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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 SignorelliINFN Sezione di Pisa

Updates on the Calibrations of the MEG

detector

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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

Reaction Resonance energy peak -lines

Li(p,)Be 440 keV 5 mb 17.6 MeV, 14.6 MeV

B(p,)C 163 keV 2 10-1 mb 4.4 MeV, 11.7 MeV, 16.1 MeV

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Legnaro VdG Properties

Energy [keV] 400-2000 300-900

Energy spread (FWHM) [keV] 15 <0.5

Angular divergence (FWHM)[mrad2] - < 3 x 3

Spot size at 3 m (FWHM) [cm] < 0.5 x 0.5 < 1x 1

Energy setting reproducibility [%] 0.2 0.1

Energy stability (FWHM) [%] 0.2 0.1

Range of the average current [A] 0.1-1 1-100

Current stability [%] 10 3

Current reproducibility [%] 10 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

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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 , 4 inch h) 1.5% solid angle

Thin Al target tube (9 cm 1mm thick) Target at 45o wrt the proton beam

Multichannel analyzer

p beam

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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 Target support

Requested Produced

material Thickness (m ) Energy loss (keV)

LiF 0.12 10 0.11±0.02

LiF 1.41 120 1.34±0.05

LiF 4.74 500 4.72±0.12

B 3 ≈300 1.84±0.18

Quartz balance

Boron target

LiF target

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Target holder

DiaphragmsTube

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

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Natural radioactivity

Fluorine lines

I = 90 nATarget: LiFThickness = 4.78 mTp = 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

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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) = 17.97 0.03 (keV) = 452.4 ± 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!

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Large NaI Energy Resolution

(E)/E = 3.09 ± 0.03 % (at 17.6 MeV)

I ~ 90 nATp = 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

40K (1.460 MeV) 214Bi (1.764 MeV) 214Bi (2.204 MeV) 208Tl (2.601 MeV)

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>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 nAThickness = 1.84 mTp = 500 keV

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R = 16 Hz @600 keVR = 5 Hz @500 keVR = 3 Hz @400 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 -line Li -line

Natural radioactivity

B -line

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4.44 MeV1st escape

2th 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 - 11.6 MeV pairs! Coincidence rate compatible with expectations

Foreseen coincidence rate in MEG calorimeter ~ 1 Hz/A

4.4 MeV Spectrum on small NaI

13Full 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 conditionssimilar to the ones foreseen for MEG, was rich in suggestions useful tothe design of the final MEG calibration equipments”

(New MEG internal note)

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New MEG internal note

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SORAD -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

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241Am in Gas Xenon

In gas xenon there is no difference between americium and polonium sources.

QE determination in gas ok.

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...but in liquid No more rings as in the

210Po case

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…simulated!

200 m

100 m thicktungsten wire

50 m thick goldplate clippedaround the wire

Our MC simulation is good! An investigation with the

factory is in progress to improve the symmetry.

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…in Italy it is carnival time

Can you guess how I am going to be dressed?

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I will be a Lxe detector!

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