Incoherent broad-band cavity enhanced absorption spectroscopy for sensitive and rapid molecular iodine detection in the presence of aerosols and water vapour

Abstract

The atmospheric chemistry of iodine is important in different environments, and particularly in case of a nuclear reactor severe accident. This paper describes the performance of an Incoherent Broad-Band Cavity Enhanced Absorption Spectroscopy (IBB-CEAS) device, based on a green LED source allowing the online detection of gaseous molecular iodine. High sensitivities and a wide dynamic range are obtained. The performances and limitations of the IBB-CEAS technique for measurements of iodine in the presence of aerosols and water vapour are discussed. The capabilities of this device to perform kinetics studies on iodine have been investigated in the framework of nuclear reactor accident research. The re-vaporization process of deposited CsI by optical monitoring of I2 concentration-time profiles is presented. The aerosols used in the experiments have been well characterized (size, distribution, concentration and mass) before interaction with iodine by a NanoScan scanning mobility particle sizer (SMPS), a PEGASOR particle sensor PPS-M and a tapered element oscillating microbalance (TEOM).

A laboratory study on the uptake of gaseous molecular iodine by clay minerals at different relative humidities

“…Each experimental run comprised preparation and injection of an I 2 –air mixture of specified relative humidity (RH), passage of the mixture through a two-phase contact chamber (contactor), and analysis of the mixture leaving the contactor in an incoherent broad-band cavity-enhanced absorption spectroscopy (IBBCEAS) instrument. 26–28 The method for injecting and flowing the gas mixture through the contactor was essentially the same as that reported for volatile organic compounds by the authors. 22 The gas flow was controlled with eight mass-flow controllers ( d in Fig.…”

“…The ( I 0 / I in ( t ) − 1) spectrum was fitted by a polynomial of order 19. 28 This smooth function was subtracted to yield a strongly varying residual spectrum: an illustrative example is shown in Fig. S2 †.…”

Chemical stability of caesium iodide deposits in air/steam atmosphere

“…The weak signal detected in the 640-680°C temperature range and interpreted as N rel ≠ 0 is nevertheless not representative of any I 2 release kinetics. Indeed, the raw spectra in this temperature range lack the fine structure of the I 2 spectrum [38] [34] and thus the signal is attributed to the light extinction due to the presence of aerosols (probably CsI) transported up to the optical cell. This online measurement experiment with a sensitive technique confirmed the absence of gaseous molecular iodine released in steam conditions.…”

“…The IBB-CEAS configuration and characteristics are extensively discussed in [38] and [34]. It is based on the I 2 fine resolved spectrum in the 510-570 nm spectral range owing to the numerous rovibronic transitions in the I 2 B←X electronic absorption spectrum [38]. The light source is a LED emitting in the 480-580 nm and the detector is a CCD camera (Andor iDus).…”

“…As explained by Bahrini et al [38] and Johansson et al [34], the I 2 spectra registered by the CCD detector require mathematical processing in order to separate the spectral contribution of gaseous molecular iodine from the continuous component of the spectra. Moreover, for practical reasons [38], a calibrated source of I 2 is analysed by the IBB-CEAS at the beginning of each experiment. Iodine concentration in the sample is then displayed as the adimensional N rel value which is the ratio of I 2 sample concentration to the calibration source concentration.…”