Ra Isotopes Research Articles

Octupole deformation in even-even Ra isotopes

The octupole deformation of even-even Raisotopes has been investigated systematically by the reflection asymmetric relativistic mean field (RAS-RMF) theory. The results are compared with the experimental data together with the results from FRDM. It is shown that RAS-RMF theory gives a good description for Ra isotopes. The calculated binding energy, two neutron separation energy and deformation agree with the experimental data well. In particular, RAS-RMF theory provides the neutron and proton densities which show clearly the shape evolution of these nuclei from nearly spherical to well-developed octupole and finally back to quadrupole deformation shapes. This is in accordance with experimental observation.

A relationship between submarine groundwater borne nutrients traced by Ra isotopes and the intensity of dinoflagellate red‐tides occurring in the southern sea of Korea

We measured short‐lived radium isotopes (223Ra and 224Ra), dissolved inorganic and organic nutrients, and photosynthetic pigments during the summers of 2006 and 2007 in the southern sea of Korea, where harmful dinoflagellate blooms occur every year. The Ra tracer measurements reveal that coastal groundwater, rather than other sources previous suggested (i.e., Yangtze River diluted water or Kuroshio currents), is the main source of nutrients that fuel red tides in this region. Although inorganic‐nutrient levels are different for different regions and different years, either dissolved inorganic nitrogen or phosphorus is depleted in the red‐tide region. This depletion is accompanied by highly elevated levels of dissolved organic nutrients, transformed from groundwaterborne dissolved inorganic nutrients either inside Yeoja Bay or in offshore red‐tide areas, thereby creating favorable conditions for the growth of dinoflagellates in competition with diatoms. The intensity of red tides correlates well with the activity of 224Ra (half life = 3.66 d) in seawater over daily or yearly time scales. Because the chemically conservative 224Ra can trace groundwater‐borne nutrients, which are utilized by marine biota in this red‐tide region, the intensity of red tides seems to be related to the amount of nutrient‐enriched groundwater supplied to the offshore red‐tide region.

Production of short lived radioactive beams of radium

Short lived Ra212,213,214 isotopes have been produced at the TRIμP facility in inverse kinematics via the fusion–evaporation reaction Pb206+C12 at 8MeV/u. Isotopes are separated from other reaction products online using the TRIμP magnetic separator. The energetic radium (Ra) isotopes at the exit of the separator were converted into low-energy ions with a thermal ionizer. Ra isotopes have been identified by observing their α decay and half-lifes. An improved half-life of Ra213 has been measured to be 162.0±1.7s.

High sensitivity measurement of 224Ra and 226Ra in water with an improved hydrous titanium oxide technique at the Sudbury Neutrino Observatory

The existing hydrous titanium oxide (HTiO) technique for the measurement of 224Ra and 226Ra in the water at the Sudbury Neutrino Observatory (SNO) has been changed to make it faster and less sensitive to trace impurities in the HTiO eluate. Using HTiO-loaded filters followed by cation exchange adsorption and HTiO co-precipitation, Ra isotopes from 200 to 450 tonnes of heavy water can be extracted and concentrated into a single sample of a few millilitres with a total chemical efficiency of 50%. Combined with beta–alpha coincidence counting, this method is capable of measuring 1.5 × 10 - 3 μ Bq / kg of 224Ra and 3.3 × 10 - 3 μ Bq / kg of 226Ra from the 232Th and 238U decay chains, respectively, for a 275 tonne D 2 O assay, which are equivalent to 4 × 10 - 16 g Th/g and 3 × 10 - 16 g U / g in heavy water.

