10Be measurements at IUAC-AMS facility

An accelerator mass spectrometry (AMS) facility for measurements of ¹⁰Be has been developed by upgrading the 15UD Pelletron accelerator at Inter-University Accelerator Centre (IUAC), New Delhi. Details of the up gradation of the facilities and the measurement procedure are described briefly. Chemical processing for the separation of ¹⁰Be from manganese nodules and results of recent experiments on ¹⁰Be are presented.     

Gamma radiolysis of erythrosine dye in aqueous solutions

Beryllium-7, mainly measured via γ-spectrometry, is used as a (natural) radiotracer for education and science. For activities?<?0.1 Bq and samples containing also longer-lived ¹⁰Be, accelerator mass spectrometry (AMS) is the method-of-choice. We demonstrate that ⁷Be and ¹⁰Be can be quantified at the Dresden AMS facility on the same prepared BeO. Detection limits (⁷Be) are?~?0.6 mBq. Samples as small as tens of millilitres of rainwater can be chemically processed (after acidification) within a few hours without expensive and slow ion exchange. Isobar (⁷Li) suppression by chemistry and AMS is sufficient to guarantee for an ultrasensitive, cheap, and fast detection method for ⁷Be allowing high sample throughput.

     

An improved method for determination of 7Be in mosses

We have measured ⁷Be activity in moss samples collected from in and around Mumbai, India. The use of heavily shielded Compton suppressor system is more efficient than the conventional gamma spectroscopic system for detection of ⁷Be. The ⁷Be accumulation capacities of mosses are more than other plant samples. Therefore monitoring of young moss samples by Compton suppressor system is an excellent tool for determination of atmospheric fallout of ⁷Be. A positive bias in the high altitude samples has been observed which might be due to any of the two reasons (i) higher cosmic ray flux in the high altitude or (ii) high pollution in the lower altitude area ultimately inhibits uptake of ⁷Be.     

Accuracy of 9Be-data and its influence on 10Be cosmogenic nuclide data

A ⁹Be-solution has been chemically prepared from phenakite (Be₂SiO₄) mineral grains as commercial ⁹Be-solutions are too high in long-lived ¹⁰Be. The solution is intended to be used as a carrier for radiochemical separation of ¹⁰Be to be measured by accelerator mass spectrometry (AMS). Thus, accurate data of the ⁹Be-concentration of this solution is essential to guarantee for high-accuracy ¹⁰Be data in the future. After devastating preliminary results (~8 % standard deviation), eight laboratories finally produced twelve individual results by four different analytical methods. A certain lab and method bias might be identified by sophisticated statistical evaluation. Some laboratories also (grossly) underestimate their uncertainties. Thus, the simple weighted mean of this round-robin exercise needed to be corrected by introducing additional allowances (Paule-Mandel-approach). The final result has been calculated to (2,246 ± 11) μg ⁹Be/(g solution) with a reasonably low weighted standard deviation of 0.49 %. The maximum deviation of a single lab value from the weighted mean is 2.4 % when removing one Grubbs outlier (11 % off from the mean) from the data set. As ¹⁰Be-data, which is usually calculated from measured ¹⁰Be/⁹Be by AMS and stable ⁹Be, cannot be more accurate than the determined ⁹Be-concentration, it seems highly advisable to establish or improve quality assurance by having self-made carrier-solutions analysed at more than a single lab and regularly taking part in round-robin exercises.     

Study of 10Be in the sediments from the Krossfjorden and Kongsfjorden Fjord System,Svalbard

The distribution of ¹⁰Be, as well as the major elements concentrations and the grain size in surface and core sediment samples, collected from Krossfjorden and Kongsfjorden, Svalbard have been studied for understanding the origin of ¹⁰Be and an estimation of its accumulation rate. The ¹⁰Be concentration in sediments varies between 0.90 × 10⁸ and 2.53 × 10⁸ atoms g^?1. Our results show that atmospherically produced ¹⁰Be dominates over terrigenous (in situ) sources of ¹⁰Be in the studied samples. The calculated ¹⁰Be accumulation rate varies from 3.1 × 10⁶ atoms cm^?2 year^?1 to 8.6 × 10⁶ atoms cm^?2 year^?1 which is higher than the accumulation rate observed in the deep sea sediment cores of the Arctic Ocean and the Norwegian Sea. The higher accumulation rate of ¹⁰Be is attributed to the higher influx of glacier melt water into the fjord system.     

