Differential cross-section measurements for the 7Li(p,p0)7Li, 7Li(p,p1)7Li, 7Li(p,α0)4He, 19F(p,p0)19F, 19F(p,α0)16O and 19F(p,α1,2)16O reactions

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Abstract

Differential cross sections of the 7Li(p,p0)7Li, 7Li(p,p1)7Li, 7Li(p,α0)4He, 19F(p,p0)19F, 19F(p,α0)16O and 19F(p,α1,2)16O reactions have been determined for proton energies Elab = 1500–7000 keV, using a variable energy step and for detection angles between 140° and 170° in steps of 10°. To validate the obtained results, benchmarking measurements were performed, using thick and mirror-polished BaF2 and LiF targets. The experimental data are compared to data from the literature, when available, and similarities and discrepancies are presented and analyzed.

Highlights

► We measured cross sections of the 7Li(p,p0–1)7Li, 7Li(p,α0)4He, 19F(p,p0)19F, 19F(p,α0)16O, 19F(p,α1,2)16O reactions. ► Measurements were performed for proton energies Elab = 1.5–7 MeV and detection angles between 140° and 170°. ► We validated the obtained data with benchmarking measurements.

Introduction

Lithium and fluorine are very common elements in nature with a huge technological interest. In particular, the quantitative determination of lithium is important for the characterization of various materials, including aluminum and magnesium alloys, ceramics, glasses, lubricants, greases, and rechargeable batteries. The quantitative determination of fluorine in various samples, on the other hand, is of great importance for material science, as well as, for medical, biological and environmental studies. The main problem concerning the depth profiling of lithium and fluorine is that since both elements are highly reactive, they are usually present in relatively complex matrices along with several medium- or high-Z elements. Thus, due to their low atomic number and their coexistence in heavy matrices, the determination of their profile concentrations presents strong analytical challenges for all IBA techniques. Among these techniques, Elastic Backscattering Spectroscopy (EBS – denoting deviations from the Rutherford formula) and Nuclear Reaction Analysis (NRA) are preferably used, due to their high analytical power for accurate and simultaneous determination of several light element concentrations in complex samples.

The existing differential cross-section datasets in the literature, necessary for the implementation of these techniques, are unfortunately inadequate and discrepant in many cases, thus limiting the applicability of both methods. More specifically, for the study of lithium concentration depth profiles, 7Li(3He,α0)6Li, 7Li(3He,d)8Be, 7Li(3He,p)9Be, 7Li(p,p0)7Li and 7Li(p,α0)4He reactions have been proposed in the past [1], [2], [3], [4], [5], [6], [7], [8]. The most promising one though, seems to be the 7Li(p,α0)4He reaction, because of its relatively high cross-section values and high Q-value, providing isolated peaks with practically no background. There is however a lack of corresponding data in the literature over a wide range of energies and detector angles. The present study aims at contributing in this field through the differential cross-section measurements of the 7Li(p,p0)7Li, 7Li(p,p1)7Li, and 7Li(p,α0)4He reactions, in the energy range of 1.5–7 MeV using a variable energy step and for detection angles between 140° and 170° in steps of 10°.

As far as fluorine is concerned, Proton Induced Γ-ray Emission (PIGE) is mainly used for the determination of its profile concentrations, due to the existence of several, narrow and strong resonances in the p+19F system (e.g. the relatively narrow, Γ = 4.5 keV resonance at Ep = 872.11 keV of the 19F(p,αγ)16O reaction). Alternatively, 19F(d,α0)17O, 19F(d,p0)20F, 19F(d,p1)20F, 19F(p,p0)19F, and 19F(p,α0)16O reactions have been proposed in the past [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. However, several differential cross-section datasets in the literature concerning various p+19F reaction channels are discrepant in many cases, mainly because of the complicated resonance structures involved. There has also been a tentative evaluation for proton elastic backscattering from 19F for a limited energy range (550–1750 keV) using SigmaCalc [21]. These evaluated differential cross sections are available to the scientific community through the IBANDL nuclear database from IAEA [www-nds.iaea.org/ibandl/].

It is important to note here, that the present work aimed mainly at studying the p+7Li system. Due to the implemented LiF target though, selected differential cross-section values have also been determined for the 19F(p,p0)19F, 19F(p,α0)16O and 19F(p,α1,2)16O reactions. It has to be pointed out however, that the adopted energy step was inadequate for a complete study of the strong and narrow resonances existing in the p+19F system. Nevertheless, the determined, coherent differential cross-section datasets from the present work may prove to be valuable for further evaluation purposes.

Section snippets

Experimental setup and procedure

The measurements were performed using the proton beam of the 5.5 MV TN11 Tandem Accelerator of N.C.S.R. “Demokritos”, Athens, Greece. Protons were accelerated to Ep,lab = 1500–7000 keV in steps of 100 and 25 keV (when close to strong resonances) and were led to a cylindrical scattering chamber of large dimensions (R  30 cm). The energy of the protons entering the scattering chamber was determined by nuclear magnetic resonance measurements (NMR) with an estimated ripple of ∼0.12–0.16%, as verified by

Data analysis and results

The determination of the differential cross-section values for 7Li and 19F reactions, respectively, was carried out following the formulas for relative measurements, compared to the differential cross section of the 197Au(p,p0) reaction, which does not deviate from the Rutherford formula over the whole proton beam energy range, for the same scattering angle and accumulated charge, as follows:dσdΩθLi=dσdΩθAuYLiNAuYAuNLidσdΩθF=dσdΩθAuYFNAuYAuNFwhere Y generally corresponds to the

Conclusions

A detailed study of differential cross sections of the 7Li(p,p0)7Li, 7Li(p,α0)4He, 7Li(p,p1)7Li, and 19F(p,p0)19F, 19F(p,α0)16O, 19F(p,α1,2)16O reactions for backward detector angles (between 140° and 170°, in steps of 10°) and for the proton energy beam range Ep,lab  1500–7000 keV, has been presented. The obtained differential cross-section values have been validated through benchmarking experiments, thus enabling their use not only for EBS and NRA purposes, but also for the evaluation of the

Acknowledgement

This research project was partially supported by the NTUA Basic Research Program ΠEBE-2009, Code No.: 65177600.

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