Short-lived Radioactive Isotopes Research Articles

Iodine in soils, pasture vegetation cuttings, and local food products of certain regions of Russia affected by the Chernobyl nuclear power plant accident

Natural iodine deficiency, which in some regions of Russia provokes thyroid diseases, increases the consequences of the entry of short-lived radioactive isotopes of this element into the food chain as a result of the Chernobyl accident (1986). The aim of the work is to assess the risk of morbidity of the population of the Kaluga, Bryansk and Oryol regions with thyroid cancer at the level of individual settlements based on experimental data. The iodine content in soils and vegetation cuttings of pastures in geochemically contrasting landscapes, as well as in cows' milk and potatoes of private household farms in the regions affected by the Chernobyl accident in 1986: Bryansk (2021), Oryol (2022) and Kaluga (2023) regions was studied. Joint expeditions of the Laboratory of Environmental Biogeochemistry of GEOKHI RAS and the Department of Human Ecology and Bioelementology of the Institute of Ecology of RUDN, carried out on the initiative and with the participation of the authors, revealed a significant variation of iodine concentration in soils and food products, which may be crucial for assessing the risk of thyroid diseases, including thyroid cancer, among the local rural population. The iodine content was found to be highly variable in both topsoil (0.31-3.04 mg/kg) and grass cuttings (0.14-0.29 mg/kg) of the study area. The maximum natural and technogenic risk of thyroid cancer morbidity in the rural population as a result of the consequences of the Chernobyl accident of 1986 is specific for the studied settlements of Zhizdrinsky district of Kaluga region, Bolkhovsky, Dmitrovsky and Sverdlovsky districts of Oryol region, Rognedinsky district of Bryansk region.

Radiochemistry: A Hot Field with Opportunities for Cool Chemistry.

Recent Food and Drug Administration (FDA) approval of diagnostic and therapeutic radiopharmaceuticals and concurrent miniaturization of particle accelerators leading to improved access has fueled interest in the development of chemical transformations suitable for short-lived radioactive isotopes on the tracer scale. This recent renaissance of radiochemistry is paired with new opportunities to study fundamental chemical behavior and reactivity of elements to improve their production, separation, and incorporation into bioactive molecules to generate new radiopharmaceuticals. This outlook outlines pertinent challenges in the field of radiochemistry and indicates areas of opportunity for chemical discovery and development, including those of clinically established (C-11, F-18) and experimental radionuclides in preclinical development across the periodic table.

Investigating radioactive negative ion production via double electron capture

The relative cross sections for radioactive negative ion production via double electron capture have been measured for collisions between a 40 keV projectile beam of uranium-238 and potassium vapor. This was performed at the collinear resonance ionization spectroscopy (CRIS) experiment at CERN-ISOLDE and is a step towards measuring the electron affinities (EAs) of elements that cannot be efficiently produced in negative ion sources at radioactive ion beam (RIB) facilities. This includes short-lived radioactive isotopes that have low production quantities and heavy and superheavy elements that systematically have smaller EAs than work functions of available ion source materials. Negative ions are particularly sensitive to electron–electron correlation effects, which make such studies ideal for benchmarking atomic structure models that go beyond the independent particle model. While the EAs of most light elements have been measured, experimental investigations on heavier elements, namely the actinides, remain scarce due to their radioactive nature and production difficulty. By developing negative ion production by charge exchange, we aim to make these studies feasible at RIB facilities.

A new versatile code for gamma-ray Monte-Carlo radiative transfer

ABSTRACTOngoing MeV telescopes such as INTEGRAL/SPI and Fermi/GBM, and proposed telescopes including the recently accepted COSI and the e-ASTROGAM and AMEGO missions, provide another window in understanding transients. Their signals contain information about the stellar explosion mechanisms and their corresponding nucleosynthesis of short-lived radioactive isotopes. This raises the need of a radiative transfer code which may efficiently explore different types of astrophysical γ-ray sources and their dependence on model parameters and input physics. In view of this, we present our new Monte-Carlo Radiative Transfer code in python. The code synthesizes the γ-ray spectra and light curves suitable for modelling supernova ejecta, including C+O novae, O+Ne novae, Type Ia and core-collapse supernovae. We test the code extensively for reproducing results consistent with analytic models. We also compare our results with similar models in the literature and discuss how our code depends on selected input physics and setting.

