An e.m. calorimeter on the Moon surface R.Battiston, M.T.Brunetti, F. Cervelli, C.Fidani MoonCal

Mooncal could : Resolve the difference of electrons spectra proposed by the many diffusion models for sources in the TeV region from Vela, Cygnus loop and Monogem Detect an excess of positrons and electrons by the excellent energy resolution and the observations with high statistics Provide complementary observations on gamma’s with respect to Glast by a better energy resolution above 100 GeV. Targets : Galactic and extra-Galactic diffuse components, supernova remnants, pulsars, AGN’s, GRB’s Observe line gamma rays from SUSY particles annihilation. As the energy resolution is better at higher energies,Mooncal will precisely measure the signature of line gamma rays Physics Perpectives O graziosa luna, io mi rammento che, or volge l’anno, sovra questo colle io venia pien d’angoscia a rimirarti G. Leopardi

The regolith as sampling material for an EM calorimeter

Simulation of Regolith Composition GEANT4 derives the Regolith Radiation Length (  0 ) from chemical composition and relative densities Regolith Radiation Length : 14.4 cm

Gamma Rays at 100 GeV: Energy Deposit vs Depth

Depth of Maximun Energy Deposit

Gamma Rays at 100 GeV: Total Energy Deposit vs Depth

Gamma Rays at 100 GeV: Tranverse Development

r = 1 cm L = 150 cm or L = 300 cm d = 7.5 cm Scintillator Geometry

The layout (1)

The layout (2)

The layout (3)

Gamma Ray at 100 GeV (1)

Gamma Ray at 100 GeV (2)

Gamma Ray at 100 GeV (3)

Gamma Ray at 100 GeV (4)

MoonCal simulation: Boundary conditions and restrictions CALORIMETER GEOMETRY: –Cylinder of 3 m radius and 1.5 m height filled with regolith and scintillators of 1 cm radius and 1.5 m height separated by 7.5 cm (on a xy grid). ENERGY RESTRICTIONS: –Lower energy cut for gammas  550 keV –Lower energy cut for electrons and positrons  1.4 MeV GEOMETRY RESTRICTIONS: –Incident angle: 45° ≤  ≤ 80°  longitudinal containment –Incident area: inside a disk of 1 m radius  lateral containment

Scintillator distance = 7.5 cm Scintillator radius= 1 cm Distance vs Scintillator Diameter (1)

The resolution  E/E has been fitted according to: RESULTS

Energy Resolution : d = 7.5

Scintillator distance = 4 cm Scintillator radius= 0.5 cm Distance vs Scintillator Diameter (2)

Energy Resolution: r = 0,5cm d= 4cm

Energy Resolution

Energy Resolution vs Incident Angle (1)

Energy Resolution vs Incident Angle (2)

Analysis Cuts: -First plot: resolution between 0.1 and 1 GeV with the following lower cuts: Gammas, electrons, positrons  1 keV -Second plot: resolution between 1 and 50 GeV with the following lower cuts: Gammas  2 keV, electrons  356 keV, positrons  347 keV Low Energies Studies

SiPM concept GM-APD gives no information on light intensity SiPM first proposed by Golovin and Sadygov in the mid ’90 A single GM-APD is segmented in tiny microdiodes connected in parallel, each with the quenching resistance. Each element is independent and gives the same signal when fired by a photon  output signal is proportional to the number of triggered cells that for PDE=1 is the number of photons Q = Q 1 + Q 2 = 2*Q 1 substrate metal

Features of a SiPM The characteristics of a SiPM are: capability to detect extremely low photon fluxes (from 1 to few hundred) giving a proportional information; extremely fast response (determined by avalanche discharge): in the order of few hundreds of ps. Other features are: Low bias voltage (20-60V) Low power consumption Insensitive to magnetic fields Compact and rugged

First prototypes The wafer includes many structure differing in geometrical details The basic SiPM geometry is composed by 25x25 cells Cell size: 40x40  m 2 1mm ITC-irst

