Yields Of Fragments Research Articles

Measurement of inclusive jet charged-particle fragmentation functions in Pb+Pb collisions at [formula omitted] with the ATLAS detector

Measurements of charged-particle fragmentation functions of jets produced in ultra-relativistic nuclear collisions can provide insight into the modification of parton showers in the hot, dense medium created in the collisions. ATLAS has measured jets in sNN=2.76 TeV Pb+Pb collisions at the LHC using a data set recorded in 2011 with an integrated luminosity of 0.14 nb−1. Jets were reconstructed using the anti-kt algorithm with distance parameter values R=0.2,0.3,and 0.4. Distributions of charged-particle transverse momentum and longitudinal momentum fraction are reported for seven bins in collision centrality for R=0.4 jets with pTjet>100 GeV. Commensurate minimum pT values are used for the other radii. Ratios of fragment distributions in each centrality bin to those measured in the most peripheral bin are presented. These ratios show a reduction of fragment yield in central collisions relative to peripheral collisions at intermediate z values, 0.04≲z≲0.2, and an enhancement in fragment yield for z≲0.04. A smaller, less significant enhancement is observed at large z and large pT in central collisions.

Reconstructed primary fragments and symmetry energy, temperature and density of the fragmenting source in Zn64+Sn112 at 40 MeV/nucleon

Symmetry energy, temperature and density at the time of the intermediate mass fragment formation are determined in a self-consistent manner, using the experimentally reconstructed primary hot isotope yields and anti-symmetrized molecular dynamics (AMD) simulations. The yields of primary hot fragments are experimentally reconstructed for multifragmentation events in the reaction system $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon. Using the reconstructed hot isotope yields and an improved method, based on the modified Fisher model, symmetry energy values relative to the apparent temperature, $a_{sym}/T$, are extracted. The extracted values are compared with those of the AMD simulations, extracted in the same way as that for the experiment, with the Gogny interaction with three different density-dependent symmetry energy terms. $a_{sym}/T$ values change according to the density-dependent symmetry energy terms used. Using this relation, the density of the fragmenting system is extracted first. Then symmetry energy and apparent temperature are determined in a self consistent manner in the AMD model simulations. Comparing the calculated $a_{sym}/T$ values and those of the experimental values from the reconstructed yields, $\rho /\rho_{0} = 0.65 \pm 0.02 $, $a_{sym} = 23.1 \pm 0.6$ MeV and $T= 5.0 \pm 0.4$ MeV are evaluated for the fragmenting system experimentally observed in the reaction studied.

Neutron density distributions of neutron-rich nuclei studied with the isobaric yield ratio difference

The isobaric yield ratio difference (IBD) between two reactions of similar experimental setups is found to be sensitive to nuclear density differences between projectiles. In this article, the IBD probe is used to study the density variation in neutron-rich 48Ca . By adjusting diffuseness in the neutron density distribution, three different neutron density distributions of 48Ca are obtained. The yields of fragments in the 80A MeV 40, 48Ca + 12C reactions are calculated by using a modified statistical abrasion-ablation model. It is found that the IBD results obtained from the prefragments are sensitive to the density distribution of the projectile, while the IBD results from the final fragments are less sensitive to the density distribution of the projectile.

Implementing visible 473 nm photodissociation in a Q-Exactive mass spectrometer: towards specific detection of cysteine-containing peptides.

Improvement of the fragmentation specificity may streamline data processing of bottom-up proteomic experiments by drastically reducing either the amount of MS/MS data to process in the discovery phase or the detection of interfering signals in targeted quantification. Photodissociation at appropriate wavelengths is a promising alternative technique to the non-discriminating conventional activation mode by collision. Here, we describe the implementation of visible LID at 473 nm in a Q-Exactive-Orbitrap mass spectrometer for the specific detection of cysteine-containing peptides tagged with a Dabcyl group. HCD cell DC offset and irradiation time were optimized to obtain high fragmentation yield and spectra free of contaminating CID product ions, while keeping the irradiation time scale compatible with chromatographic separation. With this optimized experimental set-up, the selective detection of cysteine-containing peptides in a whole tryptic hydrolysate of three combined proteins is demonstrated by comparing all ion fragmentation (AIF) spectra recorded online with and without laser irradiation.

