Long-lived Decay Products Research Articles

Explaining the ANITA anomaly with inelastic boosted dark matter

We propose a new physics scenario in which the decay of a very heavy dark-matter candidate which does not interact with the neutrino sector could explain the two anomalous events recently reported by ANITA. The model is composed of two components of dark matter, an unstable dark-sector state, and a massive dark gauge boson. We assume that the heavier dark-matter particle of EeV-range mass is distributed over the galactic halo and disintegrates into a pair of lighter -- highly boosted -- dark-matter states in the present universe which reach and penetrate the Earth. The latter scatters {\it in}elastically off a nucleon and produces a heavier dark-sector unstable state which subsequently decays back to the lighter dark matter along with hadrons, which induce Extensive Air Showers, via on-/off-shell dark gauge boson. Depending on the mass hierarchy within the dark sector, either the dark gauge boson or the unstable dark-sector particle can be long-lived, hence transmitted significantly through the Earth. We study the angular distribution of the signal and show that our model favors emergence angles in the range $\sim 25^\circ -35^\circ$ if the associated parameter choices bear the situation where the mean free path of the boosted incident particle is much larger than the Earth diameter while its long-lived decay product has a decay length of dimensions comparable to the Earth radius. Our model, in particular, avoids any constraints from complementary neutrino searches such as IceCube or the Auger observatory.

The Impact of Isotopic Composition of Lead on the Neutron-Physical Characteristics of Fast Reactor with Liquid Metal Coolant

It is well known, that lead coolant, highly enriched by 208Pb, has some advantages over other coolants. It is predicted that the use of 208Pb in the reactor core will lead to an increase in the production of plutonium and transmutation of long-lived decay products. The main objective of this paper was to investigate the influence of the isotopic composition on the fast reactor neutron-physical characteristics. For this purpose we used the RBETS-M benchmark - a fast energy reactor that includes 12 zones with different sizes and temperatures of the materials. Calculations were performed for homogeneous and heterogeneous models. Our calculations show that the replacement of the coolant with the natural lead to 208Pb and 208Pb together with Bi can substantially improve the neutron-physical characteristics of the fast reactor, in particular by reducing the initial reactivity margin. Studies of the heterogeneity effect in the reactor model showed an increase in the effective multiplication factor of about 1.5% at the end of the campaign.

Study of uranium(VI) and radium(II) sorption at trace level on kaolinite using a multisite ion exchange model

Uranium and the long-lived decay product radium-226 are abundantly present in mine wastes produced during uranium extraction activities. In the case of release to the surrounding environment, these radionuclides are at trace level compared to groundwater solutes, and the presence, content and properties of clay minerals in the host environment influence the extent of radionuclide sorption and, in turn, migration. Since clays are known to have the distinctive property of retaining ions, the aim of this work was to study the sorption of trace U(VI) and Ra(II) on a common phyllosilicate mineral, kaolinite, in the presence of excess K, a common groundwater cation, in order to obtain a thermodynamic database that describes the ion exchange equilibria occurring at the mineral–solution interface. Following a detailed experimental protocol using chemical and radiochemical analytical techniques, batch experiments over a wide pH range (from 2 to 11) and fixed concentration (ca. 10−9 M), and additional adsorption isotherms at two different solution pH (6.2 and 10.4) over a concentration range (10−10 to 10−4 M) were carried out to measure the distribution coefficient (Kd) of U(VI) and Ra(II) sorption on kaolinite. The experimental sorption data was processed according to a general multisite sorbent/multispecies sorbate ion exchange model, which allowed deducing the charge of adsorbed species and the stoichiometry of the associated adsorption equilibria on kaolinite's surface sites. Aqueous speciation calculations predicted Ra(II) as Ra2+ over the working pH range, and its adsorption curves and isotherms were explained using three sorption sites. Adsorption of U(VI) occurred on four sorption sites and was governed by its solution speciation, with positively charged hydroxylated (UO22+ and UO2(OH)+) and silicate (UO2(H3SiO4)+) species being adsorbed between pH 2 and 6, whereas its negatively charged forms (UO2(OH)3- and UO2(OH)42-) dominated U(VI) sorption at pH > 7. Nonlinear fitting of the experimental data using the ion exchange model provided the associated equilibrium constants as corrected selectivity coefficients.

