Observation of a gas-solid difference in the stopping powers of (1–10) MeV/u heavy ions

doi:10.1016/0375-9601(82)90415-7

Physics Letters A

Volume 88, Issue 1, 15 February 1982, Pages 26-28

https://doi.org/10.1016/0375-9601(82)90415-7 Get rights and content

Abstract

The stopping powers of (1–10) MeV/u Kr, Xe, Pb, and U ions were measured to be smaller in gases than in solids. This gas-solid difference which is probably caused by smaller ionic charges of the projectiles in gases was found to increase with energy and atomic number of the projectile.

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Based on the available measured energy loss data, the fitting coefficients involved in effective charge parameterization of Hubert et al. formulation are re-revised and developed the energy loss formulation for heavy ions with Z₁ = 3–36 in the energy region ~0.2–3.0 MeV/n. The computed values based on the presently developed formulation are compared with the measured values and found good agreement in both elemental and polymeric materials.
Stopping powers of LiF thin films deposited onto self-supporting Al foils for swift protons
2013, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Citation Excerpt :
Thus, e.g., a deviation from additivity exceeding 50% has been reported in [15] for a He–H2 target mixture bombarded by 8.0 keV deuterons, due to large differences in electron capture and loss cross sections of the two favorably selected gases [16]. Also, conflicting experimental data have been found for solid-gas stopping power differences, and either negative or positive physical state effects were observed [17,18]. Then, a consistent statement on the Bragg–Kleeman sum rule cannot be made actually.
The energy losses of ∼(0.273–3.334) MeV protons in LiF thin films deposited by vacuum evaporation onto self-supporting Al foils have been measured using the transmission method. The thicknesses of selected and used LiF/Al target samples were accurately determined via systematic energy loss measurements for alpha particles from a very thin mixed ²⁴¹Am/²³⁹Pu/²³³U radioactive source. The samples were investigated in detail for their stoichiometry and their impurity contents by backscattering Rutherford spectrometry and nuclear reaction analysis. Then, LiF stopping powers have been determined with overall relative uncertainty of less than 2.7% arising mainly from errors in the determination of target sample thicknesses. These S(E) data are reported and discussed in comparison to previous experimental data sets from the literature and to values calculated by the Sigmund–Schinner binary collision stopping theory both for molecular LiF, and for the LiF compound assuming Bragg–Kleeman’s additivity rule. Our S(E) data show to be in excellent agreement with the latter theory for molecular LiF over the whole proton energy range explored, which supports the use of modified electronic hydrogen wave functions for evaluating atomic shell corrections in the case of low-Z₂ target materials. In contrast, they exhibit a slightly increasing deviation from theoretical values derived for the LiF compound with assuming stopping force additivity as the proton energy decreases from E ≈ 400 keV towards lower proton velocities. This deviation in excess relative to experimental data, amounting only up to (at most) ∼2.5%, can be ascribed to strong effects of 2s-state valence electrons of Li atoms within the LiF compound. Besides, the comparison to values calculated by the SRIM-2008 computer code indicates that this program satisfactorily accounts for our S(E) data above E ≈ 1.30 MeV but underestimates them with substantially increasing deviations (up to ∼11%) towards lower proton velocities where the Bragg–Kleeman additivity rule therefore appears to be inapplicable.
Comparing experimental stopping power data for positive ions with stopping tables, using statistical analysis
2012, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Using our collection of experimental data for ions from ₁₈Ar to ₉₂U, the reliability of various stopping tables is estimated by comparing them statistically to these data. For solid elements beyond 100 MeV/nucleon, Lindhard–Sørensen is found best; between 30 and 100 MeV/n, SRIM and Hubert are slightly better. Below 30 MeV/n, on the average, SRIM is 6% high in heavy targets and 5% low in light targets. In that range, Hubert is better, and sometimes also CasP 4.0. CasP describes the “positive” solid–gas effect. SRIM does not; it is therefore too high for gases near the maximum. For solid compounds, there are larger deviations from SRIM than for elements. For gaseous compounds, SRIM is too high, as for gaseous elements. But SRIM describes all ions at all energies in all targets, and is best in most cases.
The solid-gas difference in stopping powers, and statistical analysis of stopping power data
2009, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
For the purpose of treating the difference in stopping power between condensed and gaseous substances, we first discuss our method of statistical analysis of published experimental data. We distinguish between a positive effect where the difference between mass stopping powers S_solid − S_gas is positive and a negative effect where the opposite holds true. Experimentally, the positive effect has been found so far with heavy ions at high energy, and the negative effect with light ions at low energy. The positive effect is due to the difference in ionic charges and can be described by the CasP program by Grande and Schiwietz. An apparent persistence of the positive effect down to low energy is found to be mainly an artifact inherent in the stopping table of ICRU Report 73. The negative effect can be described by a difference in mean ionization potentials between gases and condensed matter. It is large for metals, much smaller for compounds. It should be possible to see both effects in one projectile – target combination.
Z<inf>2</inf> structure and gas-solid effect in the stopping of slow ions
2007, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
A recent claim by Paul of a systematic gas–solid difference in stopping cross sections for ions such as nitrogen and oxygen in the velocity range v ≃ v₀ is studied on the basis of existing experimental data. We find that all existing data support the commonly known Z₂ structure which, by and large, follows the valence structure of the target material. Existing experimental evidence is not found to support a specific gas–solid difference in the velocity range under consideration. The possibility of such an effect due to a gas–solid difference in charge state is rejected on theoretical grounds. Data for compound gases and solids are found to be well described by the Bragg additivity rule.
We have also studied nitrogen/helium and oxygen/helium stopping ratios which determine the so-called effective-charge ratio. Taking into account the scatter of experimental data, we do not find clear evidence against Northcliffe’s assumption of a stopping ratio independent of Z₂ and common for gases and solids in the considered velocity range, although the absolute value appears too high.

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Observation of a gas-solid difference in the stopping powers of (1–10) MeV/u heavy ions

Abstract

Nucl. Instrum. Methods

Mat. Fys. Medd. Dan. Vid. Selsk.

Phys. Rev. Lett.