CERN. Geneva. ISOLDE and Neutron Time-of-Flight Experiments Committee

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1CERN/INTC 2002-031INTC-01315 October 2002ISOLDE AND NEUTRON TIME-OF-FLIGHTEXPERIMENTS COMMITTEEMinutes of the thirteenth meetingon September 23rd  2002OPEN SESSIONThe chairman, Hubert Flocard, opened the session by remarking that this year CERN has startedoperating under a shortened schedule put in place to cope with the budget problems. Despite thisconstraining environment, 2002 has witnessed major advances both for nTOF which has entereda phase of scientific production and for ISOLDE with the full start of REX-ISOLDE operation.He then mentioned that a position document on REX-ISOLDE status and operation is presentlybeing prepared by the REX-ISOLDE collaboration with a view to make this unique machine intoa facility available to a larger community of physicists.Mats Lindroos, the ISOLDE Technical coordinator, reported on ISOLDE operation. The moreintensive operation of the facility nicknamed Òpush-pull modeÓ has generally been successful.On the other hand it puts a major strain on the manpower. This year the number of Engineers-in-charge was just enough for the operation and made no allowance for unforeseen events.Moreover their participation in target tests and other development work has now become verydifficult. Then, Mats mentioned the break-down of a turbo pump on the GPS front-end, whichhas made necessary to operate with the only remaining pump. He also indicated that the level ofservices to users, especially for the alignment of experiments has been lowered due toretirements. Since no improvement is foreseen in the present conditions, he urged the users tocontact the persons in charge well ahead of any requested intervention. He continued byreporting on the consolidation programme and the development of an ECR ion source forISOLDE.The ISOLDE Scientific coordinator, Thomas Nilsson, described the status of the ISOLDEprogramme after 22 out of the 27 available weeks of operation. The push-pull mode operation,made possible by having both the GPS and the HRS operational, has led to an increase of thefacility efficiency which has partly compensated the reduction of beam time. As anticipated, thedisturbances for the experiments have increased. However, it has to be acknowledged that theuser community has generally well accepted them and shown considerable understanding andflexibility. The current number of radioactive beam shifts delivered to approved experiments,tests and developments is 295. He then presented several scientific results with an emphasis onREX-ISOLDE. The first series of experiments with REX-ISOLDE, partly using the MINIBALLGe-detector array, have globally been successful. Recently, the cooling, charge breeding andacceleration of a stable Cs-ions beam has been achieved. This success paves the way for theplanned delivery of post-accelerated beams of medium mass nuclei.2Paolo Cennini, nTOF Technical coordinator, briefly recounted the nTOF running in 2002. Theplanned measurements of neutron capture reactions have been completed beginning ofSeptember. Subsequently, the second collimator with a diameter of 8 cm has been installed topermit fission studies albeit with a two week delay with respect to the initial schedule. Presently,two detectors for fission measurements have been installed in the experimental hall. Finally,Paolo mentioned that the solution of the remaining question regarding the handling of futureradioactive targets is being looked for as part of the upgrading and use of the existinginfrastructure at ISOLDE.The nTOF scientific report was presented by P. Pavlopoulos, who showed a large amount of dataobtained during the validation and characterization of the facility within nTOF02. Thebackground, after the earlier reported shielding improvements, is now dominated by sample-related background and an in-beam gamma ray contamination. The neutron fluences at thesample position had been determined to be 8 104 n/cm2 and 1.6 105 n/cm2 per p-pulse with the 4cm and 8 cm collimator respectively. The partition of the beam-time in 2002 (using 7.0 1018protons) among the approved experiments was shown, as well as a preliminary outline for the2003 running.The following proposals were then presented:1. Coulomb excitation of neutron-rich A~140 nuclei; INTC 2002-015/P156; D.Habs.2. Coulomb excitation of neutron-rich nuclei between the N=40 and N=50 shell gaps usingREX-ISOLDE and the Ge Miniball array; INTC 2002-017/P158; P. Mayet.3. High Precision Mass Measurement of Exotic Nuclei with the triple-trap massspectrometer ISOLTRAP; INTC 2002-021/P160; K. Blaum.4. New spectroscopy by two-neutron-pickup of neutron-rich nuclei;INTC 2002-027/P161; D. Habs.CLOSED SESSIONPresent: P. Butler, P. Cennini*, E. Chiaveri*, C. Dtraz, J. -P. Duraud, H. Flocard (Chairman), M. Hauschild, H. -J. Kluge, K. -H. Langanke, M. Lewitowicz, K. -P. Lieb,  M. Lindroos, T. Nilsson (Secretary), E. Radermacher, H. Ravn, J. -P. Riunaud,  B. Rubio, W. Scobel, J. Suhonen, D. WarnerApologies: E. Migneco, D. Schinzel, J.A. Rubio* Part-time1. INTRODUCTIONThe Chairman opened the session by welcoming Peter Butler, the new ISOLDE Physics Groupleader. Due to an incomplete distribution of the minutes of the twelfth meeting to the members,their approval was deferred to the following meeting.E. Chiaveri presented an overview of the mandate and of the organizational structure of thefuture AB/ATB group responsible for nTOF technical matters and physics effort as well asISOLDE front-end and RILIS matters. In the following discussion, the following responsibilitieswithin the nTOF collaboration were confirmed:- E. Chiaveri, chairman of the nTOF Collaboration Board- P. Pavlopoulos, nTOF Collaboration spokesperson- A. Mengoni, Coordinator n_TOF-ND-ADS Project- P. Cennini, Technical coordinator (and GLIMOS from 2003)32. A DISCUSSION ON THE REPORTS AND PROPOSALS RELATED TO nTOFFOLLOWED:ISOLDE Technical and Scientific reportsThe committee noted with pleasure that so far the intensive push-pull mode operation had beensuccessful and that it was not unreasonable to expect the same number of shifts for physics thisyear as in 2001 in spite of the shorter running period. It congratulated the whole operation teamfor this demonstration of performance. However, INTC noted that the strain on the operationteam left almost no margin warranting the continuity of such an operation should any member ofthe team become temporarily unavailable. Thus, it recommended that, within CERN, measuresbe looked for to guarantee the same level of efficiency that has been achieved in 2002. It alsoencouraged the experimental groups to continue help the team accomplish the operation ashitherto done. Answering to a question whether target production was sufficient or not, M.Lindroos indicated that the limited resources have necessitated an operation in which alreadyused target units are called back for a more extensive reuse. C. Detraz commented on thisprocedure as an example of good management in a period of restriction. However, it was pointedout that in many cases, reusing old targets was liable to cause a loss of yield for the experimentscompared to operation with unused units. Moreover, it appears that the more intense operation ofISOLDE which can be anticipated in 2005 will require more target units than in the years before.A discussion of the REX-ISOLDE programme and in particular of its impact on ISOLDE wasthen started. The number of shifts already approved for both ISOLDE and REX-ISOLDE ispresently within control with respect to conditions required for an effective operation of thefacility in 2003. On the other hand, now that REX-ISOLDE has become operational, one cananticipate an increasing pressure, all the more so because experiments with the low intensitybeams delivered by REX-ISOLDE will on the average request larger number of shifts. For thisreason, INTC expressed its desire to be informed of the main lines of the strategy of thecollaboration as well as of expectations for the number of shifts deliverable by REX-ISOLDE.As a matter of fact, since constant evolution on both these points is to be expected, INTC feelsthat in order to accomplish its task efficiently, regular updating of this information will benecessary. As a conclusion of this discussion, INTC expressed its strong appreciation of theprogress of REX-ISOLDE and MINIBALL and congratulated the collaborations.nTOF Technical reportThe committee noted with pleasure that the facility is now operational. It also took note of themodification of the collimator allowing a wider beam diameter and that it was now possible tomodify the diameter of the collimator aperture with only a few hours deadtime.nTOF Scientific reportThe committee was satisfied with the preliminary information given on the facilityperformances and on the present status of the approved programme. It congratulated all personswhose action has made this successful operation possible. Although first indications ofperformance seem to be in line with expectations, a detailed comparison with the expectedperformances as described in previous nTOF documents is necessary. Thus, the importance of apresentation document given precise information on the facility and its performance wasreiterated independently of the final TDR which is expected for next year. It is the opinion of theINTC that the already obtained results are sufficient for the preparation of a presentationdocument. Thus, the committee demands that this document be made available by the first weekof November in order to be able to analyze it and discuss its content at the next INTC meeting. Itwas stated that such a document is necessary for the committee to be able to evaluate futureproposals.43. DISCUSSION ON THE OPEN SESSIONThe presentations of the new proposals made during the open meeting were then