Alpha–beta monitoring system based on pair of simultaneous Multi-Wire Proportional Counters U. Wengrowicz a,b,1 , D. Amidan a,b,1 , I. Orion a,n a Department of Nuclear Engineering, Ben Gurion University of the Negev, Beer-Sheva 84105, Israel b NRC-Negev, P.O. Box 9001, Beer-Sheva 84190, Israel article info Article history: Received 30 March 2016 Received in revised form 20 April 2016 Accepted 28 April 2016 Available online 29 April 2016 Keywords: MWPC Multi-Wire Proportional Counter Alpha–beta detection Monte Carlo MATLAB COMSOL abstract A new approach for a simultaneous alpha–beta Multi-wire Proportional Counter (MWPC) is presented. The popular approach for alpha–beta monitoring systems consists of a large area MWPC using noble gas flow such as Argon Methane. This method of measurement is effective but requires large-scale and expensive maintenance due to the needs of gas flow control and periodic replacements. In this work, a pair of simultaneous MWPCs for alpha–beta measuring is presented. The developed detector consists of a sealed gas MWPC sensor for beta particles, behind a free air alpha sensor. This approach allows effective simultaneous detection and discrimination of both alpha and beta radiation without the maintenance cost noble gas flow required for unsealed detectors. & 2016 Elsevier B.V. All rights reserved. 1. Introduction In laboratories working with open sources of radiation emitting isotopes, there is a risk of contamination to the external environ- ment. In order to avoid contamination dispersion, the laboratory personnel and their equipment should be monitored. Gamma- emitting isotopes are easily detectable using dose rate monitoring instrumentation. Alpha and beta emitting isotopes require dedi- cated instrumentation such as a hand-foot alpha–beta monitoring system. Such systems include detectors with a large sensitive area. When alpha particle-emitting isotopes are ingested or inhaled, they are far more dangerous than beta-emitting isotopes; there- fore, different counting channels are required for alpha and beta detectors. Some of the most popular types of radiation detectors are based on the effects produced when a charge particle passes through gas. Charge particles moving through a material interact primarily through Coulomb forces. The result of these interactions with the gas molecules may be ionization and excitation of atomic electrons. Ionization occurs when the electron obtains sufficient energy to leave the atom and become a free particle [1]. Typically, such kinds of detectors consist of two electrodes to which a certain potential is applied. Under the influence of the electric field, io- nized particles drift towards the electrodes. Therefore, gas-filled detectors sense the created ionization [2]. These types of detectors can be classified into three main groups: ion chambers, propor- tional counters and Geiger Muller (GM) tubes; they can be oper- ated in a current or a pulse mode. Ion chambers usually work in current mode: the average DC current is recorded so alpha and beta separation is not possible. Proportional counters and GM tubes work in pulse mode operation; here, the charge or current pulses created by individual ionizing particles are measured. GM tubes work in saturation charge amplification mode; therefore, alpha–beta separation by pulse amplitude discrimination (PAD) methods is not possible. Accordingly, for separate alpha–beta measurement, proportional counters are required. Usually, the initial electrical charge produced by direct ioniza- tion is lower than the noise level of commercial amplifiers; therefore, intrinsic charge amplification is required. Since the re- leased electrons have a large mean-free path through a gas med- ium, they can achieve much kinetic energy when undergoing a collision with another gas molecule. If this energy is greater than the ionization energy of the target molecule, it is possible that an additional ion pair will be created and secondary electrons will be released. Newly released electrons are again accelerated and the process is reproduced. This charge multiplication process forms a cascade known as a Townsend avalanche. As a result, a very large number of electron-ion pairs are eventually created just by a single ionizing particle. This process is also called gas amplification. A Townsend avalanche occurs in very high electric fields, in the or- der of 10 6 V/m. In practice these fields can be produced in a radial Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A http://dx.doi.org/10.1016/j.nima.2016.04.102 0168-9002/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. 1 U. Wengrowicz and D. Amidan contributed equally to this work. Nuclear Instruments and Methods in Physics Research A 827 (2016) 118–123