Particle-bound 10Be from a low latitude arid region

The ¹⁰Be isotope is widely used in geochronology, climate and environmental analyses and astrophysics where atmospheric deposition model estimate plays a vital role for the initial concentration. Data from arid regions have not been well constrained because of sparse measurement and here we present ¹⁰Be concentration in samples of dust, soil, marine sediments and paleosol collected from an arid to semi-arid low latitude region. These results indicate concentrations that are about a factor of three lower than values expected from latitude zonal models, but are comparable with global atmospheric depositional model. The agreement and discrepancy between model and measured data are rather vital for establishing accurate initial ¹⁰Be in the Earth’s surface environment for reconstruction of paleoclimatic variability (precipitation rates and temperature).     

Beryllium-7 activity concentration in maize during the growth period

Beryllium-7 (⁷Be) activity in maize was measured in Yangling County, Shaanxi Province, on the Loess Plateau Region of China in 2007. The ⁷Be mass activity concentration in maize leaf samples was significantly greater than in maize stem, maize root and maize grain samples. The ⁷Be activity in maize leaves accounted for 78% of the total maize ⁷Be activity. The ⁷Be mass activity concentration in maize varied from 25.4 to 122.4 Bq kg⁻¹ and areal activity concentration held by maize from 1.2 to 111.5 Bq m⁻² during the growth period. The percentage of ⁷Be areal activity concentration held by maize relative to the ⁷Be areal activity concentration measured in reference soils ranged from 0.4 to 24.2% with a mean of 13.7%.     

Optical molecular fluorescence determination of ultra-trace beryllium in occupational and environmental samples using highly alkaline conditions

Exposures to beryllium (Be), even at extremely low levels, can cause severe health effects in a percentage of those exposed; consequently, occupational exposure limits (OELs) promulgated for this element are the lowest established for any element. This work describes the advantages of using highly alkaline dye solutions for determination of Be in occupational hygiene and environmental samples by means of an optical molecular fluorescence technique after sample extraction in 1–3% (w?w^?1) aqueous ammonium bifluoride (NH₄HF₂). Improved attributes include the ability to further enhance the detection limits of Be in extraction solutions of high acidity with minimal dilution, which is particularly beneficial when NH₄HF₂ solutions of higher concentration are used for extraction of Be from soil samples. Significant improvements in Be method detection limits (MDLs) are obtained at levels manyfold below those reported previously for this methodology. Notably, MDLs for Be of <0.01 ng L^?1 /0.1 ng per sample have been attained, which are superior to MDLs routinely reported for this element by means of the most widely used ultra-trace elemental measurement technique, inductively coupled plasma mass spectrometry (ICP-MS). Very low MDLs for Be are essential in consideration of reductions in OELs for this element in workplace air by health organisations and regulatory agencies in the USA and internationally. Applications of enhanced Be measurements to air filter samples, surface wipe samples, soils and newly designed occupational air sampler inserts are illustrated.     

Atmospheric concentrations of 7Be and 210Pb in Granada, Spain

Aerosols samples in near-surface air of Granada (Spain) were collected on a weekly basis. The seasonal ²¹⁰Pb and ⁷Be concentrations were determined during the five-year period, from October 1993 to September 1997. The elements, despite their different origin and their different distribution throughout the atmosphere, present the same seasonal variation. There was a tendency for a maximum during the summer season and a minimum during fall and/or winter. In this work, the concentration of ⁷Be and ²¹⁰Pb and meteorological data have been used in order to determine the periods of the potential radioactive pollution. This study, also, shows that the deposition of ⁷Be occurs primarily by precipitation except during the investigation periods where precipitation was scarce and irregular.This revised version was published online in November 2005 with corrections to the Cover Date.     

Beryllium-7 activity at Comprehensive Nuclear-Test-Ban Treaty stations hosted by the United Kingdom

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is supported by a global network of monitoring stations that perform high-resolution gamma-spectrometry on air filter samples for the identification of radionuclides indicative of nuclear weapons tests and reactor incidents. These daily measurements have created an invaluable resource for understanding variations in natural background radioactivity, including the contribution of ⁷Be. Statistical analysis has been performed on ⁷Be data collected by CTBT stations hosted by the United Kingdom including at British Indian Ocean Territory (RN66), St Helena (RN67) and Tristan da Cunha (RN68) during 2005–2013. The results have been found to follow a lognormal distribution which implies that the ⁷Be activity is the multiplicative product of many small independent factors, such as meteorology, elevation, local station conditions, sample acquisition and analysis. This has the potential to identify discrepant measurements not attributable to the intrinsic variability of the distribution and indicative of station malfunction. Variations in ⁷Be activity have been considered on monthly, weekly and daily timescales and characterised using the geometric mean in accordance with the properties of the lognormal probability density function. Seasonal variations have been identified, with summer maxima and winter minima that are attributable to changes in mixing within the stratosphere and troposphere. Such fluctuations have been examined using the Fast Fourier Transform which may indicate variations associated with the 27 day solar cycle.     

