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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Decay spectroscopy of an isomeric state in Md251

Excited states in Md251 have been populated by decay of an isomeric state at Ex≈1174 keV and studied via delayed γ-ray spectroscopy. We observe the population of two rotational bands, one of which we identify as the Nilsson π72[514] ground-state band and the other we propose is based on the π92[624] configuration. From the observed decay pattern, we suggest that the isomer spin parity is 232+, with the three-quasiparticle configuration π72[514]⊗{ν72[624]⊗ν92[734]}Kπ=8−. We compare our results to theoretical predictions of the single- and multi-quasiparticle structure of Md251.

Morse, C↗
DOE OSTI2020

Properties of 187 Ta Revealed through Isomeric Decay

Mass-separated 187 Ta114 in a high-spin isomeric state has been produced for the first time by multi-nucleon transfer reactions, employing an argon gas stopping cell and laser ionisation. Here, internal $γ$ rays revealed a $T$ 1/2 = 7.3±0.9 s isomer at 1778±1 keV, which decays through a rotational band with perturbations associated with the approach to a prolate-oblate shape transition. Model calculations show less influence from triaxiality compared to heavier elements in the same mass region. The isomer decay reduced $E$2 hindrance factor, $f$ $ν$ = 27±1, supports the interpretation that axial symmetry is approximately conserved.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Observation of Low-Lying Isomeric States in 136 Cs: A New Avenue for Dark Matter and Solar Neutrino Detection in Xenon Detectors

We report on new measurements establishing the existence of low-lying isomeric states in 136 Cs using γ rays produced in 136 Xe(p,n) 136 Cs reactions. Here, two states with O(100) ns lifetimes are placed in the decay sequence of the 136 Cs levels that are populated in charged-current interactions of solar neutrinos and fermionic dark matter with 136 Xe. Xenon-based experiments can therefore exploit a delayed-coincidence tag of these interactions, greatly suppressing backgrounds to enable spectroscopic studies of solar neutrinos and dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1986

Isomeric bismaleimides and polyaspartimides

The properties of a series of bismaleimides and polyaspartimides synthesized from the 3,3', 3,4', and 4,4' isomers of diaminodiphenylmethane are described and compared. The effects of the amine isomerism on the characteristics of bismaleimides and their polymers are investigated. It is observed that the 3,3'-bismaleimide had the highest crystalline melting point, the 4,4' isomer the lowest, and the 3,4'-bismaleimide was slightly above the all-para compounds; for the polyaspartimides, the all-para combinations had the highest glass transition temperature (218 C) and the all-meta the lowest (168 C). The data reveal that strong, flexible films were obtained only from the polyaspartimides made from the 4,4'-diamine/4,4'bismaleimide and the 3,4'-diamine/3,4'bismaleimide combinations; and the tensile properties of the 3,4'polymer films were as good as those of the 4,4 'polymer.

Bell, Vernon L.↗
NASA NTRS2019

Solid-State Isomerization and Infrared Band Strengths of Two Conformational Isomers of Cyclopropanecarboxaldehyde, A Candidate Interstellar Molecule

At least a dozen of the known interstellar molecules possess a formyl group (HCO), suggesting that other such species exist and await discovery in the interstellar medium. Here, we examine the mid-infrared (mid-IR) spectrum and selected physical properties of one such candidate, cyclopropanecarboxaldehyde, in amorphous ices. Mid-IR transmission spectra of solid cyclopropanecarboxaldehyde are presented for the first time and used to determine the cis-to-trans ratio of conformational isomers present in amorphous samples. The measured ratio is compared to one from an electron-diffraction study of the gas-phase compound. The cis-to-trans isomerization in the amorphous compound is followed, and the activation energy is determined. The first IR band strengths for solid cyclopropanecarboxaldehyde are reported. Also presented are refractive indices and densities at 15 K for amorphous forms of two related compounds, cyclopropane and cyclopropanemethanol. Two low-temperature reactions for the interstellar formation of cyclopropanecarboxaldehyde are briefly described.

band strengths↗
DOE OSTI2020

A Study of the Conformational Isomerism of n-Propyl Nitrate by Microwave Spectroscopy

The rotational spectrum of n-propyl nitrate was measured in the frequency range between 6 to 18 GHz using a Balle-Flygare Fourier transform microwave jet/cavity spectrometer. Parent, 13C and 15N isotopologue transitions for the lower-energy anti-gauche (AG) conformer were found using this instrument. The search for spectra from other conformers was performed using a broadband chirped-pulse jet spectrometer. Transitions from the anti-anti (AA) conformer were observed in this manner. Parent, 13C and 15N isotopologue transitions for the AA conformer were rescanned using the cavity instrument to improve resolution and the signal-to-noise ratio. Rotational, centrifugal distortion, and nuclear electric quadrupole coupling constants for all conformers/isotopologues were fit using Pickett’s SPFIT program. The structure of n-propyl nitrate is discussed considering these results.

Orellana, Will D.↗
DOE OSTI2020

Local Atomic Structure in Photo-isomerized Ruthenium Sulfur Dioxide Complexes Revealed by Pair Distribution Function Analysis

SO 2 linkage photoisomerization in crystalline ruthenium-based complexes has demonstrated nanophotonic phenomena such as optical switching and nano-optomechanical transduction. Molecular insights into these materials have been explored largely via the characterization of their photoinduced crystal structures via in situ single-crystal X-ray diffraction, known as photocrystallography. Photoinduced molecular disorder is present, which photocrystallography can model to the extent that it is confined within the periodic boundary of a unit cell. However, non-periodic molecular disorder is suspected to exist as well. In situ total scattering experiments were therefore carried out on finely powdered crystals of four ruthenium-sulfur dioxide complexes. Data were modeled using light-minus-dark' difference pair distribution function analysis, which afforded photoinduced structural changes exclusively. This revealed structural features that were first compared against models of photoinduced crystal structures known a priori from photocrystallography. Furthermore, statistical inference was then employed, which evidenced generally good agreement between the total scattering data and the photocrystallographic models, while revealing real differences that are indicative of a structure with only a short-range order. Overall, our findings demonstrate that in situ light-induced total scattering experiments on finely powdered crystals are able to reveal the photoinduced structure. Overall, the evidence suggests that such structure could include a short-range order as well as photocrystallographic content. Our demonstration experiment offers a pathway to develop studies that capture the short-range order in linkage photoisomers, while we have outlined the procedure for testing the validity of associated structural models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