Oxygen detection by non-Rutherford proton backscattering below 2.5 MeV

Oxygen detection by proton backscattering has been investigated. The oxygen detection sensitivity of 2.5 MeV proton backscattering is shown to exceed that of ⁴He backscattering by even a factor of about 15 depending on the matrix. The needed proton elastic scattering cross sections of oxygen for θ_lab = 170° have been measured in the energy range E_lab = 770–2480 keV relative to Ti and Sn elastic scattering cross sections using thin TiO₂ and SnO₂ samples. The angular dependence of the cross section was measured at energies E_lab = 1790, 1990, 2191, and 2382 keV for backscattering angles. The experimental cross sections were found to be 1.1–5.7 times the pure Coulomb cross section. Theoretical calculations for the scattering cross sections were performed and their inapplicability to experimental purposes is demonstrated. Fits to experimental data are given.     

Proton elastic scattering and proton induced γ-ray emission cross-sections on Na from 2 to 5 MeV

Differential cross-sections for proton elastic scattering on sodium and for γ-ray emission from the reactions ²³Na(p,p′γ)²³Na (E_γ = 440 keV and E_γ = 1636 keV) and ²³Na(p,α′γ)²⁰Ne (E_γ = 1634 keV) were measured for proton energies from 2.2 to 5.2 MeV using a 63 μg/cm² NaBr target evaporated on a self-supporting thin C film.The γ-rays were detected by a 38% relative efficiency Ge detector placed at an angle of 135° with respect to the beam direction, while the backscattered protons were collected by a Si surface barrier detector placed at a scattering angle of 150°. Absolute differential cross-sections were obtained with an overall uncertainty estimated to be better than ±6.0% for elastic scattering and ±12% for γ-ray emission, at all the beam energies.To provide a convincing test of the overall validity of the measured elastic scattering cross-section, thick target benchmark experiments at several proton energies are presented.     

气溶胶中F和Na分析的外束质子诱发γ射线激发曲线测量

在大气颗粒物离子束分析中,质子诱发γ射线分析（PIGE）作为质子诱发X荧光发射（PIXE）的补充方法,通常用于分析轻元素。为得到外束PIGE定量分析气溶胶样品中F和Na元素的最佳实验条件,本工作在北京师范大学串列加速器上测定了质子能量在1.8～2.9 MeV范围内,核反应¹⁹F(p,p’γ)¹⁹F（E_γ=110 keV和197 keV）和 ²³Na(p,p’γ)²³Na(E_γ=440 keV)的γ射线激发函数。     

High gamma dose response of the electrical properties of polyethylene terephthalate thin films

Electrical properties of polyethylene terephthalate (PET), irradiated with gamma rays, have been investigated. The PET films were irradiated with high gamma dose levels in the range from 100 to 2000 kGy. The changes in the DC (σ_DC) and the ac (σ_ac) conductivities, with the dose, have been performed. The effect of gamma irradiation on the dielectric constant (ε′) and loss (ε″) has been determined. Also, the dose dependence of the frequency exponent index (S), the resonance frequency (Fc) and the hopping frequency (ω_P) have been obtained. The obtained results show that increasing gamma dose leads to slight increase in σ_DC, σ_ac and ε′, while no change was observed in ε″ value. Meanwhile, S, Fc and ω_P are inversely proportional to the dose. Accordingly, the study suggests the possibility of using PET films in electronic components (capacitors, resistors, etc.), especially that operate at high gamma dose environments for the frequency independent applications.     

Thermoluminescence properties of nanocrystalline K2Ca2(SO4)3:Eu irradiated with gamma rays and proton beam

Thermoluminescence properties of nanocrystalline K₂Ca₂(SO₄)₃:Eu prepared by ball milling technique have been studied and the nanophosphor’s suitability as an effective gamma radiation and proton beam dosimeter material has been examined. It is found that the nanophosphor is suitable for dosimetry over a very wide range of doses ∼1 Gy to 1 kGy for gamma radiation. And for proton beam the same nanophosphor shows a more or less linear response for the dose range 0.1-100 Gy. A comparative study of this nanophosphor with its corresponding microcrystalline form (prepared by solid-state diffusion method) as well as the nanocrystalline form prepared by (the more conventional) co-precipitation technique has shown that the nanophosphor prepared by the ball milling technique is in almost all respects better than the other two forms reported earlier.     