Isotopically enriched structural materials in nuclear devices

A large number of materials exist which have been labeled as low activation structural materials (LAM). Most often, these materials have been designed in order to substitute-out or completely remove elements that become activated and contribute significantly to shut-down activity after being irradiated by neutrons in a reactor environment. To date, one of the fundamental principles from which LAMs have been developed is that natural elemental compositions are the building blocks of LAMs. Thus, elements such as Co, Al, Ni, Mo, Nb, N and Cu that produce long-lived decay products are significantly reduced or removed from the LAM composition. These elements have an important part to play in the composition of steels and the removal/substitution can have a negative impact on materials properties such as yield stress and fracture toughness. This paper looks in more detail at whether using isotopic selection of the more mechanically desirable, but prohibited due to activation, elements can improve matters. In particular, this paper focuses on the activation of Eurofer.Carefully chosen isotopically enriched elements, which are normally considered to be on the prohibited element list, are added to EUROFER steel as potential alloying elements. The EUROFER activation results show that some prohibited elements can be used as alloying elements in LAM steels, providing the selected isotopes do not have a significant impact on waste disposal rating or shut-down dose. The economic implications of isotopically enriching elements and the potential implications for decommissioning are considered. It is shown that the addition of molybdenum and nickel in small concentrations (<2% mass) could have the potential to increase availability to such an extent that the capital investment associated with isotope enrichment is negated and profits from electricity sale increased.Another important issue for materials exposed to neutron irradiation is the production of gases, in particular helium, as a result of nuclear interactions. Helium accumulation in materials can cause embrittlement and so mitigating the rate of production is an important consideration when selecting materials. The second part of this paper considers whether helium production can be reduced in CuCrZr by isotopic tailoring. CuCrZr is a candidate bonding material for tungsten at first wall locations, however it suffers from degradation due to helium production. Inventory calculations show that isotopically enriching the copper, in CuCrZr, can reduce helium production by approximately 50%. However, cost–benefit analysis suggests that the cost of enriching copper is not cost-effective due to the high price of electromagnetic enrichment that is required for copper.

230Th and 231Pa on GEOTRACES GA03, the U.S. GEOTRACES North Atlantic transect, and implications for modern and paleoceanographic chemical fluxes

The long-lived uranium decay products 230Th and 231Pa are widely used as quantitative tracers of adsorption to sinking particles (scavenging) in the ocean by exploiting the principles of radioactive disequilibria. Because of their preservation in the Pleistocene sediment record and through largely untested assumptions about their chemical behavior in the water column, the two radionuclides have also been used as proxies for a variety of chemical fluxes in the past ocean. This includes the vertical flux of particulate matter to the seafloor, the lateral flux of insoluble elements to continental margins (boundary scavenging), and the southward flux of water out of the deep North Atlantic. In a section of unprecedented vertical and zonal resolution, the distributions of 230Th and 231Pa across the North Atlantic shed light on the marine cycling of these radionuclides and further inform their use as tracers of chemical flux. Enhanced scavenging intensities are observed in benthic layers of resuspended sediments on the eastern and western margins and in a hydrothermal plume emanating from the Mid-Atlantic Ridge. Boundary scavenging is clearly expressed in the water column along a transect between Mauritania and Cape Verde which is used to quantify a bias in sediment fluxes calculated using 230Th-normalization and to demonstrate enhanced 231Pa removal from the deep North Atlantic by this mechanism. The influence of deep ocean ventilation that leads to the southward export of 231Pa is apparent. The 231Pa/230Th ratio, however, predominantly reflects spatial variability in scavenging intensity, complicating its applicability as a proxy for the Atlantic meridional overturning circulation.

