Long-lived Isomers Research Articles

Production of [formula omitted]Xe and [formula omitted]Xe via neutron activation of 128Xe and 130Xe at ILL-RHF and NCBJ-MARIA high-flux reactors

The long-lived xenon isomers 129mXe and 131mXe are of interest for the GAMMA-MRI project, which aims at developing a novel imaging modality based on magnetic resonance of polarized unstable tracers. Here, we present the steps leading to and following the production of these two isomers via neutron irradiation of highly-enriched 128Xe and 130Xe gas samples at two high-flux reactors, the High-Flux Reactor (Réacteur à haut flux, RHF) at the Institut Laue-Langevin (ILL) and the MARIA reactor at the National Centre for Nuclear Research (NCBJ). We describe the experimental setups and procedures used to prepare the stable xenon samples, to open the irradiated samples, and to transfer xenon isomers into reusable transport vials. The activity of 129mXe and 131mXe was measured to be in the range of tens of MBq per sample of 0.8(1)mg, and was proportional to thermal neutron flux density. A small activity of unstable contaminants was also visible in the samples, but their level is not limiting for the GAMMA-MRI project’s objectives. In addition, the minimum thermal neutron flux density required to produce 129mXe and 131mXe sufficient for the project could be also determined.

^{133}In: A Rosetta Stone for Decays of r-Process Nuclei.

The β decays from both the ground state and a long-lived isomer of ^{133}In were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to β, γ, and neutron spectroscopy, the comparative partial half-lives (logft) have been measured for all their dominant β-decay channels for the first time, including a low-energy Gamow-Teller transition and several first-forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their β decays selectively populate only a few isolated neutron unbound states in ^{133}Sn. Precise energy and branching-ratio measurements of those resonances allow us to benchmark β-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the β decay of neutron-rich nuclei southeast of ^{132}Sn and will serve as a guide for future theoretical development aiming to describe accurately the key β decays in the rapid-neutron capture (r-) process.

Low-lying level structures in the transuranic n -rich Z=93 nuclei Np243 and Np244

Low-lying level structures of the neutron-rich transuranic $Z$=93 isotopes, namely, odd-mass $^{243}\mathrm{Np}$ and its odd-odd neighbor $^{244}\mathrm{Np}$, are investigated with a view to characterize the respective ground state (gs) and to identify any long-lived isomer (LLI). For $^{243}\mathrm{Np}$ levels, we critically examine all the available information from three sources, namely, experimental, systematics from isotopic and isotonic neighbor, and theoretical results from microscopic Nilsson model calculations. Our investigations conclude $^{243}\mathrm{Np}$ gs ${\mathrm{J}}^{\ensuremath{\pi}}$ and configuration to be 5/2${}^{\ensuremath{-}}[523\ensuremath{\downarrow}$] on all counts. For the odd-odd $^{244}\mathrm{Np}$, we employ our well-tested three-step two-quasiparticle rotor model (TQRM) to identify and evaluate excitation energies of low-lying (${E}_{x}\phantom{\rule{4pt}{0ex}}\ensuremath{\le}$ 400 keV) 2qp bands and respective I(I$+$1) rotational levels. These calculations yield $^{244}\mathrm{Np}$ gs to have ${\mathrm{J}}^{\ensuremath{\pi}}$ and 2qp configuration as 2${}^{+}${p:5/2${}^{\ensuremath{-}}[523]\ensuremath{\bigotimes}$ n:${9/2}^{\ensuremath{-}}$[734]} while confirming the earlier reported ${7}^{\ensuremath{-}}${p:5/2${}^{+}[642]\ensuremath{\bigotimes}$ n:${9/2}^{\ensuremath{-}}$[734]} 2.29 m high-spin isomer (HSI) to be an excited state placed around ${E}_{x}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}100$ keV. We also briefly discuss the earlier reported $^{244}\mathrm{Np}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay branches of the ${\mathrm{K}}^{\ensuremath{\pi}}$=7${}^{\ensuremath{-}}$ isomer and the admissible main $\ensuremath{\beta}$ branches of ${\mathrm{K}}^{\ensuremath{\pi}}$=2${}^{+}$ gs to the various levels in $^{244}\mathrm{Pu}$.

