1. Possible calibration methods for the final LXe calorimeter A. Papa 01/20/2004

2. The motivations a frequent and precise check of the calorimeter stability even 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 (FWHM) means:

3. Thermal neutron capture Possible 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 in moderator ~ 3 cm of the tungsten Neutron lines: 4.5 or 14 MeV (d-d or d-t reaction respectively) Typical intensity is 10 6 n/s or 10 8 n/s Typical pulse rate and pulse width 10 Hz and 1 μs Possible separation of direct from delayed reactions Price ~ 10000 $ Counts 010 MeV

4. Precise calibration rarely performed γ‘s fromdecay(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)

5. 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 8.5348.1227.698 MeV 0

6. Neutron in the Large Prototype recent measurement γ energy spectrum 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

7. 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)

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