SLIDE 11 T2HKK workshop, SNU, Nov. 21-22, 2016 Young Soo Yoon, CUP, IBS
Light and Heat Detectors and Ground Measurements
11
Metallic Magnetic Calorimeter
540 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 63, NO. 2, APRIL 2016
- Fig. 1. A schematic (above) and photographs (below left: top view; below
right: bottom view) of the detector setup consisting of a crystal and a cryogenic light detector.
we selected one with relatively low internal radioactive contam- ination to perform low-temperature measurements. Recently, we have been developing low-temperature detec- tors (LTDs) with scintillation crystals and metallic magnetic calorimeters (MMCs). The MMCs are para-mag- netic temperature sensors operating at temperature of tens of milli-kelvin. The combination of with MMCs shows promising performance in terms of energy resolution and pulse shape discrimination using phonon signals [10]. For the detec- tion of scintillation light at low temperatures, we developed a light detector consisting of a two-inch Ge wafer, used as a light absorber, as well as MMCs [11]. This article presents the principles and performance of a simultaneous heat/light measurement system based on these devices. We also discuss the prospects for the AMoRE experiment, which will use crystals with MMC sensors as low temperature detectors to search for the
.
The detector was composed of a scintillating crystal, a phonon (heat) sensor, and a light detector, as shown in Fig. 1. A
crystal with a mass of 200 g was employed as an energy absorber for the LTD in this measurement. The phonon sensor was used to measure temperature increases in the crystal caused by particle interactions, and was constructed from a gold film, gold wires, an MMC device, and a Superconducting QUantum Interference Device (SQUID). A patterned gold film 2 cm in diameter was evaporated for the collection of phonons from the crystal, and bonded gold wires provided a thermal link between the gold film and the MMC device. The light detector consisted
- Fig. 2. Scatter plot of heat and light signals obtained via simultaneous mea-
surement by low-temperature detectors.
- f a two-inch Ge wafer as a scintillation light absorber, a
gold film as a phonon collector, gold wires as a thermal link between the phonon collector and the MMC device, and a SQUID for measuring the magnetic signal from the MMC. The details of measurement principle and detector set-up have been reported in our previous publications [10], [11], [12]. The phonon sensor was attached to the bottom side of the crystal, as shown in the lower right of Fig. 1, and the light detector was assembled on the top side of the crystal, as shown in the lower left of Fig. 1. The crystal was mounted in a phosphor-bronze spring because of its good properties at low temperature and was surrounded by a VM2000 light reflector for better light collection efficiency of the Ge light absorber. The detector setup was installed in a dilution refrigerator in an aboveground laboratory, KRISS (Korean Research Institute of Standards and Science), with a 10 cm thick lead shield (except on the top side) and cooled to a temperature of 10 to 30 mK. Background and calibration data were accumulated using an NI (National Instruments) PXI (PCI eXtensions for Instrumentation) 14-bit ADC (Analog-to-Digital Converter), and the signal in the heat channel was used to trigger the simultaneous measurement of the scintillation light and heat. To collect the calibration data, a thoriated tungsten rod (containing approximately 2% ) was used as an external
- ray source. The source was placed in
between the cryostat and the lead shield.
Background data were accumulated for 71 hours at 20 mK. The temperature of the detector was set to 20 mK using the Pro- portional-Integral-Derivative (PID) system of the dilution re- frigerator for long-term measurements. Fig. 2 shows a scatter plot of the heat (on the x axis) and light (on the y axis) signals. Four distinct groups of signals are evident. A line is vis- ible with a linear correlation between the light and heat signals, and a second group of events with lower light signals can be seen below the line, which can be recognized as
- induced
- events. Events representing direct hits by environmental radia-
tion on the Ge light absorber, with essentially zero heat signal, populate the left side of the scatter plot. Events corresponding
540 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 63, NO. 2, APRIL 2016
- Fig. 1. A schematic (above) and photographs (below left: top view; below
right: bottom view) of the detector setup consisting of a crystal and a cryogenic light detector.
we selected one with relatively low internal radioactive contam- ination to perform low-temperature measurements. Recently, we have been developing low-temperature detec- tors (LTDs) with scintillation crystals and metallic magnetic calorimeters (MMCs). The MMCs are para-mag- netic temperature sensors operating at temperature of tens of milli-kelvin. The combination of with MMCs shows promising performance in terms of energy resolution and pulse shape discrimination using phonon signals [10]. For the detec- tion of scintillation light at low temperatures, we developed a light detector consisting of a two-inch Ge wafer, used as a light absorber, as well as MMCs [11]. This article presents the principles and performance of a simultaneous heat/light measurement system based on these devices. We also discuss the prospects for the AMoRE experiment, which will use crystals with MMC sensors as low temperature detectors to search for the
.
The detector was composed of a scintillating crystal, a phonon (heat) sensor, and a light detector, as shown in Fig. 1. A
crystal with a mass of 200 g was employed as an energy absorber for the LTD in this measurement. The phonon sensor was used to measure temperature increases in the crystal caused by particle interactions, and was constructed from a gold film, gold wires, an MMC device, and a Superconducting QUantum Interference Device (SQUID). A patterned gold film 2 cm in diameter was evaporated for the collection of phonons from the crystal, and bonded gold wires provided a thermal link between the gold film and the MMC device. The light detector consisted
- Fig. 2. Scatter plot of heat and light signals obtained via simultaneous mea-
surement by low-temperature detectors.
- f a two-inch Ge wafer as a scintillation light absorber, a
gold film as a phonon collector, gold wires as a thermal link between the phonon collector and the MMC device, and a SQUID for measuring the magnetic signal from the MMC. The details of measurement principle and detector set-up have been reported in our previous publications [10], [11], [12]. The phonon sensor was attached to the bottom side of the crystal, as shown in the lower right of Fig. 1, and the light detector was assembled on the top side of the crystal, as shown in the lower left of Fig. 1. The crystal was mounted in a phosphor-bronze spring because of its good properties at low temperature and was surrounded by a VM2000 light reflector for better light collection efficiency of the Ge light absorber. The detector setup was installed in a dilution refrigerator in an aboveground laboratory, KRISS (Korean Research Institute of Standards and Science), with a 10 cm thick lead shield (except on the top side) and cooled to a temperature of 10 to 30 mK. Background and calibration data were accumulated using an NI (National Instruments) PXI (PCI eXtensions for Instrumentation) 14-bit ADC (Analog-to-Digital Converter), and the signal in the heat channel was used to trigger the simultaneous measurement of the scintillation light and heat. To collect the calibration data, a thoriated tungsten rod (containing approximately 2% ) was used as an external
- ray source. The source was placed in
between the cryostat and the lead shield.
Background data were accumulated for 71 hours at 20 mK. The temperature of the detector was set to 20 mK using the Pro- portional-Integral-Derivative (PID) system of the dilution re- frigerator for long-term measurements. Fig. 2 shows a scatter plot of the heat (on the x axis) and light (on the y axis) signals. Four distinct groups of signals are evident. A line is vis- ible with a linear correlation between the light and heat signals, and a second group of events with lower light signals can be seen below the line, which can be recognized as
- induced
- events. Events representing direct hits by environmental radia-
tion on the Ge light absorber, with essentially zero heat signal, populate the left side of the scatter plot. Events corresponding G.B. Kim et al., IEEE Trans. Nucl. Sci. (2016)
540 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 63, NO. 2, APRIL 2016
- Fig. 1. A schematic (above) and photographs (below left: top view; below
right: bottom view) of the detector setup consisting of a crystal and a cryogenic light detector.
we selected one with relatively low internal radioactive contam- ination to perform low-temperature measurements. Recently, we have been developing low-temperature detec- tors (LTDs) with scintillation crystals and metallic magnetic calorimeters (MMCs). The MMCs are para-mag- netic temperature sensors operating at temperature of tens of milli-kelvin. The combination of with MMCs shows promising performance in terms of energy resolution and pulse shape discrimination using phonon signals [10]. For the detec- tion of scintillation light at low temperatures, we developed a light detector consisting of a two-inch Ge wafer, used as a light absorber, as well as MMCs [11]. This article presents the principles and performance of a simultaneous heat/light measurement system based on these devices. We also discuss the prospects for the AMoRE experiment, which will use crystals with MMC sensors as low temperature detectors to search for the
.
The detector was composed of a scintillating crystal, a phonon (heat) sensor, and a light detector, as shown in Fig. 1. A
crystal with a mass of 200 g was employed as an energy absorber for the LTD in this measurement. The phonon sensor was used to measure temperature increases in the crystal caused by particle interactions, and was constructed from a gold film, gold wires, an MMC device, and a Superconducting QUantum Interference Device (SQUID). A patterned gold film 2 cm in diameter was evaporated for the collection of phonons from the crystal, and bonded gold wires provided a thermal link between the gold film and the MMC device. The light detector consisted
- Fig. 2. Scatter plot of heat and light signals obtained via simultaneous mea-
surement by low-temperature detectors.
- f a two-inch Ge wafer as a scintillation light absorber, a
gold film as a phonon collector, gold wires as a thermal link between the phonon collector and the MMC device, and a SQUID for measuring the magnetic signal from the MMC. The details of measurement principle and detector set-up have been reported in our previous publications [10], [11], [12]. The phonon sensor was attached to the bottom side of the crystal, as shown in the lower right of Fig. 1, and the light detector was assembled on the top side of the crystal, as shown in the lower left of Fig. 1. The crystal was mounted in a phosphor-bronze spring because of its good properties at low temperature and was surrounded by a VM2000 light reflector for better light collection efficiency of the Ge light absorber. The detector setup was installed in a dilution refrigerator in an aboveground laboratory, KRISS (Korean Research Institute of Standards and Science), with a 10 cm thick lead shield (except on the top side) and cooled to a temperature of 10 to 30 mK. Background and calibration data were accumulated using an NI (National Instruments) PXI (PCI eXtensions for Instrumentation) 14-bit ADC (Analog-to-Digital Converter), and the signal in the heat channel was used to trigger the simultaneous measurement of the scintillation light and heat. To collect the calibration data, a thoriated tungsten rod (containing approximately 2% ) was used as an external
- ray source. The source was placed in
between the cryostat and the lead shield.
