Yields Of Fragments Research Articles

From fission yield measurements to evaluation: new statistical methodology applied to 235U(nth, f ) mass yields

The study of fission yields has a major impact on the characterization and understanding of the fission process and is mandatory for reactor applications. The mass and isotopic yields of the fission fragments have a direct influence on the predictions of fuel burn-up and decay heat. Moreover, these data are requested for other studies as delayed neutron evaluation, antineutrino flux assessment or reactor program. Today, the lack of covariance matrix associated to evaluated fission yields induces overestimated uncertainties of mass yields since these observables result from the sum of isotopic and isomeric yields. Our collaboration starts a new program in the field of the evaluation of fission products in addition to the current experimental program. The goal is to define a new methodology of evaluation based on statistical tests in order to provide the best estimation with consistent sets of measurements. A ranking of solutions with associated covariance based on Shannon’s entropy criterion is proposed for the mass yields from 235 U(nth, f) reaction.

High-energy ionizing radiation influence on the fragmentation of glutamine

Both experimentally, by using the mass-spectrometric technique, and theoretically, by applying Becke’s three-parameter hybrid density functional approach, the yield of the ionic products of both single- and dissociative ionization of the glutamine molecule (C5H10N2O3) under high-energy (11.5 MeV) electron impact has been studied. The experimental mass spectra measured at different irradiation doses (i.e., 0, 5, 10, and 20 kGy) have been identified and analyzed. It has been shown that high-energy electrons cause irreversible changes in the structure of the molecule under study, accompanied by a transition to the zwitterionic/deprotonated form, which may cause a change in the fragment ion production at the interatomic distance variation. It has been shown that the yield of the low-mass fragments from the zwitterionic glutamine molecular structure may increase due to an increase in the isobaric ion yield.

The surfactant-free bottom-up synthesis of ultrathin MOF nanosheets for the oxidation of isoeugenol to vanillin

The direct synthesis of ultrathin MOF nanosheets is extremely challenging. Existing methods suffer from structural deterioration, aggregation, morphological fragmentation, and low yields. The direct synthesis of MOF nanosheets remains a challenging task.

Effects of annealing on fission fragment release from electrodeposited Cf-252 thin-films

Samarium thin-films doped with a252Cf radiotracer were used to study the effects of annealing on the release of fission fragments from electrodeposited films. An ammonium acetate molecular plating technique was utilized to perform the depositions. The fission fragment yields were measured using a unique technique involving the exposure of aluminum foils to the deposited material for a fixed time followed by gamma-ray spectroscopy to determine the rate at which the fission fragments implanted into the foils. Annealing of the electrodeposited films was found to have no effect on the release of fission fragments.

Estimations of relative biological effectiveness of secondary fragments in carbon ion irradiation of water using CR-39 plastic detector and microdosimetric kinetic model.

To estimate relative biological effectiveness (RBE) ascribed to secondary fragments in a lateral distribution of carbon ion irradiation. The RBE was estimated with the microdosimetric kinetic (MK) model and measured linear energy transfer (LET) obtained with CR-39 plastic detectors. A water phantom was irradiated by a 12 C pencil beam with energy of 380MeV/u at the Gunma University Heavy Ion Medical Center (GHMC), and CR-39 detectors were exposed to secondary fragments. Because CR-39 was insensitive to low LET, we conducted Monte Carlo simulations with Geant4 to calculate low LET particles. The spectra of low LET particleswere combined with experimental spectra to calculate RBE. To estimate accuracy of RBE, we calculated RBE by changing yield of low LET particles by±10% and±40%. At a small angle, maximum RBE by secondary fragments was 1.3 for 10% survival fractions. RBE values of fragments gradually decreased as the angle became larger. The shape of the LET spectra in the simulation reproduced the experimental spectra, but there was a discrepancy between the simulation and experiment for the relative yield of fragments. When the yield of low LET particles was changed by±40%, the change in RBE was smaller than 10%. An RBE of 1.3 was expected for secondary fragments emitted at a small angle. Although, we observed a discrepancy in the relative yield of secondary fragments between simulation and experiment, precision of RBE was not so sensitive to the yield of low LET particles.

