Fragment Emission Research Articles

Electron impact excitation of glutamine molecules irradiated with an M-30 microtron with an energy of 11.5 MeV

The process of excitations of the glutamine molecules in the gas phase during collisions with low-energy electrons (0–70 eV) for samples before and after irradiation (11.5 MeV) at the M-30 microtron with doses of 10 kGy have been investigated by the optical spectroscopy method. Optical spectra were studied in the wavelength range 200–520 nm; the effects caused by both external radiation and the scanning electron beam with the 30, 50, and 70 eV energy were investigated. For the most intense emission of the molecular fragments, their thresholds and excitations’ energy dependences were determined in the range of electron energies up to 30 eV. The new effect has been established: for λ > 310 nm, the irradiated samples’ emission increased both by increasing the scanning beam’s electron energy and the emitted light wavelength. However, for values of λ < 310 nm, there is an opposite dependence. The simulation of the glutamine transformations under irradiation was carried out within the method of structural combinations, which allows determining all sets of molecular structures of glutamine without and in the presence of ‘broken’ chemical bonds. The role of radiation in the formation of metastable molecular structures, which determine the features of the optical and mass spectra of irradiated glutamine samples, is investigated.

Light fragment and neutron emission in high-energy proton induced spallation reactions * *Supported by the National Natural Science Foundation of China (11722546, 11675226) and the Talent Program of South China University of Technology

The dynamics of high-energy proton-induced spallation reactions on target nuclides of 56Fe, 58Ni, 107Ag, 112Cd, 184W, 181Ta, 197Au, and 208Pb are investigated with the quantum molecular dynamics transport model motivated by the China initiative Accelerator Driven System (CiADS) in Huizhou and the China Spallation Neutron Source (CSNS) in Dongguan. The production mechanism of light nuclides and fission fragments is thoroughly analyzed, and the results obtained thereby are compared with available experimental data. The statistical code GEMINI is employed in conjunction with a transport model for describing the decay of primary fragments. For the treatment of cluster emission during the preequilibrium stage, a surface coalescence model is implemented into the model. It is found that the available data in terms of total fragment yields are well reproduced in the combined approach for spallation reactions both on the heavy and light targets. The energetic light nuclides (deuteron, triton, helium isotopes etc) mainly created during the preequilibrium stage are treated within the framework of surface coalescence, whereas their evaporation is described in the conventional manner by the GEMINI code. With this combined approach, a good overall description of light clusters and neutron emission is obtained, and some discrepancies with the experimental data are discussed. Possible production of radioactive isotopes in the spallation reactions is also analyzed, i.e., the 6,8He energy spectra.

Emission characteristics of target black fragments in 16O-Emulsion collisions at 3.7AGeV

As a function of collision centrality, the multiplicity and angular distributions for the slowest target fragments (black particles) emitted in interactions of 16O ions with emulsion nuclei at 3.7[Formula: see text]A[Formula: see text]GeV were investigated. The multiplicity distribution is unaffected by the projectile’s energy or mass. At different impact parameters, the higher moments of multiplicity distributions of black particles were measured. The calculated values of the scaled variance (variance divided by the mean) show that the emission of slower target fragments at high energies is not a statistically independent process in all cases. At various projectile spectators, the angular distributions of the emitted black particles were investigated. The obtained data were compared to the statistical model’s predictions to describe the process responsible for producing secondary particles.

Coulomb-explosion imaging of carbon monoxide dimers

We report on experimental results obtained from collisions of slow highly charged Ar9+ ions with a carbon monoxide dimer (CO)2 target. A COLTRIMS setup and a Coulomb explosion imaging approach are used to reconstruct the structure of the CO dimers. The three dimensional structure is deduced from the 2-body and 3-body dissociation channels from which both the intermolecular bond length and the relative orientation of the two molecules are determined. For the 3-body channels, the experimental data are interpreted with the help of a classical model in which the trajectories of the three emitted fragments are numerically integrated. We measured the equilibrium intermolecular distance to be Re = 4.2 A. The orientation of both CO molecules with respect to the dimer axis is found to be quasi-isotropic due to the large vibrational temperature of the gas jet.