New insight into power-law behavior of fragment size distributions in the C₆₀ multifragmentation regime.

Previous experimental work has shown that a phase transition in C60 multifragmentation induced by nanosecond laser occurs at almost constant temperature covering a wide range of laser fluency. Here the relative yields of ionic fragments (IFs) C(n)(+) (n = 1-20) resulting from the multifragmentation are measured within the phase transition region. By excluding two small IFs and magic IFs due to their abnormal behavior, the data for residual IFs are used to estimate the size distributions of primary intermediate-mass IFs in the multifragmentation regime. The distributions are found to obey power laws n(-τ). Furthermore, the exponent τ values have sensitive dependence on lower laser fluency and converge to a constant of about 2.4 ± 0.2 for larger fluencies. These observations are in good agreement with an explanation based on the Fisher droplet model, offering the tantalizing possibility of a liquid-to-gas phase transition in C60 systems.

Photodissociation dynamics of superexcited O₂: dissociation channels O(⁵S) vs. O(³S).

The photodissociation dynamics of O2, O2 + hυ → O((3)P) + O(2p(3)((4)S)3s, (3)S/(5)S), has been studied by combining the XUV laser pump / UV laser probe and velocity map imaging methods in the photon energy range 14.64-15.20 eV. The fragment yield spectra of O((3)S) and O((5)S) and their velocity map images have been recorded using the state-selective (1+1) REMPI method to detect the fragments. The fragment yield spectra show resolved fine structure that arises from the predissociated Rydberg states I, I' and I″ ((3)Π(Ω = 0,1,2)). The branching ratios between the two decay channels have been measured by one-photon ionization of the fragments O((3)S) and O((5)S) simultaneously. It is surprising to find that the dissociation cross sections for the production of O((5)S) are larger than, or comparable to, those of O((3)S) for the I and I' states, while the cross sections for the production of O((5)S) are smaller than those of O((3)S) for the I″ state. All fragments O((5)S) arise from perpendicular transitions, which provides direct experimental evidence about the symmetry assignments of the states I, I' and I″ excited in this energy region. Although most of the fragments O((3)S) arise from perpendicular transitions, some of them are from parallel transitions. Based on the calculated ab initio potential energy curves, we propose that the neutral dissociation into O((3)P) + O((3)S) occurs mainly via the interaction of the Rydberg states I, I', and I″ with the vibrational continuum of the diabatic 8(3)Π(u) state (1π(u)⁻¹(a⁴Π(u))3sσ(g), ³Π(u)), while the neutral dissociation into O((3)P) + O((5)S) occurs mainly via the interaction of Rydberg states I, I', and I″ with the diabatic 7(3)Π(u) (1π(g)⁻¹(X²Π(g))3pσ(u), ³Π(u)).

Pathway competition of H+ in intense femtosecond laser fields

We experimentally measured the kinetic energy and angular distributions of fragment ion H+ of H2 as a function of 810 nm femtosecond laser intensity by using velocity map imaging technique. The reasonable origination of dissociation channels (1.0) and (1.1) are proposed. The analysis of the angular distribution indicates the net two-photon pathway via the 3ω crossing dominates over the direct one-photon pathway in channel (1.0). The relative yield of fragment peaks indicates that dissociation and ionization of H2+ are competitive. The lower laser intensities emphasize the dissociation probability of H2+, and the higher laser intensities favor higher ionization stages.

Control and identification of strong field dissociative channels in CO via molecular alignment

The dissociative excitation of CO was studied in the molecular frame as a function of probe laser intensity, ellipticity and polarization with respect to the molecular bond at laser wavelengths of 800 nm and 1350 nm. This allowed the identification of the main excitation pathway consisting of tunnel ionization from HOMO-2 followed by a parallel dipole transition from the second excited state B to the predissociating, third excited state C. Recollision excitation was shown to play a negligible role. Using laser induced impulsive alignment, the strong field induced coupling at 800 nm and 1350 nm of the ionic states B and C could thus be controlled by the laser polarization. This leads to a suppression of the fragmentation yield of up to 70% when the laser polarization was perpendicular to the molecular axis compared to parallel polarization. We have performed simulations of various ionization channels of CO2. Our simulations reflect the experimental findings and show that dissociation of CO is induced by tunnelling from deeper molecular orbitals HOMO-1, HOMO-2, HOMO-3, followed by laser driven hole dynamics in the ion.

