Isomeric Yield Research Articles

Measurements of isomeric yield ratios of fission products from proton-induced fission onnatU and232Th via direct ion counting

Independent isomeric yield ratios (IYR) of 81Ge, 96Y, 97Y, 97Nb, 128Sn and 130Sn have been determined in the 25 MeV proton-induced fission of natU and 232Th. The measurements were performed at the ...

Measurement of isomeric yield ratios for the 110Pd(γ,n)109m,gPd reaction

We measured the isomeric yield ratios for the 110Pd(γ,n)109m,gPd reaction by the activation method with the bremsstrahlung endpoint energies of 50-, 55-, 60-, 65-, and 70-MeV generated from an electron linear accelerator of Pohang accelerator laboratory. The induced γ-activities of the irradiated palladium foils were measured by a coaxial high purity germanium detector coupled to a PC-based multi-channel analyzer. The necessary corrections were made to improve the accuracy of the γ-activity measurements. The present experimental results measured with bremsstrahlung endpoint energies of 50-, 55-, 60-, 65-, and 70-MeV are 0.108 ± 0.007; 0.118 ± 0.008; 0.118 ± 0.007; 0.120 ± 0.008; 0.119 ± 0.008, respectively. The obtained results are compared with those existing in literature.

Pereriz zbudzhennya izomernoho stanu 11/2– yadra 137Ce v reaktsiyi (γ, n) v intervali enerhiy hamma-kvantiv 11–18 MeV

The isomeric yield ratio and the cross section of 138Ce(y, n)137m,gCe reaction in the 11–18-MeV energy interval of y quanta have been studied on an M-30 microtron using the brehmsstrahlung beam.

Proton transfer in the ground and excited state and photobehaviour of the positional isomers of E -5-[2-(pyrid- n -yl)ethenyl]oxazole’s ( n = 2, 3 and 4)

Abstract The effect of protonation on the excited state properties of the three positional isomers of E -5-[2-(pyrid- n -yl)ethenyl]oxazole’s ( n -PyEt-5Ox with n = 2, 3 and 4) was studied in buffered water by spectrophotometric, fluorimetric and chromatographic measurements. The clear shift to the red of the absorption and emission spectra by protonation indicates that the basicity of these compounds increases strongly (by ∼7 pH units) under excitation. Ground state pK a values (around 5) were measured by absorption (for n = 2 and 4) and fluorescence (for n = 3) titration and excited state pK a * values were estimated by application of the Forster cycle. For the compound with n = 3, which displays a rather higher fluorescence lifetime, it was possible to perform a direct fluorimetric titration which showed two inflection points corresponding to pK a (4.77) and pK a * (12.27). Previous works on these compounds had shown a marked deactivating effect of the pyridine n,π * states on the emitting and reactive π,π * states (proximity effect) favouring relaxation by internal conversion with a marked reduction of the competitive fluorescence and trans - cis (E–Z) isomerisation yields, particularly for n = 2 and 4 in non-polar cyclohexane. The new results indicate that the aqueous solvent, and mainly protonation, affect sensibly the spectral, photochemical and photophysical behaviour increasing again the radiative and reactive parameters of compounds with n = 2 and 4. The isomer with n = 3, whose n,π * states play a much smaller deactivating effect, shows a peculiar behaviour with a very low isomerisation yield at acid pH, reasonably due to intramolecular charge transfer from the Ox ring to the PyH + moiety, which hinders the twisting process. All these results are compared with those reported in the literature for the n -styrylpyridine analogues to point out the role of the oxazole group.

