39 research outputs found
Coded aperture imaging of nuclear fusion in the plasma focus device
No full textThe Coded Aperture Imaging (CAI) technique has been used to image the deuterium-deuterium (D-D) fusion source in the NX2 plasma focus (PF) device, using protons emitted from the D(d,p)T reaction. CAI is a form of multiplexed pinhole imaging which uses many small pinholes arranged in specific patterns so as to obtain images with the good spatial resolution expected for a small pinhole, together with high brightness and signal-to-noise ratio (SNR) associated with a much larger open aperture. Our theoretical study of CAI led us to the conclusion that for extended sources, such as the PF pinch, coded mask patterns of relatively low open fraction (i.e. significantly less than 50%) are optimal. Therefore the mask patterns used in our experimental work are based on Singer cyclic difference sets. Monte Carlo simulations of CAI and pinhole imaging were performed in order to validate our theoretical SNR formulae and test our decoding algorithm. CR-39 polymer nuclear track detectors were used to register the ~3 MeV protons emitted from the PF pinch. As an additional test of the CR-39 detector scanning procedures, theoretical formulae, and CAI decoding algorithm, various source shapes were simulated experimentally using a 226Ra alpha particle source. As anticipated, the obtained alpha particle CAI images were found to be considerably better than the corresponding single-pinhole images. Significantly, this work represents the first application of the CAI technique to imaging the fusion source in a plasma focus device.The time-integrated neutron yield and anisotropy for each NX2 plasma focus shot were measured using fast- neutron detectors based on the production of radioactive 6He via the 9Be(n,α)6He reaction. The newly fabricated detectors comprise a beryllium metal sheet sandwiched between two large-area xenon-filled proportional counters. A methodology was developed for calculating the absolute neutron response function of these beryllium activation detectors, based on: the 9Be(n,α)6He reaction cross-section, energy calibration of the proportional counters, and numerical simulations (using MCNP5) of neutron and beta-particle interactions.In one series of experiments, five CAI cameras with identical masks were employed simultaneously: one placed on-axis (0°) and four at 45° to the plasma focus axis at the distances of 10.3 cm and 4.9 cm from the source respectively, to investigate the spatial distribution of D-D fusion in the NX2 PF device operated in pure D2 gas and with a PF bank energy of 1.6 kJ. These conditions represent the neutron-optimized regime, for which the neutron yield is typically 1-3×108 n/shot. In a second series of experiments, two larger coded masks: mask-1345 (91×15 array and 341 holes each 0.3 mm side) and mask-4680 (104×45 arrays and 585 holes each 0.27 mm side) were placed at 90° to the plasma focus axis to investigate the fusion source in pure deuterium and deuterium-krypton admixture working gases. The number of proton tracks registered on the CR-39 detectors per shot was typically (1-3)×105. The results clearly show the different size, density and shape of the fusion source in pure D2 and D2-Kr admixture operation. For this second series of experiments, an x-ray pinhole imaging system with suitable filtering was employed simultaneously to record the associated xray images of the hot dense pinched plasma column for comparison with the fusion source images. A plastic scintillation detector was used to measure the time-resolved neutron signal, while the time-resolved hard x-ray pulse was measured using both cesium-iodide and barium-fluoride scintillation detectors.The results show little apparent correlation between the shape of the D-D fusion source and the corresponding soft x-ray image of the plasma pinch. For pure D2 discharges the proton CAI images show a reasonably symmetrical “cigar-shaped” fusion source surrounding the pinch column, without any appreciable indication of m = 0 or m = 1 plasma instabilities. Soft x-ray emission from the pinch column is much stronger for D2-Kr admixture operation than for pure D2 operation, and micro-pinches are frequently present within the main pinch column. Despite this, there are again no discernable indications of plasma instabilities in the associated proton CAI images. Proton CAI images show that the D-D fusion source is much narrower (i.e. of smaller diameter) for D2-Kr admixture operation of the NX2 than it is for pure D2 operation. It is concluded that a collective mechanism of deuteron acceleration occurs throughout the length of the pinch column in the NX2 device, and therefore the fusion is distributed rather evenly around the pinch column. Although m = 0 instabilities in the pinch column may initiate deuteron acceleration, the fast deuterons and resulting fusion are not concentrated within, or around, m = 0 instabilities
Plasma focus neutron anisotropy measurements and influence of a deuteron beam obstacle