discussed.P156 (CERN/INTC 2002-015): Coulomb excitation of neutron-rich A~140 nucleiThe scientific motivation of this proposal is the exploration of the weakening of neutron pairingstrength in neutron-rich nuclei. It was considered timely and interesting. The connected issuesare presently actively debated by theorists and a further analysis of this mass region will provideuseful information on level densities of nuclei involved in the r-process. However, the largenumber of different beams requested was noted. The committee was concerned that spreadingthe activity over so many beams may delay or not allow an in-depth investigation of thephenomenon. Taking into account the situation of the competition, it was recommended that thecollaboration focuses its measurements on Cd-isotopes beams which are only available at REX-ISOLDE. An allocation of 21 shifts will be recommended to the Research Board.P158 (CERN/INTC 2002-017): Coulomb excitation of neutron-rich nuclei between theN=40 and N=50 shell gaps using REX-ISOLDE and the Ge Miniball arrayThe proponents envisage to probe the structure of neutron-rich nuclei between the N=40 andN=50 shell gaps by Coulomb excitation, using REX-ISOLDE and MINIBALL. The projectbegins with Zn beams, with which part of the goals can be reached with the existing REX-ISOLDE beams of 2.2 MeV/u although the planned 3.1 MeV/u would be more favourable.Later, an extension to Ni beams requiring the 3.1MeV energy is outlined. The committeesupported the physics case and the exploration of Coulomb excitation in a new region butrecommended that all efforts be made to perform the experiment with the optimal, higherenergy. 21 shifts will be recommended for approval to the Research Board.P160 (CERN/INTC 2002-021): High Precision Mass Measurement of Exotic Nucleiwith the triple-trap mass spectrometer ISOLTRAPThis proposal contains a broad programme of mass measurements, motivated by nuclearstructure issues, CVC tests and halo nuclei, to be performed over the coming four years. Thecommittee recognized the world unique potential of ISOLTRAP and considered that theprogramme would indeed allow an exploitation of this potential. It also noted that the flexibilityof ISOLTRAP operation would help optimise ISOLDE beam scheduling. On the other hand,INTC felt that it could not approve a program over such a long period and requested that a nolonger than two-year programme be resubmitted. Moreover, INTC opinion is that clear prioritieswithin the list of measurements should be set by the collaboration. For these reasons, thecommittee deferred a full evaluation of the proposal and expects the collaboration to react on itsrequests.P161 (CERN/INTC 2002-027): New spectroscopy by two-neutron-pickup ofneutron-rich nucleiTwo-neutron transfer reactions on 10Be-targets were acknowledged by INTC as a very powerfulmethod to populate states in very neutron-rich nuclei while preserving the shape of the projectilenucleus. As a first application, the proposed measurements the spherical excited 0+ state in 32Mgwas considered appropriate. However, the committee felt that the presented status of cross-section calculations was not accurate enough to take a decision on number of shifts. INTC thusrecommend that they be pursued to the point when they can provide an accurate estimate of theneeded beam time. This could take the form of a letter to the committee. Pending the receptionof this letter the decision was deferred.5I-044 (CERN/INTC 2002-028): Study of the decrease of neutron pairing with neutronnumber by measuring the transfer of paired neutronsThis Letter-of-intent had a similar physics scope as that of P156 but involved the use of two-neutron transfer reactions which might deliver further, conclusive information on weakening ofneutron pairing in neutron-rich nuclei. The committee found the project interesting and awaits afull proposal.4. OTHER BUSINESSThe SPS/PS Coordinator, Michael Hauschild, reported on the proton beam availability for nTOFand ISOLDE. September 17, the status was that nTOF had received 5.91 1018 protons and theestimated total amount by the end of the running period was 7.5 1018, thus in slight excess overthe number initially planned. For 2003, the envisaged amount of protons for nTOF could reach12-14 1018. This increase is correlated with the cessation of data taking by the DIRACexperiment. Protons for ISOLDE Physics are planned for 181 days in 2003 compared to 192 in2002.The chairman informed the committee that Juha yst, Jyvskyl, will take over thechairmanship from the start of 2003.The next meeting is on Monday November 25, and the deadline for submission of proposals isFriday, October 18, 2002.The dates of the INTC meetings in 2003 are:24-25 February19-20 May22-23 September24-25 NovemberThomas NilssonTel.: 73809 Ð 75828 (Mobile 160985)Thomas.Nilsson@cern.ch

Minutes of the thirteenth meeting on September 23rd 2002

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