Omar F. Carvacho

Cyclotron production of NCA 99mTc and 99Mo. An alternative non-reactor supply source of instant 99mTc and 99Mo→99mTc generators

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.

Soil sample collection and analysis for the Fugitive Dust Characterization Study

A unique set of soil samples was collected as part of the Fugitive Dust Characterization Study. The study was carried out to establish whether or not source profiles could be constructed usingnovel analytical methods that could distinguish soil dust sources from each other. The soil sources sampled included fields planted in cotton, almond, tomato, grape, and safflower, dairy and feedlot facilities, paved and unpaved roads (both urban and rural), an agricultural staging area, disturbed land with salt buildup, and construction areas where the topsoil had been removed. The samples were collected usinga systematic procedure desig ned to reduce samplingbias, and were stored frozen to preserve possible organic signatures. For this paper the samples were characterized by particle size (percent sand, silt, and clay), dry silt content (used in EPA-recommended fugitive dust emission factors), carbon and nitrogen content, and potential to emit both PM10 and PM2.5. These are not the ‘‘novel analytical methods’’ referred to above; rather, it was the basic characterization of the samples to use in comparinganalytical methods by other scientists contracted to the California Air Resources Board. The purpose of this paper is to document the methods used to collect the samples, the collection locations, the analysis of soil type and potential to emit PM10, and the sample variability, both within field and between fields of the same crop type. r 2003 Elsevier Science Ltd. All rights reserved.

Cyclotron production of high-purity 123I I. A revision of excitation functions, thin-target and cumulative yields for 127I(p, xn) reactions

Excitation functions, thin-target and cumulative yields for the proton-induced reactions on 127I targets were measured in the 67.5- to 5.3-MeV energy region. These results were used primarily to define the proton-energy ranges and target thicknesses to optimize radionuclide yields and purities for 123I production from its 2.08-h 123Xe parent. Other reactions producing radioxenons of interest in nuclear medicine (i.e. 36.406-d 127Xe, 17.3-h 125Xe, 20.1-h 122Xe, and 38.85-min 121Xe), were also measured. These results are compared to other previously reported values.

Cyclotron production of no-carrier-added 206Bi (6.24 d) and 205Bi (15.31 d) as tracers for biological studies and for the development of alpha-emitting radiotherapeutic agents

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.

Source Apportionment of Soil Samples by the Combination of Two Neural Networks Based on Computer-Controlled Scanning Electron Microscopy

The apportionment of ambient aerosol mass to different sources of airborne soil is a difficult problem because of the similarity of the chemical composition of crustal sources. However, additional information can be obtained using individual particle analysis. A novel approach based on the combination of two neural networks, the adaptive resonance theory-based neural network (ART-2a) and the back-propagation (BP) neural network with electron microscopy data, has been developed to apportion the mass contributions of the crustal sources to ambient particle samples. The crustal source samples were analyzed using computer-controlled scanning electron microscopy (CCSEM). CCSEM provides elemental compositions and size parameters for individual particles as well as estimates of the shape and density from which the volume and mass of each particle can be estimated. The ART-2a neural network was first used to partition particles into homogeneous classes based on the elemental composition data. After the different particle type classes were produced by ART-2a, their mass fractions were calculated. In this way, the source profiles for the crustal dust sources can be obtained in terms of the mass fractions for different particle types. Then the BP neural network was applied to build the model between the mass fractions of different particle types and the mass contributions. Using the three physical source samples prepared for this study, artificial ambient samples were generated by randomly mixing particles from the three source samples. These samples were then used to examine the proposed method. Satisfactory predictions for the mass contributions of the three sources to the ambient samples have been obtained, indicating the proposed method is a promising tool for the source apportionment of chemically similar soil samples.