No full textThe deuterium-deuterium (DD) fusion neutron yield and anisotropy were measured on a shot-to-shot basis for the NX2 plasma focus (PF) device using two beryllium fast-neutron activation detectors at 0° and 90° to the PF axis. Measurements were performed for deuterium gas pressures in the range 6–16 mbar, and positive correlations between neutron yield and anisotropy were observed at all pressures. Subsequently, at one deuterium gas pressure (13 mbar), the contribution to the fusion yield produced by the forwardly-directed D+ ion beam, emitted from the plasma pinch, was investigated by using a circular Pyrex plate to obstruct the beam and suppress its fusion contribution. Neutron measurements were performed with the obstacle positioned at two distances from the anode tip, and also without the obstacle. It was found that ~ 80% of the neutron yield originates in the plasma pinch column and just above that. In addition, proton pinhole imaging was performed from the 0° and 90° directions to the pinch. The obtained proton images are consistent with the conclusion that DD fusion is concentrated (~ 80%) in the pinch column region.Accepted versio
Giant congenital left ventricular diverticulum associated with infective endocarditis: A diagnosis made by tissue Doppler echocardiography
Get PDFLeft ventricular (LV) diverticulum is a relatively rare condition, and it is important to differentiate it from pseudoaneurysm. The increasing use of noninvasive imaging modalities can help to demonstrate different types of ventricular outpouching structures. We report a case of congenital LV diverticulum that is much larger than the usual size and is diagnosed with tissue Doppler echocardiography and cardiac magnetic resonance imaging. Although a ventricular diverticulum is mostly asymptomatic, in the case of this particular patient, it has become complicated with infective endocarditis. © 2016 Japanese College of Cardiolog
Epidemiological aspects and clinical outcome of patients with rhinocerebral zygomycosis: A survey in a referral hospital in Iran
Get PDFIntroduction: No comprehensive reports have been published on epidemiological status of Rhinocerebral zygomycosis infections and its outcome in our population, Hence, the current study came to address epidemiological characteristics as well as clinical outcome of patients with Rhinocerebral zygomycosis infection referred to a referral hospital in Iran. Methods: This retrospective study was performed at the Rasoul-e-Akram hospital, an 800-bed tertiary care teaching hospital in Tehran, Iran. The pathology recorded charts were reviewed to identify all cases of Rhinocerebral zygomycosis from patients admitted between April 2007 and March 2014. A diagnosis of Rhinocerebral zygomycosis was based on histopathological assessments. Results: Sixty four patients with Rhinocerebral zygomycosis were assessed. The mean age of the patients was 46.07 ± 22.59 years and 51.6 were female. Among those, 67.2 were diabetic, 26.6 were hypertensive and 29.7 had history of cancer. Different sinuses were infected in 73.4 of the patients. Out of all the patients 26.6 underwent surgical procedures and 17.2 were controlled medically. Extensive debridement was carried out in 40.6. Neutropenia ( 14 days) was found in 60.9. According to the Multivariable logistic regression analysis, the main predictors of in-hospital mortality included female gender, advanced age, the presence of sinus infection, and neutropenia, while higher dosages of amphotericin administered had a protective role in preventing early mortality. In a similar Multivariate model, history of cancer could predict prolonged hospital stay, whereas using higher dose of amphotericin could lead to shortening length of hospital stay. Conclusion: There is no difference in demographic characteristics between our patients with Rhinocerebral zygomycosis and other nations. The presence of diabetes mellitus is closely associated with the presence of this infection. Sinus involvement is very common in those with Rhinocerebral zygomycosis leading to high mortality and morbidity. Besides female gender, advanced age, and presence of neutropenia was a major risk factor for increasing early mortality. The use of higher doses of antifungal treatment such as amphotericin can prevent both mortality and prolonged hospital stay. The cancer patients may need longer hospital stay because of needing comprehensive in-hospital treatment. © Vida Bozorgiet al
Coded aperture imaging of fusion source in a plasma focus operated with pure D2 and a D2-Kr gas admixture
No full textThe coded aperture imaging (CAI) technique has been used to investigate the spatial distribution of DD fusion in a 1.6 kJ plasma focus (PF) device operated in, alternatively, pure deuterium or deuterium-krypton admixture. The coded mask pattern is based on a singer cyclic difference set with 25% open fraction and positioned close to 90° to the plasma focus axis, with CR-39 detectors used to register tracks of protons from the D(d, p)T reaction. Comparing the coded aperture imagingprotonimages for pure D2 and D2-Kr admixture operation reveals clear differences in size, density, and shape between the fusion sources for these two cases.Published versio
