LNGS Wiki Pages

Newly processed dataset

new discrimination parameter:

• For selecting the ¹⁵²Gd alpha decay events: nSigmaBetaGamma < -3 ;
  
• For selecting the high energetic alpha peaks: Chi2 < 0.004 && nSigmaBetaGamma < -4.5
  

As an example, pile-up events are seen below:

1.) ¹⁴⁷Sm contamination (Q_alpha = 2311 keV)

• Identify the two peaks so we might improve the calibration curve and extract the contamination value
  
• Fit the alpha peak with a double Gaussian function (see below);
  
• Fitting results: Gaus1_mean: 9482.44, Gaus1_sigma: 341.22; Gaus2_mean: 9658.52, Gaus2_sigma: 427.95; chis/ndf = 1.33
  
• Problem: the mean values are not consistent with the calibration scale

2.) Extract events number from the two alpha triplets

• Convert the number of events to the specific activity (mBq/kg) for the contamination values;
• Starting from the possible highest energy, namely ²¹⁹Rn → ²¹⁵Po, and then trace back to ²²³Ra → ²¹⁹Rn (see below) ;
• Remove the previous triplet events, and look for the ²²⁰Rn → ²¹⁶Po (see below), and trace back to ²²⁴Ra → ²²⁰Rn
  

Note that the Previous (S.) is taken from entries for the Gaussian fit.

3.) Search for the ²²²Rn → ²¹⁸Po decays of the ²³⁸U decay chain

• Firstly, apply the coincident cuts and remove the two triplet events;
  
• Then, select the first events in the range of (28000, 34000) and the second events of (34000, 38000);
  
• Fit the distribution of the time difference between two consecutive events, and got another value instead of 3.1 min;
  
• Check the “Integral vs Time difference” 2D plot (an example seen below), which is flat;
  
• Conclusion: the signal is not found

4.) Search for the ²¹⁴Bi → ²¹⁴Po decays of the ²³⁸U decay chain

• Firstly, apply the coincident cut and remove the 7526 keV alpha events;
  
• Select beta events in the energy range of (50000, 90000) with the nSigmaBetaGamma (0, 4.5);
• Check the “Integral vs Time difference” 2D plot (an example seen below)

5.) Search for the ²¹²Bi → ²⁰⁸Tl decays of the ²³²Th decay chain|