Decay Of Nuclides Research Articles

Radiative heating of carbonaceous near-Earth objects as a cause of thermal metamorphism for CK chondrites

Metamorphic CK carbonaceous chondrites display matrix textures that are best explained by a transient thermal event with temperatures in the 550–950K range and durations in the order of days to years, longer than what is commonly admitted for shock events but shorter than what is required for nuclide decay. We propose that radiative heating of small carbonaceous meteoroids with perihelia close to the Sun could account for the petrological features observed in CK chondrites. Numerical thermal modeling, using favorable known NEOs orbital parameters (perihelion distances between 0.07 and 0.15AU) and physical properties of CV and CK chondrites (albedo in the range 0.01–0.1, 25% porosity, thermal diffusivity of 0.5–1.5Wm−1K−1), shows that radiative heating can heat carbonaceous meteoroids in the meter size range to core temperatures up to 1050K, consistent with the metamorphic temperatures estimated for CK chondrites. Sizes of known CV and CK chondrites indicate that all these objects were small meteoroids (radii from a few cm to 2.5m) prior to their atmospheric entry. Simulations of dynamic orbits for NEO objects suggest that there are numerous such bodies with suitable orbits and properties, even if they are only a small percentage of all NEOs. Radiative heating would be a secondary process (superimposed on parent-body processes) affecting meteoroids formed by the disruption of an initially homogeneous CV3-type parent body. Different petrologic types can be accounted for depending on the sizes and heliocentric distances of the objects in such a swarm.

Orbital electron capture of hydrogen- and helium-like ions

Modulated in time orbital electron capture (EC) decays have been observed recently in stored H-like $^{140}$Pr$^{58+}$ and $^{142}$Pm$^{60+}$ ions. Although, the experimental results are extensively discussed in literature, a firm interpretation has still to be established. Periodic transitions between the hyperfine states could possible lead to the observed effect. Both selected nuclides decay to stable daughter nuclei via allowed Gamow-Teller transitions. Due to the conservation of total angular momentum, the allowed EC decay can only proceed from the hyperfine ground state of parent ions. In this work we argue that periodic transitions to the excited hyperfine state (sterile) in respect to the allowed EC decay ground state cannot explain the observed decay pattern.

Cosmogenic isotope burial dating of fluvial sediments from the Lower Rhine Embayment, Germany

Cosmogenic isotope burial dating, using 10Be and 26Al, was applied to Plio–Pleistocene fluvial successions from the Lower Rhine Embayment, Germany. The approach consists of three principal steps: (1) measurement of cosmogenic nuclides in depth profiles, (2) modelling of hypothetical nuclide concentrations based on a first-order conceptualisation of the geological context and the principal succession of depositions and subsequent erosional and burial phases, and (3) using parameter estimation to identify values for the a priori unknown model parameters (burial age, initial nuclide concentrations, terrace erosion rates) that result in minimal disagreement between hypothetical and measured nuclide concentrations. The Late Pliocene Kieseloolite Formation was dated to 3650 ± 1490 ka and the Early Pleistocene Waalre Formation to 900 ± 280 ka. The unconformably overlying Upper Terrace Formation revealed ages of 740 ± 210 ka and 750 ± 250 ka for the two different sites. These findings are in good agreement with independent age control derived by bio-, magneto-, and litho-stratigraphy. Furthermore, identifiability and uncertainty analysis reveal a relationship between burial depth and sensitivity of isotope concentrations to burial age and erosion rate. Our results indicate that using shallower buried samples would enable a considerably more robust estimation of the burial age and the terrace erosion rate. Uncertainties arose mainly from nuclide measurements, and not from the uncertainties derived from modelling or insufficient knowledge of nuclide production and decay properties.

Accelerated alpha decay under laser exposure of metallic nanoparticles in aqueous solutions of uranium salt

The recent experimental results on the acceleration of alpha decay under laser exposure of metallic nanoparticles in aqueous solutions (D2O or H2O) of uranium salt UO2Cl2 are reviewed. It is demonstrated that the rate of the alpha decay of uranium branching depends on the laser wavelength and laser peak power both under exposure of the solution of uranium salt in colloidal solutions of metallic nanoparticles and under laser ablation of a bulk target in an aqueous solution. Tuning the laser wavelength to the plasmon resonance allows observation of large deviations of the contents of radio-nuclides of 238U branching from their equilibrium values. The effect of laser exposure is characterized by high isotopic selectivity towards the decay of different nuclides. Possible mechanisms of the laser-induced alpha decay of uranium isotopes and their potential applications are discussed.

