Summary of current AMS specifications for the JAEA-AMS-TONO.
The Tono Geoscience Center (TGC) of the Japan Atomic Energy Agency (JAEA) has been conducting research into the long term (several million years) stability of underground environments, in order to provide the scientific knowledge needed to ensure safety and reliability for the geological disposal of high-level radioactive waste [1–3]. The time scale for occurrence of the relevant geoscientific activities, as shown in Figure 1, i.e., earthquake/fault and volcanic activities, behavior of groundwater flow, uplift/subsidence and erosion of the ground surface, and so on, corresponds well to the duration of the Quaternary Period geology. Geochronology of the Quaternary Period has been strongly enhanced by measurement of terrestrial
Applications of accelerator mass spectrometry (AMS) using those rare radionuclides for geological studies have been summarized by various authors [4–7]. It is a well-known fact that 14C has been widely utilized in several disciplines, including geology, environmental science, archaeology, and biomedicine. With regard to research into underground geological disposal of waste, radiocarbon dating of organic samples (e.g., bulk organic, humic acid, and humin fractions) taken from faults provide an historical archive of typical conventional applications to the investigation of seismic activity [7,8]. The dates obtained, combined with other scientific and historical information, help to determine whether or not the fault is a so called “active fault”, and to estimate cyclicity of seismic events and probability for serious large fault movements during the post-closure duration of geological disposal.
Long-lived cosmogenic radionuclides, such as 10Be, 26Al, and 36Cl enable us to apply to the exposure dating methods on boulder and bedrock surfaces for exposure ages up to 107 years [4–7]. These methods can provide information relevant to geological disposal with respect to geomorphological evolution, i.e., erosion rates of rock surfaces, burial histories of rock surfaces and sediments, fault slip rates, and so on. One of the typical radionuclides for surface exposure dating is 10Be, or both 10Be and 26Al. The half-lives of 10Be and 26Al are long enough (1.6 Myr and 0.7 Myr, respectively) to span the entire Quaternary timescale. They can be produced simultaneously in a single sample of quartz where 26Al and 10Be are mainly produced through nuclear spallation from 28Si and 16O, respectively. Concentration of each depends on balance between
The measurement of 14C and 36Cl is also applicable to hydrogeologic investigations: studies of groundwater age, origin and mixing. Most of these nuclides are produced through interaction with alpha-particle/neutron emitted from radioactive elements such as Th and U within the sediment or rock dozens of meters or more underground, where there is no cosmogenic radionuclide production .
1.2. Purpose and contents of this article
Our ongoing efforts, therefore, have been dedicated to development of a multi-nuclide AMS for measurement of the rare radionuclides 10Be, 14C, 26Al, and 36Cl. In this article, the current status of the AMS system at the JAEA-AMS-TONO and our activities leading to development of a multi-nuclide AMS are presented.
The next section shows the history and present-day status of our AMS system. The detail of the AMS system and its configuration are described in Section 3. The current status for 14C, 10Be and 26Al measurements is presented in Sections 4, 5, and 6, respectively. Section 7 provides the research and development related to improvement of the isobar discrimination for the ionization chamber. Finally, Section 8 presents a summary.
2. Operation status
The history of the JAEA AMS system is depicted in Figure 2. The AMS system was installed at TGC in 1997, and routine measurement of 14C started in 1998 . The preliminary development of the 10Be-AMS started around 2002 , intensive development was implemented from 2010 to 2012 [11,12], and progress of which will be described in Section 5. After that, the routine measurement of 10Be started at the beginning of fiscal year 2013. At present, we have initiated the development of the 26Al-AMS (described in Section 6) [13,14]. Furthermore, as a part of preparatory activity for the development of the 36Cl-AMS, we have started to investigate the nature of the pulse trace that is disturbed by interfering particles in the heavy ion detector, in order to improve the discrimination performance for the detector system (presented in Section 7) .
The evolutions of the measurement time and the number of sample cathode (target) are shown in Figure 3. Total, cumulative, measurement time (the blue line) has increased more or less continuously for 15 years, and reached 15,000 hours this fiscal year. Around 2005, routine measurements ceased for a while due to system maintenance by the lab-staff. As shown on the bar chart, the average number of samples measured annually is between 800 and 1000, and the total number of samples will exceed 12,500 within the next few months. After the development of the 10Be measurement has been intensive since the start, the proportion of 10Be samples to the total sample number has increased rapidly. In fiscal year 2012, the proportion of 14C, 10Be and 26Al sample cathodes are 76%, 20%, and 4%, respectively.
In Figure 4, the pie chart on the left shows the proportion of 14C-AMS samples measured for the various study fields in fiscal year 2012. Geoscience accounted for about 60%, while environmental studies accounted for most of the balance. The proportion labeled as “Analysis” stands for the cathode number used in our technical development. The pie chart on the right in Figure 4 illustrates the relative proportion of measured samples requested by users in JAEA to other users. Almost all of the samples were requested by JAEA users. The measurement of the other samples were performed under JAEA’s common-use facility program for non-JAEA users . This program started in 2006, in order to enlarge and expand the public use of JAEA’s facilities. The study fields using the program were mostly in environmental science and archaeology.
3. AMS system
3.1. Overall features
The AMS system is a versatile system based on the PelletronTM tandem accelerator (Model 15SDH-2, 5 MV terminal voltage) . The same type (5 MV Pelletron) of the AMS system has been used in other facilities, for example, at the Micro Analysis Laboratory, Tandem accelerator (MALT) at the University of Tokyo, Japan , the AMS system at the National Institute for Environmental Studies (NIES) of Japan , at the Scottish Universities Environmental Research Center (SUERC) in the United Kingdom [20,21], and at the Uppsala 5 MV Pelletron tandem accelerator developed in the Uppsala University, Sweden [22,23].