Ultra-Weak Metal−Metal Bonding: Is There a Beryllium-Beryllium Triple Bond?

Metal-metal triple bonds featuring s-block element have not been reported until now. Only Be−Be double bonds between have been predicted theoretically based on the intuitive electron donation from four s¹ type electron-donating ligands. Herein, we theoretically predicted a novel species featuring a Be−Be triple bond in the Li₆Be₂ molecule. The molecule was found to be thermodynamically stable. The presence of the triple bond was confirmed by adaptive natural density partitioning (AdNDP), electron localization function (ELF), and atoms in molecules (AIM) analyses. Moreover, the mechanical strength of the Be−Be triple bond was analyzed by using compliance matrix, pointing towards its ultra-weak nature.     

Beryllium-7 in near-surface atmospheric aerosols in mid-latitude (40°N) city Beijing, China

A high-volume air sampler and a high-resolution gamma-ray spectrometer have been used to measure the activity of ⁷Be in near-surface atmospheric aerosols at sampling frequency of 3 days week for 1 year from August 2009 to July 2010 at Beijing in the mid-latitude region of East Asia monsoon. The measurements indicate that the average concentration of ⁷Be was 8.39 ± 0.49 mBq m^?3, which was significantly higher than values reported for other cities in the East Asia monsoon region and in the world during the same period. The maximum and minimum of the weekly means of ⁷Be concentration were observed in September and May, respectively. The ⁷Be concentrations varied in accordance with the monsoon phases. Low but frequent wet precipitation may have caused lower ⁷Be observed in July when southeasterly was prevailing. Higher seasonal mean of ⁷Be concentrations in autumn could be attributed to the abnormal atmospheric circulation in autumn 2009.     

Measurement of neutron-capture cross section and capture γ-ray spectrum of 105Pd(n,γ)106Pd reaction

We measured the neutron-capture cross section and the capture γ-ray spectrum of the ¹⁰⁵Pd(n,γ)¹⁰⁶Pd reaction with about 550 keV neutrons produced from the ⁷Li(p,n)⁷Be reaction at a 3-MV Pelletron accelerator. The capture yields of the palladium or gold sample were obtained by applying a pulse-height weighting technique to the corresponding net capture γ-ray pulse-height spectra. The neutron-capture cross section of the ¹⁰⁵Pd(n,γ)¹⁰⁶Pd reaction was determined with errors less than 5 % by using the standard capture cross sections of ¹⁹⁷Au. The neutron-capture γ-ray spectrum was obtained by unfolding the observed capture γ-ray pulse-height spectra. Theoretical calculations of cross sections and γ-ray spectra with the Empire code have been performed by utilizing the Hauser-Feshbach statistical model. The calculated results have a good agreement with present measurements.     

Studies in heavy ion activation analysis

A procedure for measuring trace amounts of Li and Be in different types of samples has been studied using a 12.5 MeV¹⁴N beam. At this energy the principal nuclear reactions are⁶Li(¹⁴N, d)¹⁸F,⁷Li(¹⁴N, t)¹⁸F, and⁹Be(¹⁴N, αn)¹⁸F. Detection limit for destructive analysis for either beryllium or lithium has been calculated at 300 ppb with a determination limit of 5 ppm for an irradiation with a beam of 1 μA·h/cm². Destructive analysis was performed on CANMET SY-2 and USGS BCR-1 (rock samples 1–10 ppm Be). Non-destructive analysis for beryllium and lithium was performed on NBS SRM 610 (500 ppm trace element glass), NBS 612 (50 ppm trace element glass), and NBS SRM 181 (Spodumene ore, 6.4% Li₂O). Detection limit of 2 ppm has been calculated for nondestructive analysis of either lithium or beryllium.     

