ISOLDE AND NEUTRON TIME-OF-FLIGHT
Minutes of the twelfth meeting
on May 13th 2002
The ISOLDE scientific coordinator, Thomas Nilsson, briefly recounted the experiments performed so far at the ISOLDE facility. Both the HRS and the GPS separator had been used for several physics runs since the start-up on April 18th, indicating that the GPS was now fully back in operation after the problems related to the front-end in 2001. An ongoing combined commissioning and first physics run involving REX-ISOLDE and the full first phase of the MINIBALL Ge-detector array was highlighted. The updated schedule for ISOLDE was then presented, covering the full operational period of 2002.
Mats Lindroos, ISOLDE technical coordinator, reported on the concluded shutdown work at ISOLDE. He took the opportunity to thank Erich Kugler, soon retiring, for having coordinated these works successfully for many years and having made major contributions to the facility. During the shutdown, major consolidation work had been performed on the power supplies, control system and the target handling robots. Furthermore, the new GPS front-end had been made operational.
Paolo Cennini, the nTOF technical coordinator, summarized the execution of the additional shielding as presented in the eleventh meeting. This was expected to diminish the background originating from muons by an additional factor ~10, rendering this effect secondary with respect to other sources of background. The planned exchange of the second collimator at 174 m from 1.8 cm diameter to 8 cm for fission measurements was discussed; the time estimated for such an exchange was one week and could be done during the 2002 running period. C. Detraz underlined that, due to the additional shielding and earlier measures taken, the background had now been reduced by more than two orders of magnitude, and reiterated the need for a reference document defining the nTOF capabilities as mentioned in the eleventh meeting.
The beam-time planning for nTOF in 2002 was presented by Alberto Mengoni.
The planning had been based on the availability of 7 1018
protons during the operational year and comprised of nTOF-02, nTOF-03 partly),
P142, a fraction of the programme of P154 232Th) and of P145,
the latter after changing the second collimator. The execution of nTOF-04
and the part concerning Mg-isotopes of nTOF-03 had been postponed. The
planned number of protons for capture experiments had been adjusted for
the exchange of the C6D6
detectors for units that are more efficient.
The following proposals were then presented:
1. Neutron Cross Sections for the Pb Isotopes
Implications for ADS and Nucleosynthesis; INTC 2001-020/P142;
2. Measurement of the neutron capture cross
sections of 232Th,
231Pa, 234U and 236U;
3. An Energy Upgrade of REX-Isolde to 3.1 MeV/u
and Acceleration of Heavier Masses up to A=150;
INTC2002-009/P152; D. Habs - O. Kester. subdivided into a presentation on the Scientific Case for increased
REX-ISOLDE energies by D. Habs and the Technical Case by O. Kester.
4. Laser spectroscopy study on the neutron-rich
and neutron-deficient Te isotopes; INTC 2002-011/P153;
The Chairman opened the session by welcoming Marek Lewitowicz, GANIL,
as a new member of the committee. He then informed the committee that his
mandate as a Chairman had been prolonged by six months, until the end of
the year. The minutes of the eleventh meeting were approved without changes.
2. A DISCUSSION ON THE REPORTS AND PROPOSALS RELATED TO nTOF FOLLOWED:
nTOF Technical report
P142 CERN/INTC 2001-020): Neutron Cross Sections for the Pb Isotopes Implications for ADS and Nucleosynthesis
P154 CERN/INTC 2002-013) Measurement of the neutron capture cross sections of 232Th, 231Pa, 234U and 236U
P145 CERN/INTC 2001-025): Measurements of Fission Cross Sections for the Isotopes relevant to the Thorium Fuel Cycle
nTOF beam planning
3. A DISCUSSION ON ISOLDE MATTERS FOLLOWED:
ISOLDE Technical and Scientific report
P152 CERN/INTC 2002-009) An Energy Upgrade of REX-Isolde to 3.1 MeV/u and Acceleration of Heavier Masses up to A=150
P153 CERN/INTC 2002-011) Laser spectroscopy study on the neutron-rich and neutron-deficient Te isotopes
The committee raised some questions regarding the urgency of the proposed
measurements and expressed its wish for a clarification of some points
discussed in the scientific case. On the other hand, the value of having
solid numbers for the ground state properties of exotic Te-isotopes was
readily acknowledged. In conclusion, while the overall scientific background
was considered in a globally positive way, the committee decided to defer
a decision on the beam time and to reconsider the experiment once the proponents
have shown the feasibility of the source with off-line tests and have clarified
some of the scientific aspects.
P155 CERN/INTC 2002-014): Fusion Reactions at the Coulomb Barrier with Neutron-rich Mg Isotopes
The scientific questions addressed by the proponents were seen as highly
interesting, but the committee expressed concerns regarding the implications
of deducing the fusion cross-sections indirectly instead of by direct measurements.
This is a consequence of the time structure of the RIB extracted from the
REXEBIS. The proponents were urged to calibrate the method by either known
stable beams or a direct measurement with stable 26Mg,
if possible using REX-ISOLDE in an off-line mode, before proceeding to
radioactive species. The requested allocation of 9 radioactive shifts for
will be recommended to the Research Board.
P159 CERN/INTC 2002-020): Evolution of single particle and collective properties in the neutron-rich Mg isotopes
This proposal on heavy Mg-isotopes was considered to have a strong physics
case, attracting a considerable theoretical interest. Although theories
agree on deviation from the shell model in this region, details differ
and the proposed measurements could clarify the experimental situation.
Being within the original scope of the REX-ISOLDE project, the proposed
experiment is well-adapted to the present facility and the requested 21
shifts will be recommended to the Research Board.
I-041 CERN/INTC 2002-012): Determination of 44Arn,g)45Ar and 46Arn,g)47Ar reaction rates by d,p) transfer reactions
The scientific goals were positively appreciated by the committee, which
recommended that tests and developments are pursued with the aim of accelerating
beams of noble gases in REX-ISOLDE and urged the proponents to actively
take part in this process. In view of the second step of the planned REX-ISOLDE
energy upgrade, reaching 4.3 MeV/u, the proponents were asked to consider
whether this energy would be more favourable than the 3.1 MeV/u mentioned
in the LoI.
I-042 CERN/INTC 2002-019) Post acceleration of rare earth isotope beams for radiotracer DLTS on SiC
Due to the unexpected absence of the two INTC members having expertise
within Solid State Physics, the physics case of this LoI could not be properly
evaluated. The evaluation was thus postponed. The Chairman will request
a written report from these two members. Depending on their answers, a
decision could be reached before next INTC meeting.
I-043 CERN/INTC 2002-016) A study of the r-process Nuclides 137,138,139Sb using the enhanced Selectivity of RILIS
The proposed measurements on the heavy Sb-nuclei were judged interesting
both from the point of view of nuclear structure and astrophysics. Consequently,
the committee expressed its support for the needed beam developments.
Solid State Physics Audit
4. OTHER BUSINESS
The Chairman raised the issue of a better workload distribution between the INTC meetings and the need for evaluation time of old decisions. To achieve this, changes in the meeting structure were considered.
The next meeting is on Monday September 23, and the deadline for submission of proposals is Friday, August 16, 2002.
The dates of the remaining INTC meeting in 2002 are: