The dynamics of relativistic electron fluxes in the near-Earth space in 2001–2005

This paper presents data on relativistic electron fluxes (1.5–3 MeV) measured at altitudes of 360–500 km onboard the CORONAS-F satellite. The monthly average fluxes of these particles in the Earth’s outer radiation belt are shown to greatly increase from August 2001 to September 2003. The monthly average fluxes of relativistic electrons in the Earth’s outer radiation belt in the period from August 2001 to July 2004 are also found to be strongly correlated with the monthly average velocities of the solar wind and values of the Kp-index, with this correlation breaking down after July 2004. This paper discusses the possible reasons for the discovered patterns.     

Deceleration of antiprotons from MeV to keV energies

Trapping of antiprotons for high precision measurements at the Low Energy Antiproton Ring (LEAR/CERN) requires the deceleration of the antiproton beam from typically 5.8 MeV energy down to 10 keV for final capture in standard Penning traps. Two methods, the degradation of the beam in thin foils and the deceleration of the beam in an inverse cyclotron are investigated so far. The foil technique was successfully demonstrated with trapping efficiencies up to a few 10⁻⁴ and is now routinely used in the high precision measurement of the antiprotonproton mass ratio. The degradation foil method is compared with the deceleration technique using an inverse cyclotron tested also at LEAR.     

Measurements of the polarization of protons from deuteron photodisintegration for photon energies between 282 and 405 MeV

The polarization of protons from deuteron photodisintegration has been measured at the proton lab. angles 60° and 80° for photon energies between 282 and 405 MeV. Carbon was taken as analyzer. The asymmetry was observed with optical spark chambers. The effective analyzing power of the experimental arrangement has been determined by a Monte-Carlo-calculation. For the proton lab. angel 60° the polarization increases from ?0.16 (Basel convention) at a photon energy of 282 MeV to ?0.51 at 405 MeV.     

Cross section measurements for (n, p) reaction on stannum isotopes at neutron energies from 13.5 to 14.6 MeV

Utilizing the cross sections for <'93>Nb(n, 2n)<'93m>Nb or <'27>Al(n, a)<'24>Na reactions as monitors, the cross sections for the reactions <'115>Sn(n, p)<'115m>In, <'116>Sn(n, p)<'116m>In, <'117m>Sn(n, p)<'117>In and <'117>Sn(n, p)<'117m>In have been measured at neutron energy ranging from 13.5 to 14.6 MeV through activation technology. Then, the results of present work were compared with the published experimental data.     

Spin-spin effect in the Ho total neutron cross section at energies of 0.4 and 1.0 MeV

Measurements of the spin-spin effect, σ_ss in the total cross section for polarized neutrons on polarized ¹⁶⁵Ho are reported at neutron energies of 0.4 and 1.0 MeV. The absence of an observable effect at 1.0 MeV is in contradiction with a recently reported experimental result. The results of an improved theoretical calculation of σ_ss for neutron energies below 8 MeV are presented and used with the new experimental data to obtain the new limit V_ss < 300 keV for the strength of the spin-spin potential.     

Elastic scattering of γ-rays from lead for energies from 0.145 to 1.33 MeV

Differential cross sections for elastic scattering of 889 and 1120 keV γ-rays from lead have been measured at angles ranging from 30° to 150°. These results and previously measured differential cross sections at 145, 279, 412, 662 and 1332 keV are compared with theoretical predictions taking into account Rayleigh scattering, nuclear Thomson scattering, and Delbrück scattering. The Rayleigh amplitudes of the K-shell were obtained from the theory of Brown et al., the amplitudes of the other shells from form factors calculated from relativistic HFS wave functions. Discrepancies are found at 145, 889, 1120 and 1332 keV while the experimental data at 279, 412 and 662 keV are in good agreement with the theory. A discussion of possible explanations and consequences is presented.     

Dynamics of electrons with energies up to several teraelectronvolts in oriented crystals

Stochastic aspects of the dynamics of electrons with energies from 150 GeV to several teraelectronvolts in silicon and germanium crystals oriented by the principal crystallographic directions along the beam axis are studied. The computations take into account the influence of emission of hard γ-quanta on the motion of electrons and also their multiple scattering from atoms of the target crystal. The lifetime of the electrons under channeling conditions are computed, and it is shown that this value (in the units of length) exactly coincides with the effective channeling length introduced earlier by Kumakhov [5].     

Ion irradiation of TNOs: from the fluxes measured in space to the laboratory experiments

Cosmic ion irradiation is believed to be one of the processes driving the evolution of the surface materials on TNOs. We review the laboratory simulations of radiation effects induced in likely TNO materials. In particular the production of new molecular species, the formation of refractory organics, and the spectral changes induced in icy targets and in natural bitumens are described. In order to establish if the effects seen in the laboratory are in fact responsible for the surface properties of the TNOs, the present knowledge of the ion fluxes is reviewed. For objects at selected solar distances, dosage time is given versus depth into the material. As suggested by recent experiments, the contribution of the electronic energy loss and that due to knock-on collisions are given separately. The relevance of ion-irradiation for the physico-chemical properties of TNOs is demonstrated, and the need for future investigations is outlined. To cite this article: G. Strazzulla et al., C. R. Physique 4 (2003).     

Measurements of the neutron-proton analyzing power in the energy range from 17 to 50 MeV

Measurements of the analyzing power A_y for neutron-proton scattering in the energy range from 17 to 50 MeV are reported. These data improve considerably the precision of the np data base in this energy range. Preliminary phase-shift analyses indicate reduced uncertainties in the np ³P(T = 1) phases and in the ³D(T = 0) phase shifts.     

