Department of Physics

The JUROSPHERE campaigns

Recoil-Decay-Tagging experiments at JYFL.

Introduction.

During the past few years there has been tremendous success in recoil-decay tagging (RDT) studies at the University of Jyväskylä. This started with the first JUROSPHERE array in 1997 and continued with the SARI array in 1998, through JUROSPHERE II and III in 1999 and 2000 respectively and ending with JUROSPHERE IV in 2001. All of these campaigns involved an array of germanium detectors coupled to the gas-filled recoil separator RITU.


Fig. 1: The JUROSPHERE Ge array at the target position of RITU.

The Recoil-Decay Tagging (RDT) Technique.

As our knowledge of the nuclear chart is extended to more neutron-deficient nuclei, the fusion-evaporation cross-sections these nuclei are greatly reduced. Since the cross-sections for competing reaction processes, such as fusion-fission, may be more than an order of magnitude larger, it becomes increasingly difficult to extract the gamma rays of interest from the high background produced by the competing processes. Fortunately, many of the neutron-deficient nuclei above 100Sn decay by emitting charged particles (alpha particles, beta-delayed protons and direct protons) from their ground states. Observation of these characteristic decay products gives a signature that a certain nuclear species has been produced, and correlation with the recoils associated with a given decay allows extraction of the gamma rays of interest. This technique is known as recoil-decay tagging.

Fig. 2: Schematic showing RDT apparatus and technique.

Prompt gamma rays produced at the target are collected by the JUROSPHERE germanium array, in coincidence with fusion-evaporation products implanted into the RITU focal plane Si-strip detector. Correlation of the implanted nuclear species to its subsequent decay allows extraction of the coincident gamma rays of interest.

Highlights of the Campaigns.

  • First observation of excited states in 160,161W.

  • Excited states in 164,165,166,167,168Os observed for the first time.

  • First observation of excited states in 168,170,171,172Pt.
  • 182,184Pb excited states observed for the first time beyond the mid shell in the Pb isotopes.
  • First observations of the extremely neutron deficient nucleus 190Po with a production cross section of approximately 200 nb.
  • Excited states in 198Rn identifed for the first time.
  • 206,208Ra levels identified for the first time.

  • First observation of excited states in 250Fm.
  • First observation of excited states in 252No.

  • Fig. 3: Detailed section of chart of the nuclides where nuclei with excited states identified for the first time using the JUROSPHERE campaigns have been highlighted in red.

    Other Information.

    Lists of experiments performed during each campaign with basic information.

    JUROSPHERE I
    JUROSPHERE II
    JUROSPHERE III
    JUROSPHERE IV

    Please direct any comments or queries to Alex Keenan