Possible calibration methods for the final LXe calorimeter

1. Possible calibration methods for the final LXe calorimeter A. Papa 02/11/2004 1

2. The motivations (FWHM) implies: An energy resolution of a frequent and precise check of the calorimeter stability even during the normal data acquisition 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 2

3. Precise calibrationrarely performed θ (degrees) • γ’s from decay (E(γ) ~ 54.9 MeV): use of a liquid hydrogen target recently tested with full success E (MeV) • Optional calorimeter calibration over range of γ energies: • γ’s from a tagged electron beam • (small magnet + MWPC’s) 3

4. Frequent calibrations 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 3) Thermal neutron capture Possible neutron sources: A) Am/Be (~ 10 KBq) B) Pulsed neutron generator Two neutron lines: at 4.5 or 14 MeV 0 12 MeV • Time separation of direct from • delayed reactions • Correlation: γ at 4.43 MeV and • n between 2-6 MeV 4

5. Frequent calibration …again about pulsed neutron generator Commercially produced (Price ~ 10000$) Already used for the boron therapy, luggage screening etc. switchable on-off • D + 2H 3He + n Q = 3.27 MeV • D + 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 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 5

6. Caution in the use of n-source(n-activation) Results: 6 Neutron activation calculator:http://www.antenna.nl/wise/uranium/rnac.html

7. 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 9.0 8.534 8.122 7.698 9.0 MeV • Plate on calorimeter wall • Single γemission highly probable 52.7% • E(γ) =9.0 MeV • (used in Super Kamiokande) 52.7% 25.6% 4.65% 1.28% 7 0

8. Neutrons in the Large Prototype recent measurement The neutron source was Am/Be (2 KBq) + diffused thermal neutron background in the experimental hall ( (?) note TN022 ) 4.43 MeV Without moderator γ energy spectrum 4.43 MeV γ energy spectrum n-edge n-edge and 9.3 MeV ADC With moderator (5 cm paraffin too thin! But space limitations) ADC 8

9. Neutron calibration:other possibilities • Isotope activation in targets far from the detector with neutron • generator or intense neutron sources • No neutron on calorimeter (apart from hall background) • E(γ) = 6.13 MeV • Decay constant τ = 7.2 s or Possible reaction: Target: teflon disk 2) Nitrogen laser UV: emission line at ~ 300 nm; use of optical fibers and a small diffuser • Gain and relative QE measurements 175 nm is PMT independent? 14 nm (FWHM) 9

10. γ γ NaI γ n LH2 Calibration from the calorimeter back Beam for calibration Normal beam Interesting possibility? π- μ+ • Liquid hydrogen target • permanently mounted close to • the Xenon calorimeter • π -/μ+ switching LXe Possibility of introducing also other particles (e-,e+ , π+,μ+ ) Locally same photocatode coverage as on the front face? 10

11. Calibration and cryostat A choice must be made for the possible location of calibration ports before completing the cryostat final project 11

12. Conclusion • Possible calibration methods were examined • Extremely important for calorimeter stability checks • Improvements studies depend of geometry, modera- • tors, sources, reactions, etc. under way 12