Volume 8, No. 2 August 2000

So far, the intensity of proton beams (E > 20 MeV) has been limited to about 20 mA due to beam losses at extraction. As was reported in an earlier Newsletter, we have a project of negative hydrogen acceleration with stripping extraction. On Friday evening, August 25 we extracted the first H^- beam by stripping. The measured proton intensity was 13 mA and the intensity of the dc-beam from the ion source at the center of the cyclotron was 110 mA, out of which 13 mA was accelerated to the stripper radius, i.e. we managed to achieve 100 % extraction efficiency as expected.

The intensity of the injected H^- beam can be increased at least to 1 mA and hence the goal of 100 mA proton beam can be achieved. The multi-cusp ion source has produced 3.8 mA of H^- beam at 5.8 kV extraction voltage. Routinely, an intensity of 2 mA can be achieved.

The high intensity proton beams from H- acceleration will be used for isotope production once a week and also the proton beam intensities for IGISOL will be increased from the current ones
 

Figure 1: A 20 degree dipole has been installed at the extraction of the cyclotron vacuum tank to bend the  stripped H- (=p) beam to the existing beam line	Figure 2: Stripper arm inside the vacuum  chamber. The foil is not installed

The first results with the new JYFL 14 GHz ECR ion source

A new 14 GHz ECR ion source has been built for the Accelerator Laboratory. This source belongs to the family of the LBNL AECR-U based ECR ion sources. The operation during the first four months has shown that the new ion source is performing well and is capable of producing intensive highly charged ion beams. For example 145 µA of O⁷⁺ ion beam was recorded. The productions of iron and boron ion beams were tested using the MIVOC method. The intensity of the ⁵⁶Fe¹¹⁺ ion beam achieved a value of 115 µA. The intensities of ¹¹B³⁺ and ¹¹B⁵⁺ ion beams were 235 µA and 52 µA, respectively. As far as we know, the iron beam intensity is the second highest and the boron beam intensities are the highest ever produced by an ECR ion source.

Table 1 is a collection of the best ion beam intensities obtained. In all the tests an extraction voltage of 10 kV and a biased Faraday cup were used.

Figure 3: The new 14 GHz ECR ion source is fully installed and has been in normal use

Another JUROSPHERE campaign comes to a close

On the 21^st August our third campaign of JUROSPHERE gamma-ray spectroscopy experiments came to an end. A total of 80 days of beam-time were dedicated to 11 experiments in the period from February to August.

The series of experiments involved 40 visitors from overseas institutions from as far afield as Australia.

The development of the RITU focal plane detector system, documented in the 1999 Annual Report [1], has allowed the use of more symmetric reactions. In an experiment led by the University of Bonn group, the ⁹⁰Zr(⁸⁶Kr, 2n)¹⁷⁴Os reaction was employed. The MWPC at the focal plane was used to provide the recoil trigger, and to discriminate recoil events from scattered beam events. Further improvement for future experiments using this type of symmetric reaction will come from the reconstruction of the RITU dipole chamber, to take place later this year.

Another highlight from the campaign was the first observation of excited states in the extremely neutron-deficient nucleus ¹⁹⁰Po, with a production cross section of approximately 200 nb. The experiment was led by Andrei Andreyev of the University of Leuven group. In the preliminary analysis, excited states up to I^p=8⁺ were observed. The systematic lowering of the 8⁺ and 6⁺ states suggests the onset of prolate deformation, as observed at the same neutron number in the Pb isotopes [2].

The JUROSPHERE array has now been replaced by the SACRED conversion electron spectrometer. SACRED consists of a 25-element annular detector upstream of the target, used for electron and electron-electron coincidence measurements. Recoil-gating and recoil-decay tagging techniques will be used to further enhance the sensitivity of the device. Further information and the current status of the SACRED commissioning can be found in the "In-beam spectroscopy" section of our internet pages.

1. H. Kettunen, JYFL Annual Report, 1999.
2. A. N. Andreyev, To be published.

Figure 4: The JUROSPHERE II Ge array at the target position of RITU

The next deadline for submission of proposals and letters of intent is September 15, 2000. Proposals should include a justification of the beam time requested, based on cross-sections, detector efficiencies, etc. If a proposal is the continuation of an existing experimental program at the JYFL Accelerator Laboratory, a summary of the status of the project should be included. Proposals and letters of intent should be sent (preferably as a postscript file) to the Program Advisory Committee secretary Peter Dendooven (address: see below) and include the Proposal Summary Sheet mailed with this Newsletter. This form is also available from the JYFL WWW-pages. You are encouraged to contact anyone in the Contact List at the end of this Newsletter for more information.

Under the Enhancing Access to Research Infrastructures (ARI) action of the E.U.'s Human Potential Programme,, experiments approved by the JYFL Programme Advisory Committee are eligible for a financial contribution (partly) covering the travel and living expenses during the experiment. This contribution can be allocated to scientists from member or associate EU, excluding those from Finnish laboratories. One-page applications for this financial support should mention the approved experiment and include the names, nationalities and affiliations of the applicants as well as an estimate of the financial needs. They should be sent to the Program Advisory Committee secretary Peter Dendooven (address: see below). The applications are refereed by a subcommittee of the JYFL PAC.

Publications resulting from research supported by this program should include the following acknowledgement: