Double Irradiation Technique Research Articles

Simultaneous radiochemical neutron activation analysis of iodine, uranium and mercury in biological and environmental samples

The determination of medium and long-lived nuclides can be combined with short-lived ones if a medium or long irradiation is made prior to the short irradiation and radiochemical processing. Thus, an RNAA method previously developed for determination of iodine based on the reaction127I(n,γ)128I (T1/2=25 m) using oxygen flask ignition of the irradiated sample, followed by solvent extraction with an iodine-iodide redox cycle, was combined with an overnight preirradiation to induce the235U fission product133I (T1/2=20.8 h). By reactivating the sample, cooled 1–2 days after the first irradiation, for few minutes both128I and133I could be quantified in the separated iodine fraction. Non-combustible inorganic materials (e.g., sediment, soil, etc.) can be successfully ignited after mixing with excess cellulose powder. Chemical yields for iodine were determined spectrophotometrically in the organic phase, while homogeneously spiked Whatman cellulose powder was used as uranium standard. Mercury is also released on ignition and collected in the absorbing solution, from where it was separated by toluene extraction. Its chemical yield was determined for each aliquot using203Hg tracer and counting on an LEPD. Results for some suitable SRMs are presented, and the general features of the double irradiation technique discussed.

Structure modification of particle track membranes

Abstract Three different structure modifications were studied in order to improve the flux and dirt loading capacity of particle track membranes without affecting their retention characteristic. A divergent irradiation is a very effective tool to decrease the number of multiple pores and to increase the porosity up to 20 per cent. The technique leads to a remarkable but not efficient enhancement of the surface porosity. An improved surface porosity produced by a double irradiation technique turns out to be very effective with respect to the filtration performance.

1H Nmr studies at 360 MHz of the methyl groups in native and chemically modified basic pancreatic trypsin inhibitor (BPTI).

In the 1H NMR spectra obtained at 360 MHz after digital resolution enhancement, the multiplet resonances of the methyl groups in the basic pancreatic trypsin inhibitor (BPTI) were resolved. With suitable double irradiation techniques the individual methyl resonances were assigned to the different types of aliphatic amino acid residues. Furthermore, from pH titration and comparison of the native protein with chemically modified BPTI, the resonance lines of Ala 16 in the active site and Ala 58 at the C-terminus were identified. Potential applications of the resolved methyl resonances as natural NMR probes for studies of the molecular conformation are discussed.

Phobic Reactions between two Adjacent Monochromatic Light Fields

Trichoms of the blue-green alga Phormidium uncinatum undergo a phobic reaction when they traverse by random movement from a field of photosystem II light (557 nm) to an adjacent field with light of a variable wavelength. According to the electron pool hypothesis, the wavelength dependency curve of organism accumulations resulting from repeated phobic reactions must be regarded as an action spectrum of photosystem I. This action spectrum is compared to one obtained with a double irradiation technique.

Orientation Effects and the Sign of Two-bond 13C–1H Coupling

Signs of two bond (2J) 13C–1H coupling in 13C–enriched carbohydrates have been determined from proton spectra by the double irradiation technique. Instances of both positive and negative 2J values are given and are characterized in terms of the relative orientations of the coupled proton and of oxygen appended to the 13C nucleus; e.g., an oxygen anti to the proton appears to make a positive contribution to 2J and a gauche oxygen a negative one. Theoretical calculations, using ethanol and 1,1-ethanediol as model compounds, are in accord with these experimental observations.

The use of threshold energies in 14 MeV neutron activation analysis

The possibility of using double irradiation techniques with 14 MeV neutron generators for the determination of elements which give radiactive nuclei having the same principal γ-energies and similar half lives has been demonstrated. The sensitivity of the method is critically dependent on neutron output but improvements in geneartor design should give increasing scope to the use of this technique.

Application limits of the double irradiation technique in the detection of nuclear interference reactions

The double irradiation technique, which is used to detect the production of a given nuclide from different chemical elements, by two different reactions in a polyenergetic neutron flux, cannot be generally applied. The application limits have been defined and calculated, based on the statistical fluctuation of the measured activities. The experimental verification and the practical applications of the calculated limits for activation analysis, and transmutation reaction cross section studies are discussed.

Field Inhomogeneity Correlation Effects in Nuclear Magnetic Double-Resonance Detection of Very Small Spin Coupling Constants

Double-irradiation techniques may be used to detect nuclear magnetic resonance splittings that are so weak as to be obscured by the broadening due to spatial inhomogeneity of the applied magnetic field. The basis for these experiments is the fact that the observable double-resonance effects result from interactions on the molecular scale (such as spin—spin coupling) with the result that the two nuclear sites, A and X, experience almost exactly correlated local fields due to nonuniformity of the applied magnetic field. One such correlation effect is the partial compensation of field inhomogeneity broadening of lines that are regressively connected to the irradiated line. A second correlation effect may be observed if the intensity of a given line with a radio-frequency field so weak that its influence is restricted to sample regions very close to the resonance condition. A comparative study of double irradiation methods based on these effects has been carried out by applying them to the problem of resolving the 0.05-Hz splitting in the 60-MHz proton magnetic resonance spectrum of 3-bromothiophene-2-aldehyde, attributed to long-range spin coupling of the aldehyde proton with the ring proton at Position 4.

