The impact parameter dependence of the K MO X-ray emission in208Pb +208Pb collisions

Abstract

The emission probabilities for quasimolecular K-x-radiation (K-MOR) have been measured in 2~176 collisions at 4.3 MeV/u and 4.8 MeV/u as a function of the scattering angle using the particle-photon-coincidence technique. The probabilities exhibit a superposition of two exponential slopes with different fall-off constants. We identify the sharp fall off at very small impact parameters (<60fm) with the K-MOR contribution from the decay of l sa-vacancies. The flatter slope for impact parameters larger than 60 fin is attributed to the radiative decay of holes in 2pl/2a molecular states.In this way, experimental "lsa-MOR-emission probabilities" could be extracted and compared with theory. For 4.3MeV/u the ls~-and 2pl/2a-excitation probabilities could also be determined and have been compared to coupled-channel calculations and to a scaling law for lsaexcitation.

X rays from quasimolecules

“…However, contributions from these transitions are small (Kirsch et ah, 1978), and since the ^-vacancy production probability is near unity in these collisions, one measures only the twovacancy production contribution for \sa MO x rays. Calculations of the coincident intensity based on measured Pb + Pb MO x-ray and K-vacancy production probabilities agree with experiment, and give additional confirmation of the separation of the measured MO x-ray probabilities into contributions from \sa and 2pa MO x rays (Stiebing et al, 1984).…”

“…Such a dependence was first proposed by Meyerhof et al (1974) and criticized by Thorson and Choi (1977). Nevertheless, reasonable agreement between theory and experiment is obtained, and the Several other measurements of K MO x-ray production probabilities have been made (Tserruya et al, 1976;Schuch et al, 1980;Stiebing et al, 1984). In 143-MeV Nb -f Nb collisions, Schuch et al (1980) found that the impact-parameter dependence of 2pa MO x-ray production follows that of AT-vacancy production, as suggested by Anholt and Meyerhof (1977).…”

“…45, from Stiebing et a/., 1984), two different slopes are observed in the impact-parameter dependence. The steeply falling segment (b < 100 fm) is thought to be due to one-collision Isa MO x-ray production.…”