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Fine grained nuclear emulsion for higher resolution tracking detector
Nuclear Instruments and Methods in Physics Research A 718 (2013) 519–521
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Fine grained nuclear emulsion for higher resolution tracking detector T. Naka a,n, T. Asada b, T. Katsuragawa b, K. Hakamata b, M. Yoshimoto b, K. Kuwabara b, M. Nakamura b, O. Sato b, T. Nakano b, Y. Tawara c, G. De Lellis d, C. Sirignano e, N. D’Ambrossio f a
Institute of Advanced Research, Nagoya University, Nagoya, Japan Graduated School of Science, Nagoya University, Nagoya, Japan c Division of Energy Science, EcoTopia Science Institute, Nagoya University, Nagoya, Japan d INFN Sezione di Napoli, Napoli, Italy e INFN Sezione di Padova, Padova, Italy f INFN, Laboratori Nazionali del Gran Sasso, Assergi (L’Aquila), Italy b
a r t i c l e i n f o
abstract
Available online 28 November 2012
Fine grained nuclear emulsion with several 10 nm silver halide crystals can detect submicron tracks. This detector is expected to be worked as dark matter detector with directional sensitive. Now, nuclear emulsion became possible to be produced at Nagoya University, and extreme fine grained nuclear emulsion with 20 nm diameter was produced. Using this emulsion and new reading out technique with expansion technique, for optical selection and X-ray microscopy, recoiled tracks induced by dark matter can be detected automatically. Then, readout efficiency is larger than 80% at 120 nm, and angular resolution for final confirmation with X-ray microscopy is 201. In addition, we started to construct the R&D underground facility in Gran Sasso. & 2012 Elsevier B.V. All rights reserved.
Keywords: Tracking detectors Nuclear emulsion Directional dark matter search
1. Introduction Nuclear emulsion is a type of photographic film, but it can come out a track of charged particle. For current nuclear emulsion, the spatial resolution is extreme higher than other particle detector (about 1210 mm). In past, the extreme higher resolution made a quite slow readout, and so it was disadvantage for nuclear emulsion. However, this disadvantage was overcome by automatic scanning system with optical microscope. Nuclear emulsion is constituted by silver halide crystals and polymer to bind the crystals (usual gelatin is used). Spatial resolution of nuclear emulsion is defined by the crystal size and density. Moreover, nuclear emulsion is very flexible to control the sensitivity by chemical and development treatment. Until now, the development of nuclear emulsion depended on company. For example, the nuclear emulsion films used in OPERA experiment had been made by Fuji Film [1]. Here, we propose the directional dark matter search with nuclear emulsion as new emulsion experiment. However, this project is required a quite new technology for nuclear emulsion because the tracks to detect are quite shorter length than ones of current emulsion experiments. Here, we report fine grained nuclear emulsion and new readout technique as the essential
n
Corresponding author. E-mail address: naka@flab.phys.nagoya-u.ac.jp (T. Naka).
0168-9002/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nima.2012.11.106
new technology for directional dark matter search experiment or other application.
2. Production of fine grained nuclear emulsion Production of nuclear emulsion had been bear by company, but it had problem for the project required flexible R&D. Therefore, we made possible to produce the nuclear emulsion itself in house by collaborating with retired engineer from company. Nuclear emulsion is constituted by silver halide crystals which dispersed in gelatin. As the size of silver halide crystal defines spatial resolution and sensitivity, it is very important factor. By this production system, we have already controlled the crystal sizes freely. This example images of the crystals are shown in Fig. 1. We found that polyvinyl alcohol (PVA) can suppress the crystal growth. This means that finer grained nuclear emulsion can be produced more stably. It has the mean crystal size of 18.070.2 nm, it is the best record for fine grained nuclear emulsion. Current density of nuclear emulsion is 3.1 g/cm3, but recent result indicated that can be produced the one of 4.0 g/cm3. This means that the number of crystals per 1 mm correspond to 41 grains=mm. By increasing the numbers, energy threshold can be brought down or accidental backgrounds can be reduced. Fine grained nuclear emulsion can detect the tracks of more than 100 nm [2]. However, such tracks should be read out
520
T. Naka et al. / Nuclear Instruments and Methods in Physics Research A 718 (2013) 519–521
Fig. 1. Controlled silver halide crystal at nuclear emulsion production facility at Nagoya University.
Fig. 3. Micrographs of recoiled heavy nuclei (Br or C) tracks induced by 14.8 MeV neutron matched between optical and X-ray microscopy. Fig. 2. Optical microscope images of recoiled nuclei tracks induced by 14.8 MeV neutron and angular distribution of that. Here, 1 of cosine corresponds to the direction of neutron.
automatically for realistic experiment. About this techniques, we go into the detail in the next section.
Using X-ray microscope system, we evaluated the readout efficiency for optical readout. As the results, original track length of 90–100 nm has 60%, 100–120 nm has 80%, and more than 120 nm has more than 90%. Here, wavelength of light for readout of 550 nm, numerical apperture (NA) of 1.25, CMOS camera of 1 Mpix, 120 fps were used.