Towards standardisation of cell-free DNA measurement in plasma: controls for extraction efficiency, fragment size bias and quantification.

Circulating cell-free DNA (cfDNA) is becoming an important clinical analyte for prenatal testing, cancer diagnosis and cancer monitoring. The extraction stage is critical in ensuring clinical sensitivity of analytical methods measuring minority nucleic acid fractions, such as foetal-derived sequences in predominantly maternal cfDNA. Consequently, quality controls are required for measurement of extraction efficiency, fragment size bias and yield for validation of cfDNA methods. We evaluated the utility of an external DNA spike for monitoring these parameters in a study comparing three specific cfDNA extraction methods [QIAamp® circulating nucleic acid (CNA) kit, NucleoSpin® Plasma XS (NS) kit and FitAmp™ plasma/serum DNA isolation (FA) kit] with the commonly used QIAamp DNA blood mini (DBM) kit. We found that the extraction efficiencies of the kits ranked in the order CNA kit > DBM kit > NS kit > FA kit, and the CNA and NS kits gave a better representation of smaller DNA fragments in the extract than the DBM kit. We investigated means of improved reporting of cfDNA yield by comparing quantitative PCR measurements of seven different reference gene assays in plasma samples and validating these with digital PCR. We noted that the cfDNA quantities based on measurement of some target genes (e.g. TERT) were, on average, more than twofold higher than those of other assays (e.g. ERV3). We conclude that analysis and averaging of multiple reference genes using a GeNorm approach gives a more reliable estimate of total cfDNA quantity. FigureComparison of single and multiple reference gene normalisation for quantification of plasma cell free DNA Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-014-7835-3) contains supplementary material, which is available to authorized users.

Origin of odd-even staggering in fragment yields: Impact of nuclear pairing and shell structure on the particle-emission threshold energy

Strong odd-even staggering (OES) of the yields of fragments, produced by fragmenting 78 Kr projectiles, has been measured by employing the combination of an in-flight fragment separator and a storage ring. It is shown that the OES of fragment yields of Tz =− 1/ 2a ndTz = 1/2 mirror nuclei critically depends on both pairing and shell structure, especially at the closed shells Z = 20 and 28. A comparison of the relative OES of yields and of particle-emission threshold energies reveals unambiguously that the origin of the OES of fragment yields is mainly determined by the OES of the particle-emission threshold energies, which contain both pairing and shell effects.

Theoretical investigation of the competitive mechanism between dissociation and ionization of H₂⁺ in intense field.

The competitive mechanism between dissociation and ionization of hydrogen molecular ion in intense field has been theoretically investigated by using an accurate non-Born-Oppenheimer method. The relative yield of fragments indicates that the dissociation and ionization channels are competitive with the increasing laser intensity from 5.0 × 10(13) to 2.0 × 10(14) W/cm(2). In the case of intensity lower than 1.0 × 10(14) W/cm(2), the dissociation channel is dominant, with a minor contribution from ionization. The mechanism of dissociation includes the contributions from the bond softening, bond hardening, below-threshold dissociation, and above-threshold dissociation, which are strongly dependent on the laser intensity and initial vibrational state. Furthermore, the ionization dominates over the dissociation channel at the highest intensity of 2.0 × 10(14) W/cm(2). The reasonable origin of ionization is ascribed as the above-threshold Coulomb explosion, which has been demonstrated by the space-time dependent ionization rate. Moreover, the competition mechanism between dissociation and ionization channels are displayed on the total kinetic energy resolved (KER) spectra, which could be tested at current experimental conditions.

