Angular Distributions Of Protons Research Articles

High-precision proton angular distribution measurements of C12(p,p′) for the determination of the E0 decay branching ratio of the Hoyle state

Background: In stars, carbon is produced exclusively via the $3\alpha$ process, where three $\alpha$ particles fuse to form $^{12}$C in the excited Hoyle state, which can then decay to the ground state. The rate of carbon production in stars depends on the radiative width of the Hoyle state. The radiative width can be deduced by combining three separately measured quantities, one of which is the $E0$ decay branching ratio. The $E0$ branching ratio can be measured by exciting the Hoyle state in the $^{12}$C$(p,p')$ reaction and measuring the pair decay of its Hoyle state and first $2^+$ state. Purpose: To reduce the uncertainties in the carbon production rate in the universe by measuring a set of proton angular distributions for the population of the Hoyle state ($0^+_2$) and $2^+_1$ state in $^{12}$C in $^{12}$C$(p,p')$ reactions between 10.20 and 10.70 MeV, used in the determination of the $E0$ branching ratio of the Hoyle state. Method: Proton angular distributions populating the ground, first $2^+$, and the Hoyle states in $^{12}$C were measured in $^{12}$C(p,p') reactions with a silicon detector array covering $22^\circ<\theta<158^\circ$ in 14 energy steps between 10.20 and 10.70 MeV with a thin ($60\ \mu$g/cm$^2$) $^{nat}$C target. Results: Total cross-sections for each state were extracted and the population ratio between the $2^+_1$ and Hoyle state determined at each energy step. By appropriately averaging these cross-sections and taking their ratio, the equivalent population ratio can be extracted applicable for any thick $^{12}$C target used in pair-conversion measurements. Conclusions: We present a general data set of high-precision $^{12}$C$(p,p')$ cross-sections that make uncertainties resulting from the population of the $2^+_1$ and $0^+_2$ states by proton inelastic scattering negligible for any future measurements of the $E0$ branching ratio in $^{12}$C.

Configuration mixing in Mg28 and the Mg26(t,p)Mg28 reaction

We have studied the $^{26}\mathrm{Mg}(t,p)^{28}\mathrm{Mg}$ reaction. The nucleus $^{28}\mathrm{Mg}$ lies between $^{24}\mathrm{Mg}$ and $^{32}\mathrm{Mg}$, the latter of which is central to the ``island of inversion'' characterized by low-lying neutron $fp$-shell configurations. The present results show that the second-excited ${0}^{+}$ state in $^{28}\mathrm{Mg}$ contains large $fp$-shell occupation for the neutrons. The experiment was performed in inverse kinematics using the HELIcal Orbit Spectrometer (HELIOS) at Argonne National Laboratory. Shell-model calculations using the SDPF-MU interaction yielded level energies and two-neutron transfer amplitudes that were used in one-step distorted-wave Born approximation calculations to provide theoretical predictions of the proton angular distributions. In many, but not all cases, the data were in good agreement with theoretical predictions.

Characterization of Energetic Protons Generated in the ShenGuang-II UP Petawatt Laser Interactions with Foil Targets

The characterization of energetic protons generated in the ShenGuang-II UP petawatt laser interactions with foil targets has been systematically studied. The proton energy spectra and angular distributions are measured with a radiochromic film stack. It shows that the proton energy spectra have a Boltzmann distribution with temperature of about 2.8 MeV and cutoff energy of about 20 MeV. The divergence angles of protons vary from 10° to 60°, dependent on the proton energy. The proton source size and location are investigated via the proton point-projection mesh imaging. The proton virtual sources are found to locate tens to hundreds of microns in front of the foil target, depending on the proton energies. A Monte Carlo simulation estimates the diameter of the virtual proton source to be about 12 μm for the protons with energy of 16.8 MeV, which is much smaller than the laser focus size of about 50 μm. The spatial resolution of the 16.8 MeV proton imaging is quantified with the point spread function to be about 15 μm, which is consistent with the proton virtual source size. These results will be important for the users conducting experiments with the protons as a backlighting source on the ShenGuang-II UP petawatt laser.

