N. Sakamoto

Stopping powers of metallic elements for 6.75 MeV protons

Abstract The stopping powers of sixteen kinds of metallic elements have been measured for 6.75 MeV protons. The results are systematically lower than the Riso data of H.H. Andersen et al. but agree very well with the Aarhus data except in the case of Au. The mean excitation potentials have been extracted from the present data by taking into account the Bloch-correction and the Z 1 3 -correction. As for the inner shell correction the Bonderup theory has been used. The I values thus extracted generally agree well with values given by other authors.

Mean excitation energies for the stopping power of atoms and molecules evaluated from oscillator-strength spectra

The mean excitation energy for the stopping power of matter, usually expressed by symbol I, is the only nontrivial material property in Bethe’s [Ann. Phys. 5, 325 (1930)] asymptotic stopping-power formula. It is therefore a crucial input for the evaluation of stopping power for swift charged particles. To calculate the I value of a material from its definition, it is necessary to know the oscillator-strength spectrum of the material in question over the entire range of the excitation energy. We evaluate the mean excitation energies of 32 atoms and molecules from the oscillator-strength spectra that were published by Berkowitz in 2002 [Atomic and Molecular Photoabsorption: Absolute Total Cross Sections (Academic, San Diego, 2002)]. We find that most of the present I values are consistent with those given in the literature. The I values of NO2, O3, and C60 in particular are evaluated in the present work. For buckminsterfullerene C60, an estimation of the I value is made also using the local-plasma approxima...

Stopping powers of Mylar for protons from 4 to 11.5 MeV

Abstract The stopping powers of Mylar for 4–11.5 MeV protons have been measured with an uncertainty of ±0.35%. The present results have been compared with experimental values obtained by Rauhala and Raisanen [Nucl. Instr. and Meth. B 35 (1998) 130] and with calculated values of the ICRU Report 49 and Janni [At. Data Nucl. Data Tables 27 (1982) 147]. These values agree well with each other within stated uncertainties. Requiring that experimental stopping powers are best reproduced by the Bethe-Bloch formula, we have extracted the mean excitation energy, I -value, for Mylar from the present results. In this analysis, we used the theory of Ashley et al. [Phys. Rev. B 5 (1972) 2393; Phys. Rev. A 8 (1973) 2402] for the estimation of the Barkas correction and regarded the I -value as an adjustable parameter. The I -values obtained are 80.2 eV if we adopted Bichsels shell correction [UCRL Report No. 17538 (1967)] and 80.8 eV when we used Bonderups shell correction [K. Dan. Vidensk. Selsk. Mat. Fys. Medd. 35 (1967) no. 17]. Considering the accuracy of theories this discrepancy is not physically significant. The present I -values agree well with the recommended value of 78.7 eV in the ICRU Reports 37 and 49 but disagree with the value of 75.3±1.1 eV which Hiraoka et al. [Med. Phys. 20 (1993) 135] have recently obtained.

Stopping powers of Al and Cu for protons from 3 TO 9 MeV

Abstract The stopping powers of Al and Cu for protons having energies from 3 to 9 MeV have been measured with an accuracy of ± 0.4%. The results have been compared with the Riso and the Aarhus data of Andersen et al. and with Tschalars data for Al. The mean excitation energies have been extracted from the present results using the Bonderup shell correction, the Barkas correction and the Bloch correction as 167.4 ± 0.5 eV for Al and 326.3 ± 0.6 eV for Cu. A set of parameters χ = 1.340 and b = 1.26 was used in these determinations. By using the mean excitation energies thus determined, the Bonderup shell corrections, the Barkas corrections and the Bloch corrections, stopping powers have been calculated up to 30 MeV for Al and up to 20 MeV for Cu. The calculated stopping powers agree very well with the Aarhus data. For A1, the agreement between the calculated stopping powers and Tschalars data is surprisingly good up to 30 MeV.

