RIKEN Accel. Prog. Rep. 47 (2014)

HIGHLIGHTS OF THE YEAR

Measurement of the 248Cm + 48Ca fusion reaction products at RIKEN GARIS
K. Morita,*1,*2 K. Morimoto,*1 D. Kaji,*1 H. Haba,*1 Y. Wakabayashi,*1 M. Takeyama,*3,*1 S. Yamaki,*4,*1 K. Tanaka,*5,*1H. Hasebe,*1 M. Huang,*1 J. Kanaya,*1 M. Murakami,*6,*1 A. Yoneda,*1 A. Yoshida,*1 T. Yamaguchi,*4 F. Tokanai,*3T. Yoshida,*3 Z. Gan,*7 L. Ma,*7 H. Geissel,*8 S. Hofmann,*8 Y. Maurer,*8 K. Fujita,*2 Y. Narikiyo,*2 T. Tanaka,*2S. Yamamoto,*2 M. Asai,*9 and K. Katori*1
The reaction, 248Cm + 48Ca  296Lv*(Livermorium, Z =116), has been studied at the RIKEN Linear Accelerator(RILAC) Facility using a gas-filled recoil ion separator
GARIS. Although this reaction was intensively studied atthe Flerov Laboratory of Nuclear Reaction (FLNR),
andGSI,
Helmholtzzentrum
fürRussia1,2),
Schwerionenforschung, Germany3), the number of observed
events is still very small because of the small production
cross sections. The first aim of the present study is toobserve more events in the region of superheavy nuclei andpossibly to obtain new spectroscopic information of thosenuclei. The second aim is to examine the performance ofthe GARIS facility using the relevant reaction for a future
project with the 50Ti beam, instead of the 48Ca beam, tosearch for new heaviest nuclei. Because of the limitation oftarget nuclear species, one needs to use beams heavier than48
Ca for further investigation of superheavy nuclei.
A 48Ca beam was accelerated by RILAC at 262 MeV, andit irradiated 248Cm targets prepared by electro deposition of248
Cm3O8 on titanium foils. Eight targets were mounted on awheel rotating at 1000 rpm. The diameter of the wheel is10 cm. The average thickness of 248Cm3O8 was 0.290
mg/cm2, which contained 0.265 mg/cm2 248Cm, and that oftitanium foils was 0.903 mg/cm2. The energy of the beam at
half depth of the target was estimated to be 250 MeV byusing a range-energy table. Reaction products wereseparated from beam particles and from unwanted particles
by GARIS and then implanted in a position-sensitive
semiconductor detector (PSD), which covered 60 mm×60mm, set on the focal plane of GARIS. Four side detectors(SSDs) of the same size were set in a box arrangement todetect the decay products (alpha particles or spontaneous
fission (SF) fragments) emitted at backward angles from thePSD. Time-of-flight counters consisting of micro-channel
plates (MCPs) were set upstream of the PSD. The average
beam intensity was 0.8 particle A. In a beamtime of10days, 4.3×1018 48Ca ions irradiated the targets. The B
value of the GARIS was set to 2.21 Tm.

We observed five correlated events during the experiment,
all of which terminated by spontaneous fission (SF). Decay
characteristics of those events agreed well with previous
studies1,2,3). Although it is difficult to identify the nuclidesof the products only from the present experimental study,
we could state that two of the events were attributed to thedecays of 293Lv (3 n evaporation channel) and three of themto the decays of 292Lv (4 n evaporation channel) by referringto the assignments in the previous studies. The two events
attributed to the 293Lv decay consisted of three consecutivealpha decays followed by SF. The two events attributed tothe 292Lv decay consisted of two alpha decays followed bySF. One of the events we tentatively assigned to the decayof 292Lv consisted of three alpha decays followed by SF.
The tentative assignment is based on the decay
characteristics of the decay energies and decay times of292
Lv and 288Fl (Flerovium, Z = 114) and the decay time of284
Cn (Copernicium, Z = 112). Because an alpha decay of284
Cn has not been observed, this possibly involves a new
decay mode of 284Cn and new isotope 280Ds decays by SF.
The production cross sections of 293Lv and 292Lv werededuced to be 2.1+2.9-1.4 pb and 3.1+3.0-1.7 pb, respectively, byassuming the transmission of GARIS to be 0.35. Observed
events are summarized in Table I.
Further analysis is now in progress.
Table I Observed decay events, energies, and time intervals of the events.
Bottom row indicates the possible assignments of nuclei
Chain 1

Chain 2Chain 3

Chain 4

Chain 510.79 MeV

10.47 MeV

2.77 MeV+

10.66 MeV

7.76 MeV++

0.032 s0.253 s0.0020 s

0.0041 s

0.032 s9.89 MeV

9.89 MeV

9.99 MeV

0.83 MeV+

9.72 MeV

0.548 s3.97 s0.243 s0.0090 s

0.666 s232 MeV

2.46 MeV+

182 MeV

9.09 MeV

1.64 MeV+

0.065 s7.76 s

0.832 s292+

RIKEN Nishina Center＊2
Department of Physics, Kyushu University＊3
Department of Physics, Yamagata University＊4
Department of Physics, Saitama University＊5
Department of Physics, Tokyo University of Science＊6
Department of Chemistry, Niigata University＊7
Institute of Modern Physics, Lanzhou＊8
GSI Helmholtzzentrum für Schwerionenforschung＊9
Advanced Science Research Center, Japan Atomic Energy Agency

7.56 s

163 MeV

221 MeV19.8 s

0.0096 s

4.63 s

292

293

293

Lv

292

Lv

Lv+++

Lv

escape energies (partly measured using PSD)

++

＊1

Lv

0.282 s

195 MeVenergies measured only using SSD. +++ tentative

References

1) Yu. Ts. Oganessian et al.: Phys. Rev. C63, 011301(R) (2000).
2) Yu. Ts. Oganessian et al.: Phys. Rev. C70, 064609 (2004).
3) S. Hofmann et al.: Eur. Phys. A48, 62 (2012).

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