QED and electron collisions in the super strong fields of K-shell actinide ions

Beiersdorfer, P.

Lawrence Livermore National Laboratory

关键词: Heavy Ion Accelerators;    Lamb Shift;    K Shell;    Uranium;    Actinides;   

DOI  :  10.2172/893999
RP-ID  :  UCRL-TR-218598
RP-ID  :  W-7405-ENG-48
RP-ID  :  893999

美国|英语

来源: UNT Digital Library

【 摘 要 】

Atomic physics of high-Z, heavy ions is very different from that encountered in low-Z or medium-Z ions. The reason is the ultra strong nuclear field found only in the heaviest ions. The highest-Z atomic systems available to physical investigation, the actinides, therefore, offer rich new physics that cannot be studied any other way. This ranges from new dominating forces in electron-ion collisions to tests of fundamental theories. A measurement of the two-loop Lamb shift in uranium is by many considered to be the ''holy grail'' of high-field QED tests of atomic systems. Such measurements have been attempted at heavy-ion accelerator facilities but have yet to succeed because of the difficulty to make measurements with the required accuracy. Also, electron collisions behave very differently in such tightly bound systems. The magnetic interaction between the ion and the incoming free electron (the so-called generalized Breit interaction) is essentially non-existent in collisions involving low and medium-Z ions. This interaction is therefore missing in essentially all electron collision codes. But in heavy, highly charged ions like uranium, the generalized Breit interaction readily is the dominant force, changing electron collision cross sections by a factor of two. This has never been experimentally observed. In fact, no K-shell emission spectrum of any heavy high-Z ion higher than krypton (Z=36) has ever been recorded from a collisional source. By studying the heaviest actinides such fundamental science can be extended to regimes where the highest precision tests can be made.