Analysis of the total activation cross section of all possible reactions producing the same radioactive nuclide for the same element

Firstly, according to the regulation of growth and decay of radioactive nuclides produced in reactions, a formula used to calculate the total activation cross section of all possible reactions producing the same radioactive nuclide for the same element is deduced, and it is pointed out that the activation formula given in two references is incorrect. Then, as an example, the so-called total activation cross section in one of the two references is analyzed and the correct results of the cross sections of 182W(n,p)182(m+g)Ta, 183W(n,p)183Ta and 206Pb(n,α)203 Hg induced by neutrons around 14 MeV calculated with the data given in the literature, the nuclear parameters and some evaluated values are given. Finally, the correct results are compared with other values collected in the literature.

Monte Carlo calibration of whole-body counters with NaI(Tl) detectors in stretcher geometry

A usercode for the EGSnrc Monte Carlo package has been developed for the simulation of whole-body counters with NaI(Tl) detectors in stretcher geometry. The geometry of the whole-body counter and the information about the detectors are specified in a plain text file, which enables users to easily adapt the codes to their installation. Bottle phantoms consisting of 1 and 2 l Cautex bottles filled with the radionuclide dissolved in water have been modelled as phantoms depicting the human body to be measured. These kind of phantoms can be defined by the users in the input file. Sets of efficiency factors for calculating activities from counts in measured spectra have been generated by two methods: 'direct simulation of nuclide decay' uses compiled data on photon energies and yields for all nuclides of interest and simulates a given number of decays of those nuclides for phantom masses from 10 to 100 kg while 'single-energy simulation' uses idealized 'nuclides' with single-energy emissions of 100 % yield to study the response of the systems over the energy range of interest (0-2000 keV in 20-keV steps). At University Hospital of Cologne and Karlsruhe Institute of Technology both methods have been successfully applied for the evaluation of spectra measured within intercomparison exercises.

Validation of IRBURN calculation code system through burnup benchmark analysis

Assessment of the reactor fuel composition during the irradiation time, fuel management and criticality safety analysis require the utilization of a validated burnup calculation code system. In this work a newly developed burnup calculation code system, IRBURN, is introduced for the estimation and analysis of the fuel burnup in LWR reactors. IRBURN provides the full capabilities of the Monte Carlo neutron and photon transport code MCNP4C as well as the versatile code for calculating the buildup and decay of nuclides in nuclear materials, ORIGEN2.1, along with other data processing and linking subroutines. This code has the capability of using different depletion calculation schemes. The accuracy and precision of the implemented algorithms to estimate the eigenvalue and spent fuel isotope concentrations are demonstrated by validation against reliable benchmark problem analyses. A comparison of IRBURN results with experimental data demonstrates that the code predicts the spent fuel concentrations within 10% accuracy. Furthermore, standard deviations of the average values for isotopic concentrations including IRBURN data decreases considerably in comparison with the same parameter excluding IRBURN results, except for a few sets of isotopes. The eigenvalue comparison between our results and the benchmark problems shows a good prediction of the k-inf values during the entire burnup history with the maximum difference of 1% at 100 MWd/kgU.

Methods of monitoring the consistency of sets of recommended data for the decay characteristics of radioactive nuclides

Methods and procedures for monitoring the consistency of sets of recommended data for radioactive nuclide decay characteristics are considered. A procedure is proposed, which combines three methods of checking the consistency of quantities related to the decay scheme of a radionuclide: the decay energy, the energies and probabilities of nuclear transitions, the internal conversion coefficients and the energies and emission probabilities of the radiations accompanying the decay.