The X-Array and SATURN: A new decay-spectroscopy station for CARIBU

A new decay-spectroscopy station has been commissioned for experiments with low-energy, fission-fragment radioactive beams from the CARIBU ion source. The new set-up consists of the ‘X-Array’, a highly-efficient array of HPGe clover detectors, and ‘SATURN’ (Scintillator And Tape Using Radioactive Nuclei), a plastic scintillator detector combined with a tape-transport system for detection of β particles and removal of long-lived isobaric decay products.

Element 117 yields long-lived decay products

Two isotopes of the newly discovered element decay to give nine more previously unobserved nuclei.

Synthetic minerals with the pyrochlore and garnet structures for immobilization of actinide-containing wastes

Complex oxides of the pyrochlore (space groups Fd3m, [8]A2 [6]B2O7) and garnet (Ia3d, [8]A3 [6]B2 [4]T3O12) structures (“A” = Ca2+, Ln3+/4+, An3+/4+; “B” = (Ti, Sn, Hf, and Zr)4+ in pyrochlore, and Al3+, Ga3+, and Fe3+ in garnet alone; “T” = (Al3+, Ga3+, and Fe3+) are promising matrices for actinide-bearing wastes. In order to identify optimal compositions of these phases, their isomorphic capacity with respect to REE, actinides, and other components of wastes was examined. The long-term behavior of the matrix at a repository was predicted based on data obtained on the behavior of pyrochlores and garnets under ion irradiation and 244Cm decay and on the determined leaching rates of REE from the matrices because of their interaction with aqueous solutions, including that after amorphization. In order to propose efficient synthesis techniques, samples prepared with the use of various methods were studied. The possibility of incorporating long-lived decay products of 99Tc into the crystalline matrices was analyzed.

A study of ion-exchange behavior of Pb in dilute HBr solutions, aimed to evaluate the possibility of on-line isolation of element 114. 228Ra-212Pb generator

Ion-exchange behavior of Pb (homolog of element 114), Ra, some actinides and Hf (homolog of Rf) in aqueous and aqueous-methanolic solutions of HBr was studied as influenced by the solution composition, acid concentration, type of ion exchanger, and other factors. The best conditions for Pb separation from other radionuclides with a high decontamination factor (≥105−106) on a cation exchanger and the conditions for its preconcentration from dilute solutions on an anion exchanger in the continuous (on-line) mode were determined. Based on the operation principle of a radioisotope generator containing a cation exchanger and HBr solutions, an efficient procedure for repeated separation of 212Pb (T 1/2 = 10.6 h) from its parent radionuclides (228Ra, 228Ac, and 228Th) was developed. The possibility of on-line isolation of element 114 formed by the 242Pu(48Ca, 3n) nuclear reaction and its detection by long-lived decay product [267Rf (T 1/2 ∼ 3.3 h)] was demonstrated.

Chemical procedure applied for the identification of Rf/Db produced in the 48Ca +243Am reaction

Summary A chemical separation procedure for Rf/Db is described which was applied to a long-lived decay product from the nuclear fusion reaction 48Ca+ 243Am. A 1.2 mg thick 243Am target was bombarded by 247 MeV 48Ca particles. The recoiling products were collected in a thick Cu catcher for about one day and then subjected to a chemical separation procedure that included an ion exchange from dilute HF solutions. Final samples were prepared on 30 μg/cm2 thick polyethylene (PE) foils and counted in 4π-geometry for α-particles and spontaneous fission (SF) coincidences. The detector arrays were surrounded by 3He detectors to also assay prompt neutrons. Decontamination factors from actinides of about 105 were achieved. Group 6 (W) to 14 (Pb) elements as models for their heavier homologues were shown to be separated from the Rf/Db fraction with more than 90%. In eight final samples, representing a total beam dose of 3.4 × 1018 particles, 15 SF events were detected. The decay pattern points to a single component with a half-life of ≈32h, which shows a chemical behavior similar to the lighter homologues of group 4 and 5 elements.

