RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Isomer identiﬁcation under high-rate-counting environment
S. Terashima,∗1,∗2 J. Zenihiro,∗1 S. Ota,∗3 A. Bracco,∗4,∗5 F. Camera,∗4,∗5 S. Chebotaryov,∗1 M. Dozono,∗3T. Harada,∗6 C. Iwamoto,∗3 K. Kawata,∗3 N. Kitamura,∗3 M. Kobayashi,∗3 A. Krasznahorkay,∗8 S. Leblond,∗8T. Lokotko,∗8 Y. Maeda,∗9 S. Masuoka,∗3 Y. Matsuda,∗10 M. Matsushita,∗3 S. Michimasa,∗3 E. Milman,∗1T. Murakami,∗1,∗11 H. Nasu,∗10 J. Okamoto,∗10 H. Sakaguchi,∗12 S. Sakaguchi,∗13 M. Takaki,∗3 K. Taniue,∗9H. Tokieda,∗3 M. Tsumura,∗11 T. Uesaka,∗1 O. Wieland,∗5 Z.H. Yang,∗1 Y. Yamaguchi,∗3 and R. Yokoyama∗3
Figure 1 shows a typical waveform of the FADC.
An FFT ﬁlter is applied to eliminate high-frequency
components in the waveform. We can identify each sequential γ-ray correctly, even under a high single rate.
Figure 2 shows an example plot of time-energy corre[Ch]After FFT filter[Ch]

WaveForm

3850

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3800

3750

3750

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3650

3650

3600360002004006008001000[Ch/4ns]

0200400600

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1000
[Ch/4ns]Fig. 1. Sample of raw waveform(left) and after FFT ﬁlter(right) with ﬁtting in Hector+ for a sequential eventwith an energy of approximately 100 keV with 200-ns
time diﬀerence.

lation of one Hector+ gated by 132 Sn with the TOFBρ-Bρ method as shown in the right panel of Fig. 2.
Delayed sequential γ-decays of 133/299/374 keV from132
Sn(8+ ), which are indicated by red arrows, are observed weakly following prompt timings within a hugebackground. Further analysis combined with proton
scattering is in progress.
Z[ch]RIBF can provide a new opportunity to study smallcross-section measurement with a highly intense secondary beam. In spring 2016, a series of experiments
RIBF113 and RIBF79 with a 132 Sn secondary beam
was performed with a new technique called the TOFBρ-Bρ method1) . Full identiﬁcation of atomic number Z and mass over charge A/Q can be achieved by a
combination of time-of-ﬂight(TOF) between F3 and F7
and magnetic rigidity(Bρ) by tracking detectors before
and after the degrader at F5, even under an extremely
high counting rate of approximately 200 kHz at F7.
In RIBF79, the μs isomer 132 Sn(8+ ) identiﬁcation wasalso investigated. The existence of the isomer in 132 Sn
forms a potential background for the study of density
distribution by proton elastic scattering. The isomerratio of 132 Sn in U-ﬁssion products had already beenmeasured at RIKEN several years ago to be of the order of 3%2) .
Four large-volume LaBr(Ce) detectors called Hector+
which was developed by INFN-Milano3) , were installedaround the plastic stopper where all ejectiles from thesecondary hydrogen target were stopped. The distance
between the stopper to the detector surface is about
10 cm. Signals from the PMT output of the Hector+
were connected to a ﬂash-ADC SIS3350(FADC). The
total time window was approximately 8 μs with 2048
samplings with 250-MHz frequency used for analysis,
which is suﬃciently long for our isomer of interest132
Sn(8+ ), the half life of which is 2.04 μs. The DAQ
for FADC was operated separately with a common trigger from the main system. The typical trigger rate anddead time were 100 Hz and 1.5 ms, respectively. Separately obtained data are merged with the time-stamp
information of the LUPO module4) . The single rate ofone Hector+ was typically 50 kHz for a beam condition
with a total intensity of 200 kHz. The purity of 132 Sn
was approximately 30%.

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2.56

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2.68
A/Q

∗1RIKEN Nishina Center
School of Physics and Nuclear Energy Engineering, BeihangUniversity∗3 Center for Nuclear Study, University of Tokyo∗4 Dipartimento di Fiscia dell Universit degli Studi di Milano∗5 Istituto Nazionale di Fisica Nucleare Serione di Milano∗6 Department of Physics, Toho University∗7 MTA ATOMKI, Debrecen∗8 Department of Physics, University of Hong Kong
∗9 Department of Applied Physics, University of Miyazaki∗10 CYRIC, Tohoku University∗11 Department of Physics, Kyoto University∗12 RCNP, Osaka University∗13 Department of Physics, Kyushu University∗2- 208 -Fig. 2. Time-energy correlation in FADC(left) with 132 Sn
gate by TOF-Bρ-Bρ method(right). Arrows indicate
the expected γ-decay line from 132 Sn(8+ ).

References
1) S. Ota et al. RIKEN Accel. Prog. Rep. 49, 15 (2015).
2) D. Kameda et al. RIKEN Accel. Prog. Rep. 43, 1(2010).
3) A. Gias et al. Nucl.Instr. Meth. A 729, 910 (2013).
4) H. Baba et al. Nucl.Instr. Meth. A 777, 75 (2015).