Synthesis and decay of nuclides in supernovae

Synthesis of chemical elements at conditions of nuclear statistical equilibrium is investigated for the ultramagnetized astrophysical plasma in supernovae and near to neutron stars. For iron group nuclides, the magnetic modification of nuclear structure shifts a maximum of nucleosynthesis products towards smaller mass numbers approaching titanium. Signals of 44Ti radioactive decay in the gamma-spectra of the supernova remnant Cassiopeia A were revealed from the integral IBIS/ISGRI observational data. The gamma-ray fluxes for 44Sc* lines with energies 67.9 and 78.4 keV are determined. The relationship between model and observational results is discussed.

26Al– 10Be– 21Ne burial dating

Cosmogenic-nuclide burial dating relies on a pair of cosmic-ray-produced nuclides that are produced in the same rock or mineral target at a fixed ratio, but have different half-lives. For example, 26Al and 10Be are produced in quartz at 26Al: 10Be = 6.75:1. If a sample of quartz is exposed at the surface for a time, 26Al and 10Be concentrations reflect this ratio; if it is then buried below the penetration depth of cosmic rays, production stops and both nuclides decay. The half-life of 26Al is half that of 10Be, so the 26Al/ 10Be ratio decreases over time and can be used to date the burial event. Because quartz derived from surface erosion and then buried by sediment accumulation is common, the method is widely applicable for dating Plio-Pleistocene clastic sediments. All (terrestrial) applications of burial dating so far have used the 26Al– 10Be pair. Here we show that coupling cosmogenic 21Ne, which is also produced in quartz, with 26Al or 10Be should improve upon both the age range and accuracy of 26Al– 10Be burial dating. We establish the feasibility of this approach by 21Ne measurements at two sites that have already been dated using 26Al– 10Be burial dating. Burial ages from all three nuclide pairs agree at both sites, which shows that currently accepted values for decay constants and production ratios are internally consistent. Thus, it is possible at present to increase the useful range of cosmogenic-nuclide burial dating by incorporating 21Ne. Fully realizing the potential improvements in accuracy would benefit from additional estimates of 21Ne/ 26Al and 21Ne/ 10Be production ratios that are independent of the 26Al and 10Be decay constants.

The distribution of short-lived radioisotopes in the early solar system and the chronology of asteroid accretion, differentiation, and secondary mineralization

We evaluate initial ( 26Al/ 27Al) I, ( 53Mn/ 55Mn) I, and ( 182Hf/ 180Hf) I ratios, together with 207Pb/ 206Pb ages for igneous differentiated meteorites and chondrules from ordinary chondrites for consistency with radioactive decay of the parent nuclides within a common, closed isotopic system, i.e., the early solar nebula. The relative initial isotopic abundances of 26Al, 53Mn, and 182Hf in differentiated meteorites and chondrules are consistent with decay from common solar system initial values, here denoted by I(Al) SS, I(Mn) SS, and I(Hf) SS, respectively. I(Mn) SS and I(Hf) SS = 9.1 ± 1.7 × 10 −6 and 1.07 ± 0.08 × 10 −4, respectively, correspond to “canonical” I(Al) SS = 5.1 × 10 −5. I(Hf) SS so determined is consistent with I(Hf) SS = 9.72 ± 0.44 × 10 −5 directly determined from an internal Hf–W isochron for CAI minerals. I(Mn) SS is within error of the lowest value directly measured for CAIs. We suggest that erratically higher values measured for CAIs in carbonaceous chondrites may reflect proton irradiation of unaccreted CAIs by the early Sun after other asteroids destined for melting by 26Al decay had already accreted. The 53Mn incorporated within such asteroids would have been shielded from further “local” spallogenic contributions from within the solar system. The relative initial isotopic abundances of the short-lived nuclides are less consistent with the 207Pb/ 206Pb ages of the corresponding materials than with one another. The best consistency of short- and long-lived chronometers is obtained for ( 182Hf/ 180Hf) I and the 207Pb/ 206Pb ages of angrites. ( 182Hf/ 180Hf) I decreases with decreasing 207Pb/ 206Pb ages at the rate expected from the 8.90 ± 0.09 Ma half-life of 182Hf. The model solar system age thus determined is T SS,Hf–W = 4568.3 ± 0.7 Ma. ( 26Al/ 27Al) I and ( 53Mn/ 55Mn) I are less consistent with 207Pb/ 206Pb ages of the corresponding meteorites, but yield T SS,Mn–Cr = 4568.2 ± 0.5 Ma relative to I(Al) SS = 5.1 × 10 −5 and a 207Pb/ 206Pb age of 4558.55 ± 0.15 Ma for the LEW86010 angrite. The Mn–Cr method with I(Mn) SS = 9.1 ± 1.7 × 10 −6 is useful for dating accretion (if identified with chondrule formation), primary igneous events, and secondary mineralization on asteroid parent bodies. All of these events appear to have occurred approximately contemporaneously on different asteroid parent bodies. For I(Mn) SS = 9.1 ± 1.7 × 10 −6, parent body differentiation is found to extend at least to ∼5 Ma post- T SS, i.e., until differentiation of the angrite parent body ∼4563.5 Ma ago, or ∼4564.5 Ma ago using the directly measured 207Pb/ 206Pb ages of the D’Orbigny-clan angrites. The ∼1 Ma difference is characteristic of a remaining inconsistency for the D’Orbigny-clan between the Al–Mg and Mn–Cr chronometers on one hand, and the 207Pb/ 206Pb chronometer on the other. Differentiation of the IIIAB iron meteorite and ureilite parent bodies probably occurred slightly later than for the angrite parent body, and at nearly the same time as one another as shown by the Mn–Cr ages of IIIAB irons and ureilites, respectively. The latest recorded episodes of secondary mineralization are for carbonates on the CI carbonaceous chondrite parent body and fayalites on the CV carbonaceous chondrite parent body, both extending to ∼10 Ma post- T SS.