Very massive star winds as sources of the short-lived radioactive isotope 26Al

Context. The 26Al short-lived radioactive nuclide is the source of the observed galactic diffuse γ-ray emission at 1.8 MeV. While different sources of 26Al have been explored, such as asymptotic giant branch stars, massive stellar winds, and supernovae, the contribution of very massive stars has not been studied so far. Aims. We study the contribution of the stellar wind of very massive stars, here, stars with initial masses between 150 and 300 M⊙, to the enrichment in 26Al of the galactic interstellar medium. Methods. We studied the production of 26Al by studying rotating and non-rotating very massive stellar models with initial masses between 150 and 300 M⊙ for metallicities Z = 0.006, 0.014, and 0.020. We compared this result to a simple Milky Way model and took the metallicity and the star formation rate gradients into account. Results. We obtain that very massive stars in the Z = 0.006 − 0.020 metallicity range might be very significant contributors to the 26Al enrichment of the interstellar medium. Typically, the contribution of the winds of massive stars to the total quantity of 26Al in the Galaxy increases by 150% when very massive stars are considered. Conclusions. Despite their rarity, very massive stars might be important contributors to 26Al and might overall be very important actors for nucleosynthesis in the Galaxy.

Role of low-lying resonances for the Be10(p,α)Li7 reaction rate and implications for the formation of the Solar System

Evidence for the presence of short-lived radioactive isotopes when the Solar System formed is preserved in meteorites, providing insights into the conditions at the birth of our Sun. A low-mass core-collapse supernova had been postulated as a candidate for the origin of $^{10}$Be, reinforcing the idea that a supernova triggered the formation of the Solar System. We present a detailed study of the production of $^{10}$Be by the $\nu$ process in supernovae, which is very sensitive to the reaction rate of the major destruction channel, $^{10}$Be(p,$\alpha$)$^{7}$Li. With data from recent nuclear experiments that show the presence of a resonant state in $^{11}$B at $\approx$~193 keV, we derive new values for the $^{10}$Be(p,$\alpha$)$^{7}$Li reaction rate which are significantly higher than previous estimates. We show that, with the new $^{10}$Be(p,$\alpha$)$^{7}$Li reaction rate, a low mass CCSN is unlikely to produce enough $^{10}$Be to explain the observed $^{10}$Be/ $^{9}$Be ratio in meteorites, even for a wide range of neutrino spectra considered in our models. These findings point towards spallation reactions induced by solar energetic particles in the early Solar System as the origin of $^{10}$Be.

Prevalence of short-lived radioactive isotopes across exoplanetary systems inferred from polluted white dwarfs

ABSTRACT In the Solar system, short-lived radioisotopes, such as 26Al, played a crucial role during the formation of planetary bodies by providing a significant additional source of heat. Notably, this led to early and large-scale melting and iron core formation in planetesimals and their loss of volatile elements, such as hydrogen and carbon. In the context of exoplanetary systems therefore the prevalence of short-lived radioisotopes is key to interpreting the observed bulk volatile budget and atmospheric diversity among low-mass exoplanets. White dwarfs that have accreted planetary material provide a unique means to infer the frequency of iron core formation in extrasolar planetesimals, and hence the ubiquity of planetary systems forming with high short-lived radioisotope abundances. Here, we devise a quantitative method to infer the fraction of planetary systems enriched with short-lived radionuclides upon planetesimal formation from white dwarf data. We argue that the current evidence from white dwarfs point towards a significant fraction of exoplanetesimals having formed an iron core. Although the data may be explained by the accretion of exomoon or Pluto-sized bodies that were able to differentiate due to gravitational potential energy release, our results suggest that the most likely explanation for the prevalence of differentiated material among polluted white dwarfs is that the Solar system is not unusual in being enriched in 26Al. The models presented here suggest a ubiquitous pathway for the enrichment of exoplanetary systems by short-lived radioisotopes, disfavouring short-lived radioisotope enrichment scenarios relying on statistically rare chance encounters with single nearby supernovae, Wolf–Rayet, or AGB stars.

Constraints on r-process nucleosynthesis from 129I and 247Cm in the early Solar system

ABSTRACT GW170817 has confirmed binary neutron star mergers as one of the sites for rapid neutron capture (r) process. However, there are large theoretical and experimental uncertainties associated with the resulting nucleosynthesis calculations and additional sites may be needed to explain all the existing observations. In this regard, abundances of short-lived radioactive isotopes (SLRIs) in the early Solar system (ESS), which are synthesized exclusively by r-process, can provide independent clues regarding the nature of r-process events. In this work, we study the evolution of r-process SLRIs 129I and 247Cm as well as the corresponding reference isotopes 127I and 235U at the solar location. We consider up to three different sources that have distinct 129I/247Cm production ratios corresponding to the varied r-process conditions in different astrophysical scenarios. In contrast to results reported in a recent study, we find that 129I and 247Cm in the ESS do not come entirely from a single major event but get contributions from at least two more minor contributors. This has a dramatic effect on the evolution of the 129I/247Cm ratio, such that the measured ESS value in meteorites may not correspond to that of the ‘last’ major r-process event. Interestingly, however, we find that the 129I/247Cm ratio, in combination with the observed 129I/127I and 247Cm/235U ratio in the ESS, can still provide important constraints on the properties of proposed r-process sources operating in the Milky Way.