Search for fission from a long-lived isomer in No250 and evidence of a second isomer

In the present work, a $K$ isomeric state in $^{250}\mathrm{No}$, which is more stable against fission than the ground state, was experimentally studied. The aim was to measure the fission branch of this isomeric state. In total, 780 fission events attributed to the decay of $^{250}\mathrm{No}$ were detected. Among them 133 cases were attributed to the ground-state decay with a half-life of 4.0(4) $\ensuremath{\mu}\mathrm{s}$, which was populated by the deexcitation of the isomeric state via electromagnetic transitions with a half-life of 23(4) $\ensuremath{\mu}\mathrm{s}$. In addition, in two more cases, this long-lived isomeric state was populated in the deexcitation of a hitherto unknown, yet higher-lying and short-lived isomeric state with a half-life of $0.{7}_{\ensuremath{-}0.3}^{+1.4}\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$. No direct fission from the long-lived isomeric state, i.e., with a lifetime of longer than 40 $\ensuremath{\mu}\mathrm{s}$, was identified. This results in an upper limit of 0.035 for the branching ratio for fission. This is a significantly more strict limit than the previously known value of 0.5. Nonobservation of fission branching of the long-lived isomer is discussed relative to theoretical predictions and within various semiempirical ways, which resulted in an attribution of a lower limit of ${10}^{4}$ for the fission-hindrance factor, caused by the $K$ quantum number. The presences of multiple high-$K$ isomeric states seemingly is a widespread phenomenon in deformed heavy nuclei.

Nuclear Data Sheets for A=186

Evaluated spectroscopic data and level schemes from radioactive decay and nuclear reaction studies are presented for 186Lu, 186Hf, 186Ta, 186W, 186Re, 186Os, 186Ir, 186Pt, 186Au, 186Hg, 186Tl, 186Pb, 186Bi, and 186Po. This evaluation for A=186 supersedes the earlier evaluation 2003Ba44 by C. M. Baglin. Highlights of this evaluation are the following: 186Re: Revised %ε and %β− branches. New values are almost same as of the earlier ones. Adopted improved level energy for the long-lived (8+) isomer at 148.2 keV 5 based on the study reported in 2015Ma60 (187Re(n, 2nγ)) compared to 149 keV 7 in previous evaluation (2003Ba44). 186Hg: Discrepancies in the level schemes between 1992Po01 and 1993Ma02 remain to resolve experimentally, arise primarily due to the assigned multipolarity of the ≈607 keV γ transition between the 1228 keV bandhead and the 2+ 621 keV level. See general comments in Adopted Levels, Gammas dataset. 186Tl: From α decay studies, 2020St11 propose spin-parity (2−) for the g.s. and (7+) for the excited level at 0.0+x of level energy of 77 keV 56. From mass measurements, 2014Bo26 propose the (7−) level energy of 20 keV 40 earlier.

Isomers in Tl203 and core excitations built on a five-nucleon-hole structure

Isomers with three- and five-nucleon-hole configurations have been established in $^{203}$Tl. These include newly identified levels with a three-nucleon structure: {\it I}$^{\pi }$ = (15/2$^{-}$) with {\it T}$_{1/2}$ = 7.9(5) ns, and {\it I}$^{\pi }$ = (35/2$^{-}$) with {\it T}$_{1/2}$ = 4.0(5) ns. In addition, five-quasiparticle states: {\it I}$^{\pi }$ = (39/2$^{-}$) with {\it T}$_{1/2}$ = 1.9(2) ns, and {\it I}$^{\pi }$ = (49/2$^{+}$) with {\it T}$_{1/2}$ = 3.4(4) ns have also been established. The previously determined long-lived decay [{\it T}$_{1/2}$ = 6.6(3) $\mu $s from this work] is associated with isomerism of the {\it I}$^{\pi }$ = (29/2$^{+}$) state. Levels above this long-lived isomer have been identified through a delayed-prompt coincidence measurement. Five-nucleon-hole states with excitation energies {\it E}$_{x}$ $\approx $ 7 MeV have been established as well as possible octupole excitations of the $^{208}$Pb core built on these levels. The level scheme of $^{203}$Tl is extended up to {\it E}$_{x}$ $\approx $ 11 MeV with the inclusion of 25 new transitions. Empirical and shell-model calculations have been performed to aid in the description of the observed states which are found to be predominantly of intrinsic character.

