Malcolm J. Joyce

Time-Dependent Rheology of Starch Thickeners and the Clinical Implications for Dysphagia Therapy

The viscosity of nonsolid foods and the stability of their viscosity over time is critical in managing dysphagia. The time-dependent viscosity of liquids thickened with starch-based thickeners was measured at constant temperature and shear rate. Viscosity was measured between 30-min intervals of rest (zero shear) over a period of 17 h at 20.0°C. Two common types of thickeners were evaluated: maize-based and maltodextrin-based (the latter commonly used in pediatrics). The maize-based thickeners undergo a significant decrease in viscosity over the initial 1–4 h following preparation. The maltodextrin-based thickener’s viscosity increases significantly 30 min following preparation and is then more stable over time than its maize-based equivalent. These findings suggest that the success of current dysphagia therapies that use thickeners could be influenced by the time-dependent nature of thickened fluid viscosity. Acknowledgment and appropriate selection of the thickener type is shown to be of great importance.

Development of a RadFET linear array for intracavitary in vivo dosimetry during external beam radiotherapy and brachytherapy

We present the details of a new linear array dosimeter consisting of a chain of semiconductors mounted on an ultra-thin (50/spl mu/m thick) flexible substrate and housed in an intracavitary catheter. The semiconductors, manufactured by NMKC Cork, have not been packaged and incorporate a passivation layer that allows them to be mounted on the substrate using flip-chip-bonding. This paper reports, for the first time, the construction of a multiple (ten) detector array suited to in vivo dosimetry in the rectum, esophagus and vagina during external beam radiotherapy, as well as being adaptable to in vivo dosimetry during brachytherapy and diagnostic radiology.

Viscosity measurement of industrial oils using the droplet quartz crystal microbalance.

The application of the droplet quartz crystal microbalance (QCM) to the measurement of viscosity for industrial oils is reported. In this approach a small-volume droplet of fluid is investigated via its influence on the resonant frequency of a quartz oscillator. The droplet QCM viscosity response is investigated for a selection of industrial oils, including commercial automotive lubricants, heavy fuel oils, calibration oils and used automotive lubricating oils. This approach shows significant analytical promise for distinguishing between heavy fuel oils dyed to indicate their duty status. It is also demonstrated that lubricating oils aged in engine tests exhibit an enhanced QCM viscosity response than accepted viscosity measurements would otherwise indicate. The locus at which the viscosity response saturates due to violation of the small loading approximation (extreme viscosities) is identified and found to be qualitatively consistent with established equivalent circuit models. The identification of commercial lubricating oils is observed to be unreliable on the basis of viscosity response alone.

A Digital Method for the Discrimination of Neutrons and

A digital method for the discrimination of neutron and γ-ray events from an organic scintillator has been investigated by using frequency gradient analysis (FGA) based on the Fourier transform. Since the scintillation process and the photomultiplier tube (PMT) anode signal are often very noisy, most pulse-shape discrimination methods in a scintillation detection system (e.g., the charge comparison (CC) method or pulse gradient analysis (PGA)) using time-domain features of the signal depend greatly on the associated de-noising algorithm. In this research, the performance of the new FGA method and the PGA method have been studied and compared on a theoretical basis and then verified by time-of-flight (TOF). The frequency-domain features extracted by the FGA method exhibit a strong insensitivity to the variation in pulse response of the photomultiplier tube (PMT) and can be used to discriminate neutron and γ-ray events in a mixed radiation field. It is shown that the FGA method results in an increased figure of merit (FOM) which corresponds to a reduction in the area of overlap between neutron and γ-ray events. The FGA method has the potential to be implemented in current embedded electronic systems to provide real-time discrimination in standalone instruments.

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A Simplified Digital Charge Collection (SDCC) method of discrimination between neutron and gamma pulses in an organic scintillator is presented and compared to the Pulse Gradient Analysis (PGA) discrimination method. Data used in this research were gathered from events arising from the 7Li(p,n)7Be reaction detected by an EJ-301 organic liquid scintillator recorded with a fast digital oscilloscope. Time-of-Flight (TOF) data were also recorded and used as a second means of identification. The SDCC method is found to improve on the figure of merit (FOM) given by PGA method at the equivalent sampling rate.

Rays With Organic Scintillation Detectors Using Frequency Gradient Analysis

The design, build and test of a digital analyzer for mixed radiation fields is described. This instrument has been developed to provide portable, real-time discrimination of hard mixed fields comprising both neutrons and γ rays with energies typically above 0.5 MeV. The instrument in its standard form comprises a sensor head and a system unit, and affords the flexibility to provide processed data in the form of the traditional scatter-plot representation separating neutron and γ-ray components, or the full, sampled pulse data itself. The instrument has been tested with an americium-beryllium source in three different shielding arrangements to replicate the case in which there are only neutrons, only γ rays and where both neutrons and γ-rays are present. The instrument is observed to return consistent results.

A Wavelet Packet Transform Inspired Method of Neutron-Gamma Discrimination

The dependence of radiation-induced charge neutralization (RICN) has been studied in metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters. These devices were first exposed to x rays under positive bias and then to further dose increments at a selection of reverse bias levels. A nonlinear empirical trend has been established that is consistent with that identified in the data obtained in this work. Estimates for the reverse bias level corresponding to the maximum rate of RICN have been extracted from the data. These optimum bias levels appear to be independent of the level of initial absorbed dose under positive bias. The established models for threshold voltage change have been considered and indicate a related nonlinear trend for neutralization cross section σN as a function of oxide field. These data are discussed in the context of dose measurement with MOSFETs and within the framework of statistical mechanics associated with neutral traps and their field dependence.

The design, build and test of a digital analyzer for mixed radiation fields

Using a modified method in the preparation of an imprinted polymer, we report here the synthesis of a uranyl-imprinted copolymer of chloroacrylic acid and ethylene glycol dimethacrylate, which—after removal of the template—selectively extracts uranium from dilute aqueous solution over a range of +2, +3 and +4 competitor metal ions.

The empirical dependence of radiation-induced charge neutralization on negative bias in dosimeters based on the metal-oxide-semiconductor field-effect transistor

The results of a recent study on the limiting uncertainties in the measurement of photon radiation dose with MOSFET dosimeters are reported. The statistical uncertainty in dose measurement from a single device has been measured before and after irradiation. The resulting increase in 1/f noise with radiation dose has been investigated via various analytical models. The limit of uncertainty in the ubiquitous linear trend of threshold voltage with dose has been measured and compared to two nonlinear models. Inter-device uncertainty has been investigated in a group of 40 devices, and preliminary evidence for kurtosis and skewness in the distributions for devices without external bias has been observed.

A selective uranium extraction agent prepared by polymer imprinting

The design, principle of operation and the results of measurements made with a four-channel organic scintillator system are described. The system comprises four detectors and a multiplexed analyzer for the real-time parallel processing of fast neutron events. The function of the real-time, digital multiple-channel pulse-shape discrimination analyzer is described together with the results of laboratory-based measurements with 252Cf, 241Am-Li and plutonium. The analyzer is based on a single-board solution with integrated high-voltage supplies and graphical user interface. It has been developed to meet the requirements of nuclear materials assay of relevance to safeguards and security. Data are presented for the real-time coincidence assay of plutonium in terms of doubles count rate versus mass. This includes an assessment of the limiting mass uncertainty for coincidence assay based on a 100 s measurement period and samples in the range 0-50 g. Measurements of count rate versus order of multiplicity for 252Cf and 241Am-Li and combinations of both are also presented.