Stopping powers of Zr, Pd, Cd, in and Pb for 6.5 MeV protons and mean excitation energies

Abstract Stopping powers of Zr, Pd, Cd, In and Pb have been measured for 6.5 MeV protons. Mean excitation energies have been extracted from the stopping power data by taking into account the Bloch correction and Z13 correction. The Bonderup shell corrections have been used. The results agree fairly well with those of other authors.

Stopping powers of Be, Al, Ti, V, Fe, Co, Ni, Cu, Zn, Mo, Rh, Ag, Sn, Ta, Pt and Au for 6.75 MeV protons

Abstract The stopping powers of sixteen kinds of metallic elements have been measured for 6.75 MeV protons. The results are compared with the Riso and Aarhus data of Andersen et al. and also with our previous data. The present results agree very well with the Aarhus data.

Magnitude of Z13 correction and the values of mean excitation potential for 21 metallic elements

Abstract Bonderups shell correction and the Z13 correction of Ashley et al. in the Bethe-Bloch stopping formula are given on the basis of the statistical description of the atom. Consequently, adjustable parameters γ and b appear in these corrections. Using 21 stopping powers of metallic elements for 6.5 MeV protons and 14 pairs of stopping powers for protons and α particles at the same velocities, we have determined these parameter values, i.e., the magnitudes of the corrections. With the values of these corrections we extracted the mean excitation potentials for 21 metallic elements, which were found to agree well with those obtained by other authors.

Geometrical effect on the measurement of stopping powers: Angle-dependent energy loss of protons in Cu in the energy range from 3 to 7 MeV

Abstract The geometrical effect on the measurement of stopping powers, which was a hitherto unnoticed effect until our previous experiments, has been measured for Cu using 3 and 5 MeV protons. It has been confirmed again that the observed energy losses increase with increasing emergence angle. The saturation values of the increase of the energy loss can be interpreted to be nearly constant, i.e. (5.0 ± 0.5)% for 3, 5 and 7 MeV protons when ΔE(0) is nearly equal to 100 keV.

Electron loss and capture cross-sections of 1.0–3.5 MeV H0 and H+ in carbon foils

Abstract The attenuation of H 0 beam transmitted thin carbon foils of 2–20 μg/cm 2 in thickness was measured in the incident energy range from 1.0 to 3.5 MeV. Considering two components of H 0 in the ground state and H + , the electron loss cross-sections of H 0 and the electron capture cross-sections of H + were derived from the measured foil-thickness dependence of the transmitted H 0 yields. Both the present electron loss and electron capture cross-sections are larger than those obtained below 2.4 MeV with quite similar experimental methods by Gaillard et al. The present results are also slightly larger than the values below 2.5 MeV derived by applying an additivity rule to the measured charge changing cross-sections with various carbon-containing gas targets by Toburen et al. The theoretical prediction based on the Born approximation by Gillespie is found to give an excellent agreement with our electron loss cross-sections. As for the electron capture cross-section, although the OBK approximation gives slightly larger values, it can well reproduce the obtained incident energy dependence.

Stopping powers of Be, Al, Ti, V, Fe, Co, Ni, Cu, Zn, Mo, Rh, Ag, Sn, Ta, Pt and Au for 13 MeV deuterons

Abstract The stopping powers of Be, Al, Ti, V, Fe, Co, Ni, Cu, Zn, Mo, Rh, Ag, Sn, Ta, Pt and Au for 13 MeV deuterons were measured with an accuracy of 0.35% using a surface barrier silicon detector. The effect of the fringing field of the analyzing magnet was considered in the determination of the incident energy of the deuterons. Results have been reduced to the stopping powers for deuterons of 12.994 MeV that have exactly the same velocity as 6.500 MeV protons and are compared with previous stopping power results using the same targets for 6.500 MeV protons. No systematic differences were observed. The stopping powers of matter for protons and deuterons at the same velocity are concluded to be equal within the experimental uncertainty of 0.35% at the present projectile velocity.