Browsing by Author "Whittlestone, S"
Now showing 1 - 12 of 12
Results Per Page
- Item222Rn calibrated mercury fluxes from terrestrial surfaces of southern Africa derived from observations at Cape Point, South Africa(EDP Sciences, 2012-09-23) Slemr, F; Brunke, EG; Whittlestone, S; Zahorowski, W; Ebinghaus, R; Kock, HH; Labuschagne, CGaseous elemental mercury (GEM) and 222Rn, a radioactive gas of primarily terrestrial origin with a half-life of 3.8 days, have been measured simultaneously at Cape Point, South Africa, since March 2007. Between March 2007 and December 2009 altogether 59 events with high 222Rn concentrations were identified. GEM correlated with 222Rn in 41 of the events and was constant during the remaining events without significant correlation. The average GEM/222Rn emission ratio of all events was -0.0047 ± 0.0054 pg mBq-1, with ± 0.0054 being the standard error of the average. With an emission rate of 1.1 222Rn atoms cm-2 s-1 and a correction for the transport duration, this emission ratio corresponds to a radon calibrated flux of about -0.53 ± 0.62 ng m-2 h-1 which is statistically not distinguishable from zero. With wet deposition, which is not included in this estimate, the terrestrial surface of southern Africa appears to be a net mercury sink. © Owned by the authors, published by EDP Sciences, 2013
- Item222Rn-calibrated mercury fluxes from terrestrial surface of southern Africa(European Geosciences Union, 2013-01-01) Slemr, F; Brunke, EG; Whittlestone, S; Zahorowski, W; Ebinghaus, R; Kock, HH; Labuschagne, CGaseous elemental mercury (GEM) and 222Rn, a radioactive gas of primarily terrestrial origin with a half-life of 3.8 days, have been measured simultaneously at Cape Point, South Africa, since March 2007. Between March 2007 and December 2011, altogether 191 events with high 222Rn concentrations were identified. GEM correlated with 222Rn in 94 of the events and was constant during almost all the remaining events without significant correlation. The average GEM / 222Rn flux ratio of all events including the non-significant ones was −0.0001 with a standard error of ±0.0030 pg mBq−1. Weighted with the event duration, the average GEM / 222Rn flux ratio was −0.0048 ± 0.0011 pg mBq−1. With an emission rate of 1.1 222Rn atoms cm−2 s−1 and a correction for the transport time, this flux ratio corresponds to a radon-calibrated flux of about −0.54 ng GEM m−2 h−1 with a standard error of ±0.13 ng GEM m−2 h−1 (n = 191). With wet deposition, which is not included in this estimate, the terrestrial surface of southern Africa seems to be a net mercury sink of about −1.55 ng m−2 h−1. The additional contribution of an unknown but presumably significant deposition of reactive gaseous mercury would further increase this sink.© 2013, European Geosciences Union
- ItemAnalysis of pulse height spectra from an organic scintillator spectrometer(Australian Atomic Energy Commission, 1980-07) Whittlestone, SA suite of three computer codes has been written to analyse the pulse height spectra from an organic scintillator neutron or gamma ray spectrometer. Data prepared by the first code are submitted to the second which unfolds the pulse height spectra. Comparison and presentation of analysed data are performed by the third code. The spectrum unfolding process was tested by unfolding the fairly complex spectrum from the 9Be(d,n)10B reaction, which was known from other measurements. The performance of the code when unfolding monoenergetic neutron responses was comparable to the performance of codes used by other workers.
- ItemBaseline environmental radon survey at Lake Way, Western Australia, September 1979(Australian Atomic Energy Commission, 1981-04) O'Brien, BG; Whittlestone, SA survey of radon and radon daughters in the air has been made at and within a few kilometres of the possible uranium mine near Millbillillie at the northern edge of Lake Way, Western Australia. The data have been correlated with meteorological measurements taken concurrently with the radon survey. In addition radon emanation rates and radon levels in water have been measured at a broad range of sites to define more closely the magnitude and extent of radon in the environment.
- ItemDevelopment of a small, nanosecond timing fast neutron spectrometer.(Australian Atomic Energy Commission, 1980-05) Whittlestone, SA neutron spectrometer has been developed for use inside a fast neutron assembly. The spectrometer is small and insensitive to gamma radiation. An optical system was developed which could collect about 80 per cent of the light from an NE213 liquid scintillator and transmit it along a 450mm quartz light guide to a high performance photomultiplier. To enable the detector to be used as a nanosecond timing spectrometer, several calibration measurements were made of the detector efficiency and response to monoenergetic neutrons.
- ItemHigh sensitivity two filter radon/thoron detectors with a wire or nylon screen as a second filter.(Australian Nuclear Science and Technology Organisation, 1994-12) Whittlestone, S; Zahorowski, W; Wasiolek, PA study is made of the use of wire and nylon screens as a second filter in two radon or thoron detectors. It is shown that acceptable detection efficiency is obtained at flow rates comparable to those used in detectors in which other types of filter are used. The main advantage of the screens is their very low flow impedance. Several designs of detector which exploit this feature are discussed. Details are given of the performance of three prototypes: a 32 L radon detector with a limit of detection of 0.0027 Bq m-3 and power consumption of 25 watts; and a portable thoron emanometer capable of detecting fluxes as low as 1 m Bq m -2 s-1. The radon detectors are rugged and simple. They can operate with no routine maintenance and are suited to remote locations where only infrequent technical support is available.