Preliminary results coupling “Stochastic Mean Field” and “Boltzmann-Langevin One Body” models with Geant4

PurposeMonte Carlo (MC) simulations are widely used for medical applications and nuclear reaction models are fundamental for the simulation of the particle interactions with patients in ion therapy. Therefore, it is of utmost importance to have reliable models in MC simulations for such interactions. Geant4 is one of the most used toolkits for MC simulation. However, its models showed severe limitations in reproducing the yields measured in the interaction of ion beams below 100 MeV/u with thin targets. For this reason, we interfaced two models, SMF (“Stochastic Mean Field”) and BLOB (“Boltzmann-Langevin One Body”), dedicated to simulate such reactions, with Geant4. MethodsBoth SMF and BLOB are semi-classical, one-body approaches to solve the Boltzmann-Langevin equation. They include an identical treatment of the mean-field propagation, on the basis of the same effective interaction, but they differ in the way fluctuations are included. Furthermore, we tested a correction to the excitation energy calculated for the light fragments emerging from the simulations and a simple coalescence model. ResultsWhile both SMF and BLOB have been developed to simulate heavy ion interactions, they show very good results in reproducing the experimental yields of light fragments, up to alpha particles, obtained in the interaction of 12C with a thin carbon target at 62 MeV/u. ConclusionsBLOB in particular gives promising results and this stresses the importance of integrating it into the Geant4 toolkit.

Ring opening dissociation of cationic twisted conformer by conformer-specific cyclopentanone photoionization.

We investigated the dissociation processes of a cationic conformer, induced by conformer-specific photoionization of cyclopentanone (CP) using a one-photon vacuum ultraviolet (VUV) laser pulse of energy in the range 9.24-9.92 eV for a few nanoseconds, generated by four-wave difference frequency mixing in a Kr cell. The adiabatic ionization energy of the CP was accurately determined to be 9.2697 ± 0.0009 eV, based on the VUV photoionization efficiency curve obtained using high-resolution VUV-photoionization time-of-flight (TOF) mass spectroscopy. The constructed potential energy contours, associated with the twisting and out-of-plane motions in the S0 and D0 states, revealed that the ionization energy value corresponded to a twisted conformer with C2 symmetry at the global minimum. Subsequently, the low photon energy above the ionization onset of the twisted conformer in the CP led to C2H4 elimination, producing a C3H4O+ fragment directly prior to CO elimination for the C4H8 + fragment. The appearance energies for the C3H4O+ and C4H8 + were determined to be 9.7068 ± 0.0017 eV and 9.7483 ± 0.0017 eV, respectively, by measuring the fragmentation yield curves for two fragments analyzed in the TOF mass spectra. The formation enthalpy for each fragment ion at 0 K, evaluated using the measured and thermochemical data, enabled the realization of plausible structures for the produced fragment ions. Consequently, based on the results of the quantum chemical calculation on the dissociation processes of the twisted CP cation (t-CP+), we suggest that the fragmentation processes to C3H4O+ and C4H8 + correspond to the methylketene and (E)-2-butene cations, respectively.

Electron-Impact-Induced Fragmentation of a Glutamine Molecule

The formation of ionized products upon single and dissociative ionization of a glutamine (C5H10N2O3) molecule by electron impact at low (70 eV) and high (11.5 MeV) energies has been studied by method of mass spectrometry. The mass spectra of glutamine molecules have been obtained upon electron irradiation to various doses (0, 5, 10, and 20 kGy) and for various threshold functions of ion fragment yield. The absolute values of ion fragment appearance energies are determined. Electron beams were generated by a three-electrode gun and electron accelerator (microtron). Comparative analysis of the measured mass spectra of unirradiated and irradiated glutamine molecules showed that high-energy irradiation produced irreversible changes in the molecular structure.

