Stopping power and energy straggling of protons in graphite and amorphous carbon obtained from a resonance in BS spectra

Backscattering (BS) spectra with a sharp 4.8-MeV resonance for carbon targets have been measured using proton beams in an energy range 4.85-6.1 MeV per 100-keV step. By systematic analyses of the resonance peak profiles, values of stopping power and energy straggling have been deduced for proton energies from 0.8 to 3.4 MeV which corresponds to a penetration depth of 88 μm. In particular, to investigate the difference in stopping power and straggling caused by target inhomogeneity, we used two target materials which were highly oriented pyrolytic graphite (HOPG, 2.26 g/cm³) as a homogeneous material and amorphous carbon (1.73 g/cm³) as an inhomogeneous material. We describe a method of measuring stopping power and straggling using a resonance in the BS spectra. The stopping powers obtained are compared with the values determined by SRIM-2006. Moreover, collision straggling and a density straggling due to the inhomogeneity of the target materials are evaluated from the width broadening of resonance peaks.     

100 MeV质子降能材料的选择研究

降能器对于提升质子单粒子效应（SEE）地面模拟试验的效率具有重要意义,而降能材料的选择是降能器设计中的首要问题。计算了100 MeV质子在4种常见降能材料铍、石墨、铝、铜中产生的能量岐离、角度岐离、中子本底以及感生放射性等对质子SEE地面模拟试验有影响的4个方面,其中感生放射性的计算中包含了降能过程在材料中产生的放射性核素种类、活度及残余剂量率。根据以上计算结果,并结合质子SEE地面模拟试验的要求,在降低相同的能量这一情况下,对4种材料作为100 MeV质子降能材料的适用性进行了分析比较,最终选择铝作为100 MeV质子的降能材料,并将应用在中国原子能科学研究院100 MeV质子回旋加速器的质子SEE地面模拟试验装置的降能器设计中。     

An experimental evaluation of spatial distribution for deeply penetrating protons in carbon material

The peak profile of the 4.8-MeV resonance by the ¹²C(p,p)¹²C reaction in backscattering geometry has been analyzed to examine two kinds of stragglings of proton, i.e. the depth straggling in the incoming path and the energy loss straggling in the outgoing path. The analysis, which is combined with existing theoretical treatments for the stopping process and the energy loss straggling, has made it possible to deduce the penetration depth and its spread at the resonance position in carbon materials. The present method, as a new tool for direct inspection of ion beams inside target material, is explained in detail.     

Stopping cross-section and energy straggling of protons in SiC obtained by nuclear resonant reaction of protons with 12C and 28Si

In order to evaluate stopping cross-section and energy straggling of protons in compound material SiC and its constituents C and Si, resonant backscattering spectra have been measured using proton beams in an energy range 4.9–6.1 MeV per a 100 keV step. We have observed two sharp nuclear resonances at proton energies of 4.808 MeV by ¹²C and 4.879 MeV by ²⁸Si. By systematic analyses of the resonance peak profiles, i.e., energy shift of the peak position and broadening of the peak width, the values of the stopping cross-section and the energy straggling have been deduced to be compared with SRIM-2006 and Bohr’s prediction.     

Interaction of slow ions with bulk and surfaces

Nonlinear density functional results for the stopping power and straggling of ions moving slowly (υ ⪡ υ_f) in an electron gas are presented. A self-energy formalism is used to estimate the charge state of a proton moving at intermediate velocities in an electron gas. The contribution of the surface to the energy loss of slow ions is also analyzed, within the specular reflection model.     

Scaling of SEU mapping and cross section, and proton induced SEU atreduced supply voltage

New experimental study of heavy ion and proton induced SEU at reduced voltage (i.e. reduced critical charge) reveals interesting results. It is shown that the heavy ion cross section and microprobe mapping scale like the threshold LET and the parameter, which is almost invariant under bias changes, is the effective charge collection depth. For studying proton induced SEU and surface-barrier-detector spectra we use protons with energies from 5.6 to 300 MeV. The results are analyzed in view of the processes involved in low energy deposition by protons. Detailed calculations show the importance of straggling in proton direct ionization which might be the leading process in very sensitive devices like photodiodes     

Proton energy loss in allotropic forms of carbon

We have investigated theoretically the electronic stopping of protons in different solid forms of carbon: glassy, amorphous, graphite, diamond and C₆₀-fullerite. The energy loss is described within the dielectric formalism and the target properties are modelled by a sum of Mennin-type energy loss functions. For each allotropic carbon form, we observe remarkable differences in the stopping cross section and in the energy loss straggling at proton velocities around and lower than that corresponding to the maximum in the energy loss. A comparison of our results with available experimental data shows a reasonably good agreement.     

