Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 52 (2019)

Development of electronics to allow vertex determination in the KISS
MSPGC
P. Schury,∗1 Y. Hirayama,∗1 H. Choi,∗1,∗2 H. Miyatake,∗1 Y. X. Watanabe,∗1 and M. Mukai∗1,∗3∗3

KEK Wako Nuclear Science CenterSeoul National University
Institute of Physics, University of Tsukuba

200 MΩ

∗21 nF∗1HV(a)10 MΩ

CR-110-Sig/2+

Ccoupling

CM50Ω

AD8138-+Sig/2

Proportional gas counter tube(b)+Sig/2+-Sig/2-Sallen-Key

AD8130
RPZRef
R1GuassianPulse

CR-200FBg = 1 + R2/R1R2+Sig/2+-Sig/2-AD8130
Ref
FB

470 pFTriggerPulse
49Ω

The goal for the KEK Isotope Separation System(KISS)1) is to provide precise nuclear data of neutronrich nuclei near N = 126. Such nuclei, which play an important role in the r-process, are diﬃcult to produce bytraditional means (e.g. in-ﬂight ﬁssion/fragmentation,fusion, ISOL) and therefore KISS uses multi-nucleon
transfer reactions to produce them. The rates of interesting nuclei are typically less than 1 s−1 .
For understanding the nature of the N = 126 bottleneck presumed to be responsible for the 3rd peak of
the r-process requires precise atomic masses and decay
half-lives. In order to provide the nuclear astrophysics
community with the necessary precise half-life data, amulti-segmented proportional gas counter (MSPGC)2)
was developed for KISS. The system as initially envisioned utilized two concentric rings of proportional gas
counter (PGC) tubes (16 in each ring), thereby allowing
the use of “hit pattern” analysis to discriminate background events such as e.g. cosmic rays. This proved tobe a successful strategy which allowed meaningfully precise half-life determination from species delivered withrates down to 0.1 s−1 .
In order to push the half-life measurements to N =126, however, will require use of the MSPGC with rates
an order of magnitude lower. To accomplish this, thePGC tubes have been upgraded to utilize a resistivewire. By detecting the charge deposited on each end of
the wire, it is possible to extract the position of the decay detection along the length of the detector. The 3D
decay vertex made possible be this added information
should allow half-life determination from yields on theorder of 0.01 s−1 .
This requires a charge-sensitive pre-ampliﬁer, shaping ampliﬁer, and trigger generator for both ends ofeach PGC tube −64 sets in total. Noise considerations require the pre-ampliﬁer to be located as close
to the PGC as possible, while space constraints makeit infeasible to pack everything into the area near theMSPGC. A small circuit board with power conditioners, a Cremat CR-110 charge-sensitive ampliﬁer (CSA)(g = 1.6 V/pC), and an AD8138 diﬀerential line driveris installed close to each end of every PGC tube. The
diﬀerential signals are immune to environmental noise.
An array of receivers, as well as power supplies,
is installed within a 3U 19” crate installed in a rack
≈ 3 m from the MSPGC. The power for the CSA circuit boards is supplied via a long ribbon cable. The differential line drivers following the CSA allow the signal
from each detector to be sent to the receiver crate via

Fig. 1. Sketch of circuitry installed (a) near to and (b) ata distance from the MSPGC. The signal from the CSA
is converted to a diﬀerential signal to allow noise-freetransmission, via long ribbon cable, prior to applicationof a shaping ampliﬁer. In the inset the trigger pulse islight blue and the Gaussian pulse is purple. The ADC istriggered by the falling edge of the trigger pulse, 2.5 µs
prior to the peak of the Gaussian pulse.

the long ﬂat ribbon cable as well. The receiver boards
use a pair of AD8130 diﬀerential receiver ampliﬁers toprovide a decoupled pair of signals, one to be processedby a CR-200 shaping ampliﬁer and the the other to trigger the 14-bit Hoshin C008 analog-to-digital converter(ADC) used to measure the pulse-height of the CR-200
output and determine the detection position along thePGC. Details are given in Fig. 1.
In the initial testing with Ccoupling = 1 nF, large∼100 kHz oscillations were observed in the CSA output. After consultation with Cremat, it was determinedthat the each CSA saw the coupling capacitor on theopposite end of the PGC as a heavy load. Reducing
Ccoupling to 100 pF gave clean, stable signals. Development is ongoing.
References

1) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res.
B 412, 11 (2017).
2) M. Mukai et al., Nucl. Instrum. Methods Phys. Res. A
884, 1 (2018).

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