2,923 research outputs found
Precise measurement of the 222Rn half-life: a probe to monitor the stability of radioactivity
We give the results of a study on the 222Rn decay we performed in the Gran
Sasso Laboratory (LNGS) by detecting the gamma rays from the radon progeny. The
motivation was to monitor the stability of radioactivity measuring several
times per year the half-life of a short lifetime (days) source instead of
measuring over a long period the activity of a long lifetime (tens or hundreds
of years) source. In particular, we give a possible reason of the large
periodical fluctuations in the count rate of the gamma rays due to radon inside
a closed canister which has been described in literature and which has been
attributed to a possible influence of a component in the solar irradiation
affecting the nuclear decay rates. We then provide the result of four half-life
measurements we performed underground at LNGS in the period from May 2014 to
January 2015 with radon diffused into olive oil. Briefly, we did not measure
any change of the 222Rn half-life with a 8*10^-5 precision. Finally, we provide
the most precise value for the 222Rn half-life: 3.82146(16){stat}(4){syst}
days.Comment: Accepted for publication in Physics Letters B, 6 pages, 6 figure
Search for correlations between solar flares and decay rate of radioactive nuclei
The deacay rate of three different radioactive sources 40K, 137Cs and natTh
has been measured with NaI and Ge detectors. Data have been analyzed to search
for possible variations in coincidence with the two strongest solar flares of
the years 2011 and 2012. No significant deviations from standard expectation
have been observed, with a few 10-4 sensitivity. As a consequence, we could not
find any effect like that recently reported by Jenkins and Fischbach: a few per
mil decrease in the decay rate of 54Mn during solar flares in December 2006.Comment: 5 pages, 3 figure
Search for time modulations in the decay rate of 40K and 232Th
Time modulations at per mil level have been reported to take place in the
decay constant of about 15 nuclei with period of one year (most cases) but also
of about one month or one day. In this paper we give the results of the
activity measurement of a 40K source and a 232Th one. The two experiments have
been done at the Gran Sasso Laboratory during a period of about 500 days, above
ground (40K) and underground (232Th) with a target sensitivity of a few parts
over 10^5. We also give the results of the activity measurement at the time of
the X-class solar flares which took place in May 2013. Briefly, our
measurements do not show any evidence of unexpected time dependence in the
decay rate of 40K and 232Th.Comment: version accepted for publication (Astroparticle Physics
Silica-based bioactive solids obtained from modified diatomaceous earth to be used as antimicrobial filler material
It is well known that microbiological spoilage in indoor surfaces has a negative impact on human health. Antimicrobial functionalized materials are intensely studied. The present work seeks the synthesis of eco-friendly and cheap bioactive hybrid filler from diatomaceous earth (DE). The activation method used proved to be efficient to enhance the amount of quaternary ammonium groups supported by DE which was corroborated by spectroscopic methods and the thermogravimetry analysis. Zeta potential measurements reviled a bilayer arrangement of the ammonium groups on the functionalized solids and the bioassays showed their antimicrobial activity.Facultad de Ingenierí
A Bayesian Networks Approach to Operational Risk
A system for Operational Risk management based on the computational paradigm
of Bayesian Networks is presented. The algorithm allows the construction of a
Bayesian Network targeted for each bank using only internal loss data, and
takes into account in a simple and realistic way the correlations among
different processes of the bank. The internal losses are averaged over a
variable time horizon, so that the correlations at different times are removed,
while the correlations at the same time are kept: the averaged losses are thus
suitable to perform the learning of the network topology and parameters. The
algorithm has been validated on synthetic time series. It should be stressed
that the practical implementation of the proposed algorithm has a small impact
on the organizational structure of a bank and requires an investment in human
resources limited to the computational area
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