Complex fragment emission in dissipative binary decay of Kr74,76

The fragment emission mechanism in the binary decay of composites formed in the reactions $^{20}\mathrm{Ne}+^{56}\mathrm{Fe}$ and $^{16}\mathrm{O}+^{58}\mathrm{Ni}$ has been studied at two different excitation energies. The inclusive energy and angular distributions of the emitted fragments $^{6,7}\text{Li}$, $^{7,8,9}\text{Be}$, $^{10,11}\text{B}$, and $^{11,12,13,14}\text{C}$ have been measured in the laboratory angles ranging from ${15}^{\ensuremath{\circ}}$ to ${35}^{\ensuremath{\circ}}$ (corresponding angles in center of mass ranging from ${20}^{\ensuremath{\circ}}$ to ${50}^{\ensuremath{\circ}}$). The energy distributions of the fragments are found to be Gaussian and peaked at energies higher than those expected from fusion-fission-type reactions. The center-of-mass angular distributions of all the fragments have been found to fall faster than $\ensuremath{\approx}1/\mathrm{sin}{\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}$-like dependence and the average $Q$ values of the fragments are found to decrease with increasing the center-of-mass angle of the emitted fragment for both the systems. The above characteristics of fragments signify that they were emitted from nonequilibrium sources, produced in a highly energy damped deep-inelastic-type reaction. The lifetimes of the dinuclear composites estimated from the angular distributions of these fragments are found to be in the range of $\ensuremath{\approx}(0.5--2.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}$ s, which are smaller than the respective compound-nuclear lifetimes $[\ensuremath{\approx}(1.0--2.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21} \mathrm{s}]$. The angular-momentum dissipations estimated from the average kinetic energies of the fragments are found to be, for lighter fragments in particular, greater than those predicted by the empirical sticking limit.

Fluoropolymer Film Formation by Electron Activated Vacuum Deposition

Polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP) and polychlorotrifluoroethylene (PCTFE) were heated to their decomposition temperature in a high vacuum. The emitted fragments passed an electron cloud, condensed on a substrate and formed fluoropolymer film. Growth rate of PTFE and PHFP films increased up to a factor five in the presence of the electron cloud. Mass spectrometry revealed changes in the mass spectra of fragments generated by thermal decomposition only and formed under electron activation. The observed changes were different for each fluoropolymer. Infrared spectroscopy (IRS) showed that the structure of the films was close to the structure of the bulk polymers. Atomic force microscopy (AFM) has revealed different morphologies of PTFE, PHFP and PCTFE films, suggesting a Volmer–Weber growth mechanism for PTFE and PHFP but a Frank-van der Merwe one for PCTFE. All films were smooth at nanoscale and transparent from ultraviolet to near-infrared region. Additional radio frequency (RF) plasma ignited in the emitted fragments at a low pressure increased mechanical characteristics of the films without losing their optical transparency and smoothness.

Impact of different hydrodynamical mass transfer approaches in the spontaneous fission of Cf isotopes

Theoretical possibilities for the spontaneous emission of fission fragments from [Formula: see text]Cf parents are investigated within the framework of preformed cluster decay model (PCM). The fragmentation potential exhibits a modification from dominated asymmetric fission profile to symmetric splitting with the rise in the N/Z ratio of parent nuclei. The calculated spontaneous fission (SF) half-life times of Cf isotopes find nice agreement with the experimental data, except for [Formula: see text]Cf nucleus. Within the PCM, the hydrodynamical mass transfer among the outgoing binary fragments occurs through a cylindrical vessel connecting them. For the overlapping configuration [Formula: see text]), the two classical models namely Model A and Model B (differ in the way the radius of the connecting cylinder is controlled) are used to estimate mass transfer flow of binary fragmentation. It is observed that with change in the overlapping distance, the radius of the cylindrical vessel changes in Model A, whereas the same remains fixed in Model B. In case of Model B, the effect of cylindrical radii parameter ([Formula: see text]) is also analyzed for [Formula: see text]Cf parents at optimum neck-length ([Formula: see text]R) in view of different observable such as most probable SF fragments, preformation probability, mass transfer, the SF half-lives and the results are compared with Model A calculations. The magnitude of mass transfer, preformation probability, and hence the SF half-lives gets significantly modified on switching from Model A to Model B. Further, a large amount of mass is transferred between the asymmetric fragments as compared to the symmetric ones. The SF half-lives are shown to depend strongly on the choice of classical models as well as on the cylindrical radius parameter, [Formula: see text]. The study infers the importance of classical models to spread further light in the understanding of the dynamical behavior of fragment formation in the fission process.