Shell effects in fission, quasifission and multinucleon transfer reaction

Results of the study of mass-energy distributions of binary fragments for a wide range of nuclei with Z= 82-122 produced in reactions of ions located between 22Ne and 136Xe at energies close and below the Coulomb barrier are reported. The role of the shell effects, the influence of the entrance channel asymmetry and the deformations of colliding nuclei on the mechanism of the fusion-fission, quasifission and multinucleon transfer reactions are discussed. The observed peculiarities of the mass and energy distributions of reaction fragments are determined by the shell structure of the formed fragments. Special attention is paid on the symmetric fragment features in order to clarify the origin of these fragments (fission or quasifission). The influence of shell effects on the fragment yield in quasifission and multinucleon transfer reactions is considered. It is noted that the major part of the asymmetric quasifission fragments peaks around the region of the Z=82 and N=126 (double magic lead) and Z=28 and N=50 shells; moreover the maximum of the yield of the quasifission component is a mixing between all these shells. Hence, shell effects are everywhere present and determine the basic characteristics of fragment mass distributions.

Fission Fragment Yield, Cross Section and Prompt Neutron and Gamma Emission Data from Actinide Isotopes

Recent experimental investigations on major and minor actinides at the JRC-IRMM are presented. Fission-fragment distributions of isotopes with vibrational resonances in the sub-threshold fission cross section, i. e. 234,238U, have been measured. For 234U, the impact of an increased neutron multiplicity for the heavy fragments with higher incident neutron energies has been studied as observed in experiment and also recently theoretically predicted. The impact is found to be noticeable on post-neutron mass yields, which are the relevant quantities for a-priori waste assessments. The fission cross sections for 240,242Pu at threshold and in the plateau region are being investigated within the ANDES project. The results show some discrepancies to the ENDF/B-VII.1 evaluation mainly for 242Pu around 1 MeV, where the evaluation exhibits a resonance-like structure not observed so clearly in the present work. The requested target accuracy in design studies of innovative reactor concepts like Gen-IV is in the range of a few percent. In order to be able to respond to requests for measurements of prompt neutron and γ-ray emission in fission JRC-IRMM has also invested in setting up a neutron and γ-ray detector array. The neutron array is called SCINTIA and has so far been tested with 252Cf(SF). For γ-ray multiplicity and spectrum measurements of 252Cf(SF) and 235U(nth, f) lanthanum- and cerium-halide detectors were successfully used.

Electron-impact-induced asparagine molecule fragmentation

The fragmentation of the hydrated and anhydrous asparagine molecule (C4H8N2O3) under a low-energy electron impact was studied both experimentally and theoretically. The main emphasis was given to the mechanisms of the fragment production of these molecules. A special attention was paid to the energy characteristics of the ionic fragment yield. The geometrical parameters of the initial molecule rearrangement were also analyzed.

Selective control over fragmentation reactions in polyatomic molecules using impulsive laser alignment.

We investigate the possibility of using molecular alignment for controlling the relative probability of individual reaction pathways in polyatomic molecules initiated by electronic processes on the few-femtosecond time scale. Using acetylene as an example, it is shown that aligning the molecular axis with respect to the polarization direction of the ionizing laser pulse does not only allow us to enhance or suppress the overall fragmentation yield of a certain fragmentation channel but, more importantly, to determine the relative probability of individual reaction pathways starting from the same parent molecular ion. We show that the achieved control over dissociation or isomerization pathways along specific nuclear degrees of freedom is based on a controlled population of associated excited dissociative electronic states in the molecular ion due to relatively enhanced ionization contributions from inner valence orbitals.

Velocity dependence of fragmentation yields in proton–naphthalene collision and comparison with electronic energy loss calculation

We investigate the interaction of a high velocity proton projectile (velocity between 1.41 and 2.68 au) with a gaseous naphthalene target. Fragmentation as well as multiple ionization yields are measured from the resulting mass spectra. The total fragmentation yields decrease with an increase in projectile velocity, which is in accordance with decreasing electronic stopping. Monte Carlo simulations have been performed within the framework of local density approximation to calculate the mean electronic energy loss. The theoretical cross sections are calculated from the energy loss distribution using a lower limit to internal energy deposition. The latter has been estimated from the resonant capture process measured concurrently for the same system. The velocity dependence of fragmentation yields obtained from the experiment is consistent with the modelled theoretical cross sections. Measurements of singly and doubly charged He projectiles with naphthalene show the effects of charge state equilibration and projectile charge screening.