Commissioning and performance of TITAN’s Multiple-Reflection Time-of-Flight Mass-Spectrometer and isobar separator

TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) has specialized in fast Penning Trap mass spectrometry of very short-lived radioactive isotopes. The facility has been upgraded with a Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) to continue its quest towards more exotic nuclides, which are critical for our understanding of nuclear structure effects far from the valley of beta stability and for the nucleosynthesis of heavy elements in explosive astrophysical environments. In this publication, we discuss the implementation, operation and performance of TITAN’s MR-TOF-MS as a stand-alone high-precision mass spectrometer and as an isobar separator. By using the novel mass-selective re-trapping technique for the isobar separation, the MR-TOF-MS can consecutively perform separation and mass measurement of the same ion population, acting as its own isobar separator. The device boosts the dynamic range and reach of the TITAN facility by several orders of magnitude. The MR-TOF-MS reaches a high mass resolving power (m/Δm∼400000), high precision and mass accuracy (δm/m<10−7), is fast (common cycle time 20ms), shows high sensitivity and very large dynamic range (ion of interest to contaminant ratios of up to 1 to 106).

Monte Carlo Investigation of the Ratios of Short-lived Radioactive Isotopes in the Interstellar Medium

Abstract Short-lived radioactive nuclei (SLR) with mean lives below ∼100 Myr provide us with unique insights into current galactic nucleosynthetic events, as well as events that contributed to the material of our solar system more that 4.6 Gyr ago. Here we present a statistical analysis of the ratios of these radioactive nuclei at the time of the early solar system (ESS) using both analytical derivations and Monte Carlo methods. We aim to understand the interplay between the production frequency and the mean lives of these isotopes, and its impact on their theoretically predicted ratios in the interstellar medium. We find that when the ratio of two SRLs, instead of the ratios of each single SLR relative to its stable or long-lived isotope, is considered, not only are the uncertainties related to the galactic chemical evolution of the stable isotope completely eliminated, but the statistical uncertainties are also much lower. We identify four ratios, 247Cm/129I, 107Pd/182Hf, 97Tc/98Tc, and 53Mn/97Tc, that have the potential to provide us with new insights into the r-, s-, and p-process nucleosynthesis at the time of the formation of the Sun, and need to be studied using variable stellar yields. Additionally, the latter two ratios need to be better determined in the ESS to allow us to fully exploit them to investigate the galactic sites of the p process.

Yttrium Oxide Freeze-Casts: Target Materials for Radioactive Ion Beams.

Highly porous yttrium oxide is fabricated as ion beam target material in order to produce radioactive ion beams via the Isotope Separation On Line (ISOL) method. Freeze casting allows the formation of an aligned pore structure in these target materials to improve the isotope release. Aqueous suspensions containing a solid loading of 10, 15, and 20 vol% were solidified with a unidirectional freeze-casting setup. The pore size and pore structure of the yttrium oxide freeze-casts are highly affected by the amount of solid loading. The porosity ranges from 72 to 84% and the crosslinking between the aligned channels increases with increasing solid loading. Thermal aging of the final target materials shows that an operation temperature of 1400 °C for 96 h has no significant effect on the microstructure. Thermo-mechanical calculation results, based on a FLUKA simulation, are compared to measured compressive strength and forecast the mechanical integrity of the target materials during operation. Even though they were developed for the particular purpose of the production of short-lived radioactive isotopes, the yttria freeze-cast scaffolds can serve multiple other purposes, such as catalyst support frameworks or high-temperature fume filters.

Distribution and kinematics of 26Al in the Galactic disc.

