Norris J. Parks

Lifetime bone cancer dose-response relationships in beagles and people from skeletal burdens of 226Ra and 90Sr.

The life-time tumor dose-response relationships observed in beagles injected with 226Ra or fed 90Sr at the University of California, Davis, provide a basis for understanding the induction of bone cancer for these bone-seeking radionuclides and for scaling to people. In these studies 385 dogs were exposed to graded dosage levels of 90Sr and 243 dogs were exposed to graded dosage levels of 226Ra with a total of 159 unexposed controls. The results show different dose-response relationships for bone cancer for the two radionuclides based upon the gravimetric average dose rates and cumulative doses to bone. These relationships were found to be well represented by three-dimensional log-normal dose-response surfaces that yield risk as a function of average dose-rate and time after beginning of exposure. All dose-rates suggested a 100% risk at some later time post-exposure but the time required to reach a given level of risk was long for low dose rates so that there exists a practical threshold in that at lower dose rates individuals may die spontaneously from causes associated with natural aging prior to the expected appearance of radiogenic cancer. The risks to people at various 226Ra body burdens (average skeletal dose rates) are estimated based on the model.

The synthesis of 13N labeled atmospheric gases via proton irradiation of a high pressure oxygen target

The bombardment of a 10–15 atm high purity O2 target with a 5–10 μA beam of 15 MeV protons produces 13N(t12 = 9·96 min) by the 16O(p,α) 13N nuclear reaction. The nitrogen atoms are incorporated into the primary products, 13N2, 13N2O and 13NO2 in a ratio of 8:1:3·5 respectively. Cryogenic recovery of 13NO2 under steady-state production conditions corresponds to 1 mCiμA. The concentration of radiolytically produced carrier NO2 is in the range of a 0·3–0·6 ppm.

Tissue and subcellular distribution of bismuth radiotracer in the rat: considerations of cytotoxicity and microdosimetry for bismuth radiopharmaceuticals

The whole-body clearance, organ distribution, and subcellular distribution of no-carrier-added and carried-added intraperitoneally administered bismuth radiotracers (205Bi-206Bi) has been determined in Sprague-Dawley rats. Differences in clearance rate kinetics were observed for this study with the administration of neutral solutions of tracers in a carbonate buffer compared to other studies with other chemical forms. The final organ distribution was not strongly dependent on administered chemical form. We provide definitive evidence that bismuth does indeed enter subcellular organelles such as the nucleus and the mitochondria, which had 30-50% and 10-25%, respectively, of activity in kidney tissue. The kidneys were the main sink for radiotracer with uptake ranging from 20 to 50% of total body activity. The calculated energy deposition by recoil nuclei after alpha emission of potentially therapeutically useful 212Bi was found to equal or exceed the alpha energy deposition per organelle if the source is inside the cell nucleus or mitochondria.

Chemistry of Nuclear Recoil 18F Atoms. V. Mechanism and Systematics in CH3CF3

Nuclear recoil 18F atoms undergo hot F‐for‐F and F‐for‐H atomic substitution and hot F‐for‐CH3 and F‐for‐CF3 alkyl replacement reactions in CH3CF3. The primary absolute yields corresponding to these processes are 3.56 ± 0.07, 8.22 ± 0.09, 5.79 ± 0.31, and 8.5 ± 2.5 % (estimated value), respectively. The total primary hot yield for organic products is 26.1 ± 2.5 %, and that for all hot reactions including F‐to‐HF and F‐to‐F2 abstraction is 83 ± 3 %. There is no evidence in favor of hot F‐for‐2F or F‐for‐2H double substitution reactions in CH3CF3. Recoil 18F exhibits approximately a sixfold systematics preference for alkyl replacement reactions at the carbon—carbon bond in CH3CF3 relative to the average of substitution reactivities at carbon—fluorine and carbon—hydrogen bonds. The per‐bond preference for primary substitution reactions at carbon—hydrogen relative to carbon—fluorine bonds is 2.30 ± 0.06. The sums of primary hot yields for organic products are comparable for recoil 18F in CH3CF3 vs recoil 3H i...

Lifetime Studies of 226Ra and 90Sr Toxicity in Beagles -A Status Report

Beagles at the University of California at Davis injected with226 Ra or fed90 Sr have been under lifetime study for over 18 years. This report summarizes the dose-response observations to June 30, 1978, based upon the temporal average dose rate (rad/day) to the skeleton from initiation of exposure to death. Bone marrow dyscrasias were more numerous than bone cancers from90 Sr (in equilibrium with

Chemistry of Nuclear Recoil 18F Atoms. VI. Approximate Energetics and Molecular Dynamics in CH3CF3

{}^{90}{\rm Y}

Skeletal Uptake and Lifetime Retention of 90Sr and 226Ra in Beagles

) at dose rates to bone of about 2 to 20 rad/day, while bone cancers have been the dominating effect of

Emulsion scintillation counting of radium and radon

{}^{226}{\rm Ra}n

PRODUCTION AND USE OF 13N GASES AND AEROSOLS

(and associated progeny) at dose rates of from 0.5 to about 20 rad/day. No radiogenic effects are yet apparent for skeletal doses below 0.05 rad/day. Results to date indicate that although bone cancer continues to be the important endpoint for226 Ra, other cancer types appear to be more important for90 Sr (such as soft-tissue cancers adjacent to bone), particularly at late times from lower skeletal dose rates. Continued study of the 3...

CHAPTER 3 – PRODUCTION AND USE OF 13N GASES AND AEROSOLS

Energetics and molecular dynamics results are reported from an extensive set of high energy recoil 18F experiments with CH3CF3. Based upon thermochemical evidence alone, substantial fractions of the primary hot F‐for‐H, F‐for‐CH3, and F‐for‐CF3 reaction products are indicated to involve minimum excitation energies of 7.9 ± 0.2, 9.3 ± 0.1, and 3.5 ± 0.2 eV, respectively. The primary F‐for‐F reaction products in CH3CF3 do not exhibit unimolecular decomposition via a carbon—carbon bond scission mode in apparent violation of RRKM theoretical predictions. The primary F‐for‐H products decompose both via β elimination of HF and via carbon—carbon bond scission in apparent accord with theory. More than one kind of microscopic dynamics is involved in the primary hot F‐for‐H and F‐for‐CH3 processes in CH3CF3 and in the primary hot F‐for‐F process in CF4. Direct, concerted, and collusive dynamics are required for the higher energy reaction modes for these processes.