Neal F. Peek

Thallium-201 yields and excitation functions for the lead radioactivities produced by irradiation of natural thallium with 15–60 MeV protons

Abstract Excitation functions, production yields and radionuclidic purities are described for 201Tl production by the 203 Tl (p,3n) 201 Pb → 205 Tl and 205 Tl (p,5n) 201 Pb → 201 Tl nuclear reactions. The yields (Ci g−1cm2/μA-hr) of the parent 201Pb(9.4 hr), as well as the radiocontaminants 200Pb(21.5 hr), 202mPb (3.62 hr), 203Pb(52.1 hr) and 204mPb(1.115 hr) were measured by irradiating a stack of thin natural Tl foils with protons from the 76-in isochronous cyclotron at the Crocker Nuclear Laboratory (CNL). The 201Tl thick-target yield (mCi/μA hr) was calculated for different target thicknesses and corresponding incident proton energies. The excitation functions for the 203 Tl (p,3n) 201 Pb and the 205 Tl (p,5n) 201 Pb reactions were measured in the 15–60-MeV energy range.

Denitrification Studies with 13N-Labeled Nitrate

Nitrate labeled with 13N (13NO3–) was produced in a cyclotron by the 16O(p, α)13N reaction with protons having energies of 14.5 million electron volts. The 13NO3– was used as a tracer for direct quantitative measurements of denitrification rates in soils from flooded rice fields. The 13N technique provides a new tracer method for the measurement of denitrification rates in natural systems over short time intervals, without changing the concentration of NO3–in the system.

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.

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.

The production of xenon isotopes with protons of energies from 320 to 590 MeV

Abstract Cross sections for the protection of 121Xe, 122Xe, 123Xe, 125Xe and 127Xe were measured from protons of energy 320–590 MeV impinging on relatively thin (0.171–0.707 g/cm2) targets of CsCl, BaCO3 and La2O3. Yields of radioactive I and Te were calculated for protons of 540 MeV based on the collection of the Xe gasses after a cyclotron bombardment time of 3 h with a processing time of 1 h vs breeding time. The practically of producing 123I with high energy protons is discussed. Ratios of the main contaminents (125I and 121Te) 24h after the Xe extraction were calculated vs breeding time using the above parameters. Also discussed in the possibility of the production of 127Xe with this method.

Correlation of bioscintigraphy, contrast venography, and iodine-125 fibrinogen uptake test

In 40 patients believed to have deep venous thrombosis, bioscintigrams performed with 1-123 fibrinogen were available for comparison with either contrast venograms or 1-125 fibrinogen uptake tests. If either contrast venography or the fibrinogen uptake test was accepted as a standard for comparison, the accuracy of bioscintigraphic imaging was 90%. Most discrepancies between the procedures could be interpreted as due to heparin treatment, although bioscintigrams often were positive in patients treated with heparin for a short interval of time. Additionally, bioscintigrams provided information to distinguish venous thrombosis from other sources for local accumulation of radioactivity. Bioscintigraphy seems to be a promising noninvasive method for the detection of deep venous thrombosis of the lower extremities.