26Al is a short-lived radioactive isotope thought to be injected into the interstellar medium (ISM) by massive stellar winds and supernovae (SNe). However, all-sky maps of 26Al emission show a distribution with a much larger scale height and faster rotation speed than either massive stars or the cold ISM. We investigate the origin of this discrepancy using an N-body+hydrodynamics simulation of a Milky-Way-like galaxy, self-consistently including self-gravity, star formation, stellar feedback, and 26Al production. We find no evidence that the Milky Way's spiral structure explains the 26Al anomaly. Stars and the 26Al bubbles they produce form along spiral arms, but, because our simulation produces material arms that arise spontaneously rather than propagating arms forced by an external potential, star formation occurs at arm centres rather than leading edges. As a result, we find a scale height and rotation speed for 26Al similar to that of the cold ISM. However, we also show that a synthetic 26Al emission map produced for a possible Solar position at the edge of a large 26Al bubble recovers many of the major qualitative features of the observed 26Al sky. This suggests that the observed anomalous 26Al distribution is the product of foreground emission from the 26Al produced by a nearby, recent SN.

Ensuring the analysis accuracy by ICP-MS method using radioactive and highly-enriched stable isotope tracers and gamma-ray spectrometry

To increase the accuracy of the analysis of silicon and rock samples by the inductively coupled plasma mass spectrometry, it is proposed to use both highly-enriched stable and short-lived radioactive isotopes with high specific radioactivity obtained in nuclear reactor to control the yield of elements on decomposition. Autoclave decomposition method for silicon and rock samples is proposed. Non-purified silicon sample irradiated in a nuclear reactor was used for testing of element recoveries during sample decomposition. Analysis of granite and black shale reference rock samples has been done using the suggested approach.

Determining the 56Ni distribution of type Ia supernovae from observations within days of explosion

Recent studies have shown how the distribution of 56Ni within the ejected material of type Ia supernovae can have profound consequences on the observed light curves. Observations at early times can therefore provide important details on the explosion physics in thermonuclear supernovae, which are poorly constrained. To this end, we present a series of radiative transfer calculations that explore variations in the 56Ni distribution. Our models also show the importance of the density profile in shaping the light curve, which is often neglected in the literature. Using our model set, we investigate the observations that are necessary to determine the 56Ni distribution as robustly as possible within the current model set. We find that this includes observations beginning at least ∼14 days before B-band maximum, extending to approximately maximum light with a relatively high (≲3 day) cadence, and in at least one blue and one red band (such as B and R, or g and r) are required. We compare a number of well-observed type Ia supernovae that meet these criteria to our models and find that the light curves of ∼70–80% of objects in our sample are consistent with being produced solely by variations in the 56Ni distributions. The remaining supernovae show an excess of flux at early times, indicating missing physics that is not accounted for within our model set, such as an interaction or the presence of short-lived radioactive isotopes. Comparing our model light curves and spectra to observations and delayed detonation models demonstrates that while a somewhat extended 56Ni distribution is necessary to reproduce the observed light curve shape, this does not negatively affect the spectra at maximum light. Investigating current explosion models shows that observations typically require a shallower decrease in the 56Ni mass towards the outer ejecta than is produced for models of a given 56Ni mass. Future models that test differences in the explosion physics and detonation criteria should be explored to determine the conditions necessary to reproduce the 56Ni distributions found here.

Development of an “[formula omitted]-TOF” detector for correlated measurement of atomic masses and decay properties

We have developed a novel detector, referred to as an “α-TOF detector”, for correlated measurements of atomic masses and decay properties of low-yield, short-lived radioactive isotopes using a multi-reflection time-of-flight mass spectrograph. By correlating measured time-of-flight signals with decay events, it will be possible to suppress background events and obtain accurate, high-precision mass and half-life values even in cases of very low event rates. An offline test of the α-TOF detector has shown that the time-of-flight detection efficiency for 5.48 MeV α-rays is more than 90% and yields a time resolution of 250.6(68) ps and an alpha-energy resolution of 141.1(9) keV. Using a two-dimensional spectrum of the correlated α-ray energy and time-of-flight, the α-rays from mixed α sources could be resolved. Subsequent testing using α-emitting nuclei extracted offline from a gas cell provide verification of the α-ray based characterization.

Imaging Recoil Ions from Optical Collisions between Ultracold, Metastable Neon Isotopes.

We present an experimental scheme that combines the well-established method of velocity-map imaging with a cold trapped metastable neon target. The device is used for obtaining the branching ratios and recoil-ion energy distributions for the penning ionization process in optical collisions of ultracold metastable neon. The potential depth of the highly excited dimer potential is extracted and compared with theoretical calculations. The simplicity to construct, characterize, and apply such a device makes it a unique tool for the low-energy nuclear physics community, enabling opportunities for precision measurements in nuclear decays of cold, trapped, short-lived radioactive isotopes.