Determination of gamma and fast neutron shielding parameters of magnetite concretes

In this study, some gamma shielding parameters such as mass attenuation coefficient (μ_ρ), effective atomic number (Z_eff), electron density (N_el) and buildup factors have been investigated for concretes with and without magnetite aggregate. The measurements have been carried out using 1.25 MeV (mean energy of 1.1732 MeV and 1.3325 MeV photons of a ⁶⁰Co radioactive source) gamma photons. The theoretical values of μ_ρ have been calculated in the energy range from 1 keV to 100 GeV by WinXCom computer code and these values were used in order to calculate the values of Z_eff and N_el. And fast neutron shielding parameter namely effective removal cross-sections (Σ_R, cm⁻¹) have been calculated. In addition, Energy absorption buildup factors (EABF) and exposure buildup factors (EBF) values of concrete samples have been calculated for photon energy 0.015–15 MeV up to 40 mfp (mean free path) penetration depths. The results of this study showed that the magnetite concrete is more efficient than the ordinary concrete for fast neutrons and gamma rays.     

Coherent pair production by energetic gamma rays incident on quasicrystals

We develop a Born-approximation theory of coherent pair production (CPP) of electrons by energetic gamma rays incident on an icosahedral quasicrystal, described by a schematic model (K model) that includes phonon and phason disorder. Our main result is a formula for the cross-section dσ_cpp/dε₊ for CPP, differential with respect to the positron energy ε₊ and of order α² in the fine-structure constant α ≈ 1/137, but which is otherwise exact. We discuss results of numerical calculations of dσ_cpp/dε₊ versus y = ε₊/k for gamma rays of energies k = 20 MeV, 200 MeV, and 3 GeV, incident on icosahedral Al-Mn-Si, described as a special case of the K model (vertex model). This consists in placing an Mn atom at each vertex of the relevant Ammann tiles. Our calculations include CPP of types A and B. Both types exhibit vertical intensity drops at irregularly distributed y-values, many of these drops being so large that they should be observable experimentally. They are analogous to the large intensity drops exhibited by coherent bremsstrahlung in quasicrystals. We predict that CPP drops also occur for realistic models of i-Al-Mn-Si at the same y-values as for the vertex model, but whose magnitudes may differ from those predicted by this model.     

Study of the long term effect of high gamma doses in the crystalline phase of P(VdF-TrFE) copolymers

Differential Scanning Calorimetry (DSC) and X-ray diffraction (XRD) of gamma irradiated poly(vinylidene fluoride–trifluoroethylene) copolymer [P(VdF-TrFE)] have been studied in connection with the use of material in industrial high gamma dose measurement. Interaction between radiation and P(VdF-TrFE) results in a decrease of its crystallinity together with the simultaneous formation of CC conjugated bonds. It has been found that the melting latent heat (L_Melt) of the crystallites is unambiguously related to the value of absorbed dose. The DSC technique can be used to evaluate high gamma doses ranging from 1.0 kGy to 1.0 MGy. The relation between L_Melt and gamma doses can be fitted by an exponential function for measurements taken until 3 months after irradiation. After this time, the relation can be fitted by a linear function for periods at least of one year. X-ray diffraction revealed an expansion of the β-phase unit cell of 5% in the b direction for gamma doses between 250 and 500 kGy. The results presented highly increases the possibility of using the melting latent heat of P(VdF-TrFE) copolymer in high dose dosimetry.     

The influence of relative humidity on iron corrosion under proton irradiation

With regard to the storage for high-level radioactive waste and the reversible period of a geological repository, the influence of proton irradiation on the indoor atmospheric corrosion of iron has been investigated in relation to the relative humidity (RH) in the atmosphere. Irradiation experiments were performed using a 3-MeV extracted proton beam. Relative humidity varies from 0% to 85%. Before and after each irradiation, the surfaces of the sample were characterised by Rutherford backscattering spectrometry in order to determine oxygen concentrations in the metal. The maximum oxidation rate was observed for 45% RH in air under proton irradiation and was compared with literature data without irradiation where the maximum oxidation rate was observed at 95% RH. The experimental results are discussed on the basis of the Langmuir-Hinshelwood (LH) model: they are explained by the contrast between the adsorption of O₂ and H₂O species on the active cathodic sites of the iron surface and by the formation of H⁺(H₂O)_n.     

Proton elastic scattering differential cross-sections for C

Carbon depth profiling presents a strong analytical challenge for all the major ion beam analysis (IBA) techniques, with elastic backscattering spectroscopy (EBS) being widely implemented. In the past, the ¹²C(p,p)¹²C reaction has been successfully evaluated for proton beam energies up to 4.5 MeV. Currently, an attempt is being made to extend this evaluation to higher energies, namely up to E_p,lab = 7 MeV. There is a certain lack of available and/or coherent datasets in literature for these relatively high proton beam energies at backward angles, suitable for IBA. Moreover, the few existing datasets are in certain cases discrepant. Thus, in the present work, the differential cross-section of proton elastic scattering on carbon were measured between 140°and 170°, in steps of 10°, for the proton beam energy range between 2.7 and 7 MeV. The experimental results obtained, along with data from literature, were evaluated applying nuclear physics models. The evaluated results were benchmarked using a thick, mirror polished glassy carbon target at different beam energies and detector angles.     

