Liquid ortho-deuterium as a converter for ultra-cold neutrons

Theoretical calculations of UCN gain factors of liquid ortho- and para-deuterium are performed, taking into account the effects of intermolecular interferences and liquid dynamics in deuterium. Calculated results of UCN production and total cross-sections give very different values from those based on the gas model. The calculation gives a UCN gain factor of 100 for a liquid ortho-deuterium converter if used in combination with a Maxwellian neutron spectrum of 50K. An experiment to measure the UCN gain factor of liquid ortho-deuterium at 20K was carried out. The experimental gain factor is about 3 times larger than the value calculated on the basis of the gas model and in good agreement with the result of the present calculation. (author)