10Be in desert sands,falling dust and loess in China

Cosmogenic ¹⁰Be is produced in the atmosphere, and deposits onto the surface of the earth mainly through wet precipitation and dust. Based on the analysis of ¹⁰Be in Chinese loess, we believe that ¹⁰Be in loess is composed of two components: locally precipitated atmospheric ¹⁰Be, and windblown ¹⁰Be adsorbed on the surface of silt grains. On the Loess Plateau, ¹⁰Be concentrations in loess and paleosol range from (1.4 to 2.8) × 10⁸ atoms/g and (2.7 to 4.5) × 10⁸ atoms/g, respectively. To investigate the sources of ¹⁰Be in loess, we measured ¹⁰Be in sand grains from deserts in western China and falling dust from the deposition regions. The results show that the ¹⁰Be concentrations in sand and dust are (1.1–5.1) × 10⁷ atoms/g and (1.3–2.8) × 10⁸ atoms/g, respectively. Loess and paleosol on the Loess Plateau both contain inherited ¹⁰Be adsorbed on silt grains from dust; most of the windblown deposited loess materials do not directly come from the Gobi and other sand deserts, but mainly from the loess–desert transitional zones, which are characterized by silt and dust holding areas.     

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.     

10Be application to soil development on Marion Island,southern Indian Ocean

Marion Island, located in the southern Indian Ocean, constitutes the summit of an active shield volcano. It is a small terrestrial environment where glacially abraded bedrock became exposed c × 10 kyr ago. These conditions provide an interesting possibility for the assessment of ¹⁰Be accumulation rates and their application to soil erosion studies on the island. ¹⁰Be concentrations were measured in precipitation, soil profiles and an Azorella selago cushion plant. The data reveal a ¹⁰Be precipitation flux several times higher than model prediction. Estimation of the ¹⁰Be accumulation based on the soil inventory suggests a span between 2000 and 7000 yr. This time span is not in accordance with the accepted notion that the island was covered with ice about 10,000 yr ago and suggests either removal of ¹⁰Be from the soil profile, an overestimated Holocene ¹⁰Be-flux or a delayed soil development history. Our results provide new data on ¹⁰Be concentrations from the sub-Antarctic islands and contribute towards enlarging the southern-hemisphere ¹⁰Be database.     

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.     

AMS measurements of 10Be and 14C in loess profile at Donglingshan,Beijing

A loess profile in Donglingshan site (40°02′N, 115°27′E) near Beijing was chosen to study the loess formation process and paleo-climate variation. Thirty eight samples were collected and analyzed for ¹⁴C, ¹⁰Be as well as MS, TOC and δ¹³C. Based on ¹⁴C measurements, we established a time scale for this loess profile during Holocene. The averaged ¹⁰Be deposition flux was found to be 4.87 × 10⁶ atoms/cm² year. This is similar to the flux of 4.2 × 10⁶ atoms/cm² year estimated for Chinese Loess Plateau in central China. High ¹⁰Be concentrations of 3.85–5.66 × 10⁸ atoms/g for the samples in layer 23–39 cm from 2965 to 528 years BP suggest a warm and humid weather during this period. MS values have similar variation with ¹⁰Be and reflect the similar paleo-climate information. TOC and δ¹³C suggest that the vegetation around Donlingshan area was C₃ type plants during entire Holocene.     

SUERC AMS ion detection

In a short time Be, C, Al, Cl, Ca and I accelerator mass spectrometry (AMS) have been established on the National Electrostatics Corporation (NEC) 5 MV pelletron system at the Scottish Universities Environmental Research Centre (SUERC). While summarising the present performance of the system, this report will focus on the details of ion detection, which sample materials are used and the analytical procedures employed for each individual species during routine analysis.All rare isotope detection is with a single flexible detector and ion event analysis system, but switching of analysed species typically requires a detector reconfiguration. Configurations for routine ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, ⁴¹Ca and ¹²⁹I detection have been established and will be presented here. Notably, there has proven to be sufficient suppression of the isobaric interferences of ³⁶Cl and ⁴¹Ca in the 5+ charge state using an argon gas stripper at a terminal voltage of 5.0 MV to allow for routine analysis of these isotopes.     

Boron suppression with a gas ionization chamber at very low energies (E < 1 MeV)

Efficient boron suppression for precise ¹⁰Be measurements with AMS is crucial. The performance of ΔE ? E_res gas ionization chambers is also very important for isobar suppression at low beam energies (<1 MeV). A boron suppression of 6–7 orders of magnitude is achievable with the ETH ΔE ? E_res gas ionization in the standard operational mode (readout of ΔE and E_res electrodes). Some physical effects such as pulse height defect or the energy focusing effect within a ΔE section will be discussed, emphasizing ¹⁰Be measurements below 1 MeV. Additionally the potential of silicon nitride membranes as passive energy degraders in front of the detector is demonstrated.     