Renewable lignin-based carbon nanofiber as Ni catalyst support for depolymerization of lignin to phenols in supercritical ethanol/water

Lignin represents the most abundant source of renewable aromatic resources, and depolymerization of lignin has been shown to be a prominent challenge in the production of low-molecular-mass aromatic chemicals. Herein, we report the preparation of Ni/LCNF catalyst by which Ni nanoparticles were inlaid in lignin-based carbon nanofibers (LCNF) to improve stability of the catalyst and adjust the interaction between the metal and its support. We also present its use in lignin depolymerization. The use of 10%Ni/LCNF catalyst resulted in exceptionally high yields of light lignin fragments (87%) and phenols (7%). The average molecular weight (Mw) of light lignin residue was significantly lower than that of the untreated lignin, and there was clear evidence of lignin depolymerization. Preliminary recycling studies showed that the Ni/LCNF catalyst could maintain its activity for over three recycling cycles; its selectivity towards phenols remained unchanged. The present method, in which Ni nanoparticles were inserted or partially embedded in carbon materials to avoid Ni nanoparticle aggregation, sintering and loss during lignin depolymerization, is an alternative way that can be applied to maximize the utilization of lignin.

Genesis Apocryphon and Related Documents

Genesis Apocryphon and Related Documents

Preventing Lignin Condensation to Facilitate Aromatic Monomer Production.

Lignin is the most abundant aromatic polymer in nature and as such is an attractive source of aromatic molecules. Efficient lignin utilization will also likely play a key role in the economic success and sustainability of biomass valorization schemes. However, traditional strategies for lignin isolation and depolymerization suffer from repolymerization issues, which result in low yield of low molecular weight fragments. This review summarizes the recent progress in lignin isolation and depolymerization methods that are able to limit lignin condensation and facilitate the high yield production of monomers and oligomers. A general trend in these methods is that condensation and repolymerization is prevented by trapping reactive intermediates during extraction or depolymerization by chemically stabilizing the β-O-4 structure and/or its derivatives, or physically removing the separated lignin fragments from the reactor. We highlight the challenges and opportunities that these methods will face as they are further developed.

Comparative study of alternative Geant4 hadronic ion inelastic physics models for prediction of positron-emitting radionuclide production in carbon and oxygen ion therapy

The distribution of fragmentation products predicted by Monte Carlo simulations of heavy ion therapy depend on the hadronic physics model chosen in the simulation. This work aims to evaluate three alternative hadronic inelastic fragmentation physics options available in the Geant4 Monte Carlo radiation physics simulation framework to determine which model most accurately predicts the production of positron-emitting fragmentation products observable using in-beam PET imaging. Fragment distributions obtained with the BIC, QMD, and INCL + + physics models in Geant4 version 10.2.p03 are compared to experimental data obtained at the HIMAC heavy-ion treatment facility at NIRS in Chiba, Japan. For both simulations and experiments, monoenergetic beams are applied to three different block phantoms composed of gelatin, poly(methyl methacrylate) and polyethylene. The yields of the positron-emitting nuclei 11C, 10C and 15O obtained from simulations conducted with each model are compared to the experimental yields estimated by fitting a multi-exponential radioactive decay model to dynamic PET images using the normalised mean square error metric in the entrance, build up/Bragg peak and tail regions. Significant differences in positron-emitting fragment yield are observed among the three physics models with the best overall fit to experimental 12C and 16O beam measurements obtained with the BIC physics model.

Range verification of radioactive ion beams of 11C and 15O using in-beam PET imaging

In advanced ion therapy, the visualization of the range of incident ions in a patient’s body is important for exploiting the advantages of this type of therapy. It is ideal to use radioactive ion beams for in-beam positron emission tomography (PET) imaging in particle therapy due to the high quality of PET images caused by the high signal-to-noise ratio. We have shown the feasibility of this idea through an in-beam PET study for 11C and 15O ion beams using the dedicated OpenPET system. In this work, we investigate the potential difference between the Bragg peak position and the position of the maximum detected positron-emitting fragments by a PET system for the radioactive beams of 11C and 15O. For this purpose, we measured the depth dose in a water phantom and performed PET scans of an irradiated PMMA phantom for the available beams of 11C and 15O at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Then, we simulated the depth dose profiles in the water phantom and the yield of the positron-emitting fragments in a PMMA phantom for both available beams using the Monte Carlo code PHITS. The positions of the Bragg peak and maximum positron-emitting fragments from the measurements were well reproduced by simulation. The effect of beam energy broadening on the positional differences between two peaks was studied by simulating an irradiated PMMA phantom. The differences in position between the Bragg peak and the maximum positron-emitting fragments increased when the beam energy spread was broadened, although the differences were zero for the ideal mono-energetic beams. Greater differences were observed for 11C ion beams compared to 15O ion beams, although both beams had the same range in water, and the higher energy corresponded to a larger difference. For the known energy spread of the beams, the predicted differences between two peaks from the simulation were consistent with the measured data within submillimetre agreement.

