A fast response and gamma-insensitive neutron detector based on parallel-plate avalanche counter.

The use of the parallel-plate avalanche counter for slow-neutron counting is described. The choice of a suitable neutron converter is discussed on the basis of Monte Carlo simulation, and some experimental results are shown. Excellent gamma-insensitivity, high rate capability, possibility of construction in large sensitive area and low production cost are among the promising features of this neutron detector.

An ultra fast, radiation-resistant fast neutron detector.

This paper describes a study on 14-MeV neutron detection based on the combination of a parallel plate avalanche chamber with a sheet of polypropylene as fast neutron-to-charged-particle converter. By employing a carefully shielded chamber, neutron-induced charged particles background from the chamber body was successfully reduced to <6 x 10(-5) count per incident neutron. Fast signals, with approximately 7 ns pulse width were observed. The obtained detection efficiency is 0.15%.

Installation and application of an intense 7Li(p,n) neutron source for 20-90 MeV region.

An intense (7)Li(p,n) neutron source was installed with the K = 110-MeV azimuthally varying field (AVF) cyclotron at the Cyclotron and Radioisotope Center (CYRIC), Tohoku University, by employing a special arrangement to allow a short target-sample distance down to 1 m. The source can deliver a neutron flux around 1.5 x 10(6) n cm(-2) s(-1) with a lithium target of thickness equivalent to 2-MeV energy loss and 3-microA proton beam, which is the highest intensity in the world. The source is successfully used for (1) measurement of neutron cross sections relevant to radiation safety and radiation effect and (2) semiconductor irradiation test for single-event effect and (3) characterisation of neutron detectors and dosemeters.

Fast response neutron emission monitor for fusion reactor using stilbene scintillator and Flash-ADC.

The stilbene neutron detector which has been used for neutron emission profile monitoring in JT-60U has been improved, to respond to the requirement to observe the high-frequency phenomena in megahertz region such as toroidicity-induced Alfvén Eigen mode in burning plasma as well as the spatial profile and the energy spectrum. This high-frequency phenomenon is of great interest and one of the key issues in plasma physics in recent years. To achieve a fast response in the stilbene detector, a Flash-ADC is applied and the wave form of the anode signal stored directly, and neutron/gamma discrimination was carried out via software with a new scheme for data acquisition mode to extend the count rate limit to MHz region from 1.3 x 10(5) neutron/s in the past, and confirmed the adequacy of the method.

Development of a quasi-monoenergetic neutron field using the 7Li(p,n)7Be reaction in the energy range from 250 to 390 MeV at RCNP.

A quasi-monoenergetic neutron field using the (7)Li(p,n)(7)Be reaction has been developed at the ring cyclotron facility at the Research Center for Nuclear Physics (RCNP), Osaka University. Neutrons were generated from a 10-mm-thick Li target injected by 250, 350 and 392 MeV protons and neutrons produced at 0 degrees were extracted into the time-of-flight (TOF) room of 100-m length through the concrete collimator of 10 x 12 cm aperture and 150 cm thickness. The neutron energy spectra were measured by a 12.7-cm diam x 12.7-cm long NE213 organic liquid scintillator using the TOF method. The peak neutron fluence was 1.94 x 10(10), 1.07 x 10(10) and 1.50 x 10(10) n sr(-1) per muC of 250, 350 and 392 MeV protons, respectively. The neutron spectra generated from various thick (stopping length) targets of carbon, aluminium, iron and lead, bombarded by 250 and 350 MeV protons, were also measured with the TOF method. Although these measurements were performed to obtain thick target neutron yields, they are also used as a continuous energy neutron field. These neutron fields are very useful for characterising neutron detectors, measuring neutron cross sections, testing irradiation effects for various materials and performing neutron shielding experiments.

Benchmark experiments for cyclotron-based neutron source for BNCT.

In the previous study, we found the feasibility of a cyclotron-based BNCT using the Ta(p,n) neutrons at 90 degrees bombarded by 50 MeV protons, and the iron, AlF(3), Al and (6)LiF moderators by simulations using the MCNPX code. In order to validate the simulations to realize the cyclotron-based BNCT, we measured the epithermal neutron energy spectrum passing through the moderators with our new spectrometer consisting of a (3)He gas counter covered with a silicon rubber loaded with (nat)B and polyethylene moderator and the depth distribution of the reaction rates of (197)Au(n,gamma)(198)Au in an acrylic phantom set behind the rear surface of the moderators. The measured results were compared with the calculations using the MCNPX code. We obtained the good agreement between the calculations and measurements within approximately 10% for the neutron energy spectra and within approximately 20% for the depth distribution of the reaction rates of (197)Au(n,gamma)(198)Au in the phantom. The comparison clarified a good accuracy of the calculation of the neutron energy spectrum passing through the moderator and the thermalization in a phantom. These experimental results will be a good benchmark data to evaluate the accuracy of the calculation code.

[Thrombotic thrombocytopenic purpura (TTP) in which plasmapheresis was ineffective but vincristine slow infusion therapy was effective with long-term remission].

A 38-year old female patient with thrombotic thrombocytopenic purpura (TTP) did not respond to plasmapheresis and treatment with corticosteroids and antiplatelet agents but did respond to subsequent high-dose gamma-globulin therapy and vincristine slow infusion therapy. Remission, thought to be due to vincristine, was achieved. The administration schedule of vincristine was 1 or 2 mg once a week by intravenous drip infusion over a period of 6 to 8 hr. Improvement tended to be seen after the 6th administration, and remission was achieved after the 12th administration (total dose: 15 mg), and continues to the time of this writing. In this case, it was thought that vincristine inhibited a certain excessive reaction in the process of PAIgG-related platelet consumption. We conclude that vincristine should be administered at least 5 to 6 times, and the therapeutic method should be established based on the experience in a larger number of clinical cases.