Dechanneling of 6-MeV protons in a tungsten single crystal

The effect of energy losses of channeled particles on the results of determination of the depth dependence of the integral dechanneling function from the backscattering spectra has been investigated.     

Polarization in the inelastic scattering of 185 MeV protons

The polarizations produced in the inelastic scattering of 185 MeV protons exciting the lowest octupole states in ¹²C and ²⁰⁸Pb are measured. The data together with earlier similar measurements for ⁴⁰Ca and ⁹⁰Zr are compared with existing theoretical models. The inclusion of a deformed spin-dependent interaction of the full Thomas form in the DWBA amplitude is found to considerably improve the theoretical fits to the data. For ¹²C, however, the DWBA fit is found to be inferior to that obtained using DWIA. The strong absorption model is found to give qualitatively good fits to the data for the heavier nuclei but again fails in the ¹²C case.     

Ultra slow muons generated by laser resonant ionization of thermal muonium produced by 500‐MeV protons with hot tungsten

We report recent progress to date on the UT‐MSL/KEK “Ultra Slow Muon” project, in which thermal muonium (Mu) atoms are generated from the surface of a hot tungsten target placed at the primary 500 MeV proton beam line and resonantly ionized by intense u.v. lasers synchronized with the emission of the Mu. The positive muon ionization fragments are collected by electrostatic beam optics to form a beam of slow positive muons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Production of low-emittance MeV protons by localized electrons

Energetic proton beam generation and the suppression of transverse proton beam divergence are investigated in this paper. In laser-foil interactions, foil ions are accelerated by an ambipolar field created by accelerated high-energy electrons. The high-energy electrons are generated by the ponderomotive force of an intense laser. When an intense laser illuminates a hydrogen foil target, the electrons are strongly accelerated longitudinally, and a localized negative electrostatic potential is generated at the opposite side of the laser illumination. Foil protons are accelerated longitudinally and at the same time extracted to the central axis of the laser by the localized potential in the transverse direction. Consequently, transverse proton divergence is suppressed and a low-emittance MeV proton beam is produced.     

Generation of MeV photons and protons in laser picosecond plasmas

The results of experiments devoted to studying the generation of MeV photons and protons in picosecond laser plasmas at a laser beam intensity of 10¹⁸ W/cm² on Be, Ta, LiF and H⁷Li targets are presented. Nuclear reactions (γ, n) and (p, n) were used to detect MeV photons and protons. The number of MeV photons and protons generated in laser plasmas was found from the measured neutron yield. Possibilities of particle acceleration due to the formation of pinch structures in laser plasmas are discussed. Calculated and experimental results are compared.     

X-ray production by 1.5–11 MeV protons

K-shell ionization andL x-ray production cross-sections by proton impact have been determined from measurements ofK x-ray yields from thin targets of Ti, Fe, Co, Cu, Ni and Ag and ofL x-ray yields from Au and Pb. The proton energies varied from 1.5 to 11 MeV. A Si(Li) semiconductor detector recorded the x-rays. The total error in the measured cross-sections is mostly less than 5%.K _β /K _α ratios andL _l,β,γ /L _α ratios have been determined. Ionization cross-sections have been compared with predictions of the plane-wave Born approximation (PWBA) and the binary-encounter approximation (BEA). Both theories describe the ionization quite well: PWBA is, however, better for higher proton energies whereas BEA is superior for lower energies. An empirical formula for ionization cross-sections is derived.     

Enhanced planar channeling of MeV protons through thin crystals

At certain tilt alignments between a MeV proton beam and a planar channeling direction, a single interface lattice rotation within a crystal can result in a lower rate of dechanneling than at planar alignment in a perfect crystal. Such planar channeling enhancement arises when the beam passes through a layer thickness which is a half-multiple of the oscillation wavelength and then encounters a small interface rotation which is matched to the beam tilt angle. The beam is projected into the center of the phase space ellipse below the interface, resulting in certain trajectories undergoing a reduction in their transverse energy, in a manner analogous to stochastic cooling or atom laser cooling.     

Photoconductivity of gallium arsenide irradiated with 5 MeV protons

Several levels which develop in GaAs before and after proton irradiation were derived from the photoconductivity spectra. It is assumed that the majority of the levels which are observed after irradiation are related to uncontrollable impurities or to impurities which are activated during irradiation. The GaAs Cu samples were used to show that it is possible to activate admixtures by proton irradiation. It was established that the absolute photoconductivity is reduced during irradiation by the development of recombination centers. The average activation energy of these centers was estimated at 0.06 eV. Lattice defects are the recombination centers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 34–40, February, 1972.     

Exotic hyperfullerenes produced by irradiation of 20 MeV protons

Transmission electron microscopy (TEM) images demonstrate that two graphitic nanoparticles, a nanoparticle and a nanotube, as well as two nanotube pairs can join together under specific angles in bump-like, neck-like and L patterns with saddle surfaces at the junction. A negatively curved surface containing eight-member rings has first been observed in the L type structure. It is suggested that the large energy transfer of the proton-carbon collision plays an important role in forming such structures.     

