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.     

Depth profiling of Mg by 2010 keV resonance of Mg(p,p′γ)Mg nuclear reaction

Studies on the characteristics of 2010 keV resonance in ²⁴Mg(p,p′γ)²⁴Mg nuclear reaction for depth profiling Mg in thin films are reported. The resonance reaction, based on the detection of characteristic 1368 keV γ-rays, enables interference free measurement of Mg down to 2 × 10²⁰ atoms/cm³ and has a probing depth of about 20 μm. The width of the resonance extracted from excitation curves for thick (>180 nm) thermally grown elemental Mg films, by SPACES is about 350 ± 50 eV. The reaction has been used to depth profile Mg in a Mg/Ti/Mg/Si film which provides interesting information on interfacial mixing involving Ti layer and the underlying Mg layer.     

RNRA and neutron threshold analyses of thick lithium coatings deposited by sputter evaporation

Li coatings on various substrates have numerous applications: Boron neutron capture therapy, super conducting tokamak, etc.Unfortunately the main difficulty using Li is its reactivity in air and diffusion into metals. It is the only metal that reacts with nitrogen at room temperature and it tarnishes and oxidizes rapidly in air.In this work, we investigate how to profile thick Li layers (50 μm) deposited on SiO₂ substrates by a method based on plasma sputtering, involving both DC sputtering and evaporation simultaneously.A thick Li layer (≈10 μm) was covered with a thin stainless steel layer to prevent oxidation during transfer of the sample from the sputtering chamber and the accelerator. Li coatings were investigated by RNRA and neutron threshold reaction to obtain interdiffusion profiles of the different components and their concentration. The depth profile using the ⁷Li(p,γ)⁸Be^∗ resonance nuclear reaction occurring at 440 keV allows us to obtain Li concentration versus depth up to 50 μm.Preliminary results indicate that homogeneous Li layers can be obtained and protected against air, even though it diffuses into the encapsulated layers.     

Proton induced γ-ray emission yields for the analysis of light elements in aerosol samples in an external beam set-up

The PIXE technique is a reliable tool for the characterisation of thin aerosol samples, but it can underestimate the lightest measurable elements, like Na, Mg, Al, Si and P, owing to the absorption of their X-rays inside the sample. The PIGE technique is a valid help to determine corrections for such effect: in order to perform PIGE measurements relative to thin reference standards in an external beam set-up, we measured, at the external beam facility of the Tandetron accelerator of the LABEC laboratory in Florence, the γ-ray yields as a function of the proton beam energy for the reactions ¹⁹F(p,p′γ)¹⁹F (E_γ = 110 and 197 keV), ²³Na(p,p′γ)²³Na (E_γ = 440 keV) and ²⁷Al(p,p′γ)²⁷Al (E_γ = 843 and 1013 keV), in the proton energy range from 3 to 5 MeV. The measured yields are shown, and the determined most suitable energies for performing PIGE quantification of Na and Al are reported, together with the corresponding minimum detection limits (MDLs). The results of some test on PIGE accuracy and an evaluation of self-absorption effects in PIXE measurements on thin aerosol samples are also presented.     

Thermal neutron cross-section and resonance integral of the W(n, γ)W reaction

We measured the thermal neutron cross-section and the resonance integral of the reaction ¹⁸⁶W(n, γ)¹⁸⁷W by the activation method using a ¹⁹⁷Au(n, γ)¹⁹⁸Au monitor reaction as single comparator. The high-purity natural W and Au metallic foils with and without a cadmium shield case of 0.5 mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the samples were measured by high-resolution γ-ray spectrometry with a calibrated p-type high-purity Ge detector. The necessary correction factors for γ-ray attenuation (F_g), thermal neutron self-shielding (G_th), and resonance neutron self-shielding (G_epi) effects, and the epithermal neutron spectrum shape factor (α) were taken into account. The thermal neutron cross-section for the ¹⁸⁶W(n, γ)¹⁸⁷W reaction has been determined to be 37.2 ± 2.1 barn, relative to the reference value of 98.65 ± 0.09 barn for the ¹⁹⁷Au(n, γ)¹⁹⁸Au reaction. The present result is, in general, in good agreement with most of the experimental data and the recently evaluated value of ENDF/B-VII.0 by 5.7%. By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral obtained is 461 ± 39 barn, which is determined relative to the reference values of 1550 ± 28 barn for the ¹⁹⁷Au(n, γ)¹⁹⁸Au reaction. The present resonance integral value is in general good agreement with the recently measured values by 9%. The present result is lower than the evaluated ones by 10-13%.     

