Measurement and simulation Measurement and simulation of the neutron response and detection efficiency of the neutron response and detection efficiency of a Pb Pb – – scintillating scintillating fiber fiber calorimeter calorimeter of a A. Ferrari A. Ferrari Fondazione CNAO ( CNAO (Milano Milano) ) Fondazione Anna Ferrari VCI 2007, Wien, February 22nd, 2007 1
The KLOE Pb Pb- -scintillating scintillating fiber fiber calorimeter calorimeter The KLOE Designed and put in operation as e.m. calorimeter Active material : • 1.0 mm diameter scintillating fiber (Kuraray SCSF-81, Pol.Hi.Tech 0046), emitting in the blue-green region: λ Peak ~ 460 nm. 1.0 mm 1.2 mm 1.35 mm • Core: polystyrene, ρ =1.050 g/cm 3 , n=1.6 High sampling structure: • 200 layers of 0.5 mm grooved lead foils (95% Pb and 5% Bi). • Glue: Bicron BC-600ML, 72% epoxy resin, 28% hardener. • Lead:Fiber:Glue volume ratio = 42:48:10 Good performance in time and energy response: σ (E)/E = 5.7 %/ √ E(GeV) σ (t)= 54 ps/ √ E(GeV) and high photon efficiency see NIMA 482 (2002) 364-386 Anna Ferrari VCI 2007, Wien, February 22nd, 2007 2
Why looking looking for for neutron neutron detection detection efficiency efficiency ? ? Why � Detection of neutrons of few to few hundreds of MeV is traditionally performed with organic scintillators (principle of operation: elastic neutron scattering on H atoms, with production of protons detected by the scintillator itself) ⇒ efficiency scales with thickness ⇒ ~ 1%/cm � On the other hand, the extended range extended range rem rem counters counters used in radiation protection are based on a structure scintillator/medium-high Z material, which enhances the neutron efficiency see C. Birattari, A.Ferrari, M.Pelliccioni et al., NIMA 297 (1990) 250-257, NIM A 338 (1994) 534-543 An estimate with KLOE data ( n are produced by K - interactions in the apparatus walls) gave: ε ∼ 40% for low energy neutrons (E kin ≤ 20 MeV) , confirmed by KLOE MC ( expected: ∼ 10% ) n are important - Measurement of the neutron e.m. form factors in the time-like region (DANTE) for the DA Φ NE-2 - Search for deeply bounded kaonic nuclei (AMADEUS) program @ LNF FLUKA code, which is � an intense Monte Carlo study has been performed with the FLUKA � an intense Monte Carlo study has been performed with the FLUKA code, which is well validated for the hadronic physics, till the low energy region well validated for the hadronic physics, till the low energy region � an experimental test has been carried out with the neutron beam � an experimental test has been carried out with the neutron beam of the The Svedberg Laboratory of Uppsala (October 2006) of the The Svedberg Laboratory of Uppsala (October 2006) [with TARI program support] [with TARI program support] Anna Ferrari VCI 2007, Wien, February 22nd, 2007 3
The neutron neutron beam beam line at TSL line at TSL The KLOE calorimeter KLOE calorimeter module module KLOE calorimeter module 5.31 m � A quasi-monoenergetic neutron beam is produced in the reaction 7 Li(p,n) 7 Be. � 42% of neutrons at the max energy � The absolute neutron flux in the peak is measured after the collimator by 2 monitors of the beam intensity. Accuracy: ~ 10% E KIN (MeV) Anna Ferrari VCI 2007, Wien, February 22nd, 2007 4
The experimental experimental setup setup and the data set and the data set The last plane not integrated in the ( 1 ) Old prototype of the KLOE calorimeter: acquisition system 60 cm long, 3 x 5 cells (4.2 x 4.2 cm 2 ), read out at both ends by Hamamatsu/Burle PMTs ( 2 ) Beam position monitor: array of 7 scintillating counters, Y 1 cm thick. X Z n (3) ( 3 ) Reference counter: NE110, 10×20 cm 2 , 5 cm thick (2) A rotating frame allows for: - vertical positions (data taking with n beam) - horizontal positions (calibration with cosmic rays) (1) � For each configuration, several scans with different trigger thresholds � Typical run: 0.5-1.5 Mevents, 1.7 kHz DAQ rate � 3 large data sets collected with different � Cosmic rays run (beam off) for calibrations with beam intensities: 1.5 kHz/cm 2 , 3.0 kHz/cm 2 MIPs. and 6.0 kHz/cm 2 Anna Ferrari VCI 2007, Wien, February 22nd, 2007 5
The measurement measurement of the of the global global efficiency efficiency The I. The The method method I. Global efficiency measurement Global efficiency measurement integrated on the full spectrum R TRIGGER ε = R NEUTRON × f LIVE × α R NEUTRON : from beam monitor via neutron f LIVE : live time fraction flux intensity measured by TSL. α : for preliminary measurement, assume full acceptance and no R TRIGGER : use coincidence between sides. background • Scintillator: T1 trig = Side 1 × Side 2 • Calorimeter: use the analog sum of 12 PMs/side (first four planes) T1 trig = Σ A × Σ B Anna Ferrari VCI 2007, Wien, February 22nd, 2007 6
