- Email: [email protected]
Background capabilities of pixel detectors for double beta decay measurements
Nuclear Instruments and Methods in Physics Research A 633 (2011) S210–S211
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Background capabilities of pixel detectors for double beta decay measurements Pavel Cermak a,n, Ivan Stekl a, Viktor Bocarov a, Joshy M. Jose a, Jan Jakubek a, Stanislav Pospisil a, Michael Fiederle b, Alex Fauler b, Kai Zuber c, Pia Loaiza d, Yuriy Shitov e a
Institute of Experimental and Applied Physics, CTU in Prague, 12800 Prague, Czech Republic Freiburger Materialforschungszentrum, Albert-Ludwigs-Universit¨ at Freiburg, D-79104 Freiburg, Germany c Institut f¨ ur Kern- und Teilchenphysik, Technische Universit¨ at Dresden, 01069 Dresden, Germany d Laboratoire Souterrain de Modane, 73500 Modane, France e Joint Institute for Nuclear Research, 141980 Dubna, Russia b
a r t i c l e in f o
a b s t r a c t
Available online 18 June 2010
We discuss the possible use of a progressive detection technique based on pixel detectors for the study of double beta decay (bb) processes. A series of background measurements in various environments (surface laboratory, underground laboratory, with and without Pb shielding) was performed using the TimePix silicon hybrid pixel device. The pixel detector response to the natural background and intrinsic background properties measured by a low-background HPGe detector are presented. & 2010 Elsevier B.V. All rights reserved.
Keywords: Double beta decay Neutrino mass Pixel detector
1. Introduction The neutrinoless mode of double beta decay (0nbb) is a promising tool to test neutrino properties and possible extensions of the Standard Model. As the half-lives of these processes are at the level of 1025 years and above, a high level of sophistication in the instrumentation has to be used. There are several ways to improve the sensitivity of 0nbb experiments: (i) to increase the mass of enriched isotope; (ii) to improve the energy resolution; (iii) to suppress the background; and (iv) to extend the acquisition time. At present, experiments can be divided into several groups according to the detection technique employed: (i) bolometers (CUORE [1]); (ii) calorimetry+ tracking (NEMO 3 [2]); and (iii) semiconductor detectors+ segmentation (GERDA [3], COBRA [4], TGV [5]). Recently, a progressive detection technology based on room temperature semiconductor pixel detectors developed mainly for high energy physics has been tested for various applications, such as medical imaging or material studies (e.g. project Medipix [6]). Using semiconductor material one can achieve good energy resolution, pixelization with the pitch at the level of tens of micrometers together with information on energy deposited in each pixel provide an excellent tool for particle identification. We consider an integration of pixel detectors within two bb experiments—CdTe pixel detectors (potentially enriched in Cd)
n
Corresponding author. Tel.: +420 224 359 393; fax: +420 224 359 392. E-mail address: [email protected] (P. Cermak).
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.06.169
for COBRA [7] and Si pixel detectors for TGV. COBRA is a general 0nbb experiment focused on the 116Cd isotope planning to use a high number of CdTe detectors in a search for the positive signal of two electrons with the sum energy of Qbb equal to 2805 keV. TGV is a smaller experiment aiming at the EC/EC decay of 106Cd with the expected signal of two X-rays with the energy of 21 keV. 2. Instrumentation and results The TimePix hybrid pixel device [8] (256 256 pixel matrix, 55 mm pitch) developed in CERN by the Medipix collaboration was used for this study. An analog circuitry and a digital counter are integrated within each pixel of this device. The TimePix device, operated in time over threshold (TOT) mode, can use the counter as a Wilkinson type ADC providing spectroscopic capabilities in each individual pixel (see the explanation in Ref. [8]). At present we have Si (pixel size 55 55 mm2, thickness 300 mm) and CdTe (55 55 mm2 or 110 110 mm2, thickness 1 mm) detection modules available. Fig. 1 shows the typical response of a TimePix detector to various types of radiation— large blobs for alpha particles, curved lines for electrons, and straight lines for muons. Such particle identification would allow us to distinguish the positive signal (e.g. two electrons with the sum energy equal to Qbb) and the background (photons, a-particles, single electrons, etc.). For future use in any low-background setup, a determination of the impurities contained in the pixel detection module itself is extremely important. The aim is to exclude most of the external
P. Cermak et al. / Nuclear Instruments and Methods in Physics Research A 633 (2011) S210–S211
S211
Fig. 1. The typical response of Si TimePix detector (300 mm thick) to various types of radiation: (a) alpha particles, (b) electrons, and (c) muons. The bottom scale represents the deposited energy in arbitrary units. For further details on capabilities and applications of pixel detectors see e.g. Ref. [9].
Table 1 The total number of events per hour in the energy range of (20-1500) keV measured by the Si TimePix detector in various environments. Environment
Integral hour
Surface Underground Underground + Pb shielding
570 206 90
3. Conclusion
8
Counts / hour
7 6 5 4 3 2 1 0
0
200
400
600
800 E, keV
shows an example of the spectrum of radioimpurities in the CdTe pixel detector module, where mostly lines from U and Th decay chains can be found.
