/sup 176/Lu: Cosmic clock or stellar thermometer
We quantitatively examine the various experimental and theoretical aspects of the stellar synthesis of the long-lived ground state of /sup 176/LU (3.6 x 10/sup 10/ yr). We discuss the various regimes of stellar temperature and free-neutron density in which either (i) the internal electromagnetic couplings between /sup 176/Lu/sup o/ and /sup 176/Lu/sup m/ (3.68 hr) are sufficiently low that they may be treated as separate nuclei, or (ii) the internal couplings are rapidly able to establish thermal equilibrium between /sup 176/Lu/sup o/ and /sup 176/Lu/sup m/. Case (i) above allows /sup 176/Lu/sup o/ to be used as a cosmic clock of galactic s-process nucleosynthesis. As experimental input to the cosmic clock, we have measured the 30 keV neutron capture cross sections: sigma(/sup 170/Yb) = 766 +- 30 mb and sigma(/sup 175/Lu) = 1266 +- 43 mb. This latter value also yields the branching ratio, B, to /sup 176/Lu/sup o/ from neutron capture on /sup 175/Lu as B(24 keV) = 0.362 +- 0.038. Using abundance and cross-section systematics, we derive an upper limit on the mean s-process age of solar material of 11 x 10/sup 9/ yr before the solidification of the meteorites. By requiring the solar abundance of /sup 170/Yb to be consistent with these same sigmaN systematics, we can also bracket the allowable range for the average s-process neutron density as 10/sup 7/ cm/sup -3/< or approx. =< or approx. =4 x 10/sup 7/ cm)/sup 3/. However, for sufficiently high stellar temperatures, case (ii) above implies that the total effective half-life of /sup 176/Lu against beta decay becomes a very strong function of the stellar temperature: t/sub 1/2/(/sup 176/Lu) = 18.5 exp (14.7/T/sub 8/) hr for T/sub 8/>1, and thus the /sup 176/Lu ..-->.. /sup 176/Hf decay would constitute a sensitive stellar s-process thermometer. We show that the fact that /sup 176/Lu does exist in the solar system can place firm constraints on the temperature and neutron density of current models for the site of the s-process.
- Research Organization:
- Kernforschungszentrum Karlsrube, Institut fuer Angewandte Kernphysik
- OSTI ID:
- 5974077
- Journal Information:
- Astrophys. J., Suppl. Ser.; (United States), Vol. 46:4
- Country of Publication:
- United States
- Language:
- English
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Neutron capture cross sections and solar abundances of /sup 160,161/Dy, /sup 170,171/Yb, /sup 175,176/Lu, and /sup 176,177/Hf have been measured
/sup 176/Lu: Cosmic clock and stellar thermometer
Related Subjects
GENERAL PHYSICS
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
LUTETIUM 176
NUCLEOSYNTHESIS
LUTETIUM 176 TARGET
NEUTRON REACTIONS
CROSS SECTIONS
STAR MODELS
S PROCESS
YTTERBIUM 170 TARGET
ABUNDANCE
BETA-MINUS DECAY
CAPTURE
GROUND STATES
HAFNIUM 176
KEV RANGE 10-100
NEUTRON DENSITY
TEMPERATURE DEPENDENCE
BARYON REACTIONS
BETA DECAY
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
DECAY
ENERGY LEVELS
ENERGY RANGE
EVEN-EVEN NUCLEI
HADRON REACTIONS
HAFNIUM ISOTOPES
HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
ISOTOPES
KEV RANGE
LUTETIUM ISOTOPES
MATHEMATICAL MODELS
NUCLEAR REACTIONS
NUCLEI
NUCLEON REACTIONS
ODD-ODD NUCLEI
RADIOISOTOPES
RARE EARTH ISOTOPES
RARE EARTH NUCLEI
STABLE ISOTOPES
STAR EVOLUTION
TARGETS
YEARS LIVING RADIOISOTOPES
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources
651825 - Nuclear Properties & Reactions
A=150-189
Experimental- Nuclear Reactions & Scattering- (-1987)