The GSI facilities open unique opportunities for gamma-spectroscopy employing very heavy UNILAC beams or, in particular, radioactive ion beams (RIB) of reasonable intensity from SIS/FRS. Therefore it is worthwhile to consider experimental campaigns with Euroball detectors which will for the first time enable investigations at medium to high multiplicities not attackable with VEGA. On this site we present helpful information on different aspects of a EUROBALL detector campaign:
The UNILAC is the only accelerator in Europe providing all stable isotopes up to 238U for near barrier nuclear strucuture experiments with the EUROBALL IV array, thus providing access to new areas of the nuclear chart using classical reactions. In addition, the velocity filter SHIP combined with EUROBALL IV can be employed for recoil tagging experiments with up to 5 times higher efficiency as compared to all previous set-ups.
The SIS / FRS facility, however, provides even more challenging new possibilities. By fragmentation or fission of relativistic heavy ions several 100 unstable rare isotopes can be generated with sufficient intensity for in-beam spectroscopy. Secondary beams can even be produced in high spin isomeric states.
A few physics examples:
Coulomb excitation at relativistic energies (50-200 MeV/u)
A few physics examples:
EUROBALL with its 239 crystals is optimized for large efficiency at high multiplicity. For classical nuclear structure experiments either at UNILAC or with slowed down fragment beams the value of an array similar to EUROBALL IV is therefore obvious.
In-beam experiments at relativistic energies are generally dealing with limited beam intensities, strong Doppler effects and are often also associated with high multiplicities from:
Depending on the velocity of the used beam two general detector arrangements have to be foreseen. Suggestions for possible lay-outs are given below:
Decay, Coulex, transfer, fusion Þ Mx < 1, Mp £ 5, Mg £ 25
Þ Pph (M=1) » 10%, Pph (M=30) » 7%
Þ Pph (M=1) » 10.4%, Pph (M=30) » 6.5%
Coulex, direct fragm., secondary fragm. Þ Mx £ 10, Mp £ 5, Mg £ 15
In the following figure rate estimates for typical experimental situations are given.
Fig.1: Beam intensity required for one photo peak count per hour. Optimized detector arrangements are assumed.
Fusion reactions with slowed down fragment beams as well as high energy secondary fragmentation reactions (probing the most exotic nuclei) can only be done within a reasonable measurement time if maximal Ge efficiency can be obtained. This requires that all the composite EUROBALL detectors are available.
and on the production cross section. Based on the EPAX parameterization a calculation of the production cross section for a particular isotope can be performed. Please note that the minimum primary beam energy for reliable EPAX calculations is 250-300 MeV/u. Keep also in mind that the transmission losses can be HUGE, especially for high-Z nuclei that suffer from broad charge state distributions. EPAX calculates fragmentation cross sections but not high energy induced fission.