Study on the Pulse Shape of Thermal and Cold Neutrons Provided by the Decoupled Moderator of JSNS

Japanese Spallation Neutron Source (JSNS) of MLF at J-PARC has launched successfully on May 30, 2008, and now provides pulsed neutrons in stable condition at 0.3 MW proton beam power. Among three moderators in JSNS, a decoupled moderator has been studied extensively by the instrument NOBORU. Most important feature of the moderator is short tail of the pulse shape realized by a silver-indium-cadmium (AIC) decoupler which has a neutron decoupling energy, Ed, up to 1 eV [1]. Two dimensionally aligned crystal, Muscovite (KAl2AlSi3O10(OH)2), was used to measure pulse shape of cold neutrons, where as single crystal diamond to measure pulse shape up to several hundreds meV. Figure 1 shows profiles of the muscovite and background in log-log scale. The results showed good agreement with the expected pulse shape calculated using a Monte Carlo simulation. In this presentation, we will show the evaluation of the pulsed structure in detail.