Producing gold at ISOLDE-CERN

The yield of 18 ion beams of radioactive gold nuclei produced in the thick uranium target at ISOLDE (CERN) by 1.4-GeV protons was measured. The production-efficiency dependence on the half-life (efficiency curve) was derived using the in-target production calculations by the FLUKA-CERN code. The irregularities in the efficiency curve for long-lived high-spin gold isomers (187,191,193Aum) were found. Three release models were tested for the efficiency-curve description.

Efficient Discovery of Visible Light-Activated Azoarene Photoswitches with Long Half-Lives Using Active Search.

Photoswitches are molecules that undergo a reversible, structural isomerization after exposure to certain wavelengths of light. The dynamic control offered by molecular photoswitches is favorable for materials chemistry, photopharmacology, and catalysis applications. Ideal photoswitches absorb visible light and have long-lived metastable isomers. We used high-throughput virtual screening to predict the absorption maxima (λmax) of the E-isomer and half-life (t1/2) of the Z-isomer. However, computing the photophysical and kinetic stabilities with density functional theory of each entry of a virtual molecular library containing thousands or millions of molecules is prohibitively time-consuming. We applied active search, a machine-learning technique, to intelligently search a chemical search space of 255 991 photoswitches based on 29 known azoarenes and their derivatives. We iteratively trained the active search algorithm on whether a candidate absorbed visible light (λmax > 450 nm). Active search was found to triple the discovery rate compared to random search. Further, we projected 1962 photoswitches to 2D using the Uniform Manifold Approximation and Projection algorithm and found that λmax depends on the core, which is tunable by substituents. We then incorporated a second stage of screening to predict the stabilities of the Z-isomers for the top candidates of each core. We identified four ideal photoswitches that concurrently satisfy the following criteria: λmax > 450 nm and t1/2 > 2 h.These candidates had λmax and t1/2 range from 465 to 531 nm and hours to days, respectively.

Impact of shell evolution on Gamow-Teller β decay from a high-spin long-lived isomer in 127Ag

The change of the shell structure in atomic nuclei, so-called “nuclear shell evolution”, occurs due to changes of major configurations through particle-hole excitations inside one nucleus, as well as due to variation of the number of constituent protons or neutrons. We have investigated how the shell evolution affects Gamow-Teller (GT) transitions that dominate the β decay in the region below 132Sn using the newly obtained experimental data on a long-lived isomer in 127Ag. The T1/2=67.5(9) ms isomer has been identified with a spin and parity of (27/2+) at an excitation energy of 1942−20+14 keV, and found to decay via an internal transition of an E3 character, which competes with the dominant β-decay branches towards the high-spin states in 127Cd. The underlying mechanism of a strong GT transition from the 127Ag isomer is discussed in terms of configuration-dependent optimization of the effective single-particle energies in the framework of a shell-model approach.

Rich band structure and multiple long-lived isomers in the odd-odd Cs118 nucleus

One of the largest sets of collective excitations built on two-quasiparticle configurations in odd-odd nuclei of the proton-rich A≈120 mass region is reported in Cs118. Several new rotational bands and long-lived isomers have been identified. The 8+ bandhead of the πh11/2⊗νh11/2 band is a short-lived isomer with a half-life in the nanosecond range, while the 7+ state below it is a long-lived isomer with a half-life of T1/2=0.55(6)μs. Two other long-lived isomers have been identified: a 66-keV transition detected at the MARA focal plane depopulates one of them, indicating a half-life in the microsecond range, while no depopulating transitions have been identified for the other, indicating a much longer half-life. Extensive particle number conserving cranked shell model calculations and alignment analysis have been employed to investigate the rich band structure of Cs118, which exhibits one of the most complete sets of two-quasiparticle configurations in nuclei close to the proton drip line.11 MoreReceived 12 May 2021Accepted 8 October 2021DOI:https://doi.org/10.1103/PhysRevC.104.044325©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsCollective modelsElectromagnetic transitionsIsomer decaysLifetimes & widthsNuclear spin & parityNuclear structure & decaysProperties90 ≤ A ≤ 149Nuclear Physics

