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

Need of radioactivity analysis and monitoring 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)

Average power – not more than 1.2 W Interface – RS232 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

“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

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

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

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

Fitmodel: Exponential + Gaussian 26/04/2017 Spectrum of 22Na Fitmodel: Exponential + Gaussian χ²/ndf =1.3

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

26/04/2017 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

experimental data calibration curve ADC channel

Energy Resolution

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

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

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

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

Monthly Mean Values σ = 0.1 11.7 Bq/l

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

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