Alpha energy

In 1967 G.N. Flerov reported that a Soviet team working at the Joint Institute for Nuclear Research at Dubna may have produced a few atoms of 260-105 and 261-105 by bombarding 243Am with 22Ne. The evidence was based on time-coincidence measurements of alpha energies. 

Element 106 was created by the reaction 249Gf(180,4N)263X, which decayed by alpha emission to rutherfordium, and then by alpha emission to nobelium, which in turn further decayed by alpha between daughter and granddaughter. The element so identified had alpha energies of 9.06 and 9.25 MeV with a half-life of 0.9 +/- 0.2 s. 

Working Level (WL)—Any combination of short-lived radon daughters in 1 liter of air that will result in the ultimate emission of 1.3x105 MeV of potential alpha energy. 

H.G. Jackson and R.P. Schuman Half-lives and alpha energies... 

Measurements of radon progeny, which are the more difficult to make, can be replaced with measurements of radon to provide information on the upper limit for the potential alpha energy exposure from radon progeny. Therefore, simple passive radon monitors for integrated measurements of 1 to 12 months (Alter and Fleischer,... 

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... 

The exposure rate characteristic for this atmosphere is then given by the potential alpha energy concentration (PAEC) Ep... 

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. 

Figure 5. Doses averaged over all epithelial cells in the bronchial and alveolar regions of the lung per unit exposure to potential alpha-energy as a function of aerosol size, compared with doses to basal cells for several models of airway size and clearance behaviour.

Table II. Reference Values of Mean Bronchial Dose from Exposure to 1 WLM Potential Alpha-energy in Homes...

Figure 6. Doses averaged over epithelial cells in segmental bronchi per unit exposure to potential alpha-energy.

Eisfeld, 1980 James, 1984). This leads to the theoretical expectation that risk is proportional to the special quantity exposure to potential alpha-energy, under otherwise similar environmental... 

In practice, it is often neither possible nor convenient to monitor exposure to potential alpha-energy, whereas monitoring of exposure to radon gas by means of the time-integral of the radon... 

Effective dose equivalent. If it is assumed that the weighting factor for bronchial dose equivalent is 0.06, the unattached fraction of potential alpha-energy in room air is typically about 570, and that the aerosol AMD is typically 0.12 pm (Reineking et al., 1985), the... 

Figure 11. Variation of unattached fraction of potential alpha-energy and equilibrium factor according to a model of room aerosol behaviour and the effect on bronchial dose rate per unit radon gas concentration.

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). 

A better way to express the activity of the radon decay products is as the Potential Alpha Energy Concentration (PAEC). This quantity incorporates the deposition of energy into the air and is expressed as MeV/nr... 

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