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A1421

Preamplifier and Discriminator for 3He tubes

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Home Modular Pulse Processing ElectronicsPreamplifiersPreamplifiers - Detectors A1421

A1421 powered directly by the R7780-Shift Register Multiplicity and Time Recorder

A1421 powered via a linear power supply

A1421 powered using the A325 and a linear power supply

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Highlights

Specifically designed for neutron detectors as 3He or BF3 tubes in counting applications
Gain: 30 mV/fc on HiZ (15 mV/fC on 50 Ω)
Discriminator with adjustable threshold and width
Analog and Logic discriminator output
Internally generated discriminator VETO
External HV input on SHV connector (feeding the internal decoupling circuits)
Detector inputs on SHV or HN connectors
Input bias voltage: ± 4 kV Max
Test input on LEMO (1 pF charge injection capacitors)
Full counting acquisition system in combination with R7771B Neutron Pulse Train Recorder or R7780 Shift Register

Overview

The A1421 is a charge-sensitive preamplifier with integrated shaping amplifier and discriminator, providing both analog and logic outputs. It is optimized for position-sensitive thermal neutron detectors (such as ³He and BF₃ tubes), where high counting rates and low-noise performance are required. It is equally suitable for counting applications in combination with monitor counters such as the R7771B Neutron Pulse Train Recorder and the R7780 Shift Register, for example in the non-destructive analysis of nuclear materials by passive or active neutron methods.

The unit features a detector input on an SHV or HN connector and a dedicated external HV input on an SHV connector feeding the internal decoupling circuits. Two rear 3-pin connectors supply the ±12 V power and allow daisy-chain operation across multiple units. Front-panel trimmers provide independent adjustment of the discriminator threshold and output pulse width. An internal VETO circuit prevents early retriggering (e.g. due to pulse reflections); the VETO duration is user-adjustable from 1.3 µs to 10 µs via an internal trimmer. A LEMO digital input enables cascading of discriminator signals between multiple A1421 units.

Two versions are available. Version A includes pole-zero compensation and is ideal for Pulse Height Analysis (PHA) and neutron spectroscopy. Version B provides bipolar output pulses without pole-zero compensation, with dedicated optimizations for fast recovery from saturation in active interrogation measurements.

The A1421 is supplied with the A324 power cable and can be powered by the R7771B, R7780, or the A325 DC/DC converter.

Developed in collaboration with Institut Laue-Langevin, Grenoble.

Ordering Options

Code	Description
WA1421AHXAAA	A1421AH – Preamp. and discriminator for He3 Tubes for passive measurements (HN Det. In Conn.)	RoHS
WA1421ASXAAA	A1421AS – Preamp. and discriminator for He3 Tubes for passive measurements (SHV Det. In Conn.)	RoHS
WA1421BHXAAA	A1421BH – Preamp. and discriminator for He3 Tubes for active measurements (HN Det. In Conn.)	RoHS
WA1421BSXAAA	A1421BS – Preamp. and discriminator for He3 Tubes for active measurements (SHV Det. In Conn.)	RoHS

