ISOLDE EXPERIMENTS COMMITTEE
Minutes of the Tenth Meeting on November 22-23, 1993
 

OPEN SESSION:

The ISC Chairman Achim Richter first called on H. Ravn and O. Tengblad to present their reports on the ISOLDE technical and programme status.

H. Ravn reported on recent target tests. Increased yields relative to the SC ISOLDE have been confirmed particularly in the wings of the mass distribution), the shock wave problem in molten metal targets understood, and typical target lifetimes of about 23 8-hour shifts achieved. Although only 200 radioactive beam shifts were planned for 1993, it has been possible to deliver 275 so far in addition to 45 shifts with stable beam). For 1994 , 200 shifts are again foreseen as the HRS will not take beam next year.
O. Tengblad added further details of the 1993 performance of ISOLDE. A total of 5 X 1019 protons has been delivered, and 12 targets have been used for 43 different experiments. For 1994 a preliminary draft schedule was presented for the 200 shift total mentioned above, making use of 15 targets. This is to be compared with the total outstanding beam time allocated by the committee of 360 shifts.

Presentations were then made of the following proposals:

1. Emission channeling studies of the lattice site of oversized alkali atoms implanted in metals Leuven -
    Konstanz - Groningen - CERN Collaboration): ISC 93-32/P58; G. Langouche.

2. Hyperfine spectroscopy of unstable EU+ isotopes in an ion trap Institut für Physik, Univ. Mainz):
     ISC 93-20/P51; G. Werth.

3. The mechanism of ß-delayed two-proton emission Aarhus - CERN - Göteborg - Jyväskyla -
     Madrid Collaboration): ISC/93-30/P56; M.J.G. Borge.

4. Experimental verification of the concept of energy amplification by high energy induced nuclear
     cascade CERN): ISC 93-31/P57, ISC 93-37/P57 Add. 1; C. Rubbia.

CLOSED SESSION

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

The minutes of the last meeting were approved without change. Discussion then took place on the proposals presented in the open session.

P57: Experimental verification of the concept of energy amplification by high energy induced nuclear
          cascade CERN)

Owing to the absence amongst the committee members of specialists in the field discussed in the proposal, the internal referees' assessments had been supplemented by expert opinion from two external ones. As neither of these had been able to attend the meeting, their written reports were presented and discussed. The committee generally agreed that the presence of both the calorimeter materials and the PSB were points in favour of making these studies at CERN, and that new nuclear cascade data in the low neutron flux regime of 1014 n/cm2 would be most useful. It was nevertheless unanimously agreed that the questions raised in the very detailed reports of the external referees concerning, for example, the adequacy of the cascade model, the extrapolation from Uranium to Thorium and the technical aspects of temperature profile measurements) were valid, and that the collaboration should be given the opportunity to address them. The Chairman will therefore write a letter to the spokesman summarising the points raised, including those concerning radiation safety issues the subject of a Memorandum from the Director for Technical Support) and will invite him to respond to these questions.

P58: Emission channeling studies of the lattice site of oversized alkali atoms implanted in metals
          Leuven - Konstanz - Groningen - CERN )

This would not only be the first metallic solid-state experiment at ISOLDE but also the first study on the implantation of oversized alkali atoms into metals. The committee was convinced that the experiment would enrich the solid state physics programme of ISOLDE. A first allocation of 12 shifts, to be used for studies on Cs and Fr, will therefore be recommended to the Research Board.

P51: Hyperfine spectroscopy of unstable EU+ isotopes in an ion trap
          Institut für Physik, Univ. Mainz)

It was agreed that the techniques described for making precise measurements of magnetic dipole moments and g-factors in Eu isotopes were both elegant and interesting. The quality of the theoretical models available for interpreting the results is clearly not commensurate with the power of the technique, although the experiment might trigger off new activity in this direction. It was decided to allocate 4 shifts for a test case two masses) to check among other things that the chemical separation works, before recommending the full scale experiment to the Research Board.

P56: The mechanism of ß-delayed two-proton emission Aarhus - CERN - Göteborg - Jyväskyla -
           Madrid)

The committee believed that this experiment on correlations between the protons in two proton decay of Ar31 was of definite interest and that Ar31 was the most favourable candidate for such studies. The experiment will therefore be recommended to the Research Board for the full 24 shift request. The possibility of parasitic running with IS334 should also be investigated, although it should be made clear which is the primary experiment in this case.

Other Business

a) P54 Add. 1.: Mass measurement of very short half-lived nuclei M. de Saint-Simon)

This addendum was presented in response to the request made by the committee at its ninth meeting for more information on some technical aspects of the experiment and its effect on the ISOLDE schedule. In reacting to this request the group has been able to reduce its request for beam time by almost a factor three, largely by deciding to construct an auxiliary ion source and by transferring certain tests to Orsay. The committee took note of these developments. It was decided to defer approval of the experiment until this preparatory work has been done.

b) The committee took note of two letters of intent:

I8: Search for 73Rb nuclide. Determination of the border region of the astrophysical rp-process path

I9: Precise mass measurement of Hg, Au and Pt Isotopes.

c) It had been suggested at the ninth meeting that the number of shifts already allocated as well as those allocated to new experiments could perhaps be renormalised in view of the improved target yields referred to above and in the minutes of that meeting. H. Ravn and O. Tengblad have prepared an assessment on these lines, which suggests that such a course would be somewhat impractical for the already approved experiments. A flexible approach will therefore be adopted, with shift allocations for new experiments generally being decided in accordance with current yields, and the allocations for already approved experiments remaining unchanged.

d) In view of the proximity of the next Research Board meeting 24 November), it was decided that the matters arising from the present ISC meeting will not be reported to the Research Board until its next meeting in February 1994.