PIGE analysis of magnesium and beryllium

In this work, we present an alternative method for PIGE analysis of magnesium and beryllium in thick samples. This method is based on the ERYA – Emitted Radiation Yield Analysis – code, which integrates the nuclear reaction excitation function along the depth of the sample. For this purpose, the excitations functions of the ²⁵Mg(p,p′γ)²⁵Mg (E_γ = 585 keV) and ⁹Be(p,γ)¹⁰B (E_γ = 718 keV) reactions were employed. Calculated gamma-ray yields were compared, at several proton energy values, with experimental yields for thick samples made of inorganic compounds containing magnesium or beryllium. The agreement is better than 5%. Taking into consideration the experimental uncertainty of the measured yields and the errors related to the stopping power values, this agreement shows that effects as the beam energy straggling, ignored in the calculation, seem to play a minor role.     

Elaboration and characterization of hydrogen standard stable under heavy ion irradiation: Application to nuclear astrophysics

A hydrogen standard has been carried out by ion implantation in silicon. The silicon wafer was implanted with hydrogen at different energies and fluences to provide a ∼100 nm flat distribution to the specimen. The samples obtained were characterized by mean of elastic recoil detection analysis (ERDA) and resonant nuclear reaction analysis (RNRA). All important properties of the hydrogen standard have been controlled: isotopic purity, depth profile, stability under ion irradiation and reproducibility. The standards were validated by the measurement of the resonant cross-section of the ¹³C(p,γ)¹⁴N reaction. The similarity of the resonance energy, the resonance width and the resonance strength measurements with those reported in literature confirms the validity of the proposed procedure for hydrogen standards. Therefore, this kind of target could be used to investigate all nuclear reactions in which a proton is involved, from reactions with astrophysical interest to the ones with concern in material analysis.     

Thermal neutron cross-section and resonance integral of the Mo(n,γ)Mo reaction

We measured the thermal neutron cross-section and the resonance integral of the ⁹⁸Mo(n,γ)⁹⁹ Mo reaction by the activation method using a ¹⁹⁷Au(n,γ)¹⁹⁸ Au monitor reaction as a single comparator. The high-purity natural Mo and Au metallic foils with and without a cadmium shield case of 0.5 mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a calibrated p-type high-purity Ge detector. The necessary correction factors for the γ-ray attenuation (F_g), the thermal neutron self-shielding (G_th) and the resonance neutron self-shielding (G_epi) effects, and the epithermal neutron spectrum shape factor (α) were taken into account. In addition, for the ⁹⁹Mo activity measurements, the correction for true coincidence summing effects was also taken into account. The thermal neutron cross-section for the ⁹⁸Mo(n,γ)⁹⁹Mo reaction has been determined to be 0.136 ± 0.007 barn, relative to the reference value of 98.65 ± 0.09 barn for the ¹⁹⁷Au(n,γ)¹⁹⁸ Au reaction. The present result is, in general, in good agreement with most of the experimental data and the recently evaluated values of ENDF/B-VII.0, JENDL-3.3, and JEF-2.2 by 5.1% (1σ). By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral for the ⁹⁸Mo(n,γ)⁹⁹Mo reaction is 7.02 ± 0.62 barn, which is determined relative to the reference values of 1550 ± 28 barn for the ¹⁹⁷Au(n,γ)¹⁹⁸Au reaction. The present resonance integral value is in general good agreement with the previously reported data by 8.8% (1σ).     

Measurement of differential cross-sections and widths of resonances in S(p,p′γ) S reaction in the 3.0-4.0 MeV region

The paper reports the widths and differential cross-sections of resonances at 3.089, 3.379 and 3.717 MeV in the ³²S(p,p′γ)³²S nuclear reaction. The cross-sections are computed at 0° and 90° angles (relative to the beam direction) from thick target excitation curves constructed by measuring 2230 keV γ-rays, characteristic of the reaction. The differential cross-sections of resonances are about 18, 64 and 70 mb/sr respectively at 0° angle and decrease by about half around an angle of 90°. The first resonance, the sharpest among the three, exhibits a width of about 400 eV while those at 3.379 and 3.717 MeV are in 1.0-1.5 keV range. The widths of the resonances are extracted from the respective thick target excitation curves by an interquartile separation method and also by simulating their leading edges. A study of thick target yields in the 3.0-4.0 MeV proton energy region for several sulphide forming elements shows the absence of any significant interference. These resonances, as a result, can be effectively utilised for sensitive and high resolution depth profile measurements of sulphur in films and materials surfaces.     

