First Observation of Electron Scattering from Online-Produced Radioactive Target

We successfully performed electron scattering off unstable nuclei which were produced online from the photofission of uranium. The target ^{137}Cs ions were trapped with a new target-forming technique that makes a high-density stationary target from a small number of ions by confining them in an electron storage ring. After developments of target generation and transportation systems and the beam stacking method to increase the ion beam intensity up to approximately 2×10^{7} ions per pulse beam, an average luminosity of 0.9×10^{26}  cm^{-2} s^{-1} was achieved for ^{137}Cs. The obtained angular distribution of elastically scattered electrons is consistent with a calculation. This success marks the realization of the anticipated femtoscope which clarifies the structures of exotic and short-lived unstable nuclei.

DISCRIMINATION METHOD FOR GAMMA RAY DOSES IN NEUTRON FIELDS USING AN IONIZATION CHAMBER WITH ATTENUATION FILTERS

Neutron fields produced by an accelerator-driven neutron source are generally mixed radiation fields that consist of fast neutrons and gamma rays. To estimate the biological effects of fast neutrons precisely, the gamma ray dose contamination must be evaluated in neutron fields. In this work, we developed a discrimination technique for absorbed doses (60Co gamma-ray equivalent) of fast neutrons and gamma rays using an ionization chamber. The filter thickness dependences of the absorbed doses of fast neutrons and gamma rays are different for a given filter material. Thus, the absorbed doses of each type of radiation were distinguished by fitting the dose attenuation curve, which was measured with an ionization chamber and attenuation filters, with a two-component exponential function. The absorbed dose of fast neutrons and gamma rays with no attenuation filter was evaluated from the y-intercept of the fitting function. This technique was demonstrated in two neutron fields produced by 4 MeV proton and deuteron bombardment of a 9Be target. The thicknesses of the polyethylene attenuation filters were 0-350 mm. The dose attenuation coefficients of fast neutrons obtained by the two-component exponential fitting function for the 9Be(p,n)9 and 9Be(d,n) reactions showed differences of 1.5 and 1.7%, respectively, from the reference measurements using a CR-39 plastic nuclear track detector. The absorbed dose contributions of gamma rays in neutrons fields of the 9Be(p,n)9B and 9Be(d,n) reactions were evaluated as 30.2 ± 3.24% and 20.4 ± 5.16%, respectively, without polyethylene filters.

Signal pulse emulation for scintillation detectors using Geant4 Monte Carlo with light tracking simulation

The anode pulse of a photomultiplier tube (PMT) coupled with a scintillator is used for pulse shape discrimination (PSD) analysis. We have developed a novel emulation technique for the PMT anode pulse based on optical photon transport and a PMT response function. The photon transport was calculated using Geant4 Monte Carlo code and the response function with a BC408 organic scintillator. The obtained percentage RMS value of the difference between the measured and simulated pulse with suitable scintillation properties using GSO:Ce (0.4, 1.0, 1.5 mol%), LaBr3:Ce and BGO scintillators were 2.41%, 2.58%, 2.16%, 2.01%, and 3.32%, respectively. The proposed technique demonstrates high reproducibility of the measured pulse and can be applied to simulation studies of various radiation measurements.

Feasibility study on signal separation for spontaneous alpha decay in LaBr3: Ce scintillator by signal peak-to-charge discrimination

A novel analysis method named peak-to-charge ratio (V(p)/Q(total)) discrimination, aiming at background rejection especially for alpha decay self-activity in LaBr3: Ce scintillators has been developed. This method is based on a waveform analysis using the peak-to-charge ratio in the output waveform of a photomultiplier tube. The discrimination of alpha-induced events was achieved by using a threshold function based on the error propagation of the V(p)/Q(total) value. The accidental rejection ratio of gamma-induced events was evaluated to be 0.17%. Furthermore, a total absorption peak spectrum processed with the V(p)/Q(total) discrimination method for (68)Ga 1.883 MeV gamma rays, where the energy was overlapped with background alpha events, reproduced exactly the same result as that of the background subtraction method. The difference in measured peak counts of both methods was 0.716%, and the statistical error in the V(p)/Q(total) discrimination method and background subtraction was 4.81% and 8.70%, respectively. Thus a higher-accuracy measurement could be achieved using the V(p)/Q(total) discrimination method. The present study demonstrates that the V(p)/Q(total) discrimination method is a promising method for background rejection of the spontaneous alpha decay in LaBr3:Ce scintillators.

[Subarachnoid anesthesia with hyperbaric bupivacaine]

The effect, duration and complications of subarachnoid anesthesia with hyperbaric bupivacaine solution, adjusted at a gravity of 1.044 and 1.033 by adding glucose, were compared with those of isobaric 0.5% bupivacaine anesthesia. Thirty patients undergoing surgical operations on lower abdomen or lower extremities were divided into three groups and given 2.0 to 4.0 ml of bupivacaine at L3-4 according to the body height. The upper margin of analgesic zone at 15min and 60min after the subarachnoid injection of bupivacaine was higher in the hyperbaric groups, but it receded thereafter and significant differences were found at 120min compared with the isobaric group. Hypotension occurred less frequently in the hyperbaric groups. The short duration of analgesia in the hyperbaric groups may be attributable to the lower concentrations of bupivacaine, 0.40 and 0.45%, but the low frequency of hypotension might be due to the younger mean ages of these two groups. No notable complications were found in any group. Bupivacaine solution of 0.5% with a higher gravity is desired in the market.