Discrimination between natural and other gamma ray sources from environmental gamma ray dose rate monitoring data.

In this study, a method to discriminate between natural and other γ-ray sources from environmental γ-ray dose rate monitoring data was developed, and it was successfully applied to actual monitoring data around nuclear facilities. The environmental dose rate is generally monitored by NaI(Tl) detector systems in the low dose rate range. The background dose rate varies mainly as a result of the deposition of (222)Rn progeny in precipitation and shielding of the ground by snow cover. Increments in the environmental dose rate due to radionuclides released from nuclear facilities must be separated from these background variations. The method in the present study corrects for the dose rate variations from natural sources by multiple regression analysis based on the γ-ray counting rates of single-channel analysers opened in the energy ranges of γ-rays emitted by (214)Bi and (208)Tl. Assuming a normal distribution of the results and using the one-sided type I error of 0.01 while ignoring the type II error, the detection limit of the γ-ray dose rate from artificial sources was 0.77 nGy h(-1).

[Detection of rifampicin-resistant strains of Mycobacterium tuberculosis by a non-radioactive PCR-SSCP method].

PCR-SSCP method to detect genetic mutations in rpoB gene as a marker of rifampicin-resistance was developed by Telenti et al., and we have modified it applying non-radioactive PhastSystem for more practical use in the detection of rifampicin-resistance of Mycobacterium tuberculosis. PCR products amplified with the primers specific to rpoB gene using extracted DNA from 89 strains of M. tuberculosis were sequenced and the amino acid sequences were morphism was determined by the PhastSystem. The bands were stained by silver staining. Among 89 strains of M. tuberculosis, 43 were confirmed as rifampicin-resistant (RFPr) and 46 were rifampicin-sensitive (RFPs) by the culture on the drug-containing media. All of the 43 RFPr strains had one or more mutations in the DNA sequence of rpoB gene, while none of the RFPs strains had such mutations. However, by PCR-SSCP, only 20 out of 43 RFPr strains showed clear differences in the band pattern of electrophoresis from that of RFPs strains. Other 23 RFPr strains had only slight differences in the band pattern of the PCR-SSCP from that of RFPs strains. But it was noticed that the main bands of RFPr strains were distinguishable from the main bands of RFPs strains even their patterns were similar. Thus, it is possible to apply a non-radioactive PCR-SSCP for the detection of rifampicin resistance of M. tuberculosis with further improvement of the condition of gel electrophoresis or staining techniques.

[Studies on the generation mechanism of non-biological response in distortion product OTO-acoustic emission].

We investigated the effect of non-biological artifacts on the measurement of distortion product oto-acoustic emission (DPOAE) using guinea pigs, and the generation mechanism of this phenomenon is discussed in the present paper. When a sound pressure of a stimulating tone was too large, an overtone was produced within the acoustic probe. When the difference in sound pressure between f1 and f2 was too large, artifacts appeared at frequencies of 2f1-f2 or 2f2-f1. Similar responses were generated when f1 and f2 were identical in sound pressure but exceeded a certain critical level. These non-biological responses could be easily differentiated from biological responses by subjecting the animal to anoxia. The input-output curve of DPOAE was biphasic and clearly showed this critical level in each animal. The results obtained in the present study suggest that the levels of f1 and f2 should be almost equal and should not exceed the observed critical level when measuring DPOAE.