Isomeric yield ratios for the formation of Sc in the Sc(γ,n), Ti(γ,xnp), Fe(γ,xn5p) and Cu(γ,xn8p) reactions with 2.5 GeV bremsstrahlung

We measured the isomeric yield ratios for the ^44m,gSc isomeric pairs produced from four different photonuclear reactions ⁴⁵Sc(γ,n)^44m,gSc, ^natTi(γ,xn1p)^44m,gSc, ^natFe(γ,xn5p)^44m,gSc, and ^natCu(γ,xn8p)^44m,gSc by using the activation method. The high purity natural Sc, Ti, Fe, and Cu metallic foils in disc shape were irradiated with uncollimated 2.5 GeV bremsstrahlung beams of the Pohang Accelerator Laboratory. The induced activities in the irradiated foils were measured by the high-resolution γ-ray spectrometry with a calibrated high-purity Germanium (HPGe) detector. In order to improve the accuracy of the experimental results the necessary corrections were made in the gamma activity measurements and data analysis. The obtained isomeric yield ratios for the ⁴⁵Sc(γ,n)^44m,gSc, ^natTi(γ,xn1p)^44m,gSc, ^natFe(γ,xn5p)^44m,gSc and ^natCu(γ,xn8p)^44m,gSc reactions are 0.25 ± 0.03, 0.43 ± 0.05, 1.38 ± 0.14, and 1.89 ± 0.21, respectively. The present result for the ^natCu(γ,xn8p)^44m,gSc reaction is in good agreement with the existing data. Our results for the ⁴⁵Sc(γ,n)^44m,gSc, ^natTi(γ,xn1p)^44m,gSc, and ^natFe(γ,xn5p)^44m,gSc reactions are the first measurements at 2.5 GeV bremsstrahlung. The obtained results are compared with the corresponding values found in the literature. The relation between the isomeric yield ratios and the complexity of the photonuclear reactions is discussed.     

Monte Carlo study of ion-induced backward and forward secondary electron emission from thin Al foil

A direct Monte Carlo program has been developed to calculate the backward (γ_b) and forward (γ_f) electron emission yields from 20 nm thick Al foil for impact of C⁺, Al⁺, Ar⁺, Cu⁺ and Kr⁺ ions having energies in the range of 0.1-10 keV/amu. The program incorporates the excitation of target electrons by projectile ions, recoiling target atoms and fast primary electrons. The program can be used to calculate the electron yields, distribution of electron excitation points in the target and other physical parameters of the emitted electrons. The calculated backward electron emission yield and the Meckbach factor R = γ_f/γ_b are compared with the available experimental data, and a good agreement is found. In addition, the effect of projectile energy and mass on the longitudinal and lateral distribution of the excitation points of the electrons emitted from front and back of Al target has been investigated.     

Production and characterization of thin Li targets fabricated by ion implantation

Very high fluence implantation of ⁷Li⁺ ions was used to promote the formation of a thin and high density ⁷Li target in the surface region of Al samples. The implanted volume was characterized by particle induced gamma-ray emission, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy and nuclear reaction analysis, revealing that the implanted surface is a combination of Li₂CO₃, metallic lithium, LiOH and C, with almost no Al present. Radiation damage effects by proton beams were studied by observing the evolution of the ⁷Li(p, α)⁴He nuclear reaction yield with the accumulated charge, at different proton energies, revealing high stability of the produced Li target.     