Abstract 5136: Adapting long read sequencing technologies for targeted and single cell applications

Abstract Structural variations (SV), a hallmark of genomic instability in cancer, include insertions, deletions, duplications, inversions, or translocations that can either activate oncogenes or inactivate tumor suppressor genes. These variants contribute to the complexity of the cancer genome but have not been successfully resolved yet. While short-read sequencing has aided cancer genomics, it has performed poorly in SV detection, with false positive and false negative rates of 50% or more. Long-read sequencing generates reads that are >10 kb long and has helped identify thousands of genomic features pertinent to cancer that were previously missed by short-read sequencing. Long reads can span SV with a single continuous read, giving a clearer idea of the variation, its position, and size. Currently, long-read sequencing methods are greatly limited by the DNA preparation step, with fragment lengths and yield often compromised by standard extraction methods. The potential to generate reads at the megabase level relies greatly on library preps using large amounts (several μg) of DNA input, which prevents its application to samples like patient tumors that are often limited in DNA. Our overarching goal is to develop a targeted approach that generates large contiguous reads from moderate to low input DNA masses. To this end, we use different extraction, amplification, fragmentation, and enrichment strategies to efficiently target and resolve complex regions of the genome that are often associated with disease conditions. Development of a targeted long-read sequencing strategy using low DNA input would give us the potential to explore the landscape of genetic variation across several individuals and heterogeneous cell populations. We are currently employing and adapting CRISPR-based targeting techniques to enrich for specific regions of the genome from intact cells and/or high-molecular-weight DNA. Citation Format: Shruti Iyer, Sara Goodwin, W. Richard McCombie. Adapting long read sequencing technologies for targeted and single cell applications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5136.

Vibrationally mediated photodissociation dynamics of pyrrole

We investigate photodissociation of vibrationally excited pyrrole molecules in a velocity map imaging experiment with IR excitation of N–H bond stretching vibration v1 = 1, νIR= 3532 cm−1, and UV photodissociation at λUV= 243 nm. In the IR+UV experiment, the H-fragment signal is enhanced with respect to the 243 nm UV-only photodissociation due to a more favorable Franck-Condon factor for the vibrationally excited molecule. In the measured H-fragment kinetic energy distribution, the maximum of the fast peak in the IR+UV experiment is shifted by 0.23 eV compared to the UV-only photodissociation which corresponds to 53 % of the vibrational energy deposited into the fragment kinetic energy. We compare our results with an isoenergetic UV-only photodissociation at λUV= 224 nm. About 72 % of the total available energy, is released into the fragment kinetic energy in the IR+UV experiment, while it is only 61 % in the UV-only photodissociation. This can be substantiated by the coupling of the N–H bond stretching vibration into the kinetic energy of the departing H-fragment. We also probe the time-dependent dynamics by a nanosecond pump-probe experiment. The IR excitation enhances the N–H bond dissociation even when the UV photodissociation is delayed by 150 ns. This enhancement increases also the yield of the fast fragments at the position of the peak corresponding to the IR+UV excitation, i.e. even 150 ns after the IR vibrational excitation, the same amount of the IR excitation energy can be converted into the H-fragment velocity as immediately after the excitation.