Binary fission in Tb and Ag by 600 MeV protons

The binary fission process in ¹⁵⁹Tb and ^natAg induced by 600 MeV protons has been investigated yielding fission cross sections (1.9 and 1.0 mb, respectively) and mean values of the total kinetic energies (100 and 62 MeV, respectively).     

Model independent optical potential for protons at 155 MeV

Using the model independent procedure, 155 MeV proton optical potentials are deduced from the elastic scattering data. The nuclear interior of these potentials are less attractative than predicted by a phenomenological potentials. A comparison is done with a self consistent meson model.     

Pion production by 600 MeV protons on light nuclei

The forward cross section at E_p=600 MeV is calculated for the reaction $\text{p}\text{+(N, Z)→(N+1, Z)}{}^1\text{+π}{}^{\mathrm{+}}$ using a single-nucleon mechanism, distorted pion and proton wave functions and bound-state nucleon wave functions with realistic asymptotic behavior. Good agreement with experiment is found for ⁴He, ¹²C, and ¹⁴N.     

Breakup of 4He with polarized protons at 65 MeV

For the ⁴He(p, p³H)¹H reaction, large negative analyzing powers are observed in the FSI regions. For the inelastic scattering of protons, the angular dependence of the analyzing power is well reproduced by the single and double scattering terms of the Faddeev breakup theory.     

Inelastic scattering of 185 MeV protons from Mg and Al

A magnetic spectrometer was used for the energy analysis of protons scattered from targets of magnesium (natural isotopic composition) and aluminium. The mean energy of the incident protons in the targets was 185 MeV. A total energy resolution of 350 keV (FWHM) was achieved, which made possible the observation of the excitation of a large number of discrete levels. Energy spectra were measured in the angular region of 4° to 40° (lab system).

The results are presented partly in the form of tables giving measured excitation energies and maximum cross sections for resolved levels and partly in the form of graphs of angular distributions of the differential cross sections.

A qualitative discussion of the results is given in terms of the multipolarities of the transitions involved and comparisons are made with similar results from other experiments in inelastic scattering and in a few cases with theoretical predictions.     

Multipole-analysis in π0-photoproduction on protons belowE=234 MeV

Taking ReM _1? as a parameter ReE ₀₊, ReE ₁₊ and ReM ₁₊ are determined by a phenomenological analysis using the measurements ofHitzeroth andGovorkov et al. Taking for ReM _1? the present theoretical values ReE ₁₊ turns out to be negative. ¦ReE ₀₊¦ is smaller than former theoretical calculations suggest. The influence of the imaginary parts and of the higher multipoles is discussed.     

Deflection of MeV protons by an unbent half-wavelength silicon crystal

The interaction of a 2?MeV proton beam with an ultrathin unbent Si crystal was studied through simulation and experiment. Crystal thickness along the beam was set at 92?nm, i.e., at half the oscillation wavelength of the protons in the crystal under planar channeling condition. As the nominal beam direction is inclined by less than the critical angle for planar channeling with respect to the crystal planes, under-barrier particles undergo half an oscillation and exit the crystal with the reversal of the transverse momenta; i.e., the protons are "mirrored" by the crystal planes. Over-barrier particles suffer deflection, too, to a direction opposite that of mirroring with a dynamics similar to that of volume reflection in a bent crystal. On the strength of such coherent interactions, charged particle beams can be efficiently steered through an ultrathin unbent crystal by the same physical processes as for thicker bent crystals.     

Polarization effects in pion-photoproduction on protons below 500 MeV. II

Using the same model as in the previous paper a prediction for the polarization of the recoil protons is given in case of polarized photons. The determination ofE ⁰⁺ andE ¹⁺ from measurements is discussed. Furthermore the influence of theππ-interaction on polarization is considered. In the case ofπ ⁺-production the polarization of the recoil neutrons is investigated and the dependence of the cross section on the polarization state of the target protons is discussed.     

Dechanneling by twins

Twinned regions in Si exhibit enhanced dechanneling and narrower critical angles than the host crystal. MeV ⁴He backscattering spectra along <111> in twinned Si can be interpreted on the basis of additive contributions from host and twinned lattices.     

Atomic K-shell ionization induced by 20–50 MeV protons

By varying the energy of fast protons incident on gold, europium, silver, ribidium and copper targets, it has been possible to produce several self consistent sets of relative K-shell ionization cross sections covering the region from below to above the velocity matching peak.     

Collinear three-body disintegrations of tungsten nuclei by 1-GeV protons

The (2E, 2V) measurement method is applied to analyze the kinematics of the separation of two complementary collinear fragments of the disintegration of tungsten nuclei by 1-GeV protons. In addition to the main process of binary fission, three branches of collinear three-body disintegration, which are associated with various mechanisms of the excitation of a deformed fissioning nucleus, are observed.