Barkas-effect Parameter Research Articles

Stopping power of palladium for protons in the energy range 0.300–3.100 MeV

The stopping power of palladium for protons has been measured using the transmission method with an overall uncertainty of around 5% over the energy range Ep=(0.300–3.100)MeV. These stopping power data are then compared to stopping power values calculated by the SRIM-2010 code and to those derived from a model based on the dielectric formalism. Subsequently, and within the framework of the modified Bethe–Bloch theory, this stopping power data were used for extracting Pd target mean excitation and ionization potential, (I=468±5eV), and Barkas effect parameter, (b=1.51±0.06). A good agreement is found between the obtained results and values reported in literature.It is worth mentioning that these are the first reported results for protons on palladium over this energy range, which is often used in IBA applications, such as Rutherford Backscattering Spectrometry (RBS) and Proton Induced X-ray Emission (PIXE).

Effects of the projectile electronic structure on Bethe–Bloch stopping parameters for Ag

Abstract Energy losses of protons and alpha particles in silver have been accurately measured under the same experimental conditions over the velocity range E lab = ( 0.192 – 2.595 ) MeV/amu using the transmission method. Deduced S ( E ) stopping powers are compared to most accurate ones from the literature, to values generated by the SRIM-2008 computer code and to ICRU-49 compilation. They were analyzed in the framework of modified Bethe–Bloch theory for extracting Ag target mean excitation and ionization potential, I, and Barkas effect parameter, b. Values of ( 466 ± 5 ) eV and 1.20 ± 0.01 for these two parameters were inferred from the proton S ( E ) data while the alpha particle data yielded values of ( 438 ± 4 ) eV and 1.38 ± 0.01 , respectively. The (I, b) stopping parameters thus exhibit opposite variations as the projectile charge increases, similarly as we have found previously for nickel [6] . This can be ascribed only to an effect of the projectile electronic structure at low velocities. The obtained results are discussed in comparison to previous ones reported in the literature.

Effects of the projectile electronic structure on stopping parameters for nickel

The stopping powers of nickel foils for 1H+, 2H+ and 4He2+ ions have been accurately measured over the energy range E≈(0.166−2.725)MeV/amu. The data were compared to those reported in the literature and to values derived by the SRIM-2003 code. They were analysed in the framework of the modified Bethe–Bloch theory to extract the target mean excitation and ionisation potential, I, and the Barkas effect parameter, b. The values derived from the proton and the alpha particle data are {I=(311.11±2.61)eV, b=1.38±0.01} and {I=(276.12±2.84)eV, b=1.58±0.01}, respectively. They thus show opposite variations of the I and b parameters as the projectile charge increases, presumably due only to the incident ions electronic structure. Besides, the reduced stopping power data for incident deuterons show to be fully consistent with those for protons indicating no effect of the projectile isotopic structure on the target stopping parameters. These results are discussed in comparison with ones reported in the literature.

Stopping powers of polycarbonate for 0.36–5.94-MeV protons and 1.0–24.0-MeV α particles

The stopping powers of polycarbonate for protons of energy 0.6–5.9 MeV and α particles of energy 2.0–24.0 MeV have been measured in a transmission experiment employing thin-foil targets. The essence of the novel experimental method employed in the present measurements is to record both projectile energy and time of flight while constantly alternating measurements with and without the target foil in place. The accuracies of the proton data and α-particle data range from 2.0% to 3.0% and 2.2% to 2.7%, respectively. All of the resulting measurements were analyzed in terms of modified Bethe–Bloch theory in order to extract values of the target mean excitation energy (I) and Barkas-effect parameter (b). The composite results for the two projectiles are that I=71.52 eV and b=1.13, the former value lying about one standard deviation below the additivity value and the latter value lying about one standard deviation below the expected value of 1.4±0.1. Previous measurements of the stopping power of polycarbonate for Li7 ions were analyzed by the same method, but with the inclusion of an effective charge parameter (λ). The proton and α-particle data, with a few lower-energy points included, were analyzed for a three-parameter fit, also. Results for the three projectiles studied indicate both internal consistency and agreement with expectations based on modified Bethe–Bloch theory.

Evidence for observed projectile- z dependence in values of target parameters extracted from stopping power measurements

One version of modified Bethe–Bloch stopping power theory features two parameters characteristic of the target material, the mean excitation energy and the Barkas-effect parameter, that can be evaluated through fits to accurate stopping power measurements. In several recent investigations, the values of these parameters thus determined have revealed a dependence on projectile atomic number. Most of those studies have featured target materials possessing aggregation effects, such as solid compounds and alloys. In the current investigation, the search for systematics in projectile- z dependence has been extended to encompass other target materials, including elemental targets. Most of the results are corroborative of the previously reported trends.

