Dear all,
This is an announcement of the Spin-Isospin Seminar;
Date: Nov. 19, 2012
Time: 15:00 -
Place: Nishina hall
Lecturer: Dr. Patrick Hautle (Paul Scherrer Institut, senior researcher)
Title: Dynamic Nuclear Polarization - from Polarized Targets to Metabolic
Imaging.
Abstract:
Dynamic nuclear polarization (DNP) is a most powerful tool to obtain high
nuclear spin polarization. Originally used to build polarized targets to
study the role of spin in nuclear and particle interactions, it has also
opened new possibilities in neutron science by exploiting the strong spin
dependence of the neutron scattering on protons. Its potential to achieve
strong signal enhancement has now become a driving force in different fields
of magnetic resonance. The huge increase in contrast obtained in magnetic
resonance imaging (MRI) has recently opened the way to clinical
applications. In a first part the talk will overview applications of
classical methods of DNP in the different fields. The classical DNP schemes
are applied to solid samples that contain spatially immobile electron spins
in addition to the nuclear spins of interest and have the clear disadvantage
that they require temperatures of 1 K or lower and fields of several tesla.
The second part presents very recent work on a promising DNP method that
relieves this drawback. It uses short-lived photo-excited triplet states and
requires neither low temperatures nor high fields. This is immediately
attractive in view of applications as technically simpler systems with open
geometries become feasible. A proven system for this method is naphthalene
doped with pentacene in which high proton spin polarizations can be
obtained. Recently we have demonstrated that the triplet method can be used
to build a reliably working spin filter for neutrons operating at 0.3 T at a
temperature of 100K. So far all triplet DNP experiments in naphthalene
crystals have been performed with pentacene-h14. We found that triplet DNP
using fully deuterated pentacene-d14 is at least as efficient to polarize
the proton spins in the host naphthalene crystal. In a field of 0.3 T a
proton polarization of 0.50 has been achieved. As technique for DNP the
integrated solid effect (ISE) scheme was employed to transfer the large
electron polarization of the triplet states directly to the proton spins on
naphthalene.