Fig. 3-4 Two-dimensional plots of beam profile measured with imaging plate technique for 24 GeV proton incidence Beam profiles for 1.5 GeV and 7 GeV proton incidence were also measured. The total number of incident protons was measured by the activation reaction of Cu(p,x)24Na. The resultant total number of incident protons was estimated as (6.61 0.74) x 1013, (3.57 0.40) x 1013 and (1.84 0.21) x 1013 for 1.5 GeV, 7 GeV and 24 GeV proton incidence, respectively.

Fig. 3-5 Cross section view of the mercury target Proton beam from the AGS comes from the left hand side of the mercury target in the figure. Reaction rates in the mercury target are measured by using various activation foil detectors with different threshold neutron energies.

Fig. 3-6 Measured neutron reaction rate distributions on the mercury target The figure shows the measured reaction rate distributions of the 115In(n,n')115mIn reaction on the mercury target bombarded with incident protons of 1.5 GeV, 7 GeV and 24 GeV. Values on the vertical axis in the figure correspond to the number of reactions of indium with spallation neutrons generated from a mercury nucleus bombarded with a proton. The measured reaction rates enable us to accurately estimate the number of generated spallation neutrons and their distribution in the mercury target.

Neutron scattering research is one of the most important themes in the Neutron Science Project. The neutron scattering experiment would be conducted by using rich spallation neutrons within a target bombarded by high energy protons from an accelerator. Mercury is considered as the most promising target material for an intense spallation neutron source, since it can effectively remove the heat generated in the target bombarded with protons and it also has a sufficiently high atomic number to produce a large number of spallation neutrons. Experimental confirmation of the feasibility of mercury as a spallation target is indispensable, because of the lack of experimental data associated with a mercury target. In this context, an international collaboration program has been initiated by using the Alternating Gradient Synchrotron (AGS) of the Brookhaven National Laboratory (BNL), USA, in order to study the neutronic, thermal and mechanical characteristics of a mercury target for a spallation neutron source. The spatial profile and the number of incident protons from the AGS to the target were measured by using the imaging plate technique developed at JAERI and elsewhere (Fig. 3-4). The measured results are used as the initial conditions to analyze the experiments related not only to the neutronic characteristics but also to the thermal and mechanical ones of the mercury target. The experiments related to the neutronic characteristics of a mercury target were carried out for the first time in the world, by injecting protons with an incident energy of 1.5 GeV - 24.0 GeV from the AGS into the target with 20 cm diameter and 120 cm long cylinder (Fig. 3-5). Reaction rate distributions of various activation reactions with neutrons were measured by arranging the activation foil detectors with different threshold neutron energies on the mercury target (Fig. 3-6). The number of generated spallation neutrons and their transport behavior in the mercury target can be estimated accurately by using the measured reaction rate distributions. The successful experiments could accelerate the development of a mercury target for a spallation neutron source.

Reference H. Nakashima et al., Measurement of Incident Proton Beam Characteristics for AGS Spallation Target Experiment, Proc. of the 14th Mtg. of the Int. Collaboration on Advanced Neutron Sources, Jun. 14-19, 1998, Starved Rock Rodge, Utica, Illinois, ANL 98/33 (II), 448 (1998).

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