Analysis of measurements of stopping powers of formvar, polyimide, polysulfone, and vyns for 3.6 to 10.5 MeV 7Li ions

AbstractThe stopping powers of formvar, polysulfone, polyimide, and vyns for 7Li projectiles have been measured with the transmission technique and thin foil targets. The experimental data have been analyzed in terms of modified Bethe–Bloch theory to extract characteristic values of the mean excitation energy and Barkas effect parameter, as well as to study the effects of including a single effective charge parameter. Results of this investigation are in general supportive of the outcomes of earlier similar studies with protons and α‐particles traversing the same target materials in the sense that previously reported trends in projectile‐dependent behavior of values of mean excitation energy and Barkas effect parameter are followed in most cases. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Analyses of stopping power measurements for 0.90–2.50 MeV protons and deuterons traversing Al 2O 3 targets

Recently reported measurements of the stopping power of Al 2O 3 for 0.90–2.50 MeV protons and deuterons have been analyzed in terms of modified Bethe–Bloch theory. Values of the mean excitation energy ( I) and Barkas-effect parameter ( b) have been extracted from the data, yielding results for I and b, respectively, of 176.8 eV and 0.83 for protons, and of 182.7 eV and 1.02 for deuterons. These values of I exceed the additivity-based value by 32% for proton data and by 36% for deuteron data. Moreover, both extracted values of b lie well below the expected interval of 1.3–1.5.

Values of modified Bethe–Bloch stopping power parameters for polysulfone extracted from stopping power measurements with light projectiles

Recent measurements of the stopping powers of polysulfone for 0.66–1.74 MeV protons and 1.04–3.20 MeV alpha particles have been analyzed in terms of the modified Bethe–Bloch theory in order to extract values of the parameters characterizing the formalism utilized. Resulting values of mean excitation energy ( I) and Barkas-effect parameter ( b), respectively, were 83.3 eV and 1.05 for proton data, and 81.1 eV and 1.38 for alpha particle data. The lower energy alpha particle data were included by employing a single effective charge parameter ( λ) evaluated at 1.63. The composite weighted value of mean excitation energy, 82.9 eV, lies some 6% above the additivity-based estimate, whereas the corresponding value of Barkas-effect parameter, 1.22, agrees quite well with the prescribed interval of 1.4±0.1.

Values of Bethe–Bloch stopping power parameters for Vyns (vinylchloride–vinylacetate copolymer) extracted from stopping power measurements with 0.55–1.75 MeV protons and 1.03–3.22 MeV alpha particles

Recent transmission-type measurements of the stopping powers of Vyns (a vinylchloride–vinylacetate copolymer) for 0.55–1.75 MeV protons and 1.03–3.22 MeV alpha particles have been analyzed in terms of modified Bethe–Bloch stopping power theory in order to extract values of the parameters known as the mean excitation energy ( I) and Barkas-effect parameter ( b). The weighted average value of I thus established, 110.8 eV, exceeds the prediction based on linear additivity by some 3%, and the weighted average of b, 1.54, agrees very well with expectations. The results of this analysis are compared with those from a previous similar study of another material having essentially the same average atomic number and atomic weight but quite different atomic composition, called Kapton.

Bethe-Bloch stopping-power parameters for GaAs and ZnSe

If one is to calculate the stopping power for a specified projectile–target combination within the energy interval of applicability of modified Bethe–Bloch theory, values of several parameters appearing in the formulation must be ascertained. In the past, the author has established such values for numerous target materials through fits of stopping-power measurements with modified Bethe–Bloch theory. However, the semiconductor materials ZnSe and GaAs have not yet been thus characterized. A set of very recent measurements of the stopping powers of each compound for low-energy protons and alpha particles, reported by members of the Helsinki group, has been analyzed in order to remedy this dearth of parameter values. Moreover, some corresponding measurements for 7Li ions traversing ZnSe have been analyzed for the purpose of obtaining the value of a single effective charge parameter. Results of these studies are reasonably consistent with expectations, and values are recommended for the mean excitation energy and the Barkas-effect parameter for each compound. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 919–924, 1998

Bethe-Bloch Stopping Power Parameters for Al, Cu, and Ag Extracted from Recent Accurate Measurements

Accurate measurements of the stopping powers of Al, Cu, Ag, and Au for protons, ..cap alpha.. particles, and Li ions have been analyzed to extract values of mean excitation energy (I) and Barkas-effect parameter (b) for each target material. Two versions of shell corrections were employed, with only one yielding consistent, plausible results. Recommended values of I and b for Al, Cu, and Ag are, respectively, 165 +/- 3 eV and 1.37 +/- 0.05, 329 +/- 4 eV and 1.36 +/- 0.06, and 483 +/- 5 eV and 1.30 +/- 0.07.