Determination of Low Levels Activities of Natural Alpha Emitting Radionuclides such as Uranium Isotopes in Angolan Environmental Samples (Water, Fish, Uranium Ores) by Alpha-Particle Spectrometry and Gamma Spectrometry

Activity concentrations of U-238, U-235 and U-234 in Angolan environmental samples such as water samples (tap water/drinking water, river water, sea water/ocean water), marine fish samples (Sardinella reed/Sardinella Maderensis, Dentex macophthalmus, Trachurus capensis) as well as in uranium ore bodies were determined. white samples (dose rate < 2.5 microsievert/hour) were measured by alpha-particle spectrometry based on Passivated Implanted Planar Silicon Detectors (PIPS) and blue samples (2.5 microsievert/hour ≥ dose rate ≤ 250 microsievert/hour) were measured by gamma spectrometry based on Hyper-Pure Germanium detector (HPGe). Water samples recoveries ranged between 92.82% - 104.45%, and in marine fish samples recoveries ranged between 72.5% - 91.8%, 56.32% - 60.14% and 22.6% - 40.04% for Sardinella reed/Sardinella Maderensis, Dentex macophthalmus and Trachurus capensis respectively. Recoveries in IAEA reference materials and uranium ore bodies ranged between 63% - 113%, except for uranpyrochlore, monazite, uranothorite and pitchblende ore bodies whose recoveries were below 25%. The accuracy assessed as relative errors for water control and IAEA reference materials digested for 48 hours ranged between 2,96% - 6,15% and 2.45% - 26.7% respectively. For IAEA reference materials digested for 120 hours the accuracy ranged between 6.97% - 13.24%. The accuracy and precision for U-235 are not as good as that of U-234 and U-238 due to the fact that U-235 activity concentrations are relatively low in most of the samples. The nearly unity of Linearity between the measured values and recommended values demonstrates that the method and procedures used in the paper are as unbiased as requested and gives reliable results. The data were evaluated according to ISO Guide 33 for assessment of the trueness of the method. The quality of Angolan uranium ore bodies was also evaluated. In the total of 100% of all naturally occurring uranium that exist, 50% of it forms the Earth's inner core and the other 50% is distributed almost everywhere in different levels of uranium activities. Isotopic ratios, uncertainties and expanded uncertainties were estimated. (author)