Measurement of thermal neutron cross-section and resonance integral for the Yb(n,γ)Yb reaction by the cadmium ratio method

The thermal-neutron cross-section and the resonance integral for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction were measured by the activation method using a ⁵⁵Mn monitor as single comparator. Analytical grade MnO₂ and Yb₂O₃ powder samples with and without a cylindrical 1 mm Cd shield box were irradiated in an isotropic neutron field obtained from three ²⁴¹Am-Be neutron sources. The gamma-ray spectra from the activated samples were measured with a calibrated n-type high-purity Ge detector. The experimental results were corrected for the correction factors calculated for thermal and epithermal neutron self-shielding effects, epithermal neutron spectrum shape and gamma-ray self attenuation. Thus, the thermal neutron cross-section for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 126.5 ± 6.6 b, relative to that of the ⁵⁵Mn monitor. The resonance integral value for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 59.6 ± 8.5 b, at cadmium cut-off energy of a 0.55 eV. Using the measured cadmium ratios of ⁵⁵Mn and ¹⁷⁴Yb, the result for resonance integral of the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction has also been obtained relative to the reference value of the ⁵⁵Mn monitor. The present results for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction agree well only with the recent experimental ones obtained by Kafala et al. [1] and De Corte and Simonits [2] within uncertainty limits. However, the previously reported experimental data for the thermal neutron cross-section for this reaction are distributed between 24 and 141 b, and similarly the experimental values for the resonance integral value also show a large scatter in the range of 30-69 b.     

Cross section measurements for As isotope at neutron energies from 13.5 to 14.8 MeV

Cross sections which is relevant in research of neutron transmutation doping of some important semiconducting materials were measured at neutron energies from 13.5 to 14.8 MeV for the reactions ⁷⁵As(n, 2n)⁷⁴As, ⁷⁵As(n, p)^75m+gGe, ⁷⁵As(n, α)^72m+gGa by activation relative to the ²⁷Al(n, α)²⁴Na reaction. Measurements were carried out by γ-detection using a coaxial HPGe detector. Natural realgar (As₂S₂) powder of 99.9% purity was used as samples. Fast neutrons were produced by the T(d, n)⁴He reaction. The results obtained are compared with existing data.     

Experimental study of the Ho(p,n) nuclear reaction for production of the therapeutic radioisotope Er

The 10.3 h half life radionuclide ¹⁶⁵Er, decaying by electron capture to stable ¹⁶⁵Ho, is an excellent candidate for Auger-electron therapy. In the frame of a systematic study of charged particle production routes of ¹⁶⁵Er, the excitation function of the ¹⁶⁵Ho(p,n)¹⁶⁵Er reaction was measured up to 35 MeV by using a stacked foil irradiation technique and X-ray spectroscopy. The measured excitation function shows a significant energy shift when compared to the only experimental dataset measured earlier and an acceptable agreement with the results of different nuclear reaction model codes. The thick target yields calculated from the excitation function at typical energies available at small cyclotrons (E_p = 11 MeV and E_p = 15 MeV) are 41 MBq/μAh = 11 GBq/C and 75 MBq/μAh = 21 GBq/C, respectively.     

Improved energy resolution of a cyclotron beam for RBS measurements

For RBS (Rutherford Back Scattering) analysis, the quality of the beam is of premium importance because the depth profile resolution of the method is strongly dependent on the energy resolution of the probing beam. A magnetic analyzer, consisting of two 90 left-right bending magnets forming an achromatic doublet has been adapted to the Liege 20 MeV (proton) AVF (Azimuthal Varying Field) cyclotron. The energy resolution of that system has been measured by recording the resonance width of a ³²S(p,p′γ)³²S (3.38 MeV. p⁺ lab. energy). We have obtained a value of ΔE = ± 2 keV, reducing by a factor of 20 the natural dispersion of our cyclotron.We describe our magnetic analyzer system and present the results of our RBS measurements at energies up to 14 MeV α.     

Measurement of thermal neutron cross-sections and resonance integrals for Hf(n,γ)Hf and Hf(n,γ)Hf reactions at the Pohang neutron facility

The thermal-neutron cross-sections and the resonance integrals for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been measured by the activation method. The high purity Hf and Au metallic foils within and without a Cd shield case were irradiated in a neutron field of the Pohang neutron facility. The gamma-ray spectra from the activated foils were measured with a calibrated p-type high-purity Ge detector.In the experimental procedure, the thermal neutron cross-sections, σ₀, and resonance integrals, I₀, for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been determined relative to the reference values of the ¹⁹⁷Au(n,γ)¹⁹⁸Au reaction, with σ₀ = 98.65 ± 0.09 barn and I₀ = 1550 ± 28 barn. In order to improve the accuracy of the experimental results, the interfering reactions and necessary correction factors were taken into account in the determinations. The obtained thermal neutron cross-sections and resonance integrals were σ₀ = 0.424 ± 0.018 barn and I₀ = 6.35 ± 0.45 barn for the ¹⁷⁹Hf(n,γ)^180mHf reaction, and σ₀ = 12.87 ± 0.52 barn and I₀ = 32.91 ± 2.38 barn for the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reaction. The present results are in good agreement with recent measurements.     

