Energy Distribution Of Protons Research Articles

Spectral measurements of neutrons, protons, deuterons and tritons produced by 100 MeV/nucleon He bombardment

We measured angular and energy distributions of neutrons, protons, deuterons and tritons produced by 100 MeV/nucleon He ions stopping in thick carbon, aluminum, copper and lead targets using the HIMAC (Heavy Ion Medical Accelerator in Chiba) of NIRS (National Institute of Radiological Sciences), Japan by using the time-of-flight method coupled with the Δ E– E counter system. The Δ E counter of the NE102A plastic scintillator was used to discriminate charged particles from noncharged particles and to measure charged particle energy spectra. The E counter of the NE213 liquid scintillator was used to measure neutron energy spectra. The experimental spectra were compared with the calculation using the LCS code and the calculated spectra are generally in rather good agreement with the measured spectra of these four secondary particles.

Probing the two-temperature paradigm: observational tests for the basic assumptions in advection-dominated accretion flows

We calculate the flux and spectrum of synchrotron radiation produced by high-energy electrons and positrons (e±) in an advection-dominated accretion flow (ADAF) around a black hole. The e± are from the decay of charged pions which are created through proton--proton collisions. We consider both thermal and power-law energy distributions of protons, and show that the resulting e± synchrotron emission produces a characteristic spectrum between radio and X-ray frequencies. While previous signatures of the hot protons were only possible at gamma-ray energies, via the production of gamma-rays through neutral pion decay, the present results provide a more observationally tractable way of probing the proton energy distribution and the two-temperature structure in these accretion flows. We discuss a number of strong observational predictions from these systems, as well as the recent results of Mahadevan, which appear to confirm the two-temperature structure in ADAFs. We show that the results provide support for both power-law and thermal distributions of protons, with at least a third of the viscous energy going into the power law.

Mechanism of the forward-angle(d,pn)reaction at intermediate energies

The elastic breakup of the deuteron has been measured in a kinematical condition of ${\ensuremath{\theta}}_{p}={\ensuremath{\theta}}_{n}=0\ifmmode^\circ\else\textdegree\fi{}$ at ${E}_{d}=140\mathrm{MeV}$ and 270 MeV on seven targets ranging from $Z=6$ to 82. A double-peaked structure with its minimum at ${E}_{p}\ensuremath{\simeq}{E}_{n}$ is observed for all the measured triple-differential cross sections, which indicates a large contribution from Coulomb breakup. While a symmetric shape is expected for an $E1$ transition, the observed proton-energy distribution is asymmetric, showing considerable dependence on both the target and the incident energy. These data and previous data at 56 MeV have been analyzed using the post-form of the distorted-wave Born approximation (DWBA) theory. Although the calculations account reasonably well for the asymmetric shape, by including the nuclear potential, they consistently overestimate the magnitudes of the cross sections over the whole measured region. Limitations of the post-form DWBA are discussed.

Calculation of the spatial variation of relative biological effectiveness in a therapeutic proton field for eye treatment

The relative biological effectiveness (RBE) of protons under conditions suitable for eye treatment has been studied. A complete three-dimensional modelling of the beam delivery system has been performed. Proton Monte Carlo transport calculations have been performed to obtain the proton energy distributions at different positions in a water phantom including the influence of range shifter, modulator wheel, scattering foils and collimators. A beam with a kinetic energy of keV has been simulated with respect to the HMI-Berlin eye treatment facility. The dependence of the RBE on absorbed dose and position within a spread-out Bragg peak (SOBP) has been investigated with the track structure model. Due to a decreasing proton energy with depth, the energy transfer per pathlength within the SOBP increases, affecting the RBE. An RBE increasing with depth as well as with decreasing absorbed dose has been found for the endpoint inactivation of V79 and CH2B2 hamster cells. RBE values at the distal end of the SOBP up to 1.3 and 1.5 have been found at a dose of 14 Gy and 2 Gy respectively. Within the SOBP plateau, no lateral variation of RBE has been found for a given depth. The model used offers the possibility of introducing a variable RBE in treatment planning.

