On the Energy resolution optimization of CsI(Tl) crystals forthe R3B Calorimeter

Martın GASCON

Particle Physics DepartamentUniversidad de Santiago de Compostela

June 1, 2007

Martın GASCON Energy-resolution of CsI(Tl) crytals

FAIR: Facility for Antiproton and Ion Research

Characteristics:

New accelerator facility in Darmstadt(Germany)

protons, stable- and radioactive-ion beams

Primary intensity: (1012 ions/s)@ 2−30GeV/u.

Good beam quality (beam-coolingtechniques)

FAIR.MPG

Martın GASCON Energy-resolution of CsI(Tl) crytals

R3B experimentReactions with Relativistic Radioactive Beams

R3B

R3B is a versatile experimental setup for full kinematics studies of exotics beams reactions atrelativistic energies (around 700 MeV/nucleon in the laboratory system)

Martın GASCON Energy-resolution of CsI(Tl) crytals

R3B CalorimeterCALIFA: A Calorimeter for in-flight emitted gammas and light charged-particles for R3B Experiment

R3B

The crystal array will surround the R3B target, measuring both gammas (0.5-10 MeV in CoM)and protons (up to 300 MeV).

It must fulfils two requirements: to provide the γ-ray multiplicities and their sum energy, and forother experiments, it must measure the individual γ-ray energies for spectroscopic purposes.

The detector has to stop and measure the total energy of high-energy light charged particleswith high energy-resolution

The required polar angle segmentation and the lenght of the scintillating crystals has beencalculated (GEANT4) for different angular regions.

CALIFA

Martın GASCON Energy-resolution of CsI(Tl) crytals

Experimental setup

Martın GASCON Energy-resolution of CsI(Tl) crytals

Experimental setupCrystals and APDs

Figure: 20 cm CsI(Tl) tapered crystal

Figure: 10x10 mm2 S8664-1010 APD fromHamamatsu

Figure: SD630-73-70-500 APD from API coupledto a 1 cubic cm CsI(Tl) crystal

Martın GASCON Energy-resolution of CsI(Tl) crytals

CsI(Tl) crystals testsMeasurements: APD Gain

APD Gain vs Bias Voltage

Figure: 5 cm length crystal Figure: small crystals Figure: 20 cm tapered crystal

The best energy-resolution can be found by adapting the amplifier gain to keep the photopeakin a constant channel

around 380 V→∆Gain

∆V= 2.84% (1)

The energy resolution depends on both Bias Voltage and Amplifier Gain

Martın GASCON Energy-resolution of CsI(Tl) crytals

CsI(Tl) crystals testsMeasurements: Shapping time

Dependence on Shapping time

For small crystals, 4 µs is a good compromise between energy-resolution loss and pile-upnegative effects.

Martın GASCON Energy-resolution of CsI(Tl) crytals

CsI(Tl) crystals testsMeasurements: Acquisition time

Dependence on Acquisition time

Best values are obtained between 30 and 60 seconds depending on the counting rate

The showed curve has two components: statistics and bias voltage drift, that could beeliminated by controling both temperature and bias voltage

Martın GASCON Energy-resolution of CsI(Tl) crytals

CsI(Tl) crystals testsMeasurements: Amplifier gain

Dependence on Amplifier gain

Energy-resolution improves by increasing the amplifier gain

Martın GASCON Energy-resolution of CsI(Tl) crytals

CsI(Tl) crystals testsMeasurements: Energy resolution

Dependence on Energy resolution

The APDs from API show the best energy-resolution for the CsI(Tl) crystal

The APDs from Hamamatsu show an acceptable energy-resolution and it is almostindependent on the crystal size

Martın GASCON Energy-resolution of CsI(Tl) crytals

Outline

Conclusions

Several tests (wrapping, optical coupling, amplifier gain, shapping time, ...) have beenperformed to optimize the crystal peformance using APDs from API and Hamamatsu

APDs from API shown the best energy-resolution for the CsI(Tl) crystal, nevertheless thosefrom Hamamatsu shown a similar energy-resolution, almost independently on the crystal size

The main drawback of using APDs instead of PMTs is the strongly dependence of the gainwith temperature and voltage.

The limited energy-resolution in the tapered crystal is mainly due to a deficient opticalcoupling with the light guides.

These results fulfil the calorimeter requirements at least for the Barrel section

Martın GASCON Energy-resolution of CsI(Tl) crytals

Outline

Conclusions

Several tests (wrapping, optical coupling, amplifier gain, shapping time, ...) have beenperformed to optimize the crystal peformance using APDs from API and Hamamatsu

APDs from API shown the best energy-resolution for the CsI(Tl) crystal, nevertheless thosefrom Hamamatsu shown a similar energy-resolution, almost independently on the crystal size

The main drawback of using APDs instead of PMTs is the strongly dependence of the gainwith temperature and voltage.

The limited energy-resolution in the tapered crystal is mainly due to a deficient opticalcoupling with the light guides.

These results fulfil the calorimeter requirements at least for the Barrel section

Martın GASCON Energy-resolution of CsI(Tl) crytals

Outline

Conclusions

Several tests (wrapping, optical coupling, amplifier gain, shapping time, ...) have beenperformed to optimize the crystal peformance using APDs from API and Hamamatsu

APDs from API shown the best energy-resolution for the CsI(Tl) crystal, nevertheless thosefrom Hamamatsu shown a similar energy-resolution, almost independently on the crystal size

The main drawback of using APDs instead of PMTs is the strongly dependence of the gainwith temperature and voltage.

The limited energy-resolution in the tapered crystal is mainly due to a deficient opticalcoupling with the light guides.

These results fulfil the calorimeter requirements at least for the Barrel section

Martın GASCON Energy-resolution of CsI(Tl) crytals

The end

Wernher von Braun

Basic research is what I am doing when I don’tknow what I am doing

Martın GASCON Energy-resolution of CsI(Tl) crytals