The properties of a good target material are:
high ratio of free polarizable nucleons and to the total amount of nucleons (e.g. Butanol: 0.135)
high polarization degree (90%)
short polarization build up time (1 hour)
long relaxation time (several days)
good polarization resistance against radiation damage
simple handling and preparation of the target
For the dynamic nuclear polarization the materials have to be doped with free radicals. Two different ways are usual:
chemical doping (mixing with free radicals like TEMPO, Porphyrexid or Cr-V complexes)
irradiation in an intensive electron beam
Important target materials are Butanol, Ammonia, Li-Hydrides and their deuterated counterparts. A very interesting material is HD, because of the maximal content of polarizable nucleon.
The 6LiD although also is a very promising material: The larmor frequency is very close to that of the deuteron, so it is obvious that the 6Li is a compound of an alpha and a deuteron.
In the following pictures different
target materials are shown: Butanol is chemically doped , Ammonia and
Li-Hydrides are doped in an intensive electron beam at the Bonn