- Email: [email protected]
Study on the performance of large area MRPC with high position resolution
Nuclear Instruments and Methods in Physics Research A 661 (2012) S159–S162
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Study on the performance of large area MRPC with high position resolution$ Yue Qian a,b,, Wu Yucheng a,b, Li Yuanjing a,b, Ye Jin a,b, Cheng Jianping a,b, Wang Yi a,b, Li Jin a,b a b
Department of Engineering Physics, Tsinghua University, Beijing 100084, China Key Laboratory of Particle & Radiation Imaging, Tsinghua University, Ministry of Education, China
a r t i c l e in fo
abstract
Available online 1 September 2010
Multi-gap resistive plate chamber (MRPC), which is mostly developed in high energy physics domain with excellent time resolution, is also highlighted in imaging applications. A set of 50 cm 50 cm large area MRPC with high position resolution was successfully developed by our group and different experiments have been done to test its performances. Cosmic ray muons were used to do the test and proper high voltage and working gas were chosen. Data analysis indicates its good detection efficiency and good position resolution, which encourages further study of its application in RPC-PET and muon tomography. & 2010 Elsevier B.V. All rights reserved.
Keywords: MRPC Large area Working parameters Position resolution
1. Introduction In 2003, a new form of cosmic ray muon radiography, which is based on the multiple Coulomb scattering of muons when passing through materials, was proposed by LANL for detection and 3D imaging of dense high-Z objects [1–3]. By tracking the scattering angles of incoming and outgoing muons one by one with two groups of detectors with sub-millimeter-scale high position resolution, one can scan the density distribution of materials, especially heavy nuclear materials in the sensitive space between the two groups of detectors. In their study, drift chambers were used for precise measurement of muon tracks, and many exciting and inspiring results have been achieved. In this paper, a kind of large area multi-gap resistive plate chamber (MRPC) with high position resolution is studied for the possible application in muon tomography.
2. Structure of the MRPC As shown in Fig. 1, the MRPC detector is composed of two parallel resistive plate electrodes with five gas gaps divided by four resistive floating glasses with bulk resistivity of about 1012 O cm, while Nylon fishing lines are used to hold the thickness of gas gap. Each gap has a width of 0.33 mm, so the total sensitive thickness is about 1.7 mm. High voltage is applied on the carbon film (surface resistivity of 4 105 O=&) to provide homogeneous electric field, and outside of the carbon film, separated by a layer of 350 mmthick Mylar film, is the readout module on PCB to pick $
Supported by the National Natural Science Foundation of China (10875071).
Corresponding author at: Department of Engineering Physics, Tsinghua
University, Beijing 100084, China. E-mail address: [email protected] (Y. Qian). 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.08.088
up induced signals. A kind of two-dimensional readout method with strips and pads has been developed for the MRPC detector. The readout pitch is set to 2 mm for both X and Y dimension. The detailed structure of the readout electrodes is shown in Fig. 2. A method of two-dimensional read out electrode has been developed with certain PCB technology. All the pads in a line orthogonal to strips are connected together on the rear surface of the PCB. Thus the two-dimensional readout structure can pick up the induced signal when an avalanche occurs in the gas gaps of MRPC. The width of the long strip is 0.64 mm. The pad has a dimension of 1.7 mm 0.76 mm. The internal width between the strip and pad is 0.3 mm, and the same width is for neighboring pads. The prototype large area MRPC has the dimension of 500 mm 500 mm and effective region is about 440 mm 440 mm. The number of readout channels in each dimension is 222 with the pitch of 2 mm. Due to the limited number of electronic channels; we just use 80 channels of electronics to study the performance of the prototype MRPC.
3. Test experiment 3.1. Experiment setup Cosmic ray muons were used as the charged particle source to test the performance of the MRPC. The induced current signals from every detector channel were picked up by a current-sensitive preamplifier and then fed into a home-made main amplifier and FADC for digitization. The DAQ system was based on VME bus, and a PowerPC (Motorola MVME5100) interface was used for taking data. The experimental setup was designed to use triggering for signal selection. The trigger came from a coincident output of two scintillators that were served as cosmic ray telescopes for muon
S160
Y. Qian et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S159–S162
Fig. 1. The structure of the prototype MRPC detector.
Fig. 2. (a) Structure of readout electrode, (b) unit area.
tracking. The DAQ system recorded the current pulse shapes from all the channels when the system is triggered. Fig. 3 shows the schematic layout of the experimental setup. The induced charges from several adjoined strips describe the space distribution of the induced charge of an MRPC detector. The position of the incident muon can be obtained by applying the charge center method with signals from several adjoined strips both in two dimensions.
Fig. 3. The schematic layout of experimental setup for MRPC.
3.2. Operating gas The gas mixture of three ingredients has been used as the working gas as follows: F134a, iso-butane, and sulfur hexafluoride.
The contents of each gas will be changed to get optimum performance of MRPC. Fig. 4 shows curves of efficiency versus high voltage for the MRPC. The maximum efficiency, including both
Y. Qian et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S159–S162
S161
100
Efficiency (%)
95
90
85 F134a: iso-butane: SF6 92:5:3 92:5:3 90:5:5
80
90:5:5 87:8:5 87:8:5
75 7400
7450
7500
7550
7600
7650
7700
7750
7800
7850
7900
High Voltage (V) Fig. 4. Detection efficiency versus high voltage of different gas mixtures. The hollow circle represents total effective events, and the solid square unsaturated events. The saturated events mean those whose amplitudes of pulse shapes are beyond the dynamic range of FADC.
x104 2.0 Qx Qy
1.8 1.6
Counts
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0
5 10 Q value (FADC channel)
15 x104
Fig. 6. The spectra of unsaturated signal only from two dimensions.
saturated and unsaturated signals, reaches 95% at a voltage of 77550 V. We have chosen 77550 V as the optimal voltage for our MRPC. The working gas has been chosen as 87% F134a, 8% iso-butane and 5% sulfur hexafluoride. 3.3. Position resolution The central 80 channels of each dimension have been selected to study the position resolution of our MRPC detector. As described in Refs. [4,5], two-Gauss function is employed for fitting: 2
Fig. 5. Fitting of a event with two-Gauss function: (a) X dimension (b) Y dimension.
f ðxÞ ¼ p0 eðxp1Þ
=2p22
2
þp3 eðxp4Þ
=2p52
:
S162
Y. Qian et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S159–S162
2
χ / ndf Constant
×104
Mean Sigma
3
0.1322 / 18 2.855 ± 0.06414 0.5106 ± 0.002134 0.08416 ± 0.002285
Counts
2.5
charge distribution of whole unsaturated induced signals is Landau like, and the total charge is distributed approximately equally in two dimensions: Qx and Qy as shown in Fig. 6. Moreover, the ratio of charges in X-dimension over the total charges of two dimensions has a mean value of 0.5 as shown in Fig. 7, which validates the design of our two-dimensional readout method.
2 1.5
4. Summary 1 0.5 0 0
0.2
0.4
0.6
0.8
1
A kind of large area MRPC detector has been produced and its performance has been discussed. Proper operating gas as well as high voltage is chosen. Due to its high position resolution, one can say that the MRPC is a possible candidate of detector in muon radiography.
Qx/Qall Fig. 7. Distribution of the ratio between charge in X-dimension and the total charge of two dimensions.
A fitting result of both dimensions for one event is shown in Fig. 5, and the statistical position resolution is defined as sp1 2 ðmmÞ. For all events we have measured, the statistical errors of the fitting result of p1 are less than 0.25, totally which demonstrates the position resolution better than 0.5 mm statistically only, not including the systematic error. 3.4. Avalanche charge distribution If integrated the whole unsaturated pulse shape, we can obtain the Q value of every event in each dimension. One can see that the
Acknowledgments We thank Ms. Chunling Hui and her working group for their hard and careful work in producing MRPC detectors.
