PbK-shell ionization probability in high-energy Xe+Pb collisions

Abstract

Probabilities for Pb K-shell ionization in 5.9-, 7.2-, and 8.5-MeV/a.m.u. Xe+ Pb collisions for impact parameters between 10 and 60 fm are reported. The measured probabilities are compared with theories of 1so--vacancy production.

K-vacancy production in high-energy U+U and U+Pb collisions at small impact parameters

“…Hence, if at least one 7-ray in the cascade can be detected, the effects of the entire cascade can be eliminated by rejecting the event. This method was successfully applied in our earlier experiment [1]. In this work, there was an additional difficulty due to the high degree of nuclear Coulomb excitation of the projectile or target 238U nucleus.…”

“…Extending our earlier investigation of Pb K-shell ionization in elastic Xe+ Pb collisions near and above the nuclear Coulomb barrier [1], we have determined Pb and U K-shell ionization probabilities in elastic U + Pb and U + U collisions in a similar energy regime. In these heavy-ion -atom collisions, the molecular model is appropriate, according to which the ionization of an inner (K) shell of the projectile or target atom can be described in terms of ionization of electrons in the l sa and 2pa molecular orbitals (MO) [21.…”

“…To overcome this problem, we made use of a 7-ray anticoincidence method described in our earlier work [1]. This method relies on the fact that the 7-rays produced in heavy-ion inelastic nuclear reactions usually occur in cascades of increasing multiplicity as the reaction becomes more inelastic [7].…”

K-shell ionization in 7.5- and 8.6-MeV/a.m.u. U+U collisions at very small impact parameters

“…When we had determined a bin size such that the ratios of the x-rays to particles was constant over at least the three highest energy bins, we summed over these bins to determine the K-vacancy production probability due to atomic excitation. This technique is described in greater detail in [1] and [8].…”

“…Previously, we used a "f-ray anticoincidence method [8] which worked well in Xe + Pb collisions where the projectile energy exceeded the Coulomb barrier. But, this anticoincidence method does not reject all internal conversion events due to Coulomb excitation.…”