Comparison of 41Ca analysis on 0.5 MV and 5 MV-AMS systems

A comparative study was made between the compact AMS system at the PSI/ETH Laboratory of Ion Beam Physics in Zurich with 0.5 MV terminal voltage and the 5 MV-AMS system at the Scottish Universities Environmental Research Centre (SUERC), Glasgow. Overall 34 urinary samples with ⁴¹Ca/⁴⁰Ca ratios in the range from 4 × 10^?11 to 3 × 10^?10 were processed to CaF₂ and aliquots of the same material were measured on both instruments.Measurements on the compact AMS system were performed in charge state 3+ achieving a transmission of 4% at 1.7 MeV beam energy. Under these conditions a suppression of the interference ⁴¹K is virtually impossible. However, samples with an excess of potassium can be identified by a shift of the ⁴¹Ca/⁴¹K peak in the ΔE ? E histogram of the gas ionization detector employed and a criterion for data rejection can be defined. An overall precision of ～4% and a ⁴¹Ca/⁴⁰Ca background level of 5 × 10^?12 have been reached.For studies with higher demands on the detection limit AMS systems like the one at SUERC are attractive: in charge state 5+ and using a gas stripper beam energy of 27 MeV, a transmission of 5%, a ⁴¹K suppression factor of ～500 and a ⁴¹Ca/⁴⁰Ca background level of 3 × 10^?14 are achieved.We demonstrate that both systems are well suited for large-scale ⁴¹Ca biomedical applications.     

Improved 10Be and 26Al-AMS with a 5 MV spectrometer

Detector and ion source changes have increased Be and Al count rates and reduced measurement background at SUERC. Low energy 16 MeV ²⁶Al³⁺ ions can be separated from interferences by adopting thin silicon nitride membrane detector windows. In contrast, a thick Havar detector window is used to preferentially slow boron ions for simplified ¹⁰Be vs. ¹⁰B separation without an additional gas cell.     

Boron lattice site location in (BGa)As and (BGa)P thin films studied using RBS and NRA with a channeled He+ ion beam

In this study the boron lattice site location in ternary B_xGa_1?xAs and B_xGa_1?xP thin films grown on (0 0 1) GaAs and (0 0 1) GaP, respectively, using low pressure metal-organic vapour-phase epitaxy (MOVPE) with boron concentrations between x = 0.8% and x = 3.2% was investigated with RBS and the ¹⁰B(α,p)¹³C nuclear reaction using a 2.3 MeV He⁺ ion beam. For this purpose, the ion beam was aligned with the [0 0 1], [0 1 1] and [1 1 1] axis and the RBS and proton yield from the nuclear reaction compared with random ion incidence. For comparison, theoretical proton yields which assume boron to be located on substitutional lattice sites only were calculated for each sample/axis combination and compared with the experimental yields. The RBS/channeling measurements show a very good crystal quality of the films with χ_min being in the range of 3–5% for the [0 1 1] axis. The best crystal qualities, i.e. the lowest χ_min values and dechanneling rates, are achieved for low boron concentrations. From NRA/channeling it can be deduced that in the B_xGa_1?xAs films the fraction of interstitial boron is approximately 5% for low boron concentrations of x = 1% and 6–10% for concentrations up to x = 3.2%, whereas the fraction of interstitial boron is less than 3% in the B_xGa_1?xP film studied despite a concentration of x = 2.0%. This indicates that antisite effects of the boron incorporation are more likely in GaAs compared to GaP.     

Elastic scattering of 7Li + 27Al at several angles in the 7–11 MeV energy range

Elastic cross sections for the ⁷Li + ²⁷Al system were measured at laboratory energies between 7 and 11 MeV in steps of 0.25 MeV, and angles between 135° and 170° in steps of 5°. Excitation functions for the elastic scattering were measured using an array of eight Si surface-barrier detectors whereas a solid-state telescope was used to estimate and subtract background from other reactions. Contamination from α particles arising from the ⁷Li breakup process at E_lab ? 10 MeV makes the use of these energies inadvisable for RBS applications. The present results are compared with previous data obtained at 165° (E_lab ? 6 MeV), 140° and 170° (E_lab ? 8 MeV). The experimental data were analyzed in terms of the Optical Model. Two different energy-independent potentials were found. These optical potentials allow an interpolation with physical meaning to other energies and scattering angles. The experimental cross sections will be uploaded to the IBANDL database.     