Background data were accumulated for 71 hours at 20 mK. The temperature of the detector was set to 20 mK using the Pro- portional-Integral-Derivative (PID) system of the dilution re- frigerator for long-term measurements. Fig. 2 shows a scatter plot of the heat (on the x axis) and light (on the y axis) signals. Four distinct groups of signals are evident. A line is vis- ible with a linear correlation between the light and heat signals, and a second group of events with lower light signals can be seen below the line, which can be recognized as
- induced
- events. Events representing direct hits by environmental radia-
tion on the Ge light absorber, with essentially zero heat signal, populate the left side of the scatter plot. Events corresponding
KIM : HEAT AND LIGHT MEASUREMENT OF A CRYSTAL FOR THE AMoRE DOUBLE BETA DECAY EXPERIMENT 541
to the penetration of muons into the Ge light absorber, with a constant value of the light signal, are distributed horizontally at the top of the scatter plot. The energy of the heat signals was calibrated on an electron- equivalent energy scale using an external
tioned in the previous section. In the scatter plot, environmental
- rays populate the region below 2.6 MeV. The
line con- tinues up to a few tens MeV because of the large flux of muons interacting in the crystal in the aboveground laboratory. The line shows good proportionality up to the high energy region. The FWHM energy resolutions were measured to be 4.8 keV to 9.3 keV for
- rays of 510.7 keV to 2614.5 keV. This energy
resolution, observed with a relatively high environmental back- ground, was worse than the performance of the detector itself because of the high frequency of pileup events. The resolution will be much improved in an environment with less background, such as an underground laboratory with heavy shielding. In ad- dition,
- induced events appear differently from
- induced
events, and internal events can be discriminated by their heat/ light ratios by virtue of the quenching effect in scintillating crys-
ratio of the crystal was measured to be 0.2 for the 5.49 MeV particles from an radioac- tive source, and the quenching factors for different alpha decay isotopes in the crystal are reported in ref. [9]. The internal radioactive contamination of a scintillating crystal is a critical background in the search for decay. In the case of , the most dangerous isotopes are , with MeV (in equilibrium with from the family), and , with MeV (in equilibrium with from the family). The crystal’s internal background was previously confirmed to be sufficiently low for decay ( MeV, in the family), and decay ( MeV in the family) based on a time-amplitude analysis at room temperature. The levels of and could not be measured in the low-temperature setup because of the longer signal window
- f the low-temperature detector. However, we could measure
and identify the majority of the other alpha events caused by and
- contamination. In particular,
, , and (in equilibrium with from the family) alpha decay events, which could not be measured in previous room-temperature setup, were measured at few hundreds of Bq/kg in the low-temperature crystal. Fortunately, we did not measure any alphas caused by decays and thus could simply establish a limit of Bq/kg on this decay. To calculate the discrimination power achievable using the heat and light measurements, we selected events near the decay ( MeV). These events were fitted with two Gaussian functions, as shown in Fig. 3. The discrimination power was determined to be for energies near 5.41 MeV. There is room to improve the discrimination power by using an improved light detector, which is an ongoing project not
decay experiment but also for a dark matter search experiment with the same detection principle. As mentioned in ref. [10], pulse-shape discrimination (PSD) using phonon signals can also be used to distinguish different
- Fig. 3. A histogram of the
parameter for decays ( MeV, solid line). Two Gaussian functions were used to fit the two peaks (dashed lines). The discrimination power was measured to be for energies near 5.41 MeV.
- Fig. 4. The different shapes of the cryogenic light detector signals for different
scintillation processes (above) and a magnified view of the rising part of the signal (below). (Solid line:
- induced scintillation light signals; Dashed line:
- induced scintillation light signals; Dotted line: self-triggered signal.)
incident particles. Such phonon PSD can be achieved based on the slow decay of scintillation light at low temperature. A slower scintillation decay time for crystals has previously been reported in ref. [13], where the scintillation decay time was measured to be a few hundreds of s at 7 K [13]. Recently, an updated result for the scintillation decay time for crys- tals at 17 mK has been obtained by using a photomultiplier tube to measure the scintillation light as triggered by a neutron trans- mutation doped germanium (NTD-Ge) phonon sensor in a di- lution refrigerator. It was confirmed that the scintillation decay time was continuously delayed as the temperature was reduced below 1 K, and the slow component was measured to be 3.4 ms
Ground measurements at KRISS
