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GEMS: UNDERWATER SPECTROMETER FOR LONG-TERM RADIOACTIVITY MEASUREMENTS

GEMS: UNDERWATER SPECTROMETER FOR LONG-TERM RADIOACTIVITY MEASUREMENTS. Sartini L., Simeone F., Pani P., Lo Bue N.,Marinaro G., Grubich A., Lobko A., Etiope G., Capone A., Favali P.,Gasparoni F., Bruni F. for the KM3NeT Consortium.

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GEMS: UNDERWATER SPECTROMETER FOR LONG-TERM RADIOACTIVITY MEASUREMENTS

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  1. GEMS: UNDERWATER SPECTROMETER FOR LONG-TERM RADIOACTIVITY MEASUREMENTS Sartini L., Simeone F., Pani P., Lo Bue N.,Marinaro G.,Grubich A., Lobko A., Etiope G., Capone A., Favali P.,Gasparoni F., Bruni F. for the KM3NeT Consortium

  2. GEMS(Gamma Energy Marine Spectrometer) is a prototype of an autonomous radioactivity sensor for underwater measurement, developed in the framework of the KM3NeT Dessign Study Project. The spectrometer is sensitive to gamma rays produced by 40K decay and it’s suitable to detect total gamma spectrum in ocean seawater Need of radioactivity analysis and monitoring 40K (source of background for PMT's) is not only contained in sea salt but also in suspended matter and sediments Benthic sediment mobilisation, bottom currents, far-field landslides, volcanic fall-out and other processes may induce 40K variations Seawater 40K (12 Bq/kg) particulate salt diffusion Sediments 40K (225 Bq/kg)

  3. 40K ≥ 10 Bq/Kg Dimensions: 190x460 mm Sensor – NaI(Tl) 150x100 mm Supply voltage – 12 V Average power – not more than 1.2 W Interface – RS232

  4. “Marinisation” The process of adaptation of the Sensor into a version capable to operate in deep-sea conditions, into a Seafloor Observatory or integrated into a multisensor probe

  5. Analysis of Calibration Data ---Background Noise ---- 137Cs Data • 137Cs • 133Ba • 60Co • 22Na

  6. Spectrum of 137Cs Fitmodel: Fermi-Dirac+ Gaussian χ²/ndf = 5

  7. Spectrum of 60Co Fitmodel: Fermi Dirac + Gaussian χ²/ndf =2.7

  8. Spectrum of 22Na Fitmodel: Exponential + Gaussian χ²/ndf =1.3

  9. Spectrum of 40K Fitmodel: Exponential + Gaussian χ²/ndf =7.4

  10. Fit: Y=mx+q 40K m1 = (353.62 ± 0.12) [Channel/MeV ] q1 = (6.974 ± 0.075)[Channel] 60Co χ²/ndf = 0.044 22Na m2=(309.8 ± 9.4) [ Channel/MeV] q2=(59 ± 14) [Channel] 137Cs χ²/ndf=16 133Ba

  11. experimental data calibration curve ADC channel

  12. Energy Resolution

  13. Deployment in the Capo Passero-site 3200 m depth 36°18.915’ N 16°65.531’ E

  14. Quality check on data collected GEMS, previously calibrated and set for an autonomous acquisition of six months-period, was deployed in mooring on the 4th November 2008 and recovered on 11th May 2009. During this period GEMS acquired 751 spectra (one spectra every 6h) A preliminary quality-check on the data shows that there aren’t any gaps or lacks in the acquisition series

  15. The peak of 40K is visible in every spectrum for the entire period of acquisition

  16. Time series analysis of 40K activity shows a very stable behaviour during the six months of deployment 12.1 Bq/l Bq/l 11.4 Bq/l Six Months Sample Number

  17. Monthly Mean Values σ = 0.1 11.7 Bq/l

  18. Preliminary Peaks Identification 40K-1460 KeV 214Bi-2614 KeV 214Bi-1760 KeV 208Tl-550 KeV 208Tl-2190 KeV

  19. Conclusions: • the instrument was built, calibrated and employed in a long-term monitoring with good results. • - Strong electronics • - No acquisition series incompleted • - Clean spectra • More refined analisys are in progress • Next Developments: • perform a Monte Carlo Simulation • extend the analysis to the other radionuclides • perform the study of the correlations with the oceanographic variables

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