Solid oxygen as converter for the production of ultra-cold neutrons

Abstract

We have investigated solid oxygen as a converter material for the production of ultra-cold neutrons. In a first series of experiments the crystal preparation was examined. An optically semi-transparent solid alpha-oxygen crystal has been prepared. In a second series of experiments this crystal has been exposed to the cold neutron flux of the MEPHISTO beam line of the FRM II. Ultra-cold neutrons produced inside the oxygen crystal have been extracted and the count rates have been measured at different converter temperatures. The results of these measurements give a clear signal of the superthermal production mechanism due to antiferromagnetic lattice excitations in alpha-oxygen. The mean free loss length of UCN inside the crystal was determined to be approximately 30cm.