Astromers in the Radioactive Decay of r-process Nuclei

Abstract Certain nuclear isomers are well known to affect nucleosynthesis with important observable consequences (e.g., 26Al and 180Ta). We study the impact of nuclear isomers in the context of rapid neutron capture process (r-process) nucleosynthesis. We demonstrate that nuclear isomers are dynamically populated in the r process and that some are populated far from thermal equilibrium; this makes them astrophysical isomers, or “astromers.” We compute thermally mediated transition rates between long-lived isomers and the corresponding ground states in neutron-rich nuclei. We calculate the temperature-dependent β-decay feeding factors, which represent the fraction of material going to each of the isomer and ground state daughter species from the β-decay parent species. We simulate nucleosynthesis following the decay of a solar-like r-process composition and include as separate species nuclear excited states with measured terrestrial half-lives greater than 100 μs. We introduce a new metric to identify those astromers most likely to be influential and summarize them in a table. Notable entries include many second peak nuclei (e.g., the Te isotopic chain) and previously overlooked isomers in stable nuclei (e.g., 119Sn, 131Xe, and 195Pt). Finally, we comment on the capacity of isomer production to alter radioactive heating in an r-process environment.

Nuclear clocks for testing fundamental physics

The low-energy, long-lived isomer in 229Th, first studied in the 1970s as an exotic feature in nuclear physics, continues to inspire a multidisciplinary community of physicists. It has stimulated innovative ideas and studies that expand the understanding of atomic and nuclear structure of heavy elements and of the interaction of nuclei with bound electrons and coherent light. Using the nuclear resonance frequency, determined by the strong and electromagnetic interactions inside the nucleus, it is possible to build a highly precise nuclear clock that will be fundamentally different from all other atomic clocks based on resonant frequencies of the electron shell. The nuclear clock will open opportunities for highly sensitive tests of fundamental principles of physics, particularly in searches for violations of Einstein’s equivalence principle and for new particles and interactions beyond the standard model. It has been proposed to use the nuclear clock to search for variations of the electromagnetic and strong coupling constants and for dark matter searches. The 229Th nuclear optical clock still represents a major challenge in view of the tremendous gap of nearly 17 orders of magnitude between the present uncertainty in the nuclear transition frequency (about 0.2 eV, corresponding to ∼48 THz) and the natural linewidth (in the mHz range). Significant experimental progress has been achieved in recent years, which will be briefly reviewed. Moreover, a research strategy will be outlined to consolidate our present knowledge about essential 229mTh properties, to determine the nuclear transition frequency with laser spectroscopic precision, realize different types of nuclear clocks and apply them in precision frequency comparisons with optical atomic clocks to test fundamental physics. Two avenues will be discussed: laser-cooled trapped 229Th ions that allow experiments with complete control on the nucleus–electron interaction and minimal systematic frequency shifts, and Th-doped solids enabling experiments at high particle number and in different electronic environments.

Level structures of the transfermium odd-odd nucleus Md252

Low-energy level scheme of doubly odd transfermium nucleus ${}_{101}^{252}{\mathrm{Md}}_{151}$ is constructed using our well-tested two-quasiparticle rotor model with explicit inclusion of residual n-p interaction contribution. Energy levels thus deduced are examined critically to assign spin-parity ${J}^{\ensuremath{\pi}}K$ and two-quasiparticle (2qp) configurations to the $^{252}\mathrm{Md}$ ground state and other energy levels with ${E}_{x}<400$ keV. Our low-energy level structures are then examined to predict a high-spin $({J}^{\ensuremath{\pi}}={8}^{+})$ long-lived isomer with ${E}_{x}\ensuremath{\approx}125$ keV and possibly also a lower-lying short-lived isomeric state. Comparison with $^{256}\mathrm{Lr}$ $(\ensuremath{\alpha})$ populated $^{252}\mathrm{Md}$ excited states leads to ${J}^{\ensuremath{\pi}}K$ and 2qp assignment to each of these experimentally postulated levels. Further, the five $\ensuremath{\gamma}$'s ascribed to $^{252}\mathrm{Md}$ from $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence experiments are placed in our evaluated levels corresponding to $\mathrm{\ensuremath{\Delta}}I=2$ transition in each case. Additionally, exploration of the upward extended radioactive connection of $^{232}\mathrm{Th}$ heading the $A=4n$ naturally occurring radioactive series to the heaviest known superheavy element with $A=4n$, namely ${}_{111}^{272}{\mathrm{Rg}}_{161}$, has led us to establish landmark position of $^{252}\mathrm{Md}$ in this $^{272}\mathrm{Rg}\text{\ensuremath{-}}^{232}\mathrm{Th}$ extended decay chain.