Chemical identification of dubnium as a decay product of element 115 produced in the reaction 48Ca + 243Am

The recent discovery of the elements 115 and 113 in the reaction 48Ca + 243Am was confirmed by an independent radiochemical experiment based on the identification of the long-lived decay product dubnium.

Seasonal variations of aerosol residence time in the lower atmospheric boundary layer

During a one year period, from Jan. 2002 up to Dec. 2002, approximately 130 air samples were analyzed to determine the atmospheric air activity concentrations of short- and long-lived ( 222Rn) decay products 214Pb and 210Pb. The samples were taken by using a single-filter technique and γ-spectrometry was applied to determine the activity concentrations. A seasonal fluctuation in the concentration of 214Pb and 210Pb in surface air was observed. The activity concentrations of both radionuclides were observed to be relatively higher during the winter/autumn season than in spring/summer season. The mean activity concentration of 214Pb and 210Pb within the whole year was found to be 1.4±0.27 Bq m −3 and 1.2±0.15 mBq m −3, respectively. Different 210Pb: 214Pb activity ratios during the year varied between 1.78×10 −4 and 1.6×10 −3 with a mean value of 8.9×10 −4±7.6×10 −5. From the ratio between the activity concentrations of the radon decay products 214Pb and 210Pb a mean residence time (MRT) of aerosol particles in the atmosphere of about 10.5±0.91 d could be estimated. The seasonal variation pattern shows relatively higher values of MRT in spring/summer season than in winter/autumn season. The MRT data together with relative humidity (RH), air temperature (T) and wind speed (WS), were used for a comprehensive regression analysis of its seasonal variation in the atmospheric air.

Limitations in the use of RICH counters to detect tau-neutrino appearance

Abstract A comprehensive simulation study of the feasibility of an earlier proposed tau-neutrino appearance experiment based on a RICH with liquid radiator (C6F14) has been performed. Tau leptons, that are created in charged current interactions of incident tau neutrinos with the same momentum spectrum as that of the planned Gran Sasso beam (average 17 GeV /c ), have an average track length of about 0.5 mm . Cherenkov photons emitted in the liquid radiator from the short track of the tau lepton provide a characteristic pattern for tau-neutrino appearance. In the present report it is shown, on the basis of simulations performed with the GEANT4 code, that Cherenkov radiation from delta electrons, originating from the interaction of the long-lived tau decay products with the Cherenkov radiator, constitutes a severe background that renders the detection of the millimeter-short tau track unfeasible. Increasing the incident neutrino beam momentum results in longer tau tracks and therefore more signal photons, but this does not solve the background problem since the kink angle between the tau track and the secondary decay particle decreases with increasing neutrino momentum, leading to an increased overlap between the Cherenkov rings of these two particles.

Chemical isolation of dubnium (element 105) in fluoride media

SummaryThe isotope262Db was produced by irradiation of a248Cm target with 106-MeV19F ions at the 15 MV MP Tandem accelerator of Orsay (France). The reaction products were continuously and rapidly transported with a KCl aerosol helium jet system to the chemistry setup. They were dissolved in HF medium and the solution was passed through three successive ion exchange columns, allowing a continuous high level purification of Db from actinides on a first cation exchange column, the isolation of Db on an anion exchange one, and the retention of the long-lived decay products of262Db (3.24 h–254Fm) on a second cation exchange column. Just after the end of irradiation, the decay products were desorbed from this column, purified and α-sources were prepared on carbon foil by electrospray. In 13 effective irradiation hours, 22 events corresponding to the α-decay of254Fm were recorded. Almost 70 atoms of262Db, produced in the reaction248Cm +19F were isolated in dilute HF medium. Like its homologues/analogues Nb, Ta and Pa, dubnium forms, with fluoride ions, negatively charged complexes which are strongly retained on anion exchanger.

