A novel approach to neutron dosimetry

Purpose: Having been overlooked for many years, research is now starting to take into account the directional distribution of neutron workplace fields. Existing neutron dosimetry instrumentation does not account for this directional distribution, resulting in conservative estimates of dose in neutron workplace fields (by around a factor of 2, although this is heavily dependent on the type of field). This conservatism could influence epidemiological studies on the health effects of radiation exposure. This paper reports on the development of an instrument which can estimate the effective dose of a neutron field, accounting for both the direction and the energy distribution. Methods: A 6Li-loaded scintillator was used to perform neutron assays at a number of locations in a 20 × 20 × 17.5 cm3 water phantom. The variation in thermal and fast neutron response to different energies and field directions was exploited. The modeled response of the instrument to various neutron fields was used to train an artificial neural network (ANN) to learn the effective dose and ambient dose equivalent of these fields. All experimental data published in this work were measured at the National Physical Laboratory (UK). Results: Experimental results were obtained for a number of radionuclide source based neutron fields to test the performance of the system. The results of experimental neutron assays at 25 locations in a water phantom were fed into the trained ANN. A correlation between neutron counting rates in the phantom and neutron fluence rates was experimentally found to provide dose rate estimates. A radionuclide source behind shadow cone was used to create a more complex field in terms of energy and direction. For all fields, the resulting estimates of effective dose rate were within 45% or better of their calculated values, regardless of energy distribution or direction for measurement times greater than 25 min. Conclusions: This work presents a novel, real-time, approach to workplace neutron dosimetry. It is believed that in the research presented in this paper, for the first time, a single instrument has been able to estimate effective dose

Diversification of shrub frogs (Rhacophoridae, Pseudophilautus) in Sri Lanka - Timing and geographic context

US National Science Foundation (DEB 0345885) to CJS and JH; National Geographic Society (7612-04) to CJS; and Society of Systematic Biologists Graduate Student Award for Research to MM. MM was also supported by a Harvard University Center for the Environment (HUCE) Ziff Environmental Postdoctoral Fellowship. (DEB 0345885 - US National Science Foundation; 7612-04 - National Geographic Society; Society of Systematic Biologists Graduate Student Award for Research; Harvard University Center for the Environment (HUCE) Ziff Environmental Postdoctoral Fellowship)Accepted manuscrip

Detecting Alpha-induced Radioluminescence in the UVC Wavelength Range Using a UVTron Flame Sensor, and the Effect of a Gas Flow on Detection Rates as Compared to an Air Atmosphere

Alpha-induced radioluminescence provides a potential avenue for the detection of alpha-emitting materials from a distance far greater than the travel of alpha-particles themselves. This work details experiments carried out into the detection of this radioluminescence in the ultraviolet C wavelength range (180-280 nm) using an off-the-shelf flame sensor, the UVTron (Hamamatsu, Japan). There is less interference from natural and artificial background lighting in the ultraviolet C wavelength range than at other ultraviolet wavelengths. A UVTron flame sensor (R9533, Hamamatsu, Japan), which is sensitive only in the ultraviolet C wavelength range, was used to detect the presence of a 6.95 MBq 210 Po source at a distance of approximately 20 mm. The signal (0.3280 counts per second) was over 147 times that of the background, which was very low (2.224 × 10 -3 counts per second) under the general laboratory/commercial lighting conditions. The limit of detection, where the signal can be distinguished from background, can be calculated to be approximately 240 mm under these conditions, assuming a standard 1/r 2 , which is much greater than the alpha particle travel. Gas was flowed over the alpha sample to determine if this would enhance the radioluminescence and hence the detection by the UVTron. Gases of Ar, Xe, Ne, N2, Kr and P10 were tested, all of which increased the signal detected by the UVTron sensor. The greatest increase was found to be in a flow of Xe, which greater than doubled the counts per second of the detector in one instance. The ability of the UVTron to detect the radioluminescence from alpha-emitting materials and the enhancement which may be possible using a flow of gas, indicate the potential of the UVTron sensor for inclusion in an alpha-emitting materials detection system which could be operated at a distance in the field, for example for nuclear decommissioning characterisation purposes or nuclear security applications