Astromers: Nuclear Isomers in Astrophysics

We develop a method to compute thermally-mediated transition rates between the ground state and long-lived isomers in nuclei. We also establish criteria delimiting a thermalization temperature above which a nucleus may be considered a single species and below which it must be treated as two separate species: a ground state species, and an astrophysical isomer ("astromer") species. Below the thermalization temperature, the destruction rates dominate the internal transition rates between the ground state and the isomer. If the destruction rates also differ greatly from one another, the nuclear levels fall out of or fail to reach thermal equilibrium. Without thermal equilibrium, there may not be a safe assumption about the distribution of occupation probability among the nuclear levels when computing nuclear reaction rates. In these conditions, the isomer has astrophysical consequences and should be treated a separate astromer species which evolves separately from the ground state in a nucleosynthesis network. We apply our transition rate methods and perform sensitivity studies on a few well-known astromers. We also study transitions in several other isomers of likely astrophysical interest.

Spin-trap isomers in deformed, odd-odd nuclei in the light rare-earth region near N=98

Masses of neutron-rich, odd-odd Pm, Eu, and Tb nuclei near $N=98$ were measured using the Canadian Penning Trap mass spectrometer at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility. High-resolution mass measurements yielded the discovery of spin-trap isomers at $N=97$ in $^{162}\mathrm{Tb}$, and in the $N=99$ isotones of $^{160}\mathrm{Pm}$ and $^{164}\mathrm{Tb}$. Furthermore, no evidence of long-lived isomers were observed at $N=95$ in $^{158}\mathrm{Eu}$, at $N=97$ in $^{158}\mathrm{Pm}$, nor at $N=101$ in $^{164}\mathrm{Eu}$ and $^{166}\mathrm{Tb}$. These experimental observations are compared to results from multiquasiparticle blocking calculations.

Radionuclide generator-based production of therapeutic\xa0177Lu from its long-lived isomer 177mLu

BackgroundIn this work, a lutetium-177 (177Lu) production method based on the separation of nuclear isomers, 177mLu & 177Lu, is reported. The 177mLu-177Lu separation is performed by combining the use of DOTA & DOTA-labelled peptide (DOTATATE) and liquid-liquid extraction.MethodsThe 177mLu cations were complexed with DOTA & DOTATATE and kept at 77 K for periods of time to allow 177Lu production. The freed 177Lu ions produced via internal conversion of 177mLu were then extracted in dihexyl ether using 0.01 M di-(2-ethylhexyl) phosphoric acid (DEHPA) at room temperature. The liquid-liquid extractions were performed periodically for a period up to 35 days.ResultsA maximum 177Lu/177mLu activity ratio of 3500 ± 500 was achieved with [177mLu]Lu-DOTA complex, in comparison to 177Lu/177mLu activity ratios of 1086 ± 40 realized using [177mLu]Lu-DOTATATE complex. The 177Lu-177mLu separation was found to be affected by the molar ratio of lutetium and DOTA. A 177Lu/177mLu activity ratio up to 3500 ± 500 was achieved with excess DOTA in comparison to 177Lu/177mLu activity ratio 1500 ± 600 obtained when lutetium and DOTA were present in molar ratio of 1:1. Further, the 177Lu ion extraction efficiency, decreases from 95 ± 4% to 58 ± 2% in the presence of excess DOTA.ConclusionThe reported method resulted in a 177Lu/ 177mLu activity ratio up to 3500 after the separation. This ratio is close to the lower end of 177Lu/177mLu activity ratios, attained currently during the direct route 177Lu production for clinical applications (i.e. 4000–10,000). This study forms the basis for further extending the liquid-liquid extraction based 177mLu-177Lu separation in order to lead to a commercial 177mLu/177Lu radionuclide generator.

