Measurement of isomeric yield ratios of the 104m,g,106m,gAg in the 45- and 55-MeV bremsstrahlung induced reactions of natural silver

The isomeric yield ratios for the ^natAg(γ,xn)^{104m,g,106m,g}Ag reactions with the end-point bremsstrahlung energies of 45- and 55-MeV have been determined by the off-line γ-ray spectrometric technique using 100 MeV electron linac at Pohang accelerator laboratory, Korea. The present data were compared with literature data in comparable compound nucleus from the ^natAg(γ,xn), ^natPd(p,xn), and ¹⁰³Rh(α,xn) reactions to examine the effects of an excitation energy and an input angular momentum. It is observed that the isomeric yield ratios of ^104,106Ag in ^natAg(γ,xn), ^natPd(p,xn) and ¹⁰³Rh(α,xn) reactions increase with the end-point bremsstrahlung energy, proton and alpha energy, which indicate the role of excitation energy. It is also found that for the similar compound nucleus at same excitation energy, the isomeric yield ratio of ^104m,gAg is higher in the ^natPd(p,xn) and ¹⁰³Rh(α,xn) reactions than those in ^natAg(γ,xn) reaction, which indicate the effect of an input angular momentum.     

Analytical reactions of isomeric methoxycycloheptatrienes

Methods for distinguishing among the isomeric 1-, 3- and 7-methoxycycloheptatrienes are reported. Treatment with anisaldehyde in strong perchloric acid produced a blue solution for the first two compounds only (with detection limits of the order of 2 μg), while irradiation ar 256 nm prior to treatment gave magenta solutions for the first and third compounds only. Absorbance was linear with respect to concentration, at least in the range 0.5–8 μg m^?1. Both the 1- and 3-isomers were oxidized by cerium(IV) to tropylium salts while the 7-isomer was resistant to attack. Similarly, the 7-isomer did not react with sodium tetrachloropalladate(II) on filter paper while the other two compounds gave black spots.     

Activation cross-section and isomeric cross-section ratio for the 122Te(n,2n)121m,gTe process

Journal of Radioanalytical and Nuclear Chemistry - Measurements of the cross-section for the 122Te(n,2n)121mTe and 122Te(n,2n)121gTe reactions and their ratio within the energy range of...     

Measurement of isomeric yield ratios for the 44m,gSc isomeric pairs produced from 45Sc and natTi targets at 50-, 60-, and 70-MeV bremsstrahlung

We measured the isomeric yield ratios for the ^44m,gSc isomeric pairs produced from different reaction channels ⁴⁵Sc(??,n)^44m,gSc and ^natTi(??,xnp)^44m,gSc by using the activation method and ??-ray spectroscopic methods at 50-, 60-, and 70-MeV bremsstrahlung energies. The high-purity natural Sc and Ti foils in disc shape were irradiated with uncollimated bremsstrahlung beams generated from an electron linear accelerator at Pohang Accelerator Laboratory. The induced activities in the irradiated foils were measured by the high-resolution ??-ray spectrometric system which consists of a high-purity Germanium detector and a multichannel analyzer. In order to improve the accuracy of the experimental results the necessary corrections were made in the ??-ray activity measurements and data analysis. The measured isomeric yield ratios for the ⁴⁵Sc(??,n)^44m,gSc reaction are 0.20 ± 0.02, 0.21 ± 0.02, and 0.21 ± 0.02 and those for the ^natTi(??,xnp)^44m,gSc reaction are 0.063 ± 0.012, 0.079 ± 0.014, and 0.124 ± 0.022 at 50-, 60-, and 70-MeV bremsstrahlung energies, respectively. The obtained results are compared with the corresponding values found in the literature. We observed that the isomeric yield ratios for the ⁴⁵Sc(??,n)^44m,gSc reaction increase rapidly with the increasing bremsstrahlung energies from the reaction threshold up to giant resonance region, and then those are almost constant in the energy range from about 30 to 2.5 GeV. The isomeric yield ratios for the ^natTi(??,xnp)^44m,gSc reaction increase with increasing bremsstrahlung energies in a wide range of bremsstrahlung energies from 50 to 2.5 GeV.     

Liquid-phase reactions of isomeric methylphenols with ozone

Ozonation of isomeric methylphenols in acetic anhydride was studied. Here, acetic anhydride acts simultaneously as solvent and acylating agent. In the presence of a mineral acid methylphenols were converted into methylphenyl acetates during preparation of solutions for ozonation. The major products in the oxidation of isomeric methylphenyl acetates with ozone were aliphatic peroxides (80–90%); oxidation of the methyl group gave rise to the corresponding acetoxybenzyl acetates (7–14%) and acetoxybenzylidene diacetates (3–6%). A probable scheme for the liquid-phase oxidation of methylphenyl acetates with ozone in acetic anhydride was proposed.     