Optical contrast formation in amorphous silicon carbide with high-energy focused ion beams

Thin films (d ～ 1 μm) of hydrogenated amorphous silicon carbide (a-Si_1?xC_x:H), deposited by RF reactive magnetron sputtering with different carbon content x, have been implanted with high fluences (Φ = 1016–1017 cm^?2) of high-energy (E = 0.2–1 MeV) He⁺ ions as the implant species. The induced structural modification of the implanted material results in a considerable change of its optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies as obtained from photo-thermal-deflection spectroscopy (PDS) data. This shift is accompanied by a remarkable increase of the absorption coefficient over one order of magnitude (photo-darkening effect) in the measured photon energy range (0.6–3.8 eV), depending on the ion fluence, energy and carbon content of the films. These effects could be attributed both to additional defect introduction and increased graphitization, as confirmed by Raman spectroscopy and infra-red (IR) optical transmission measurements. The optical contrast thus obtained (between implanted and unimplanted film material) could be made use of in the area of high-density optical data storage using focused high-energy He⁺ ion beams.     

New results on the neutron-induced fission cross-section of 231Pa for incident neutron energies En = 0.8–3.5 MeV

New results on the neutron-induced fission cross-section of ²³¹Pa in the incident neutron energy range between E_n = 0.8 and 3.5 MeV are presented. The individual cross-section data are obtained within an uncertainty of less than 5% and meets the accuracy required by the IAEA in the summary report of the consultants’ meeting on “Assessment of Nuclear Data Needs for Thorium and other Advanced Cycles” from 1999. With the new data the hitherto existing large spread between evaluated data files may be removed.     

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.     

Competitive 10Be measurements below 1 MeV with the upgraded ETH–TANDY AMS facility

Competitive ¹⁰Be measurements at energies as low as 0.75 MeV are now possible with the compact ETH AMS system TANDY. In this paper we describe and discuss the modifications that led to the significantly improved performance for ¹⁰Be at the 0.6 MV accelerator. Results from the first routine measurement show that ¹⁰Be on the upgraded TANDY is now fully competitive with larger AMS systems with respect to background and measurement precision. The total efficiency for ¹⁰Be is comparable to our large 6 MV Tandem system and thus sufficient for the full range of applications in the Earth and Environmental Sciences.     

Challenges and opportunities in high-precision Be-10 measurements at CAMS

We determined the overall efficiency for ¹⁰Be of the high-intensity LLNL modified Middleton cesium sputter source in combination with the CAMS FN mass spectrometer. BeO^? ionization efficiency is >3%. Charge exchange efficiency including transmission through the tandem for 7.5 MeV Be⁺³ is ～34%, resulting in a total system efficiency of just over 1%. At this efficiency and with very low backgrounds, we estimate our detection limit to be ～1000 ¹⁰Be atoms. Cathodes prepared with only ～80 μg of ⁹Be show only an ～33% reduction in ⁹Be beam current compared to a sample with ～200 μg. These same samples, prepared from 07KNSTD1032 standard material, contained 1 × 10⁷ and 5 × 10^{6 10}Be atoms and exhibited similar ionization and total system efficiency. These results demonstrate the feasibility of pursuing applications that require precise measurement of samples with low ¹⁰Be concentrations and/or small sample size.     

Fluorides or hydrides? 41Ca performance at VERA’s 3-MV AMS facility

Recent improvements in isobaric suppression for medium-mass isotopes, e.g. ⁴¹Ca, offer new possibilities for tandem accelerators with terminal voltages of 3 MV or lower; i.e. when dealing with particle energies ?1 MeV/amu. In particular, detection of ⁴¹Ca requires sufficient discrimination of the stable isobar ⁴¹K. We explored the limits of ⁴¹Ca detection at our 3-MV AMS facility by means of different types of particle detectors: The ΔTOF method, which is based on the different flight-time of isobars after passing a thick absorber foil. The second method makes use of a new type of compact ionization chamber: ⁴¹K and ⁴¹Ca are separated in energy due to their different energy loss in the detector entrance foil and the detector gas, which is measured via a segmented anode.At VERA we measured ⁴¹Ca/Ca ratios below 10^?13 for commercial CaF₂ material serving as blank samples. CaH₂ sputter targets, with the extraction of ${\text{CaH}}_3^{-}$, yielded background ratios as low as ⁴¹Ca/Ca = 1 × 10^?15. The typical measurement precision at VERA for ⁴¹Ca measurements was between 2% and 5%. These results demonstrate that AMS facilities based on 3-MV tandems have reached the sensitivity level of larger AMS facilities for a wide range of applications, with the advantage of high overall efficiency and sample throughput.     

