M. Tosaki

Charge state dependent energy loss of high velocity oxygen ions in the charge state non-equilibrium region

Mean energy losses of high velocity bare H-like, He-like and Li-like O ions in thin carbon foils were measured in the charge state non-equilibrium region and a clear charge state dependence was observed. The screening effect of bound projectile electrons on energy losses are deduced and compared with theoretical predictions.

Energy loss of high velocity 6Li2+ ions in carbon foils in charge state non-equilibrium region

Abstract Mean energy losses of high velocity H-like Li ions in thin carbon foils were measured in the charge state non-equilibrium region. Owing to the screening effect of the bound electron, the fixed-charge stopping power for 6 Li 2+ was smaller than that for 6 Li 3+ . The projectile atomic number dependence of the fixed-charge stopping powers for H-like ions is discussed including our previous data of He, C and O ions with the same velocity. The present result is also compared with the theoretical prediction.

Energy-loss straggling caused by the inhomogeneity of target material

Rutherford backscattering spectroscopy (RBS) accompanying with the sharp 4.808-MeV resonance of proton beams in carbon has been applied to examine the energy-loss straggling in detail, which causes the broadening of proton beam energy in the penetrating path. In the present measurements, RBS peak profiles of homogeneous and inhomogeneous carbon materials have been obtained with an incident energy of 5.5MeV. Careful analyses of those profiles have revealed that the energy-loss straggling can be separated into two parts; one is collision straggling and the other is density straggling. The collision straggling is caused by the statistical fluctuation in collisions of proton with target atoms, which has been intensively studied since the theoretical work by Bohr [Philos. Mag. 30, 581 (1915)]. The density straggling is caused by the statistical fluctuation in local density of target material, which has been discussed in the present work. The random inhomogeneity as a measure of the fluctuation in the local den...

ENERGY LOSS OF 10 MEV/AMU ATOMIC HELIUM IN CARBON

Abstract Mean energy losses of 31.8 MeV neutral 3He atoms penetrating through thin carbon foils of 1.6–7.2 μg/cm2 were measured using a high-resolution magnetic spectrograph. The measured particles are those entered into the carbon foil as 3He0 and emerged from it as 3He0. From the attenuation measurement of 3He0 in the foils, we can regard the measured energy losses as those of 3He0 in a frozen charge state. The measured stopping power of carbon for 31.8 MeV 3He0 is 58.2 ± 4.9 eV/μg/cm2. Including our previous data for other partially clothed ions of the same velocity, the projectile atomic number dependence of the screening effect due to the bound electrons is roughly reproduced by the theoretical predictions based on the Born approximation.

Effect of self-induced space charge in a high pressure position-sensitive proportional counter

The response of a position-sensitive proportional counter filled with Ar + 30%CH4 counting gas under a pressure of 7 atm has been studied in detail for 8-keV incident X-rays. The counter was operated in the region of limited proportionality, where the avalanche growth is greatly affected by self-induced space charge and hence an unfamiliar distorted energy spectrum is often observed. It is confirmed that the avalanches caused by the halo effect of Ar K X-rays, emitted in photoelectric absorption of incident X-rays, have higher gas amplification as compared to other photopeak avalanches due to different origin of primary electrons. The analysis has revealed that the effect of self-induced space charge hinders the avalanche growth of photopeak events to the extent of 50% of the observed avalanche charge. Comprehensive analysis of the complicated counter response in the region of limited proportionality under high pressure is provided.

Energy losses and straggling of light ions transmitted through thin carbon foils

Abstract The energy losses of 10 MeV/amu 3 He 2+,1+ , 6 Li 3+,2+ , 12 C 6+,5+,4+ and 16 O 8+,7+,6+,5+ ions passing through carbon foils of 5–110 μg/cm2 in thickness were measured with a high resolution magnetic spectrograph. The measurement was carried out for ions emerging from foils in the same charge state as the incident beam. The measured fixed-charge stopping powers have been reported in our previous papers. In this paper, the energy loss straggling of partially clothed ions in the charge-state nonequilibrium region is reported for the first time. A double peak structure in energy loss spectra of 3 He 1+ and 6 Li 2+ ions transmitted through carbon foils of 40–50 μg/cm2, which is due to charge changing contributions, was also described before. The present study shows that these contributions also bring about a characteristic behavior in the foil thickness dependence of the straggling values. For partially clothed C and O ions, a linear relation between the foil thickness and the straggling does not hold in the thicker foil region and the straggling exhibits an abrupt increase, although the double peak structure did not appear in the energy loss spectra. A Monte Carlo simulation taking account of the charge exchange can well reproduce the energy loss straggling of 3 He 1+ and 6 Li 2+ emerging from thicker foils.

Application of a pressurized position-sensitive proportional counter to X-ray measurement

Abstract We have developed a position-sensitive proportional counter for X rays by utilizing high-pressure counting gases, up to 10 atm, with the aim of improving detection efficiency and position resolution. We show that the counter response in the region of the limited proportionality under high pressure has a specific nature, which is found to be advantageous for position measurement. The position resolution of 100 μm (FWHM) was obtained for 8-keV X rays with the use of 7 atm Ar + 30% CH4. The feasibility of the counter combined with a flat crystal of LiF (220) was examined in PIXE measurement with 5-MeV protons and an energy resolution of ∼ 20 eV was observed for Cu Kα X-rays.

Quasifree scattering in the 6Li(α, 2α)2H reaction at Eα between 77 and 119 MeV

Abstract The 6 Li(α, 2α) 2 H breakup reaction has been measured at E α = 77−119 MeV in coplanar, symmetric geometry. The projected energy spectra of the 2α correlation maps on the E 1 axis were obtained and analyzed with DWIA and PWIA calculations. The positions of the quasifree-scattering peaks are well reproduced by both calculations, which at the higher incident energies reproduced well the widths of the experimental peaks. At lower energies, the widths obtained from the DWIA calculation are wider than those observed. Spectroscopic factors, S α d , for breakup into α + d deduced from the DWIA calculation averaged 0.58. Effective numbers of α-clusters, N eff , deduced from the PWIA calculation averaged 0.22.

Energy losses and straggling of 10 MeV/amu C5+,4+ ions in charge state non-equilibrium region

Abstract It was found that the energy loss straggling of 10 MeV/amu 3He1+ and 6Li2+ ions transmitted through thin carbon foils exhibits a bump structure at the foil-thickness region where the charge-changed H-like component becomes comparable to the frozen-charged one. This characteristic behavior could be reproduced well by a Monte Carlo simulation taking account of the electron loss and capture processes. An abrupt increase of the straggling values were also observed for 12C5+ and 12C4+. In order to improve a quantitative understanding, not only the attenuation of H-like and He-like beams as a function of the foil thickness but also the electron-captured fractions for the incidence of bare and H-like beams have been measured and charge changing cross sections among the bare, H-like and He-like charge states are evaluated. A computer simulation taking account of charge exchanges can reproduce quite well the measured energy losses and straggling of partially clothed C ions in the thicker foils.

Electron loss cross sections of high velocity H-like ions in carbon

Abstract The attenuation of hydrogen atoms and H-like He, Li, C and O ions of about 10-MeV/amu due to the electron loss collisions in thin carbon foils was measured as a function of foil thickness. At the thinner foil region, the incident beams attenuated exponentially as the foil thickness increased. From the attenuation rates, we have determined the electron loss cross sections of the ground state H-like ions. The obtained cross sections are larger than the theoretical predictions based on the Born approximation, especially for projectiles of higher atomic number. They can be well explained quantitatively taking account of the contribution from the projectile excitation which leads to the ionization by the subsequent collision in the foils.