Effects of ESI conditions on kinetic trapping of the solution-phase protonation isomer of p-aminobenzoic acid in the gas phase

The effects of electrospray ionization (ESI) solvent and source temperature on the relative abundance of the preferred solution-phase (N-protonated; i.e. amine) versus preferred gas-phase (O-protonated; i.e., acid) isomers of p-aminobenzoic acid (PABA) were investigated. When PABA was electrosprayed from protic solvents (i.e., methanol/water), the infrared multiple photon dissociation (IRMPD) spectrum recorded was consistent with that for O-protonation, according to both calculations and previous studies. When aprotic solvent (i.e., acetonitrile) was used, a different spectrum was recorded and was assigned to the N-protonated isomer. As the amine is the preferred protonation site in solution, this suggests that an isomerization takes place under certain conditions. Photodissociation at the diagnostic band for the O-protonated isomer (NH2 stretching mode) was used to quantify the relative contributions of each isomer to ion signal as a function of ESI conditions. For mixtures of methanol and acetonitrile, the relative contribution of the O-protonated gas-phase structure increased as a function of methanol content. Yet, substituting methanol for water resulted in a marked decrease of isomerization to the O-protonated structure. The source temperature (i.e., temperature of a heated desolvation capillary) was found to play a key role in determining the extent of isomerization, with higher temperatures yielding increased presence of gas-phase structures. These results are consistent with a protic bridge mechanism, in which the ESI droplet desolvation, dependent on the solvent system and radiative heating from the capillary, may determine the isomerization yield.

Lack of evidence for phase-only control of retinal photoisomerization in the strict one-photon limit.

The concept of shaping electric fields to steer light-induced processes coherently has fascinated scientists for decades. Despite early theoretical considerations that ruled out one-photon coherent control (CC), several experimental studies reported that molecular responses are sensitive to the shape of the excitation field in the weak-field limit. These observations were largely attributed to the presence of rapid-decay channels, but experimental verification is lacking. Here, we test this hypothesis by investigating the degree of achievable control over the photoisomerization of the retinal protonated Schiff-base in bacteriorhodopsin, isorhodopsin and rhodopsin, all of which exhibit similar chromophores but different isomerization yields and excited-state lifetimes. Irrespective of the system studied, we find no evidence for dissipation-dependent behaviour, nor for any CC in the strict one-photon limit. Our results question the extent to which a photochemical process at ambient conditions can be controlled at the amplitude level, and how the underlying molecular potential-energy surfaces and dynamics may influence this controllability.

Excitation of 11/2− isomeric state in 137Ce in (γ,n) reaction within 10–22MeV energy range

Isomeric yields ratios and energy differential cross-section of metastable state excitation in the [Formula: see text] reaction has been studied in the 10–22[Formula: see text]MeV end-point energy range of bremsstrahlung beams. Experimental data are compared with Hauser–Feshbach calculations performed with TALYS-1.6 statistical model code.

Preparation of NiAlO x and NiSiO x Complex Oxides with High Surface Areas for the Isomerization Reactions of 1-Hexene

The NiAlO x and NiSiO x complex oxides with high surface areas were prepared by the co-precipitation method through the control of acidity of solutions. Nickel species were found to be highly dispersed in these complex oxides and a remarkable feature was that the incorporation of large amount of nickel cations into SiO2 generated the great amount of surface acid sites. Upon the sulfidation by CS2, the sulfided catalysts were found to be highly active for the conversion of 1-hexene to different products formed from the three main competitive reactions (skeletal isomerization, double bond isomerization and hydrogenation of all hexenes). The high yield of skeletal isomerization of 1-hexene on a sulfided NiSiO x (55 %) could be attributed to the high density of acid sites for the adsorption of 1-hexene as well as the low hydrogenation activity of nickel species on this catalyst. In contrast, the high yields of direct hydrogenation and double bond isomerization of 1-hexene on the sulfided NiAlO x might be due to the high hydrogenation activity of nickel species as well as the surface acidity and basicity on the catalyst. The sulfided NiAlO x and NiSiO x complex oxides were highly active for the conversion of 1-hexene to different products. The high yield of skeletal isomerization of 1-hexene on the sulfided NS10 (55 %) could be attributed to the high density of acid sites for the adsorption of 1-hexene.

Study on mechanism of isomerization between ammonium thiocyanate and thiourea

Application of ammonium thiocyanate that can be separated from wastewater in coking plant is limited. It may isomerize to thiourea which has widely applied in industry. However, the isomerization yield is low. Moreover, the isomerization temperature is more than 145 °C. In this paper, the isomerization was investigated. The mechanism of the isomerization was supposed based on quantum chemistry calculations. Ammonia was employed as a catalyst to lower isomerization temperature and improved the yield of thiourea in the isomerization reaction. Results of quantum chemical calculation and experiments support the supposed mechanism. The mechanism can be applied in production of thiourea from isomerization of ammonium thiocyanate. The paper suggests a useful way of resourcizing ammonium thiocyanate in wastewater.

