Alpha energy concentration measurement

Figure 1. Variations in the hourly mean alpha-energy concentration during an integrating radon gas measurement of three weeks The alpha-energy concentration calculated from the radon level (4860 Bq/m3) and the typical equilibrium factor (0.45) is also given.

An equilibrium factor of 0.35, derived from measurements made during the local surveys, has been assumed to typify conditions in UK dwellings. This value has been used to convert the average radon concentrations measured in the national survey to potential alpha-energy concentration of radon decay-products. On average, persons in the UK spend 75% of their time in their homes and 15% of their time elsewhere indoors (Brown, 1983). The occupancy factor of 0.75, together with an equilibrium factor of 0.35, results in an annual exposure of 1.3 10"5 J h m"3 (0.0037 Working Level Months,... 

Radon concentrations were measured by use of calibrated Lucas scintillation flasks, while radon and thoron daughters and the resulting potential alpha energy concentration (PAECj were determined using filter samples (Thomas, 1972) and a continuous electrostatic precipitator (Andrews et al., 1984). The radon daughter positive... 

It has been demonstrated that it is possible to lower the level of airborne radon progeny by filtering and/or expose the air to an electric field. If the radiological risk is measured by the potential alpha energy concentration (PAEC) or exposure rate, for instance expressed in J m 3 or WL, the level may be lowered to about 10-20 % of the value in untreated air, while the reduced level may only be about 40-50 % of the untreated one if the average dose to a certain part of the respiratory tract, for instance expressed in Gy year 1, is considered. 

The same kind of optimization has been performed for the thoron daughters. In the calculations the sampling period was set at 30 min and the first decay time interval is started after the decay of the radon daughters (270 min). For a total measurement time of 16 hours the optimized MMC of Pb-212 and Bi-212 are respectively 0.02 Bq/m and 60 Bq/m (270-370 min, 540-960 min). Better results for Bi-212 are obtained with only one decay time interval and an estimation of the ratio of Pb-212 to Bi-212 out of the removal processes (ventilation and deposition of the attached thoron daughters). The influence of the removal rate on the potential alpha energy concentration is small. For the decay interval (270-960 min) the MMC of Pb-212 is 0.014 Bq/m, assuming the sum of the removal rates to be 0.6+0.5/h. 

Continuous measurements of the potential alpha energy concentration of the radon decay products were made with a Continuous Working Level Monitor (WLM-300) (EDA Instruments Inc., Toronto). 

In industrial exposure, continuously operated filter samplers can be used to measure the potential alpha energy concentration, but in houses passive dosimeters are more commonly used and these measure concentrations of radon, not radon daughters. Since... 

In the estimation of the dose conversion factor, DCF, by dose model calculations, the activity size distribution in terms of potential alpha energy concentration (PAEC) is an important input parameter. For practical reasons related to measurements, the activity size distribution should be divided into three parts as follows ... 

Fig. 5.7. Relative size distribution in terms of potential alpha energy concentration, PAEC, of the unattached radon decay product clusters measured in indoor air.

Half-life Potential alpha energy (PAE) The time it takes for one-half of any quantity of identical radioactive atoms to undergo decay. The total energy emitted during ot-decays if a quantity of tadon decay Working level (WL) A measure of decay product concentration that indicates the extent of a-particle release from short-lived products. Also a measure of the total a-activity in air. 

The radon in the air i/as measured continuously by electroprecipitation of the positively charged Po-218 ions in an electric field (10 kV) on a surface barrier detector (Porstendorfer, et al., 1980). For this purpose the air i/as dried, filtered and sucked into an aluminium sphere ( 2 1) with a flowrate of 0.5 lmin-1. The counts due to Po-218 and Po-214 were proportional to the radon activity concentration. Their disintegrations were directly detected by alpha spectroscopy with an energy resolution of about 80 keV. The monitor could detect down to 5 Bq m 3 with a two hour counting time and 30 % statistical accuracy. 

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