1000
1200
1400
Fig. 2. The spectrum of radioimpurities in the CdTe pixel detection module measured by the low-background HPGe detector in LSM.
sources of background and measure the response of the detector to the radiation coming mainly from the components of the detection unit. Table 1 compares the background signal (the total number of events) in the energy range 20–1500 keV in various environments: (i) surface—standard laboratory, (ii) underground— Modane Underground Laboratory (LSM, 4800 m.w.e.), and (iii) underground+Pb shielding (5 cm thick). To establish the internal contamination of the detection module we measured both Si and CdTe pixel detector modules using the ultra-low background setup located in LSM. It employs a planar type HPGe detector with a volume of 150 cm3. The amount of contaminants for the CdTe module is as follows: 228Th—(1567 10) mBq, 226Ra—(124711) mBq, and 40K—(122714) mBq. Fig. 2
We present first results of testing Si and CdTe pixel detectors for bb measurements. The energy sensitive tracking capabilities show that pixel detectors are a very promising technology for this application. This option should be considered in future R&D projects (such as a semiconductor Time Projection Chamber). However, the results of background measurements also indicate that the tested pixel detector modules are not yet ready for use in ultra-low background setups. The first thing that could be adapted is the design—part of electronic devices can be separated by e.g. re-designing the printed circuit board. Nevertheless, the readout chip and the indispensable components of the bump bonding technology (bumps, under-bump metallization) have to be always located in an immediate vicinity of the sensor. Another necessity is a selection of low-activity materials. All components should be verified using an ultra-low background HPGe detector. Presently, Monte Carlo studies towards the bb applications (pixel size and detector thickness optimization) are in progress.
Acknowledgments This activity is supported by Grant no. LA07050. We would also like to acknowledge the staff of the LSM for their support during all low-background measurements. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
C. Arnaboldi, et al., Nucl. Instr. and Meth. A518 (2004) 775. R. Arnold, et al., Phys. Rev. Lett. 95 (2005) 182302. I. Abt et al., hep-ex/0404039, 2004. K. Zuber, Phys. Lett. B519 (2001) 1. P. Benes, et al., Nucl. Instr. and Meth. A569 (2006) 737. /http://medipix.web.cern.chS. K. Zuber, AIP Conf. Proc. 942 (2007)96. X. Llopart, et al., Nucl. Instr. and Meth. A581 (2007) 485. J. Jakubek, JINST 4 (2009) P03013.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Background capabilities of pixel detectors for double beta decay measurements Pavel Cermak a,n, Ivan Stekl a, Viktor Bocarov a, Joshy M. Jose a, Jan Jakubek a, Stanislav Pospisil a, Michael Fiederle b, Alex Fauler b, Kai Zuber c, Pia Loaiza d, Yuriy Shitov e a
Institute of Experimental and Applied Physics, CTU in Prague, 12800 Prague, Czech Republic Freiburger Materialforschungszentrum, Albert-Ludwigs-Universit¨ at Freiburg, D-79104 Freiburg, Germany c Institut f¨ ur Kern- und Teilchenphysik, Technische Universit¨ at Dresden, 01069 Dresden, Germany d Laboratoire Souterrain de Modane, 73500 Modane, France e Joint Institute for Nuclear Research, 141980 Dubna, Russia b
a r t i c l e in f o
a b s t r a c t
Available online 18 June 2010
We discuss the possible use of a progressive detection technique based on pixel detectors for the study of double beta decay (bb) processes. A series of background measurements in various environments (surface laboratory, underground laboratory, with and without Pb shielding) was performed using the TimePix silicon hybrid pixel device. The pixel detector response to the natural background and intrinsic background properties measured by a low-background HPGe detector are presented. & 2010 Elsevier B.V. All rights reserved.
Keywords: Double beta decay Neutrino mass Pixel detector
1. Introduction The neutrinoless mode of double beta decay (0nbb) is a promising tool to test neutrino properties and possible extensions of the Standard Model. As the half-lives of these processes are at the level of 1025 years and above, a high level of sophistication in the instrumentation has to be used. There are several ways to improve the sensitivity of 0nbb experiments: (i) to increase the mass of enriched isotope; (ii) to improve the energy resolution; (iii) to suppress the background; and (iv) to extend the acquisition time. At present, experiments can be divided into several groups according to the detection technique employed: (i) bolometers (CUORE [1]); (ii) calorimetry+ tracking (NEMO 3 [2]); and (iii) semiconductor detectors+ segmentation (GERDA [3], COBRA [4], TGV [5]). Recently, a progressive detection technology based on room temperature semiconductor pixel detectors developed mainly for high energy physics has been tested for various applications, such as medical imaging or material studies (e.g. project Medipix [6]). Using semiconductor material one can achieve good energy resolution, pixelization with the pitch at the level of tens of micrometers together with information on energy deposited in each pixel provide an excellent tool for particle identification. We consider an integration of pixel detectors within two bb experiments—CdTe pixel detectors (potentially enriched in Cd)
n
Corresponding author. Tel.: +420 224 359 393; fax: +420 224 359 392. E-mail address: [email protected] (P. Cermak).
