Bulletin #12                                       November 21, 2000

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                 ATOMIC        MASS        DATA       CENTER

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    I - END OF FTP ANONYMOUS

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    II - NEWS FROM EXPERIMENTS ON MASSES

    74Rb mass at MISTRAL and ISOLTRAP      /  Dave Lunney  November 2000

    In  early  November,  both  the  MISTRAL and ISOLTRAP collaborations
    succeeded  in  measuring  the mass of the dripline nuclide 74Rb. The
    special  properties  of  this  nuclide, possesing an equal number of
    protons  and  neutrons  and  beta-decaying via super-allowed (Fermi)
    transition   to  74Kr,  make  it  a  microlaboratory  for  the  weak
    interaction.

    The  Q-value  of  this  decay  is important for determination of the
    vector  coupling constant, supposed identical for all such decays by
    the  conserved vector current (CVC) hypothesis. This is the heaviest
    system  for  which  data is now available and will present a telling
    test   for   the  three-generation  standard  model:  the  unitarity
    condition  of  the  Cabibbo-Kobayashi-Maskawa  quark  mixing matrix.
    These  measurements  are  particulary  exciting  since  tests of the
    standard  model  are  usually  the  territory  of the worlds largest
    particle accelerators.

    While  the  radiofrequency  mass  spectrometer MISTRAL was conceived
    especially  for  short-lived nuclei, the 65 ms half-life of 74Rb was
    considered  by  many to be far too short to be successfully measured
    by the tandem Penning trap spectrometer ISOLTRAP.

    In  the  game  of high precision mass determination, measurements by
    different  instruments in the same regime of precision are important
    for  cross  checking  any  hint  of  systematic error. ISOLTRAP also
    succeeded  in  improving  the  mass  of the daughter nuclide 74Kr in
    order to constrain the Q-value. All measurements are currently under
    analysis.

    The  INTC-P-121  proposal to the ISOLDE and NTOF Committee (document
    CERN-INTC-2000-012),  "Precision study of the beta decay of 74Rb" is
    available   via  the  Isolde  website  http://isolde.cern.ch/  under
    experiment  IS-384.  For  MISTRAL see the same link under IS-373 and
    IS-346 and for ISOLTRAP see IS-302.


    III - GENERAL INFORMATION

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