Stopping powers of LiF thin films deposited onto self-supporting Al foils for swift protons

Abstract

The energy losses of ~ ሺ0.273 െ 3.334ሻ 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 241 Am/ 239 Pu/ 233 U 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 ܵሺ‫ܧ‬ሻ 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 ܵሺ‫ܧ‬ሻ 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 hydrogenic wave functions for evaluating atomic shell corrections in the case of low-Z 2 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 ‫ܧ‬ ൎ 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 2 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 ‫ܧ‬ ൎ 1.30MeV 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.

Stopping powers and energy loss straggling for (0.9–3.4) MeV protons in a kapton polyimide thin film

“…elsewhere [12][13][14][15][16][17]25]. Then, only an account of the main experimental aspects is given in the following subsection.…”

“…The energy loss and energy loss straggling measurements were carried out at the Algiers 3.75-MV Van de Graaff accelerator whose energy calibration has been checked [16] by exploring narrow resonances in the 19 F(p, ¡ ) 16 O and 27 Al(p, ) 28 Si nuclear reactions. A primary proton beam with energy in the range 0.9 3.4 MeV, mean current intensity of ~30 nA and circular spot of ~1.5 mm diameter was directed onto a very thin Au-Si scattering target through a series of electrostatic lenses and focusing slits.…”

“…This method [12][13][14][15][16][17]25] is very powerful for macroscopic non-uniformity scanning [25] since it relates only to ∆ ( measurements achieved with good accuracy. Multi-Gaussian curves were fitted to the experimental energy loss distributions recorded for alpha particles from the mixed radioactive source crossing the kapton target.…”

“…The experimental data of energy loss and energy loss straggling widths, Δ and 5 67 , were respectively deduced from the peak positions and widths (FWHM) of the measured proton energy loss distributions. Similarly as in [12,16] the latter have been carefully inspected for their Gaussian shapes by evaluating the overall dimensionless path-length [43,44] and distribution 8 9 -skewness [12,45,46] parameters both for small (3% ≲ 01 1 ≲ 5%,) and large (20% 01 1 36%) energy loss fractions, respectively. The energy loss distributions recorded without and with the kapton foil exposed to a beam of 900 keV protons are reported in Fig.…”

“…The ion mean energy loss and energy loss straggling variance are statistical quantities of crucial importance regarding both the understanding of the fundamental aspects of ion-matter interactions and ion beam analysis various applications [1][2][3][4][5][6][7][8]. The ion mean energy loss per travelled path length, i.e., the target material stopping power, , has been extensively investigated for various ion-target combinations over a wide range of ion bombarding energies [9][10][11][12][13][14][15][16][17][18][19]. In contrast, the energy loss straggling variance, Ω…”