Quantifying glacial moraine age, denudation, and soil mixing with cosmogenic nuclide depth profiles

Glacial boulders and soils on moraines are often dated to quantify the timing of glaciations and/or rates of chemical weathering in moraine chronosequences. A common assumption is that moraine crest erosion and soil mixing are unimportant. However, several studies suggest moraine denudation may be substantial. We evaluate the magnitude of moraine denudation and soil mixing in the Pinedale (∼21 ka) and Bull Lake (∼140 ka) moraines at Fremont Lake (Wyoming, United States) using cosmogenic nuclide depth profiles and a numerical model of moraine erosion and nuclide production and decay. Depth profiles indicate mixing of the surface layer from 40 to 60 cm depth. Age constraints from depth profile dating of cosmogenic nuclides result in ages of 17–24 ka for the Pinedale moraine and 70–127.5 ka for the Bull Lake moraine. These ages are comparable to ages based on the Lal and Chen approach which uses a sample from the mixed layer and the unmixed layer. However, the Lal and Chen approach is difficult to apply in real environments as the mixing depth needs to be determined independently. We find our best fit model based ages for the Bull Lake moraine are younger than independent age constraints from boulder exposure dating due to incomplete mixing. Exposure age constraints from boulders are more straightforward for moraines than ages based on depth profile dating. Finally, we find that moraine crests do significantly erode and are mixed, suggesting that previous weathering and dust accumulation rate studies on moraines provide minimum estimates for these processes.

Sources: A code for calculating (alpha, n), spontaneous fission, and delayed neutron sources and spectra

SOURCES is a computer code that determines neutron production rates and spectra from (alpha, n) reactions, spontaneous fission, and delayed neutron emission due to the decay of radionuclides in homogeneous media, interface problems, and three-region interface problems. The code is also capable of calculating the neutron production rates due to (alpha, n) reactions induced by a monoenergetic beam of alpha particles incident on a slab of target material. The (alpha, n) spectra are calculated using an assumed isotropic angular distribution in the center-of-mass system with a library of 107 nuclide decay alpha-particle spectra, 24 sets of measured and/or evaluated (alpha, n) cross sections and product nuclide level branching fractions, and functional alpha particle stopping cross sections for Z < 106. Spontaneous fission sources and spectra are calculated with evaluated half-life, spontaneous fission branching, and Watt spectrum parameters for 44 actinides. The delayed neutron spectra are taken from an evaluated library of 105 precursors. The code outputs the magnitude and spectra of the resultant neutron sources. It also provides an analysis of the contributions to that source by each nuclide in the problem.