References [1] [2] [3] [4] [5]
K.N. Borozdin, G.E. Hogan, et al., Nature 433 (2003) 277. L.J. Schultz, et al., in: Proceedings of AccApp03, San Diego, CA, June 2003. W.C. Priedhorsky, K.N. Borozdin, et al., Rev. Sci. Instr. 74 (10) (2003) 4294. J. Ye, et al., Nucl. Instr. and Meth. A 591 (2008) 411. J. Ye, J.P. Cheng, et al., in: Proceedings of the IEEE NSS/MIC, vols. 1–9, 2008, p. 192.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Study on the performance of large area MRPC with high position resolution$ Yue Qian a,b,, Wu Yucheng a,b, Li Yuanjing a,b, Ye Jin a,b, Cheng Jianping a,b, Wang Yi a,b, Li Jin a,b a b
Department of Engineering Physics, Tsinghua University, Beijing 100084, China Key Laboratory of Particle & Radiation Imaging, Tsinghua University, Ministry of Education, China
a r t i c l e in fo
abstract
Available online 1 September 2010
Multi-gap resistive plate chamber (MRPC), which is mostly developed in high energy physics domain with excellent time resolution, is also highlighted in imaging applications. A set of 50 cm 50 cm large area MRPC with high position resolution was successfully developed by our group and different experiments have been done to test its performances. Cosmic ray muons were used to do the test and proper high voltage and working gas were chosen. Data analysis indicates its good detection efficiency and good position resolution, which encourages further study of its application in RPC-PET and muon tomography. & 2010 Elsevier B.V. All rights reserved.
Keywords: MRPC Large area Working parameters Position resolution
1. Introduction In 2003, a new form of cosmic ray muon radiography, which is based on the multiple Coulomb scattering of muons when passing through materials, was proposed by LANL for detection and 3D imaging of dense high-Z objects [1–3]. By tracking the scattering angles of incoming and outgoing muons one by one with two groups of detectors with sub-millimeter-scale high position resolution, one can scan the density distribution of materials, especially heavy nuclear materials in the sensitive space between the two groups of detectors. In their study, drift chambers were used for precise measurement of muon tracks, and many exciting and inspiring results have been achieved. In this paper, a kind of large area multi-gap resistive plate chamber (MRPC) with high position resolution is studied for the possible application in muon tomography.
2. Structure of the MRPC As shown in Fig. 1, the MRPC detector is composed of two parallel resistive plate electrodes with five gas gaps divided by four resistive floating glasses with bulk resistivity of about 1012 O cm, while Nylon fishing lines are used to hold the thickness of gas gap. Each gap has a width of 0.33 mm, so the total sensitive thickness is about 1.7 mm. High voltage is applied on the carbon film (surface resistivity of 4 105 O=&) to provide homogeneous electric field, and outside of the carbon film, separated by a layer of 350 mmthick Mylar film, is the readout module on PCB to pick $
Supported by the National Natural Science Foundation of China (10875071).
Corresponding author at: Department of Engineering Physics, Tsinghua
University, Beijing 100084, China. E-mail address: [email protected] (Y. Qian). 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.08.088
up induced signals. A kind of two-dimensional readout method with strips and pads has been developed for the MRPC detector. The readout pitch is set to 2 mm for both X and Y dimension. The detailed structure of the readout electrodes is shown in Fig. 2. A method of two-dimensional read out electrode has been developed with certain PCB technology. All the pads in a line orthogonal to strips are connected together on the rear surface of the PCB. Thus the two-dimensional readout structure can pick up the induced signal when an avalanche occurs in the gas gaps of MRPC. The width of the long strip is 0.64 mm. The pad has a dimension of 1.7 mm 0.76 mm. The internal width between the strip and pad is 0.3 mm, and the same width is for neighboring pads. The prototype large area MRPC has the dimension of 500 mm 500 mm and effective region is about 440 mm 440 mm. The number of readout channels in each dimension is 222 with the pitch of 2 mm. Due to the limited number of electronic channels; we just use 80 channels of electronics to study the performance of the prototype MRPC.
3. Test experiment 3.1. Experiment setup Cosmic ray muons were used as the charged particle source to test the performance of the MRPC. The induced current signals from every detector channel were picked up by a current-sensitive preamplifier and then fed into a home-made main amplifier and FADC for digitization. The DAQ system was based on VME bus, and a PowerPC (Motorola MVME5100) interface was used for taking data. The experimental setup was designed to use triggering for signal selection. The trigger came from a coincident output of two scintillators that were served as cosmic ray telescopes for muon
S160
Y. Qian et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S159–S162
Fig. 1. The structure of the prototype MRPC detector.