A simple way to analyze infrared reflectivity spectra of p-type Hg0.78Cd0.22Te implanted in various conditions

Different ion-implanted p-type Hg_0.78Cd_0.22Te samples were analyzed by infrared reflectivity in the 2–20 μm wavelength range. We show how to derive some characteristic values of the free carriers induced by ion implantation from simple models of the implanted samples. For low energy implantations (Al (320 keV)) an excess of electrons with concentration n⁺ ≈ 5 × 10¹⁷ cm⁻³ for doses 10¹² and 10¹⁴ ions cm⁻² is observed between the surface and the projected range R_p of the ions, in agreement with the well-known change of type of the free carriers induced by the ion implantation in this kind of samples. High energy α particle (0.8 and 2 MeV, 10¹⁴ ions cm⁻²) implantations lead to a pronounced inhomogeneous concentration of free electrons with n⁺ ≈ 9.2 × 10¹⁶ cm⁻³ between the surface and R_p where a negligible amount of defects due to the nuclear energy loss is formed, and n⁺ ≈ 1.6 × 10¹⁷ cm⁻³ between R_p and R_p + ΔR_p, ΔR_p being the longitudinal straggling, where the defect production rate through the nuclear energy loss mechanism is maximum.     

Measurements and model calculations of activation cross sections for 232Th(n,2n)231Th reaction between 13.57 and 14.83 MeV neutrons

In this study, activation cross sections were measured for the reaction of ²³²Th(n,2n)²³¹Th (T_1/2 = 25.5 h) by using neutron activation technique at six different neutron energies from 13.57 and 14.83 MeV. Neutrons were produced via the ³H(²H,n)⁴He reaction using SAMES T-400 neutron generator. Irradiated and activated high purity Thorium foils were measured by a high-resolution γ-ray spectrometer with a high-purity Germanium (HpGe) detector. In cross section measurements, the corrections were made for the effects of γ-ray self-absorption in the foils, dead-time, coincidence summing, fluctuation of neutron flux, low energy neutrons. For this reaction, statistical model calculation, which the pre-equilibrium emission effects were taken into consideration, were also performed between 13.57 and 14.83 MeV energy range. The cross sections were compared with previous works in literature, with model calculation results, and with evaluation data bases (ENDF/B-VII, ENDF/B-VI, JEFF-3.1, JENDL-4.0, JENDL-3.3, and ROSFOND-2010).     

Study and optimization of boronization in Alcator C-Mod using the Surface Science Station (S3)

A Surface Science Station (S³) on the Alcator C-Mod tokamak is used to study and optimize the location and rate of boron film deposition in situ during electron cyclotron (EC) discharge plasmas using 2.45 GHz radio-frequency (RF) heating and a mixture of helium and diborane (B₂D₆) gasses. The radial profile of boron deposition is measured with a pair of quartz microbalances (QMB) on S³, the faces of which can be rotated 360° including orientations parallel and perpendicular to the toroidal magnetic field B_T ～0.1 T. The plasma electron density is measured with a Langmuir probe, also on S³ in the vicinity of the QMBs, and typical values are ～1 × 10¹⁶ m^?3. A maximum boron deposition rate of 0.82 μg/cm²/min is obtained, which corresponds to 3.5 nm/min if the film density is that of solid boron. These deposition rates are sufficient for boron film applications between tokamak discharges. However the deposition does not peak at the EC resonance as previously assumed. Rather, deposition peaks near the upper hybrid (UH) resonance, ～5 cm outboard of the EC resonance. This has implications for RF absorption, with the RF waves being no longer damped on the electrons at the EC resonance. The previously inferred radial locations of critical erosion zones in Alcator C-Mod also need to be re-evaluated. The boron deposition profile versus major radius follows the ion flux/density profile, implying that the boron deposition is primarily ionic. The application of a vertical magnetic field (B_V ～0.01 T) was found to narrow the plasma density and boron deposition profiles near the UH resonance, thus better localizing the deposition. A Monte Carlo simulation is developed to model the boron deposition on the different QMB/tokamak surfaces. The model requires a relatively high boron ion gyroradius of ～5 mm, indicating a B⁺¹ ion temperature of ～2 eV, to match the deposition on QMB surfaces with different orientation to B_T. Additionally, the boron ion trajectories become de-magnetized at high neutral gas throughput (～0.5 Pa m³ s^?1) and pressure (～2 Pa) when the largest absolute deposition rates are measured, resulting in deposition patterns, which are independent of surface orientation to B_T in optimized conditions.     

