Intercomparison study of inductively coupled plasma mass spectrometry, thermal ionization mass spectrometry and fission track analysis of µBq quantities of 239Pu in synthetic urine

Even today, some Marshall Islanders are looking forward to permanentlyresettling their islands after five decades. The U.S. Department of Energyand the resettled residents require reasonable but cost-prudent assurancethat the doses to residents from residual ²³⁹Pu will not exceedrecognized international standards or recommendations, as estimated from theexcretion of ²³⁹Pu in urine. The goal of this study was to evaluatethe bias, uncertainty and sensitivity of analytical techniques that measure3–56 µBq ²³⁹Pu in synthetic urine. The analytical techniquesstudied in this work included inductively coupled plasma mass spectrometry,thermal ionization mass spectrometry and fission track analysis. The resultsof the intercomparison demonstrated that all three techniques were capableof making the measurements, although not with equal degree of bias and uncertainty.The estimated minimum detectable activity was 1 µBq of ²³⁹Puper synthetic urine sample. This exercise is also the first effort to certifytest materials of plutonium in the nBq . g –1 range.     

The NIST natural-matrix radionuclide standard reference material program for ocean studies

In 1977, the Low-level Working Group of the International Committee on Radionuclide Metrology met in Boston, MA (USA) to define the characteristics of a new set of environmental radioactivity reference materials. These reference materials were to provide the radiochemist with the same analytical challenges faced when assaying environmental samples. It was decided that radionuclide bearing natural materials should be collected from sites where there had been sufficient time for natural processes to redistribute the various chemically different species of the radionuclides. Over the succeeding years, the National Institute of Standards and Technology (NIST), in cooperation with other highly experienced laboratories, certified and issued a number of these as low-level radioactivity Standard Reference Materials (SRMs) for fission and activation product and actinide concentrations. The experience of certifying these SRMs has given NIST the opportunity to compare radioanalytical methods and learn of their limitations. NIST convened an international workshop in 1994 to define the natural-matrix radionuclide SRM needs for ocean studies. The highest priorities proposed at the workshop were for sediment, shellfish, seaweed, fish flesh and water matrix SRMs certified for mBq per sample concentrations of ⁹⁰ Sr, ¹³⁷ Cs and ²³⁹ Pu + ²⁴⁰ Pu. The most recent low-level environmental radionuclide SRM issued by NIST, Ocean Sediment (SRM 4357) has certified and uncertified values for the following 22 radionuclides: ⁴⁰ K, ⁹⁰ Sr, ¹²⁹ I, ¹³⁷ Cs, ¹⁵⁵ Eu, ²¹⁰ Pb, ²¹⁰ Po, ²¹² Pb, ²¹⁴ Bi, ²²⁶ Ra, ²²⁸ Ra, ²²⁸ Th, ²³⁰ Th, ²³² Th, ²³⁴ U, ²³⁵ U, ²³⁷ Np, ²³⁸ U, ²³⁸ Pu, ²³⁹ Pu + ²⁴⁰ Pu, and ²⁴¹ Am. The uncertainties for a number of the certified radionuclides are non-symmetrical and relatively large because of the non-normal distribution of reported values. NIST is continuing its efforts to provide the ocean studies community with additional natural matrix radionuclide SRMs. The freeze-dried shellfish flesh matrix has been prepared and recently sent to participating laboratories for analysis and we anticipate receiving radioanalytical results in 2000. The research and development work at NIST produce well characterized SRMs that provide the world's environment-studies community with an important foundation component for radionuclide metrology.     

PIC code simulation of pulsed radiation in a tapered closed-cavitygyrotron

MAGIC, a two-and-one-half-dimensional particle-in-cell (PIC) code, has been used to investigate mode locking in closed-cavity gyrotrons. A cavity, with equally spaced modal frequencies, composed of a radially tapered section and a straight section of waveguide, is designed, built, and cold-tested. Experimental cold test results agree well with the MAGIC PIC code simulations. Using a sinusoidal current density modulation with an amplitude of 5% of the dc current and frequency of 280 MHz, the simulation results show radiation output in a train of narrow pulses (full width at half maximum ~1 us) at a 280 MHz repetition rate. Though the gyrotron does not appear to be mode locked, uniform pulse trains of 30-50 pulses can be obtained     

On the possibility of analytically continuing stabilization graphs to determine resonance positions and widths accurately

Previous efforts to extract resonance widths by analytic continuation of stabilization graphs were limited by non-analytic behavior of the eigenvalues as functions of the stabilization parameter. We describe a procedure which avoids this difficulty by numerical analytic continuation of the characteristic polynomial, truncated to low order, of the hamiltonian matrix.     

Investigation of phenolic bioisosterism in opiates: 3-sulfonamido analogues of naltrexone and oxymorphone

[formula: see text] The phenolic hydroxy group of opiate-derived ligands is of known importance for biological activity. On the basis of its putative role as a hydrogen-bonding donor in the interaction with opioid receptors, it was replaced with a sulfonamide group because of their similar pKa values. The first thebaine-derived 3-amino (8a, 8b) and subsequent sulfonamide analogues (10a, 10b) were synthesized from naltrexone (1a) and oxymorphone (1b) in a linear nine-step synthesis. The sulfonamides were tested in vitro and found inactive.     

Neuropeptide delivery to the brain: a von Willebrand factor signal peptide to direct neuropeptide secretion

Background  

Multiple neuropeptides, sometimes with opposing functions, can be produced from one precursor gene. To study the roles of the different neuropeptides encoded by one large precursor we developed a method to overexpress minigenes and establish local secretion.