Interpretation of measurements of ICRF heated minority proton distributions in JET

Neutral particle analyser (NPA) measurements of emitted hydrogen flux, integrated along a chord through the plasma centre, have been used to infer a perpendicular tail temperature T⊥ of minority ion cyclotron range of frequencies (ICRF) heated protons in the Joint European Torus (JET). A relation is established between T⊥ and the perpendicular proton temperature T⊥(0) at the position of maximum power deposition. At energies E >> T⊥(0), the value of T⊥ inferred from the NPA is nearly equal to T⊥(0). In the opposite limit E << T⊥(0), it is shown that T⊥ << T⊥(0). Applying this model to NPA measurements from a JET pulse with varying ICRF power PRF, it is found that the scaling of T⊥(0) with PRF in the 2 to 10 MW range is almost linear, as expected. Moreover, calculated values of the ICRF heated proton energy content, based on deduced values of T⊥(0), agree with diamagnetic measurements. The NPA measurements thus give access to a fundamental property of the heated proton energy distribution, which plays a crucial role in sawtooth stabilization

Impurity induced neutralization of megaelectronvolt energy protons in JET plasmas

A neutral particle analyser was deployed on JET for a measurement of the distribution function of megaelectronvolt energy protons driven by the high power ion cyclotron resonance frequency heating of deuterium plasmas in the hydrogen minority scheme. Unexpectedly, efficient neutralization of megaelectronvolt energy protons was observed in the plasma centre without recourse to injection of a beam of atoms to provide electron donors for charge exchange neutralization reactions. A model is presented that elucidates the role of carbon and beryllium, the main intrinsic impurities in JET plasmas, in this process and establishes charge exchange between hydrogen-like ions of the impurities and protons as the main neutralization process. A model calculation for deducing the proton energy distribution function f(Ep) from the measured hydrogen flux is described. The effects of uncertainties in neutralization cross-sections on the inferred f(Ep) are examined. The validity of this model of impurity induced neutralization (IIN) is tested by using it to describe the measured hydrogen flux in different conditions of plasma heating and fuelling. A crucial point in making these tests was to use measured local values of bare impurity ion densities; the required measurements were realized using charge exchange spectroscopy. Using IIN modelling and a procedure in which a known change in the density of deuterium atoms at the plasma centre was made by applying neutral beam injection, we have deduced the background thermal deuterium atom density at the plasma centre, which is an important new diagnostic result. Concerning future experiments, the model predicts that carbon and beryllium impurities will be major contributors to neutralization of hydrogenic ions (protons, deuterons and tritons) in ITER plasmas, for ion energies E<or=1 MeV/u. According to these estimates measurements of the distribution function, in the megaelectronvolt energy range, of ion cyclotron resonance frequency heating driven ions of hydrogen isotopes

Enhancement of stratospheric aerosols after solar proton event

Abstract. The lidar measurements at Verhnetulomski observatory (68.6°N, 31.8°E) at Kola peninsula detected a considerable increase of stratospheric aerosol concentration after the solar proton event of GLE (ground level event) type on the 16/02/84. This increase was located at precisely the same altitude range where the energetic solar protons lost their energy in the atmosphere. The aerosol layer formed precipitated quickly (1–2 km per day) during 18, 19, and 20 February 1984, and the increase of R(H) (backscattering ratio) at 17 km altitude reached 40% on 20/02/84. We present the model calculation of CN (condensation nuclei) altitude distribution on the basis of an ion-nucleation mechanism, taking into account the experimental energy distribution of incident solar protons. The meteorological situation during the event was also investigated.

