The development of the integrated circuit AlphaRad as a new System-on-Chip for detection of α-particles has already been reported. This paper deals with electronic monitoring of atmospheric radon, which is one of the promising applications of the chip. The future electronic radon monitor (ERM) is designed to be compact, inexpensive, operating at low voltage and fully stand-alone. We present here the complete electronic board of the future ERM: it is made of three independent AlphaRad chips running in parallel, mounted on a small printed-circuit board which includes a numeric block for data treatment based on a Xilinx programmable gate array. The maximal counting rate of the AlphaRad chip has been pushed to at least 3×106 α-particles cm−2. The complete system for detection of the solid aerosols will be published separately, and this paper will focus on the electronic board alone. Already 20 times faster than our first measurement with a CMOS pixel sensor, the system was tested at low and high activities, showing an excellent linearity for 222Rn levels up to 80 kBq m−3.
[Show abstract][Hide abstract] ABSTRACT: An integrated System-on-Chip (SoC) has been designed in CMOS mixed analog/digital technology, and tested for high rate alpha particle counting. The sensor is the most innovative part of the chip, with a total active area of . The two-stage charge-to-voltage amplification scheme includes a numerical block for offset compensation. Designed with a gain of 700, the chip has been tested in alpha sources: a very high signal over noise ratio was obtained, leading to a detection efficiency of 5 MeV alpha particles close to 100%. The chip is working at room temperature and has been tested up to 300 kHz reset frequency.Future applications of this SoC will focus on detection of fast and thermal neutrons free of gamma contamination.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 12/2006; 569(3-569):845-852. DOI:10.1016/j.nima.2006.09.110 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A CMOS active pixel sensor (APS), originally designed for the tracking of minimum ionizing charged particles, has been used for α-particle counting inside a tank containing 1200 Bq/m3 of 222Rn. We present the APS results and those obtained with well-established methods for a run in the Rn tank. This study opens the way towards a fully electronic compact Rn dosimeter.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 09/2004; 225(3-225):418-422. DOI:10.1016/j.nimb.2004.05.017 · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In indoor and mining environments, deposition to “plate-out” of radon progeny onto walls occurs simultaneously with the attachment of progeny of airborne particles. Attachment and plate-out processes affect the atmosphere in which radon exposure takes place by reducing concentrations and shifting activity size distributions. Deposition of fine particles on paintings and other art objects is also a concern in museums. Here we describe plate-out measurements of radon progeny and aerosol particles in a spherical chamber under controlled laboratory conditions. The temperature and velocity profiles in still and turbulent air were monitored. A laboratory mixer with variable speeds and speed control was used to increase turbulence in the chamber. During mixing, air velocity was detected when rotational speeds were higher than 500 rpm. Monodisperse silver aerosols and polystyrene latex particles in the size range of 5 nm to 2 μm were used in the deposition study. Nanometer particles between 0.88 to 1.80 nm were generated by passing Rn gas into the chamber and letting the gas decay into Pb. The deposition rates of particles and radon progeny (Pb) in the chamber were determined by monitoring the concentration decay of the aerosol as a function of time. Our data confirmed that the homogeneous turbulence model can be used to describe the wall deposition rate in still and mixing conditions. Higher deposition rates were observed during increased air mixing. Higher rates were more significant for particles smaller than 1.0 μm, indicating that the turbulence produced by mixing increased the turbulent diffusional deposition. The coefficient of eddy diffusivity was predicted by the mass transfer equation. The coefficient was also reasonably predicted from a technique using velocity measurement and from an energy dissipation equation.
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