Measurement of thermal neutron cross section and resonance integral for 165Ho(n, γ)166gHo reaction by the activation method

The thermal neutron cross section and the resonance integral of the reaction ¹⁶⁵Ho(n, γ)^166gHo were measured by the activation method using ⁵⁵Mn(n,γ)⁵⁶Mn monitor reaction. The sufficiently diluted MnO₂ and Ho₂O₃ samples with and without a cylindrical Cd case were irradiated in an isotropic neutron field of the ²⁴¹Am–Be neutron sources. The γ-ray spectra from the irradiated samples were measured with a calibrated n-type high purity Ge detector. Thus, the thermal neutron cross section for ¹⁶⁵Ho(n,γ)^166gHo reaction has been determined to be 59.2 ± 2.5 b relative to the reference thermal neutron cross section value of 13.3 ± 0.1 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction, and it generally agrees with the recent measurements within about 1 to 12%. The resonance integral has also been measured relative to the reference value of 14.0 ± 0.3 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction using an epithermal neutron spectrum of the ²⁴¹Am–Be neutron source. The resonance integral for ¹⁶⁵Ho(n, γ)^166gHo reaction obtained was 667 ± 46 b at a cut-off energy of 0.55 eV for 1 mm Cd thickness. The existing experimental and evaluated data for the resonance integral are distributed from 618 to 752 b. The present resonance integral value agrees with most of the previously reported values obtained by ¹⁹⁷Au standard monitor within the limits of error.     

129I AMS at 0.5 MV tandem accelerator

The ¹²⁹I measurement program has been established at the 0.5 MV ‘Tandy’ accelerator of the PSI/ETH Zürich AMS facility. This development was made possible by using a SiN window instead of Mylar one in a gas ionization detector. The setting up of the ¹²⁹I measurement at Tandy is simple, the acquired performance is stable and reliable, and the quality of results is equal to or better than at our larger EN-tandem. With this setup, high sample throughput, which is required in many ¹²⁹I studies, can be easily achieved. The measurements are performed in the +3 charge state. At this charge state the major difficulty in the ¹²⁹I⁺³ identification is caused by a highly abundant 43⁺¹ (m = 43, q = +1) molecule interference. This is a positive molecular ion, because its intensity reduces exponentially with an increase in gas stripper pressure. We conclude that this molecule is ²⁷Al¹⁶O⁺ (m/q = 43/1 = 129/3) and comes from the break-up of (Al₂O₃ + Al)^? (m = 129) precursor at the terminal: (Al₂O₃ + Al)^? → ²⁷Al¹⁶O⁺. The expected isobaric interferences ⁴³Ca⁺¹ and ⁸⁶Sr⁺², which also originate from the break-up of molecules in the stripper, were found to be low and do not disturb the ¹²⁹I⁺³ measurements. The best repeatable performance with our standard sample material was achieved at 0.14 μg/cm² Ar gas stripper pressure with machine blanks showing ～6 × 10^?14 normalized ¹²⁹I/I ratio and 9% transmission through the accelerator. However, high ²⁷Al¹⁶O⁺ molecular rates were observed from the user samples, and in order to destroy these molecules we had to increase the stripper pressure to ～0.22 μg/cm². This increase in the stripper pressure degraded the machine blank values to ～9 × 10^?14 and reduced transmission to 8%. Nevertheless, the achieved measurement conditions are sufficient for measurement of nearly all ¹²⁹I samples that have been submitted to PSI/ETH over the last few years.     

