BGO 45.7 g

ROSEBUD is dedicated to develop and optimize scintillating bolometers of different materials and to use them in Nuclear and

Particle Physics experiments focusing on DM search

Integrated in Supported by

• CNRS (Centre National de la Recherche Scientifique)• PNCG (Programme National de Cosmologie et Galaxies)• CICYT (Comisión Interministerial de Ciencia y Tecn.)• DGA (Gobierno de Aragón)

PRESENT OBJECTIVESPRESENT OBJECTIVES

N. Corona, C. Cuestab, E. Garcíab, J. Gironneta, J. Leblanca, P. de Marcillaca, M. Martínezb, Y. Ortigozab, A. Ortiz de Solórzanob, C. Pobesb, J. Puimedónb, T. Redona, T. Rolónb, M.L. Sarsab,

L. Torresa, J. A. Villarb

a Institut d’Astrophysique Spatiale, CNRS & Université Paris Sud, Bât 121, 91405 Orsay, Paris, France.b Laboratorio de Física Nuclear y Astropartículas, Universidad de Zaragoza, 50009 Zaragoza, España.

BGO SCINTILLATING BGO SCINTILLATING BOLOMETERBOLOMETER

Its application in dark matter experimentsROSEBUD (Rare Objects ROSEBUD (Rare Objects SEarchSEarch

with Bolometers with Bolometers UnDergroundUnDerground))

TAU

P 20

09TA

UP

2009

OutlineOutline

The BGO scintillating bolometerROSEBUD experimental set-up in the LSCBGO as WIMP detector and as γ-rays spectrometer

(tests performed in the Canfranc Underground Laboratory)

Characterization of the BGO scintillating bolometer Energy partition (αl

/αh ratio, scintillation at low T, Ge

optical bolometer efficiency)Energy estimate of saturated β/γ

and α

events

BGO heat and light relative efficiency factors (REFs)Conclusions

The BGO scintillating bolometer

252Cf

heat

light

heat

light

ROSEBUD Experimental Set-up in Canfranc Underground Laboratory (LSC)

LiFMass 33 g

Sapphire (Al2

O3

)Mass 50 g

Low background environment at LSC (2450 m.w.e.)• Internal shield (Cu & Pb pieces)

• Externnal shield (Pb, polyethylene, μ-metal, Rn removal)

BGO (Bi4

Ge3

O12

)Mass 46 g209Bi 100%: ↑A (heavy material) with J = 9/2It’s sensitive SI and SD interactions (209Bi, 73Ge)207Bi contamination (~3 Bq/kg) β/γ

spectrometer Z↑

BGO as WIMP detector Particle discrimination threshold and nuclear recoils

252Cf calibration

Lower particle discrimination threshold and background are needed

Background

BGO as γ-

rays spectrometerSpectrum of 71.94 h

Peak energy (keV)

FWHM(keV)

∼15 3.4 ± 0.1

88.0 3.3 ± 0.0

242.0 5.0 ± 1.5

295.2 4.4 ± 0.5

351.9 4.9 ± 0.3

511.0 6.8 ± 1.9

569.7 7.5 ± 0.1

584.7 7.6 ± 0.5

609.3 7.4 ± 0.3

657.7 7.7 ± 0.4

768.4 7.3 ± 2.2

1063.6 11.0 ± 0.3

1120.3 12.3 ± 1.7

BGO and experiment background

Scintillating bolometer: Energy partitionPhoton interaction

E

αl ·

E αh ·

E α0 ·

E

Not detectableTraps, lattice defects …

Heat channel

ε

ε

· αl ·

E

Light channel

αl

+ αh + α0 = 1

BGO αl

/ αh ratio

88.0 keV

β/γ

events Mean weighted αℓ

/αh = 0.125 ±

0.021

BGO scintillation at low T

BGO light response constant below 100 K:

23700 ± 2600 photons/MeV @ 6 KJ. Gironnet et al. NIM A 594 (2008) 358-361

Bi4 Ge3 O12 scintillation study with α

irradiation (241Am) down to 6 K

IAS (fr), Paul Scherrer Institut (ch), University of Oxford (uk)