Effects of cluster correlations on fragment emission in C12+C12 at 50 MeV/nucleon

The effects of cluster correlations have been studied in the $^{12}\mathrm{C}+^{12}\mathrm{C}$ reaction at 50 MeV/nucleon, using three antisymmetrized molecular dynamics (AMD) models, the AMD (AMD/D) without any additional cluster correlations, AMD/D-COALS with nucleon correlations based on a coalescence prescription for light cluster formations with $A\ensuremath{\le}4$, and AMD-cluster with an extended cluster correlation in two-nucleon collision processes and a special treatment for intermediate fragment formation with $A\ensuremath{\le}9$. The angular distributions and energy spectra of fragments have been simulated and compared with the available experimental data. It is found that the cluster correlations take a crucial role to describe the productions of light charged particles (LCPs) and intermediate mass fragments (IMFs), and the AMD-cluster studied here provides a consistent overall reproduction of the experimental data. It is also shown that the significant effects of the secondary decay processes are involved for the fragment production besides the dynamical productions in the AMD stage. Detailed LCP and IMF production mechanisms involved in the intermediate energy heavy ion collisions are discussed.

Inter-fractional monitoring of ^{12}C ions treatments: results from a clinical trial at the CNAO facility

The high dose conformity and healthy tissue sparing achievable in Particle Therapy when using C ions calls for safety factors in treatment planning, to prevent the tumor under-dosage related to the possible occurrence of inter-fractional morphological changes during a treatment. This limitation could be overcome by a range monitor, still missing in clinical routine, capable of providing on-line feedback. The Dose Profiler (DP) is a detector developed within the INnovative Solution for In-beam Dosimetry in hadronthErapy (INSIDE) collaboration for the monitoring of carbon ion treatments at the CNAO facility (Centro Nazionale di Adroterapia Oncologica) exploiting the detection of charged secondary fragments that escape from the patient. The DP capability to detect inter-fractional changes is demonstrated by comparing the obtained fragment emission maps in different fractions of the treatments enrolled in the first ever clinical trial of such a monitoring system, performed at CNAO. The case of a CNAO patient that underwent a significant morphological change is presented in detail, focusing on the implications that can be drawn for the achievable inter-fractional monitoring DP sensitivity in real clinical conditions. The results have been cross-checked against a simulation study.

Fragment emission and critical behavior in light and heavy charged systems * *Supported Council of Scientific and Industrial Research (CSIR), Govt. of India (03 (1388)/16/EMR-II)

We study the emission of fragments in central collisions of light and heavily charged systems of 40Ar+45Sc and 84Kr+197Au, respectively, using the Quantum Molecular Dynamics (QMD) model as the primary model. The fragments are identified using an energy based clusterization algorithm, i.e., the Simulated Annealing Clusterization Algorithm (SACA). The charge distributions of intermediate mass fragments [3≤ ≤12] are fitted with power-law ( ) and exponential ( ) fits in order to extract the parameters τ and whose minimum values are also sometimes linked with the onset of fragmentation or the critical point for a liquid-gas phase transition. Other parameters such as the normalized second moment , , average size of the second largest cluster , phase separation parameter ( ), bimodal parameter (P), information entropy (H), and Zipf's law are also analyzed to find the exact energy of the onset of fragmentation. Our detailed analysis predicts that an energy point exists between 20-23.1 MeV/nucleon, which is very close to the experimentally observed value of 23.9 MeV/nucleon for the 40Ar+45Sc reaction. We also find that the critical energy deduced using Zipf's law is higher than those predicted from other critical exponents. Moreover, no minimum is found for τ values of the highly charged system of 84Kr+197Au, in agreement with experimental findings and various theoretical calculations. We observe that the QMD + SACA model calculations are in agreement with the experimental observations. This agreement supports our results regarding the energy point of the liquid-gas phase transition and the onset of fragmentation.