Application of in-situ produced terrestrial cosmogenic nuclides to archaeology: A schematic review

Abstract. The wide applicability of in-situ produced Terrestrial Cosmogenic Nuclides (TCNs) to geological problems and experiences in development and testing gained over the past decade is encouraging for its application to archaeological questions, where there is a distinct need for an additional independent dating tool beyond the limits of radiocarbon (~ 40 ka). Just as TCNs are applicable to a broader time period with considerable precision in archaeology, so also are they applicable to all lithologies. Application of TCNs to archaeological problems is relatively simple: either surface exposure dating (using cosmogenic nuclide production) or burial dating (using decay of radioactive cosmogenic nuclides) can be applied. For a successful application, close collaboration between archaeologists and TCN experts is required. The total exposure from 100 a to 5 Ma of a given surface of archaeological origin can be determined by surface exposure dating. The range of burial dating is from ~0.1 to 5 Ma. TCNs have been successfully applied to many archaeological problems during the last decade and both surface exposure dating and burial dating show high potential in the solving of archaeological problems.

Accurate γ-ray spectrometry measurements of the half-life of 92Sr

Studies of the nuclear fuel cycle require an accurate knowledge of the energy release from the decay of radioactive nuclides produced in a reactor, including precise half-life data for the short-lived radionuclides. Moreover, short-lived fission products are crucial for fission rate distribution measurements performed in low-power facilities, such as EOLE and MINERVE of CEA Cadarache [Fougeras, P., 2005. EOLE, MINERVE and MASURCA facilities and their associated neutron experimental programs. In: 13th International Conference on Nuclear Engineering, Beijing, China, 16–20 May 2005], and their nuclear decay data need to be known to high precision. For these reasons, the half-life of 92Sr has been measured to solve a recently observed inconsistency identified with the quoted value in the main nuclear applications libraries (including JEFF3.1): T 1/2=2.71±0.01 h [Parsa, B., Ashari, A., Goolvard, L., Nobar, Y.M., 1971. Decay scheme of 2.71 h 92Sr. Nucl. Phys. A 175, 629–640]. An overestimation of 4.5% has been identified in this work, based on two independent methods. Specific γ-ray spectrometry measurements on activated fissile foils have been carried out, using two HPGe detectors. Influencing factors such as net area measurements of photopeaks, pulse pile-up accuracy and dead time corrections in the presence of decaying activity are discussed. A new value has been obtained by combining eight series of measurements: T 1/2=2.594±0.006 h. The uncertainty has been reduced by a factor of two with respect to previous evaluations. This measured value also shows good agreement with the most recent studies of T 1/2=2.627±0.009 h [Nir-El, Y., 2003. Private Communications. Soreq Research Centre, Yavne, Israel].

Status of the PHOENIX electron cyclotron resonance charge breeder at ISOLDE, CERN

We report here on the last progresses made with the PHOENIX electron cyclotron resonance charge breeder test bench at ISOLDE. Recently, an experiment was performed to test the trapping of (61)Fe daughter nuclides from the decay of (61)Mn nuclides. Preliminary results are given.

Analytical modeling for colloid-facilitated transport of N-member radionuclides chains in the fractured rock

A previous analytical model for N-member radionuclide decay chains has been extended to include the effect of radionuclide sorption with groundwater colloids. Published distribution coefficients were employed in the nuclide decay chain to illustrate the present model. The colloid concentration was assumed constant in time and space owing to equilibrium between colloid generation and sedimentation by chemical and/or physical perturbations. Furthermore, the diffusion of colloids into the rock matrix was ignored because the diameter of colloid is relatively large and colloids and fracture surfaces are like-charged. The results indicated that colloids could facilitate the transport of radionuclides and the large adsorbability of nuclides with colloids enlarged the effect of acceleration by colloids. The influence of colloids on the radionuclide transport was expected to be crucial to the actinides with large adsorbability; however, the present results revealed that the low-adsorbing nuclides whose parent nuclides have large capability of sorption could be also facilitated significantly by colloids indirectly. Therefore, the role of colloids played in the transport of the radionuclides decay chain should be assessed carefully in the radioactive waste disposal. The analytical method presented herein is helpful to verify/validate further complex far-field models.

