New detector design improves radon risk assessment |
| By Magnus Fritzson, Market Communications Manager at Hectronic AB |
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Gammadata’s new instrument for radon detection measures the content of radon progenies (products of radon decay) content rather than the content of the radon gas itself and improve the level of reliability in risk assessment because of the fact that these elements can be caught in filters.
Radon progenies are the radioactive isotopes of polonium, bismuth and lead and are products of radon decay. They exist attached to particles in the air or freely as clusters. Unattached radon progenies are much more dangerous to humans than the ones that are attached to aerosols.
Reliability in risk assessment is further improved by measuring these two types of radon progenies.
– The uniqueness of our instrument is the two detectors to collect and measure contents of both types of radon progenies, says Dag Sedin, President of Gammadata Instrument.
The instrument measures and displays the content of radon progenies and actually also the content of thoron progenies. The potential alpha energy concentration for thoron progenies is 14 times higher than for radon progenies. That’s why the thoron progeny concentration is relevant as well. The gas content is calculated from that data and can be displayed as an option. |
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Gammadata is currently developing an instrument for radon and thoron detection based on a unique technology. The picture shows one of the instruments from the pre-series. Two detectors measuring radon and thoron progenies* instead of radon and thoron gas has drastically improved the reliability in risk level assessment. Analogue electronics design was challenging. The detectors emit currents of only picoamperes. *Products of radon decay |
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Discussions about this new instrument begun back in 2005. The old radon gas instrument ATMOS 12, introduced in 1988, was becoming expensive to manufacture because of an old electronic design.
– We still sell it and it’s still the world’s most sensitive instrument on the market for radon detection, says Dag Sedin.
Gammadata’s aim was to develop a smaller and faster instrument with at least a similar level of sensitivity. Dr. Rainer Rolle at the University of Göttingen had already developed a prototype of a radon progeny monitor. The decision was made to develop a new instrument based on Dr. Rolles detector design and calibration routines for radon and thoron progenies. |
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New ways to measure limit values |
The existing limit value for radon in houses is specified as a content level of radon gas. Whether or not the limit value will be changed to a content of radon and thoron progenies is not clear. The matter is under debate.
– There is a risk involved in developing an instrument that doesn’t use the standardized measurement method, says Dag Sedin.
Properties and functions of the new instrument make it interesting to customers even though the authorities don’t change the way limit values are measured. Instruments detecting radon gas need a long period of time to determine the value accurately if the gas content in the surrounding air is low.
– We will reach new customers because the instrument is five times faster than others, says Dag Sedin. The existing instrument in our product line needs about 15 minutes to verify if the value is above or under 200 Bq/m³ (Becquerel/m³). The new instrument verifies 40 Bq/m³ in the same period of time.
The new measurement method used in this development project gives advantages to environmental consultants in the construction business. The speed and independent measurement of attached and unattached radon progenies allow the instrument to be used evaluating ventilation. Information describing ventilation properties is valuable input to choosing and evaluating measures for radon decontamination of buildings. |
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Protecting mine workers health |
Customers can be found also in the mining industry. Mine workers exposure to radon needs to be limited to specific doses and periods of time. Workers may need to switch to alternative work for some time when limits are exceeded.
– We believe that the greater amount of customers is found on the Chinese market where there is a demand for instruments for radon detection in mines, says Dag Sedin. |
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 | The Hectronic H6042 is an ARM module with FPGA in the same category as the module used by Gammadata to develop the new instrument for Radon and Thoron detection. Read more » |
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Engineers at Gammadata took on the challenges in development bearing the customer requirements in mind. The instrument was developed to pump surrounding air through two filters, a paper filter for attached radon and thoron progenies and a metal filter for unattached ones. The two filters have one detector each. The detectors are in principle large diodes and emit pulses with specific energy content.
– Pulse amplitudes are proportional to the energy of the radiation, says Ove Johansson, Electronics Design Engineer at Gammadata Instrument AB.
The detector signals are connected to an analogue electronic circuitry. Requirements for shielding and component quality were strict to handle the weak signals. A typical current pulse from a detector is measured in picoamperes. Each pulse contains a couple of million electrons. |
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Shielding against electromagentic disturbances |
Power components are separated from components for detection on the board. A ground plane and a metal housing further improve the protection against electromagnetic disturbances. Major sources of disturbance are internal, for instance the motor pumping air through the filters.
An integrating amplifier converts the current to a voltage. Amplification in two steps, first up to a couple of millivolts and then to a couple of Volts and pulse width extension, adapts the signal for AD conversion. Signal strength decides the type of particle that is detected.
– Then it’s just a matter of counting pulses, says Ove Johansson.
The instrument needs to be able to detect up to 100 000 particles/s in each detector in real-time. Fast distribution of data and flexibility was two important reasons for choosing an FPGA together with an ARM processor according to Ove Johansson.
– We will have a possibility to easily add and change functions in the instrument in the future. |
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The first instrument on the market |
Gammadata developed the electronics on a carrier board, mechanics and software. Hectronic was engaged in developing the computer module to be mounted on the carrier board. Ove Johansson is satisfied with what Hectronic delivered.
– I’m aware of the challenges involved in development based on an FPGA. Things have worked smoothly and the computer module worked more or less on delivery.
A pre-series of instruments has been produced. Competitors are on the market but not any using two separate detectors. Discussions about limit values and measurement methods continue among national radiation safety authorities.
– If the authorities make agreements and decisions along the lines we think they will our instrument will be the first on the market to measure accordingly, says Dag Sedin. |
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