Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 48 (2015)

Pulse shape analysis for short-lived decay of superheavy elements
S. Yamaki,∗1,∗2 K. Morimoto,∗1 D. Kaji,∗1 Y. Wakabayashi,∗1 M. Takeyama,∗1,∗3 K. Tanaka,∗1,∗4 H. Baba,∗1
T. Yamaguchi,∗2 T. Suzuki,∗2 and K. Morita∗1,∗5
In heavy or superheavy element research, it is important to know the α decay energies and half-lives ofthe nuclei to conﬁrm that objective nuclei have been
formed. The α decay half-lives of these nuclei are very
short (0.1-1 µs) for heavier Z according to some theoretical calculations. However in the traditional system,
the combination of a shaping ampliﬁer and PH-ADC
cannot separate sequential events within 1 µs. To measure the α decay properties of such short-lived nuclei,
a digital data acquisition system with ﬂash-ADC wasimplemented in the GARIS-II1) read-out system. In
the new system, waveforms from a preampliﬁer are directly registered with ﬂash-ADC SIS3301 to avoid thesumming phenomena caused by pileup in the shaping ampliﬁer. Figure 1 shows the PH-ADC read-outand ﬂash-ADC read-out systems. The DAQ systems
for the PH-ADC and ﬂash-ADC are operated independently. Separately obtained data are synchronized by
the LUPO time-stamp module.

170 ns). The larger MTOT events from this peak correspond to pileup ones. For example the MTOT
∑116 forthe waveform in Fig.2(a) is calculated as ( t=83 t +∑305
∑116
∑305
t=273 t)/(t=83 +t=273 ) − 83 = 109.8 (> 17).
Therefore, this event is treated as a pileup one.
(a)pileup events

single eventsvthFig. 2. (a) An example of a pileup pulse (upper panel)and its diﬀerential (lower panel). (b) MTOT histogram
when 241 Am α was implanted in the PIN diode.

In the second stage, template ﬁtting for each pulse
was performed3) . The template was made by averaging
10000 241 Am α waveforms for each channel. The ﬁtting
function is given as:
f (t) = A[0] · template(t − A[1]) + baseline,

Fig. 1. The setup of PH-ADC and ﬂash-ADC read-out systems.

In a recent study, a pulse shape analysis (PSA) algorithm for the waveforms from the GARIS-II read-out
system was developed2) . PSA was tested using oﬀ-line
tests. 241 Am α was implanted in a Si PIN photodiode(Hamamatsu S3204) and the signal was preampliﬁedby the Clear Pulse 579. The sampling rate was 100
MHz. Some pileup events occurred when the α source
was set close to the detector. Figure 2(a) shows an example of a pileup pulse. In order to distinguish pileup
events from single events, the weighted mean in timeover threshold (MTOT) method for the diﬀerentiatedwaveforms was developed and applied. MTOT is deﬁned as:∑tm{twt
1 (vt ≤ vth )MTOT = ∑t=0−T,w=, (1)ttm
0 (vt > vth )
wt

(b)

(2)

where the free parameters (A[i]; i = 0, 1) represent thepulse height and time oﬀset. The baseline is an averageof the data from t = 0 to the start of the pulse. For asingle pulse, an energy resolution of 25 keV (FWHM)
for 5486 keV α was obtained, while a resolution of 20
keV was obtained using the original PH-ADC system.
In addition the shortest time interval between sequential events identiﬁed by PSA was 349 ns (Fig. 3). Theenergies of the ﬁrst and second pulses were 5494 keV
and 5444 keV, respectively. Further development ofPSA is now underway.

t=0

ɹ where t is the time, tm is the sampling period (800clock), vt is the voltage, vth is the voltage threshold,and T is the minimum t when wt = 1. Figure 2(b)shows a histogram of the MTOT. The peak that corresponds to single events is seen around 17 clock (=Fig. 3. Pileup pulse (dotted line) and ﬁtting of this event(solid line). From this ﬁtting, the time interval between
two events was determined to be 349 ns.

∗1References

∗2
∗3
∗4
∗5RIKEN Nishina Center
Department of Physics, Saitama Univ.
Graduate School of Science and Engineering, Yamagata
Univ.
Faculty of Science and Technology, Tokyo Univ. of Science
Department of Physics, Kyusyu Univ.

1) D. Kaji et al.: Nucl. Instr. and Meth. B 317, 311 (2013).
2) S. Yamaki et al.: Proc. ARIS2014 in print.
3) S.N. Liddick et al.: Nucl. Instr. and Meth. A 669, 70(2012).

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