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The Czech Radon Program and Instrumentation
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Radon legislation and the radon program in the Czech Republic:
Following the political changes in 1989, the political climate was favourable for addressing problems
associated with radon in the Czech Republic as - there was a strong radon lobby and Parliamentary
will to do something about the "dangerous radon situation"
- at that time, the Ministry of Finance did not have an estimate of the total costs of the radon program
and was concerned with "more important matters".
In 1990, the Government appointed the Radon Commission and the Ministry of Health issued Regulation
No. 76/1991 on the requirements for protection of health against the radon risk.
Requirements of the new regulation:
- for new dwellings, EER must be below 100 Bq/m3,
- for older dwellings, EER must be below 200 Bq/m3; if this requirement is not met, the radon level must be reduced by remedial measures.
In 1993, Government Decree No. 703/1993 approved financial support for the
- program to find dwellings with elevated radon concentrations and for radon risk mapping,
- regulation of allocation of state assistance for implementation of remedial measures.

What has been achieved?
1.Finding dwellings with elevated radon concentrations: about 300 000 track detectors were distributed,
100 000 residences were studied in detail, and 5100 residences were found with EER above 200 Bq/m3
(by 1996).
2.A map of the radon risk on a scale of 1 : 50 000 was published (Barnet, Matolín)
3.By 1996, about 900 000 mil. CZK (about 30 mil. EUR) had been spent from the state budget for remedial
measures (2000 residences, 215 schools, etc.). By 2002, the Czech radon program had cost 40 mil. EUR.
4.140 companies have received approval for measurement of radon in soils and about 70 companies
have been approved for measuring indoor radon levels.
5.A metrological system has been established for radon concentrations and for the concentrations of radon
progeny (a primary standard for radon concentrations, a secondary
standard for DpR); an equipment and personal certification system has been organised to ensure the
correctness of measurements.

Radon instrumentation and conditions in the Czech Republic
The success of the radon program depends on the availability of a sufficient number of instruments of
sufficient quality at an acceptable price. Measuring techniques can be classified as:
- passive tracker detectors for long-term measurement of radon concentrations,
- radon monitors and electrets for indoor radon measurements,
- instruments for measuring the concentrations of radon progeny,
- instruments for measuring radon in soils.
In 1991, there were only about 5 suitable "radon" instruments in the Czechoslovak Republic.
Consequently, a great many new instruments had to be developed and produced.

Measuring radon in soils. Why and when?
There is a strict regulation in the Czech Republic that the results of radon measurement
at the construction site are a requisite
when someone applies for a construction permit.
The results of the radon concentration measurement are combined with a soil permeability test
and the site is classified in one of three categories. Low, middle and high risk ground. When the site
is in the middle or high category, the building construction plans must take this into account and must
include measures to reduce the indoor radon concentration below 200 Bq/m3.
The final construction inspection prior to occupancy then includes measurements to ensure that this
levelis maintained.

How should samples be taken?
All of the 140 companies carrying out radon soil measurements use the same technique
- the "lost tip" method, which was originally suggested by the Radon company (the Neznals brothers):
- The tip is inserted into the end of a tube (the tube has a length of 150 cm and diameter of 10mm)
- The tube is hammered 80 cm into the ground
- Using a rod, the tip is pushed out of the tube
- An air sample is taken from the tube using a 150 ml syringe.

Additional requirements:
More than 10 samples must be taken from the construction site; meteorological conditions must be
recorded and the permeability of the ground must be determined. The Radon company studied the effects
of the meteorological conditions, the sampling depth,etc.
There are three radon reference sites in the Czech Republic, used to study radon in soil and for measure-
ments by companies applying for certification.

How should the air sample taken from the soil be measured? Principal aspects.
Suitable detector: as 10-15 samples must be measured over 2-3 hours, the main difficulty
lies in the increasing background level caused by radon progeny. Consequently, a large ionisation chamber
or detector, based on precipitation of progeny, is not suitable.
The Lucas cell is the optimum design, but it is necessary to have 20 - 30 cells; the cell is contaminated
following the measurement and can be used again only after 3 hours.
Thus, the Lucas cells must be inexpensive.

Statistics: A statistical error below 10% must be attained in a measuring interval of less than 2-5 minutes
when the concentration is about 20 kBq/m3.