Hokutolite collected from riverbed at Peitou Hot Spring in Taiwan: With emphasis on radiochemical studies

Hokutolite, and hot spring water and river water collected recently at Peitou Hot Spring in Taiwan were analyzed for U, Th, Ra and 210Pb isotopes. Concentrations of major chemical elements were also measured. Hokutolite had its typical chemical composition make-up for this area. The concentrations of 238U, 234U, 232 Th, 230 Th, 228 Th, 226Ra, 228Ra and 210Pb in samples scrapped into 7 layers from the surface to the bottom of a hokutolite specimen were 0.0021-0.0068, 0.0022-0.0075, 1.47-2.07, 1.00-1.29, 1.56-1.97, 56.7-68.6, 1.46-2.06 and 25.9-36.0 Bq/g, respectively. All the radionuclides exhibited a relatively uniform distribution, and radioequilibrium was confirmed among 232 Th, 228Ra and 228 Th. From the relationship between the decay and growth of Th-series nuclides it was considered that the hokutolite studied was isolated from the stream water at least 70-80 years ago. The U/Th-series radionuclides in the hot spring water were in rather high concentrations and the enrichment of 228Ra and 228 Th to 232 Th was the most prominent feature. Evaluation of the distribution coefficients (Kd) using the data on hot spring water or river water and hokutolite indicated that Th (Kd = 104-105) in water was likely to be precipitated (and/or co-precipitated) with BaSO4 as Th(SO4)2 with a relatively high concentration into hokutolite, together with Ra (Kd = 106-107).

Three-dimensional maximum a posteriori (MAP) imaging with radiopharmaceuticals labeled with three Cu radionuclides

Background One of the limiting factors in achieving the best spatial resolution in positron emission tomography (PET), especially in small-animal PET, is the positron range associated with the decay of nuclides, and usual PET image reconstruction algorithms do not provide a correction for the positron range. This work presents initial results obtained with the maximum a posteriori (MAP) algorithm, which has been developed to include an accurate model of the camera response, the Poisson distribution of coincidence data and the fundamental physics of positron decay including the positron range. Methods Phantoms were imaged with three positron emitting isotopes of Cu ( 60Cu, 61Cu and 64Cu), and mice and rats were imaged with two radiopharmaceuticals labeled with these isotopes in a microPET-R4 camera. These isotopes decay by positron emission with very different end-point energies resulting in wildly different spatial resolutions. Spatial resolution improvement and image quality offered by the MAP algorithm were studied with the line source phantom and a miniature Derenzo phantom. In addition, three mice and three rats were sequentially injected over a 48-h period with Cu-pyruvaldehyde bis( N 4-methylthiosemicarbazone) (for blood flow to organs) and Cu-1,4,7,10-tetraazacyclododecane-1,4,7-tri(methanephosphonic acid) (for bone imaging) labeled with the said three isotopes of Cu. Results The line source experiment showed that comparable spatial resolution is possible with all three isotopes when using the positron range correction in MAP. The in vivo images obtained from 60Cu and 61Cu and reconstructed with 2D filtered back projection algorithms provided by the camera manufacturer show reduced clarity due to degraded spatial resolution arising from the extended positron ranges as compared with 64Cu. MAP reconstructions exhibited a higher resolution with clearer organ delineation. Conclusion Inclusion of a positron range model in the MAP reconstruction algorithm may potentially result in significant resolution recovery for isotopes with larger positron ranges.

収集データの精度向上を目的としたＰＥＴ画質評価実験法の検討

Multiple data evaluation is desirable for data obtained by positron emission tomography (PET), as the data follow the Poisson distribution. Such evaluation, however, tends to be very complicated, since the count- rates change with nuclide decay. To solve this problem, we propose a new data scan protocol in this communication. With this method, the true+scatter coincidence counts were computed during the initial one-minute scanning, which was fixed as the standard. A dynamic scan was then performed with the fixed counts from the high count-rate region. Regions with +/-2.5% of the image noise of the standard image was chosen to provide the data for evaluation. These were found to be the regions of 16.5-25.5 kcps (2D) and 81.1-138.5 kcps. Image quality was found to be affected by noise (2D) and random coincidence. Using this method, multiple data could be obtained by a single experiment, and very reliable image evaluation could be done.