Energy loss straggling of energetic 1H and 2H ions crossing polypropylene foils

An indirect transmission method as nuclear technique in precise measurement of energy loss straggling in polymer foils is presented. The details of experimental procedures related to the combination of Rutherford backscattering spectrometry and transmission technique are described. Advantages of the application of such a method in energy straggling experiments are discussed. The energy loss straggling measurements have been performed in the energy range of 900–3000 keV for protons and deuterons in thin films of polypropylene. The obtained values of energy straggling are compared to those deduced from Bohr and Bethe–Livingston theoretical predictions. This comparison was made by using Bragg’s rule as model of calculation over the investigated energy range.     

Energy loss and straggling in LR-115 and Kapton polymeric foils for energetic ions

The energy loss and straggling in LR-115 and Kapton polymeric foils for Li, C, O and Si ions in the energy range ∼1.0-6.5 MeV/u have been measured, utilizing 15 UD Pelletron accelerator facility available at Inter University Accelerator Centre (IUAC), New Delhi, India. The measured energy loss and straggling values have been compared with the corresponding computed values adopting some widely used energy loss and straggling formulations. The aim of such a comparison is to check the reliability and validity of the existing energy loss and straggling formulations.     

Energy straggling of 60 MeV 58Niq+ ions in thin carbon foils and gases

Energy straggling of 60 MeV ⁵⁸Ni^q+ ions in thin carbon foils and gas layers has been measured with a Q3D magnetic spectrograph in dependence of the incident and analysed charge state of the ions. The straggling increases with the number of electrons per gas molecule, thus showing strong correlation effects. In solid carbon, however, energy straggling is close to the data of deuterium gas. The small straggling in carbon is interpreted as an effect of the long range interaction of the heavy ions in dense solids. Furthermore, it is observed that energy straggling depends on the charge state of the projectiles unless the equilibrium charge state is reached.     

Energy loss and straggling of Li ions in the polymer foils

Energy loss and straggling of 0.18-0.78 MeV/amu ⁷Li ions in polycarbonate, polyethylene terephthalate and polypropylene foils were measured by means of a transmission technique with a half-covered detector. The stopping force measurements are compared with the SRIM 2006 calculation and the database of the ICRU report 73. The measured energy loss straggling are in satisfactory agreement with the results yielded using the empirical formula at the higher energy region. The obtained data also demonstrated that the validity of Bragg’s rule applied to stopping force and energy loss straggling for ⁷Li ions in polymer foils.     

Energy loss straggling in thick mylar polymeric foils for swift heavy ions in fractional energy loss limits ΔE/E ∼ 5-80%

The energy loss straggling in thick mylar (monomer composition: C₁₀H₈O₄) polymeric foils has been measured for swift heavy ions covering Z = 3-22, in the fractional energy loss limits ΔE/E ∼ 5-80%. These measured straggling values have been compared with the most commonly used Bethe-Livingston collisional straggling formulation after modifying it suitably for thick targets. Further, the charge-exchange straggling values have been extracted from the measured values and were found to be consistently higher than the corresponding values deduced from Yang’s et al. formulation. Finally, an analytical expression has been developed for charge-exchange straggling for ion-polymer combinations, considered in the present study.     

Energy loss straggling of Si and Cl ions in polymeric foils

The energy loss straggling has been measured for Si and Cl ions in three polymers viz. Polypropylene PP (C₃H₆), Polyethylene terepthalate PET (C₁₀H₈O₄), Polyethylene naphthalate PEN (C₇H₅O₂), in the energy range ∼1.50 to 4.50 MeV/u. The measured energy loss straggling values have been compared with the corresponding computed values based on Bohr, Lindhard and Scharff, Bethe-Livingston and Yang et al., formulations, in order to check the reliability and validity of these formulations. Further, based on the experimental data, an empirical relation for the calculations of energy loss straggling has been developed. The predicted values from this relation are in close agreement with the experimental data.     

