ISOLTRAP's harvest in 2000           / Alban Kellerbauer    May 2001

    The  year  2000 has been a highly eventful year for the Penning trap
    mass  spectrometer ISOLTRAP. Throughout the summer and fall, we were
    able to conduct a total of six successful beam times.

    In  the first beam time using a uranium carbide target in conjuction
    with   the   resonant-ionization  laser  ion  source,  the  nuclides
    128-130,132Sn  were measured. The mass of the the ground state 130Sn
    and  the  isomeric  state 130Snm (with an excitation energy of about
    2 MeV)  were determined separately by selectively removing the other
    isomer from the precision trap.

    The second beam time was dedicated to neutron-deficient Sr isotopes.
    The  masses of 76Sr and 77Sr were measured by determining the masses
    of  SrF2  molecules.  76Sr  is  a  possible  waiting  point  on  the
    astrophysical rp-process path.

    One  highlight  in  2000  was  the measurement of the Q value of the
    super-allowed  beta  decay  of  74Rb.  Two  separate beam times were
    performed  to  measure  the  masses of 74Rb and its daughter nucleus
    74Kr.  The  challenges involved in these two measurements were quite
    different.   74Rb,   with   a  half-life  of  only  65  ms,  is  the
    shortest-lived  nuclide  ever  investigated  in  a Penning trap. The
    precision  of  the measurement of its mass was limited by production
    rate  and  the efficiency of the apparatus on one hand and its short
    half  life  on  the  other  hand. Finally, a relative mass precision
    below  3.0e-7  was  reached.  In  the  case  of 74Kr, the short-time
    fluctuations  of  the  magnetic field had to be carefully controlled
    and  a  large number of measurements performed in order to reach the
    unprecedented  relative precision of less than 3.0e-8. The masses of
    73Kr and 75Kr were also measured.

    A  molten-lead  target was used for measurements aimed at completing
    our  knowledge of binding energies for the neutron-deficient mercury
    isotopes.  The  isotopes 179-181Hg were measured for the first time,
    thereby closing the gap in the binding energy systematics.

    The  last  beam  time  in  2000 was used to measure the mass of 34Ar
    produced  in  a  CaO  target.  This  value  is needed with very high
    accuracy   in   the   context   of   the  Ft-value  systematics  for
    super-allowed  Fermi  beta  decays.  ISOLTRAP succeeded in measuring
    this mass with a precision better than 1 keV.

    Articles  concerning  the  results  of the 1999 beam times have been
    submitted  for publication. An up-to-date list of these publications
    as  well  as  downloadable  versions  of  preprints are available at
    ISOLTRAP's web site: http://cern.ch/isoltrap/