Measurement of flux-weighted average cross-sections and isomeric yield ratios for 103Rh( $\gamma$ ,xn) reactions in the bremsstrahlung end-point energies of 55 and 60 MeV

We measured the flux-weighted average cross-sections and the isomeric yield ratios of 99m, g, 100m, g, 101m, g, 102m, gRh in the 103Rh( $ \gamma$ , xn) reactions with the bremsstrahlung end-point energies of 55 and 60MeV by the activation and the off-line $ \gamma$ -ray spectrometric technique, using the 100MeV electron linac at the Pohang Accelerator Laboratory (PAL), Korea. The flux-weighted average cross-sections were calculated by using the computer code TALYS 1.6 based on mono-energetic photons, and compared with the present experimental data. The flux-weighted average cross-sections of 103Rh( $ \gamma$ , xn) reactions in intermediate bremsstrahlung energies are the first time measurement and are found to increase from their threshold value to a particular value, where the other reaction channels open up. Thereafter, it decreases with bremsstrahlung energy due to its partition in different reaction channels. The isomeric yield ratios (IR) of 99m, g, 100m, g, 101m, g, 102m, gRh in the 103Rh( $ \gamma$ , xn) reactions from the present work were compared with the literature data in the 103Rh(d, x), 102-99Ru(p, x) , 103Rh( $ \alpha$ , $ \alpha$ n) , 103Rh( $ \alpha$ , 2p3n) , 102Ru(3He, x), and 103Rh( $ \gamma$ , xn) reactions. It was found that the IR values of 102, 101, 100, 99Rh in all these reactions increase with the projectile energy, which indicates the role of excitation energy. At the same excitation energy, the IR values of 102, 101, 100, 99Rh are higher in the charged particle-induced reactions than in the photon-induced reaction, which indicates the role of input angular momentum.

Measurement of isomeric ratios for 89g,mZr, 91g,mMo, and 97g,mNb in the bremsstrahlung end-point energies of 16 and 45-70 MeV

The independent isomeric yield ratios of 89g,mZr from the natZr(\( \gamma\),xn) reactions and those of 91g, mMo and 97g,mNb from the natMo(\( \gamma\),x) reactions with the bremsstrahlung end-point energy of 45-70 MeV were determined by an off-line \(\gamma\)-ray spectrometric technique using the 100 MeV electron linac at the Pohang Accelerator Laboratory, Korea. The isomeric yield ratios of 89g,mZr and 97g,mNb from the natZr(\( \gamma\), xn) and natMo(\( \gamma\),x) reactions at the bremsstrahlung end-point energy of 16MeV were also determined by the same technique using the 20MeV electron linac at Helmholtz-Zentrum Dresden-Rossendorf, Germany. The measured isomeric yield ratios of 89g,mZr, 91g,mMo, and 97g,mNb were compared with literature data to examine the role of the Giant Dipole Resonance (GDR). The isomeric yield ratios of the 89g,mZr, 91g,mMo, and 97g,mNb from the above reactions were also calculated by using the computer code TALYS 1.6 and compared with the experimental data to examine the validity of the theoretical model for independent isomeric yield ratio calculations.

Measurement of flux-weighted average cross sections for 197Au(γ, xn) reactions and isomeric yield ratios of 196m,gAu with bremsstrahlung

Photo-neutron cross sections of 197Au were experimentally determined for the bremsstrahlung end-point energies of 50, 60, and 70 MeV, by utilizing activation and off-line γ-ray spectrometric technique, using the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Pohang, Korea. The 197Au(γ, xn; x=1–6) reaction cross sections were calculated as a function of the bombarding photon energy by using the TALYS 1.6 computer code with default parameters. The flux-weighted average cross sections were obtained from the literature data and the theoretical values of TALYS 1.6 and TENDL-2014, for mono-energetic photons, and are found to be in good agreement with the present data. Isomeric yield ratios of 196m2,gAu from the 197Au(γ, n) reaction were also determined for the bremsstrahlung end-point energies of 50, 60, and 70 MeV, from the reaction cross sections of m2- and g-states, based on the present experimental data, and are found to be in good agreement with the theoretical values based on TALYS 1.6 and TENDL-2014.