Determinations of the Neutron-Neutron Scattering Length a nn from Kinematically Incomplete Neutron-Deuteron Breakup Data Revisited

We review published analyses of the final-state-interaction enhancement observed in proton energy distributions obtained from kinematically incomplete neutron-deuteron breakup experiments. We compare the results derived from these analyses for the neutron-neutron scattering length, ann, with our results based on a rigorous treatment of the three-nucleon Faddeev equations in conjunction with the use of realistic nucleon-nucleon potentials. Our values for ann deviate outside the quoted uncertainties from the ones obtained in the previous analyses where simplified nucleon-nucleon interaction models were employed. In contrast to the previous determinations, the present results for ann are in clear disagreement with the values for ann based on π−-deuteron capture experiments. Unless inconsistencies in the experimental neutron-deuteron breakup data at low energies can be resolved and the neutron-deuteron breakup data at low energies can be resolved and the influence of possible three-nucleon-force effects can be reliably determined, we recommend that one not resort to the kinematically incomplete neutron-deuteron breakup reaction as a tool for determining a quantity as important for nuclear and particle physics as is the neutron-neutron scattering length ann.

Effects of nuclear interactions on energy and stopping power in proton beam dosimetry

Abstract Most experimental methods for proton beam dosimetry require stopping power values and proton energy distributions in the irradiated materials. At proton energies of interest in radiotherapy, nuclear interactions in biological tissue or in tissue-equivalent materials are not negligible. As a consequence of nuclear interactions the primary proton fluence is attenuated and lower energy secondary protons and other charged particles are generated. Whenever the proton energy has to be determined along the beam path also this low-energy component should be accounted for. The energy spectra due to primary and secondary protons in a tissue-equivalent material were obtained by a Monte Carlo simulation based on the FLUKA code. The results obtained for various incident energies from 60 to 300 MeV show that the proton energy spectra along the depth of the irradiated material can appreciably depend on the amount of proton nuclear interactions. If the effect of nuclear interactions is not accounted for in determining the proton energy distribution, deviations even greater than 10% can occur in the corresponding stopping powers. The consequences of this effect on absorbed dose determination are discussed and quantitatively assessed in the energy range of interest.

Electron impact ionization of

The electron impact ionization cross section of is calculated using a distorted-wave approximation. The calculated cross section is compared to the experimental results of Peart and Dolder. The simplicity of the system allows an assessment of the accuracy of the distorted-wave approximation without complications from inaccuracies in the target state, initial continuum state, or final continuum states. The agreement with experiment is poor at low energies but improves substantially at higher energies. A differential cross section at an incident electron energy of 103 eV is presented. The proton energy distribution after the ionization is presented for large incident electron energy.

Determination of the flux and energy distribution of energetic solar protons in the past 2 Myr using lunar rock 68815

Cosmogenic 21Ne, 22Ne, 38Ar, and 3He produced by nuclear interactions of energetic (>10 MeV) solar protons were determined in 11 depth samples of lunar rock 68815. Concentrations of these proton-produced, SCR nuclides smoothly decrease from the rock surface down to 4.3 cm, where a galactic cosmic ray (GCR) component dominates. The cosmogenic 21Ne 22Ne isotopic ratio shows a systematic change with depth, from the characteristic GCR value of 0.79 at 4.9 cm to a mixed SCR + GCR ratio of 0.66 near the surface. The surface exposure age for 68815 calculated from both SCR and GCR components for 21Ne, 22Ne, and 38Ar agrees with the reported 81Kr-Kr exposure age of 2.04 Myr. Theoretical SCR + GCR depth profiles were calculated from cross-section data for different assumed spectra of energetic solar protons ( R 0, or rigidity, values of 50–125 MV) and for different rock surface erosion rates (0–3 mm/Myr). These theoretical SCR profiles were added to GCR profiles and statistically compared with measured data by minimizing the standard deviation of the least squares statistical fit and by requiring the GCR component in the 4.3 cm sample to be >90% of the measured concentration. SCR 21Ne, 22Ne, and 38Ar give the following results for energetic solar protons over the last 2 Myr. For a preferred erosion rate of 1 mm/Myr and R 0 of 80–90 MV, J(4 π, E > 10 MeV) − 58–73 p/cm 2/ s; for the broader possible range of R 0 values of 70–100 MV, J(4 π, E > 10 MeV) − 49–92 p/cm 2/ s. These proton fluxes increase by ~ 12 and ~ 24% for erosion rates of 2 mm/Myr and 3 mm/Myr, respectively. These same data analysis techniques were also applied to literature depth profiles for SCR radionuclides in rock 68815. 26Al and 53Mn give proton fluxes comparable to those obtained from neon and argon at R 0 values of 70–85 MV, but give somewhat higher J values at larger values of R 0. Proton fluxes characterized by 81Kr and 14C tend to be higher compared to the other nuclides. The most likely reason for different J values determined from different SCR nuclides is errors in cross section data, although measurement errors and temporal variations in J cannot be excluded.