Room-Temperature Photogeneration of Nitrosyl Linkage Isomers in Ruthenium Nitrosyl Complexes.

The conditions for the photogeneration of NO linkage isomers at room temperature are studied. By pulsed laser irradiation in the blue spectral range, the long-lived Ru-ON isomer can be generated at room temperature, which is crucial for potential applications, such as holography and data storage. By using static and time-resolved spectroscopy (UV/Vis and IR), we give evidence that the liftime of the Ru-(η2 -(NO)) isomer is a decisive parameter for the formation of the Ru-ON isomer at high temperature owing to a two-step isomerization mechanism Ru-NO→Ru-(η2 -(NO))→Ru-ON. Furthermore, we report the low-temperature structures for each isomer, which were revealed by photocrystallography.

Nuclear Data Sheets for A=268,272,276,280,284,288,292

Spectroscopic information such as production, identification, half-lives, decay modes and possible excited states for experimentally known nuclides of mass numbers 268, 272, 276, 280, 284, 288, and 292 are presented together with the recommended values, superseding information and data in the previous ENSDF and NDS evaluation by 2005Gu33. No nuclides have yet been identified for A=296 and 300. In the last 14 years, large amounts of new and definitive data on the superheavy nuclides (SHN) have become available, thus changing almost entirely the landscape of nuclear data in this mass region, as also indicated by a number of recent review articles: 2017Og01, 2016Ho09, 2016Ho06 (for fission barriers), 2016Fo10, 2015Og05, 2015Og07, and 2013Th02. See 2003Ka71 and 2001Ka70 for IUPAC technical discussions about the discovery of Z=111 (Rg) and 2009Ba62 for discovery of Z=112(Cn), 2011Ba54 for discovery of Z=114 (Fl) and Z=116 (Lv) and 2016Ka49 for discovery of Z=113 (Nh) and Z=115 (Mc). A special issue of Nuclear Physics A444 (2015) is devoted to research on superheavy elements (SHE) with 27 articles. In particular, see article by 2015Ko20 on mass spectrometric searches for superheavy elements in terrestrial matter. See also Proceedings of Nobel Symposium NS160 ‘Chemistry and Physics of Heavy and Superheavy Elements’ published in Eur. Phys. Jour. Web of Conferences 131 (2016), in particular 2016UtZZ, 2016DmZZ and 2016HoZY.A=268: 268Db, 268Hs and 268Mt are the only experimentally identified nuclides with A=268.A=272: 272Bh and 272Rg are the only experimentally identified nuclides with A=272. A tentative level scheme for 272Bh has been proposed from the decay of 276Mt. Search for 272Ds in 235U(40Ar,3n),E=5.1-5.4 MeV/nucleon reaction and subsequent α decays at GSI (1990Sc11) proved negative with σ<0.8nb.A=276: 276Mt is the only experimentally identified nuclide with A=276. A tentative level scheme has been proposed for this nuclide.A=280: 280Rg is the only experimentally identified nuclide with A=280. A tentative evidence is reported (2017Ka66) for 280Ds, based on one possible α-α-α correlated event at RIKEN.A=284: 284Cn, 284Nh and 284Fl are the only experimentally identified nuclides with A=284. First measurement of mass/charge (A/q) ratio has been made by 2018Ga34, resulting in the determination of A=284 for 284Nh.A=288: 288Fl and 288Mc are the only experimentally identified nuclides with A=288. Two independent experiments, first by Dubna-Livermore-ORNL collaboration using DGFRS at FLNR-JINR-Dubna (2004Og07,2004Og12), and the second at GSI using TASCA (2010Du06,2011Ga19) have confirmed the existence of 288Fl and 288Mc; and a third experiment at LBNL-Berkeley using BGS (2015Ga24) further confirmed the existence of 288Mc. Chemistry-related experiments for 288Fl have been reported by 2014Ya33 and 2010Ei01. First measurement of mass/charge (A/q) ratio has been made by 2018Ga34, resulting in the determination of A=288 for 288Mc. Search for 288Ds in natural Pt, Pb and Bi samples (2011De21) using accelerator mass spectroscopy (AMS) proved negative, with extremely low upper limits established.A=292: 292Lv is the only experimentally identified nuclide with A=292. Two independent experiments, one by Dubna-Livermore collaboration (2004Og12,2004OgZZ), and the other at GSI-SHIP facility (2012Ho12) confirm the identification of 292Lv, with the assignment of ten correlated events composed of Evaporation Residues (EVR)-α1-α2-SF correlated decay chains. Search for 292Rg in natural gold materials (2011De03), and for 292Ds and 292Fl in natural Pt, Pb and Bi samples (2011De21) using accelerator mass spectroscopy (AMS) proved negative, with extremely low upper limits established. 2010Ma03 proposed the existence of a very long-lived isomer in 122292 in their search of superheavy elements in natural Th sample using inductively-coupled plasma sector field mass spectroscopy, and interpreted the observed events as due to high-spin isomers of superdeformed or hyperdeformed character. This claim, however, for other nuclides in the superheavy element region has not been verified, for example in the AMS studies of natural samples such as Pt, Os, Au, Pb and Bi by 2011De21 and 2011De03. See also the publications of the Joint Working Party (JWP) of the IUPAC-IUPAP with critical appraisal of studies dealing with search of superheavy elements in natural samples. Specifically, for A=292, 2011De21 and 2011De21, using AMS technique, found no evidence for the existence of 292Ds, 292Rg and 292Fl in natural Pt, Pb, Bi and Au samples. See also replies to above critiques by 2009Ma19, Marinov et al., arXiv:0909.1057 (2009), and 2004MaZSA=296: Search for 296Rg in natural gold materials (2011De03), and for 296Fl and 296Mc in natural Pt, Pb and Bi samples (2011De21) using accelerator mass spectroscopy (AMS) proved negative, with extremely low upper limits established. See 2016DuZX for future prospects of discovery of elements beyond Z=118. There are no data tables for A=296.A=300: Search for 300Mc in natural Pt, Pb and Bi samples (2011De21) using accelerator mass spectroscopy (AMS) proved negative, with extremely low upper limits established. There are no data tables for A=300.

