Lecturer: O. Klepper (GSI Darmstadt, Germany)

Title:  Measurements of Nuclear Masses and Half-lives
        in the Cooler-Storage Ring ESR

Date:   9/21/2001 (Fri.) 14:00 -

Place:  RIKEN Main Bldg. 1F Seminar Room

                           The seminar will be given in English.

Abstract:
The unique combination of the in-flight separator FRS and the 
cooler-storage ring ESR with its element-independent scheme for 
the production, separation, and storage of fast radioactive ion 
beams allows survey measurements of basic nuclear properties as 
masses and half-lives. In a first-generation experiment, Schottky 
mass spectrometry (SMS) produced about 100 new mass values of 209Bi 
fragments, the half-lives of which were limited to be longer than 
about 10 s due to the available beam cooling. The analysis of the
directly observed masses and of those indirectly derived via known
decay-chains has just been finished.

In the second-generation experiments the trend goes to improved data 
taking techniques and to the investigation of nuclei with shorter 
half-lives. Recently a survey of masses in the lead region has been 
performed with a new data acquisition system (Time Capture). Here the 
digitised Schottky noise is continuously stored, and the fast Fourier 
transformation is applied only off-line. This allows more efficient 
data taking and studying the dynamical influences of nuclear decays 
and of cooler instabilities. The high sen-si-tivity permits the 
observation of single ions and of their decay.

Isochronous mass-spectrometry (ISM) has been pioneered for short-lived 
nuclides for which cooling cannot be applied. For observation times 
of typically 200 ms, the revolution times of stored 52Cr and 84Kr 
fragments have been determined. E.g. for 48Mn(T1/2=158 ms) and 
neighbouring nuclei, mass values are presently being derived with 
expected accuracies of about 310-6.

The storage of radioactive fragments (or of primary ions) in the ESR 
permits to study  fully ionised nuclei or ones with a few electrons 
only and to systematically investigate the in-flu-ence of the electron 
cloud on nuclear decays. In the first experiments substantial 
pro-long-ation of half-lives (in the region of hours ) due to 
switching off the electron capture was observed via the decrease of 
the Schottky-signal of the mother nuclei. On the other hand, beta 
decay into empty atomic orbits opens up new decay channels and may 
dramatically decrease the nuclear half-life compared to the one in a 
neutral atom. The first two cases 163Dy and 187Re were discovered by 
stripping off the orbiting beta particle in the daughter ion after 
some hours of storing and breeding. This was necessary to separate 
mother and daughter nuclei. Based on the larger decay energies of  
206,207Tl81+  and on the improved Schottky technique, the bound-state 
beta-decays of these bare ions with half-lives in the minute region 
have recently been studied by a different technique: the intensities 
of mother and daughter nuclei have been observed simultaneously as 
function of time. This simpler and potentially more ac-curate 
tech-nique opens a new way to study radioactive decays.

In this talk the current technical development and the ongoing data 
analysis of recent experiments will be presented.