43 research outputs found
Characterization of high-temperature PbTe p-n junctions prepared by thermal diffusion and by ion-implantation
We describe here the characteristics of two types of high-quality PbTe
p-n-junctions, prepared in this work: (1) by thermal diffusion of In4Te3 gas
(TDJ), and (2) by ion implantation (implanted junction, IJ) of In (In-IJ) and
Zn (Zn-IJ). The results, as presented here, demonstrate the high quality of
these PbTe diodes. Capacitance-voltage and current-voltage characteristics have
been measured. The measurements were carried out over a temperature range from
~ 10 K to ~ 180 K. The latter was the highest temperature, where the diode
still demonstrated rectifying properties. This maximum operating temperature is
higher than any of the earlier reported results.
The saturation current density, J0, in both diode types, was ~ 10^-5 A/cm2 at
80 K, while at 180 K J0 ~ 10^-1 A/cm2 in TDJ and ~ 1 A/cm2 in both
ion-implanted junctions. At 80 K the reverse current started to increase
markedly at a bias of ~ 400 mV for TDJ, and at ~550 mV for IJ. The ideality
factor n was about 1.5-2 for both diode types at 80 K. The analysis of the C-V
plots shows that the junctions in both diode types are linearly graded. The
analysis of the C-V plots allows also determining the height of the junction
barrier, the concentrations and the concentration gradient of the impurities,
and the temperature dependence of the static dielectric constant. The
zero-bias-resistance x area products (R0Ae) at 80 K are: 850 OHMcm2 for TDJ,
250 OHMcm2 for In-IJ, and ~ 80 OHMcm2 for Zn-IJ, while at 180 K R0Ae ~ 0.38
OHMcm2 for TDJ, and ~ 0.1 OHMcm2 for IJ. The estimated detectivity is: D* ~
10^10 cmHz^(1/2)/W up to T=140 K, determined mainly by background radiation,
while at T=180 K, D* decreases to 108-107 cmHz^(1/2)/W, and is determined by
the Johnson noise
Influence of Annealing on the Optical and Scintillation Properties of CaWO Single Crystals
We investigate the influence of oxygen annealing on the room temperature
optical and scintillation properties of CaWO single crystals that are being
produced for direct Dark Matter search experiments. The applied annealing
procedure reduces the absorption coefficient at the peak position of the
scintillation spectrum ( nm) by a factor of and leads to an
even larger reduction of the scattering coefficient. Furthermore, the annealing
has no significant influence on the \emph{intrinsic} light yield. An additional
absorption occurring at nm suggests the formation of O hole
centers. Light-yield measurements at room temperature where one crystal surface
was mechanically roughened showed an increase of the \emph{measured} light
yield by and an improvement of the energy resolution at 59.5 keV by
for the annealed crystal. We ascribe this result to the reduction of
the absorption coefficient while the surface roughening is needed to compensate
for the also observed reduction of the scattering coefficient after annealing
GATE : a simulation toolkit for PET and SPECT
Monte Carlo simulation is an essential tool in emission tomography that can
assist in the design of new medical imaging devices, the optimization of
acquisition protocols, and the development or assessment of image
reconstruction algorithms and correction techniques. GATE, the Geant4
Application for Tomographic Emission, encapsulates the Geant4 libraries to
achieve a modular, versatile, scripted simulation toolkit adapted to the field
of nuclear medicine. In particular, GATE allows the description of
time-dependent phenomena such as source or detector movement, and source decay
kinetics. This feature makes it possible to simulate time curves under
realistic acquisition conditions and to test dynamic reconstruction algorithms.
