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Accueil > Groupes de recherche > Structure du noyau > GABRIELA > Campaigns


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2004 Campaign

In the spring and summer of 2004, GABRIELA was commissionned. The characteristics of the setup and the results of the comissioning runs are described in the article by K. Hauschild, A. Yeremin et al., published in Nucl. Instr. and Meth. Phys. Res. A 560 (2006) 38.

In the fall of 2004, the nuclei 253,254,255No, 255Lr and 227Np were studied with GABRIELA. A new excited state was observed in 249Fm and internal conversion coefficients extracted for the observed transitions. The N=151 systematics of the low-lying isomeric 5/2+ state was extended to 251Fm and 253No. High K isomeric states were observed in 253No and 255Lr. The analysis of the excited states populated in the alpha decay of 255No is still ongoing.

2005 Campaign

In 2005, a radioactive 210Pb target was used. The aim was to produce 257No via the 5-neutron evaporation channel and study its alpha-decay to 253Fm. Unfortunately, no events were observed due to lack of target material.

The experimental setup was modified in the spring-summer of 2006: the 37 degree magnet was removed and the original 8 degree magnet put back in its place. The ToF detector is now more compact and the secondary-electron-emitting foils thinner in order to reduce the energy losses of the recoils produced in light ion induced reactions. The efficiency of the Germanium array was increased by nearly a factor of 2 by reducing the distance between the Germanium crystal and the front face of the Aluminium end cap of the detector closest to the implantation detector.

2006 Campaign

The characteristics of the new setup were measured during a test run in mid-September 2006. 22Ne induced reactions products (from Au, Pb, W and Pt targets) were transported to the focal plane of Vassilissa. The background conditions were considerably improved and the transmission/detection efficiency was measured to be 6% (3 times higher than with the old setup!).

The actual 2006 campaign started with a test-run with 238U targets. Initially, we ran with the standard ToF set-up (2 emissive foils) and no 255No alpha-decays were seen at the focal plane of VASSILISSA. Extensive tests have shown that even with a vacuum separator, one can only work with 1 ToF foil due to the important angular straggling of 255No recoils produced in asymmetric fusion-evaporation reactions induced by light projectiles. Finally, 1500 255No alpha-decays could be observed at the focal plane of VASSILISSA and the transmission and detection efficiency of No recoils was estimated to be of the order of 1%. Unfortunately, problems with the fabrication of the 242Pu targets did not allow us to perform the scheduled 3-week experiment to study the decay properties of 259Rf.

2008 Campaign

During February/March 2008 we performed our 4th one-month long campaign. Our initial plan was to study 259Rf following the bombardment of a 242Pu target with a 22Ne beam. In order to achieve this goal the emissive foils used in the time-of-flight measurement were reduced to 15 μg/cm2. Tests were performed using 22Ne+197Au and a transmission of over 6% was achieved. The next incremental step was to tune the separator parameters using the 22Ne+238U reaction since it has approximately 40 times the cross-section of 22Ne+242Pu. Surprisingly we were unable to detect 255No alpha decay at the focal plane, even though we had managed to do this in the 2006 campaign. We have therefore abandoned the program of light beams on actinide targets until the upgrade of VASSILISSA has been completed. Changing to a 40Ar beam we then studied the decay properties of 245,246Fm, obtained complementary statistics for the decay of 217Pa and, in preparation for isomeric studies in 218U, searched for isomers in 214Th.

2009 Campaign

We had envisaged to study 256,257Rf but problems with the beam preparation forced us to revert to the detailed study of the isomeric- and alpha-decay properties of 253No using a 48Ca beam. The focal plane detector and its electronics have been modified and successfully tested for the first time during this campaign (Feb-March 2009). The detector is now a 48x48-strip DSSD equipped with 3 pre-amplification ranges, which allows it to be sensitive to low-energy electrons (100 keV) as well as high-energy fission events (∼ a few hundreds of MeV). The transmission of VASSILISSA was also much improved but we suffered from many quadrupole power supply brake downs during the 5 week irradiation time. During the campaign, it was attempted to investigate beta-delayed fission of 196At produced in the reaction 40Ca + 159Tb. This was abandonned because of the power supply problems. Finally, the last days of the campaign were dedicated to collect more statistics on light Np isotopes produced with a Ta target. This run was ended abruptly when the high voltage of one of the electrostatic dipoles failed.