Angular straggling associated with fluctuations in charge state of the projectile in grazing ion-surface scattering

We have studied the angular straggling of a few keV ions scattered off metal surfaces at grazing scattering condition. The angular straggling of scattered particles is large when the charge state of the particle fluctuates significantly in the surface region. The important physical parameters responsible for the angular straggling are the particle induced density of states and the rate of change of the energy of the atomic level with distance from the surface. An implication for the mechanism underlying skipping motion is discussed.     

Energy loss straggling in carbon foils by 1-2 MeV/atom lithium and carbon cluster-ions

Energy loss straggling of lithium and carbon cluster-ions with 1-2 MeV/atom energies incident upon thin carbon foil were measured to investigate the difference of energy loss straggling between a single ion and cluster-ions. The results show that the enhancement of the energy loss straggling is observed at lower energies for two different cluster-ions in a 5 μg/cm² carbon foil. For a thicker sample, i.e. a 15 μg/cm² carbon foil, the ratio of cluster-ions to the one of a single atom at equivalent energies lies slightly close with the unity. As increasing the number of the cluster-ions, no enhancement of energy loss straggling was observed in this study.     

Pathlength distributions of low energy electrons in water

The pathlength distributions of low energy electrons (below 10 keV) in liquid water have been studied. The stragglings of the energy loss and pathlength for electrons were investigated by the use of the straggling function. From the differential and sum distributions of the straggling function, we have determined the mean, extrapolated and most probable pathlengths. Results of this work have been compared with the continuous slowing down approximation (CSDA) pathlengths and available experimental data.     

First direct-write lithography results on the Guelph high resolution proton microprobe

The recently completed high-resolution proton microprobe at the University of Guelph is Canada’s first one-micron nuclear microprobe, which represents the country’s state-of-the-art technology for various nuclear microprobe applications, e.g. direct-write microlithography. Its probe-forming system is comprised of a triplet Oxford Micro beams magnetic quadrupole lenses, along with high-precision objective slits. High energy protons coming off a 3 MV particle accelerator can achieve a nominal resolution of one micro and a beam current of several hundred of picoamperes when arriving at the target. This proton probe is ideal for the use of direct-write lithography with the incorporation of a magnetic scanning system and motorized sample stage.Preliminary lithography results have been obtained using spin-coated PMMA photoresist as specimen. The beam spot size, beam range and straggling inside the substrate and the exposure conditions are investigated by using scanning electron microscopy. This facility is the first in Canada to perform focused direct-write ion beam lithography, which is ideal for modification and machining of polymer and semiconductor materials for biological, microfluidic and ultimate lab-on-chip applications.     

Stopping force and straggling of 0.6–4.7 MeV H,He and Li ions in the polyhydroxybutyrate foil

Stopping force and straggling of 0.6–3.5 MeV ¹H ions, 2.0–4.7 MeV ⁴He ions and 1.4–4.4 MeV ⁷Li ions in the polyhydroxybutyrate (PHB) foil were measured by means of a transmission technique. The measured stopping forces are in well agreement with the SRIM 2008 calculation and the ICRU Report tables, except for the lower energy region. The obtained energy loss straggling deviates from the Bohr’s value by as much as 23.6% for the energies under study. The validity of the Bragg’s rule has also been demonstrated in the stopping force and straggling for ¹H, ⁴He and ⁷Li ions in the PHB foil.     

3 MV加速器质谱测量36Cl

在端电压为3 MV的AMS装置上实现³⁶Cl及其他中重核素的高灵敏测量是AMS技术发展的重要方向之一。为进一步提高充气飞行时间探测方法中³⁶S的压低能力,本文研究了³⁶S和³⁶Cl在P10、异丁烷和丙烷气体中的能量歧离和角度歧离。在32 MeV的入射能量下测量了几个地下水样品中³⁶Cl的[JP2]含量,测量结果与72 MeV能量下的测量结果相符。测量结果表明,采用充气飞行时间探测方法在3 MV的串列加速器上测量³⁶Cl时,探测限为³⁶Cl/Cl≈10^-14,当样品中³⁶Cl/Cl≈10^-13时测量不确定度为30%。     

Deconvolution of neutron depth profiling spectra

Iterative methods for determining deconvolued depth profiles from measured neutron depth profiling (NDP) energy spectra are presented. The methods account for energy broadening caused by system noise, energy straggling, multiple small angle scattering, and geometrical acceptance angles. Examples of the methods are given for known and unknown profiles of helium-3 and nitrogen-14.