BVR, 2006 February 15

1. Updates on the Calibrations of the MEG detector Giovanni Signorelli INFN Sezione di Pisa -ray production by the reactions Li(p,)Be and B(p,)C tested at the Legnaro INFN Laboratory Monte Carlo simulation of point-like Americium a-sources BVR, 2006 February 15

2. Gamma line measurements Main method to check the energy scale and stability of the calorimeter on almost-daily basis We tested the calibration method by means of p(N,g)N’ reactions with the Legnaro VdG accelerator coupled to a custom target tube with different home made targets: We studied the reliability of the method paying attention to: • Reactions rates at different energies • Different target thickness • Quality of the -lines

3. Legnaro VdG Properties • The Legnaro Van de Graaff proton accelerator has characteristics somewhat different from those of the foreseen MEG Cockroft-Walton. • Presence of a bending and focusing system Legnaro VdG MEG CW

4. Experimental set-up • Large square NaI detector (28 x 28 x 35 cm3) • 6.3% solid angle on average • Small cylinder NaI detector (4 inch f, 4 inch h) • 1.5% solid angle • Thin Al target tube (9 cm f, 1 mm thick) • Target at 45o wrt the proton beam • Multichannel analyzer p beam

5. Boron target Target production • Targets deposited on polished copper discs • Thermal evaporation • Lithium Fluoride • High vapor pressure @ low temperature • Good uniformity • Electron gun evaporation • Boron • High melting point • Slow deposition - tends to explode LiF target Quartz balance Target support

6. Target supporting pipe • Beam monitoring and current measurements (normalization) • Isolated tube (Faraday cup) • Series of the diaphragms • Preliminary centering of the beam • Light from protons on CsI with perspex window Target holder Diaphragms Tube

7. Li(p,)Be reaction • Target:LiF “easier” to prepare compared to Li alone • Fluorine has a large cross section for gamma production • The raw spectrum shows radioactivity, F lines and Li lines I = 90 nA Target: LiF Thickness = 4.78 m Tp = 500 keV Natural radioactivity Fluorine lines Li(p, 1) at 14.6 MeV Li(p, 0) at 17.6 MeV Cosmics in NaI

8. LiF target excitation curve • Number of collected photons in Li peak as a function of the proton energy • We checked the energy scale and resolution of Legnaro VdG! Thick target: during slowing down in target all protons eventually reach the resonance Thickness = 1.34 m Thin target: only resonant protons do react Thickness = 0.11 m (keV) = 17.97 ± 0.03  (keV) = 452.4 ± 0.5 (keV) = 10 ± 1  (keV) = 446 ± 1

9. The 17.6 MeV -line • Gamma lines from natural radioactivity are used to calibrate the energy scale 40K (1.460 MeV) 214Bi (1.764 MeV) 214Bi (2.204 MeV) 208Tl (2.601 MeV) Large NaI Energy Resolution (E)/E = 3.09 ± 0.03 % (at 17.6 MeV) I ~ 90 nA Tp = 500 keV Rate(17.6 MeV) on LXe = 1.8 kHz / mA

10. B(p,)C reaction • From the de-excitation of Carbon ~ 94% of the times the 16.1 level decays in two photons • Three energetic gamma lines • Powerful tool to explore the capability of the MEG calorimeter to reject pile-up events. >16.1 MeV >11.7 MeV 4.4 MeV I = 240 nA Thickness = 1.84 m Tp = 500 keV Background subtracted

11. Boron single rates • The Legnaro VdG could not reach at the correct energy (too low) • Production rate increases with energy (see cross section in previous slide) • The 11.6 MeV and 16.1 MeV lines undergo Doppler-shift • No good energy reference for this test • MEG CW accelerator will be operated at the correct energy! • Foreseen single rate of the 16.1 MeV line ~ 1 Hz/mA in MEG calorimeter Natural radioactivity B -line R = 16 Hz @600 keV R = 5 Hz @500 keV R = 3 Hz @400 keV F -line Li -line

12. Coincident -lines • We triggered on the 11.6 MeV line on one detector and recorded the spectrum on the other NaI • Almost all coincidences were 4.4 MeV - 11.6 MeV pairs! • Coincidence rate compatible with expectations • Foreseen coincidence rate in MEG calorimeter ~ 1 Hz/mA 4.4 MeV Spectrum on small NaI 4.44 MeV 1st escape 2th escape

13. Conclusions • Good quality of the 17.6 MeV -line for the MEG calibration • Bad quality of the 16.1 MeV -line at Tp = 500 keV • Good quality of the 4.4 MeV -line • The MEG CW will be operated at lower energy • Boron as a source of coincident ’s • Study of pile-up rejection capability • Good agreement of the rates between predictions and experimental data “The use of an electrostatic machine for several days, under conditions similar to the ones foreseen for MEG, was rich in suggestions useful to the design of the final MEG calibration equipments” (New MEG internal note) Full success of the Legnaro test

14. New MEG internal note MEG TN032

15. SORAD a-source Photos • Am sources much larger half-life (kyears instead of 130 days) • Difficult to prepare • 210Po electrodeposited • Not possible for 241Am • Clipping of Au foils on thin wire

16. 241Am in Gas Xenon • In gas xenon there is no difference between americium and polonium sources. • QE determination in gas ok.

17. ...but in liquid • No more rings as in the 210Po case

18. …simulated! • Our MC simulation is good! • An investigation with the factory is in progress to improve the symmetry. 50 mm thick gold plate clipped around the wire 100 mm thick tungsten wire 200 mm

19. …in Italy it is carnival time • Can you guess how I am going to be dressed?

20. I will be a Lxe detector!