Localised Response Retrieval from Hamamatsu H9500 for a Coded-aperture Dual-particle Imaging System Based on an Organic Pixelated Plastic Scintillator (EJ-299-34)

Localised response of a sensitive light detector, such as Hamamatsu H9500 multi anode photomultiplier tube (MAPMT), is of vital importance for coded-aperture imaging systems. When coupled with a suitable sensitive detector (e.g. EJ-299-34 plastic scintillator), output signals of the MAPMT can be retrieved to infer the interaction location in the pixelated scintillator. Given the number of anodes in H9500 (256), significant processing power would be necessary to handle each pulse individually. Therefore, a readout electronics system was developed, based on resistive network approach, which reduces the number of output signals to individual X and Y coordinates, and subsequently allows particle identification. Coordinates retrieved in this manner can be analysed in real time and used to infer the two-dimensional location. Particle type can be also exploited by pulse shape discrimination (PSD) application to the scintillator’s response. In this study, 169 anodes were used (due to coded-aperture design rules), and reduced to two X and Y output signals. These have been digitised using a bespoke FPGA based two channel 14-bit 150 MSPS digitiser. The digital data are transferred to a host application using UART to USB converter operating at 12 Mbits/s. Promising results have been observed when the scintillator’s response was tested in single particle field of 137Cs. However, further tests performed in the mixed-field environment of 252Cf suggest that faster digitiser may be required to obtain the required PSD performance

Ferroelectric Nematic Droplets in their Isotropic Melt

The isotropic to ferroelectric nematic liquid transition had been theoretically studied over one hundred years ago, but its experimental studies are rare. Here we present polarizing optical microscopy studies and theoretical considerations of ferroelectric nematic liquid crystal droplets coexisting with the isotropic melt. We find that the droplets have flat pancake-like shapes that are thinner than the sample thickness as long as there is a room to increase the lateral droplet size. In the center of the droplets a wing shaped defect with low birefringence is present that moves perpendicular to a weak in-plane electric field, and then extends and splits in two at higher fields. Parallel to the defect motion and extension, the entire droplet drifts along the electric field with speed that is independent of the size of the droplet and is proportional to the amplitude of the electric field. After the field is increased above 1V/mm the entire droplet gets deformed and oscillates with the field. These observations led us to determine the polarization field and revealed the presence of a pair of positive and negative bound electric charge due to divergences of polarization around the defect volume

Low Densities of Serotonin and Peptide YY Cells in the Colon of Patients with Irritable Bowel Syndrome

Background The gut hormones are important in regulating gastrointestinal motility. Disturbances in gastrointestinal motility have been reported in patients with irritable bowel syndrome (IBS). Reduced endocrine cell density, as revealed by chromogranin A, has been reported in the colon of IBS patients. Aims To investigate a possible abnormality in the colonic endocrine cells of IBS patients. Methods A total of 41 patients with IBS according to Rome Criteria III and 20 controls were included in the study. Biopsies from the right and left colon were obtained from both patients and controls during colonoscopy. The biopsies were immunostained for serotonin, peptide YY (PYY), pancreatic polypeptide (PP), entroglucagon, and somatostatin cells. Cell densities were quantified by computerized image analysis. Results Serotonin and PYY cell densities were reduced in the colon of IBS patients. PP, entroglucagon, and somatostatin- immunoreactive cells were too few to enable reliable quantification

Combined digital imaging of mixed-field radioactivity with a single detector.

We have performed combined digital imaging of neutrons and gamma rays in mixed radiation fields. An organic liquid fast scintillation detector has been integrated into a system with a digitizer, collimator and an equatorial mount to characterize two mixed-field environments. Images have been produced corresponding to the angular distribution of events and the three-dimensional Cartesian coordinate system for both gamma rays and neutrons, simultaneously. These data indicate that mixed fields can be readily imaged with a single detector in terms of their gamma-ray and neutron components at the same time

Localised Response Retrieval from Hamamatsu H9500 for a Coded-aperture Dual-particle Imaging System Based on an Organic Pixelated Plastic Scintillator (EJ-299-34)

No abstract available