MoonCal An electromagnetic calorimeter on the lunar surface R.Battiston, M.T.Brunetti, F. Cervelli, C.Fidani, F.Pilo
Why the Moon for astroparticle physics? The Moon does not have atmosphere nor water. This means that: there is no absorption of the radiation reaching our satellite from space. Vacuum is cheap; the Moon is thermally quiet except at sunrise and sunset. Even a more stable thermal environment could be achieved by burying the instrument under the Moon dust; there are no winds, no weather effects. Materials are not attacked by rust, they last unaltered for long periods (aside of thermal expansions effects). The Moon does not have a magnetic field nor a magnetosphere.
In the energy range between 100 GeV and 10 TeV, MOONCAL could: Detect the diffuse gamma ray background and monochromatic emissions in a completely unexplored energy interval: Galactic and extra-galactic diffuse components, supernova remnants, pulsars, AGN s, GRB s The Universe is mostly made of non luminous Dark Matter Detect an excess of positrons and electrons in the primary CR spectra by observations with high statistics Observe line gamma rays from SUSY particles annihilation by the very good energy resolution at high energies
Compared to recent detectors A large aperture, large area post-glast Gamma Ray observatory GLAST MOONCAL Energy Range 20MeV 300GeV 100GeV 100TeV Geometric Area 2.8 m2 25 30 m2 Energy Resolution @ 100GeV 15 20% <10% A Cosmic Rays observatory to measure their composition and spectra. 1 Day data taking of MOONCAL corresponds to: 30 days of AMS-02 experiment (Acc. 5000 cm2sr)
DETECTOR DESIGN Three main constraints: use (as far as possible) of local material in order to reduce the weight to be carried in the flight and also the number of flights; detector design simple and easy to assemble, in view of fully automatic mission; modularity of the detector, which allow to operate the detector since the first flight to the Moon by covering an area which can be expanded by adding more modules in the following missions. An E.M. SAMPLING CALORIMETER where the passive material is the lunar regolith and the active material are scintillators bars
The regolith as sampling material Astronauts already drilled the lunar surface to sample the regolith down to depths of 3 meters At the depth of 40 cm the temperature is quite stable around 20±3 C The core tube sampler used by the astronauts to collect the lunar regolith during the Apollo missions
Scintillator Geometry A circular flat area on the lunar surface with a radius of some meters is filled with scintillator bars. The bars are positioned on a xy grid with a step of few centimeters. r d d Top View L
Light Collection System A SiPM consist of a matrix of GM-APD s connected in parallel. Each element is independent and gives the same signal when fired by a photon Q = Q1 + Q2 = 2*Q1 output signal is proportional to the number of triggered cells that for PDE=1 is the number of photons Area: 1 1 mm2 metal substrate The characteristics of a SiPM are: capability to detect extremely low photon fluxes giving a proportional information; extremely fast response (in the order of few hundreds of ps); low power consumption; low bias voltage (20-60V); compact and rugged; insensitive to magnetic fields. The basic SiPM geometry is composed by 25x25 cells (Cell size: 40x40µ 40x40µm2)
MOONCAL Simulation: : the Regolith Composition Monte Carlo code GEANT4 (developed at CERN) has been used to simulate the response of the regolith-scintillator calorimeter The elemental composition and the density of the regolith employed in the simulation are taken from the measurements of samples collected in the lunar maria during Apollo and Luna Missions Material: Regolith density: 1.600 g/cm3 temperature: 273.15 K pressure: 1.00 atm RadLength: 14.400 cm ---> Element: Silicon (Si) Z = 14.0 N = 28.1 A = 28.09 g/mole ElmMassFraction: 20.47 % ElmAbundance 16.64 % ---> Element: Oxygen (O) Z = 8.0 N = 16.0 A = 16.00 g/mole ElmMassFraction: 42.26 % ElmAbundance 60.32 % ---> Element: Titanium (Ti) Z = 22.0 N = 47.9 A = 47.87 g/mole ElmMassFraction: 2.58 % ElmAbundance 1.23 % ---> Element: Aluminum (Al) Z = 13.0 N = 27.0 A = 26.98 g/mole ElmMassFraction: 6.99 % ElmAbundance 5.91 % ---> Element: Chromium (Cr) Z = 24.0 N = 51.0 A = 51.00 g/mole ElmMassFraction: 0.24 % ElmAbundance 0.11 % ---> Element: Iron (Fe) Z = 26.0 N = 55.8 A = 55.84 g/mole ElmMassFraction: 12.90 % ElmAbundance 5.28 % ---> Element: Manganese (Mn) Z = 25.0 N = 54.9 A = 54.94 g/mole ElmMassFraction: 0.17 % ElmAbundance 0.07 % ---> Element: Magnesium (Mg) Z = 12.0 N = 24.3 A = 24.30 g/mole ElmMassFraction: 5.61 % ElmAbundance 5.27 % ---> Element: Calcium (Ca) Z = 20.0 N = 40.1 A = 40.08 g/mole ElmMassFraction: 8.15 % ElmAbundance 4.64 % ---> Element: Sodio (Na) Z = 11.0 N = 23.0 A = 22.99 g/mole ElmMassFraction: 0.30 % ElmAbundance 0.29 % ---> Element: Potassio (K) Z = 19.0 N = 39.1 A = 39.10 g/mole ElmMassFraction: 0.14 % ElmAbundance 0.08 % ---> Element: Phosphorus (P) Z = 15.0 N = 31.0 A = 30.97 g/mole ElmMassFraction: 0.09 % ElmAbundance 0.07 % ---> Element: Sulfur (S) Z = 16.0 N = 32.1 A = 32.06 g/mole ElmMassFraction: 0.11 % ElmAbundance 0.08 % The Radiation Length (X 0 ) is the Scaling variable for the lateral and longitudinal development of electron-photon cascades. The Regolith Radiation Length turned out to be 14.4 cm
MOONCAL Simulation: boundary conditions CALORIMETER GEOMETRY Cylinder of 3 m radius filled with regolith and scintillators. ENERGY RESTRICTIONS Photon and electron events in the energy interval between 100 MeV and 100 GeV. GEOMETRY RESTRICTIONS Shower longitudinal containement Æ Incident angle: 45 θ 80. Lateral containement Æ Incident point: inside a disk of 1 m radius. Top view and lateral view of the electromagnetic shower induced by a 100 GeV gamma ray
MOONCAL Simulation: Energy Resolution The resolution has been fitted according to: E b =a+ E E0 Different geometric configurations has been tested Good solution with d=4 cm, r= 0.5 cm, L= 3 m The energy resolution of 1 TeV photons extrapolated from the results is below 7%
Numbers and Weight as a CONCLUSION Surface covered by MoonCal: ~28 m 2 Number of scintillator bars: d = 15 cm 5000 d = 4 cm ~17700 Weight of a single rod (length: 300 cm): r = 0.5 cm 0.3 Kg r = 1cm 1 Kg Further Developments: Longitudinal segmentation of Scintillator Rods with Steps of 5 or 10 cm
RISERVA
OUTLINE Physics Goals Design Requirements Detector Layout First Simulations
Depth of Maximun Energy Deposit (the probability of occurrence of bremsstrahlung and pair production in gamma induced showers) Area covered by a single rod: cm 7.5 cm cm Area ~ 7 cm2 Area ~ 24 cm2 Area ~ 97 cm2 d=4 d= d = 15 d = 4 7.5 cm r = 0.5 1 cm L = 150 300 cm
Gamma Rays at 100 GeV: Energy Deposit vs Depth Tranverse Development
Regolith Physical Properties 40 cm of regolith Æ T=-20 ± 3 C