- ItemMeasurement of the thermal neutron wave dispersion relations in BeO.(Australian Atomic Energy Commission, 1971-05) Ritchie, AIM; Whittlestone, SThe amplitudes and phase shifts of thermal neutron waves were measured in a block of BeO 60.96 x 60.96 x 58.42 cm3 of average density 2.87 g cm-3 and having nominal transverse buckling of 0.0048 cm-2. The attenuation constants (α) and phase shift constants (ζ) were derived from such measurements at 18 different frequencies covering the range 52.4 to 506.1 Hz. The parameters of α2 - ζ2 and 2αζ were evaluated, normalised to a reference density of 2.96 g cm-3, and corrected for the density normalised transverse buckling of 0.00513 cm-2. The normalised and corrected parameters α2 - ζ2 and 2αζ were fitted to polynomials in the angular frequency ω, and the resulting thermal neutron diffusion parameters were compared with those derived from a λ(B2) experiment carried out on the same block of BeO. The parameters λα and L determined by the two methods are in good agreement, but the diffusion coefficient and diffusion cooling constant derived from the sine wave experiment are significantly higher. The high diffusion coefficient (by ~ 9 per cent) could be due to the effect of the sub-Bragg continuum although the values of the parameters α and ζ appeared to be independent of the distance from the source. Agreement of the parameters α2 - ζ 2 and 2αζ with the theoretical values is not good and reasons for the discrepancy are advanced.
- ItemMeasurement of thermal neutron waves at high frequencies in BeO(Australian Atomic Energy Commission, 1972-03) Ritchie, AIM; Whittlestone, SThe amplitudes and phases of neutron waves have been measured in a BeO assembly in the frequency range 515.7 Hz. The results confirm earlier measurements that below ~ 520 Hz the neutron wave has the properties of a discrete mode of propagation. At frequencies > 720 Hz the attenuation α(z) and phase shift parameters ζ(z) change with distance from the source, the change being more marked the higher the frequency. The observed spatial variations of α(z) and ζ(z) do not agree with present theoretical predictions. Interference effects predicted by theory have not been observed.
- ItemMeasurement of time-dependent fast neutron energy spectra in a depleted uranium assembly.(Australian Atomic Energy Commission, 1980-10) Whittlestone, STime-dependent neutron energy spectra in the range 0.6 to 6.4 MeV have been measured in a depleted uranium assembly. By selecting windows in the time range 0.9 to 82 ns after the beam pulse it was possible to observe the change of the neutron energy distributions from spectra of predominantly 4 to 6 MeV neutrons to spectra composed almost entirely of fission neutrons. The measured spectra were compared to a Monte Carlo calculation of the experiment using the ENDF/B-IV data file. At times and energies at which the calculation predicted a fission spectrum the experiment agreed with the calculation confirming the accuracy of the neutron spectroscopy system. However the presence of discrepancies at other times and energies suggested that there are significant inconsistencies in the inelastic cross sections in the 1 to 6 MeV range. The time response generated concurrently with the energy spectra was compared to the Monte Carlo calculation. From this comparison and from examination of time spectra measured by other workers using 235U and 237Np fission detectors it would appear that there are discrepancies in the ENDF/B-IV cross sections below 1 MeV. The predicted decay rates were too low below and too high above 0.8 MeV.
- ItemNeutron energy spectra from the thick target beryllium 9(d,n) boron 10 reaction.(Australian Atomic Energy Commission, 1976-12) Whittlestone, SThe energy spectrum of neutrons emitted when deuterons impinge on a thick beryllium target has been measured using an NE213 scintillation detector and the time-of-flight technique. Spectra were measured at angles of 0, 30, 45, 60, 90, 120 and 150º for deuteron energies of 1.4, 1.8, 2.3 and 2.8 MeV. Tables are presented of these angle-dependent energy spectra, the angle-integrated energy dependent yields, and the total neutron yield as a function of deuteron energy.
- ItemSquare and sine wave modulation of the beam from a 3 MeV Van de Graaff accelerator(Australian Atomic Energy Commission, 1967-09) Fraser, HJ; Ritchie, AIM; Whittlestone, SMethods of producing square and sine wave modulation of a 3 MeV Van de Graaff accelerator are described. Square pulses are produced at frequencies from 100kc/s to d.c. with up to a 100 per cent duty cycle and a minimum pulse length of 8 μs. The ratio of the off-current level to the on-current level is less than 5 x 10 -4 and can be further reduced by a post-acceleration deflection system to less than 10 -5. The unit, which is triggered from a command pulse external to the machine, is in the top terminal of the Van de Graaff and has shown itself to be highly reliable over some 1,000 hours of machine operation. The sine wave modulation unit described here operates in the range 80-1000 c/s with a modulation depth of up to 90 per cent and higher harmonic contamination of less than 1 per cent.
- ItemA time-of-flight measurement system using the elevated target facility for the AAEC 3 MV Van de Graaff accelerator(Australian Atomic Energy Commission, 1977-09) Whittlestone, SNeutron time-of-flight measuring system is described. A 3 MV Van de Graaff accelerator is equipped with a beam pulsing system which can produce pulses as narrow as 3 ns FWHM with residual beam less than 10" times the peak current. An elevated target station reduces scattered neutron and gamma-ray background by more than a factor of four compared with a conventional near-ground location. Neutrons are detected by an NE213 scintillator, for which construction and calibration details are given. A computer-based control and data acquisition system allows automatic measurements of angular distributions.