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%.     

On the measurement of 10Be on the 1 MV compact AMS system at the Centro Nacional de Aceleradores (Spain)

In this work we present the most recent improvements performed by our group on ¹⁰Be measurements on the 1 MV AMS system recently set up at the CNA (Centro Nacional de Aceleradores), in Seville (Spain). Our efforts have been focused on the study of the viability of our system for BeO and BeF^? measurements. To achieve this, different standard materials have been measured to demonstrate the reliability of the system for BeO measurements in a wide ¹⁰Be/⁹Be atomic ratio range and several environmental samples have been studied both at the 1 MV AMS CNA facility and at the 6 MV AMS ETH-PSI facility of Zurich to validate our measurements. The results show a good agreement between laboratories. New experiments also have been carried out selecting 1+ and 2+ charge states at the exit of the accelerator and inserting Si₃N_3.1 foils with different thicknesses to separate ¹⁰Be from its isobar, ¹⁰B. The influence of each foil on the overall transmission (detected ¹⁰Be compared to BeO^? injected into the accelerator) and background level was also assessed. In addition some tests were also done to assess the viability of BeF₂ and BaBeF₄ measurements at our system. Several metal matrices and cathode preparation procedures for BeO samples were investigated to maximize current and cathode lifetime.     

Au implantation into various types of silicate glasses

The implantation of gold ions into three types of silicate glass was studied. The energies of the implanted Au⁺ ions were 1701 keV, and the fluences of the ions were 1 × 10¹⁴, 1 × 10¹⁵, 3 × 10¹⁵ and 1 × 10¹⁶ cm^?2. The as-implanted samples were annealed in air at two temperatures (400 and 600 °C). The Au concentration depth profiles were investigated using Rutherford Backscattering Spectrometry (RBS) and compared to simulated profiles from the SRIM. The structural changes were studied by UV–vis absorption spectroscopy. The obtained mono-mode waveguides were characterised using Dark Mode Spectroscopy at 671 nm to yield information on the refractive index changes. The results showed interesting differences depending on the type of glass and the post-implantation treatment. The obtained data were evaluated on the basis of the structure of the glass matrix, and the relations between the structural changes, waveguide properties and absorption, which are important for photonics applications, were formulated.     

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.     

Thermal stress resistance of ion implanted sapphire crystals

Monocrystals of sapphire have been subjected to ion implantation with 86 keV Si⁻ and 80 keV Cr⁻ ions to doses in the range of 5 × 10¹⁴–5 × 10¹⁶ cm⁻² prior to thermal stress testing in a pulsed plasma. Above a certain critical dose ion implantation is shown to modify the near-surface structure of samples by introducing damage, which makes crack nucleation easier under the applied stress. The effect of ion dose on the stress resistance is investigated and the critical doses which produce a noticeable change in the stress resistance are determined. The critical dose for Si ions is shown to be much lower than that for Cr⁻ ions. However, for doses exceeding 2 × 10¹⁶ cm⁻² the stress resistance parameter decreases to approximately the same value for both implants. The size of the implantation-induced crack nucleating centers and the density of the implantation-induced defects are considered to be the major factors determining the stress resistance of sapphire crystals irradiated with Si⁻ and Cr⁻ ions.     

Electrical and structural characterization of ion implanted GaN

Ion implantation induced defects and their consequent electrical impact have been investigated. Unintentionally doped n-type gallium nitride was implanted with 100 keV Si⁺ and 300 keV Ar⁺ ions in a fluence range of 10¹⁴–10¹⁵ ions/cm². The samples were characterized with Rutherford backscattering/Channeling method for damage buildup. Time of flight elastic recoil detection analysis was implied on the Si implanted samples to see the ion depth distribution. Ar implanted GaN samples were studied electrically with scanning spreading resistance microscopy. Our results show that an Ar fluence of 5 × 10¹⁴ cm^?2 increases the resistance by five orders of magnitude to a maximum value. For the highest fluence, 6 × 10¹⁵ cm^?2, the resistivity decreases by two orders of magnitude.     