The determination of copper in zinc materials by neutron activation analysis using the 65Cu(n,γ) 66Cu reaction

The nondestructive and destructive determinations of copper in zinc materials by neutron activation using 65Cu(n,γ) 66Cu reaction are described. Observed cross-sections of 64Zn(n,p) 64Cu and 66Zn(n,p) 66Cu reactions for fission spectrum neutrons were 28 and 0.51 mb respectively. A double irradiation technique with one sample wrapped in cadmium foil and another bare, was employed for the correction of the concurrent formation of 66Cu by (n,p) reaction. 100 p.p.m. of copper in zinc sulfide was determined nondestructively by γ-ray spectrometry using a thermal flux of 5 · 10 11 n/cm 2/sec, while 0.5 p.p.m. of copper in zinc was determined by a thermal flux of 2.5 · 10 10 n/cm 2/sec, and by a rapid chemical separation involving copper(I) thiocyanate precipitation. The proposed activation procedures were compared with the spectrophotometric dibenzyldithiocarbamate procedure.

14N chemical shifts in thioamides

The 14N chemical shifts in some thioamides have been measured using double irradiation techniques whilst observing the proton spectra of the compounds. These values are compared with those of the corresponding amides and the results support the proposal that the variation in 14N chemical shifts within the amide range is governed by the degree of delocalization of the nitrogen lone pair of electrons. The 14N chemical shift of one selenium derivative, selenobenzamide, has also been determined.

14N chemical shifts in primary and secondary amides

The 14N chemical shifts in a series of primary and secondary amides have been obtained from the proton spectra by double irradiation techniques. The 14N shifts in the primary amides are affected only slightly by changes in the substituent on the carbonyl group, but a wider range is found for secondary amides. A qualitative explanation of the observed shift changes is put forward in terms of the effect that the various substituents, have upon the nitrogen lone pair of electrons.

Simultaneous Determination of Sulfur and Phosphorus in Water by Neutron Activation Analysis.

The determination of both sulfur and phosphorus in solution by measurement of the total beta activity in terms of P/sup 32/ by neutron activation analysis is described. Sulfur and phosphorus may be determined in water by irradiation of two samples containing these constituents, one sample being shielded with cadmium foil and the other unshielded. The results indicate that phosphorus can be reasonably detected at the 0.01--10.0 ppm level, when sulfur is also in solution, without serious interference. Sulfur may be detected at a minimum concentration of 0.1 ppm if the phosphorus content in solution does not exceed 1.0 ppm. In natural water sulfur can be semiquantitatively detected in the range 100 to 200 ppm without serious error by the double irradiation technique.

The determination of sulphur and phosphorus in steel by neutron activation analysis

Sulphur and phosphorus in steel were determined by neutron activation analysis, being counted as 35S and 32P respectively. For steels with sulphur to phosphorus ratios larger than 10, it seems possible to determine both elements by counting 32P, making use of a double irradiation technique at different fast to slow neutron fluxes.

Energy Transfer within a Spin System

The nature of the transfer, within a single nuclear spin system, of energy absorbed from an external source of radio-frequency magnetic field has been investigated by a double-irradiation technique. Energy from a high-power oscillator running at fixed frequency is absorbed by the nuclear spin system. The frequency of a second, low-level oscillator is then swept through the nuclear resonance, sampling the line shape existing in the presence of the strong rf field from the fixed-frequency oscillator. Particular spin systems investigated were the proton system in single crystalline CaS${\mathrm{O}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O, and the ${\mathrm{Al}}^{27}$ system in aluminum metal. In aluminum, the technique gives direct experimental verification of a completely homogeneous saturation behavior, a behavior expected from elementary considerations. It also gives further verification of the Redfield saturation theory. In CaS${\mathrm{O}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O, an enhancement effect is observed which allows one to determine the importance of double-flip spin-lattice relaxation processes. The technique could be usefully applied to many spin systems to determine the degree of inhomogeneity in the resonance line broadening.

Nuclear spin-spin coupling between fluorine and hydrogen in fluorobenzene

High resolution proton and fluorine nuclear magnetic resonance (nmr) spectra of fluorobenzene, 4D-, 2,4,6-D 3−, and 2,3,5,6-D 4-fluorobenzene have been obtained and analyzed. Double irradiation techniques were employed to eliminate the effects of the deuterium nuclear spin. The secular equation for 4D-fluorobenzene has been solved and the parameters adjusted for the best correspondence between the predicted and observed spectra. The nuclear spin couplings between the fluorine nucleus and the ortho, meta, and para protons are found to be, respectively, 9.4 ± 0.2 cps, 5.8 ± 0.2 cps, and 0.0 ± 0.5 cps. These couplings are found to have the same sign as the proton-proton couplings in the fluorobenzene molecule. This result is discussed and related to previous work on fluorobenzenes.