Dose impact of a brass aperture on low dose tails for a proton wobbling nozzle with a multileaf collimator — A Monte Carlo study

At the Chang Gung Memorial Hospital, a wobbled beam together with a set of single scatterers produces a uniform proton field at the first and second gantries for proton radiotherapy. Conformal field shaping was accomplished by using only a multileaf collimator (MLC) or a combination of an MLC and a brass aperture (downstream of the MLC). The MLC-only technique typically delivered extra low dose tails in penumbra compared to the dose delivered using both the MLC and brass aperture/block. This study attempted to provide a physical explanation of this phenomenon by Monte Carlo simulation and phase space analysis. The Particle Therapy System Simulation Framework was used as the Monte Carlo tool for beam propagation simulation. This research team investigated four possible causes for low dose tails including, (a) same-side MLC scattering; (b) opposite-side MLC scattering; (c) MLC transmission; and (d) proton angular distribution broadened by the wobbling magnets. The results indicated that the proton angular distribution broadened by the wobbling magnets is the single cause of low dose tails and can be stopped by inserting a downstream brass aperture.

Angular Distributions of Protons for the Two-Proton Decay of Superfluid Nuclei and Diproton Correlations

The approach proposed by A.B. Migdal for describing the virtual singlet diproton state is used to show the effect diproton decay channel has on the width and the angular distribution of emitted protons in the two-proton decay of a parent 45Fe nucleus is negligible. A conclusion is reached on the leading role of the two-stage virtual mechanism of the two-proton decay of the abovementioned nucleus, which corresponds to the sequential emission of two uncorrelated protons and is described in terms of the multiparticle shell nuclear model with allowance for superfluid nucleon–nucleon correlations.

Cluster Structure of 9Be by Scattering of Deuterons

Angular distributions of protons, deuterons, tritons and alpha particles emitted in the reaction 2H+9Be at Elab=19.5 MeV were measured with an aim to shed light on the internal cluster structure of 9Be and to study possible cluster transfer of 5He. The analyses suggest a significant contribution of five-nucleon transfer in the reaction channel 9Be(d,4He)7Li.

Study of the Mechanism of the 13C(d, p)14C Reaction at E d = 15.3 MeV

The angular dependences of the differential cross sections of the 13C(d, p)14C reaction at the deuteron energy of 15.3MeV are presented according tomeasurements for the cases where the final nucleus is produced in the ground state (0+) and in the 1− excited state at 6.094 MeV. The angular distribution of protons corresponding to the sum 0+ (6.589 MeV) + 3− (6.728 MeV) + 0− (6.903 MeV) of states of the 14C nucleus that were not separated experimentally is also obtained. These experimental results are compared with their counterparts calculated by means of the FRESCO code for the mechanisms of neutron stripping and sequential neutron and dineutron transfer. The neutron and dineutron spectroscopic amplitudes are calculated for pure and mixed shell configurations. The best set of optical-potential parameters is determined for the entrance and exit reaction channels. It is shown that the neutron-stripping mechanismpermits describing themeasured angular distributions for all states of the 14C nucleus that were investigated here.

Differential cross section for the 16O(t, p)18O reaction and determination of the size of the two-neutron periphery in the 18O nucleus

Within the theoretical formalism that combines a four-body problem with themultiparticle shell model, it is shown that the cross section for the dineuteron-stripping mechanism is consistent with the experimental angular distribution of protons from the 16O(t, p)18O reaction. This makes it possible to find the wave function for the relative motion of the dineutron and 16O and to obtain thereby the probability density W(r) for the dineutron in 18O, the nn–16O interaction potential, and the root-mean-square distance 〈L〉 nn between the dineutron and 16O. The respective calculations reveal that, at r ≈ 8 fm, the dineutron probability density and a rather deep nn–16O potential become negligible, which leads to the absence of a dineuntron periphery in 18O. It seems that one can explain this fact by a rather large value (12.19 MeV) of the dineutron binding energy in this nucleus. Thus, the 18O nucleus is quite compact an object, despite the excess of two neutrons, and has a neutron skin rather than a periphery.

Some Evidence of the Cluster Struture Inside of9Be

Angular distributions of protons, deuterons, tritons and alpha-particles emitted from the reactions in the2H+9Be-system at Elab=19.5 MeV were measured with an aim to shed light on the internal cluster structure of9Be and the study of possible cluster transfer of5He. The analyses suggest a significant contribution of five-nucleon transfer in the reaction channel9Be(d,4He)7Li.

Channeling of protons in radially compressed chiral carbon nanotubes

Channeling of 10MeV protons in various types of point and area radially compressed chiral carbon nanotubes (CNTs) is considered. Monte Carlo simulation program is used for the calculation of the trajectories, energy losses and angular distributions of protons in (6,4) and (11,9) CNTs of 2000nm length, where the potential in Doyle-Turner approximation is used to describe the interaction between a proton and a nanotube. Carbon nanotubes, which are considered, are radially compressed at two points (500nm and 1500nm each), at a middle area of various lengths, at three points (both ends and at the centre) and at both ends with a middle area remaining uncompressed. The results show that in a specific case of compressed nanotube a decreased angular distribution of the beam is observed, compared even with propagation in a straight uncompressed nanotube. Furthermore, the energy distribution of channeled protons depends on the type of compression.

