Possible calibration methods for the final LXe calorimeter

A. Papa 02/11/2004

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The motivations

An energy resolution of

Causes for gain instabilities:

• Beam intensity variations• Variable background rates (photons and neutrons in the experimental hall)• Effects of the temperature T variation on the photocathode Q.E. and resistivity• Effects due to the capacitive coupling• Possible hysteresis phenomena as a function of T

4%E/E (FWHM) implies:

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a frequent and precise check of the calorimeter stability

even during the normal data acquisition

• γ’s from decay (E(γ) ~ 54.9 MeV): use of a liquid hydrogen targetrecently tested with full success

• Optional calorimeter calibration over range of γ energies:γ’s from a tagged electron beam (small magnet + MWPC’s)

θ (degrees)

E (MeV)

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Precise calibration rarely performed

Frequent calibrations

3) Thermal neutron capture

1) α from Am source in detector (already used)

2) γ from Am/Be source out of the detector • E(γ) = 4.43 MeV 60 % of Am decays

0 12 MeV

Possible neutron sources:

A) Am/Be (~ 10 KBq)

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B) Pulsed neutron generator

Two neutron lines: at 4.5 or 14 MeV

ndEdN

nE

• Correlation: γ at 4.43 MeV and n between 2-6 MeV

• Time separation of direct fromdelayed reactions

Commercially produced (Price ~ 10000$)Already used for the boron therapy, luggage screening etc.

D + 2H 3He + n Q = 3.27 MeVD + 3H 4He + n Q = 17.59 MeV • Intensities from 106 n/s to 108 n/s• Typical pulse rate and pulse width 10 Hz and 1 μs • Time separation of direct from delayed reactions

Frequent calibration

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Moderator:~ 10 cm of the polyethylene • 40% thermalized n• 10% n captured in moderator

γ shield:~ 3 cm of the tungsten or ~ 5 cm of the lead

…again about pulsed neutron generator

switchable on-off

Caution in the use of n-source (n-activation)

Neutron activation calculator:http://www.antenna.nl/wise/uranium/rnac.html 6

Results:

Thermal neutron capture

On Xe

• Absorption length ~ 3 cm• Capture close to calorimeter walls• Multi γ, Σ E(γ) = 9.3 MeV• Possible spill-out

On Ni

• Plate on calorimeter wall• Single γ emission highly probable 52.7%• E(γ) = 9.0 MeV (used in Super Kamiokande)

52.7% 25.6% 4.65% 1.28%

9.0 9.0 8.534 8.122 7.698 MeV

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Neutrons in the Large Prototype recent measurement

γ energy spectrum

ADC

ADC

Without moderator

With moderator (5 cm paraffintoo thin! But space limitations)

n-edge and 9.3 MeV

The neutron source was Am/Be (2 KBq) + diffused thermal neutron background in the experimental hall ( (?) note TN022 )

γ energy spectrum

12216 scmn

4.43 MeV

n-edge

4.43 MeV

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Neutron calibration: other possibilities1) Isotope activation in targets far from the detector with neutron generator or intense neutron sources

• E(γ) = 6.13 MeV• Decay constant τ = 7.2 s

Possible reaction: or

2) Nitrogen laser UV: emission line at ~ 300 nm; use of optical fibers and a small diffuser • Gain and relative QE measurements

is PMT independent?

• No neutron on calorimeter (apart from hall background)

)175(

)330(

nmQE

nmQE

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175 nm

14 nm (FWHM)

Target: teflon disk

Calibration from the calorimeter back

LXe

π - μ +

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• Liquid hydrogen target permanently mounted close tothe Xenon calorimeter• π -/μ+ switching

Locally same photocatode coverage as on the front face?

NaI

LH2

γ γ

γn

Normal beamBeam for calibration

Interesting possibility?

Possibility of introducingalso other particles (e-,e+ ,π+,μ+ )

Calibration and cryostatA choice must be made for the possible location of calibration ports

before completing the cryostat final project

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Conclusion

• Possible calibration methods were examined• Extremely important for calorimeter stability checks • Improvements studies depend of geometry, modera-tors, sources, reactions, etc. under way

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