Influences of Proline and Cysteine Residues on Fragment Yield in Matrix-Assisted Laser Desorption/Ionization In-Source Decay Mass Spectrometry

Matrix-assisted laser desorption/ionization in-source decay produces highly informative fragments for the sequencing of peptides/proteins. Among amino acids, cysteine and proline residues were found to specifically influence the fragment yield. As they are both frequently found in small peptide structures for which de novo sequencing is mandatory, the understanding of their specific behaviors would allow useful fragmentation rules to be established. In the case of cysteine, a c•/w fragment pair originating from Xxx-Cys is formed by side-chain loss from the cysteine residue. The presence of a proline residue contributes to an increased yield of ISD fragments originating from N-Cα bond cleavage at Xxx1-Xxx2Pro, which is attributable to the cyclic structure of the proline residue. Our results suggest that the aminoketyl radical formed by MALDI-ISD generally induces the homolytic N-Cα bond cleavage located on the C-terminal side of the radical site. In contrast, N-Cα bond cleavage at Xxx-Pro produces no fragments and the N-Cα bond at the Xxx1-Xxx2Pro bond is alternatively cleaved via a heterolytic cleavage pathway.

Mixed Scrub Typhus Genotype, Shandong, China, 2011

Mixed Scrub Typhus Genotype, Shandong, China, 2011

Novel determination of density, temperature, and symmetry energy for nuclear multifragmentation through primary fragment-yield reconstruction

For the first time primary hot isotope distributions are experimentally reconstructed in intermediate heavy ion collisions and used with antisymmetrized molecular dynamics (AMD) calculations to determine density, temperature and symmetry energy coefficient in a self-consistent manner. A kinematical focusing method is employed to reconstruct the primary hot fragment yield distributions for multifragmentation events observed in the reaction system $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon. The reconstructed yield distributions are in good agreement with the primary isotope distributions of AMD simulations. The experimentally extracted values of the symmetry energy coefficient relative to the temperature, $a_{sym}/T$, are compared with those of the AMD simulations with different density dependence of the symmetry energy term. The calculated $a_{sym}/T$ values changes according to the different interactions. By comparison of the experimental values of $a_{sym}/T$ with those of calculations, the density of the source at fragment formation was determined to be $\rho /\rho_{0} = (0.63 \pm 0.03 )$. Using this density, the symmetry energy coefficient and the temperature are determined in a self-consistent manner as $a_{sym} = (24.7 \pm 1.9) MeV$ and $T=(4.9 \pm 0.2)$ MeV

Double Cation Formation from the Photo-Fragmentation of the closo-Carboranes

Abstract Time-of-flight mass analysis with multi-stop coincidence detection has been used to study the multi-cation ionic fragmentation via fission of three isomeric carborane icosahedral cage compounds closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H12) following inner-shell excitation at or above the B 1s regime. Photoelectron-photoion-photoion coincidence (PEPIPICO) spectroscopy was used to study the dominant fission routes in the core level excitation regime. Series of ion pairs are identified, where asymmetric fission dominates, leading to ion pairs of different mass. The fragmentation yields and charge separation mass spectra of all three isomers are generally quite similar in that the ion pairs (H+, Y+), (Y+, Y11 +), and (Y3 +, Y9 +) dominate, where Y+ denotes the mass region from B+ to CH+. Slight differences are observed at the B 1s-threshold, where the H+ and BH2 +/CH+ ion pairs dominate for ortho- and meta-carborane, while (Y+, Y11 +) ion pairs dominate the multi-photofragment ion yield of paracarborane. These similarities and distinct differences in charge separation are discussed by considering the energetics of these three major species of ion pairs, as well as charge distributions in closo-carboranes and charge distributions in the carborane cage. It is shown that product formation via charge separation is driven by electronic relaxation, so that the lowest energy products are not necessarily formed.