Temporal Variations in U-series Disequilibria in an Active Caldera, Rabaul, Papua New Guinea

Intra-caldera eruptions have been speculated to sample the last batches of magma remaining from earlier caldera-forming eruptions. Rabaul Caldera, New Britain, Papua New Guinea has erupted several times since the last caldera-forming eruption in AD 640, with the most recent intra-caldera eruptions in 1878, 1937^1941 and 1994^ present from the Tavurvur and Vulcan vents. U-series isotopes, in conjunction with Sr/Sr and Nd/Nd, were analyzed on 16 samples collected from 1994 to 2001 to monitor short-term changes in magma composition to model magmatic processes and to test whether there is evidence of recent fresh magma input. Inflections on MgO diagrams imply that fractional crystallization is an important process in long-term magma evolution, and the homogeneity in Sr/Sr and Nd/Nd shows that assimilation of isotopically distinct material has not occurred. A vertical array on a Th^U isochron diagram requires open-system behavior and could support a model of differentiation of multiple magma batches over 26 kyr. However, the presence of (Ra/Th) excesses requires introduction of new magma within the past 8000 years and is permissible of a model in which the currently erupting magmas were emplaced at or since the last caldera-forming event. Other than the presence of mafic enclaves in the 1878 and 1937 eruptions, no evidence exists to suggest open-system magma injection. Systematic variation in U-series disequilibria between 1994 and 2001 is lacking, which may indicate that the system is broadly in steady state or that the processes acting to produce the limited compositional variation have time scales that are too short to be resolved by Ra isotopes (i.e. are less than a few hundred years).

Ra–Po–Pb isotope systematics in waters of Sambhar Salt Lake, Rajasthan (India): geochemical characterization and particulate reactivity

The Sambhar Salt Lake hydrological system, including river waters, groundwaters, evaporating pans and sub-surface brines, has been analyzed for the salt content (TDS) and naturally occurring radionuclides ( 210Po, 210Pb and 226,228Ra). The abundance of these radionuclides and their activity ratios show a wide variation in different hydrological regimes, which helps to geochemically characterize the lake system. A significantly lower Ra to total dissolved solids (TDS) ratio in the brines (by two to three orders of magnitude), when compared to the groundwaters and river waters, suggests removal of dissolved Ra by co-precipitation with Ca–Mg minerals at an early stage of the brine evolution. The concentration of Ra in evaporating lake/pan waters saturates at a value of about 35 Bq L −1 over the salinity range of 100–370 g L −1; attributable to its equilibration with the clay minerals. The two distinct regimes, saline lake system (lake water, evaporating pans and sub-surface brines) and groundwaters have been identified based on their differences in the distribution of 226,228Ra isotopes. This observation points to the conclusion that the groundwaters and the lake brines are not intimately coupled in terms of their origin and evolution. The abundances of 210Po and 210Pb along with their activity ratios ( 210Po/ 210Pb) are markedly different among the surface lake waters/evaporating pans, sub-surface lake brines and groundwaters. These differences are explained in terms of different geochemical behaviour of these nuclides in presence of algae and organic matter present in these water regimes.

The Systematic Behavior of the Spontaneous Fission Branching Ratios of Even-Z Isotopes

The spontaneous fission branching ratios (B) of even-Z, 90 ≤ Z ≤ 100, nuclei were found to be correlated to log B = 1.6247 × Z – 1.0361(2Z – N) – 114.66. Based on this correlation, it is predicted that the isotopes 226Ra and 228Th are spontaneous fission isotopes.

Negative parity bands in even–even isotopes of Ra, Th, U and Pu

There are negative parity bands, conveniently labelled Kπ = 0−, 1− and 2−, with very similar patterns of excitation energies in many of the even–even isotopes of Ra, Th, U and Pu. Furthermore, the 3− states in many of these bands decay to the 0+ ground state with reduced B(E3) transition strengths closely similar to one another and comparable to the strengths found in the isotopes of Pb. We propose a Pb core plus exotic cluster model explanation of these observations. Such a treatment accounts for the persistence of these features across many isotopes and gives a good description of the excitation energies and E3 rates for all of them. The wavefunctions generated are intermediate between the weak and strong coupling limits. They suggest that the Kπ = 1− bands consist of doublets, possibly inverted, and thereby give rise to a novel proposal for a unification of some of the disparate band structures seen in 238U.

