Radon-222 on the island of Hawaii.

The island of Hawaii, like other locations in a marine environment, has low levels of atmospheric 222Rn. The low concentrations of 222Rn and its decay products result from a low average flux density of 9.8 mBq m-2 s-1, the mixing of marine air from the Pacific having a 222Rn concentration of only 0.04 Bq m-3 with air from over the island, and the decay of 222Rn as it is transported in air masses across the Pacific primarily from the Asian continent. The overall mean concentration over the Island The overall mean concentration over the Island was found to be 0.44 Bq m-3 compared with a figure of about 8 Bq m-3 for air over continents. A consideration of the island as a source of 222Rn must take into account the relatively low average flux density associated with the lava fields and accompanying thin soils. The 222Rn formed from the U and 226Ra present in the lava cannot escape to the atmosphere. The deep agricultural soils, on the other hand, provide relatively high flux densities. When the areas of the soil types are taken into account, the exhalation for the lava fields, thin organic soils, and deep agricultural soils were 0.25, 1.7, and 32 MBq s-1, respectively. Measurements of indoor 222Rn on the island indicate levels of approximately 25 Bq m-3 which is appreciably lower than 40 Bq m-3 taken as an average for indoor levels on the mainland. Based on an assumed indoor occupancy level of 0.8, the effective dose equivalent for inhaled 222Rn and its decay products on Hawaii is 1.2 mSv y-1. This is only a little more than one-half of that for a resident of the continental United States who is estimated to receive an effective dose equivalent of 2 mSv y-1. The relatively low effective dose equivalent for the population on the island may have interesting effects in comparison with people living in areas where the inhaled dose from 222Rn is much higher.

An electrostatic precipitator for the study of airborne radioactivity.

An system has been developed to measure airborne radioactivity using electrostatic precipitation for collection and alpha-particle spectroscopy for detection. Features include good energy resolution (e.g. 170 and 300 KeV for full-width half maximum and full-width tenth maximum for 7.7-MeV alpha particles using a 7-cm2 area detector; and 52- and 122-KeV, respectively, using 1.2-cm2 area detector) and versatile computer control for collection, counting and data reduction. Aerosols bearing the radioactive atoms are deposited on a foil tape by electrostatic precipitation for a predetermined time after which the foil is moved under a solid-state detector to count the alpha-particle emissions. Activities are determined at the same frequency as samples are collected. Helium gas can be introduced at the detector to reduce energy loss and improve resolution. Although in principle certain aerosol sizes could be difficult to collect, in practice no difficulties were observed for typical environmental conditions, provided sufficiently low air-sampling rates were used. One important application is the measurement of 222Rn daughters. The sensitivity is such that detection of individual daughter concentrations less than 0.1 pCi/l. with only a 10% counting error is possible.

Two-filter monitor for atmospheric 222Rn.

A two-filter, continuous monitor has been developed for atmospheric (222)Rn. Features include a sensitivity of better than 0.01 pCi/l, a high specificity for (222)Rn, and immediate start up capability. The monitor has been computer modeled to facilitate calibration and selection of operating parameters. The filters are stationary and require no moving parts for control. Field trials indicate high reliability and maintenance-free operation for periods of a week and longer.

Radon-222 from the island of hawaii: deep soils are more important than lava fields or volcanoes.

The mean flux of radon-222 atoms from the island of Hawaii is 0.45 atom per square centimeter per second. Lava fields occupy 50 percent of the land area, but their radon flux is only 1 percent of that from deep volcanic soils. The island yields approximately 10 curies of radon-222 per hour to the air surrounding it. The radon-222 contribuition of volcanoes is negligible.