Ion-Exchange Procedure Developed for Isolation of Element 106 (Seaborgium) and Study of Its Chemistry in H2SO4 and H2SO4/HF Solutions, with W as Imitator

Ion-exchange behavior of W, Hf, Sr (homologs of elements 106, 104, and 102, respectively), U (pseudohomolog of element 106), Cm, and Eu in H2SO4 and H2SO4/HF solutions was studied. The static and dynamic ion-exchange properties of these elements were determined as influenced by the solution composition and the nature of the ion exchanger. The best conditions were found for separating element 106 (seaborgium) from daughter elements (Rf, No, and Fm) and its pseudohomolog, U, on a single cation-exchange column with the purification coefficients of ≥105-106. A possibility of using the anion exchanger for concentrating element 106 and separating it from the long-lived decay products was demonstrated. The speciation of these elements in dilute sulfuric acid solutions and in solution containing strong complexing agents was discussed.

Retrospective assessment of historic radon concentrations in Norwegian dwellings by measuring glass implanted Po-210 — an international field intercomparison

The first Norwegian study of historic radon concentrations in 17 dwellings in the high radon areas in Norway has been conducted as part of an international field intercomparison during 1998. The retrospective radon concentration is estimated via measurements of Po-210, the long-lived decay product of Rn-222 implanted in glass surfaces of objects like pictures, mirrors, cabinet-glass, etc. the method called ‘surface trap’. Three different surface trap techniques to assess the implanted Po-210 activity and two different procedures to estimate retro radon from Po-210 data were used. The Po-210 and the retrospectively estimated radon results agree reasonably well over a wide range of concentrations. Historic radon concentrations were also estimated from analysis of a smaller number of ‘volume trap’ samples (pieces of spongy materials), and the results compared to those from ‘surface traps’. The retro radon results correlate with contemporary radon results with a correlation coefficient of 0.877. To evaluate uncertainty in Po-210 measurements due to varying position on the glass a study of spatial homogeneity of three sample glasses was conducted and variations between 12% and 18% were found.

Experience from retrospective radon exposure estimations for individuals in a radon epidemiological study using solid-state nuclear track detectors

The relation between increased risk of lung cancer and exposure to indoor radon is assessed in epidemiological studies. Both the quality and reliability of smoking data and the radon exposure data are of primary importance. Contemporary measurement of radon concentration in the dwellings of individuals in a case-control study is traditionally used to assess past history of radon exposure. These assessments are somewhat unreliable since presently measured radon concentration might not be representative for a given location long ago. The measurement of long-lived decay products from 222Rn remaining indoors on hard surfaces, such as glass, makes it possible to assess the exposure to indoor radon. At the Swedish Radiation Protection Institute, a combination of two different solid-state nuclear track detectors has been developed to assess the 210Pb activity implanted in glass surfaces by measuring 210Po alpha activity. This detector (a RETRO detector) is used in the Swedish radon epidemiological case-control study of non-smokers with the aim to provide an alternative estimate of individual radon exposure and to evaluate the usefulness of RETRO measurements. A total of 576 different objects were found and 568 were measured. For 225 individuals, we measured two personal objects that had been in the same person's possession for more than 20 years. The standard deviation of the average radon concentration obtained from these two objects had a median value of 13 Bq/m 3 indicating a precision of exposure of approximately 20%. The correlation between 210Po surface activity measured earlier and the mean values of radon concentrations in a number of Swedish dwellings is used to estimate the historical, average radon concentration. This average correlation factor seems also to be valid for measurements in the non-smoker epidemiological study.

