65 research outputs found
Scintillation efficiency measurement of Na recoils in NaI(Tl) below the DAMA/LIBRA energy threshold
The dark matter interpretation of the DAMA modulation signal depends on the
NaI(Tl) scintillation efficiency of nuclear recoils. Previous measurements for
Na recoils have large discrepancies, especially in the DAMA/LIBRA modulation
energy region. We report a quenching effect measurement of Na recoils in
NaI(Tl) from 3keV to 52keV, covering the whole
DAMA/LIBRA energy region for light WIMP interpretations. By using a low-energy,
pulsed neutron beam, a double time-of-flight technique, and pulse-shape
discrimination methods, we obtained the most accurate measurement of this kind
for NaI(Tl) to date. The results differ significantly from the DAMA reported
values at low energies, but fall between the other previous measurements. We
present the implications of the new quenching results for the dark matter
interpretation of the DAMA modulation signal
Source Evaluation and Trace Metal Contamination in Benthic Sediments from Equatorial Ecosystems Using Multivariate Statistical Techniques
race metals (Cd, Cr, Cu, Ni and Pb) concentrations in benthic sediments were analyzed through multi-step fractionation scheme to assess the levels and sources of contamination in estuarine, riverine and freshwater ecosystems in Niger Delta (Nigeria). The degree of contamination was assessed using the individual contamination factors (ICF) and global contamination factor (GCF). Multivariate statistical approaches including principal component analysis (PCA), cluster analysis and correlation test were employed to evaluate the interrelationships and associated sources of contamination. The spatial distribution of metal concentrations followed the pattern Pb>Cu>Cr>Cd>Ni. Ecological risk index by ICF showed significant potential mobility and bioavailability for Cu, Cu and Ni. The ICF contamination trend in the benthic sediments at all studied sites was Cu>Cr>Ni>Cd>Pb. The principal component and agglomerative clustering analyses indicate that trace metals contamination in the ecosystems was influenced by multiple pollution sources
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