Some cross-sections for the photo-production of neutral Pi-mesons from hydrogen at energies from 360 to 938 MeV

Some cross-sections for the photo-production ofπ ⁰-mesons from hydrogen for pion c.m. angles in the range 60°–125° are presented. The data have been obtained by measuring proton yields from a hydrogen target, thus permitting separation of single-pion production from the strong background caused by double-pion production. The values, which extend from 360 to 938 MeV, show reasonable agreement with the results of a recent phase-shift analysis.     

Measurement of helicity-dependent photoabsorption cross sections on the neutron from 815 to 1825 MeV

Helicity-dependent total photoabsorption cross sections on the deuteron have been measured for the first time at ELSA (Bonn) in the photon energy range from 815 to 1825 MeV. Circularly polarized tagged photons impinging on a longitudinally polarized LiD target have been used together with a highly efficient 4pi detector system. The data around 1 GeV are not compatible with predictions from existing multipole analyses. From the measured energy range an experimental contribution to the GDH integral on the neutron of [33.9 +/- 5.5(stat) +/- 4.5(syst)] microb is extracted.     

Analysis of neutron spectra and fluxes obtained with cold and thermal moderators at IBR-2 reactor: Experimental and computer-modeling studies

The results of experimental and computer-modeling investigations of neutron spectra and fluxes obtained with cold and thermal moderators at the IBR-2 reactor (Joint Institute for Nuclear Research (JINR), Dubna) are presented. These studies are for the YuMO small-angle neutron scattering (SANS) spectrometer (IBR-2 beamline 4). The neutron spectra have been measured for two methane cold moderators for the standard configuration of the SANS instrument. The data from both moderators under different conditions of their operation are compared. The ratio of experimentally determined neutron fluxes of cold and thermal moderators is shown at different wavelengths. Monte Carlo simulations have been carried out to determine the spectra for cold-methane and thermal moderators. The results of calculations of the ratio of neutron fluxes of cold and thermal moderators at different wavelengths are demonstrated. In addition, the absorption of neutrons in the air gaps on the way from the moderator to the investigated sample is presented. SANS with the protein apoferritin was done with both cold methane and a thermal moderator and the data were compared. The prospects for the use of a cold moderator for a SANS spectrometer at IBR-2 are discussed. The advantages of using the YuMO spectrometer with a thermal moderator with respect to the tested cold moderator are shown.     

Experimental study of the reactions of Si+(2P) ions with several small organic molecules at near thermal energies

The kinetics of the reactions of ground state silicon ions Si⁺(²P) with C₂H₆, CH₃OH, and CH₃CH₂OH has been investigated using a Selected Ion Flow Drift Tube technique (SIFDT). The reaction rate coefficients and the product distributions have been determined as functions of the reactant ion/reactant neutral average centre-of-mass kinetic energy (E _CM). The reactions studied are fast at thermal and near thermal energies and the reaction rate coefficients decrease by nearly one order of magnitude withE _CM increasing up to a few eV. It is shown that the energy dependences of the measured reaction rate coefficients can be described by the function of the formk ≈ 1/[1+ (E _CM/E _CM1) ^m ], whereE _CM1 andm are parameters which can be determined from the experimental data. The results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived complexes. These intermediate complexes decompose with unimolecular rate coefficientsk _?1 andk ₂ back to the reactants and forward to the products, respectively. The ratiosk _?1/k ₂ can be approximated for reactions studied by a power law functionk _?1/k ₂ ∞ (E _CM) ^m .     

Cross-sections for the formation of isomeric pair Ge through (n, 2n), (n, p) and (n, α) reactions measured over 13.73 MeV to 14.77 MeV and calculated from near threshold to 20 MeV neutron energies

The cross-sections for formation of isomeric pair, ⁷⁵Ge^m(σ_m) and ⁷⁵Ge^g(σ_g), through ⁷⁶Ge(n, 2n), ⁷⁵As(n, p) and ⁷⁸Se(n, α) reactions were measured at 13.73 MeV, 14.42 MeV and 14.77 MeV neutrons and also estimated using EMPIRE-II and TALYS codes over neutron energies from near threshold to 20 MeV. For each (n, 2n), (n, p) and (n, α) reaction, the cross-section initially increases with neutron energy, but starts decreasing as the neutron energy exceeds the respective threshold of (n, 3n), (n, pn) and (n, αn) reactions. The higher values of σ_m relative to σ_g reveal that the transitions of the excited ⁷⁵Ge from higher energy levels to metastable state (7⁺/2) are favored as compared to unstable ground state (1⁻/2). The present values of cross sections for formation of ⁷⁵Ge^m,g through (n, 2n) and (n, α) reactions are lower, and that of (n, p) reaction are higher compared to most of the corresponding literature cross-sections.     

Electron scattering from levels in 208Pb with excitation energies up to 6.2 MeV and spins up to J = 10

Spectra of electrons scattered inelastically from ²⁰⁸Pb have been measured in the region of excitation energies up to 6.2 MeV. The measured form factors are indicative for spins of the excited states up to J = 10.     

Excitation functions of evaporation residues in the interaction of 16O with 103Rh at incident energies up to 400 MeV

The excitation functions for production of 48 residues in the interaction of ¹⁶O with ¹⁰³Rh have been measured at incident energies varying from about 40 to 400MeV. Their analysis shows that many competing reaction mechanism contribute to the formation of these residues including complete fusion, break-up-fusion reactions and ¹⁶O inelastic scattering. The cross-sections of most of these mechanisms are obtained by independent measurements of the spectra of intermediate-mass fragments observed in the interaction of ¹⁶O on ⁹³Nb. The agreement between measured and calculated excitation functions is satisfactory in most of the cases.