Press Release J-PARC Center March 21, 2013 J-PARC won world record of neutron beam intensity!  ○ J-PARC raised proton beam power to 300 kW on November 22, 2012 and started operation for user programs with high-intensity pulsed neutron beams.  ○ The neutron beams were examined and analyzed in detail and the number of neutrons turned out to be 6.5�~1013 per pulse. We proudly announce that J-PARC provide the strongest pulsed neutron beams in the world.  ○ The world strongest pulsed neutron beams must bring breakthroughs to the cutting edge of materials science and life science. Their application to industries would be also promoted extensively, such as high functional materials or new medicines.

J-PARC is a multi-purpose and multidisciplinary facility for fundamental science and industrial applications. The accelerators accelerate protons very close to the light speed and the experimental facilities produce high-intensity quantum beams through collisions between proton beams and target materials. In the Materials and Life Science Experimental Facility (MLF) , the pulsed neutron source generates neutrons with spallation reaction of mercury nuclei. The neurons are extracted as pulsed beams to spectrometers and applied for wide range of research fields.   At MLF the first neutron beams were generated in May 2008 and the beam operation for user programs was commenced in December 2008 at the proton beam power of 4 kW. The neutron beam intensity has been increasing with increasing the proton beam power. Meanwhile the design of a mercury target vessel was improved to reduce the impact force of pressure waves due to the proton beam injection to a target using the cushioning effect of dispersed helium micro-bubbles. The proton beam power reached to 300 kW on November 22, 2012, and since then we stably have been supplying these high-intensity neutron beams to the user program.   The beam characteristics were studied during this high-power operation, and it revealed that each beam pulse had 6.5�~1013 neutrons. This value is more than the design value of the Spallation Neutron Source (SNS) in USA (5.3�~1013 neutrons per pulse at 1-MW proton beam power) and it means that the MLF has the world strongest pulsed neutron source for research usage (see Table below) . This significance is resulted from the intensive study of the target source system, including shape, size, material and arrangement of every component, to realize its maximal performance. As the neutron beam transport systems were also upgraded, required sample size can be shrunk and measurement time can be shortened in users' experiments.   The MLF now has two world most intense beam sources : One is that of neutrons and the other is muons. The number of researchers who used either the neutron facility or the muon facility increases to 700 per month, compared to ˜580 per month before the Great East Japan Earthquake.   We plan to upgrade J-PARC accelerators to ramp up proton beam power to 1-MW. At the realization, the neutron beams will have much higher instantaneous intensities that we have never experienced and will contribute further breakthroughs in the wide range of science fields.

【 Table 】    Comparison of neutron beam intensity at major pulsed neutron facilities in the world

neutron facility	# of neutrons per pulse
J-PARC (Japan)	6.5�~1013
SNS (USA)	5.3�~1013
ISIS (UK)	4.9�~1013

* Click here to enlarge.

【 Media Contact 】   Shinichi Sakamoto Leader, Public Relations Section, J-PARC Center, Japan TEL : +81-29-284-3587 FAX : +81-29-284-5996 E-mail : shinichi.sakamoto@j-parc.jp

The neutron source is housed in the steal container (10 m in diameter and 9 m in height) and the mercury target vessel is placed at the center of the source. In the near future it is expected to produce the high-intensity neutron beams (1017 neutrons per second) through spallation reactions of mercury nuclei and 3-GeV proton beams at 1-MW power (1015 protons per second).   Three moderators, in which hydrogen at cryogenic temperature (20 K) is circulated, have been installed at the top and bottom of the mercury target vessel. Whereas the energies of the neutrons generated in the mercury vessel are quite high, which are equivalent to ˜1010 K in temperature, these moderators slow down neutrons and reduce the energies to be suitable for neutron experiments, ˜250 K in equivalent temperature.   These low-energy neutrons are extracted radially through 23 beamlines to various neutron instruments. A user at each instrument can switch on and off neutron beams independently with operating a neutron shutter of each beamline.   The neutron source is filled with iron and concrete shields to prevent neutrons from leaking out to unnecessary directions.

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