A public release of GATE licensed under the GNU Lesser General Public License
can be downloaded at the address http://www-lphe.epfl.ch/GATE/
Derivation and validation of a risk-factor model for detection of oral potentially malignant disorders in populations with high prevalence
Background:Oral and pharyngeal cancers constitute the sixth most common type of cancer globally, with high morbidity and mortality. In many countries, most cases of oral cancer arise from long-standing, pre-existing lesions, yet advanced malignancies prevail. A new approach to early detection is needed. We aimed to validate a model for screening so that only high-risk individuals receive the clinical examination.Methods:A community-based case-control study (n1029) in rural Sri Lanka assessed risk factors and markers for oral potentially malignant disorders (OPMD) by administering a questionnaire followed by an oral examination. We then developed a model based on age, socioeconomic status and habits of betel-quid chewing, alcohol drinking and tobacco smoking, with weightings based on odds ratios from the multiple logistic regression. A total, single score was calculated per individual. Standard receiver-operator characteristic curves were plotted for the total score and presence of OPMD. The model was validated on a new sample of 410 subjects in a different community.Results:A score of 12.0 produced optimal sensitivity (95.5%), specificity (75.9%), false-positive rate (24.0%), false-negative rate (4.5%), positive predictive value (35.9%) and negative predictive value (99.2%).Conclusion:This model is suitable for detection of OPMD and oral cancer in high-risk communities, for example, in Asia, the Pacific and the global diaspora therefrom. A combined risk-factor score of 12.0 was optimal for participation in oral cancer/OPMD screening in Sri Lanka. The model, or local adaptations, should have wide applicability
Randomized clinical study: Partially hydrolyzed guar gum (PHGG) versus placebo in the treatment of patients with irritable bowel syndrome
An improved analytical detector response function model for multilayer small-diameter PET scanners
Use of the analysis of the volatile faecal metabolome in screening for colorectal cancer
Diagnosis of colorectal cancer is an invasive and expensive colonoscopy, which is usually carried out after a positive screening test. Unfortunately, existing screening tests lack specificity and sensitivity, hence many unnecessary colonoscopies are performed. Here we report on a potential new screening test for colorectal cancer based on the analysis of volatile organic compounds (VOCs) in the headspace of faecal samples. Faecal samples were obtained from subjects who had a positive faecal occult blood sample (FOBT). Subjects subsequently had colonoscopies performed to classify them into low risk (non-cancer) and high risk (colorectal cancer) groups. Volatile organic compounds were analysed by selected ion flow tube mass spectrometry (SIFT-MS) and then data were analysed using both univariate and multivariate statistical methods. Ions most likely from hydrogen sulphide, dimethyl sulphide and dimethyl disulphide are statistically significantly higher in samples from high risk rather than low risk subjects. Results using multivariate methods show that the test gives a correct classification of 75% with 78% specificity and 72% sensitivity on FOBT positive samples, offering a potentially effective alternative to FOBT
Diverticulosis and diverticulitis form no risk for polyps and colorectal neoplasia in 4,241 colonoscopies
Use of an analytical model for optimizing the design of a small-animal PET scanner with DOI capability - Size 7.4E-02 m Size 1.14E-01 m
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An improved analytical detector response function model for multilayer small-diameter PET scanners
The optimization of spatial resolution is a critical consideration in the design of small-diameter positron emission tomography (PET) scanners for animal imaging, and is often addressed with Monte Carlo simulations. As a faster and simpler solution, we have developed a new analytical model of the PET detector response function, and implemented the model for a small single-slice, multilayer PET scanner. The accuracy of the model has been assessed by comparison with both Monte Carlo simulations and experimental measurements published in the literature. Results from the analytical model agreed well with the Monte Carlo method, being noise free and two to three orders of magnitude faster. The only major discrepancy was a slight underestimation of the width of the point spread function by the analytical method as inter-crystal scatter is neglected. We observed good agreement between the predictions of the model and experimental measurements. For two large-diameter scanners additional discrepancies were seen due to photon acollinearity, which is not considered in the model. We have shown that the simple and fast analytical detector response function model can provide accurate estimates of spatial resolution for small-diameter PET scanners, and could be a useful tool for several applications, complementing or cross-validating other simulation methods