RESUMEN
The Farallon Islands Nuclear Waste Dump Site (FINWDS), approximately 30 miles west of San Francisco, California, received at least 500 TBq encapsulated in more than 47,500 containers from approximately 1945 to 1970. During several seasons in 1986/87 deep-sea bottom feeding fishes (Dover sole = Microstomus pacificus; sablefish = Anoplopoma fimbria; thornyheads = Sebastolobus spp.) and intertidal mussels (Mytilus californianus) were collected from the vicinity of the FINWDS and from comparable depths at a reference site near Point Arena, CA. Tissues were analyzed for several radionuclides (137Cs, 238Pu, 239+240Pu, and 241Am). Radionuclide concentrations for fish mussel tissue ranged from non-detectable to 4,340 mBq kg(-1) wet weight, with the following means for Farallon fishes: 137Cs = 1,110 mBq kg(-1); 238Pu = 390 mBq kg(-1); 239+240Pu = 130 mBq kg(-1); and 241Am = 1,350 mBq kg(-1). There were no statistically significant differences in the radionuclide concentrations observed in samples from the Farallon Islands compared to reference samples from Point Arena, CA. Concentrations of both 238Pu and 241Am in fish tissues (from both sites) were notably higher than those reported in literature from any other sites world-wide, including potentially contaminated sites. Concentrations of 239+24OPu from both sites were typical of low values found at some contaminated sites worldwide. These results show approximately 10 times higher concentrations of 239+240Pu and approximately 40-50 times higher concentrations of 238Pu than those values reported for identical fish species from 1977 collections at the FINWDS. Radionuclide concentrations were converted to a hypothetical per capita annual radionuclide intake for adults, yielding the following values of annual Committed Effective Dose Equivalent (CEDE) from ionizing radiation emitted from these radionuclides: 0.000 mSv y(-1) for 137Cs, 0.009 mSv Y(-1) for 228Pu, and 0.003 mSv y(-1) for 239+240Pu. For 241Am, projected CEDE for Dover sole, sablefish, and thornyheads were higher, averaging 0.03 mSv y(-1). The observed isotopic ratio of 238Pu/239+240Pu was about 4 (which is two orders of magnitude higher than the ratio of 0.03 associated with fallout from weapons tests and accidental releases in the north temperate zone of the earth), indicating a considerably higher environmental mobilization for 238Pu compared to 239+240Pu. Likewise, the observed ratio of 241Am/239+240Pu of about 30 was nearly two orders of magnitude higher than the fallout ratio of 0.43 in the north temperate zone of the earth. The projected ionizing radiation CEDE to people from the ingestion of fish with fallout radionuclides was three times higher for 241Am than from the plutonium isotopes.
Asunto(s)
Bivalvos , Peces , Residuos Radiactivos , Contaminantes Radiactivos del Agua , Partículas alfa , Animales , California , Ecología , Rayos gamma , Monitoreo de Radiación , Contaminantes Radiactivos del Suelo , Contaminantes Radiactivos del Agua/análisisRESUMEN
The direct production of no-carrier-added (NCA) 6.02 h 99mTc and of 66 h 99mMo using proton beams of natural Mo targets was investigated. The major objective of this work was to evaluate the potential of utilizing high-intensity proton accelerators as a supply source of 99mTc and 99Mo for use in diagnostic nuclear medicine. The excitation functions for the production of the directly-made 99mTc via the 100Mo(p, 2n)99mTc (Q = -7.85 MeV) reaction, and of its parent 99Mo via the 100Mo(p, pn) 99Mo (Q = -8.30 MeV) and 100Mo(p, 2p)99mNb(15 s)----99Mo (Q = -11.14 MeV) reactions, were measured in the 68-8 MeV energy range. Single and cumulative yields for 99mTc and 99Mo, and for other Tc, Mo, Zr, Nb and Y radiocontaminants were also determined. The prospects of integrating the use of enriched 100Mo targets with high-intensity, dual beam, H- accelerators was analyzed. The potential of this combined method to replace or complement the current reactor-based supply sources of 99Mo----99mTc generators, is also discussed. Finally, a brief analysis is made on the potential use of this combined technology to support the anticipated expansion of nuclear medicine in developing nations.
Asunto(s)
Molibdeno , Aceleradores de Partículas , Generadores de Radionúclidos , Tecnecio , RadioisótoposRESUMEN
The production and radiochemical purification of no-carrier-added (NCA) bismuth isotopes (i.e. 6.24 d 206Bi and 15.31 d 205Bi) was studied. The Bi isotopes are intended for use as tracers in biodistribution studies and in the design and testing of alpha-emitting radiotherapeutic agents. The total cross sections and yields for the production of 206Bi and 205Bi from the proton bombardment of natural Pb targets were measured using the stacked-foils technique. A radiochemical method for the separation and purification of NCA Bi radioactivities from a multi-gram Pb target was also tested, modified, and improved to provide aqueous solutions of chemically and biologically useful amounts of NCA 206,205Bi for measuring tissue and subcellular-distributions, and for studies covering several chemical aspects of the development of Pb/Bi radiotherapeutic agents.