Observation of the competing fission modes in 178Pt

Fragment mass distributions from fission of the excited compound nucleus 178Pt have been deduced from the measured fragment velocities. The 178Pt nucleus was created at the JAEA tandem facility in a complete fusion reaction 36Ar + 142Nd, at beam energies of 155, 170 and 180 MeV. The data are indicative of a mixture of the mass-asymmetric and mass-symmetric fission modes associated with higher and lower total kinetic energies of the fragments, respectively. The measured fragment yields are dominated by asymmetric mass splits, with the symmetric mode contributing at the level of ≈1/3. This constitutes the first observation of a multimodal fission in the sub-lead region. Most probable experimental fragment-mass split of the asymmetric mode, AL/AH≈79/99, is well reproduced by nuclear density functional theory using the UNEDF1-HFB and D1S potentials. The symmetric mode is associated by theory with very elongated fission fragments, which is consistent with the observed total kinetic energy/fragment mass correlation.

Test of isospin conservation in thermal neutron-induced fission of $$^{245}\mathrm{Cm}$$ 245 Cm

We have recently shown that the general trends of partition-wise fission fragment mass distribution in heavy-ion-induced compound nuclear (CN) fission of heavy nuclei can be reproduced reasonably well by using the concept of isospin conservation, hence providing a direct evidence of isospin conservation in neutron-rich systems [Jain et al, Nucl Data Sheets 120, 123 (2014); Garg and Jain, Phys. Scr. 92, 094001 (2017); Jain and Garg, EPJ Web of Conference 178, 05007 (2018); Garg et al, Phys. Scr. 93, 124008 (2018)]. In this paper, we test the concept of isospin conservation to reproduce the fission fragment mass distribution emerging from thermal neutron-induced CN fission reaction, $$^{245}\mathrm{Cm}(n_{\mathrm{th}}, \hbox {f})$$ . As earlier, we use Kelson’s conjectures [I Kelson, Proceedings of the Conference on Nuclear Isospin (Academic Press, New York, 1969)] to assign isospin to neutron-rich fragments emitted in fission, which suggest the formation of fission fragments in isobaric analogue states. We calculate the relative yields of neutron-rich fragments using the concept of isospin conservation and basic isospin algebra. The calculated results reproduce the experimentally known partition-wise mass distributions quite well. This highlights the usefulness of isospin as an approximately good quantum number in neutron-rich nuclei. This also allows us to predict the fragment distribution of the most symmetric Cd–Cd partition and the heavier mass fragment distributions, both not measured so far.

Optimization of Enzymatic Antibody Fragmentation for Yield, Efficiency, and Binding Affinity.

Enzymatic antibody fragmentation has been well studied for various hosts and isotypes, but fragmentation patterns also vary unpredictably by clone, and optimizing Fab or F(ab')2 production by trial and error consumes large quantities of antibodies. Here, we report a systematic strategy for optimizing functional F(ab')2 production via pepsin digestion from small quantities of IgG. We tested three key parameters that affect fragmentation, pH, enzyme concentration (% pepsin w/w), and reaction time, and found that pH had the greatest impact on fragmentation yield and efficiency. We then developed a systematic approach to obtaining acceptable yields, digestion efficiency, and binding affinity. Three case studies are described to illustrate the approach. We anticipate that this work will provide a quick and cost-effective method for researchers to produce antibody fragments from whole IgG, avoiding haphazard trial and error.

Odd--Even Staggering in the Yields of Intermediate Mass Fragments from $p$+Ag collisions at $Ep=480$ MeV

Odd--Even Staggering in the Yields of Intermediate Mass Fragments from $p$+Ag collisions at $Ep=480$ MeV

Фрагментация молекулы глютамина электронным ударом

Using the mass-spectrometric analysis technique, formation of the ionic products of the single and dissociative ionization of the glutamine molecule (C5H10N2O3) at its interaction with the low (70 eV) and high (11.5 MeV) energy electrons has been studied. The experimental mass-spectra of the above molecule measured at different irradiation doses (5, 10 and 20 kGy) and the near-threshold areas of the ionic fragment yield functions have been analyzed, the absolute ion fragment appearance energies have been found. The three-electrode electron gun and the electron accelerator (microtron) were used as the electron beam sources. The analysis of the behaviour of the measured glutamine molecule mass-spectra irradiated at the above doses demonstrates, as compared to the irradiated molecule mass-spectrum, that the high-energy irradiation of the initial molecule results in the irreversible changes of its structure.