LIS for RIBs generation

[Sergey Egorov]

The intensity and physical composition of radioactive
ion beams (RIBs), produced at on-line mass separators,
are strongly dependent on the type of ion source used
to ionize the element of interest. The general
requirements of the ion source are the following: the
ionization efficiency should be high; the element
selectivity large; the intrinsic delay short; the ion
beam emittance small; and the energy spread should be
minimal. The laser resonance photoionization technique
fulfills these requirements. In particular, it is
outstanding concerning efficiency and selectivity. As
the interest in production of exotic nuclei far from
stability increases, a demand of high ionization
efficiency and high selectivity is becoming more
important. Therefore, laser ion sources based on
resonant excitation of atomic transitions by
wavelength tunable lasers have been implemented at a
number of RIB facilities.
Several approaches to the practical realization of the
chemically selective laser ion source (LIS) have been
suggested and developed. It is possible to divide
these sources into three groups according to the
physical environment of laser produced ions: 
1) laser ionization of free atoms at low pressure in a
hot cavity;
2) laser ionization in a cell, filled with a buffer
gas;
3) deposition of radioactive species on a cold surface
followed by laser ablation and ionization.
Up to now only the first two groups of sources have
been implemented in direct connection with target
units at on-line mass separator facilities. In
particular, RIBs have been generated using hot cavity
LISs at the IRIS facility of Leningrad Nuclear Physics
Institute since 1990; at CERN-ISOLDE since 1991; and
at the on-line mass separator at GSI Darmstadt since
1993. Using the gas cell LIS, the first RIB of 55Ni
was produced in 1994 at LISOL (Leuven Isotope
Separator On Line).
DelMar Ventures, a California entity have recently
teamed up with leading research groups from Leuven and
CERN in order to build Laser Ion Sources of
Radioactive Ion Beams at other RIB facilities
worldwide http://delmar.webjump.com/LIS/. The method
of step-wise resonance ionization can be applied for
an even broader range of chemical elements. Using
copper vapor laser systems efficient ionization
schemes are expected for 79 atoms, including all of
the metals.




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