40 cm of regolith  T=-20 ± 3 C Regolith Physical Properties

Further Developments Longitudinal segmentation of Scintillator Rods Steps: 5 or 10 cm

Numbers and Weight as a CONCLUSION Area covered by a single rod Surfice covered by Moon Cal d = 4 cm Area ~ 7 cm 2 ~28 m 2 d = 7.5 cm Area ~ 24 cm 2 d = 15 cm Area ~ 97 cm 2 Scintillator rod : Wrapping in Carbon fiber Weight of a single rod (length: 150 cm): r=0.5 cm.15 Kg r= 1cm.5 Kg

Energy deposit on scintillators

Properties of a SiPM The properties described for the GM-APD are valid for the SiPM with two additional complications: 1) Further term in the photodetection efficiency: PDE = N pulses / N photons = QE x P 01 x A e Ae = (Active area) / (total SiPM area) Dead area is given by the structures at the edges of the microcell (metal layers, trenches, resistor…)

Properties of a SiPM 2) Optical cross-talk During an avalanche discharge photons are emitted. 3x10 -5 photons with energy higher than 1.14eV emitted per carrier crossing the junction. [from A. Lacaita et al., IEEE TED, vol. 40, n. 3, 1993:] Those photons can trigger the avalanche in an adjacent cell: optical cross-talk. Solutions: - operate at low over-voltage => low gain => few photons emitted - optical isolation structure: cell1 cell2 cell1 cell2

SiPM manufacturers Russian groups: Obninsk/CPTA,Moscow(Golovin) Mephi/PULSAR,Moscow(Dolgoshein) JINR, Dubna(Sadygov) They have been working on this since the beginning. New labs/companies involved in SiPM production: ITC-irst Hamamatsu SensL MPI

ITC-irst Development of SiPM is done in the framework of an agreement between INFN and ITC called MEMS: role of ITC-irst: to produce a matrix of SiPMs with detection efficiency optimized in the short-wavelength region. role of INFN (Pisa, Perugia, Bologna, Bari, Trento): to couple the SiPM with a scintillator, to develop a read-out electronics for calorimetry, PET, TOF applications. Project started at the beginning of Details on the status of the project:

First production Completed in september Characteristics of the first fabrication run: 1) 11 photolithografic masks 180 process steps (3 months in clean room) 180 process steps (3 months in clean room) 2) Substrate: p-type epitaxial, 4  m thick 3) Quenching resistance made of doped polysilicon 4) No structure for optical isolation 5) Geometry not optimized for maximum PDE Main objective was to study the breakdown properties!

Electrical characterization IV characteristics of 10 devices Breakdown voltage 31V Uniform V BD all over the wafer surface position of the tested devices T=22 o C

Signal characteristics V BIAS =35.5V Dark signal single cell signal double signal (optical cross-talk) Single 32.5, 34 and 35.5V Rise time ~1ns Recovery time ~70ns SiPM read-out by means of a wide-band voltage amplifier on a scope

Single electron spectrum Single electron spectrum in dark condition Integration time = 100ns. 35V 34V 33V

Gain Gain vs Bias voltage Q=C microcell *(V bias -V breakdown ) => C = 80-90fF T=22 o C Linear dependence, as expected.

Preliminary optical characterization Trigger from pulse gen. Dark signals Example of a Signal Response to light excitation ( =470nm) V BIAS =33.5V T=22 o C bunch of photons No measurement of PDE has been done yet.

Preliminary optical characterization 1pe 2pe 3pe Pulse height spectrum from low-intensity light flashes (red LED) Each peak corresponds to a different number of fired cells Very good single photoelectron resolution! T=22 o C  V=1.5V T=22 o C  V=2V 1pe 2pe

Conclusion September 2005: first production of Silicon Photomultipliers at ITC-irst. Extremely good results: Gain ~ 10 6 Dark count ~ MHz Recovery time ~ 70ns PDE measurement in progress, encouraging first results Second production run just completed. Implemented trenches for optical cross-talk isolation. Characterization in progress. Next goal: to reduce dark count acting on the technology