Monte Carlo simulations for angular and spatial distributions in therapeutic-energy proton beams

The purpose of this study is to compare the angular and spatial distributions of therapeutic-energy proton beams obtained from the FLUKA, GEANT4 and MCNP6 Monte Carlo codes. The Monte Carlo simulations of proton beams passing through two thin targets and a water phantom were investigated to compare the primary and secondary proton fluence distributions and dosimetric differences among these codes. The angular fluence distributions, central axis depth-dose profiles, and lateral distributions of the Bragg peak cross-field were calculated to compare the proton angular and spatial distributions and energy deposition. Benchmark verifications from three different Monte Carlo simulations could be used to evaluate the residual proton fluence for the mean range and to estimate the depth and lateral dose distributions and the characteristic depths and lengths along the central axis as the physical indices corresponding to the evaluation of treatment effectiveness.The results showed a general agreement among codes, except that some deviations were found in the penumbra region. These calculated results are also particularly helpful for understanding primary and secondary proton components for stray radiation calculation and reference proton standard determination, as well as for determining lateral dose distribution performance in proton small-field dosimetry. By demonstrating these calculations, this work could serve as a guide to the recent field of Monte Carlo methods for therapeutic-energy protons.

Enhanced proton acceleration by intense laser interaction with an inverse cone target

The generation and control of high-quality proton bunches using focused intense laser pulse on an inverse cone target is investigated with a set of particle-in-cell simulations. The inverse cone is a high atomic number conical frustum with a thin solid top and open base, where the laser impinges onto the top surface directly, not down the open end of the cone. Results are compared with a simple planar target, where the proton angular distribution is very broad because of transverse divergence of the electromagnetic fields behind the target. For a conical target, hot electrons along the cone wall surface induce a transverse focusing sheath field. This field can effectively suppress the spatial spreading of the protons, resulting in a high-quality small-emittance, low-divergence proton beam. A slightly lower proton beam peak energy than that of a conventional planar target was also found.

Structure of the spatial periphery of the 11Li and 11Be isobars

On the basis of the shell model with an extended basis, the structure of 9Li-9Be to 11Li-11Be nuclei is examined with allowance for the competition of jj coupling and Majorana exchange forces via considering the sequential addition of neutrons, and the respective wave functions are determined. A formalism for calculating the spectroscopic factor for a dineutron and for individual neutrons in nuclei whose wave functions incorporate the mixing of shell configurations is developed. The reactions 9Li(t, p)11Li and 9Be(t, p)11Be treated with allowance for the mechanisms of dineutron stripping and a sequential transfer of two neutrons are considered as an indicator of the proposed structure of lithium and berylliumisotopes. The parameters of the optical potentials, the wave functions for the bound states of transferred particles, and the interaction potentials corresponding to them are determined from a comparison of the theoretical angular distribution of protons from the reaction 9Be(t, p)11Be with its experimental counterpart. It is shown that a dineutron periphery of size about 6.4 fm is present in the 11Li nucleus and that a single-neutron periphery of size about 8 fm is present in the 11Be nucleus.

Characteristics of Protons Exiting from a Polyethylene Converter Irradiated by Neutrons with Energies between 1 keV and 10 MeV

Monte Carlo method has been used to determine the efficiency for proton production and to study the energy and angular distributions of the generated protons. The ENDF library of cross sections is used to simulate the interactions between the neutrons and the atoms in a polyethylene (PE) layer, while the ranges of protons with different energies in PE are determined using the Stopping and Range of Ions in Matter (SRIM) computer code. The efficiency of proton production increases with the PE layer thickness. However the proton escaping from a certain polyethylene volume is highly dependent on the neutron energy and target thickness, except for a very thin PE layer. The energy and angular distributions of protons are also estimated in the present paper, showing that, for the range of energy and thickness considered, the proton flux escaping is dependent on the PE layer thickness, with the presence of an optimal thickness for a fixed primary neutron energy.

Image potential and stopping force in the interaction of fast ions with carbon nanotubes: The extended two-fluid hydrodynamic model

We study the interaction of charged particles with a (6, 4) single-walled carbon nanotube (SWNT) under channeling conditions by means of the linearized, two dimensional (2D), two-fluid extended hydrodynamic model. We use the model to calculate analytically and numerically the image potential and the stopping force for a proton moving parallel to the axis of the SWNT, both inside and outside the nanotube at the speeds from 0.5a.u. to 15a.u. The effects of different angular modes on the velocity dependence of the image potential are compared for a proton moving in different types of SWNTs. We also compute the spatial and angular distributions of protons in the 2D two-fluid extended hydrodynamic model and compare them with the 2D two-fluid hydrodynamic model with zero damping.