3. Readout technique for submicron tracks
4. Near future planning
Our concept is high speed readout by optical microscope in first and observation to confirm the selected candidate tracks in detail by X-ray microscope finally. Track length threshold for readout with optical microscope is limited by optical resolution. In particular, around 100 nm length tracks are complicated to distinguish as tracks. To resolve that, we developed expansion technique [3]. By this technique, as tracks are elongated to two times, we can distinguish those as elliptical configuration. Here, as major length corresponds to direction of tracks and length, we can select the candidate tracks by ellipticity parameter. This were simulated using 14.8 MeV neutron due to D–T nuclear fission reaction. Recoiled tracks induced by neutron are detected by optical microscope scanning like Fig. 2, which indicates the angular distribution of directionality for incoming neutron. On the X-ray microscope stage, we confirmed whether those are true tracks. This matching efficiency between optical and X-ray images was more than 99%. The example images compared between those are shown in Fig. 3. Angular resolution for such very short length tracks is expected to be about 201 or better.
We progress the construction of underground facility for R&D in Gran Sasso, Italy. In here, we will start the background study and neutron flux measurement. Our first aim is to search DAMA region [4] by directional detection with several 10 kg year.
5. Conclusion We developed the new nuclear emulsion with very higher resolution and new readout technique for directional dark matter search. Nuclear emulsion became capable to produce by ourselves. As crystal size is essential factor for spatial resolution, to produce fine grained nuclear emulsion was important subject for detection of recoiled nuclei induced by dark matter. We became possible to produce the very fine crystal of 20 nm with high density by mix of gelatin and PVA. In addition, the tracks with more than 100 nm could be read out with optical microscope automatically, and final confirmation became possible by X-ray microscope system. From now, using this detector and readout system, background study will be started in Gran Sasso, Italy.
T. Naka et al. / Nuclear Instruments and Methods in Physics Research A 718 (2013) 519–521
521
Acknowledgments
References
This work is supported by the Grant-in-Aid for Research Activity Start-up (23840018) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The synchrotron radiation experiments were performed at the BL47XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2011A1415/ BL47XU, 2011B1562/BL47XU).
[1] Taku Nakamura, et al., Nuclear Instruments and Methods in Physics Research Section A 556 (2006) 80. [2] Tatsuhiro Naka, et al., Status of Directional Dark Matter Search with Nuclear Emulsion, PoS040, 2010. [3] M. Kimura, T. Naka, Nuclear Instruments and Methods in Physics Research Section A 680 (2012) 12. [4] R. Bernabei, et al., New Results from DAMA/LIBRA, arXiv:1002.1028v1, 2010.
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Fine grained nuclear emulsion for higher resolution tracking detector T. Naka a,n, T. Asada b, T. Katsuragawa b, K. Hakamata b, M. Yoshimoto b, K. Kuwabara b, M. Nakamura b, O. Sato b, T. Nakano b, Y. Tawara c, G. De Lellis d, C. Sirignano e, N. D’Ambrossio f a
Institute of Advanced Research, Nagoya University, Nagoya, Japan Graduated School of Science, Nagoya University, Nagoya, Japan c Division of Energy Science, EcoTopia Science Institute, Nagoya University, Nagoya, Japan d INFN Sezione di Napoli, Napoli, Italy e INFN Sezione di Padova, Padova, Italy f INFN, Laboratori Nazionali del Gran Sasso, Assergi (L’Aquila), Italy b
a r t i c l e i n f o
abstract
Available online 28 November 2012
Fine grained nuclear emulsion with several 10 nm silver halide crystals can detect submicron tracks. This detector is expected to be worked as dark matter detector with directional sensitive. Now, nuclear emulsion became possible to be produced at Nagoya University, and extreme fine grained nuclear emulsion with 20 nm diameter was produced. Using this emulsion and new reading out technique with expansion technique, for optical selection and X-ray microscopy, recoiled tracks induced by dark matter can be detected automatically. Then, readout efficiency is larger than 80% at 120 nm, and angular resolution for final confirmation with X-ray microscopy is 201. In addition, we started to construct the R&D underground facility in Gran Sasso. & 2012 Elsevier B.V. All rights reserved.
Keywords: Tracking detectors Nuclear emulsion Directional dark matter search
1. Introduction Nuclear emulsion is a type of photographic film, but it can come out a track of charged particle. For current nuclear emulsion, the spatial resolution is extreme higher than other particle detector (about 1210 mm). In past, the extreme higher resolution made a quite slow readout, and so it was disadvantage for nuclear emulsion. However, this disadvantage was overcome by automatic scanning system with optical microscope. Nuclear emulsion is constituted by silver halide crystals and polymer to bind the crystals (usual gelatin is used). Spatial resolution of nuclear emulsion is defined by the crystal size and density. Moreover, nuclear emulsion is very flexible to control the sensitivity by chemical and development treatment. Until now, the development of nuclear emulsion depended on company. For example, the nuclear emulsion films used in OPERA experiment had been made by Fuji Film [1]. Here, we propose the directional dark matter search with nuclear emulsion as new emulsion experiment. However, this project is required a quite new technology for nuclear emulsion because the tracks to detect are quite shorter length than ones of current emulsion experiments. Here, we report fine grained nuclear emulsion and new readout technique as the essential
n
Corresponding author. E-mail address: naka@flab.phys.nagoya-u.ac.jp (T. Naka).