Identification of high- K rotation in Ba130 : Testing the consistency of electromagnetic observables

The band built on the Kπ=8−,T1/2=9.4 ms isomer of Ba130 has been identified, filling the gap in the systematics of the dipole bands built on the 8− isomers in the N=74 isotones from Xe128 to Gd138. The use of the GALILEO array in conjunction with its ancillaries EUCLIDES and Neutron Wall, helped to firmly place the newly identified transitions on top of the long-lived isomer. The extracted gK and gR gyromagnetic factors are in agreement with the 7/2+[404]⊗9/2−[514] two-neutron Nilsson configuration. Particle-rotor model calculations give an understanding of the limited degree of K mixing. The experimental information on the Kπ=8− isomer of Ba130 is now the most complete among the K isomers of the N=74 isotones.1 MoreReceived 24 September 2018DOI:https://doi.org/10.1103/PhysRevC.99.014307©2019 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsIsomer decaysNuclear structure & decaysProperties90 ≤ A ≤ 149TechniquesCollective modelsNuclear Physics

Formation of a long-lived cyclic isomer of ethylenedione.

A century of unsuccessful attempts to identify the neutral ethylenedione molecule combined with the results of quantum-chemical computations resulted in the conclusion on the instability of this molecule. In this article, we demonstrate that although the lowest energy isomer of ethylenedione with linear geometry is indeed unstable, a higher energy three-membered cyclic isomer can be stabilized, and at low temperature has a life-time longer than one millisecond. In our study, the ethylenedione C2O2 molecule was synthesized in the low-temperature reaction CO2 + C → C2O2 inside liquid helium nanodroplets. To study the reaction, a newly developed calorimetric technique was applied. Single pairs of reactants were incorporated into tiny helium droplets having a temperature of 0.37 K. The reaction energy was transferred to liquid helium stabilizing an intermediate gas-phase reaction product. The energy transfer also resulted in the evaporation of helium atoms. Therefore, the change of the helium droplets' size allowed precise calorimetry on a molecular scale.