Radiative Decay Lifetime Research Articles

Far-ultraviolet background observations at high galactic latitude. I - The Coma Cluster

A series of high-galactic-latitude observations made with the Voyager 2 ultraviolet spectrometer are used to place stringent upper limits on the far-ultraviolet emissions from the central regions of the Coma Cluster of galaxies. In particular, consideration of the 912-1150 A region yields lower limits upon the radiative decay lifetimes of any neutrino species with masses in the range 22.1-27.8 eV, assuming massless decay products. Limits on the radiative decay lifetimes of such neutrinos are found to vary from 2.4 x 10 to the 25th to 7.1 x 10 to the 24th s, respectively, as a function of neutrino rest mass. This represents a substantial improvement over previous measurements.

Redistribution of radiation in the absence of collisions

Redistribution and depolarization of near-resonant radiation is studied for the He 2(1P)-3(1D) line (668 nm) and some data for H-alpha (656 nm) are also presented. A Nd:YAG pumped dye laser, with a bandwidth of 0.1/cm and a power density of 100 kW/sq cm, is used in the experiment. The transitions have lower levels with natural line widths that are large compared with their upper-level natural widths, and, under experimental conditions, their collisional widths are also small. The ratio of fluorescence to Rayleigh intensity is measured and the results indicate that while the Rayleigh emission has the same temporal development as the laser pulse (5 ns FWHM), the fluorescent intensity has a decay time determined by the radiative decay lifetime and by collisional quenching. The prediction that redistribution of radiation occurs in the absence of collisions for transitions having significant lower-level radiative widths is confirmed. Depolarization rates by collisions with helium are also inferred from the measurements.

Radiative decay lifetimes and optical excitation functions for the e 3Σ−(v = 2, 3, 4) states of CO

The radiative lifetimes and optical excitation functions have been measured for the e 3Σ−(v = 2, 3, 4) levels of CO using pulsed low energy electron impact excitation and delayed coincidence detection. The v = 2, 3, and 4 lifetimes were found to be 4.12±0.14, 4.08±0.29, and 3.73±0.06 μs, respectively. Cascade components were observed to feed all three vibrational levels and these lifetimes were measured to be 13.8±6.5, 11.8±1.3, and 14.9±3.6 μs. The threshold energies of these states are discussed. The optical excitation functions indicated the presence of thresholds above those of the e states which appear to be due to nearby Asundi band vibrational levels ranging from v = 8 to v = 16.

Radiative decay lifetime of neutrinos and the evolution of the universe after the recombination era

If the radiative decay lifetime τ of massive neutrinos is less than 10 25 s, but exceeding present constraints, the epoch of neutral hydrogen in the history of the universe could have been short or altogether absent. Erasure of small scale fluctuations in the cosmic microwave background radiation and other consequences of such lifetimes are discussed. From observations of neutral hydrogen in the nearby galaxy M 31 a lower limit τ ⩾ 10 24 s is obtained (for neutrino masses in the range 30 eV ⩽ m ⩽ 150 eV).

Neutrino-Lifetime Constraints from Neutral Hydrogen in the Galactic Halo

Massive neutrinos may dominate the universe's rest mass and compose galactic halos. By requiring that the photoionization of the high-velocity clouds of neutral hydrogen near our galaxy not exceed observational limits, we find that the radiative decay lifetime for ionizing photon production by neutrinos (m/sub ..nu../>27.2 eV) composing our galactic halo must exceed 10/sup 24/ sec.

Characteristic radiative decay lifetimes and symmetry distribution in KCl:Sm 2+

Sm 2+ ions enter the KCl lattice in a distribution of site symmetries each of which is prescribed by the nature and relative position of the compensation defect. This site distribution is manifested in a corresponding distribution in characteristic radiative decay lifetimes measured from 4.2°K narrow line fluorescence transitions originating from the 5D 0 level in several symmetry types of Sm 2+.