Crystals and related topics

J. Gerl, GSI

NUSTAR Calorimeter

Working Group Meeting

June 17, 2005

Valencia

Properties of scintillators

Energy resolution of LaBr3:Ce

E = 60 keV E = 668 keV

Crystal at room temperature,

Read-out: APD at -23 °C

K.S. Shah et al., IEEE NS/MIC/RTSD 2003

FWHM < 2% @ 1.3 MeV

Energy resolution limitations

(E/E)2 = 5.6·(1/N·) + Rsci2 + Rnoise

2

Photon statistics and quantum efficieny: N·

Crystal inhomogeinity, non-proportionality, light losses: Rsci

Electronic noise: Rnoise

Cooling to improve N and Rnoise?

Spectrum of LaCl3:Ce

Crystal at room temperature,

Read-out: PMT at +20 °C

FWHM ~ 2% @ 1.3 MeV

K.S. Shah et al., IEEE NS Vol. 50 (2003) 2410

Time resolution of LaBr3:Ce

Time resolution depends on Ce dopant concentration

5% Ce

Manufacturer's view

limited crystal size (LaBr3: 1" x 2", LaCl3 3" x 3")

very hygroscopic → sealed housing, glass window?

hard and brittle → cutting and polishing problematic

Best suited for medical imaging → Attractive market

Crystal treatment is expensive

Lot of development is going on

Costs:

Raw LaBr3 crystal: ~ 30€

Scint. detector: ~ 1500€ + 300€/cm3

Size considerations

Facts:

Full light collection requires Length / Diameter < 3

Cost / Volume decreases with detector size

Cost / Volume increases with surface area

Options:

1. Build blocks of small (~ 1 cm3) cubes read-out by PIN-diodes or APDs

2. Build position sensitive detectors of large size read-out by several PMTs or APDs

Long conical crystals are not appropriate

Large position sensitive LaBr3:Ce detector

A B

a b

A

C

B

D

E = (Ea...ED)

pos(x,y,z) = centroid of light distribution

5 cm

6 cm

Requires cooling to reduce noise

Features •Gain above 1,000 at operating condition of best signal-to-noise ratio. (Maximum gain of 10,000.) •Large active area •High quantum efficiency (QE) extends beyond visible spectrum •High speed at 1064 nanometer wavelength of YAG lasers •Pulse counting mode is the most-frequent style of use. •Optical Photon Counting (2-3 photons) when cooled

14x14 pixel APD

APDs from Radiation Monitoring Devices Inc.

RMD produces also LaBr3 and LaCl3 crystals