Pre-amplifiers for multi-wire proportional counters

Arti Gupta1,∗ J. Gehlot2, S. Nath2, and S. Venkataramanan1

1Electronics Laboratory, Inter University Accelerator Centre, New Delhi 110067, India and2Nuclear Physics Group, Inter University Accelerator Centre, New Delhi 110067, India

1. Introduction

Position sensitive multi-wire proportionalcounters (MWPC) are regularly used infusion-fission experiments for detection ofevaporation residues following fusion and mea-surements of mass, angle and total kinetic en-ergy of fission fragments. MWPC with fourelectrodes geometry; cathode followed by Y -position electrode, anode and X-position elec-trode; are being used as focal plane detectorsof Heavy Ion Reaction Analyzer (HIRA) [1]and HYbrid Recoil mass Analyzer (HYRA) [2]at IUAC. MWPC with five electrde geometry,having an extra cathode, are used in fissionexperiments [3]. The fast timing and posi-tion signals from MWPC electrodes need fur-ther amplification by fast pre-amplifiers whilea charge-sensitive pre-amplifier (CSPA) is re-quired to process cathode signal to extract en-ergy information without degrading rise timeand signal to noise ratio.

Typical MWPC front end electronics set-upusing commercial modules would require vari-ety of pre-amplifiers and cables. We have de-veloped a compact custom-made pre-amplifierunit, which houses all its components in a die-cast aluminium box of dimensions 145 mm ×95 mm × 49 mm, for this purpose at IUAC.

2. MWPC pre-amplifier unit

Block diagram of the newly-developedMWPC pre-amplifier unit is shown in Fig.1. The unit accommodates seven channelsof different types of pre-amplifiers which in-clude two independent channels of charge-sensitive pre-amplifiers and a wideband pre-amplifier with five channels. This widebandpre-amplifier has one channel of non-inverting

∗Electronic address: arti@iuac.res.in

gain while other four are of inverting typeto retrieve timing and position informationfrom the anode and position electrodes (Xleft,Xright, Yup and Ydown), respectively. In orderto extract energy information, cathode signalis processed through a charge-sensitive pre-amplifier.

FIG. 1: Block diagram of the compact MWPCpre-amplifier unit.

All the input and output interconnections ofthe wideband pre-amplifier are made throughSMA connectors in order to preserve band-width of the signal, reduce noise and maintainreliablity of the connections. A common testinput is utilized to test the functionality ofboth CSPA channels simultaneously. Detec-tor bias is provided through an SHV connec-tor whereas input, output (energy and tim-ing) and test signals are provided throughBNC connectors. The unit receives DC sup-ply through a 9-pin D-connector, as per NIMstandard.

A. Charge-sensitive pre-amplifier

Charge-sensitive pre-amplifiers are based onconventional circuit with JFET as input stagefollowed by a very high gain transistorizedtransimpedance amplifier. The silicon equiv-alent conversion gain is ∼ 44 mV/MeV whiledecay time is kept as 100 µs. This providestwo identical and isolated outputs (E and T )for energy and timing spectroscopy, respec-tively. High quality SMT components are usedto assemble these boards for compactness.

B. Wideband pre-amplifier

The wideband pre-amplifier is designed toamplify very fast linear signals with rise timeless than 1 ns. The circuit is implemented us-ing cascaded ac-coupled common emitter am-plifiers with common collector stage incorpo-rated as the output buffer amplifier to improvedriving capabilities [4]. To achieve good tim-ing characteristics, microstrip line techniqueis utilized to realize the PCB. All SMD com-ponents are mounted on the top side whilecontinuous ground plane is provided on thebottom side which is flush-mounted on thealuminium panel of a die-cast box for effi-cient heat removal. SMA connectors are di-rectly mounted on the PCB to reduce para-sitics. Four channels are implemented withinverting configuration and the fifth channelis implemented with non-inverting configura-tion. Gains of all the channels are ∼ 250. In-put protection diodes are wired to clip anytransients at the input, thus protecting theamplifier from avalanche-related damage.

3. Test resultsTo evaluate noise and rise time performance

of the charge-sensitive pre-amplifiers, theseare characterized for detector equivalent ca-pacitance from stray (0 pF) to 1000 pF andcompared with the general purpose preampli-fier ORTEC 142IH [5] (Tables I and II).

The wideband pre-amplifier is tested withHP Network Analyzer 8752A (300 kHz to 1.3GHz). Identical performance, with voltagegain ∼ 250 and bandwidth greater than 350MHz, is observed in all the channels. Fre-quency response of one channel of this pre-amplifier is shown in Fig. 2.

TABLE I: Noise comparison between IUAC CSPAand ORTEC 142IH pre-amplifier.

Detector equiv. IUAC CSPA ORTEC 142IHcapacitor (pF) noise (keV) noise (keV)

0 1.3 1.9100 2.3 4.61000 12.0 35.0

TABLE II: Rise time comparison between IUACCSPA and ORTEC 142IH pre-amplifier.

Detector equiv. IUAC CSPA ORTEC 142IHcapacitor (pF) rise time (ns) rise time (ns)

0 23 20100 94 50

FIG. 2: Frequency response of the wideband pre-amplifier.

AcknowledgementsThe authors are thankful to Dr. D. Kanjilal

and Dr. N. Madhavan for their continuoussupport to accomplish the project.

References[1] A. K. Sinha et al., Nucl. Instrum. Methods A

339, 543 (1994).[2] N. Madhavan et al., Pramana –J. Phys. 75,

317 (2010).[3] A. Jhingan, Pramana –J. Phys. 85, 483

(2015).[4] Allen Mottershead, Electronic Devices and

Circuits: An Introduction (Prentice Hall ofIndia, New Delhi, 1990).

[5] https://www.ortec-online.com/-

/media/ametekortec/manuals/142ih-mnl.pdf