| Research Abstract |
In 1998, further works on the cryostat Mark 3001, which had been developed with the Grant-in-Aid for Scientific Research on Priority Area (Ultracold Neutrons) till 1996, have newly started. For a possible experimental site, ILL and PSI were investigated as the candidates. As the result, the collaboration with University of Sussex, the main research institute of edm measurement up till now, and RNL was launched. Two young researchers visited Japan in this period. The cooling of the superconducting solenoid has started from 1999/6, and the persisitent current mode has been achieved on 1999/7/25. It was confirmed that necessary magnetic field of 10 mG was generated in the superstable state. In the meantime, the collaboration with Sussex group was pushed forward. Consequently a joint proposal by Kure Univ. and Univ. of Sussex of an experiment "CryoEDM" was made on 1999/8/30 to the ILL steering committee. This proposal was officially approved by the organizing committee later in mid-October
… More
. In the meantime Mombusho executed an inspection of the scene on 1999/9/20 in Japan. From mid-December tests were carried out upon the cryostat (Cooling Tower II), and the liquid helium temperature attained a record breaking temperature, 0.48K, on 2000/2/4. On 2000/3/15 a confirmative document of the proposal made August of the previous year was sent to ILL. The committee allocated 40 days beam time to the project (11.22-12.7, 3.15-4.10). In order to comply with this developing situation, the whole members in the project, thirteen altogether have met at ILL. From the summer of 2000, shipping the experimental equipments began. The improved Cooling Tower I was completed on June 29, and together with other hundreds of pieces of equipment were sent from Japan on 2000/7/10. I went to Europe on 2000/8/ 7-21, 9/7-23 and 11/9-12/15 to help the construction of the beam H53 for PF1. In 2001/3, a great number of UCNs far more than expected for foreign researchers were produced, showing the high efficiency and the superiority of the superthermal method to the world. It was found however the beam intensity of H53 was 1/60 of the specification made by ILL. These results were published at an international UCN workshop held at Pushkin, Russia, in June. From January to March of 2002, UCN production rate vs incident cold neutron wavelength has been measured very accurately by inserting an elaborate velocity selector in the beam. This measurement showed that the multiphonon UCN production did exist but only about one tenth of the single phonon production rate. The saturated UCN density was 8/cm^3 with 0.7/cm^3/s production rate. Both are record breaking numbers (PhysLetterA308(03)p67) and with the advent of improved cold neutron beam the final UCN density will be 4000/cm^3, which will be good enough to reach even 10^-28 e.cm level in several years. The 10^-26 e.cm level we proposed as a target level at the outset of this project has been cleared by the Sussex group working at the normal temperatures (PRL82(1999 )904). Ebisu of Univ. of Kobe continued his studies on the detection of slow neutrons by means of superconducting granules (Sb) and made a progress confirming such detection mechanism as he had anticipated is taking place clearly by using a stronger neutron source. This result can be applied to further developments of detetors not only for neutrons but also for neutral particles such as dark matter. Less
|