2013 Campaign

The modernized recoil separator SHELS (Separator for Heavy Element Spectroscopy) was commissioned in the first 2 weeks of may 2013. Transmission measurements and separator tuning were carried out with an alpha-particle source at the target position but also with a 22Ne beam on a 198Pt target. An increase in acceptance as compared to the previously standing VASSILISSA separator was measured with the alpha source and transmission efficiencies up to 3.5% were measured in beam (the size of the focal plane detector was 60x60 mm2).

2014 Campaign

The commissioning of the newly installed recoil separator SHELS continued in 2014 with evaporation residue transmission tests performed with 22Ne, 40Ar and 50Ti beams. The new, large area (10x10cm2), highly pixelated (128x128 strips) DSSD was used for the first time. At least a factor of two increase in transmission has been realised experimentally.

2015 Campaign

In may, a commissioning experiment was performed to re-measure the transmission of SHELS in the case of asymmetric reactions with a 22Ne beam and the large area implantation detector. It was concluded that some modifications have to be made to the electrostatic dipole plates to reach better transmission. New plates are being made.

2016 Campaign

Experiments with a 48Ca beam were carried out in January to continue investigating the different optical regimes of SHELS as well as to test the efficiency of the new CLODETTE clover detector.

In spring and autumn 2016, the first experiment with the full new GABRIELA detection system was performed. 259Db compound nuclei were produced with a metallic Bi target and an intense 50Ti beam at 3 different energies.

2017 Campaign

In may 2017, a 50Ti beam was used to produce excited nuclei of 255Rf with a 207Pb target. The experiment was continued in the autumn with a longer ToF distance, a BGO marker instead of VETO and a more intense 50Ti beam. Another run dedicated to the production of the compound nucleus 259Db was carried out at the end of the year at 3 different beam energies and with a highly enriched Bi target.

2018 Campaign

In January, a test with a 22Ne beam and one of the new electric deflectors of SHELS was performed. The ToF detector system was modified in such a way as to maximise the transparency to evaporation residues. 214,215Ra as well as 255No residues were identified at the focal plane. Some issues with the DAQ system related to high event rates were also solved. The second deflector should be tested in the autumn. 50Ti was then accelerated to produce 256,257Rf nuclei via the reaction 50Ti(208Pb,1-2n).

In the Spring of 2018, 254Rf was produced via the reaction 50Ti(206Pb,2n). Fast fission from the ground state as well as from isomeric states was observed.

In September 2018, the second set of deflector plates was commissioned with a 22Ne beam and 198Pt, 208Pb and 236U targets. No Ge detectors were used for the test. Transmission efficiencies of SHELS were measured for 213-215Ra evaporation residues as well as for 253No residue.

In November 2018, more data on 256Rf was collected. Problems with the DSSD back-side electronics were solved. Issues with the 50Ti beam intensity at the ion source resulted in a maximum of 250 pnA on target.

2019 Campaign

In January 2019, 254,252,250No were studied with a 48Ca beam and high purity Pb targets. The aim was to study the electromagnetic and fission branches of the known K isomers in these nuclei. Problems with the 48Ca beam intensity have resulted in a limited statistics for certain nuclei.
In April, the 238U(22Ne,xn)260-xNo reaction was used to produce No nuclei. 256No was successfully transported to the focal plane of SHELS.A transmission & detection efficiency of 6% was deduced for these very slow ions synthesized in asymmetric fusion evaporation reactions.