Download Specific heat measurement of crystals to be used in

ILIAS
ILIAS GENERAL MEETING - 2006
2006
PARALLEL
PARALLEL SESSION
SESSION ON
ON DBD
DBD (EXPERIMENTS)
(EXPERIMENTS)
Specific
Specific heat
heat measurement
measurement of
of
crystals
crystals to
to be
be used
used in
in scintillating
scintillating
bolometers
bolometers for
for Double
Double Beta
Beta Decay
Decay
Marco Barucci - INFN Firenze
Outline
In view of the realization of a TeO2 scintillating
bolometer, measurements of heat capacity have been
carried out on two crystals.
The TeO2 crystals were grown from pure Pt crucible by
Czochralski method, in the Research Institute for Solid
State Physics and Optics (Budapest, Hungary).
Marco Barucci
2
Outline
Preliminary tests showed that intrinsic low temperature
scintillation of the TeO2 material is increased in the
case of Nb and Mn doping.
Marco Barucci
3
Samples
The main features of the two samples are:
Sample 1
Sample 2
test sample n. 80505
test sample n. 80507
undoped TeO2
mass: 18.687 g
Nb doped: TeO2+Nb2O5
(10-4 mol/mol in the melt)
dimensions: ~ 3x1x1 cm3
mass: 18.671 g
dimensions: ~ 3x1x1 cm3
Marco Barucci
4
Goals
Present measurements were aimed to:
detecting possible increase of the low temperature
specific heat in the case of Nb doping
(possible paramagnetic effects at very low
temperatures from Nb3+ uneven ions)
check the value of specific heat for TeO2 crystals
made by different manufacturers.
Marco Barucci
5
Experimental Set-Up
The measurements were carried out in a low power
dilution refrigerator by the thermal relaxation method.
R(T)
Thermo
Heat sink
Thermal coupling
Heater
Power
C(T)
R(T)=G-1(T)
Temp
Crystal sample
τ(T)
Heat capacity
C(T) = G(T) x τ(T)
time
Marco Barucci
6
Experimental Set-Up
The sample was sustained by
two thin Sn cylinders, which also
gave the thermal conductance to
the bath
Two copper springs ensured the
mechanical stability of the
sample
A Ge thermometer (NTD 35B
3x3x1 mm3) and a Si heater,
glued onto the sample, were
connected by NbTi wires 25 µm
in diameter.
Cu springs
NbTi wires
Sn cylinders
(8mmØ
(8mmØ, 3mm long,
0,2mm thikness)
thikness)
NTD Ge
thermometer
Si heater
(other side)
TeO2 sample
Marco Barucci
7
Experimental Set-Up
This configuration allows to minimize the spurious
contributions (the addendum) to the heat capacity of
the sample.
The heat capacity measurements have been carried
out from 50 to 130 mK.
The range of temperature was limited at the lowest
temperature by the small mass of the samples (the
thermal discharge time constant became very short)
and at the highest temperature by the low sensitivity
of the Ge NTD thermometer.
Marco Barucci
8
Results
specific heat of sample 1
(pure TeO2)
sample 2
(Nb doped TeO2)
Marco Barucci
9
Results
the specific heat of the two measured samples are
reported together with data for the TeO2 of Chinese
production (at present used for the CUORICINO
bolometers) measured by our group a few years ago.
M. Barucci,et al., J.Low Temp. Phys.,
123,p. 303, 2001.
Marco Barucci
Within the
experimental errors,
the specific heat of
the three samples in
the investigated
temperature range is
the same
10
Conclusion
We cannot exclude spurious contributions to the
specific heat at temperature below 50 mK.
However, since we do not detect tails of lower
temperature contributions in our temperature range, it
is unlike that such contributions exist.
Thus, we suggest the test of a scintillation bolometer
based on the niobium doped tellurium dioxide crystal.
Marco Barucci
11