Correlations between fission fragment and neutron anisotropies in neutron-induced fission

Several sources of angular anisotropy for fission fragments and prompt neutrons have been studied in neutron-induced fission reactions. These include kinematic recoils of the target from the incident neutron beam and the fragments from the emission of the prompt neutrons, preferential directions of the emission of the fission fragments with respect to the beam axis due to the population of particular transition states at the fission barrier, and forward-peaked angular distributions of pre-equilibrium neutrons which are emitted before the formation of a compound nucleus. In addition, there are several potential sources of angular anisotropies that are more difficult to disentangle: the angular distributions of prompt neutrons from fully accelerated fragments or from scission neutrons, and the emission of neutrons from fission fragments that are not fully accelerated. In this work, we study the effects of the first group of anisotropy sources, particularly exploring the correlations between the fission fragment anisotropy and the resulting neutron anisotropy. While kinematic effects were already accounted for in our Hauser-Feshbach Monte Carlo code, $\mathtt{CGMF}$, anisotropic angular distributions for the fission fragments and pre-equilibrium neutrons resulting from neutron-induced fission on $^{233,234,235,238}$U, $^{239,241}$Pu, and $^{237}$Np have been introduced for the first time. The effects of these sources of anisotropy are examined over a range of incident neutron energies, from thermal to 20 MeV, and compared to experimental data from the Chi-Nu liquid scintillator array. The anisotropy of the fission fragments is reflected in the anisotropy of the prompt neutrons, especially as the outgoing energy of the prompt neutrons increases, allowing for an extraction of the fission fragment anisotropy to be made from a measurement of the neutrons.

Development of INC-ELF version 2 and incorporation into PHITS: Extension to lower incident energies down to 30 MeV

Version 2 of the Intranuclear Cascade with Emission of Light Fragments (INC-ELF) code is developed and incorporated into the Particle and Heavy Ion Transport code System (PHITS). The aim of INC-ELF2 is to expand it to the lower incident-energy range of 30–200 MeV, where the original INC theory is not applicable. The refinement of the code is based faithfully on the results of basic research on direct reactions within the framework of the INC model. INC-ELF2 can deal with the emission of light fragments from nuclear reactions induced by protons and neutrons. Double-differential cross-sections are calculated by a two-step model combining INC-ELF2 and GEM (generalized evaporation model) in PHITS, and they are compared with experimental data to examine the predictive ability. Excellent agreement is confirmed for various reactions over a wide range of target masses and over the incident-energy range of 30–200 MeV.

Study of emission characteristics of the projectile fragments produced in the interaction of 84Kr36 with nuclear emulsion detector at 1 GeV

This article is focused on the characteristics of the projectile fragments of charge 1 ≤ Z ≤ 10 produced in the interaction of the 84Kr36 with nuclear emulsion detector at 1 GeV per nucleon. We have studied the average charge distribution and multiplicity distribution of the projectile fragments having charge 1 ≤ Z ≤ 10. We have also studied the emission behavior of various projectile fragments produced from the interaction with different target groups of nuclear emulsion detector. From this study we have observed that the emission of projectile fragments is strongly dependent on the interaction with different type of the target groups of nuclear emulsion detector as well as on the mass of the projectile beam. The results are compared with other experimental observations carried out at relativistic energy and found to be consistent.