Galactic Chemical Evolution of Radioactive Isotopes

The presence of short-lived ($\sim$\,Myr) radioactive isotopes in meteoritic inclusions at the time of their formation represents a unique opportunity to study the circumstances that led to the formation of the Solar System. To interpret these observations we need to calculate the evolution of radioactive-to-stable isotopic ratios in the Galaxy. We present an extension of the open-source galactic chemical evolution codes NuPyCEE and JINAPyCEE that enables to track the decay of radioactive isotopes in the interstellar medium. We show how the evolution of isotopic ratio depends on the star formation history and efficiency, star-to-gas mass ratio, and galactic outflows. Given the uncertainties in the observations used to calibrate our model, our predictions for isotopic ratios at the time of formation of the Sun are uncertain by a factor of 3.6. At that time, to recover the actual radioactive-to-stable isotopic ratios predicted by our model, one can multiply the steady-state solution (see Equation~1) by $2.3^{+3.4}_{-0.7}$. However, in the cases where the radioactive isotope has a half-life longer than $\sim$\,200\,Myr, or the target radioactive or stable isotopes have mass- and/or metallicity-depended production rates, or they originate from different sources with different delay-time distributions, or the reference isotope is radioactive, our codes should be used for more accurate solutions. Our preliminary calculations confirm the dichotomy between radioactive nuclei in the early Solar System with $r$- and $s$-process origin, and that $^{55}$Mn and $^{60}$Fe can be explained by galactic chemical evolution, while $^{26}$Al cannot.

182W evidence for core-mantle interaction in the source of mantle plumes

Tungsten isotopes are the ideal tracers of core-mantle chemical interaction. Given that W is moderately siderophile, it preferentially partitioned into the Earth’s core during its segregation, leaving the mantle depleted in this element. In contrast, Hf is lithophile, and its short-lived radioactive isotope 182Hf decayed entirely to 182W in the mantle after metal-silicate segregation. Therefore, the 182W isotopic composition of the Earth’s mantle and its core are expected to differ by about 200 ppm. Here, we report new high precision W isotope data for mantle-derived rock samples from the Paleoarchean Pilbara Craton, and the Reunion Island and the Kerguelen Archipelago hotspots. Together with other available data, they reveal a temporal shift in the 182W isotopic composition of the mantle that is best explained by core-mantle chemical interaction. Core-mantle exchange might be facilitated by diffusive isotope exchange at the core-mantle boundary, or the exsolution of W-rich, Si-Mg-Fe oxides from the core into the mantle. Tungsten-182 isotope compositions of mantle-derived magmas are similar from 4.3 to 2.7 Ga and decrease afterwards. This change could be related to the onset of the crystallisation of the inner core or to the initiation of post-Archean deep slab subduction that more efficiently mixed the mantle.

Statistical neutron capture in the limit of low nuclear level density

A major barrier in the study of neutron-induced nuclear reactions is the impossibility of direct measurements with short-lived radioactive isotopes. For these exotic nuclei, theoretical inputs such as the photon strength function (PSF) are poorly constrained. At Los Alamos National Laboratory, the Detector for Advanced Neutron Capture Experiments (DANCE) provides direct measurements of $\ensuremath{\gamma}$-ray cascades following neutron capture reactions on stable or long-lived radioactive nuclei. While Hauser-Feshbach calculations can provide reasonable predictions for neutron capture on heavy nuclei, their application to neutron-rich light nuclei with low nuclear level densities and low neutron separation energies is questionable. In this paper, we report on the $\ensuremath{\gamma}$-ray spectra from individual neutron resonances from the $^{96}\mathrm{Zr}(n,\ensuremath{\gamma})$ reaction, with an emphasis on the sensitivity of of the $\ensuremath{\gamma}$-ray spectra to different PSF models. The comparison of the measured $\ensuremath{\gamma}$-ray spectra with predicted spectra does not support the addition of a low-energy enhancement of the size reported in many charged-particle reaction measurements, but the sensitivity of the $\ensuremath{\gamma}$-ray spectra to different PSF models is weak.

Experimental setup and procedure for the measurement of the 7Be(n,p)7Li reaction at n_TOF

Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron induced reactions with charged particles in the exit channel even employing targets made out of small amounts of short-lived radioactive isotopes. After the successful measurement of the 7Be(n,α)α cross section, the 7Be(n,p)7Li reaction was studied in order to provide still missing cross section data of relevance for Big Bang Nucleosynthesis (BBN), in an attempt to find a solution to the cosmological Lithium abundance problem. This paper describes the experimental setup employed in such a measurement and its characterization.