Development and validation of a technique for the determination of 226Ra and 228Ra by liquid scintillation in liquid samples.

Radium isotopes are dispersed in the environment according to their physicochemical characteristics. Considering their long half-lives and radiological effects, (226)Ra and (228)Ra are very important issues in radiological protection. In Brazil, radium isotopes represent an exposure problem both in nuclear fuel cycle installations and in high natural radiation background areas. The experimental part of this work includes the development of a technique for the determination of (226)Ra and (228)Ra by liquid scintillation with potential application in biological samples. Radium was concentrated and then separated from other constituents of the sample by co-precipitation/precipitation with Ba(Ra)SO(4). The precipitate was filtered and weighted to calculate the chemical yield. The filter containing the precipitate of Ba(Ra)SO(4) was transferred to a scintillation vial. Two methods were used to prepare the sources. The first one consisted of the addition of water (8 ml), Instagel XF (8 ml) and UltimaGold (4 ml) in the vial containing the filter and the precipitate, forming a gel suspension. In the second method, the precipitate was dissolved with 0.2 M ethylene-diamine-tetra-acetic-acid solution (9 ml) and 11 ml of scintillation solution (Optiphase Hisafe 3) was added to the vial, forming an aqueous and an organic phase. The solutions obtained were counted in a low background scintillation spectrometry system (Quantulus) suitable for the detection and identification of both alpha and beta particles for the determination of (226)Ra and (228)Ra. The activity values of (226)Ra and (228)Ra calculated by the two methods are in good agreement with the reference values, indicating that both methods are suitable for the determination of (226)Ra and (228)Ra.

Optimization of 99Mo measurement in 99mTc eluate samples using a scintillation detection system.

During elution of 99Mo-99mTc generators used in nuclear medicine, 99Mo might be extracted becoming a radionuclidic impurity. According to the International Atomic Energy Agency, the activity ratio between 99Mo and 99mTc in the eluate, at the moment of administration to the patient, should not exceed 0.015%. The aim of this work is to optimize a methodology to determine 99Mo activity in 99mTc eluates. Efficiency curves were obtained using a NaI(Tl)8"×4" scintillation detector. The methodology was validated by measuring a standard solution of 99Mo. It was concluded that the technique is sensitive to detect 99Mo in 99mTc eluates at levels below international limits.

Lung counting: summing techniques to reduce the MDA.

The new dose limits recently adopted in Canada (and elsewhere in the world) have made it more difficult to detect some radionuclides by in vivo counting at the average dose limit of 20 mSv. This is particularly true for natural uranium. Two techniques have been developed by the Human Monitoring Laboratory to reduce the Minimum Detectable Activity (MDA) for the lung counting of this nuclide. The first technique, developed in collaboration with Cameco, is to either sum sequential counts of an individual or to sum spectra of a group of workers similarly occupationally exposed. This technique offers a reduction in the MDA of up to a factor of three. The second technique, developed in collaboration with CNEN, involves the summing of photopeaks within an individual spectrum and offers a reduction in the MDA of up to a factor of two.