Tetrahedral {HPO3} and {WO4} group simultaneously directing tri-Tb(III)-containing antimonotungstate and its photoluminescence properties

A tetrahedral {HPO3} and {WO4} group simultaneously directing tri-Tb(III)-containing antimonotungstate (AT) K3Na21H[Tb3(Ac)3(HPO3)(WO4)][B-α-SbW9O33]3·36H2O (1) has been triumphantly isolated by the aqueous reaction of Na9[B-α-SbW9O33]·19·.5H2O, Na2WO4·2H2O, H3PO3 and Tb(NO3)3·6H2O. Notably, tetrahedral {HPO3} and {WO4} groups may play the template-directing function in the formation of polyoxoanion of 1. Under the excitation at 380 nm, the emission spectrum and the decay lifetime curve of 1 have been measured. Upon the O → W LMCT excitation at 260 nm, energy transfer from AT fragments to Tb3+ ions has occurred because Tb3+ ions can absorb energy from the O → W LMCT emission of AT fragments. By switching the excitation wavelength from 250 to 390 nm, it’s available to tune the emission color of 1 from blue to green.

Conjugates of 3,4-dimethoxy-4-styrylnaphthalimide and bacteriochlorin for theranostics in photodynamic therapy

New conjugates of fluorophore based on 3,4-dimethoxy-4-styryl-1,8-naphthalimide and photosensitizer bacteriochlorin e differing in the nature of spacer fragments were synthesized and their spectral-luminescent properties were studied. The conjugates efficiently generate singlet oxygen in solution, however, the emission of the naphthalimide fragment of the conjugates is quenched to varying degrees as a result of the photoexcitation energy transfer to bacteriochlorin.

Emission characteristics of intermediate mass fragments by the $${^{84}_{36}{\hbox {Kr}}}$$ projectile in nuclear emulsion detector at 1 GeV per nucleon

This article is focused on the intermediate mass fragments emission induced by the Kr projectile at relativistic energy in nuclear emulsion. The study of correlation between intermediate mass fragments and the total charge confined in fragments for $$Z\ge $$ 2 with different targets (such as H, CNO and AgBr) shows that there is increase in mean multiplicity of intermediate mass fragments with increase in target mass. The observed anti-correlation between the mean multiplicities of particles emitted from the target and the bound system charge $$(Z_{\mathrm{b}})$$ reflects the relation of the $$Z_{\mathrm{b}}$$ to the centrality of the collision.

Anticipating Xenogenic Pollution at the Source: Impact of Sterilizations on DNA Release From Microbial Cultures.

The dissemination of DNA and xenogenic elements across waterways is under scientific and public spotlight due to new gene-editing tools, such as do-it-yourself (DIY) CRISPR-Cas kits deployable at kitchen table. Over decades, prevention of spread of genetically modified organisms (GMOs), antimicrobial resistances (AMR), and pathogens from transgenic systems has focused on microbial inactivation. However, sterilization methods have not been assessed for DNA release and integrity. Here, we investigated the fate of intracellular DNA from cultures of model prokaryotic (Escherichia coli) and eukaryotic (Saccharomyces cerevisiae) cells that are traditionally used as microbial chassis for genetic modifications. DNA release was tracked during exposure of these cultures to conventional sterilization methods. Autoclaving, disinfection with glutaraldehyde, and microwaving are used to inactivate broths, healthcare equipment, and GMOs produced at kitchen table. DNA fragmentation and PCR-ability were measured on top of cell viability and morphology. Impact of these methods on DNA integrity was verified on a template of free λ DNA. Intense regular autoclaving (121°C, 20 min) resulted in the most severe DNA degradation and lowest household gene amplification capacity: 1.28 ± 0.11, 2.08 ± 0.03, and 4.96 ± 0.28 logs differences to the non-treated controls were measured from E. coli, S. cerevisiae, and λ DNA, respectively. Microwaving exerted strong DNA fragmentation after 100 s of exposure when free λ DNA was in solution (3.23 ± 0.06 logs difference) but a minor effect was observed when DNA was released from E. coli and S. cerevisiae (0.24 ± 0.14 and 1.32 ± 0.02 logs differences with the control, respectively). Glutaraldehyde prevented DNA leakage by preserving cell structures, while DNA integrity was not altered. The results show that current sterilization methods are effective on microorganism inactivation but do not safeguard an aqueous residue exempt of biologically reusable xenogenic material, being regular autoclaving the most severe DNA-affecting method. Reappraisal of sterilization methods is required along with risk assessment on the emission of DNA fragments in urban systems and nature.