Measurement: in the home (the Lucas cells are filled in the field and then measured in the laboratory)
is a comfortable arrangement, but the seal of the Lucas cell must be very good to maintain a vacuum;
when the sampling is not successful or a sample is taken from a geological fault, it is necessary to return
to the site.

In the field: requires a special instrument and a manual pump - see LUK; however, when the sampling is
not successful or a sample is taken from a geological fault, the sampling can be repeated and the fault
can be traced.

Data treatment: As some people do not have the time to properly calculate the concentration from
the measured number of pulses, the instrument should display the results as Bq/m3.

Price: A price of about 2000 EUR for the entire system was acceptable for Czech clients in
1991; now the price should not exceed 3000 EUR.

Conditions in 1991: About 5 instruments were available (old Tesla, Pylon and Scintrex instruments).
About 50 instruments were needed; however Pylon AB5 cost about 4000 USD +3000 USD for 30 Lucas
cells, i.e. about 315 000 CZK (i.e. 10 000 EUR) at that time.

There was a great need for development of our own, Czech instruments for an acceptable price.
Consequently, the Jiří Plch - SMM company was established.

Indoor radon measurement in the Czech Republic and Instrumentation.
The long-term indoor radon concentrations are determined by means of tracker detectors - see above.
The Czech legislation requires short-term measurements for the construction inspection prior
to occupancy when medium and high-ground risk was found at the construction site for a new building
or when an older house was reconstructed. The main postulate for the measurements is that
the shortest measuring interval is one week and that all the rooms in the building must be measured.
Diagnosis of the building is required to obtain a state contribution for mitigation of the radon risk, i.e.
one-week measurements of the entire building + ventilation experiments.
Units: Between 1991 and 2002, the radon risk was expressed in EER and, when the radon concentration
was measured, EER was calculated using an F-factor equal to 0.5.
Since 2002, the radon risk has been expressed in terms of the radon concentration. There was
no equipment in 1991 for large numbers of measurements.

As the radon risk was expressed as EER, radon progeny monitors were developed at the Faculty of Nuclear
Science in Prague, Geotechnica-Brno and also Fritra 3 and Fritra 4. However, these monitors
are too expensive to be used on a large scale and are currently used only for diagnosis.
Consequently, mostly the radon concentration is measured and EER is calculated using the F - factor.
The following are used to measure radon concentrations:
- electrets,
- Fritra2, Fritra3 and Fritra4 radon and radon progeny monitors,
- Radim-type instruments.
Advantage of electrets: low price
Disadvantage of electrets: stochastic self-discharge, requirement of being charged by the manufacturer,
high price of the reading instrument.

A short "Radim story".
To compete with electrets, the "electronic electret" - Radim1 was developed in 1993 and distributed in
relatively large numbers. It was a very simple and cheap device registering the number of counts in a
one-week interval and the mean concentration was calculated using the known response (Imp/hour)/(Bq/m3). The detection principle was based on "precipitation of radon progeny".
The Radim1 instrument had relatively high humidity dependence and low sensitivity.
Considerable efforts were exerted in 1994 - 95 to improve the detection properties of the Radim instrument
and the new "electronic electret" - Radim2C and then radon monitor Radim2P were developed.
The improvement in the Radim series continued with the very popular Radim3, and the latest model is Radim5. As the detection system of Radim2, Radim3 and Radim5 has peak parameters, it will be described in
some detail here.
The detection principle of Radim-type instruments is very old - "precipitation of progeny":
the radon diffuses into the detection chamber, which is covered by a special filter, which absorbs radon
progeny produced in the air. The radon activity is determined by measuring RaA formed by radon
decay and collected by an electric field on the surface of a semiconductor detector.
Radim3 has very high sensitivity: (0.8 impulse/hour)/(Bqm3).
Dependence of the sensitivity of Radim3 on the relative humidity: 15% for a change
in the relative humidity of 50%.
Several other commercial instruments working on the same principle are available on the market.
(Sarad 2000, Durridge RAD7, etc.)
… but Radim has the highest sensitivity and is least affected by the humidity. Why?
The shape of the detection chamber, with a very effective electric lens, was designed
by computer modelling and there is a special feature to reduce the effect of "electro-negative" ions
.

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