Analysis of boron using the (p, α) reaction

The applicability of the strong and broad resonance of the reaction ${}^{11}\text{B(p}\text{, α)}{}^8\text{Be}$ at E_p = 675 keV to the elemental analysis of boron has been studied. To eliminate matrix effects and to optimize the measuring conditions a systematic study of the absolute thick-target yields of α-particles following proton bombardment has been carried out at E_p = 0.7 and 1.0 MeV for the elements Z = 3?9, 11?17s by. Summary spectra showing the α-peaks of light elements of interest in the elemental analysis of boron are given. An external beam measurement system has been developed to allow measurements to be carried out in He-gas at atmospheric pressure. Thus, problems arising in vacuo with insulating, medical and biological samples can be avoided. The detection limits of boron range from 0.1 ppm for biological samples containing nitrogen to below 0.01 ppm for samples with a low nitrogen concentration. An additional advantage of the method is that Li, F and N can be determined simultaneously with the boron analysis.     

Effects of proton irradiation on electronic structure of NdFeB permanent magnets

Effects of proton irradiation on electronic structure and atomic local structure of N35EH-type NdFeB permanent magnet were investigated by soft X-ray absorption spectrometry and Mössbauer spectrometry. The local coordination environment of Fe atoms changes after proton irradiation, and the average hyperfine field H_in of the magnets decreases from 288.4 to 286.9 kOe. The effects of irradiation on Fe atoms local environment at different lattice sites are different. The near edge structure of Fe L₃ edge is changed, indicating the density of unoccupied state of Fe 3d electrons increases after proton irradiation.     

Mass transfer process of hydrogen via ceramic proton conductor membrane of electrochemical hydrogen pump

The blanket tritium recovery system using the electrochemical hydrogen pump with proton conductor membrane has been proposed. The feature of the electrochemical hydrogen pump is that the driving force of hydrogen transportation is a potential difference. Therefore, it might be effective to apply the hydrogen pump to the blanket sweep gas (the low hydrogen and water vapor pressure). Perovskite-type ceramic such as SrCe_0.95Yb_0.05O_3−α, is one of the candidate proton conductor for hydrogen pump and its ionic hydrogen transportation properties have been investigated. In this work, the basic mass transfer equation for hydrogen, in which the apparent proton conductivity is used as the over-all mass transfer coefficient, is proposed. And then, the apparent proton conductivities were estimated from experimental data using these equations, and mass transfer of hydrogen via proton conductor membrane was discussed by using the apparent conductivity.     

Radioactive products from boron CTR reactions

The nuclear reaction rates for ¹⁰B(p, α)⁷Be and ¹⁰B(p, γ)¹¹C have been measured by a thick target technique using proton energies from 75 keV to 3.0 MeV. The results are valid for proton temperatures near 3 · 10⁹K where the ¹¹B(p, 3α) reaction has been suggested for power generation. At this temperature, the rates N_A〈συ〉 are 2.66 · 10₇ and 8.3 · 10² cm³ g^?1 s^?1 for ⁷Be and ¹¹C, respectively. As such, these rates suggest the possibility of serious radioactive contamination in using natural boron as a fuel in CTR devices.     

FTIR and DSC studies on gamma irradiated P(VdF-HFP) fluoropolymers applied to dosimetry

Radiation effects on semicrystalline poly(fluorovinylidene-co-hexafluoropropylene) copolymer [P(VdF-HFP)] induced by high-energy irradiation were investigated. Films with 150 μm thickness were irradiated with gamma doses ranging from 1.0 kGy to 3.0 MGy. Fourier transform infrared (FTIR) spectroscopy was used to follow the radio-induction of new molecular bonds. Differential scanning calorimetry (DSC) was employed to study the crystalline degradation of the irradiated samples. P(VdF-HFP) copolymers have fluorinated monomers [-CF₂-CF-CF₃-] randomly added to the [-CH₂-CF₂-] main chain of PVdF homopolymer. In this case, the [-CF₃-] molecular bonds are branched to the main chain. There is an increasing interest about the effect of high gamma radiation dose on the P(VdF-HFP) radiolysis, once it could enhance some of their already known interesting properties such as biomedical applications and electrostrictive transducers/actuators. FTIR spectroscopic data revealed two optical absorption bands at 1730 and 1754 cm⁻¹ whose intensities are unambiguously related to gamma delivered dose ranging from 0.0 to 1000 kGy. Fading analysis has demonstrated no loss of signal until 11 months after irradiation. DSC and XRD data revealed a continuous decrease in both the melting latent heat and crystalline dimensions for doses ranging from 250 to 3000 kGy. Because of the low fading and the linear behavior with respect to delivered gamma doses of the absorption band at 1754 cm⁻¹, P(VdF-HFP) copolymers are good candidates for being explored for high gamma dose dosimetry application.     