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Image	Name	FORM FACTOR	NO. OF CHANNELS	DESCRIPTION	SENSITIVITY	COMPATIBLE DETECTORS
	A1422H	Single in-line package	1	Low Noise Fast Rise Time Charge Sensitive Preamplifiers (SIP)	1/5/45/90/400/450<br>mV/MeV (Si)	Silicon (Si)
	A1424	Desktop	1	Fast Charge Sensitive Preamplifier	3.6 mV/fC	Diamond
	A1422C/D	Desktop	8	Low Noise Fast Rise Time Charge Sensitive Preamplifier	5 (mV/MeV) (Si)	He3 / BF3 Tubes
	A1422	Desktop	1 / 4 / 8	Low Noise Fast Rise Time Charge Sensitive Preamplifiers	1/5/45/90/400/450<br>mV/MeV (Si)	He3 / BF3 Tubes<br>Proportional Counters<br>Ionization Chambers<br>Segmented Silicon <br>Silicon (Si)
	A1429	Desktop	64	Charge Sensitive Preamplifier	20/45/90/200/400<br>mV/MeV (Si)	GEM Segmented Silicon
	A1427	Desktop	1	Low Noise Fast Current Neutron Flux Preamplifier	FC: 700÷2500<br>(Trimmer adjustable)<br>PR: 500÷1500<br>(Trimmer adjustable)	Fission Chambers<br>Proton Recoil
	A1422E/F	Desktop	2 / 4	Low Noise Fast Rise Time Charge Sensitive Preamplifiers	200 mV/MeV (Si)	Silicon (Si)
	A1442	Desktop	16 / 32	Charge Sensitive Preamplifier	Selectable 20/100<br>mV/MeV (Si)	GEM Segmented Silicon
	New A1421	Desktop	1	Preamplifier and Discriminator for 3He tubes	30 mV/fC on HiZ<br>(15 mV/fC on 50 Ω)	He3 / BF3 Tubes
	R1443	19” rack unit	32 / 64	Preamplifier Unit for 3He tubes	2.25 V/pC	He3 / BF3 Tubes
	A1423B	Desktop	1	Wideband Preamplifier	Selectable From+18 dB to +54 dB	Diamond / PMT / Scintillators / SiPM / MPPC
	A1426 CARDARELLI	Desktop	1	Matched Charge Preamplifier	Up to 5 mV/fC	Diamond
	A1436 / A1436A	Desktop	1 / 8	Differential Input Low Noise Transimpedance Amplifiers	Programmable 10⁹/10⁸/10⁷/10⁶/10⁵/10⁴/10³ (V/A), 10⁹ V/A (A1436 only)	Diamond PMT / Scintillators Silicon (Si)
	A1425	Desktop	1	Fast Charge Sensitive Preamplifier	3.6 mV/fC	Diamond
	A422A	Desktop	1	Charge Sensitive Preamplifier with Timing	5/30/60 mV/MeV (Si)	Proportional Counters<br>Ionization Chambers<br>Silicon (Si)


GENERAL	Form Factor: Enclosure Aluminum box. Size: 94 W x 157.5 L x 38 H mm³ (including SHV connectors) 94 W x 155.5 L x 38 H mm³ (including HN connectors) 94 W x 119.5 L x 38 H mm³ (without connectors) Weight 350 g.
POWER CONSUMPTION	+12 V 65 mA (Typ) -12 V 45 mA (Typ) Two rear 3-pin male tiny XLR connectors for power daisy chain
DETECTOR INPUT	Input connector: SHV or HN AC coupled Positive or negative input polarity accepted Input charge range: ± 90 fC ESD protected input
HV IN (Detector Bias)	Bias connector: SHV Operating voltage: max ± 4 kV
TEST	LEMO connector Injection capacitance: 1 pF 10:1 Attenuation 50 Ω Impedance
Preamplifier and Shaper (A OUT)	Non inverting Output impedance: 50 Ω Gain: 30 mV/fc on HiZ (15 mV/fC on 50 Ω) Shaping: Rise time: 120ns Fall time: 460 ns FWHM: 350 ns Time to baseline (5% of the maximum amplitude: 750 ns (A1421A), 2000 ns (A1421) Output range: ± 2.6 Vpp on HiZ (± 1.3 Vpp on 50 Ω) Recovery time after saturation: A1421A: 2 ms A1421B: 60 µs Noise 3 mV RMS on 50 Ω (on the baseline, with open input) Resolution 0.32 fC @ Qin = 80 fC (=0.4%) Output on LEMO connector
DISCRIMINATOR (D OUT/D IN)	Variable threshold, adjustable from –1V to +1 V via front panel 12 turn trimmer Minimum threshold: 30 mV (min. threshold above the noise) Minimum detectable signal (min 99% signal detected): 18 mV (0.86 fC) Threshold voltage monitor output on testpoint TTL output on LEMO Connector Programmable output width between 10 ns to 1µs via front panel 12 turn trimmer Can drive 50 Ω TTL In on LEMO connector (Zin = 1 kΩ) for cascade summing LED for signal activity (green when inactive, RED when active) Pulse pair resolution (minimum separation between pulses): 800 ns
VETO	Programmable width between 1.3 to 10 µs via internal trimmer and dedicated internal Test-point
ENVIRONMENTAL	Indoor use Operating Humidity: 10% ± 90% RH non condensing Storage Humidity: 5% ± 90% RH non condensing Pollution Degree: 2 Altitude: <2000 m Overvoltage Category: II EMC Environmental Commercial Operating Temperature range: 0°C +50°C Storage Temperature range: -10°C +80°C

A1421