II. The scintillator scintillator efficiency efficiency II. The � The measurement of the scintillator efficiency gives a cross calibration of the measurement method and of the beam monitor accuracy, with small corrections due to the live time fraction � The energy scale was calibrated with a 90 Sr β source. 10% accuracy for horizontal scale (threshold) and the vertical one ( ε ) ε (%) Results agree with “thumb rule” (1%/cm): 5% for 5 cm thick scintillator (with a threshold of ∼ 2.5 MeV electron equivalent energy) Agreement within errors with previous published measurements in the same energy range, after a rescaling of them to our thickness Threshold (MeV e − equiv. energy) Anna Ferrari VCI 2007, Wien, February 22nd, 2007 7
III. The calorimeter calorimeter efficiency efficiency III. The ε (%) � Energy scale setting done by MIP ε calibration of all channels, and using the MIP/MeV scale factor used in KLOE � 10% uncertainty on both horizontal and vertical scales � Stability wrt very different run conditions: a factor 4 variations of both live time fraction (e.g. f LIVE =0.2 → 0.8) and beam intensity (1.5 → 6.0 kHz/cm 2 ). Thr (MeV e − equiv. energy) Very high efficiency , about 4 times Very high efficiency Very high efficiency , about 4 times larger than the expected if only the amount of larger than the expected if only the amount of Compare with our scintillator scintillator is taken into account: ~ 8% for 8 cm scintillator is taken into account: ~ 8% for 8 cm efficiency measurement, of scintillating fibers. of scintillating fibers. scaled by the scintillator ratio factor 8/5 Anna Ferrari VCI 2007, Wien, February 22nd, 2007 8
The neutron neutron spectrum spectrum from from ToF ToF The n � Correct raw spectra for T0 and convert into ns ToF (ns) � Since the trigger is phase locked with the RF ( time structure: 45 ns), rephasing is needed for neutrons with E kin < 50 MeV (5.3 m far from the target) � From ToF spectrum obtain β of the neutron � Assuming neutron mass, obtain E kin Anna Ferrari VCI 2007, Wien, February 22nd, 2007 9
Energy vs vs ToF ToF Energy � The collected charge is here expressed as the energy of an electron that gives the same charge response Energy released vs Energy released vs ToF ToF Charge response Charge response Energy (MeV eq. el.) ToF (ns) Energy (MeV eq. el.) threshold: 15 mV Anna Ferrari VCI 2007, Wien, February 22nd, 2007 10
The calorimeter calorimeter simulation simulation with with FLUKA FLUKA The LEAD base module � Using the FLUKA tool LATTICE the fiber structure of the whole calorimeter module has been designed. � In the base module the calorimeter is GLUE FIBERS simulated in detail, both under the geometrical point of view and with respect replicas to the used materials � All the compounds have been carefully simulated. - for the fibers, an average density between cladding and core has been used : ρ = 1.044 g/cm 3 - glue: 72% epoxy resin C 2 H 4 O, ρ =1.14 g/cm 3 , 200 layers + 28% hardener, ρ =0.95 g/cm3 Polyoxypropylediamine C 7 H 20 NO 3 90% hardener composition Triethanolamine C 6 H 15 NO 3 7% Aminoethylpiperazine C 6 H 20 N 3 1.5% Diethylenediamine C 4 H 10 N 2 1.5% Anna Ferrari VCI 2007, Wien, February 22nd, 2007 11
The readout simulation The readout simulation Fluka gives energy deposits in the fiber. The light is propagated by hand at the end of the fiber taking into account the attenuation. The energy read-out has been simulated by including: the generation of photoelectrons the generation of photoelectrons � � the constant fraction distribution the constant fraction distribution � � the discriminator threshold. the discriminator threshold. � � No trigger simulation is included at the moment. � The simulation of the Birks effect The simulation of the Birks effect The energy deposits are computed in Fluka taking into account the Birks effect , that is the saturation of the light output of a scintillating material when the energy release is high, due to the quenching interactions between the excited molecules along the path of incident particles: In literature and in GEANT: dL/dx = k dE/dx / [ 1 + c 1 dE/dx + c 2 (dE/dx) 2 ] c 1 = 0.013 c 2 = 9.6×10 -6 Anna Ferrari VCI 2007, Wien, February 22nd, 2007 12
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