Measurement of proton energy distribution sputtered from hydrogenated metallic glass alloy

Abstract The energy distribution of protons sputtered from a metallic glass sample Zr50Ni25Cu25 with 90% hydrogen embedded in the lattice was investigated. The energy distribution was measured for various energies of the primary Ar+ ions. It turns out that the energy dependence of the emitted protons is well represented by a combination of a Maxwell-Boltzmann distribution function for the sputtered neutrals and the ionisation probability of the hydrogen atoms. We conclude that the hydrogen atoms embedded in the disturbed lattice of the alloy behave like an ideal gas with a high atom temperature. The temperature determined in the experiments is in a good agreement with the energy transferred from the primary ions to the hydrogen atoms at the surface calculated by computer simulations.

Electron impact ionisation of H 2 (D 2) molecules: kinetic energy distributions of H + (D +)

The electron impact dissociative ionisation of H 2 and D 2 molecules, at 40 and 100eV electron impact energy, has been studied using the time of flight technique, to determine the whole kinetic energy distribution of protons and deuterons, including the low energy part of the distributions. The contribution of autoionising states to the dissociative ionisation is discussed.

The dissociative ionization of hydrogen by fast He + ions

The energy and angular distribution of fragment protons produced in 5–25 keV He + −H 2 collisions has been investigated. The fragment protons are found to have energies corresponding (a) to Franck-Condon transitions to well known one excited electron repulsive states giving protons with energies of 4–15 eV and (b) especially at energies below 10 keV to two electron autoionizing states which produce protons with energies ≤ 5 eV. The observed angular distributions show that this latter process occurs predominantly in the C 2v conformation in accord with predictions based on a triatomic correlation diagram which indicates that the primary excitation mechanism is an avoided crossing along with rotational coupling in this conformation.

A discussion of the compared advantages and drawbacks of the use of the α parameters matrix effects correction method of PIXE measurements on infinite or intermediate thickness targets

The α parameters method for calculating matrix effects correction factors in PIXE has been initially established for intermediate thickness samples. It consists of the simultaneous acquisition of the PIXE spectrum along with the energy distribution of protons elastically scattered by a thin carbon foil located behind the PIXE target. These experimental data, associated with an experimental measurement of the X-rays transmission factor T, allow the calculation of the matrix correction factors CF. The main interest of the α parameters method is that contrary to other correction methods it does not require a priori knowledge of the major element composition of the matrix. We have demonstrated that the formalism of the α parameters method can be extrapolated to deal with infinitely thick samples. In this case, one obtains α's by two PIXE measurements performed either at different beam energies or in different geometric configurations. In this paper we summarize and compare the two methods for permitting one to choose between them when the type of sample to be studied allows it.