Swift heavy ion induced modifications of optical and microstructural properties of silver–fullerene C60 nanocomposite

In this paper, we study the optical and microstructural properties of silver–fullerene C₆₀ nanocomposite and their modifications induced by swift heavy ion irradiation. Silver nanoparticles embedded in fullerene C₆₀ matrix were synthesized by co-deposition of silver and fullerene C₆₀ by thermal evaporation. The nanocomposite thin films were irradiated by 120 MeV Ag ions at different fluences ranging from 1 × 10¹² to 3 × 10¹³ ions/cm². Optical absorption studies revealed that the surface plasmon resonance of Ag nanoparticles showed a blue shift of ～49 nm with increasing ion fluence up to 3 × 10¹³ ions/cm². Transmission electron microscopy and Rutherford backscattering spectroscopy were used to quantify particle size and metal atomic fraction in the nanocomposite film. Growth of Ag nanoparticles was observed with increasing ion fluence. Raman spectroscopy was used to understand the effect of heavy ion irradiation on fullerene matrix. The blue shift in plasmonic wavelength is explained by the transformation of fullerene C₆₀ matrix into amorphous carbon.     

Soft X-ray fluorescence measurements of irradiated polymer films

Fluorescent soft X-ray carbon Kα emission spectra (XES) have been used to characterize the bonding of carbon atoms in polyimide (PI) and polycarbosilane (PCS) films. The PI films have been irradiated with 40 keV nitrogen or argon ions, at fluences ranging from 1 × 10¹⁴ to 1 × 10¹⁶ cm⁻². The PCS films have been irradiated with 5 × 10¹⁵ carbon ions cm⁻² of 500 keV and/or annealed at 1000°C. We find that the fine structure of the carbon XES of the PI films changes with implanted ion fluence above 1 × 10¹⁴ cm⁻² which we believe is due to the degradation of the PI into amorphous C:N:O. The width of the forbidden band as determined from the high-energy cut-off of the C Kα X-ray excitation decreases with the ion fluence. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is close to either to that in diamond-like films or in silicidated graphite, respectively.     

SHI induced re-crystallization of Ge implanted SiO2 films

Ge nanocrystals embedded in SiO₂ matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO₂ films. In the present study, 400 keV Ge⁺ ions were implanted into SiO₂ films at dose of 3 × 10¹⁶ ions/cm² at room temperature. The as-implanted samples were irradiated with 150 MeV Ag¹²⁺ ions with various fluences. Similarly 400 keV Ge⁺ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au⁸⁺ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO₂ matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.     

Microstructure of ion-implanted region in TiNi alloy

TiNi alloy samples implanted with various fluences of 3 MeV Cu²⁺ ions were characterized by transmission electron microscope (TEM) and X-ray diffractometer. Cross-sectional TEM images of the samples showed that amorphous region was seen at the fluence of 10¹⁴ ions cm^?2 in case of ion implantation at 300 K of the substrate temperature, but in case of ion implantation at 100 K it did not appear even at 10¹⁵ ions cm^?2. These results were also confirmed by X-ray diffraction profiles of the same samples. Consequently, the extent of microstructure change of TiNi alloy by ion implantation was different depending on the substrate temperature.     

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.     

ERD analysis and modification of TiO2 thin films with heavy ions

Titanium dioxide (TiO₂) films have been deposited on Si substrates using reactive magnetron sputtering. The resulting films, having a polycrystalline anatase phase with a dense columnar structure, were analysed by time-of-flight elastic recoil detection analysis (ToF-ERDA) using 40 MeV I⁹⁺ ions. A clear decrease in the areal atomic density (atoms/cm²) of Ti and O was observed during measurement, but the stoichiometry remained essentially constant up to a fluence of 4 × 10¹³ ions/cm².To investigate this effect in more detail, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were applied in order to characterize the films prior to and after ion irradiation with fluences in the range of 10¹⁰–10¹³ ions/cm². Distinct morphological and structural changes of the polycrystalline film were observed. XRD revealed that the crystallinity of the film was gradually destroyed, and the film became amorphous at a fluence above 5 × 10¹² ions/cm². SEM and AFM measurements revealed topographical changes in the form of surface recession and smoothing compared to the pristine polycrystalline surface. The observed change in areal atomic density during ERD measurement is believed to be due to the combined effects of electronic sputtering, amorphization and ion hammering.     

Carrier-free measurements of natural 10Be/9Be ratios at low energies

At ETH Zurich a new method to measure directly the natural ¹⁰Be/⁹Be ratio of a sample with the compact (0.6 MV) AMS system Tandy has been developed, which allows us to use standard sample preparation methods and AMS techniques. Our results show that carrier-free measurements with compact AMS machines represent a fast, less expensive and more precise alternative for applications where only the relative variation of the ¹⁰Be/⁹Be ratio is needed. Increased source efficiency for (artificial) low carrier samples has been found. If this effect could be exploited for natural samples, it would open the field for other applications like in situ ¹⁰Be-dating of quartz with compact, low energy AMS systems.