ISOLDE EXPERIMENTS COMMITTEE
Minutes for the twentieth meeting on
Monday 10 February, 1997
 

OPEN SESSION

After welcoming Geirr Sletten of the Niels Bohr Institute Tandem Accelerator Laboratory in Roskilde, Denmark, to his first meeting as member of the ISC, the Chairman called on the ISOLDE technical group leader, to make his report. H. Ravn first noted that the severe recent problems with the target handling robot seem to have been satisfactorily resolved by the upgrade agreed upon with AEA. Various technical matters under way during the current 1997 shutdown period were also described, including the installation of the beamline for NICOLE and Mistral and the development of the laser ion source for beryllium and silver. On the other hand, the help expected from CERN for meeting the additional safety requirements imposed by TIS division in connnection with use of the robot has not so far been forthcoming. Improvement of the high resolution separator resolving power beyond 6000 has now been delayed by about a year, while unexpected reductions in agreed manpower and services to ISOLDE may result in perturbations to the 1997 physics programme as severe as those caused in 1996 by the robot problems.

The ISOLDE coordinator then presented a summary of the ISOLDE programme in the last period of 1996 and a draft schedule for 1997. As previously decided, 1996 ISOLDE operation ceased on December 16 to allow modifications to the experimental hall for Rex-ISOLDE to be carried out. From 1997 onwards, all CERN machines including ISOLDE will cease running at the end of November as an economy measure, but a further three week reduction suggested in November was considered incompatible with existing commitments of the ISOLDE programme.

Presentations were then made of the following new proposal and progress reports:

1. Proposal: Beta decay asymmetry in mirror nuclei: A = 9 Aarhus - CERN - Göteborg - Madrid -
    Stockholm Collaboration) ; CERN/ISC 97-2/P88.

2. Progress Report: ß-NMR study on microscopic structure and diffusion behaviour of Li implanted
    into ZnSe Marburg - Mainz - Leuven - ISOLDE/CERN Collaboration); CERN/ISC 97-8/P67 Add.1.

3. Progress Report: Status Report on Experiment IS351 and request for beam time: Search for 73Rb and
     investigation of nuclear decay modes near the Z=N line in the border region of the astrophysical
     RP-process path CERN - Gatchina - Jyväskylä - Leuven - Lyon - Strasbourg - IN2P3 Collaboration);
     CERN/ISC 97-3/P63 Add.2.

4. Progress Report: Electron paramagnetic resonance investigations of Erbium and Silver related defects
    Technische Universität Berlin - CERN/ISOLDE Collaboration); CERN/ISC 97-7/P83 Add.1.

5. Progress Report: The mechanism of ß-delayed two-proton emission in the 31Ar decay Addendum to
     experiment IS339: Aarhus - CERN - Göteborg - Jyväskylä - Madrid Collaboration;
     CERN/ISC 97-4/P56 Add.1:

CLOSED SESSION

Present: B.W. Allardyce, R. Ammerlaan, G. Bollen, J. Eades Secretary), D. Fick, L. Foà,
              D. Forkel-Wirth, W. Gelletly, D. Habs, E. Moya de Guerra, H. Nifenecker, H. Ravn,
              A. Richter Chairman), G. Sletten, F.-K. Thielemann.

Apologies: G. Goggi

The Chairman welcomed G. Sletten to the closed session, and the minutes of the nineteenth meeting were approved after minor typographical errors had been recognised.

In discussion of the technical group leader's report, the commmittee expressed satisfaction with the news that the target handling robot problems now appear to have been solved. It also expressed hope that the problems encountered by H. Ravn in satisfying the new TIS requirements could be solved in spite of the current inability of CERN to provide the agreed help as outlined in the minutes of the last ISC meeing.
L. Foà pointed out that these problems have their origin in the difficult circumstances arising from recently imposed funding cutbacks, but promised that CERN will do everything in its power to ensure that ISOLDE is able to comply with the new requirements without endangering its physics programme. This, he suggested, is in many ways less severely affected by the present difficulties than many other CERN experimental programmes.

Referring to the Coordinator's report, L. Foà expressed full agreement with the necessity to continue the ISOLDE programme throughout November, both in 1997 and in subsequent years. The committee noted this with satisfaction.

The meeting continued with a discussion of the proposals and progress reports presented in the open session, as follows:

P88: Beta decay asymmetry in mirror nuclei: A = 9

After a brief discussion it was agreed that although the interpetation of the beta decay asymmetry in A=9 nuclei might be difficult, it was essential to carry out a good measurement of it. The Chairman will therefore recommend to the Research Board that P88 be allocated the requested 15 radioactive beam and three stable beam shifts.

It was agreed that decisions on the following progress reports, being of the nature of extensions to previously agreed programmes, would not require further recourse to the Research Board:

P67 Add.1: ß-NMR study on microscopic structure and diffusion behaviour of Li implanted into ZnSe

The proposal forms part of a collection of experiments on II-VI semiconductors, and it was agreed in February 1995 that 9 shifts would be allocated to P67 among these. It was also decided at that time that the results of P67 and the other II-VI experiments would be collectively evaluated and presented to the Research Board before committing ISOLDE to further II-VI work. It was therefore agreed to allocate only 10 further shifts to P67 of the 24 requested, and to await results on outstanding II-VI experiments before proceeding any further with this joint programme.

P63 Add.2: Search for 73Rb and investigation of nuclear decay modes near the Z=N line in the border region of the astrophysical RP-process path

The nature of the original proposal has clearly undergone some metamorphosis since it was approved in May 1994 and extended in May 1995. It was agreed that the new programme might yield welcome physics results, but that as foreseen in the present addendum, development of suitable targets would be essential for these. It was therefore decided to allocate the three shifts requested for the latter, but to ask the team to reformulate the proposal meanwhile in terms of its new goals.

P83 Add.1: Electron paramagnetic resonance investigations of Erbium and Silver related defects

There had been some discussion in the last meeting concerning both the possible conflict between P83 and P81 Gold and platinium in silicon - isolated impurities and impurity complexes) and the sensitivity of P83.The first matter has been adequately resolved, especially by the clear refocussing of the present addendum on erbium, but some questions remain about the sensitivity with respect to the number of implanted ions. It was agreed to schedule P83 for 9 of the 16 requested shifts, after which a status report should be presented.

P56 Add.1: The mechanism of ß-delayed two-proton emission in the 31Ar decay

The committee agreed that the new, large solid angle geometry of the counter setup discussed in the present addendum to P56 will result in a vastly improved statistical significance in investigating two proton decay in 31Ar, and that one good clean experiment should be done on this topic. The 18 shift request, added to the 4 shifts outstanding from the previous allocation, should suffice to settle the question for
once and for all and will therefore be scheduled as requested.

OTHER BUSINESS

The committee took note of two Letters of Intent : Measurement of the 7Bep,g)8B absolute cross section in inverse kinematics CERN/ISC 97-1/I20), and Dipole Coulomb Polarizability in the scattering of Halo Nuclei CERN/ISC 97-10/I21). Concerning I20, it was agreed that since another 7Be experiment is being planned, the authors should be invited to make contact with the team concerned.

The dates of the remaining ISC meetings in 1997 are: