1,049 research outputs found
Portable Gamma Spectrometry Surveys of Sites in Portugal in Support of the VADOSE Project
The VADOSE project involves the use of multiple techniques to evaluate dose rate variability
on different spatial scales. Several sites in central northern Portugal, mostly in the vicinity of
Aveiro, have been investigated.
As part of this investigation, portable gamma spectrometry techniques were used to map
areas of approximately 100x100m around each sampling location. The SUERC portable
gamma spectrometry system used consists of a 3x3â NaI(Tl) spectrometer with integral GPS
receiver. Measurements were conducted with 10s integration time. Maps of the dose rate
variability in each area were generated in the field, and used to confirm data quality and
coverage and identify any remaining locations that would benefit from further measurements
prior to leaving the site. Maps of natural radionuclide distribution (40K, 214Bi from the 238U
decay series, and 208Tl from the 232Th decay series) were produced after the conclusion of
measurements each day. Natural radionuclide specific activities (Bq kg-1
) were estimated
using a spectral windows method with stripping1
, using a working calibration assuming
planar geometry and uniform activity distribution. As agreed prior to the start of work, a
working calibration derived from field measurements and photon fluence calculations
conducted for similar detectors in the 1990s2
has been used here, with calibration parameters
given in the appendix.
This report presents the dose rate maps produced during the field work, with a very brief
description of the data. Summary statistics for each data set are presented in Table 1. All data
have been mapped using a UTM (zone 29T) grid, with the approximate location of ground
features added by hand as a guide. Further work could be conducted to produce more
accurate overlays of ground features. At each site in-situ gamma spectrometry measurements
were also conducted by ITN, and the data collected by the two detector systems and the soil
samples will be compared at a later date
From Family to Peer Setting: Food Choices of College Freshmen
Food Consumption/Nutrition/Food Safety,
A Comparison of Methods for Imposing Curvature on the Normalized Quadratic Indirect Profit Function
Research Methods/ Statistical Methods,
Luminescence Dating of Sediments from Ancient Irrigation Features, and Associated with Occupation of the Hinterland around Anuradhapura, Sri Lanka
This study supports a new investigation into the development and decline of irrigation and associated human activity in the Anuradhapura Hinterland, Sri Lanka (section 2). Optically stimulated luminescence (OSL) age determinations have been made for a variety of sediments from bund and tank systems, irrigation channels, palaeosols and ceramic scatter horizons in the Anuradhapura hinterland (section 3). The geomorphological and archaeological significance of the age determinations has been reviewed in the light of the luminescence results and the samplesâ depositional contexts, to constrain the deposition/formation dates of the sampled sediments integrate the OSL results with independent archaeological and historical expectations (section 6).
A total of 26 age determinations were made (section 5.3). Dose rate determinations were made using thick source beta counting, high-resolution gamma spectrometry, field gamma spectrometry, measured water contents and calculated cosmic dose rates (sections 4.2.1, 5.1). Equivalent dose determinations were made (sections 4.2.2, 5.2) using the OSL signals from sand sized grains of quartz separated from each sample. Dose rates ranged from 1.1 to 5.0 mGy/a, equivalent dose values ranged from 0.29 to 33 Gy. Age estimates for these samples ranged from 0.14 to 13 ka, the average being 2.9 ka ± 3.1 (section 5.3). Uncertainties on the age estimates were commonly 7% at
one standard error.