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.06.169
for COBRA [7] and Si pixel detectors for TGV. COBRA is a general 0nbb experiment focused on the 116Cd isotope planning to use a high number of CdTe detectors in a search for the positive signal of two electrons with the sum energy of Qbb equal to 2805 keV. TGV is a smaller experiment aiming at the EC/EC decay of 106Cd with the expected signal of two X-rays with the energy of 21 keV. 2. Instrumentation and results The TimePix hybrid pixel device [8] (256 256 pixel matrix, 55 mm pitch) developed in CERN by the Medipix collaboration was used for this study. An analog circuitry and a digital counter are integrated within each pixel of this device. The TimePix device, operated in time over threshold (TOT) mode, can use the counter as a Wilkinson type ADC providing spectroscopic capabilities in each individual pixel (see the explanation in Ref. [8]). At present we have Si (pixel size 55 55 mm2, thickness 300 mm) and CdTe (55 55 mm2 or 110 110 mm2, thickness 1 mm) detection modules available. Fig. 1 shows the typical response of a TimePix detector to various types of radiation— large blobs for alpha particles, curved lines for electrons, and straight lines for muons. Such particle identification would allow us to distinguish the positive signal (e.g. two electrons with the sum energy equal to Qbb) and the background (photons, a-particles, single electrons, etc.). For future use in any low-background setup, a determination of the impurities contained in the pixel detection module itself is extremely important. The aim is to exclude most of the external
P. Cermak et al. / Nuclear Instruments and Methods in Physics Research A 633 (2011) S210–S211
S211
Fig. 1. The typical response of Si TimePix detector (300 mm thick) to various types of radiation: (a) alpha particles, (b) electrons, and (c) muons. The bottom scale represents the deposited energy in arbitrary units. For further details on capabilities and applications of pixel detectors see e.g. Ref. [9].
Table 1 The total number of events per hour in the energy range of (20-1500) keV measured by the Si TimePix detector in various environments. Environment
Integral hour
Surface Underground Underground + Pb shielding
570 206 90
3. Conclusion
8
Counts / hour
7 6 5 4 3 2 1 0
0
200
400
600
800 E, keV
shows an example of the spectrum of radioimpurities in the CdTe pixel detector module, where mostly lines from U and Th decay chains can be found.
1000
1200
1400
Fig. 2. The spectrum of radioimpurities in the CdTe pixel detection module measured by the low-background HPGe detector in LSM.
sources of background and measure the response of the detector to the radiation coming mainly from the components of the detection unit. Table 1 compares the background signal (the total number of events) in the energy range 20–1500 keV in various environments: (i) surface—standard laboratory, (ii) underground— Modane Underground Laboratory (LSM, 4800 m.w.e.), and (iii) underground+Pb shielding (5 cm thick). To establish the internal contamination of the detection module we measured both Si and CdTe pixel detector modules using the ultra-low background setup located in LSM. It employs a planar type HPGe detector with a volume of 150 cm3. The amount of contaminants for the CdTe module is as follows: 228Th—(1567 10) mBq, 226Ra—(124711) mBq, and 40K—(122714) mBq. Fig. 2
We present first results of testing Si and CdTe pixel detectors for bb measurements. The energy sensitive tracking capabilities show that pixel detectors are a very promising technology for this application. This option should be considered in future R&D projects (such as a semiconductor Time Projection Chamber). However, the results of background measurements also indicate that the tested pixel detector modules are not yet ready for use in ultra-low background setups. The first thing that could be adapted is the design—part of electronic devices can be separated by e.g. re-designing the printed circuit board. Nevertheless, the readout chip and the indispensable components of the bump bonding technology (bumps, under-bump metallization) have to be always located in an immediate vicinity of the sensor. Another necessity is a selection of low-activity materials. All components should be verified using an ultra-low background HPGe detector. Presently, Monte Carlo studies towards the bb applications (pixel size and detector thickness optimization) are in progress.
Acknowledgments This activity is supported by Grant no. LA07050. We would also like to acknowledge the staff of the LSM for their support during all low-background measurements. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
C. Arnaboldi, et al., Nucl. Instr. and Meth. A518 (2004) 775. R. Arnold, et al., Phys. Rev. Lett. 95 (2005) 182302. I. Abt et al., hep-ex/0404039, 2004. K. Zuber, Phys. Lett. B519 (2001) 1. P. Benes, et al., Nucl. Instr. and Meth. A569 (2006) 737. /http://medipix.web.cern.chS. K. Zuber, AIP Conf. Proc. 942 (2007)96. X. Llopart, et al., Nucl. Instr. and Meth. A581 (2007) 485. J. Jakubek, JINST 4 (2009) P03013.