Fig. 2. (a) Structure of readout electrode, (b) unit area.
tracking. The DAQ system recorded the current pulse shapes from all the channels when the system is triggered. Fig. 3 shows the schematic layout of the experimental setup. The induced charges from several adjoined strips describe the space distribution of the induced charge of an MRPC detector. The position of the incident muon can be obtained by applying the charge center method with signals from several adjoined strips both in two dimensions.
Fig. 3. The schematic layout of experimental setup for MRPC.
3.2. Operating gas The gas mixture of three ingredients has been used as the working gas as follows: F134a, iso-butane, and sulfur hexafluoride.
The contents of each gas will be changed to get optimum performance of MRPC. Fig. 4 shows curves of efficiency versus high voltage for the MRPC. The maximum efficiency, including both
Y. Qian et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S159–S162
S161
100
Efficiency (%)
95
90
85 F134a: iso-butane: SF6 92:5:3 92:5:3 90:5:5
80
90:5:5 87:8:5 87:8:5
75 7400
7450
7500
7550
7600
7650
7700
7750
7800
7850
7900
High Voltage (V) Fig. 4. Detection efficiency versus high voltage of different gas mixtures. The hollow circle represents total effective events, and the solid square unsaturated events. The saturated events mean those whose amplitudes of pulse shapes are beyond the dynamic range of FADC.
x104 2.0 Qx Qy
1.8 1.6
Counts
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0
5 10 Q value (FADC channel)
15 x104
Fig. 6. The spectra of unsaturated signal only from two dimensions.
saturated and unsaturated signals, reaches 95% at a voltage of 77550 V. We have chosen 77550 V as the optimal voltage for our MRPC. The working gas has been chosen as 87% F134a, 8% iso-butane and 5% sulfur hexafluoride. 3.3. Position resolution The central 80 channels of each dimension have been selected to study the position resolution of our MRPC detector. As described in Refs. [4,5], two-Gauss function is employed for fitting: 2
Fig. 5. Fitting of a event with two-Gauss function: (a) X dimension (b) Y dimension.
f ðxÞ ¼ p0 eðxp1Þ
=2p22
2
þp3 eðxp4Þ
=2p52
:
S162
Y. Qian et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S159–S162
2
χ / ndf Constant
×104
Mean Sigma
3
0.1322 / 18 2.855 ± 0.06414 0.5106 ± 0.002134 0.08416 ± 0.002285
Counts
2.5
charge distribution of whole unsaturated induced signals is Landau like, and the total charge is distributed approximately equally in two dimensions: Qx and Qy as shown in Fig. 6. Moreover, the ratio of charges in X-dimension over the total charges of two dimensions has a mean value of 0.5 as shown in Fig. 7, which validates the design of our two-dimensional readout method.
2 1.5
4. Summary 1 0.5 0 0
0.2
0.4
0.6
0.8
1
A kind of large area MRPC detector has been produced and its performance has been discussed. Proper operating gas as well as high voltage is chosen. Due to its high position resolution, one can say that the MRPC is a possible candidate of detector in muon radiography.
Qx/Qall Fig. 7. Distribution of the ratio between charge in X-dimension and the total charge of two dimensions.
A fitting result of both dimensions for one event is shown in Fig. 5, and the statistical position resolution is defined as sp1 2 ðmmÞ. For all events we have measured, the statistical errors of the fitting result of p1 are less than 0.25, totally which demonstrates the position resolution better than 0.5 mm statistically only, not including the systematic error. 3.4. Avalanche charge distribution If integrated the whole unsaturated pulse shape, we can obtain the Q value of every event in each dimension. One can see that the
Acknowledgments We thank Ms. Chunling Hui and her working group for their hard and careful work in producing MRPC detectors.
References [1] [2] [3] [4] [5]
K.N. Borozdin, G.E. Hogan, et al., Nature 433 (2003) 277. L.J. Schultz, et al., in: Proceedings of AccApp03, San Diego, CA, June 2003. W.C. Priedhorsky, K.N. Borozdin, et al., Rev. Sci. Instr. 74 (10) (2003) 4294. J. Ye, et al., Nucl. Instr. and Meth. A 591 (2008) 411. J. Ye, J.P. Cheng, et al., in: Proceedings of the IEEE NSS/MIC, vols. 1–9, 2008, p. 192.