In the 1970s it was statistically proved that exposure to radon daughter products caused lung cancer in miners. High concentrations of radon daughters have since been found in houses. Any epidemiological radon study begun today is hampered because relevant exposure data are difficult to obtain owing to the long latency period between exposure and tumour manifestation. Here I present a method for measuring cumulative radon daughter levels, which takes advantage of the fact that the first long-lived radon daughter (210Pb, half-life 22 yr) becomes firmly attached to glass surfaces in a house. By measuring the surface activity concentration of the alpha-emitter 210Po, the time-integrated radon, or radon daughter, concentration can be estimated. Thus, indoor glass can act as a long-term retrospective or prospective exposure meter for radon in dwellings.

Concerning different approaches to automatic PoS tagging: EngCG-2, a constraintbased morphological tagger, is compared in a double-blind test with a state-of-the-art statistical tagger on a common disambiguation task using a common tag set. The experiments show that for the same amount of remaining ambiguity, the error rate of the statistical tagger is one order of magnitude greater than that of the rule-based one. The two related issues of priming effects compromising the results and disagreement between human annotators are also addressed.

Concerning different approaches to automatic PoS tagging: EngCG-2, a constraintbased morphological tagger, is compared in a double-blind test with a state-of-the-art statistical tagger on a common disambiguation task using a common tag set. The experiments show that for the same amount of remaining ambiguity, the error rate of the statistical tagger is one order of magnitude greater than that of the rule-based one. The two related issues of priming effects compromising the results and disagreement between human annotators are also addressed.

Explanation-based generalization is used to extract a specialized grammar from the original one using a training corpus of parse trees. This allows very much faster parsing and gives a lower error rate, at the price of a small loss in coverage. Previously, it has been necessary to specify the tree-cutting criteria (or operationality criteria) manually; here they are derived automatically from the training set and the desired coverage of the specialized grammar. This is done by assigning an entropy value to each node in the parse trees and cutting in the nodes with sufficiently high entropy values.

Different numerical strategies in searching for orphan radioactive sources in the environment by means of a mobile detector system have been evaluated. A carborne 3- by 3-inch NaI(Tl) spectrometric system was used with an unshielded 2 GBq 137Cs source as a test source. In this paper, a previous method (MB method), based on a moving average algorithm applied on the gross count rate, was extended and compared with three moving average algorithm methods involving different natural background subtraction strategies. For each method the distance from the road that an orphan source can be detected with a probability of 50% (the critical distance, CD) when driving by is determined. The CD for a 2 GBq 137Cs source improved from 105 m to 130 m when the interference from 40K was subtracted from the 137Cs spectral window. However, when the contribution of other natural gamma-emitting nuclides also was subtracted, the ability to find the 137Cs source was reduced.