Calculation of response matrix of CaSO4:Dy based neutron dosimeter using Monte Carlo code FLUKA and measurement of 241Am–Be spectra

Response matrix for CaSO₄:Dy based neutron dosimeter was generated using Monte Carlo code FLUKA in the energy range thermal to 20 MeV for a set of eight Bonner spheres of diameter 3–12″ including the bare one. Response of the neutron dosimeter was measured for the above set of spheres for ²⁴¹Am–Be neutron source covered with 2 mm lead. An analytical expression for the response function was devised as a function of sphere mass. Using Frascati Unfolding Iteration Tool (FRUIT) unfolding code, the neutron spectrum of ²⁴¹Am–Be was unfolded and compared with standard IAEA spectrum for the same.     

Comparison of detector systems for the separation of 36Cl and 36S with a 3-MV tandem

The possibility of detecting ³⁶Cl for geological exposure dating has been explored for several years at VERA (the Vienna Environmental Research Accelerator). First results on real samples were obtained with an ionization chamber (developed at the ETH/PSI, Zürich, Switzerland) with two anodes. To improve the suppression of ³⁶S, we equipped the ionization chamber with an exit window and added a Time-of-Flight (TOF) system with a double-sided silicon strip detector (50 × 50 mm²) as stop detector. We optimized the TOF setup by using silicon nitride foils to reduce scattering tails in the energy spectra.At 3 MV terminal voltage, corresponding to a particle energy of 24 MeV of ³⁶Cl⁷⁺, we achieved a ³⁶S⁷⁺-suppression of 21,500 (50% ³⁶Cl-detector-efficiency).     

Determination of differential cross-sections for the natK(p, p0) and 39K(p, α0) reactions in the backscattering geometry

In the present work, new, differential cross-section values are presented for the ^natK(p, p₀) reaction in the energy range E_lab = 3000–5000 keV (with an energy step of 25 keV) and for detector angles between 140° and 170° (with an angular step of 10°). A qualitative discussion of the observed cross-section variations through the influence of strong, closely spaced resonances in the p + ³⁹K system is also presented. Information has also been extracted concerning the ³⁹K(p,α₀) reaction for E_lab = 4000–5000 keV in the same angular range. As a result, more than ～500 data points will soon be available to the scientific community through IBANDL (Ion Beam Analysis Nuclear Data Library – http://www-nds.iaea.org/ibandl/) and could thus be incorporated in widely used IBA algorithms (e.g. SIMNRA, WINDF, etc.) for potassium depth profiling at relatively high proton beam energies.     

Nondestructive Magnetic Adaptive Testing of nuclear reactor pressure vessel steel degradation

Inspection of neutron-irradiation-generated degradation of nuclear reactor pressure vessel steel (RPVS) is a very important task. In ferromagnetic materials, such as RPVS, the structural degradation is connected with a change of their magnetic properties. In this work, applicability of a novel magnetic nondestructive method (Magnetic Adaptive Testing, MAT), based on systematic measurement and evaluation of minor magnetic hysteresis loops, is shown for inspection of neutron irradiation embrittlement in RPVS. Three series of samples, made of JRQ, 15CH2MFA and 10ChMFT type steels were measured by MAT. The samples were irradiated by E > 1 MeV energy neutrons with total neutron fluence of 1.58 × 10¹⁹–11.9 × 10¹⁹ n/cm². Regular correlation was found between the optimally chosen MAT degradation functions and the neutron fluence in all three types of the materials. Shift of the ductile–brittle transition temperature, ΔDBTT, independently determined as a function of the neutron fluence for the 15CH2MFA material, was also evaluated. A sensitive, linear correlation was found between the ΔDBTT and values of the relevant MAT degradation function. Based on these results, MAT is shown to be a promising (at least) complimentary tool of the destructive tests within the surveillance programs, which are presently used for inspection of neutron-irradiation-generated embrittlement of RPVS.     

Improved 36Cl AMS at 5 MV

Small changes to our ion source and gas ionization detector have significantly improved Cl measurement by reducing source memory and increasing interference rejection. Gas stripped low energy 30 MeV ³⁶Cl⁵⁺ ions are still efficiently transported to the detector but ³⁶S vs. ³⁶Cl separation is improved by an order of magnitude. Accordingly ³⁶Cl/Cl background is <10^?15 before additional interference correction that is also newly automated. ³⁵Cl^? currents have increased to 30 μA and ³⁶Cl/Cl inter-cathode repeatability is 3%.