Measurement of the para-hydrogen concentration in the ISIS moderators using neutron transmission and thermal conductivity

作者：Romanelli Giovanni^*; Rudic Svemir; Zanetti Matteo; Andreani Carla; Fernandez Alonso Felix; Gorini Giuseppe; Krzystyniak Maciej; Skoro Goran

来源：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment , 2018, 888: 88-95.

DOI：10.1016/j.nima.2018.01.039

• Neutron transmission
• Neutron cross sections
• Hydrogen thermal conductivity
• Para hydrogen
• Neutron moderators

We present an experimental study to determine the para-hydrogen concentration in the hydrogen moderators at the ISIS pulsed neutron and muon source. The experimental characterisation is based on neutron transmission experiments performed on the VESUVIO spectrometer, and thermal conductivity measurements using the TOSCA para-hydrogen rig. A reliable estimation of the level of para-hydrogen concentration in the hydrogen moderators is of crucial importance in the framework of a current project to completely refurbish the first target station at ISIS. Moreover, we report a new measurement of the total neutron cross section for normal hydrogen at 15 K on the broad energy range 3 meV -10 eV suggesting a revision of the most recent nuclear libraries for incident neutron energies lower than 10 meV. Finally, we characterise systematic errors affecting the para-hydrogen level estimation due to conversion from para to ortho hydrogen, as a function of the time a batch of gas spends in every component of our gas panel and apparatus.

• 出版日期2018-4-21