Net Peak Area Research Articles

Detection limits for some transuranic nuclides using low-energy photon spectrometry

During the past 40 years, artificially produced transuranium nuclides have been introduced in the aquatic systems as consequences of atmospheric fallout from nuclear testing and of controlled release from nuclear reprocessing plants; the study of the behaviour of long-lived transuranic elements in oceanic media is of great importance from the projected development breeder technology. Usually, picocurie amounts of these isotopes are mainly determined in environmental sample by α spectrometry after tedious radiochemical separations. Otherwise, we tested [1] the availability of non-destructive low-energy photon spectrometry to measure activity levels of fission products after a nuclear test; in actual experiments, we attempted to give the sensitivities attained by this method for transuranic elements. The activities were measured with a X-ray spectrometer which consists to a 200 mm 2 area, 10 mm depth planar HPGe detector; the pulses given by the linear amplifier were analysed on a 4096 channels MCA. The energy resolution (FWHM) obtained with this system was better than 180 eV at Fe K α line. The samples used for counting were: 1. standard activity sources of 241Am, 243Am and 244Cm provided by L.M.R.I. or by I.A.E.A. 2. brown algae Fucus vesiculosus coded AGI/1: intercalibration sample provided by the International Laboratory Of Marine Radioactivity (I.A.E.A.). 3. many surface sediments from Nord Cotentin (France). Standard solutions of transuranic elements were electroplated on stainless disks using the Talvitie's method [2]; as concerns solid sample, accurately weighted quantities were packed in thin plastic containers. The samples were counted for time intervals between 50 and 360 ks. The absolute efficiency of the HPGe system was plotted against energy using counting runs with well known 152Eu, 133Ba and 241Am sources. The Minium Detectable Activity (MDA) attained by low energy photon or X-ray spectrometry is related to the branching ratio Γ = Nγ/Nα or X + N x/N α of the isotope under consideration. The MDA (in pCi) is calculated from the formula: MDA = 27.02N p γ·ϵ·t with t = counting time (s); ϵ = absolute detection efficiency. The net peak area N p and the subtracted background area N γ were related by: N p 3 ̆ √N b. The Table gives the MDA obtained in this method: 241Am 243Am 244Cm 237U 59.54 1.2 74.67 0.7 42.84 15.3 59.54 1.2 NpL β 2.5 NpL α 2.6 NpL β 2.5 E(keV) MDA E(keV) MDA E(keV) MDA E(keV) MDA

Improved system for energy-dispersive x-ray diffraction with synchrotron radiation

A number of improvements in a facility developed over the past three years at the Stanford Synchrotron Radiation Laboratory for the study of pressure and/or temperature effects on materials are described. These include improved beam collimation to both reduce background and eliminate gasket scatter, a remote, pneumatically operated pressurizer, and introduction of a variety of electronics hardware to allow both computer control of experiments and on-line data analyses. Considerations are given to the possible effects of heating of the pressure cavity by the incident beam and to possible fluctuations of the incident beam intensity/energy profile. In both cases, there was no evidence to indicate that these phenomena warranted any further consideration, i.e., they are not considered to be problems in terms of analyzing the data. Extended measurements of a well-defined diffraction peak indicated that a considerable improvement over our earlier work has been realized in terms of the precision in the determination of the energy of the peak, viz., a precision of better than 0.04% for measurement periods as short as 10 s; the estimated precision in the net peak area is less than 3%. The system was used to examine the kinetics of the B1-to-B2 pressure-induced phase transition in KBr. The volume change in the two-phase region is measured to be 10.41%±0.10%, in excellent agreement with most of the previous measurements. A plot of the time dependence of the growth rate of the high-pressure phase indicates that the phase transformation can be described by the Avrami equation. Constants for the phase transition kinetics are given.

Quantitative gamma spectroscopy at very high counting rates

Loss-free net peak areas at variable input rates of more than 690 000 c/s have been obtained by means of a high-rate gamma spectroscopy system with real-time compensation of counting losses, thus providing evidence for the feasibility of quantitative gamma spectroscopy at counting rates not attained until now.

A simple program in “basic” language for analysis of gamma-spectra using an on-line minicomputer

A program in “INSTRUMENT BASIC” language is proposed for analysis of gamma-ray spectra obtained with Ge(Li) detectors and accumulated in multichannel analysers on-line with minicomputers. The program locates the peaks, evaluates the corresponding energy values, the net peak areas and the standard deviations on the areas.

Determination of Molecular Weight and Its Distribution of Phenolic Resins by Gel Permeation Chromatography

A few factors which affect the accuracy of the determination of molecular weight and its distribution of phenolic resins were discussed. For the purpose of improving the accuracy, a new calculation method for molecular weight is proposed. The method can be applied to discontinuous GPC curves of phenolic resins, epoxy resins and other thermosetting uncured oligomers. The net peak area which corresponded to the dimer fraction was obtained by integrating the peak area from the middle point between the monomer peake and the dimer peak to the middle point between the dimer peak and the trimer peak. Similarly, the net peak areas of a trimer, a tetramer, a pentamer and so forth can be obtained in the same way as above.The other successive calculation procedures for molecular weight determination were the same as taken for GPC curves of such polymer as polyethylene. Pore sizes of polystyrene gels were 5000-45000A, 700-2000A, 350-700A and 50-80A. Tetrahydrofuran was used as carrier solvent at room temperature. The flow rate was 1 ml/min.Mw was found more available than Mn as the cure index of phenolic resins because of its high sensitivity to high molecular weight fractions. The range of polydispersity (Mw/Mn) of phenolic, p-terbutylphenolic and p-phenylphenolic novolac resins was between 1-2, and Mw/Mn of fractions by the solvent fractionation method was between 1.12 and 1.36 to 1.44 of the original resin.Furthermore, it was found that a small amount of molecular weight fraction above 5000 exists in uncured phenolic novolac and resole resins.