The effect of metal cation binding on the protein, lipid and retinal isomeric ratio in regenerated bacteriorhodopsin of purple membrane

The effect of metal cation binding on bacteriorhodopsin (bR) in purple membrane has been examined using in situ attenuated total reflection-Fourier transform infrared difference spectroscopy in aqueous media. It is known that adding metal cations to deionized bR regenerates the purple state from its blue state and recovers the proton pump function. During this process, infrared spectral changes in the frequency region of 1800-1000 cm-1 are monitored. The results reveal that metal cation binding affects the protein conformation, the retinal isomeric composition as well as lipid head groups. It is also observed that metal cation binding induces conformational changes in the alpha 1-helix region of bR, converting the portion of its alpha 1-helical domain into beta-turn or disordered coil. In addition, the influence of Ho3+ binding on the protein and lipid is observed to be larger than that of Ca2+. These results suggest that some of the metal cation binding sites are on the membrane lipid domain, while others could be on the intrahelical domain or interhelical loops where the Asp and Glu are located (binding with their COO- groups). Our results also suggest that the removal of the C-terminal of bR increase the accessibility of the binding site of metal cations, which affects protein conformational structure. All these observations are discussed in terms of the two proposals given in the literature regarding the metal cation binding sites.     

The isomeric cross-section ratio in double neutron capture of 93Nb

The yields of ⁹⁵Nb isomers were investigated by means of the double neutron capture of ⁹³Nb target. The effective cross section of ⁹⁴Nb(n,γ)^95mNb and ⁹⁴Nb(n,γ)^95gNb reactions were found, by the activation method, to be 0.61 ± 0.03 barn and 14.6 ± 0.3 barn, respectively, with the choice of Wescott's epithermal index r√(T/T₀) = 0.022. The observed isomeric cross section ratio of the reaction was compared with the theoretical prediction on the basis of the statistical model. As a result, the spin of the compound nucleus was assigned and the contribution of the quadrupole transition was deduced in the gamma cascade process.     

Measurement of half-lives for 87m,gY and 196m,g,194Au produced from the photon and neutron induced reactions of 89Y and 197Au

Journal of Radioanalytical and Nuclear Chemistry - We have measured the half-lives of 87mY and 87gY produced from the 89Y(γ, 2n) and 89Y(n, 3n) reactions with the bremsstrahlung end-point...     

The effect of nuclear spin on the polarisation ratio of resonance fluorescence

The nuclear quadrupole interaction causes the rotational angular momentum of a molecule with nuclear spin to precess about the total angular momentum whose projection along a space fixed axis is conserved. This effects the degree of orientation in the excited state of molecules optically pumped with circularly polarised light and reduces the polarisation ratio of fluorescence from molecules with large nuclear spin. Calculations are presented for the circular polarisation ratio of the forward scattered fluorescence when the exciting radiation is sufficiently broad-banded that it excites the full manifold of quadrupole split components of a given J″ → J′ transition. Results are also presented for the variation of the polarisation ratio and intensity as a narrow excitation source is tuned across the absorption.     

A nuclear magnetic resonance study of three isomeric dinaphthothiophenes

The ¹H and ¹³C NMR spectra of three isomeric dinaphthothiophenes are recorded. Chemical shift assignments were made on the basis of substituent chemical shift (SCS) effect arguments, coupling considerations, proton—proton auto-correlated homonulcear (COSY) two-dimensional spectroscopy, and proton—carbon heteronuclear correlation (HETCOR) two-dimensional spectroscopy. Some previously published ¹H chemical shifts and coupling constants are compared with our data and some divergences are noted.     

Chemical effects of neutron induced nuclear reactions in KIO4 at different pH of dissolution

Dissolution effect on recoil¹²⁸I retention in the form of IO ₄ ^– ion following /n,/ process in potassium periodate target has been studied. A remarkable variation in retention is found both in solid and solution phase with the pH of dissolution. A suitable mechanism is suggested to explain the observed results.     

Porphyrins. 25. Use of the nuclear overhauser effect for establishment of the structure of isomeric meso-substituted metalloporphyrins

Nickel complexes of the dimethyl esters of meso-dimethylaminomethyl derivatives of mesoporphyrin-II and mesoporphyrin-IX are synthesized. The structure of the prepared isomeric compounds is determined by analysis of their chromatographic properties, visible spectra, as well as of their PMR spectra using the nuclear Overhauser effect.See [1] for Communication 24.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1378–1384, October, 1989.     