Visualization of bond rearrangements in acetylene using near single-cycle laser pulses.

The migration of hydrogen atoms resulting in the isomerization of hydrocarbons is an important process which can occur on ultrafast timescales. Here, we visualize the light-induced hydrogen migration of acetylene to vinylidene in an ionic state using two synchronized 4 fs intense laser pulses. The first pulse induces hydrogen migration, and the second is used for monitoring transient structural changes via Coulomb explosion imaging. Varying the time delay between the pulses reveals the migration dynamics with a time constant of 54 ± 4 fs as observed in the H+ + H+ + CC+ channel. Due to the high temporal resolution, vibrational wave-packet motions along the CC- and CH-bonds are observed. Even though a maximum in isomerization yield for kinetic energy releases above 16 eV is measured, we find no indication for a backwards isomerization - in contrast to previous measurements. Here, we propose an alternative explanation for the maximum in isomerization yield, namely the surpassing of the transition state to the vinylidene configuration within the excited dication state.

Photonuclear Studies for the Isomeric Yield Ratios in the Production ofnatFe(γ,xnp)52m,gMn with 50-,60-, and 70-MeV Bremsstrahlung

The isomeric yield ratios in the production of nat Fe(γ ,xnp)52m,g Mn have been measured with photonuclear reactions. The high purity natural Fe metallic foils were used and irradiated with bremsstrahlung beams of end point energy 50-, 60-, and 70-MeV. The bremsstrahlung beams are produced with high energy electron beam struck with 0.1mm thin tungsten target. The activation method has been used and hence the induced activities in the irradiated foils were measured by off-line γ -ray spectrometric technique using HPGe detector coupled to a PC-based 4K MCA. The experimental values of isomeric ratios are compared with the theoretical values by statistical model code TALYS. The detail of the formation of isomers by photonuclear reactions together with the literature values of the investigated nuclides are compared and discussed.

Fission yield measurements at IGISOL

The fission product yields are an important characteristic of the fission process. In fundamental physics, knowledge of the yield distributions is needed to better understand the fission process. For nuclear energy applications good knowledge of neutroninduced fission-product yields is important for the safe and efficient operation of nuclear power plants. With the Ion Guide Isotope Separator On-Line (IGISOL) technique, products of nuclear reactions are stopped in a buffer gas and then extracted and separated by mass. Thanks to the high resolving power of the JYFLTRAP Penning trap, at University of Jyvaskyla, fission products can be isobarically separated, making it possible to measure relative independent fission yields. In some cases it is even possible to resolve isomeric states from the ground state, permitting measurements of isomeric yield ratios. So far the reactions U(p,f) and Th(p,f) have been studied using the IGISOL-JYFLTRAP facility. Recently, a neutron converter target has been developed utilizing the Be(p,xn) reaction. We here present the IGISOL-technique for fission yield measurements and some of the results from the measurements on proton induced fission. We also present the development of the neutron converter target, the characterization of the neutron field and the first tests with neutron-induced fission.

Elucidation of the active phase in PtSn/SAPO-11 for hydrodeoxygenation of methyl palmitate