Octupole bands in even isotopes of Ra, Th, U and Pu

Many heavy nuclei have low-lying Kπ = 0− bands. Furthermore, several even isotopes of Ra, Th, U and Pu have Kπ = 1− bands with bandhead excitation energies very close to 1 MeV. The E3 transitions from the 0+ ground state to the 3− members of these bands have reduced strengths B(E3; 0+ → 3−) comparable to those measured in the isotopes of Pb. An exotic cluster model with a Pb core is proposed to account for these observations. A good account of the data is given, and higher lying Kπ = 2− and 3− bands are predicted. The intermediate strength quadrupole-quadrupole coupling between cluster and core leads to irregular, inverted doublets in the calculated Kπ = 1− bands.

Precise measurement of 228Ra/226Ra for 226Ra determination employing total integration and simultaneous 228Th correction by multicollector ICP-MS using multiple ion counters

A precise method of measuring 228Ra/226Ra for 226Ra determination used in U-series disequilibrium studies has been developed using the total integration method with simultaneous 228Th isobaric interference correction by multicollector ICP-MS with multiple ion counters (MIC). A sample solution of 0.2 ml was separately taken into a test tube, and all 226Ra+ and 228Ra+ signals as well as 229Th+ and 228Th16O+ from beginning to end were integrated simultaneously using four channeltrons, IC1, IC3, IC4 and IC5, respectively. Gains between IC1 and IC3 and the mass discrimination factor for 228Ra/226Ra determination were canceled out by measurement of a Ra spike solution with an accurately known Ra isotope ratio determined by TIMS, with which samples were bracketed. The isobaric interferences of 228Th+ were simultaneously corrected from the signal of 228Th16O+ and the oxide forming ratio of 228Th, which was separately determined by simultaneous measurements of 229Th+ and 229Th16O+ by IC3 and IC5. The gains between IC3 and IC5 for the Th correction were also canceled out. The ion yield of Ra in MIC-ICP-MS was ∼1.5%. The intermediate precision using 6.6, 3.3, 1.7, 0.83 and 0.41 fg of 226Ra with 228Ra/226Ra = ∼5 was 0.33, 0.93, 0.76, 1.6 and 1.5%, respectively. The 228Ra/226Ra ratio showed no systematic change dependent on 228Th/228Ra up to 0.25, indicating the validity of the 228Th correction. At similar amounts of Ra, our method gives intermediate precision values similar to or better than previous MC-ICP-MS and TIMS studies. The precision of the method was verified using another Ra spike with 228Ra/226Ra = ∼1 determined by TIMS. The analytical performance of the method was further investigated using the silicate samples JB-2 and JB-3 basalts issued by GSJ.

Submarine groundwater discharge to Great South Bay, NY, estimated using Ra isotopes

There is increasing evidence that submarine groundwater discharge (SGD) in many areas represents a major source of dissolved chemical constituents to the coastal ocean. In Great South Bay, NY, previous studies have shown that the discharge of nutrients with SGD may cause harmful algal blooms. This study estimates SGD to Great South Bay during August 2006 by performing a mass balance for each of the dissolved Ra isotopes ( 224Ra, 223Ra, 228Ra, 226Ra). The budget indicates a major unknown source (between 30 and 60% of the total input) of Ra to the bay. This imbalance can be resolved by a flux of Ra-enriched groundwater on the order of 3.5–4.5 × 10 9 L d − 1 , depending on the Ra isotope. The Ra-estimated SGD rates compare well with those previously estimated by models of flow that decreases exponentially away from shore. Compared to previous reports of fresh groundwater discharge to the bay, the Ra-estimated discharge must comprise approximately 90% recirculated seawater. The good agreement between Ra- and model-estimated flow rates indicates that the primary SGD endmember may be best sampled at shallow depths in the sediments a short distance bayward of the low tide line.

Activity Ratios of Ra and Th Isotopes Leached from Euxenite

The activity ratios of 224Ra/228Ra and 228Th/232Th in leachate from euxenite increased with increasing pH, while the activity ratio of 230Th/232Th decreased. The leaching behavior of 224Ra which is formed through four decay processes of232Th, was different from that of 228Ra which is formed by a single decay of 232Th. Thorium-228, decay products of232Th, was also leached more effectively than 232Th. However, 230Th which is formed through four decay processes of 238U showed different leaching behavior from 224Ra and 228Th. Variation in the activity ratio of 228Ra/226Ra in leachate from euxenite sample in metamict state with pH of the solution in contact showed no apparent tendency and was observed to be almost as same as that in the euxenite sample partly because of so small activity ratio in the sample. The leaching efficiency of Ra isotopes and 228Th was estimated to be mainly dependent on the difference in the history of decay processes which have formed the nuclides. This estimation was consistent with the observation with the monazite sample reported previously.

