Possible calibration methods for the final LXe calorimeter

A. Papa 01/20/2004

The motivations

a frequent and precise check of the calorimeter stabilityeven during the normal data acquisition

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) means:

Thermal neutron capturePossible source:

Pulsed neutron generator (commercially produced)(switchable on-off)

Am/Be (~10 KBq)

• Continuous n spectrum

Moderator: ~10-20 cm of the polyethylene

γ shield:

• 40% thermalized n• 10% n captured inmoderator~ 3 cm of the tungsten

•Neutron lines: 4.5 or 14 MeV (d-d or d-t reaction respectively) • Typical intensity is 106 n/s or 108 n/s• Typical pulse rate and pulse width 10 Hz and 1 μs • Possible separation of direct from delayed reactions • Price ~ 10000 $

Counts

0 10 MeV

Precise calibration rarely performed

• γ‘s from decay (E(γ) ~ 54.9 MeV): use of a liquid hydrogen target

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

θ (degrees)

E (MeV)

Calibrations to be frequently performed (A)

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

Capture on Ni plate on calorimeter wall • Single γ emission highly probable 52.7%• E(γ) = 9.0 MeV (used in SK)52.7% 25.6% 4.65% 1.28%

9.0 9.0 8.534 8.122 7.698 MeV

0

Neutron in the Large Prototyperecent measurement

γ energy spectrum

ADC

ADC

Without moderator (paraffin)

With moderator

Peak at 9.3 MeV

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

It can be improved: test with source on the calorimeter back and thicker moderator

γ energy spectrum

12216 scmn

Calibration to be frequently performed (B)

Other possibility (less recommanded):

Isotope activation far from detector with neutron generator and energetic neutron sources

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

Possible reaction: or

Nitrogen laser UV: emission line at ~ 300 nm; use of the optical fibre and a small diffusor

• Gain and relative QE measurements

is PMT independent?

• No neutron on calorimeter (apart from hall background)

)175(

)330(

nmQE

nmQE

Conclusion

• Possible calibration methods were examined• Extremely important for calorimeter stability checks • Improvements studies on geometry, moderators, sources, reactions, etc under way