Many different kinds of paleoclimatic, geological and archaeological records can be characterized by measuring their radionuclide concentrations using accelerator mass spectrometry (AMS). The purpose ...of this paper is to highlight some applications of AMS, using studies conducted at the Arizona AMS Facility as examples. These include studies of 14C, 10Be, 26Al, and 129I. The work can be generally divided into two types: (1) methodological studies designed to refine and improve the capabilities of AMS, and (2) studies which utilize radiogenic isotopes as geochronometers or as geochemical tracers. Studies of the first type include the development of our 26Al measurement capabilities, the construction on an automated sample preparation line and the construction of a plasma oxidation line. Studies of the latter type include 14C dating of corals, speleothems and bones; new records of 10Be from marine sediments and extraterrestrial materials; and 129I studies of the pathways of this isotope in the surface ocean.
Radioactivity levels of natural
210Po and anthropogenic
137Cs in sea water and biota (fish and shellfish) have been estimated for the FAO fishing areas on the basis of measurements carried out in ...recent years. Collective doses resulting from seafood consumption are calculated for each FAO area using radioactivity data for water and biota. Good agreement is observed between the results calculated by these two methods, with the exception of the doses from
210Po via shellfish consumption. The collective effective dose commitment from
137Cs in marine food in 1990 has been estimated at 160 man Sv with an uncertainty of 50%. The corresponding dose from
210Po is 30000 man Sv with an estimated uncertainty of a factor of 5. The results confirm that the dominant contribution to doses derives from natural
210Po in fish and shellfish and that the contribution from anthropogenic
137Cs (mainly originating from nuclear weapons tests) is negligible.
Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay (\(2\nu\beta\beta\)) half-life of \(^{82}\)Se as \(T_{1/2}^{2\nu} = \left 9.39 \pm ...0.17\,\left(\mbox{stat}\right) \pm 0.58\,\left(\mbox{syst}\right)\right \times 10^{19}\) y under the single-state dominance hypothesis for this nuclear transition. The corresponding nuclear matrix element is \(\left|M^{2\nu}\right| = 0.0498 \pm 0.0016\). In addition, a search for neutrinoless double beta decay (\(0\nu\beta\beta\)) using 0.93 kg of \(^{82}\)Se observed for a total of 5.25 y has been conducted and no evidence for a signal has been found. The resulting half-life limit of \(T_{1/2}^{0\nu} > 2.5 \times 10^{23} \,\mbox{y} \,(90\%\,\mbox{C.L.})\) for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of \(\langle m_{\nu} \rangle < \left(1.2 - 3.0\right) \,\mbox{eV}\), where the range reflects \(0\nu\beta\beta\) nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other \(0\nu\beta\beta\) mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set.
Geostatistical analysis of experimental isotope data has been carried out with the aim to study spatial variations in the distribution of water isotopes and radiocarbon in groundwater of Žitný ostrov ...(Rye Island), which is the largest reservoir (about 10 Gm3) of groundwater in the Central Europe. Subsurface water profiles showed enriched δ18O levels at around 20 m water depth and depleted values below 30 m, which are similar to those observed in the Danube River. The core of the subsurface 14C profile represents contemporary groundwater with 14C values above 80pMC.
We report the results of a search for the neutrinoless double-\(\beta\) decay (0\(\nu\beta\beta\)) of \(^{100}\)Mo, using the NEMO-3 detector to reconstruct the full topology of the final state ...events. With an exposure of 34.7 kg.y, no evidence for the 0\(\nu\beta\beta\) signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of \(T_{1/2}(0\nu\beta\beta)>1.1 \times 10^{24}\) years (90% C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the Nuclear Matrix Elements this corresponds to an upper limit on the Majorana effective neutrino mass of \(< m_{\nu} > < 0.3-0.9\) eV (90% C.L.). Constraints on other lepton number violating mechanisms of 0\(\nu\beta\beta\) decays are also given. Searching for high-energy double electron events in all suitable sources of the detector, no event in the energy region 3.2-10 MeV is observed for an exposure of 47 kg.y.
14C is one of the most important anthropogenic radionuclides released to the environment by human activities. Weapon testing raised the 14C concentration in the atmosphere and biosphere to +100% ...above the natural level. This excess of atmospheric C at present decreases with a half-life of ca 7 years. Recently, a new source of artificially produced 14C in nuclear reactors has become important. Since 1967, the Bratislava 14C laboratory has been measuring 14C in atmospheric 14CO2 and in a variety of biospheric samples in densely populated areas and in areas close to nuclear power plants. We have been able to identify a heavy-water reactor and the pressurized water reactors as sources of anthropogenic 14C. 14C concentrations show typical seasonal variations. These data are supported by measurements of 3H and 85Kr in the same locations. Results of calculations of future levels of anthropogenic 14C in the environment due to increasing nuclear reactor installations are presented.
We report the results of a first experimental search for lepton number violation by four units in the neutrinoless quadruple-\(\beta\) decay of \(^{150}\)Nd using a total exposure of \(0.19\) ...kg\(\cdot\)y recorded with the NEMO-3 detector at the Modane Underground Laboratory (LSM). We find no evidence of this decay and set lower limits on the half-life in the range \(T_{1/2}>(1.1-3.2)\times10^{21}\) y at the \(90\%\) CL, depending on the model used for the kinematic distributions of the emitted electrons.
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