Horizontal mixing of Great Barrier Reef waters: Offshore diffusivity determined from radium isotope distribution

The Great Barrier Reef (GBR), northern Australia, is the largest coral reef system in the world and provides habitat for highly diverse tropical marine ecosystems. Mixing in the coastal waters of the GBR is an important parameter influencing the health of these ecosystems. We have used the distribution of the four naturally occurring radium isotopes to determine the rate of mixing of nearshore waters of the central part of the GBR lagoon with water from the Coral Sea. The observed radium distribution is modeled using a one‐dimensional diffusion model. The model improves on previous radium offshore mixing models by incorporating the benthic flux of radium diffusing across the sediment‐water interface and offshore changes in water column depth. We find that the inner lagoon diffusivity (<20 km offshore) is best estimated using the short‐lived isotopes 224Ra and 223Ra. The concordance of Kx estimated using the two different isotopes and the apparent consistency between measured riverine inflows to the lagoon and inflows inferred from the modeled salinity distribution provide confidence in the results. The mean value of Kx for the inner lagoon region of the southern central zone between latitudes 15.8°S and 19.0°S (265 ± 36 m2 s−1) is more than twice that in the northern central zone (14.3°S to 15.8°S). This difference likely reflects the different reef matrix density in the two zones. The distribution of the longer‐lived isotope 228Ra indicates more rapid mixing in the middle and outer lagoon. These results indicate that central GBR water within 20 km of coast is flushed with outer lagoon water on a timescale of 18–45 days, with the flushing time increasing northward.

226Ra and 228Ra in the seawater of the western Yellow Sea

Radium isotopes 226Ra and 228Ra in seawater of the western Yellow Sea were measured by using the Mn-fiber adsorption—HPGe γ spectrum method. The distribution features of the two isotopes have been studied. The activities of 226Ra and 228Ra are 2.72–5.57 Bqm−3 and 7.51–34.3 Bqm−3, respectively. The activities of 226Ra and 228Ra from surface to bottom for each depth profile station are comparable within the experimental error, but the mean activities decrease with distance from the shore. From the distribution data of 228Ra, the horizontal eddy diffusion coefficient was estimated at 29×106 cm2s−1.

Large submarine groundwater discharge and benthic eutrophication in Bangdu Bay on volcanic Jeju Island, Korea

We estimated the submarine discharge of groundwater (SGD) and associated nutrients into the semienclosed Bangdu Bay on a volcanic island, Jeju, Korea, by analyzing 222Rn, Ra isotopes (224Ra and 226Ra), and nutrients in seawater, pore water, and coastal groundwater. The submarine inputs of groundwater into Bangdu Bay of 120–180 m3 m−2 yr−1 (on the basis of 222Rn, 224Ra, 226Ra, and Si mass balances) were much higher than those reported from typical continental margins. The nutrient fluxes from SGD were about 90%, 20%, and 80% of the total input (except from open ocean waters) for dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved inorganic silicate (DSi), respectively. These excess nutrient inputs from SGD are the major sources of “new nutrients” in this bay. On the basis of photosynthetic pigments and benthic algal distributions, we suggest that the large fluxes of excess nutrients from SGD can cause benthic eutrophication in a semienclosed bay on this highly permeable volcanic island.