Measurements of activation cross sections for Lu(n, α)Tm,Lu(n, α)Tm and Lu(n, p)Yb reactions induced by neutrons around 14 MeV

The cross sections for the ¹⁷⁵Lu(n, α)¹⁷²Tm, ¹⁷⁶Lu(n, α)¹⁷³Tm and ¹⁷⁵Lu(n, p)^175m+gYb reactions have been measured in the neutron energy range of 13.5–14.8 MeV using the activation technique. The first data for ¹⁷⁵Lu(n, α)¹⁷²Tm reaction cross sections are presented. In our experiment, the fast neutrons were produced via the ³H(d, n)⁴He reaction on K-400 Neutron Generator at Chinese Academy of Engineering Physics (CAEP). Induced gamma activities were measured by a high-resolution (1.69 keV at 1332 keV for ⁶⁰Co) gamma-ray spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The neutron fluences were determined by the cross section of ⁹³Nb(n, 2n)^92mNb or ²⁷Al(n, α)²⁴Na reactions. The neutron energy in the measurement was by the cross section ratios of ⁹⁰Zr(n, 2n)^89m+gZr and ⁹³Nb(n, 2n)^92mNb reactions. The results were discussed and compared with experimental data found in the literature and with results of published empirical formulae.     

Measurement of thermal neutron and resonance integral cross sections of the reaction V(n,γ)V using a 20 Ci Am–Be isotopic neutron source

The thermal neutron capture cross section (σ_o) and the resonance integral (I_o) of the ⁵¹V(n,γ)⁵²V reaction were measured with an activation method to provide fundamental data for reactor calculation, activation analysis, and other theoretical and experimental uses concerning the interaction of neutron with matter. The vanadium and manganese samples were irradiated within and without a Cd shield case using a 20 Ci Am–Be neutron source. The activities of the samples were measured using gamma-ray spectroscopy. The thermal neutron capture cross section and the resonance integral were determined relative to the reference reaction ⁵⁵Mn(n,γ)⁵⁶Mn and the values obtained are 5.16 ± 0.19 barns and 2.53 ± 0.1 barns respectively. The previous measurements of the σ_o and I_o of the reaction ⁵¹V(n,γ)⁵²V were reviewed and the difference between the present values and the previous results were discussed.     

Heat deposition in thick targets due to interaction of high energy protons and thermal hydraulics analysis

Heat deposition inside thick targets due to interaction of high energy protons (E_p ∼ GeV) has been estimated using an improved version of the Monte Carlo simulation code CASCADE.04.h. The results are compared with the available experimental data for thick targets of Be, Al, Fe, Cu, Pb and Bi at proton energies of 0.8 GeV, 1.0 GeV and 1.2 GeV. A more continuous heat deposition approach which has been adopted in CASCADE.04.h yields results which are in better agreement with the experimental data as compared to the ones from the earlier version of CASCADE.04. The results are also compared with the predictions of the FLUKA Monte Carlo code. Both CASCADE.04.h and FLUKA predictions are nearly similar for heavy targets and both agree with the experimental measurements. However, they do have differences in predictions for lighter targets where measurements also differ from the predictions. It is observed that the maximum heat loss in thick targets occurs at the beginning of the target due to increasing nuclear reaction contributions. This aspect is crucial in designing the window of a spallation neutron target employed in an accelerator driven sub-critical system (ADS) as this is the first material to be traversed by the proton beam and is subjected to the maximum temperature gradient. Optimization of the target-window parameters requires a careful estimation of heat deposition in the window region and this has been demonstrated through thermal hydraulic studies related to the design of a realistic lead bismuth eutectic (LBE) spallation neutron target for an ADS system.