Electron trapping in strong-field dissociative frustrated ionization of CO molecules

We experimentally investigate the laser-induced dissociative frustrated multiple ionization of CO molecules; in this process one of the released electrons does not escape to the continuum but is eventually trapped into high-lying Rydberg states of the outgoing positively charged nuclear fragments at the ends of the laser pulse, leading to the formation of neutral Rydberg fragments, i.e., ${\mathrm{C}}^{*}$ or ${\mathrm{O}}^{*}$. By measuring the ejected neutral Rydberg and ionic nuclear fragments as well as the freed electrons in coincidence, we trace the probability of electron trapping by different nuclear fragments and find that formation of ${\mathrm{C}}^{*}$ is preferred to ${\mathrm{O}}^{*}$. Furthermore, the electron trapping to one of the outgoing nuclear fragments of the breaking molecule can be steered by using a phase-controlled two-color laser pulse. Our results show that Rydberg fragments are more likely to be produced for CO molecules when they are exposed to a laser field pointing from C to O. This orientation-dependent asymmetric emission of the neutral Rydberg fragments is further confirmed in the multiple ionization of CO molecules by using a single-color elliptically polarized femtosecond laser pulse.

Simulations of Fragment Correlations in the Disintegration of Non-Compact Nuclear Configurations

Non-spherical and hollow nuclear configurations have been predicted for intermediate-energy heavy-ion collisions. We have developed a simulation of the emitted heavy fragments in order to establish observables indicative of non-spherical break-up geometries. Starting with a spherical, bubble, spheroidal or a toroidal freeze-out volume configuration, a primary fragment distribution is defined with a given radial collective energy, thermal momentum distribution and intrinsic excitation energy. The outgoing fragments are allowed to propagate along their Coulomb trajectories in a self-consistent manner. Account is taken of the de-excitation of the primary fragments by nucléon and cluster evaporation. Considering 5-fragment partitions, azimuthal distributions and two-fragment correlation functions are constructed and discussed in connection with their associated break-up geometries.

Fragmentation of polymer nanocomposites: modulation by dry and wet weathering, fractionation, and nanomaterial filler.

In recent years, an increasing number of polymeric composites incorporating engineered nanomaterials (ENMs) have reached the market. Such nano-enabled products (NEPs) present enhanced performance through improved mechanical, thermal, UV protection, electrical, and gas barrier properties. However, little is known about how environmental weathering impacts ENM release, especially for high-tonnage NEPs like kaolin products, which have not been extensively examined by the scientific community. Here we study the simulated environmental weathering of different polymeric nanocomposites (epoxy, polyamide, polypropylene) filled with organic (multiwalled carbon nanotube, graphene, carbon black) and inorganic (WS2, SiO2, kaolin, Fe2O3, Cu-phthalocyanines) ENMs. Multiple techniques were employed by researchers at three laboratories to extensively evaluate the effect of weathering: ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), optical microscopy, contact angle measurements, gravimetric analysis, analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectroscopy. This work aimed to elucidate the extent to which weathering protocol (i.e. wet vs. dry) and diverse filler characteristics modulate fragment release and polymer matrix degradation. In doing so, it expanded the established NanoRelease protocol, previously used for analyzing fragment emission, by evaluating two significant additions: (1) simulated weathering with rain events and (2) fractionation of sample leachate prior to analysis. Comparing different composite materials and protocols demonstrated that the polymer matrix is the most significant factor in NEP aging. Wet weathering is more realistic than dry weathering, but dry weathering seems to provide a more controlled release of material over wet. Wet weathering studies could be complicated by leaching, and the addition of a fractionation step can improve the quality of UV-vis measurements.