Ion/molecule reactions of isomeric bromobutene radical cations with ammonia

The ion/molecule reaction of the radical cations of three isomeric bromobutenes (2-bromobut-2-ene 1, 1-bromobut-2-ene 2, 4-bromobut-1-ene 3) with ammonia were studied by Fourier transform ion cyclotron resonance spectrometry to reveal the effect of a different position of the bromo substituent relative to the C-C double bond. Further, the reaction pathways of the ion/molecule reactions were analyzed by theoretical calculations at the level B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d). All three bromobutene radical cations 1(.+) to 3(.+) react efficiently with NH(3). The reactions of 1(.+) carrying the halogen substituent at the double bond follow the pattern observed earlier for other ionized vinylic halogenoalkenes. The major reaction corresponds to proton transfer to NH(3) as to be expected from the high acidity of but-2-ene radical cations exposing six acidic H atoms at allylic positions. The other, still important, reaction of 1(.+) is substitution of the Br substituent by NH(3). Although the radical cations 2(.+) and 3(.+) are expected to be as acidic as 1(.+), proton transfer is the minor reaction pathway of these radical cations. Instead, 2(.+) displays bomo substitution as the major reaction. It is suggested that the mechanism of this reaction is analogous to S(N)2' of nucleophilic allylic substitution. Substitution of Br is not efficient for the reactions of 3(.+)-the two major reactions correspond to C-C bond cleavage of the two possible beta-distonic ammonium ions which are generated by the addition of NH(3) to the ionized double bond of 3. This observation, as well as the results obtained for 1(.+) and 2(.+), emphasize the role of the fast and very exothermic addition of a nucleophile to the ionized double bond for the ion/molecule reactions of alkene radical cations. Clearly the energetically-excited distonic ion arising from the addition fragments unimolecularly by energetically accessible pathways. In the case of a halogene subsituent (except F) at the vinylic or allylic position, this is loss of thesubsituent. In the case of remote halogeno substituents, this is C-C bond cleavage adjacent to the radical site of the distonic ion.     

A comparison of the relative energies of isomeric intermediates formed in electrophilic,radical, and nucleophilic aromatic substitution reactions

The relative energetics of isomeric σ-complex intermediates formed in electrophilic, free radical, and nucleophilic attack of Cl, H, and Me on PhCl and PhMe are compared for all positions: o, m, p, and ipso. The results are presented as ΔH, computed by the MINDO/3 method, for the appropriate isodesmic reaction with benzene. For the chlorobenzene intermediates, there is a marked increase in the relative preference for the ipso-position as the reactions change from electrophilic to free radical to nucleophilic. For toluene intermediates, the order of stability-p > o > m > ipso-is seen in all reactions except for one case, free radical methylation. In general, the free radical intermediates show the smallest range of energy differences. Comparison of predictions from these calculations with experimental results (largely partial rate factors and product ratios) shows some qualitative agreement.     

Migration of fission product137Cs in mud near a nuclear reactor

Due to the mismanagement of nuclear waste as well as heat exchanger degradation for the primary coolant of the one megawatt nuclear research reactor, the fission product¹³⁷Cs has been leaking to the environment ever since 1969. In the past thirty years, the long-lived¹³⁷Cs was accumulated and eventually trapped in the mud of the discharge pond right in front of the waste storage and the reactor facility. The distribution of¹³⁷Cs in mud was measured and contour-mapped to reveal the migration of trace levels of¹³⁷Cs in a period of three decades.     

Differentiation of the isomeric 1,2-cyclopentanediols by ion-molecule reactions in a triple-quadrupole mass spectrometer

Collisionally activated decompositions and ion-molecule reactions in a triple-quadrupole mass spectrometer are used to distinguish between cis- and trans-1,2-cyclopentanediol isomers. For ion kinetic energies varying from 5 eV to 15 eV (laboratory frame of reference), qualitative differences in the daughter ion spectra of [MH]⁺ are seen when N₂ is employed as an inert collision gas. The cis ?1,2-cyclopentanediol isomer favors H₂O elimination to give predominantly [MH- H₂O]⁺. In the trans isomer, where H₂O elimination is less likely to occur, the rearrangement ion [HOCH₂CHOH]⁺ exists in significantly greater abundance. Ion-molecule reactions with NH₃ under single-collision conditions and low ion kinetic energies can provide thermochemical as well as stereochemical information. For trans ?1,2-cyclopentanediol, the formation of [NH₄]⁺ by proton transfer is an exothermic reaction with the maximum product ion intensity at ion kinetic energies approaching 0 eV. The ammonium adduct ion [M + NH₄]⁺ is of greater intensity for the trans isomer. In the proton transfer reaction with the cis isomer, the formation of [NH₄]⁺ is an endothermic process with a definite translational energy onset. From this measured threshold ion kinetic energy, the proton affinity of cis ?1,2-cyclopentanedioi was estimated to be 886 ± 10 kJ mol^?1.     

Hydrogen study in solids by nuclear reactions

The use of nuclear reaction methods for hydrogen or deuterium analysis and its applications to hydrogen profiling and lattice location by channelling experiments is briefly reviewed. The application of these methods to various problems such as the measurement of surface hydrogen and its stability under ion bombardment, the study of solid solutions of hydrogen metal systems obtained by implantation, and the correlation of the amount of hydrogen with the physical properties of some amorphous semiconductors, is described.