 summarizes the experimental conditions. The BigRIPS setting in this work
included regions of new isotopes on the more neutronrich side. This allowed us to search for new isotopes inparallel with the measurements of the BRIKEN campaign.

30

∗4∗5Z

yr
animi

28
26
24ler
P

22103

102

1012.55 2.6 2.65 2.7 2.75 2.8 2.85 2.9 2.95 3A/QFig. 1. Two-dimensional PID plot of Z versus A/Q. Redline indicates the limit of known isotopes5–7) as of January 2018.

such as 92 Br and 94 Br, by using two clover-type highpurity germanium detectors placed at the F7 achromatic focus; this technique is called isomer tagging.4)
Figure 1 shows a two-dimensional PID plot of Z versus A/Q. The solid red line indicates the limit of identified isotopes5–7) as of January 2018. The relativeroot mean square (rms) Z resolution and the relativerms A/Q resolution were typically 0.61% and 0.081%,respectively. We can see some candidates for new isotopes such as 79 Co, 84 Cu, 86 Zn, and 93 As.
Detailed analysis is currently in progress.8)
References

Particle identification (PID) was performed using
the ∆E-TOF-Bρ method in which the energy loss(∆E), time of flight (TOF), and magnetic rigidity (Bρ)
were measured to allow the event-by-event determination of atomic number Z and mass-to-charge ratio A/Qof fragments.3) The PID was confirmed by measuring
the delayed γ-rays emitted from short-lived isomers,∗310432Target (mm)Be 3.87Bρ a (Tm)
8.272
Degrader at F1 (mm)Al 5.01
Degrader at F5 (mm)Al 3.45
F1 slit (mm)+58.0 / −64.2
F2 slit (mm)+20.0 / −20.0
F5 slit (mm)+110.0 / −110.0
F7 slit (mm)+25.0 / −25.0
82
Central particle
Cu
Irradiation time (h)191.8Live time of DAQ (%)
95.5
Trigger rate (Hz)97.8
Total dose
2.44 × 1017
aThe values from the magnetic fields of the first dipole
magnet.

∗210534

Table 1. Summary of the experimental conditions.

∗1Known New361) A. Tarifeño-Saldivia et al., J. Instrum. 12, 04006 (2017).
2) T. Kubo, Nucl. Instrum. Methods Phys. Res. B 204, 97(2003).
3) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res. B
317, 323 (2013).
4) R. K. Grzywacz et al., Phys. Lett. B 355, 439 (1995).
5) M. Bernas et al., Phys. Lett. B 415, 111 (1997).
6) T. Ohnishi et al., J. Phys. Soc. Jpn. 79, 073201 (2010).
7) T. Sumikama et al., Phys. Rev. C 95, 051601R (2017).
8) K. P. Rykaczewski et al., in this report.

RIKEN Nishina Center
Oak Ridge National Laboratory (ORNL)
Department of Physics and Astronomy, University of Tennessee
Instituto de Física Corpuscular, CSIC-Universidad de Valencia
TRIUMF- 84 -