1 1.  - ray production by the reactions Li(p,  )Be and B(p,  )C tested at the Legnaro INFN Laboratory 2.Monte Carlo simulation of point-like Americium  -sources BVR, 2006 February 15 Giovanni Signorelli INFN Sezione di Pisa Updates on the Calibrations of the MEG detector

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,  )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 ReactionResonance energy  peak  -lines Li(p,  )Be 440 keV 5 mb17.6 MeV, 14.6 MeV B(p,  )C 163 keV mb 4.4 MeV, 11.7 MeV, 16.1 MeV

3 Legnaro VdG Properties Energy [keV] Energy spread (FWHM) [keV]15<0.5 Angular divergence (FWHM)[mrad 2 ]-< 3 x 3 Spot size at 3 m (FWHM) [cm]< 0.5 x 0.5< 1x 1 Energy setting reproducibility [%] Energy stability (FWHM) [%] Range of the average current [  A] Current stability [%]103 Current reproducibility [%]10 Legnaro VdG MEG CW 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

4 Experimental set-up Large square NaI detector (28 x 28 x 35 cm 3 )  6.3% solid angle on average Small cylinder NaI detector (4 inch , 4 inch h)  1.5% solid angle Thin Al target tube (9 cm  mm thick)  Target at 45 o wrt the proton beam Multichannel analyzer p beam

5 Target production Targets deposited on polished copper discs Thermal evaporation  Lithium Fluoride  High vapor low temperature  Good uniformity Electron gun evaporation  Boron  High melting point  Slow deposition - tends to explode Target support RequestedProduced material Thickness (  m ) Energy loss (keV) LiF ±0.02 LiF ±0.05 LiF ±0.12 B3≈ ±0.18 Quartz balance Boron target LiF target

6 Target holder Diaphragms Tube 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

7 Natural radioactivity Fluorine lines I = 90 nA Target: LiF Thickness = 4.78  m T p = 500 keV Li(p,  0 ) at 17.6 MeV Li(p,  1 ) at 14.6 MeV 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 Cosmics in NaI

8 Thick target: during slowing down in target all protons eventually reach the resonance Thickness = 1.34  m  (keV) = 10 ± 1  (keV) = 446 ± 1 Thin target: only resonant protons do react Thickness = 0.11  m  (keV) =  0.03  (keV) = ± 0.5 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!

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

10 >16.1 MeV>11.7 MeV 4.4 MeV 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. Background subtracted I = 240 nA Thickness = 1.84  m T p = 500 keV

11 R = 16 keV R = 5 keV R = 3 keV 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/  A in MEG calorimeter F  -lineLi  -line Natural radioactivity B  -line

MeV 1 st escape 2 th escape 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 MeV pairs! Coincidence rate compatible with expectations  Foreseen coincidence rate in MEG calorimeter ~ 1 Hz/  A 4.4 MeV Spectrum on small NaI

13 Full success of the Legnaro test 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)

14 New MEG internal note

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

Am 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 210 Po case

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

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

20 I will be a Lxe detector!

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