Design optimization of a fast-neutron detector with scintillating fibers for triton burnup experiments at fusion experimental devices.

Time-resolved triton burnup studies have been carried out to estimate the behavior of alpha particles in DD fusion experimental devices. In those studies, 14 MeV neutrons emitted through DT reactions in DD plasmas should be measured selectively in the backgrounds of DD neutrons and gamma rays. For this purpose, a scintillating-fiber (Sci-Fi) based fast-neutron detector has been adapted because of its advantages such as fast response, design flexibility in detection efficiency by changing the number of Sci-Fi, and discrimination property against 2.4 MeV neutrons produced through DD reactions and gamma rays. However, its length had conventionally been set to around 10 cm without an optimization study of its design parameters to meet the requirements as 14 MeV neutron detector. In the present study, we tested three types of Sci-Fi detectors with three different lengths and compared with the simulated results of energy deposition, through which we tried to understand the phenomena in the detection process of fast neutrons. From the results, it has been shown that, due to the self-shielding of neutrons by Sci-Fi and the attenuation of scintillation photons during the transmission process to the photomultiplier tube, the optimal length of Sci-Fi is concluded to be about 6 cm.

Probabilistic n/γ discrimination with robustness against outliers for use in neutron profile monitors.

A method to stochastically discriminate neutron and γ-ray signals measured with a stilbene organic scintillator is proposed. Each pulse signal was stochastically categorized into two groups: neutron and γ-ray. In previous work, the Expectation Maximization (EM) algorithm was used with the assumption that the measured data followed a Gaussian mixture distribution. It was shown that probabilistic discrimination between these groups is possible. Moreover, by setting the initial parameters for the Gaussian mixture distribution with a k-means algorithm, the possibility of automatic discrimination was demonstrated. In this study, the Student's t-mixture distribution was used as a probabilistic distribution with the EM algorithm to improve the robustness against the effect of outliers caused by pileup of the signals. To validate the proposed method, the figures of merit (FOMs) were compared for the EM algorithm assuming a t-mixture distribution and a Gaussian mixture distribution. The t-mixture distribution resulted in an improvement of the FOMs compared with the Gaussian mixture distribution. The proposed data processing technique is a promising tool not only for neutron and γ-ray discrimination in fusion experiments but also in other fields, for example, homeland security, cancer therapy with high energy particles, nuclear reactor decommissioning, pattern recognition, and so on.

A study on fast digital discrimination of neutron and gamma-ray for improvement neutron emission profile measurement.

Neutron and γ-ray (n-γ) discrimination with a digital signal processing system has been used to measure the neutron emission profile in magnetic confinement fusion devices. However, a sampling rate must be set low to extend the measurement time because the memory storage is limited. Time jitter decreases a discrimination quality due to a low sampling rate. As described in this paper, a new charge comparison method was developed. Furthermore, automatic n-γ discrimination method was examined using a probabilistic approach. Analysis results were investigated using the figure of merit. Results show that the discrimination quality was improved. Automatic discrimination was applied using the EM algorithm and k-means algorithm.

Rapid deterioration of renal insufficiency after magnetic resonance imaging with gadolinium-based contrast agent.

Gadolinium (Gd)-based contrast media were introduced as alternatives to iodinated media for magnetic resonance imaging (MRI). Although originally thought to be non-nephrotoxic, Gd-based contrast media have recently been reported to be associated with acute kidney injury. The underlying mechanism of Gd-induced renal injury is not completely understood. We report an 80-year-old patient with buccal mucosa cancer for whom MRI with Gd-based contrast agent was conducted 3 times within 3 weeks. The patient developed rapid deterioration of preexisting renal insufficiency, and developed uremic symptoms and pulmonary edema. The patient was hemodialyzed 3 times. This resulted in improvement of renal function and clinical symptoms. This case emphasizes the potential nephrotoxicity of Gd-based contrast media and suggests that renal insufficiency, diabetes mellitus, old age and high dose of Gd-based contrast medium are risk factors for acute kidney injury.

Reversible posterior leukoencephalopathy syndrome in a patient with severe uremic encephalopathy.

A 59-year-old male presented at our hospital with disturbance of consciousness. He had severe neurological disturbances associated with uremia caused by severe renal insufficiency. Cranial computed tomography (CT) was normal on admission. FLAIR-weighted MRI showed increased signal intensities bilaterally in the cortical and subcortical areas of the occipital lobe. Repeated hemodialysis resulted in improvement of the clinical symptoms and blood chemistry, and normalization of the MRI findings. Although the patient was discharged without neurological deficit, he had to be maintained on regular intermittent hemodialysis due to persistent renal failure. These reversible neuroradiological abnormalities may have been caused by reversible brain edema, but other pathoetiological factors should be also considered, such as abnormalities of cerebral metabolism and effects of uremic toxins.

Facile and rapid high-performance liquid chromatography method for simultaneous determination of allopurinol and oxypurinol in human serum.

OBJECTIVE: To develop a rapid and sensitive assay for the simultaneous determination of allopurinol and oxypurinol in serum. METHOD: High-performance liquid chromatography (HPLC) with UV-detection. Sample preparation consists of protein precipitation by an addition of trichloracetic acid. RESULTS: Percentage recovery and intra-assay coefficient of variation (CV%) for allopurinol were 97.4-101.3 and 0.66-5.13, respectively, in the concentration range 0.5-5.0 microg/mL. For oxypurinol, the percentage recovery and the intra-assay CV% were 93.2-98.1 and 0.88-5.62, respectively, in the concentration ranges 0.4-20 microg/mL. There was no interference of endogenous compounds in this assay. CONCLUSION: This method is useful for routine therapeutic drug monitoring of allopurinol in a clinical setting.

[A case of tuberous sclerosis with congenital brain tumor; an immunohistochemical study].

A case of tuberous sclerosis with congenital brain tumor was reported. The diagnosis was made on the basis of the pathological findings of subependymal giant cell astrocytoma, after surgery at the newborn period. After the neonatal period, the patient presented the classical triad of seizures, white spot of skin and mental retardation. The exact nature of tumor-forming giant cells remains controversial. We studied the nature of these cells using immunohistochemical method. GFAP, S-100 protein and NSE stains were all positive. This result suggested that the tumor cells had the features of both neurons and astrocytes.