Performance of the TPC with Micro Pixel Chamber Readout: micro-TPC

Micro-TPC, a time projection chamber(TPC) with micro pixel chamber($\mu$-PIC) readout was developed for the detection of the three-dimensional fine(sub-m illimeter) tracks of charged particles. We developed a two-dimensional position sensitive gaseous detector, or the $\mu$-PIC, with the detection area of 10$\times$10 cm${}^{2}$ and 65536 anode electrodes of 400 $\mu$m pitch. We achieved the gas gain of over 10000 without any other multipliers. With the pipe-line readout system specially developed for the $\mu$-PIC, we detected X-rays at the rate as high as 7.7 Mcps. We attached a drift cage with an 8 cm drift length to the $\mu$-PIC and developed a micro-TPC. We measured the basic performances of the micro-TPC and took three-dimensional tracks of electrons. We also developed a prototype of the MeV gamma-ray imaging detector which is a hybrid of the micro-TPC and NaI(Tl) scintillators and confirmed its concept by reconstructing the obtained data.Comment: 6 pages 16 figures, submitted for IEEE/TNS 200

Clonal origin of Epstein-Barr virus-infected T/NK-cell subpopulations in chronic active Epstein-Barr virus infection

Clonal expansion of Epstein-Barr virus (EBV) infected B-cells occasionally occurs in immunocompromized subjects. EBV-infected T/natural killer (NK)-cells proliferate in patients with chronic active EBV infection (CAEBV) that is a rare mononucleosis syndrome. It is classified into either T-cell type or NK-cell type according to the primary target of infection, while the pathogenesis remains unclear. To search the clonal origin of EBV-infected T/NK-cells, virus distribution and clonotype were assessed by using highly purified cell fractions obtained from 6 patients. Patient 1 had a monoclonal proliferation of EBV-infected T-cell receptor Vδ2/Vγ9-expressing cells, and carried lower copy number of EBV in αβT-cells. Patients 2 and 3 had a clonal expansion of EBV-infected CD4+T-cells, and lower EBV load in CD56+cells. Patients 4, 5 and 6 had an expansion of CD56+cells with higher EBV load than CD3+cells. EBV-terminal repeats were determined as clonal bands in the minor targeted populations of 5 patients. The size of terminal repeats indicated the same clonotype in minor subsets as in major subsets of 4 patients. However, EBV was not detected in bone marrow-derived lineage negative CD34+cells of patients. These results suggested that EBV could infect T/NK-cells at differentiation stage, but spared bone marrow CD34+hematopoietic stem cells in CAEBV patients

Novel Heterogenous CHS1 Mutations Identified in Five Japanese Patients with Chediak-Higashi Syndrome

Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive disorder characterized by oculocutaneous albinism, recurrent bacterial infections and progressive neurological dysfunction. We demonstrate novel heterogenous mutations of CHS1, the responsive gene of CHS, identified in five Japanese patients with CHS. Patients 1, 2, and 3 were siblings, and they had albinism of the skin and hair. They all had a heterogenous two-base deletion (c.5541-5542 del AA, p.Q1847fsX1850) in exon 18. Patient 4 had a heterogenous single-base insertion (c.3944-3945 ins C, p.T1315fsX1331) in exon 10. The patient exhibited severe early-onset phenotype and suffered from hemophagocytic lymphohistiocytosis. Patient 5 had two heterogenous nonsense mutations; c.7982C>G, p.S2661X in exon 30 and c.8281A>T, p.R2761X in exon 31. The patient suffered from infections in childhood and had visual disturbance and albinism of the skin and hair. The CHS1 mutations described here have not been reported previously

Performance of a micro-TPC for a time-resolved neutron PSD

We report on the performance of a micro-TPC with a micro pixel chamber($\mu$-PIC) readout for a time-resolved neutron position-sensitive detector(PSD). Three-dimensional tracks and the Bragg curves of protons with energies of around 1 MeV were clearly detected by the micro-TPC. More than 95% of gamma-rays of 511 keV were found to be discriminated by simple analysis. Simulation studies showed that the total track length of proton and triton emitted from the $\rm {}^{3}He$(n,p(573 keV))$\rm {}^{3}H(191 keV)$ reaction is about 1.2 cm, and that both particles have large energy losses ($\rm > 200 keV/cm$) in 1 atm Ar+$\rm C_{2}H_{6}(10$+${}^{3}$He($< 1$). These values suit the current performance of the micro-TPC, and we conclude that a time-resolved neutron PSD with spatial resolution of sub-millimeters shall be developed as an application of the micro-TPC.Comment: 13 pages, 10 figures, to appear in NIM

Simulation study of electron drift and gas multiplication in Micro Pixel Chamber

The physical processes of charge collection and gas multiplication of a Micro Pixel Chamber (mu-PIC) were studied in detail using a three-dimensional simulation. The collection efficiencies of primary electrons and gas multiplication factors were calculated for several electrode structures. Based on those studies, we analyzed the optimization of the electrode structure of the mu-PIC, in order to obtain a high gas gain of more than 10^4 and a simultaneous suppression of discharges. Consequently, we found that these characteristics strongly depend on the substrate thickness and the anode diameter of the mu-PIC. In addition, a gas gain of 10^5 would be expected for a mu-PIC having a thick substrate of > 150um.Comment: 16 pages, 14 figures, Submitted to Nucl. Instr. Methods