Energy Loss Straggling Of Protons Research Articles

The free electron model and the electronic energy losses of protons at low velocities interacting with polycrystalline tantalum

In this letter, we report experimental data and theoretical work on the electronic energy loss and energy loss straggling of protons transmitted through self-supported thin films of tantalum in a polycrystalline tetragonal phase . Low-energy protons with energies below 10 keV and Ta films with nominal thickness of 6, 9 and 12 nm are used. The aim of this work is to understand the unexpected values of the Ta stopping power for low-energy proton backscattering reported recently, which are far from the prediction of the standard free electron gas model and semi-empirical approaches. This had led the authors to conclude the failure of the free electron model. Our transmission measurements confirm these experimental results. In this work, a qualitative discussion and quantitative explanation of our experimental results is given, using an approach based on the density functional theory within the framework of the free electron gas (FEG) model. We performed semiclassical deterministic trajectory simulations and employ the local density approximation model, using an inhomogeneous electron density distribution and the polycrystalline character of Ta samples.

Target electron collision effects on energy loss straggling of protons in an electron gas at any degeneracy

The purpose of the present paper is to describe the effects of target electron collisions on proton energy loss straggling in plasmas at any degeneracy. Targets are considered fully ionized so electronic energy loss is only due to the free electrons. The analysis is focused on targets with electronic density around solid values ne≃1023cm−3 and with temperature around T≃10eV; these targets are in the limit of weakly coupled electron gases. These types of plasma targets have not been studied extensively, though they are very important for inertial confinement fusion. The energy loss straggling is obtained from an exact quantum-mechanical evaluation, which takes into account the degeneracy of the target plasma, and later it is compared with common classical and degenerate approximations. Then electron collisions in the exact quantum-mechanical straggling calculation are considered. Now the energy loss straggling is enhanced for energies smaller than the energy before the maximum, then decreases around this maximum, and finally tends to the same values with respect to noncollisional calculation. Differences with the same results but not taking into account these collisions are as far as 17% in the cases analyzed. As an example, proton range distributions have been calculated to show the importance of an accurate energy straggling calculation.

Large energy loss straggling of protons and He ions in Mylar foils

Nuclear reaction analysis often requires polymer or thin metal foils to be inserted in front of the detection system to stop scattered incident ions from entering the detector. It is important to completely understand the straggling processes in the foil if true target depth profiles are to be extracted from the energy loss profiles of the reaction product particles. Generally Bohr straggling is used to account for energy spreads in these foils. This, however, has no ion energy dependence, is good mainly for energy losses much less than 20% and can underestimate straggling by a factor of 5 or more for large energy losses. This paper reports on proton and helium ion straggling in foils where the fractional energy loss ( ΔE / E ) exceeds the Bohr limit of 20% and gives simple methods of calculating the straggling from the stopping power of the ions in the foils.

Energy loss straggling of protons and He ions in gold from 0.1 to 1.0 MeV/u

Abstract Energy loss straggling of protons (atomic and molecular beams) and He ions in gold has been measured in the region of the stopping power maximum with a high resolution electrostatic analyser. The results are compared with the predictions of Bethe-Livingston and Lindhard-Scharff theories. Contributions from additional stragglings are investigated in solids, where they are of practical interest. Some results for energy loss and straggling of 14N and 16O ions in the range 20 keV/u to 60 keV/u are also given and compared to the velocity proportional theory.

Dependence of energy loss of light ions in Au on scattering angle and target thickness in the energy interval 25 to 500 keV/amu

The integral energy losses of H +, He + and He 2+ ions in thin gold foils at incident energies 40 to 500 keV have been determined experimentally. Pre-equilibrium stopping in the near-surface metal layers is found. Measurements of the energy loss straggling of protons in Au in the 9–45 nm thickness range are also been made. The straggling data are compard with the theories. The experimental angular dependence of the energy loss for protons are compared with the results of a Monte Carlo simulation of particle penetration through a foil.

Energy Loss Straggling of Protons in Water Vapour

This paper describes a calculation of energy loss and energy deposition distributions in a 1 µm diameter spherical site in a water medium irradiated by 20 MeV or 2 MeV protons. The calculation is designed to indicate the effects of proton energy loss straggling and of energy transport by secondary electrons.

Energy Loss Straggling of Protons in Water Vapour

This paper describes a calculation of energy loss and energy deposition distributions in a 1 µm diameter spherical site in a water medium irradiated by 20 MeV or 2 MeV protons. The calculation is designed to indicate the effects of proton energy loss straggling and of energy transport by secondary electrons.

Energy-loss straggling of protons, deuterons and α-particles in copper

Energy-loss straggling for protons, deuterons and α-particles in thin copper foils was measured using a transmission technique. The reduced straggling for helium and hydrogen ions are found to be the same within experimental error. Significant deviations from the theoretical calculations based on the free electron gas model are observed.

Energy loss straggling of protons and helium ions in carbon

Energy loss straggling of protons and helium ions in carbon

Energy loss straggling of protons in thick absorbers

The straggling of protons due to passage through thick absorbers has been measured with protons of about 6, 9 and 12 MeV. The technique consisted of transmitting protons through absorbers of uniform thickness and subsequently measuring the energy distribution of the emergent protons with a semiconductor detector. Relative energy losses in the range between 2% and 75% were obtained for Al, V, Ni, Mo, Ag, Ta and Au by using several absorbers for each element. Comparison was made with theoretical calculations due to Tschala¨r which take into account the variation of proton energy over the thickness of the absorber. After correction for finite detector resolution the values obtained for the full width at half maximum are 10 to 25% higher than those obtained from the Tschala¨r calculations.

Energy loss straggling of protons in nickel

The distribution of energy losses of 17 MeV protons in passing through nickel foils of various thickness ( t) was measured. The widths of the distributions at 1 2 , 1 4 and 1 10 maximum agree well with the theoretical predictions. For small t, the widths vary linearly with t as predicted by the theory rather than with t 1 2 as might be naively expected. The skewness of the distributions is also in agreement with the theory.

Energy-Loss Straggling of Protons in Silicon

The energy-loss straggling distributions for protons incident on a 200-\ensuremath{\mu} silicon surface-barrier detector were measured in the energy region between 5 and 42 MeV. Experimental results were compared to the predictions of the Vavilov theory and found to be in excellent agreement at the higher energies. However, a systematic difference between theory and experiment was observed for proton energies less than 20 MeV, the discrepancy increasing with decreasing incident proton energy. This effect is due to appreciable variation of proton energy over the thickness of the detector. Tschal\"ar's distribution functions, which specifically consider this variation, yield good fits to the data for energy losses as much as 80% of the incident proton energy.