A New Method for Measurement of 210Bi on Glass Sheets to Estimate Retrospective Radon Exposure

In 1992 a living area was discovered in Hungary where the radon exhalation rate was extremely high. One of the questions asked was whether this level of concentration has existed for a long time. Because radon daughters are continuously embedded on the surface of glass sheets by alpha recoil, it means that old glass sheets can 'remember' past radon concentration levels via long-lived decay products. Traditionally 210 Po (daughter of 210 Bi) surface activity concentration is measured with an ionisation chamber or solid state nuclear track detectors (SSNTD). A new and fast radiochemical method has been developed to investigate surface beta activity concentration of 210 Bi. The new method was checked by comparing it with SSNTD. It is concluded that the radon concentrations in the radon prone area where the glass samples were analysed have not changed by more than a factor of two over the last 8-55 years.

Retrospective assessment of radon exposure by measurements of 210Po implanted in surfaces using an alpha track detector technique

The radon exposure of the past is important in epidemiological studies where an assessment of lung cancer risk from indoor radon exposure is evaluated. The long-lived decay product, 210Pb ( T 1 2 = 22 y ), is implanted into indoor surfaces by alpha recoils and can be monitored to give information about the previous radon history. This gives an alternative or complementary method to the traditional measurements of the current average radon concentration. Autoradiographic alpha-track methods to assess the 210Pb activity implanted in glass surfaces by measurement of 210Po alpha activity were investigated to find a simple and reliable method for field use. One limiting factor at low exposure levels is the alpha background activity in the sub-surface material. In the search for a practical field method, the use of two different alpha-track detector materials was found successful. By exposing one Kodak LR-115 cellulose-nitrate film and one CR-39 detector side by side on glass panes, the background of the glass is measured with the LR-115 and both the background and the signal by the CR-39 detector. Results from measurements in 31 dwellings show that an exposure of more than 1000 Bq·y·m −3 to a glass surface can be measured with the (CR-LR) difference technique. Experiences from the field measurements show the method to be accurate, simple, and reliable and therefore a promising tool for future radon epidemiological studies.

Level lifetimes in neutron-rich Ru isotopes

The neutron-rich Ru isotopes are situated between the strongly deformed Sr-Zr region with axial deformation of f l _ 0.40 [1] and the spherical Cd-Sn region. Evidence for triaxiality of even-even Ru isotopes has been presented in [2-5], and lifetimes of some of their 2 + states have been measured in fission studies [6-9]. It seems, however, that in these experiments the nearly identical energies of the 2 + ---* 0 + transitions in l~ and 11~ could not be separated. Therefore, high-resolution measurements are required in order to perceive the evolution of deformation with increasing neutron number. So far only few measurements by the delayed-coincidence method [10] have been performed on chemically or massseparated isotopes. Therefore, a systematic study of level lifetimes in neutron-rich Ru nuclei has been undertaken at the Mainz TRIGA reactor. Fission products were obtained from thermal-neutron induced fission of 249Cf. Technetium isotopes were chemically separated within 2 s by the on-line SISAK method [11], allowing the study of levels and lifetimes of their/3decay daughters. Primarily, the short-lived activities of 1~ to 111Tc were measured, whereas long-lived decay products were kept at a low level due to the continuous flow of the liquid phase (containing the technetium activity) passing the detectors. Apart from Tc, also small contaminations of short-lived Ag isotopes were observed in the 7-spectra. The detector setup consisted of a thin plastic scintillator for fi-particles and two Ge-detectors for 7-rays, one being a planar diode with good energy resolution and timing properties (7 ns at 100 keV) and the other a medium-size coaxial detector. Coincidence events from all detector pairs were recorded with the GOOSY mult iparameter system. The delayed coincidences between the fl-scintillator and the planar 7-detector were used for the measurement of the shortest lifetimes. With this setup, a systematical accuracy of the order of 0.05ns could be obtained for the strongest "/-peaks. The 7-7 coincidences were used to check for contaminations in the 7-gates from the planar detector applied for the fl-