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.     

(p,p) non-Rutherford backscattering analysis of silicon carbide

In this paper, (p,p) non-Rutherford elastic backscattering (NBS) measurements with 1.6 MeV proton beams have been used to determine the areal density and C/Si stoichiometric ratio in 300–1000 nm SiC_x(H_y) films deposited on silicon substrates by Chemical Vapour Deposition (CVD) using two different gas sources, methane (CH₄) and ethylene (C₂H₄). At the same time, oxygen is also found in some of these samples. The results show that (p,p) NBS can be used to determine the areal density and C/Si ratio with a reasonable accuracy, especially when samples are thick or the terminal energy of the accelerator is low for analysis using a helium beam.     

Proton induced L-shell X-ray production cross-sections for Pb in the energy range 225–400 KeV

The L-shell X-ray production cross-sections in lead (Pb) by proton impact over the energy range 225–400 keV, with an interval of 25 keV, have been measured. The thick target X-ray yields have been obtained using a HPGe detector. The experimental results for σ_L1, σ_Lα, σ_Lβ and σ_Lγ have been compared with perturbed stationary state theory with relativistic (R), energy loss (E) and Coulomb (C) corrections (ECPSSR theory). The comparison of L_α, L_β and L_γ, X-ray production cross-sections shows a fairly good agreement, except at the lowest energy. The L₁ X-ray production cross-sections are higher by ≈ 20–30% than their theoretical estimates.     

Proton energy determination using activated yttrium foils and ionization chambers for activity assay

Excitation functions of the ⁸⁹Y(p, xn) nuclear reactions were measured up to 18 MeV by the conventional activation method using the stacked-foil technique, and the irradiation of single foils. Activity assays of the irradiated foils were performed via ionization chamber and gamma spectroscopy methods. Activity ratios of the activation products were measured in two different facilities and evaluated for use as a practical and simple method for proton energy determinations. Cross section values measured in this work were compared with published data and with theoretical values as determined by the nuclear reaction model code EMPIRE II. In general, there was a good agreement between the experimental and theoretical values of the cross section data. Activity ratios of the isomeric and ground state of ⁸⁹Zr measured via ionization chamber were found to be useful for proton energy determinations in the energy range from 7 to 15 MeV. Proton energies above 13 MeV were accurately determined using the ^89gZr/⁸⁸Zr and ^89gZr/⁸⁸Y activity ratios measured via gamma spectroscopy.     

Modifications in structural, cation distribution and magnetic properties of Co gamma irradiated Li-ferrite

Polycrystalline samples of Li_0.5Fe_2.5O₄ ferrite precursor were prepared by conventional standard double sintering ceramic technique and then irradiated with three different doses of ⁶⁰Co gamma rays. The crystal structure and phase orientation of the irradiated and unirradiated samples of Li_0.5Fe_2.5O₄ ferrite was done by using X-ray diffraction technique at room temperature. The lattice parameter of the studied samples increased due to the formation of Fe²⁺ ions under the ionizing effect of gamma radiation. The strain in the materials due to the irradiation was calculated from XRD data. Scanning electron microscope (SEM) studies indicate that the irradiation causes amorphization, especially at the grain boundaries. The cation distribution was calculated from XRD data analysis. By using cation distribution structural parameters such as theoretical lattice constant, ionic radii of available sites and the oxygen parameter ‘u’ have been calculated. The estimated cation distribution and other structural parameters shows strong influence of gamma rays on polycrystalline Li-ferrite. The magnetic properties of irradiated and unirradiated lithium ferrite were performed by using pulse field hysteresis loop technique at room temperature. Electrical properties such as diffusion coefficient and dielectric properties were carried out with the influence of gamma irradiation. Activation energy of diffusion process decreased after irradiation. The increase of diffusion coefficient with increasing dose rate of gamma irradiation was reinforced by the increase of Fe²⁺ ions and the displacement of metal ions from its original sites under the effect of gamma irradiation.