Cyclotron production of PET radionuclides: 18F (109.77 min; β+ 96.9%; EC 3.1%) from high-energy protons on metallic aluminum targets

Abstract The production of no-carrier-added (NCA) 18 F (109.77 min) from proton induced reaction on 27 Al (100%) targets was investigated in the 67.5- to 7-MeV proton energy range. In this energy range, the reaction 27 Al(p, 2 α 2n) 18 Ne→ 18 F was found to predominate over other channels, suggesting the possible use of a 18 Ne (1.67 s)→ 18 F parent-daughter system as a generator. Total cross sections (millibarns) and single and cumulative yields (mCi/μAh or μCi/μAh) for the production of 18 F were measured. The total cross section peaked at 63 ± 0.6 (1%) MeV, with a value of 8.3 ± 0.8 (9%) mbarn. In the 67.5- to 7.0-MeV energy range, the cumulative 18 F yield was measured as 23.2 ± 2.1 (9%) mCi/ μ Ah. The possibility of using high beam currents in a solid metallic target to provide large Ci batches of NCA 18 F was also investigated. The 18 Ne→ 18 F generator system is also discussed in terms of its potential as a source of different radiochemical forms of 18 F. In addition to 18 F, the cross sections and yields for the production of 24 Na (15.03 h) and 22 Na (2.602 a) from Al, are also reported.

Cyclotron production of PET radionuclides: 118Sb (3.5 min; β+ 75%; EC 25%) from high-energy protons on natural Sb targets

The indirect production of the 3.5 min positron emitter 118Sb (β+ 75%, max. 2.70 MeV, EC 25%) from its longer-lived 118Te (6.00 d) parent was studied using 67.5, 60.0 and 42.0 MeV proton beams to irradiate natural Sb targets. The purpose of this study was to develop the basis for a 118Te (6.0 d) → 118Sb (3.5 min) generator system capable of supplying a short-lived positron emitter for the synthesis of 118Sb-labeled compounds and for the evaluation of their potential as radiopharmaceuticals for use in positron emission tomography (PET). Radionuclide yields (μCi/μAh) and total cross sections (mbarn) were measured in the 67.5–25.0 MeV energy range for all the Te radioactivities induced and detected in the Sb targets. The cumulative 118Te yield in the 67.5–25.0 MeV energy range was measured as 5.37 ± 0.54 mCi/μAh at end-of-bombardment (EOB). Maximization of yield and purities and several target options for large-scale production are also discussed. Radiochemistry and animal studies with NCA 118Sb labeled complexes were initiated at UC Berkeley and will be reported elsewhere.

Radionuclides in fishes and mussels from the Farallon Islands Nuclear Waste Dump Site, California

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.

Analysis of aerosol particles and coarse particulate matter concentrations in Chillán, Chile, 2001-2003.

Abstract Daily particle samples were collected in Chillán, Chile, at six urban locations from September 1, 2001, through September 30, 2003. Aerosol samples were collected using monitors equipped with a Sierra Andersen 246-b cyclone inlet on Teflon filters. Average concentrations of coarse particulate matter (PM10) for the 2001–2003 period ranged from 43.4 μg/m3 to 81.8 μg/m3 across the six sites. Annual PM10 concentration levels exceeded the European Union concentration limits. Mean PM10 levels during the cold season (April through September) were more than twice as high as those observed in the warm season (October through March). Average contributions to PM10 from organic matter, soil dust, nitrate (NO3 −), elemental carbon, ammonium (NH4 +), and sulfate (SO4 2−) were 31%, 27%, 11%, 8%, 7%, and 5%, respectively. The chemical analyses indicated that carbonaceous substances were the most abundant components of PM10 in cold months, whereas crustal material was the most abundant component of PM10 during warm months. Higher concentration levels were observed in the downtown area suggesting a clear anthropogenic origin, whereas in the rural sites the source was mainly natural, such as resuspended soil dust associated with traffic on unpaved roads and agricultural activities.

CHEMICAL CHARACTERIZATION OF THE INHALABLE PARTICULATE MATTER IN CITY OF CHILLAN, CHILE

Inhalable particulate matter (PM10) measurements were performed in six different sites in the city of Chillan, Chile, during September 2001 to September 2002. Chemical composition of PM10 was performed to samples of 47 mm diameter Teflon membranes within the city of Chillan. The spatial and temporal variability of the chemical composition of PM10 was evaluated taking into account additional data from meteorology and further air pollutants. The chemical analyses of PM10 showed that carbonaceous substances and crustal material were the most abundant components of PM10 during the winter and summer, respectively. The concentrations of PM10 were higher during the cold season than during the warm season. This was explained mainly due to the massive use of wood as fuel for residential heating within the city of Chillan, producing a dense smoke cloud in those days of atmospheric stability. The PM10 concentrations were higher in the downtown area of the city of Chillan, where also the chemical composition was more variable due to urban traffic and other anthropogenic sources