SAPO-11 zeolite-supported PtSn bimetallic catalysts (PtSn/SAPO-11) were prepared using a co-impregnation method for simultaneous selective hydrodeoxygenation of methyl palmitate and isomerization of deoxygenated hydrocarbons. The PtSn catalyst exhibited high isomerization activity and hydrodeoxygenation selectivity, and was superior to the monometallic Pt/SAPO-11 catalyst. The Pt/SAPO-11 catalyst was more active for CC bond cleavage, resulting in a considerable formation of C15 hydrocarbons. The PtSn/SAPO-11 catalyst was more efficient for CO bond hydrogenation, affording higher selectivity to C16 hydrocarbons. In the studied PtSn catalyst, the platinum content was constant at 0.3wt% and the atomic ratio of Sn/Pt was varied from 1 to 3. The result of the catalytic test suggests that it is necessary to control tin surface density in order to obtain a well-balanced Pt–SnO2−x function and a Pt–Sn alloy as well. The highest performance in the tandem hydrodeoxygenation–isomerization of methyl palmitate was observed at the Sn/Pt ratio of 2; for this catalyst, the isomerization yield obtained at 375°C was 4 times higher than the monometallic Pt catalyst. After tin addition, Pt nanoparticles were highly dispersed on the support with an average size of ∼4nm. HRTEM observations and FT-IR studies of CO adsorption indicate that a portion of Sn interacted with Pt, forming Pt–Sn alloys; other Sn species were formed in the form of tin oxides, likely SnO2−x (0<x<2), and were mainly present on the periphery of Pt nanoparticles. The occurrence of SnO2−x species is crucial for the hydrodeoxygenation pathway; however, excessive addition of tin would block the Pt and PtSn active sites, resulting in a decrease in the catalytic activity. The presence of Pt–Sn alloys is the most remarkable reason for its high isomerization activity.

Study of projectile fragmentation reaction with isochronous mass spectrometry

Relative yields of fragments following the 78Kr projectile fragmentation in a beryllium target were measured in a storage ring by using isochronous mass spectrometry (IMS). Odd–even staggering of the relative fragment yields is observed and can be explained by the odd–even staggering of the particle-emission threshold energies. IMS is a complementary technique to γ-ray spectroscopy for measuring isomeric ratios, in particular for nuclides with long lifetimes. It was found that the isomeric yield ratios in 53Fe are almost constant for different longitudinal momenta.

Measurement of isomeric yield ratios of 197m,gPt and 190m2,g+m1Ir from the 198Pt(γ,n) and natPt(γ,xn1p) reactions induced by 55-, 60-, and 65-MeV bremsstrahlung

We have measured the isomeric yield ratios of 197m,gPt from the 198Pt(γ,n) reaction and 190m2,g+m1Ir from the natPt(γ,xn1p) reaction, induced with the bremsstrahlung end-point energies of 55-, 60-, and 65-MeV. The measurements were carried out by the activation method in combination with the direct γ-spectrometry. The experiments were performed at the 100MeV electron linac of the Pohang Accelerator Laboratory (PAL). The obtained results at 55-, 60- and 65-MeV for the 197m,gPt from the 198Pt(γ,n) reaction are 0.166±0.012, 0.174±0.011, and 0.175±0.011, whereas for the 190m2,g+m1Ir from the natPt(γ,xn1p) reaction are 0.072±0.006, 0.084±0.006 and 0.087±0.006, respectively. The present results are measured for the first time over the investigated energy range. The present data are compared with the similar literature data at lower energy to examine the role of excitation energy.

Изомерные отношения и средние угловые моменты фрагментов фотоделения 235U, 237Np и 239Pu

Изомерные отношения и средние угловые моменты фрагментов фотоделения 235U, 237Np и 239Pu

Measurement of isomeric yield ratios in the photo-production of 133m,g;137m,gCe from natCe using 55-, 60-, and 65-MeV bremsstrahlung

The isomeric yield ratios of 133m,gCe and 137m,gCe produced from the natCe(γ,xn) reactions were determined by using the activation and the off-line γ-ray spectrometric technique with the end-point bremsstrahlung energies of 55-, 60-, and 65-MeV at 100-MeV electron linac of the Pohang accelerator laboratory. The induced activities in the irradiated foils were measured by using an energy- and efficiency-calibrated HPGe detector coupled to a PC based multi-channel analyzer. The necessary corrections were made to improve the accuracy of the experimental results. The experimental results at bremsstrahlung energies of 55-, 60-, and 65-MeV were 0.324±0.089, 0.331±0.086, and 0.403±0.089 for the 133m,gCe, and 0.210±0.062, 0.221±0.061, and 0.262±0.061 for the 137m,gCe, respectively. The present results for natCe(γ,xn)133m,g;137m,gCe in this energy region were obtained for the first time which has no comparable literature data. The obtained isomeric yield ratios are compared with the calculated values based on the statistical model code TALYS 1.6.