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

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

3. γ’s fromdecay(E(γ) ~ 54.9 MeV): use of a liquid hydrogen target recently 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) 3 Precise calibration rarely performed

4. 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) 4 B) Pulsed neutron generator Two neutron lines: at 4.5 or 14 MeV Correlation: γ at 4.43 MeV and n between 2-6 MeV Time separation of direct from delayed reactions

5. Commercially produced (Price ~ 10000$) Already used for the boron therapy, luggage screening etc. D + 2 H 3 He + n Q = 3.27 MeV D + 3 H 4 He + n Q = 17.59 MeV Intensities from 10 6 n/s to 10 8 n/s Typical pulse rate and pulse width 10 Hz and 1 μs Time separation of direct from delayed reactions Frequent calibration 5 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

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

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 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 8.5348.1227.698 MeV 0 7

8. Neutrons in the Large Prototype recent measurement γ energy spectrum ADC Without moderator With moderator (5 cm paraffin too 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 4.43 MeV n-edge 4.43 MeV 8

9. Neutron calibration: other possibilities 1)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) 9 175 nm 14 nm (FWHM) Target: teflon disk

10. Calibration from the calorimeter back LXe π -π - μ +μ + 10 Liquid hydrogen target permanently mounted close to the Xenon calorimeter π - /μ + switching Locally same photocatode coverage as on the front face ? NaI LH 2 γγ γ n Normal beamBeam for calibration Interesting possibility? Possibility of introducing also other particles (e -,e +, π +,μ + )

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