Efforts towards a dynamically polarised HD-target☆

Abstract The molecular hydrogen isotopes contain no unpolarisable background. From this point of view they appear to be the material of choice for a polarised bulk target in scattering experiments. The fast nuclear relaxation of H 2 and D 2 is one reason that these substances are not highly polarisable. This fact brings hydrogendeuteride (HD) into focus. In Bochum a device to freeze out gases into the consisting 4 He -cryostat has been built up. The principle of the Dynamic Nuclear Polarisation requires a sufficient amount of paramagnetic electrons. These have been produced by cracking HD molecules at 1 K using a 90 Sr β -source with an activity of 3.7 GBq . Six days of effective irradiation resulted in a density of paramagnetic centres in the order of 10 18 spins/cm 3 . This could be estimated from bolometric electron paramagnetic resonance (EPR) measurements. Dynamic polarisation could not be achieved. This is accounted to isotopic impurities in the used HD, which accelerate the nuclear relaxation. The constant of ortho–para conversion in H 2 could be confirmed to be 1.9%/h.