Measurements of Pu and Ra isotopes in soils and sediments by AMS

Plutonium fallout from atmospheric nuclear weapons testing in the 1950s and 1960s constitutes an artificial tracer suitable for the study of recent soil erosion and sediment accumulation rates. Long-lived Pu isotopes provide an alternative tracer to the more widely used 137Cs (t1/2=30 a), the concentration of which is decaying at a rate that will limit its long-term application to these studies. For 239,240Pu, the sensitivity of AMS is more than an order of magnitude better than that afforded by α-spectroscopy. Furthermore, AMS can provide a simple, direct measure of the 240Pu/239Pu ratio. Sample profiles from two sites along eastern Australia have been determined with both AMS and α-spectroscopy to provide comparative measurements of the sediment accumulation rate in water bodies and of the soil erosion rate. The two methods are in good agreement.The 228Ra/226Ra ratio potentially provides a probe for tracing the dispersion of uranium mining residues into the neighboring environment. Soil depth profiles of the ratio may provide information on the rate at which mining-derived radioactivity is spread by surface waters, and could be used to assess the effectiveness of remediation and rehabilitation technologies. AMS offers several advantages over the more usual α- and γ-spectroscopy techniques in that it can directly and quickly measure both isotopes in a sample of small size and with simple sample preparation.We show that AMS can be used to measure these isotopes of radium at the sensitivity required for environmental samples using RaC2− as the injected beam species.

Measurements of Pu and Ra isotopes in soils and sediments by AMS

Measurements of Pu and Ra isotopes in soils and sediments by AMS

The transport of U- and Th-series nuclides in sandy confined aquifers

Abundances of 238U, 234U, 232Th, 226Ra, 228Ra, 224Ra, and 222Rn were measured in groundwaters of the Ojo Alamo aquifer in northwest New Mexico. This is an arid area with annual precipitation of ∼22 cm. The purpose was to investigate the transport of U-Th series nuclides and their daughter products in an old, slow-moving groundwater mass as a means of understanding water-rock interactions and to compare the results with a temperate zone aquifer. It was found that 232Th is approximately at saturation and supports the view of Tricca et al. (2001) that Th is precipitated irreversibly upon weathering, leaving surface coatings of 232Th and 230Th on aquifer grains. Uranium in the aquifer waters has very high [ 234U/ 238U] ∼ 9 and low 238U concentrations. These levels can be explained by low weathering rates in the aquifer ( w 238U ∼ 2 × 10 −18 to 2 × 10 −17s −1) using a continuous flow, water-rock interaction model. The Ra isotopes are roughly in secular equilibrium despite their very different mean lifetimes. The 222Rn and 228Ra isotopes in the aquifer correspond to ∼10% of the net production rate of the bulk rock. This is interpreted to reflect an earlier formed irreversible surface coating of Th that provides Ra and Rn to the aquifer waters. The surface waters that appear to be feeding the aquifer have low [ 234U/ 238U] and high 238U concentrations. The flow model shows that it is not possible to obtain the high [ 234U/ 238U] and low [ 238U] values in the aquifer from a source like the present vadose zone input. It follows that the old aquifer waters studied cannot be fed by the present vadose zone input unless they are greatly diluted with waters with very low U concentrations. If the present sampling of vadose zone sources is representative of the present input, then this requires that there was a major change in water input with much larger rainfall some several thousand years ago. This may represent a climatic change in the Southwest.

A new analytical approach for 226 Ra and 228 Ra in environmental waters

The concentration of Ra isotopes in environmental water can be determined from the amount of Ra isotopes recovered in two successive batch operations using a cation exchange resin. The present analytical method is applicable to 10 liter of sample water having a Ra concentration larger than 10 mBq/l and is also applicable to ordinary underground water of less than 1 mBq/l by use of 50 liter of sample water. In the case where Ra concentration is extremely low, Mn-impregnated acrylic fiber can be used with a larger volume of water sample as an absorbent by soaking it in the water.

Validation of isotope signatures in sediments affected by anthropogenic inputs from uranium series radionuclides

This paper aims to show the usefulness of 226Ra/228Ra activity ratios and confirm the possibility of using 230Th/232Th activity ratios as chronological markers in sediment cores from an estuarine system strongly contaminated by discharges from non-nuclear industries (fertiliser plants). The validation was carried out using an independent, well-established dating technique based on the analysis of the 137Cs fallout profile, which comprises the same time interval as that covered by both isotope ratios. The advantage of using the 226Ra/228Ra activity ratio profile instead of the Th-isotope profile is that determination can be accomplished with a non-destructive, simpler and less time-consuming technique, because both Ra isotopes can be determined by gamma-ray spectrometry.