Determination of excitation energies and transition moments in a second order polarization propagator approach. Application to the Be atom and the CH+ molecule

Excitation energies and transition moments have been determined from a second order polarization propagator and the effect of including energy shifted denominators has been investigated. Results for Be and CH⁺ show a change of 2–5% for the transition moments and of 0–20% for the singlet excitation energies in a second order approach compared to a first order (time-dependent Hartree-Fock) approximation. Both Be and CH⁺ are triplet unstable in the time-dependent Hartree-Fock approximation. The triplet instability is removed for Be but not for CH⁺ in a second order polarization propagator approach.     

7Be and 210Pb concentrations in air in Málaga (Spain)

Measurements of ⁷Be and ²¹⁰Pb in atmospheric air (1 m above the ground) have been carried out each week over one and a half year period. The method used to determine ⁷Be and ²¹⁰Pb activities is based on the total amount of radioactive aerosols filtered from the air. The activities of ⁷Be and ²¹⁰Pb were determined by a hyper-pure germanium detector using standard gamma-spectrometry. The average weekly concentrations of ⁷Be were in the range of 1.21-12.1 mBq^.m^-3 and for ²¹⁰Pb in the range of 0.8-2.4 mBq^.m^-3. The weekly variations were discussed in relation to various meteorological factors. It can be said that our results showed a prevailing influence of weekly average temperature for ⁷Be concentration and the weight of aerosols and wind speed for ²¹⁰Pb oncentrations.     

Evaluation of the radioactivity in concrete from accelerator facilities

For evaluation of radioactivity induced in the concrete samples from accelerator facilities, the residual radioactivity in concrete sample, collected from seven accelerator facilities, was determined by γ-ray spectrometry. The tritium was extracted by the heating method using an IR furnace, and measured with a liquid scintillation counter. It was found that the major radioisotopes activated mainly by neutrons in the concrete samples were ¹⁵²Eu, ⁶⁰Co, ¹³⁴Cs and ³H. The concentrations of radioactivities induced by thermal neutron capture are the highest at a depth of 10 cm in the concrete wall. The correlation between tritium, ⁶⁰Co and ¹⁵²Eu activity was investigated by measuring many concrete samples for seven accelerator facilities. The results indicate that their activities are strongly correlated with each other. So it would also be concluded that the total activity in shielding concrete could be estimated on the basis of the activities of ⁶⁰Co and ¹⁵²Eu.     

Seasonal variation of natural radionuclides and some elements in plant leaves

Leaf and aerosol samples were monthly collected in Mt. Sefuri (Fukuoka Prefecture). Radioactivities of ⁷Be, ²¹⁰Pb and ⁴⁰K were determined with gamma-ray spectrometry. The concentrations of some elements in the leaf samples were determined by neutron activation analysis. Similar seasonal variation of ⁷Be and ²¹⁰Pb was observed between leaf and aerosol samples, high in spring and winter and low in summer. Correlation factors for trace elements contained in the leaf show large variations. This indicates that the contribution of two sources (atmospheric deposition and uptake from soil) is very variable.     

Variation of 7Be concentration in surface air at Nagano, Japan

The concentration of ⁷Be in surface air at Nagano City has been measured during the period from August 2000 to March 2005. The average monthly concentrations of ⁷Be in surface air were in the range of 3.3–14 mBq/m³ with pronounced two peaks in spring and autumn. It took 30–40 hours to recover the ⁷Be concentrations observed before, once ⁷Be was washed out by wet precipitations. For a pronounced increase in the concentrations of ⁷Be found in winter, a low-pressure trough coming close to the Japanese Islands with high concentrations of ⁷Be is responsible under the characteristic distribution of atmospheric pressure around the Japanese Islands.     

Neutron energy spectra of 252Cf, Am-Be source and of the D(d,n)3He reaction

The neutron energy spectrum of the following sources were measured using a fast neutron spectrometer with the NE-213 liquid scintillator: ²⁵²Cf, Am-Be and D(d,n)³He reaction from a 3 MeV Pelletron accelerator in Tokyo Institute of Technology. The measured proton recoil pulse height data of ²⁵²Cf, Am-Be and D(d,n)³He were unfolded using the mathematical program to obtain the neutron energy spectrum. The ²⁵²Cf and Am-Be neutron energy spectra were measured and the results obtained showed a good agreement with the spectra usually published in the literature. The neutron energy spectrum from D(d,n)³He was measured and the results obtained also showed a good agreement with the calculation by time of flight (TOF) methods.