⟨Ephoton ⟩

= 2.4 eV @ 77 K

Measured intensity at 77 K obtained by Johann Gironnet at IAS (fr), Paul

Scherrer Institut (ch)

BGO light yield: αl

= 0.057 ± 0.006

Ge

optical bolometer efficiciency

Ge optical efficiency estimated with 55Fe x-rays 5.9 keV

)keV3.841(keV9.5

EE

deposited

absorbed

ll α=

α=ε

BGO Ge optical sensor efficiency

%1201.012.0 →±=ε

Energy partition in BGOPhoton interaction

E

αl

·

E αh ·

E α0 ·

E

Not detectableTraps, lattice defects …

Heat channel

ε

ε

· αl

·

ELight

channel

α0 = 0.487 ±

0.090αl

= 0.057 ±

0.006 αh = 0.456 ±

0.090BGO

ε

= 0.12 ±

0.01

Negative correlation:

αℓ

/αh = 0.125 ±

0.021

Scintillation at low temperature:

αl

= 0.057 ±

0.00655Fe x-rays calibration:

ε

= 0.12 ±

0.01

• αl

+ αh + α0

= 1:

α0

= 0.487 ±

0.091

Full characterization including energy trapping

Energy estimate of saturated β/γ

eventsLow energy β/γ

saturated events

αsa

tura

ted

even

ts

High energy β/γ

and α

saturated events

1063

.7 k

eV11

20.3

keV

609.

3 ke

V56

9.7

keV

1633.4 keV (207Bi)

1764.5 keV (214Bi)1633.4 keV (207Bi)

1764.5 keV (214Bi)

Light channel 1400Heat amplitude

Light channel 1475Heat channel 1700

Energy estimate of saturated α

events Irradiation with 241Am α

source

Low Gain

Low GainHeat spectrum

α

eventsHigh Gain

Heat spectrumα

eventsThis method allows us to identified events from the background but loosing energy

resolution!

High Gain

Light channel 1215Heat channel 1205

α events not saturating α events saturating

β/γev

ents

β/γ e

vent

s

Heat REF(237Np nuclear recoils:β/γ)BGO irradiation with 241Am α

source

Energies of 237Np recoils92.71 ±

0.17 keV

(84.5%)

92.05 ±

0.18 keV

(13.0%)

Qα

= 5637.81 ±

0.12 keVEα

= 5485.56 ±

0.12 keV

(84.5%)Eα

= 5442.80 ±

0.13

keV

(13.0%)241Am → 237Np + α

Heat REF(237N nuclear recoils:β/γ)

Heat REF(237Np recoils:β/γ)

0.937 ±

0.015stat syst302.0004.0

+−

Mean weighted kinetic energy237Np nuclei

92.40 ±

0.09 keV

Heat pulse amplitude electron recoilsKinetic energy 92.40 ±

0.009 keV

912.56 ±

0.85stat syst mV20.273.294

+−

Heat pulse amplitude237Np recoils

854.96 ±13.36stat ±

2.98syst mV

BGO irradiation with 241Am α

+ 252Cf n sources

Light REF(β/γ:nuclear recoils)

Recoils induced by n

(mainly oxygen recoils)

Recoils induced by n

(mainly oxygen recoils)

237Np recoils237Np recoils

Light REF(β/γ:nuclear recoils)

Light REF(β/γ:nuclear recoils)

Light REF(β/γ:nuclear recoils(mainly O))

10.5 ±

0.4stat ±

0.8syst

Light REF(β/γ:237Np nuclear recoils)

39.5 ±

7.2stat ±

13.7syst

Conclusions1)

The BGO scintillating bolometer has been tested in the LSC showing discrimination capabilities of 23.5 keV

(90% CL) for

WIMP detection. But, we need lower threshold and background in the nuclear recoil band for dark matter experiments.

2)

BGO shows excellent capabilities as γ-rays spectrometer allowing to analyze the background of the experiment. Identification and estimation of the energy of saturated events in low energy experiments (dark matter) is also feasible.

3)

The energy partition (light, heat and trapping) has been studied.

4)

We have estimated heat and light REF for nuclear recoils identifying different light scintillation values dependent on the recoiling nucleus mass.