ISOLDE EXPERIMENTS COMMITTEE
Minutes of the 9th meeting, August 23-24, 1993

OPEN SESSION:

The ISC'S new Chairman, Achim Richter, first thanked the outgoing Chairman, Bjorn Jonson, for the excellent job he had done for the ISC and for CERN during the last two years. He then introduced the new members of the ISC: Doris Forkel-Wirth, Wolfgang Hillebrandt, Alex Mueller and Karsten Riisager.

H. Ravn then gave a progress report on recent target-ion source tests. He presented two encouraging results: first that the initial problems with shock waves in molten metal targets have been overcome, and second that the combined effect of shorter delay times, higher cross-sections at 1 GeV proton beam energy and improved focussing of the proton beam have resulted in radioactive beam yields better than expected by a factor two or more.

O. Tengblad then showed some statistics on the PSB ISOLDE performance to date. A total of 1.87 x 1019 protons has been taken at an average 2 x 1013 protons per pulse. The PSB ISOLDE now has 35 approved experiments, for which a total of 645 shifts has been allocated. In 1992, 45 shifts were delivered. Of the 200 shifts planned for 1993, 125 have so far been delivered and it now seems that a further 161 shifts of runtime can be expected by the end of 1993. A schedule for achieving this was then presented.

Presentations were then made of the following proposals:

1. Shape coexistence and shell-model intruder states in the lead region studied by alpha decay
     Institut voor Kern- en Stralingsfysica, K.U. Leuven ; ISC 93-17/P49; P. Van Duppen.

2. Saturation of deformation and identical bands in very-neutron rich Sr Isotopes
     Department of Physics, Jyväskylä - Kernchemie Mainz - ISOLDE Collaboration);
     ISC 93-23/P52; G. Lhersonneau.

3. Single-particle states in 133Sn Strasbourg - Studsvik - Oslo - Göteborg - Mainz - Warsaw -
     Lyon - Bergen Collaboration); ISC 93-25/P53; P. Hoff.

4. Mass measurement of very short half-lived nuclei Aarhus - Bucharest - CERN - Giessen -
     Göteborg - Mainz - Montreal - Orsay Collaboration; ISC 93-27/P54; M. de Saint Simon.

5. Towards the proton drip-line along the cadmium isotopic chain Warsaw - CERN Collaboration);
     ISC 93-28/P55; J. Zylicz.

CLOSED SESSION

Present: J.V. Allaby, J. Aystö, P. Darriulat, J. Eades Secretary), W. Hillebrandt, A. Mueller,
              H. Ravn, D.J. Simon, D. Forkel-Wirth, A. Poves, A. Richter Chairman), K.Riisager,
              O. Tengblad.

Apologies: R. Helbig, E.W. Otten.

The Research Director of CERN, Pierre Darriulat thanked Achim Richter for taking on the arduous task of commmittee Chairman. The minutes of the last meeting were then approved without change. Discussion then took place on the five new proposals presented in the open session.

P49:

The referees were in no doubt as to the scientific merit of this proposal. Given the increase in target yields referred to above, and the still large discrepancy between the total number of shifts allocated and the number so far fulfilled, it was recommended that the Research Board allot six of the 12 shifts requested. The coordinator will use his discretion in providing more runtime if the expected yield increase does not occur.

P52:

The reaction of the Committee was again generally positive, and both referees stressed the theoretical challenge which would be offered by studies of the new element 102Sr forming the first 12-shift request. The second part of the experiment, for which a further 12 shifts were requested was thought to require a new setup, and the opinion of the Committee was that it should not at the present time be approved. Again taking into account the expected factor of two in improved yield, the Committee will advise the Research Board to allot six shifts for the first part.

P53:

The referees were enthusiastic about this proposal, which they thought was carefully presented and well reasoned and would fill an important gap in our knowledge. The Committee's recommendation is to accept the proposal but for half the number of shifts requested i.e. three for 133In, four for 134In), effectively allowing a factor of two for improved target yields.

P54:

The referees were of the opinion that mass measurements of short-lived nuclei by this type of mass spectrometer have clear scientific merit, and would represent a worthwhile addition to the PSB-ISOLDE programme. However, the technical questions raised by this proposal are significant, and the commitments on the ISOLDE scheduling would be very substantial. It was felt that there should be a strong indication that these can be surmounted before the Committee recommends the proposal to the Research Board. Specific questions include a) whether low enough separator emittance can be achieved without sacrificing yield and timing, and b) whether the high resolution separator will be required or not and c) what the optimal high voltage stepping will be. The collaboration will be encouraged to work closely with the ISOLDE separator group in doing the experimental work required to answer these and other questions. An addendum to the proposal should then be presented in the light of the results obtained.

P55:

Concerning this proposal it was thought that while the technical developments proposed for using molten tin targets were interesting and in line with the future development of ISOLDE, better physics motivation for undertaking these can be found in the 100Sn region than the understanding of Gamow-Teller quenching. The three shifts for target tests should be allocated and the group will be encouraged to assist H. Ravn and colleagues in carrying these out. The Committee being unfavourable to the Gamow-Teller topic as the sole basis for an approved experiment, the collaboration is therefore requested to develop further their arguments for investigating the 100Sn region.

OTHER BUSINESS

1. It was agreed to invite P. van Duppen to join the Committee as an ex-officio member in his capacity as
     leader of the CERN ISOLDE group.

2. For the next meeting, H. Ravn and O. Tengblad were asked to prepare an assessment of the effect
    of the improved target yields referred to several times above on the ISOLDE schedule, and in particular
    on a possible renormalisation of the number of shifts already allocated.

3. ISC meetings 1994:

The dates proposed for the 1994 ISC meetings are:

Last meeting of 1993: November, 22/23.