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Long-term record of tritium in precipitation – can we deduce influence of solar activity cycles on tritium production?

Krajcar Bronić, Ines; Borković, Damir (2021) Long-term record of tritium in precipitation – can we deduce influence of solar activity cycles on tritium production?. In: Jakšić, Aleksandar; Karamarković, Jugoslav, (eds.) INTERNATIONAL CONFERENCE ON RADIATION APPLICATIONS (RAP 2021). Niš, Srbija, Sievert Association, Niš, Serbia, p. 13 .

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Tritium (3H) is a natural cosmogenic isotope of hydrogen with the half-life of 12.32 years. It is formed in the upper atmosphere through reactions of thermal neutrons with 14N and oxidizes to tritiated water, H3HO, and thus as a part of water molecule enters the natural water cycle. Tritium is also an anthropogenically produced isotope, either “bomb-produced” or of technogenic source. Massive injections of 3H from weapons tests in the 1950s and 1960s, mostly in the Northern Hemisphere, caused an almost 100-fold increase in the tritium activity concentration in precipitation, known as the bomb peak that had its maximum during 1963. After the cessation of atmospheric nuclear weapons tests, a gradual decrease in 3H activity concentration in precipitation was observed worldwide approaching presently the natural pre-bomb level. The value of tritium for studying hydrologic processes was quickly recognized, and for the past five decades tritium has been widely used to obtain time scales for physical mixing processes in oceanographic and hydrologic systems, i.e., for dating of modern waters. However, the scientific value of tritium in precipitation for hydrological applications is no more as high as in the second half of the 20th century. Monitoring of tritium activity concentration, A, in monthly precipitation at a station in Zagreb (Croatia) has been performed since 1976. Long-term record exhibited a pattern typical of continental stations of the Northern Hemisphere. Seasonal variations were superposed on the basic decreasing trend of mean annual values until approximately 1996. The decrease in mean annual tritium activity concentration values continued after 1996, but to a much lesser extent. Data recorded between 1996 and 2019 resulted in a mean value of 8.5 ± 1.2 TU (1 TU represents one tritium atom per 1018 atoms of hydrogen, equivalent to 0.118 Bq l-1). Seasonal variations remained observable, with winter activities close to the natural pre-bomb 3H activity concentrations (<5 TU) and summer values up to 21 TU. The relation between the solar activity and production of some cosmogenic isotopes has already been proven. However, bomb-produced tritium in precipitation until about 1995 prevented studies on whether the natural production of tritium was influenced by variations in solar activities. The modulation of cosmogenic tritium production by an 11-year solar cycle has been recently shown in precipitation at several stations worldwide [Palcu et al., Sci. Rep. 2018, 8, 12813]: local maxima in the tritium activity concentration in precipitation were observed simultaneously with maxima in neutron flux (minima in sunspot numbers). Our long-term data will be evaluated by applying frequency analysis cross correlation analysis. The preliminary analysis has shown local maxima in mean annual values and larger variability in 1996, 2007, and 2018, when also neutron flux maxima where observed.

Item Type: Conference or workshop item published in conference proceedings (UNSPECIFIED)
Uncontrolled Keywords: Tritium activity concentration ; Precipitation ; Zagreb ; Cosmogenic tritium ; The solar cycle
Subjects: NATURAL SCIENCES > Physics
NATURAL SCIENCES > Interdisciplinary Natural Sciences
NATURAL SCIENCES > Interdisciplinary Natural Sciences > Environmental Science
Divisions: Division of Experimental Physics
Depositing User: Ines Krajcar Bronić
Date Deposited: 10 Nov 2021 15:34

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