Image potential in the interaction of fast ions with carbon nanotubes: A comparison between the one- and two-fluid hydrodynamic models

We study the interaction of charged particles with four different types of single-walled carbon nanotubes (SWNTs) under channeling conditions by means of the linearized, two dimensional, one-fluid and two-fluid hydrodynamic models. The models are used to calculate the image potential for protons moving parallel to the axis of the SWNTs at the speeds up to 10a.u. Numerical results are obtained to show the influence of the damping factor, the nanotube radius, and the particle position on the image potential inside the nanotube. We also compute the spatial and angular distributions of protons and compare them for the two models.

Channeling of protons in various types of radially compressed carbon nanotubes

Channeling of 10MeV protons in various types of radially compressed chiral carbon nanotubes is considered. Monte Carlo simulation program is used for the calculation of the trajectories, energy losses and angular distributions of protons in nanotubes of various lengths, where the potential in Doyle–Turner approximation is used to describe the interaction between a proton and a nanotube. Carbon nanotubes, which are considered, are radially compressed at the centre or at both ends. The results show that in some cases a decreased angular distribution of the beam is observed, compared with propagation through a straight nanotube. Furthermore, the energy distribution of channeled protons in nanotubes present a series of small peaks besides a main one, the number of which depends on the nanotube length and the angle of incidence, which in some cases are significantly high.

Single-neutron orbits near 78Ni: Spectroscopy of the [formula omitted] isotope 79Zn

Single-neutron states in the Z=30, N=49 isotope 79Zn have been populated using the 78Zn(d, p)79Zn transfer reaction at REX-ISOLDE, CERN. The experimental setup allowed the combined detection of protons ejected in the reaction, and of γ rays emitted by 79Zn. The analysis reveals that the lowest excited states populated in the reaction lie at approximately 1 MeV of excitation, and involve neutron orbits above the N=50 shell gap. From the analysis of γ-ray data and of proton angular distributions, characteristic of the amount of angular momentum transferred, a 5/2+ configuration was assigned to a state at 983 keV. Comparison with large-scale-shell-model calculations supports a robust neutron N=50 shell-closure for 78Ni. These data constitute an important step towards the understanding of the magicity of 78Ni and of the structure of nuclei in the region.

Angular Distribution of Protons Measured by the Energetic Particle Telescope on PROBA-V

Angular distribution and contamination of proton spectra measured at LEO are considered as possible sources of discrepancies between fluxes obtained by different instruments. In particular, not accounted for pitch angle distribution and East/West asymmetry of energetic proton fluxes have been suspected of leading to the reported underestimates of these fluxes by the NASA Model AP8. The Energetic Particle Telescope (EPT) was designed as a science-class instrument aimed at providing uncontaminated fluxes of electrons (0.5 – 20 MeV), protons (9.5 – 300 MeV) and α-particles (38 – 1200 MeV) getting into the instrument from within a well-defined Field Of View (FOV). The PROBA-V satellite with EPT was launched on May 7th, 2013 on a LEO, 820 km altitude, 98.7° inclination and a 10:30 – 11:30 Local Time at Descending Node. Based on the data acquired by the EPT on board PROBA-V, we account for flux angular distribution effects to provide a definitive reply to the basic question: “does AP8 underestimate E > 100 MeV proton fluxes around B/B0 = 1.1, L = 1.3”?

On determining the cross section of the supposed pentaquark $ \Theta^{+}_{}$ in the reaction pp $ \rightarrow$ $ \Theta^{+}_{}$ $ \Sigma^{+}_{}$ $ \rightarrow$ pK0 $ \Sigma^{+}_{}$

This paper addresses the problem of how to extract an upper limit on the cross section for $ \Theta^+$ production via the reaction $ pp\rightarrow\Theta^+\Sigma^+$ , where the $ \Theta^+$ is assumed to decay into the $ pK^0$ subsystem. Recent data of the COSY-TOF Collaboration, namely the angular distribution of protons in the $ \Sigma^+K^0$ helicity frame and the invariant mass spectrum of the $ pK^0$ system, were scrutinised with regard to a resonance by applying the profile likelihood method. It is found that the former distribution is best suited for setting an upper limit on the $ \Theta^+$ production, which varies between 90nb for an assumed $ \Theta^+$ mass of 1500MeV/c^2 and 56nb for 1540MeV/c^2.