When the RAM aerosol monitors are provided with a gamma measuring head, they are able to detect elemental iodine, attached to particles, but are practically insensitive to gaseous radioactive iodine. This can be measured by the RTS RIM models used as stand alone monitors or as monitoring units coupled to the aerosol equipment. The RIM monitors are real time, continuous measuring devices based on the gamma spectrometry method with NaI(Tl) detector.
The RIM-01 is the single cartridge standard unit with manual replacement while the RIM-14 is the multiple (14) cartridge special unit with automatic replacement. In normal condition the autonomy of the RIM-14 may be about 3-4 months, depending on application and/or plant condition. Both the iodine monitoring heads are usually controlled by a dedicated processor (RTS LPU-02), but can be also managed by the RAM LPU main processor.
Iodine is sampled with a constant flow rate on a 2 1/4″ D x 1″ H cartridge (TEDA impregnated charcoal or silver zeolite), plastic type, placed in front of the gamma detector. The measuring head is enclosed in a lead shield 5 cm thick. Together with the cartridge replacing assembly (in case of the RIM-14 automatic model), due to its weight, it is placed at the bottom of a standard 19″ rack cabinet. In the RIM-14 the cartridge is automatically replaced at software selectable intervals, otherwise in the RIM-01 the cartridge is manually replaced by means of a simple ‘holder/slide’. Sampling time and measuring cycle are programmable and can be automatically changed according to the measurement range if needed. All parts of the measuring chamber around the cartridge are realised in stainless-steel for easy decontamination.
The RIM series uses an integrated stabilised electronic assembly to ensure long term stability and temperature independent calibration. The detection unit is coupled to a tube base voltage divider / preamplifier / HV bias supply (PA-04HV) and to a microprocessor based multi-channel analyser (MAB-03G Monitoring Processor) that allows the control of the measurement parameters via software from the LPU. Using a MCA device for the spectrometric measurement allows also to have well defined Regions of Interests (ROIs) for the evaluation of the relevant peak of I-131. The ROIs can be properly set by the operator, but they are in any case set at factory. The net area of the peak is directly used with background subtraction in order to increase both sensitivity and dynamic range. I-131 net counts/cps and gamma activity/concentration are automatically computed during (refresh step usually set at 60 or – default – 120 s) and at the end of each counting interval.
The system automatically checks each measurement against the preset alarm and alert thresholds (programmable) and any data found to be outside the thresholds or anomalous is also indicated as a diagnostic in a log file. Measurement parameters, including thresholds, measuring time and measuring cycle, may be set through the LPU both locally and remotely. All measurements are qualified with a diagnostic indicating the current status of the system and measured values against set thresholds, with error (sigma selectable). The system is factory calibrated using a source having a properly correlated geometry with respect to the sampling cartridge.
At the end of each counting interval the monitor stores all needed data including date and time of the measurement and spectrum. Three types of files are generated and stored into the related local folders: Measurement data and associated spectra, Alarm data and associated spectra, Records with relevant data (at a programmable sequence and for eventual automatic transmission).
The operating software provides for the following main functions: Pump control and Flow-rate measurement, Gamma spectrum acquisition and readout, ROIs processing and readout, Evaluation of the I-131 collected activity (Bq) and concentration in air (Bq/m3) with error, Alert/Alarm and failure management, Test and calibration procedure, I/O management, Data storage and communication, eventual compensation of Pb-214.
The measuring units are the ones defined by the International Standard, but can be optionally provided different under specific customer’s request. Complex monitoring station including aerosol and iodine sections, gas section, gamma dose-rate section, meteo section, etc. can be configured around the RAM and RIM units.
The units are usually supplied with: air inlet including particulate filter holder, iodine cartridges, holder/slide for cartridge holding/replacement (RIM-01), optional cartridge mock-up for test/calibration source housing.