Proton induced differential cross sections on 14N and 28Si from 3 to 4 MeV

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Abstract

In this work commercially available self-supporting thin silicon-nitride films were applied to measure the differential cross sections for the reactions 28Si(p,p′γ)28Si (Eγ = 1779 keV) and 14N(p,p′γ)14N (Eγ = 2313 keV) in the proton energy range of 3–4 MeV. For an additional validation of the data, the cross section from the present work and from the literature were integrated and compared to experimental thick target yields. Gamma-rays were detected simultaneously with backscattered particles using a HPGe detector at 55° and an ion implanted Si detector at 135° with respect to the beam direction. As a by-product, differential gamma-ray and particle production cross sections were measured for the first time in the 29Si(p,p′γ)29Si (Eγ = 1273 keV) reaction at 55°, as well as in the natN(p,po)natN, natSi(p,po)natSi and 28Si(p,p1)28Si elastic and inelastic scatterings at 135° from 3 to 4 MeV proton energies.

Introduction

Ion Beam Analytical methods are powerful, non-invasive techniques in material science. The detection of nuclear reaction products by PIGE (Particle induced gamma-ray emission), NRA (Nuclear reaction analysis) and the elastically scattered projectiles by EBS (Elastic backscattering spectrometry) provides sensitive quantitative information on light element composition and depth distribution. However, the high precision realization of these techniques requires either comparison with well-characterized materials, called as a standard, or consistent, high resolution differential cross section data of the individual nuclear reactions.

In order to provide a comprehensive and uniform database of the required cross sections for IBA, Coordinated Research Projects (CRP) were initiated by IAEA [1], [2], [3]. The aim of these research projects was the critical assessment and compilation of available cross section data and measurements of nuclear reactions in energy regions where they are required.

Silicon and nitrogen analysis plays an important role in several fields of science. The quantitative, standardless determination of these elements by PIGE and NRA requires reliable differential cross section data with reasonable energy resolution (mainly in the vicinity of resonances) covering large ion beam energy regions.

The use of commercially available silicon nitride (SiN) films makes it possible to study differential cross section data for both elements simultaneously. Silicon can be analyzed by the 28Si(p,p′γ1-0)28Si (Eγ = 1779 keV) and 29Si(p,p′γ1-0)29Si (Eγ = 1273 keV) nuclear reactions. Wide range of differential cross section data [4], [5], [6] and thick target yields [7], [8], [9], [10] are available in literature regarding these transitions below 4 MeV proton energy. However, the available data do not cover the full proton energy range or the energy resolution of the excitation function is not sufficient. Additionally, the strong anisotropy of the cross sections in the vicinity of resonances requires further cross section measurements at various detection angles. Nitrogen analysis below 4 MeV can be performed using the gamma-ray line at Eγ = 2313 keV of the 14N(p,p′γ1-0)14N nuclear reaction. In this energy region, resonances of the 14N(p,p′γ1-0)14N reaction around Ep = 3903 and 3996 keV [11] are the main contributors for the production of Eγ = 2313 keV. The available cross section data [6], [11], [12] and thick target yields [7], [9] show discrepancies in terms of resonance energy and width, which justify further experiments.

Moreover, the available experimental and theoretical elastic scattering cross sections of natN(p,po)natN [13], [14] and natSi(p,po)natSi [14], [15] reactions cover only part of the 3–4 MeV proton energy region at a single detection angle of 135°. This lack of data calls for further measurements.

The aim of the present research work is to provide a comprehensive experimental differential cross section dataset for the 28Si(p,p′γ)28Si (Eγ = 1779 keV), 14N(p,p′γ)14N (Eγ = 2313 keV) and 29Si(p,p′γ)29Si (Eγ = 1273 keV) nuclear reactions in the proton energy range 3–4 MeV. Moreover, we also provide differential proton elastic and inelastic scattering cross sections of natN(p,po)natN, natSi(p,po)natSi and 28Si(p,p1)28Si measured at 135°detection angle. In Section 2 the detailed description of the experimental setup is given. The obtained results and their comparison with the available data are presented in Section 3. This is followed by a summary in Section 4.

Section snippets

Experimental

The measurements were carried out at the 2.0 MV Medium-Current Plus Tandetron Accelerator, manufactured by High Voltage Engineering Europa (HVEE), at MTA Atomki, Debrecen, Hungary. The relationship between the energy of the outgoing particles from the accelerator and the nominal terminal voltage is obtained by the generating voltmeter (GVM) of the accelerator. The technical specification of the accelerator involving also short and long-term stability of the terminal voltage, as well as its

Gamma-ray production cross sections

Differential gamma-ray production cross sections were calculated according to the following equation:dσ(E0,θ)dΩ=Yγ(E0,θ)NpNTεabsEγwhere Yγ(E0,θ) is the measured γ-ray yield (i.e. the net area of the γ-ray peak corrected for dead time) at projectile energy E0 and γ-ray detection angle θ, Np is the number of incident projectiles, NT is the number of target nuclei per square centimeter and εabs(Eγ) is the absolute efficiency of the HPGe detector at Eγ energy.

In order to provide an independent test

Summary

In the present work we applied thin SiN films to accurately measure proton induced gamma-ray production cross sections for the 28Si(p,p′γ)28Si (Eγ = 1779 keV) and the 14N(p,p′γ)14N (Eγ = 2313 keV) reactions at 55° with respect to the ion beam direction, in the proton energy range of 3–4 MeV. Comparing calculated thick target gamma-yields from our and Jokar et al. [5] data with measured thick target yields of Chiari et al. [9], the large difference between the cross sections obtained in our

Acknowledgement

This study was partly supported by the IAEA Coordinated Research Project ‘‘Reference Database for Particle-Induced Gamma-ray Emission (PIGE) Spectroscopy”. The support of the Hungarian Academy of Sciences is appreciated in the frame of the Infrastructure Grants. The financial support of the Hungarian Government, Economic Development and Innovation Operational Programme (GINOP-2.3.3-15-2016-00005) grant, co-funded by the EU is acknowledged. Partial funding of the Hungarian Scientific Research

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