The OSL age estimates from the largest bund and some ceramic scatter sites were greater than 2000 BC. This is older than expected on archaeological grounds and further investigation of these sites may be warranted. The OSL results from the other samples in the present study date bund construction during the initial urbanisation of Anuradhapura c. 400BC, coincident with the major Nachchaduwa bund construction c. 300AD, and in the Late Iron Age / Early Mediaeval period c. 600AD. They date abandonment of one irrigation channel to the 8th Century AD and its infill up to the late 10th Century when Anuradhapura was finally sacked. A further 8 age estimates, from silts and colluvium, relate to the collapse of infrastructure in the Anuradhapura hinterland during the 10th century and continued landscape response during the 11th century, followed by the lead-in to restoration of the irrigation system during the colonial era
The Discovery of a High Redshift X-ray Emitting QSO Very Close to the Nucleus of NGC 7319
A strong X-ray source only 8" from the nucleus of the Sy2 galaxy NGC 7319 in
Stephan's Quintet has been discovered by Chandra. We have identified the
optical counterpart and show it is a QSO with . It is also a ULX
with . From the optical spectra of the QSO
and interstellar gas in the galaxy (z = .022) we show that it is very likely
that the QSO and the gas are interacting.Comment: 8 figures, 5 color, minimized ps siz
QSOs Associated with Messier 82
The starburst / AGN galaxy M82 was studied by Dahlem, Weaver and Heckman
using X-ray data from ROSAT and ASCA, as part of their X-ray survey of edge-on
starburst galaxies. They found seventeen unresolved hard-X-ray sources around
M82, in addition to its strong nuclear source, and other X-rays within the main
body of M82. We have measured optical point sources at these positions, and
have obtained redshifts of six candidates at the Keck I 10-m telescope, using
the low-resolution imaging spectrograph (LRIS). All six are highly compact
optical and X-ray objects with redshifts ranging from 0.111 to 1.086. They all
show emission lines. The three with the highest redshifts are clearly QSOs. The
others with lower redshifts may either be QSOs or compact emission-line
galaxies. In addition to these six there are nine QSOs lying very close to M82
which were discovered many years ago. There is no difference between optical
spectra of these latter QSOs, only two of which are known to be X-ray sources,
and the X-ray emitting QSOs. The redshifts of all fifteen range between 0.111
and 2.05. The large number of QSOs and their apparent association with ejected
matter from M82 suggest that they are physically associated with the galaxy,
and have large intrinsic redshift components. If this is correct, the absolute
magnitudes lie in the range -8 < M_v < -10. Also we speculate that the luminous
variable X-ray source which has been detected by Chandra in the main body of
M82 some 9 arcseconds from the center is another QSO in the process of ejection
from the nucleus, and propose some observational tests of this hypothesis.Comment: 16 pages aastex, 3 eps figures, accepted for publication on Ap
The Distribution of Redshifts in New Samples of Quasi-stellar Objects
Two new samples of QSOs have been constructed from recent surveys to test the
hypothesis that the redshift distribution of bright QSOs is periodic in
. The first of these comprises 57 different redshifts among all
known close pairs or multiple QSOs, with image separations 10\arcsec,
and the second consists of 39 QSOs selected through their X-ray emission and
their proximity to bright comparatively nearby active galaxies. The redshift
distributions of the samples are found to exhibit distinct peaks with a
periodic separation of in identical to that claimed
in earlier samples but now extended out to higher redshift peaks and 4.47, predicted by the formula but never seen before. The periodicity
is also seen in a third sample, the 78 QSOs of the 3C and 3CR catalogues. It is
present in these three datasets at an overall significance level -
, and appears not to be explicable by spectroscopic or similar
selection effects. Possible interpretations are briefly discussed.Comment: submitted for publication in the Astronomical Journal, 15 figure
Contrasting copper evolution in Omega Centauri and the Milky Way
Despite the many studies on stellar nucleosynthesis published so far, the
scenario for the production of Cu in stars remains elusive. In particular, it
is still debated whether copper originates mostly in massive stars or type Ia
supernovae. To answer this question, we compute self-consistent chemical
evolution models taking into account the results of updated stellar
nucleosynthesis. By contrasting copper evolution in Omega Cen and the Milky
Way, we end up with a picture where massive stars are the major responsible for
the production of Cu in Omega Cen as well as the Galactic disc.Comment: 5 pages, 4 figures; accepted for publication in MNRAS Letter
- âŠ