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Physical Sciences and Engineering

Helical Orbit Spectrometer

The Helical Orbit Spectrometer (HELIOS) is a charged-particle spectrometer designed to study reactions with radioactive ion beams.

HELIOS offers excellent resolution, solid-angle acceptance and versatility, allowing its use in a broad range of experiments for nuclear structure determinations and nuclear astrophysics.

HELIOS is ideally suited to the study of single- and multi-nucleon transfer reactions in the inverse kinematics regime. Such an approach is necessary for nuclear structure studies with radioactive-ion beams, such as those from CARIBU and RAISOR.

The concept is based on a superconducting solenoidal spectrometer with uniform axial field. The target and detector are both on the solenoid axis in the field with the reaction products bent back to the axis. The target-to-detector distance and the energy of the particles translate to give the desired information of excitation energy and center-of-mass angle, both key properties for revealing nuclear structure information.

    The device consists of a 0.9m bore, and 2.35m long 2.85-T superconducting solenoid (repurposed MRI magnet). Following a very successful implementation at ATLAS, other similar devices been developed such as the ISOLDE Solenoidal Spectrometer (ISS) at the ISOLDE facility at CERN and plans are underway for establishing one at the future FRIB facility, called SOLARIS.

      The HELIOS instrument has a number of attractive features:

      • Greatly improved effective resolution over conventional techniques
      • Large solid angle
      • Compact detectors and electronics
      • Easy particle identification based on the cyclotron period

      HELIOS is well suited to experiments that probe the structure of the exotic nuclei that are currently of high interest:

      • Single-nucleon transfer reactions
      • Pair/cluster transfer
      • Inelastic scattering

      Alan Wuosmaa (UConn)