[Triumf-seminars] TRIUMF Special Seminar today at 14:00

[TRIUMF Seminars]

Date/Time: Thu 2012-07-26 at 14:00

Location:  Auditorium          

Speaker:   Maxime Brodeur (National Superconducting Cyclotron Laboratory)

Title:     Mass measurements and surfing of the shortest-lived nuclei

Abstract: Over the past two decades, the high-precision direct mass measurements of short-lived nuclei have provided valuable information on a wide range of topics, including the neutron halo structure in very exotic nuclei. In some of the most neutron-rich systems, the last neutrons are extremely weakly bound resulting in their wavefunction extending far outside the nuclear core forming a so-called halo. The motion, size and deformation of the halo nuclei core is described by their charge radius, while the extent of the diffuse region, is linked to the neutron separation energy of their valence neutrons. Recent advances in laser spectroscopy and high-precision atomic physics calculations have allowed a precise, model-independent determination of the charge radius, with the remaining source of uncertainty steaming from the atomic mass value. We will present the first direct mass measurements of the halo nuclei 6,8He using the TITAN Penning trap. Using the precise charge radii and binding energies obtained from the new masses, we provide a test of various ab-initio nuclear theories, giving insight on the interactions at play in the nucleus.

While the ISAC facility offers the highest yields of a wide range of isotopes, including light short-lived halo nuclei, it is limited to non-refractory elements. High-precision mass measurements can be performed on refractory elements at fragmentation facilities, but the addition of a gas cell to thermalize the energetic beams is necessary. The ion transport in these gas-filled chambers is conventionally done using an electrostatic gradient applied on a set of electrodes. The steepness of this gradient, which defines the transport velocity, is breakdown-voltage limited. This restriction can be removed by replacing the potential gradient with a travelling wave, allowing the delivery of shorter-lived nuclei. Results from recent extensive studies of this so-called “ion surfing” transport method will be presented together with its implementation in a proposed gas cell that would thermalize transfers-reaction recoils in ISACII for delivery to a new high-precision mass spectrometer, extending the reach of TRIUMF’s successful scientific program based on mass measurements.

Stimulants available 15 minutes before the talk.

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