0168-9002/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nima.2012.11.106
new technology for directional dark matter search experiment or other application.
2. Production of fine grained nuclear emulsion Production of nuclear emulsion had been bear by company, but it had problem for the project required flexible R&D. Therefore, we made possible to produce the nuclear emulsion itself in house by collaborating with retired engineer from company. Nuclear emulsion is constituted by silver halide crystals which dispersed in gelatin. As the size of silver halide crystal defines spatial resolution and sensitivity, it is very important factor. By this production system, we have already controlled the crystal sizes freely. This example images of the crystals are shown in Fig. 1. We found that polyvinyl alcohol (PVA) can suppress the crystal growth. This means that finer grained nuclear emulsion can be produced more stably. It has the mean crystal size of 18.070.2 nm, it is the best record for fine grained nuclear emulsion. Current density of nuclear emulsion is 3.1 g/cm3, but recent result indicated that can be produced the one of 4.0 g/cm3. This means that the number of crystals per 1 mm correspond to 41 grains=mm. By increasing the numbers, energy threshold can be brought down or accidental backgrounds can be reduced. Fine grained nuclear emulsion can detect the tracks of more than 100 nm [2]. However, such tracks should be read out
520
T. Naka et al. / Nuclear Instruments and Methods in Physics Research A 718 (2013) 519–521
Fig. 1. Controlled silver halide crystal at nuclear emulsion production facility at Nagoya University.
Fig. 3. Micrographs of recoiled heavy nuclei (Br or C) tracks induced by 14.8 MeV neutron matched between optical and X-ray microscopy. Fig. 2. Optical microscope images of recoiled nuclei tracks induced by 14.8 MeV neutron and angular distribution of that. Here, 1 of cosine corresponds to the direction of neutron.
automatically for realistic experiment. About this techniques, we go into the detail in the next section.
Using X-ray microscope system, we evaluated the readout efficiency for optical readout. As the results, original track length of 90–100 nm has 60%, 100–120 nm has 80%, and more than 120 nm has more than 90%. Here, wavelength of light for readout of 550 nm, numerical apperture (NA) of 1.25, CMOS camera of 1 Mpix, 120 fps were used.
3. Readout technique for submicron tracks
4. Near future planning
Our concept is high speed readout by optical microscope in first and observation to confirm the selected candidate tracks in detail by X-ray microscope finally. Track length threshold for readout with optical microscope is limited by optical resolution. In particular, around 100 nm length tracks are complicated to distinguish as tracks. To resolve that, we developed expansion technique [3]. By this technique, as tracks are elongated to two times, we can distinguish those as elliptical configuration. Here, as major length corresponds to direction of tracks and length, we can select the candidate tracks by ellipticity parameter. This were simulated using 14.8 MeV neutron due to D–T nuclear fission reaction. Recoiled tracks induced by neutron are detected by optical microscope scanning like Fig. 2, which indicates the angular distribution of directionality for incoming neutron. On the X-ray microscope stage, we confirmed whether those are true tracks. This matching efficiency between optical and X-ray images was more than 99%. The example images compared between those are shown in Fig. 3. Angular resolution for such very short length tracks is expected to be about 201 or better.
We progress the construction of underground facility for R&D in Gran Sasso, Italy. In here, we will start the background study and neutron flux measurement. Our first aim is to search DAMA region [4] by directional detection with several 10 kg year.
5. Conclusion We developed the new nuclear emulsion with very higher resolution and new readout technique for directional dark matter search. Nuclear emulsion became capable to produce by ourselves. As crystal size is essential factor for spatial resolution, to produce fine grained nuclear emulsion was important subject for detection of recoiled nuclei induced by dark matter. We became possible to produce the very fine crystal of 20 nm with high density by mix of gelatin and PVA. In addition, the tracks with more than 100 nm could be read out with optical microscope automatically, and final confirmation became possible by X-ray microscope system. From now, using this detector and readout system, background study will be started in Gran Sasso, Italy.
T. Naka et al. / Nuclear Instruments and Methods in Physics Research A 718 (2013) 519–521
521
Acknowledgments
References
This work is supported by the Grant-in-Aid for Research Activity Start-up (23840018) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The synchrotron radiation experiments were performed at the BL47XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2011A1415/ BL47XU, 2011B1562/BL47XU).
[1] Taku Nakamura, et al., Nuclear Instruments and Methods in Physics Research Section A 556 (2006) 80. [2] Tatsuhiro Naka, et al., Status of Directional Dark Matter Search with Nuclear Emulsion, PoS040, 2010. [3] M. Kimura, T. Naka, Nuclear Instruments and Methods in Physics Research Section A 680 (2012) 12. [4] R. Bernabei, et al., New Results from DAMA/LIBRA, arXiv:1002.1028v1, 2010.