H+-H- coincidences from the three-body dissociation of excited H3+

The laboratory energy distribution of protons in coincidence with an H[sup [minus]] ion, resulting from the dissociation of excited H[sub 3][sup +], has been measured for H[sup +]-H[sup [minus]] pairs emitted along the beam for 4.0-keV H[sub 3][sup +]-He collisions. An approximate energy distribution of H[sup +]-H[sup [minus]] pairs for the collinear configuration of the dissociation products is obtained by transforming the measured laboratory spectrum to the H[sub 3][sup +] center-of-mass (c.m.) frame. Coincidence data suggest that the reaction producing H[sup +]-H[sup [minus]] pairs where the H[sup +] ion has near-zero energies ([lt]0.5 eV) in the c.m. frame is a low-probability process. We have also computed the adiabatic Born-Oppenheimer energies of H[sub 3][sup +] ions using a full configuration-interaction calculation with a basis set of atomic orbitals consisting of 1[ital s], 1[ital s][prime], 1[ital p][prime], 2[ital s], and 2[ital p] centered on the protons forming an isosceles ([ital C][sub 2[ital v]] symmetry) or an equilateral ([ital D][sub 3[ital h]] symmetry) triangle. The states leading to asymptotic H[sup +]+H[sup +]+H[sup [minus]] limits have been identified by calculating [l angle]1/[ital r][sub 12][r angle][sup [minus]1], the inverse of the expectation value of the electron-electron repulsion term. The states identified by this procedure have more » adiabatic Born-Oppenheimer energies of 40--45 eV above the H[sub 3][sup +] ground state at the H[sub 3][sup +] equilibrium separation. The limits on the total available internal energy to be shared by the three dissociation products that one obtains from the experimentally determined H[sup +]-H[sup [minus]] coincidence spectrum are consistent with the identified H[sub 3][sup +] excited states. « less

Characterisation of thin layers in processed silicon

Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA), are routinely used in the analysis of electronic materials. Application of these techniques together provides both light and heavy elemental concentration profiles to a depth of several microns. Examples are given of the analysis of layers of CVD produced Si 3N 4 and metallised porous silicon using RBS, ERDA and (d,p)-NRA), with elemental depth profiles being extracted to a depth of about 5 μm. Computer simulations of (d,p) spectra from carbon, nitrogen and oxygen, illustrating the expected proton energy distributions, are also presented.

Search for nuclear-structure effects in proton evaporation spectra.

The energy distribution of protons from many reaction channels were studied following the fusion of $^{29}\mathrm{Si}$ and $^{58}\mathrm{Ni}$ at 110 MeV. Channel-dependent and angular-momentum-dependent effects were clear, but no evidence was found for structural effects within any final nucleus, contrary to recent claims.

Fluorine studies with a small accelerator

A small (700 kV) accelerator has been used for studying fluorine in various solids and thin films, via the resonant nuclear reaction (RNR) technique. The strong and relatively narrow resonance in the 19F(p, αγ) 16O reaction at 340 keV proton energy turns out to be the most convenient way of determining this element with a high sensitivity at low proton energies. With a typical beam resolution of 1 keV, and a resonance width of 2.4 keV, the depth resolution of fluorine in most materials is in the 0.01 mg/cm 2 range. A program for a microcomputer that calculates the excitation curve, given a certain F profile, has been developed and applied to various cases. The proton energy distribution is assumed to be Gaussian; straggling is considered. The F profile may be entered point by point or with any given function. By comparing the calculated and measured F excitation functions, a sensitivity of 10 19 atoms/cm 3 is estimated.

An on-line beam energy monitoring technique for a compact proton cyclotron

A well-collimated proton beam from the AEG-Compact Cyclotron of Technische Universität, Berlin was scattered with a 125 μm thick nickel foil by placing it at 45° and 135° with the beam direction. The proton energy distributions were detected with a Si(Li) surface barrier detector. The energy shifts of the elastic scattering peak, caused by angular orientation of the foil, were calculated using the Bethe-Bloch stopping power formula and compared with the observed values. An in situ channel calibration curve was constructed to estimate the mean energy the cyclotron proton beams. The uncertainty of the energy estimation was calculated from the half width at half maximum (HWHM) of the scattering peaks.