This AMS system is designed for the AMS analysis with most radio-isotopes including 10Be, 14C, 26Al, 36Cl, and 129I. Although technological advances in recent years have enabled practical use of compact AMS systems below 1 MV allowing the measurement of 10Be, 14C, and 26Al [24–26], the relatively wide range of high terminal voltage greater than several megavolts has, even now, been generally recognized to be beneficial to efficient suppression of signal background, resulting in further potential for expandability for a multi-nuclides measurement.
3.2. System description 
Figure 5 is a schematic of the AMS system layout. The system can be divided into five major subsystems: the ion sources, the sequential injection system, the tandem Pelletron accelerator, the post-accelerator beamline with the high-energy mass spectrometer components, and the heavy ion detection system by means of the ionization chamber. There are eight vacuum turbomolecular pumping systems attached along the beamline, where, several beam steerers and magnetic or electrostatic lenses are located, and the total length of the system is around 31 metres. Summary of the system configuration for rare isotopes are presented individually in Table 1.
|Target||Graphite with Fe|
|BeO with Nb|
|Al2O3 with Ag|
|Current||20 μA (C-)||2 μA (BeO-)||0.1 μA (Al-)|
|Injection||Sequential (12C: 0.3 ms ,|
13C: 0.9 ms, 14C: 98.6 ms)
(26Al: 98 ms, 27Al: 1 ms)
|Transmit.||58% (12C)||21% (9Be)||39% (27Al)|
(60 cps@ HOxII)
(70 cps @S5-1)
(15 cps @S4-1)
|Background||< 7x10-16 (< 0.06 pMC) @WAKO Powder||< 7 x 10-15|
|< 3 x 10-14|
(with gas cell)
The ion sources, the Multi-Cathode, Source of Negative Ions by Cesium Sputtering (MC-SNICS) for solid samples (40 cathodes) and the Multiple Gas Feed, SNICS (MGF-SNICS) for CO2-gas samples (12 cathodes) are connected to the main beamline through the 45° electrostatic spherical analyzer (ESA). The sources consist of a cesium oven generating Cs vapour, a heated ionizer electrode producing a focused Cs+ beam at the sample cathode, and extraction and focus electrodes. Particles sputtered from the sample cathode by Cs+ bombardments pick up electrons as they pass through the cesium layer condensed on the sample; thus, negative ions are produced. To stabilize the cesium vapour feed to the source, we added a simple auto-controllable electrical heating subsystem to the cesium oven and its feeder pipe; the standard deviation of the temperature monitored during the routine measurement has been kept within a range of ±0.5C° . This type of simple technical addition or modification is commonly used for the same purpose . The acceleration voltage of the ion source is usually set to 55 kV. By using the beam-slit located at the image point of the ESA (before the injection magnet), the “tail” of the beam profile can be trimmed, where the tail is due to an energy spread in the sputtering process. This trimming assures open-aperture optical properties (often called “flat top transmission”) on the downstream side of that slit. The combination of the ESA and the injection magnet (
The AMS system employs the sequential injection method for the precise measurement of the ratio of rare to abundant isotopes regardless of fluctuations of source conditions. This method, or the rapid switching of the masses (isotopes) to be injected toward the accelerator, (so called sequence “bounced” or “jumping” beams) is accomplished by applying an appropriate bias potential to the electrically insulated bent chamber inside the injection magnet. Most of the duration (~99%) in the sequential injection is allocated for the measurement of the rare isotope (details in Table 1).
In the tandem Pelletron accelerator (15-SDH), there are two parallel chains charging the high-voltage terminal with current up to 300 μA. The consequent maximum terminal potential of 5 MV leads to the suitable stripped ionization state of 4+ for carbon by using a gas stripper (the ion beam energy is up to 25 MeV). For the chlorine, the charge state is designed to be 7+ or 8+ by using a foil stripper and its energy would be lie in the range of 42-45 MeV. The pressure of the stripper gas is typically 10 μTorr, 9 μTorr, and 5 μTorr for 14C-, 10Be-, and 26Al-measurement, respectively.
The high-energy mass spectrometer in the post-accelerator region is composed of magnetic and electrostatic filters and detector systems. The analyzing magnet (produced by Danfysik A/S) is a double focusing 90° sector magnet with a nominal radius of 1.270 m, having parameters of
The final detector for counting the rare isotopes, the “heavy ion detector”, is the gas ionization detector that contains multiple
4. 14C measurement
4.1. Stability and reliability
In the 14C-AMS operation, the stability and reliability of the routine measurements have been checked continuously against measuring standards. The typical standards are, IAEA-C1, -C5, and -C6 , and the oxalic acid HOxII (SRM-4990C) that is produced by the National Institute of Standards and Technology, NIST in the USA. Such checks have been performed simultaneously with routine measurements. In our AMS analysis, usually only the HOxII is used for obtaining the normalization constant that is given by the δ13C corrected activity divided by the
The left column of rectangles on Figure 6 shows the evolution of pMC for IAEA-C6, -C5, and -C1 in the year 2013. In some periods no 14C measurements were performed. The period from May to June was allotted for 10Be measurements. Intensive system maintenance was carried out (normally annually) in August, and then 10Be measurements were performed until the end of September. Almost all measured pMC-values for both C6 and C5 are in agreement with the nominal values within 3σ of each point (σ is basically the statistical uncertainty that is inversely proportional to the square root of 14C counts). A few irregular points in C6 could be due to surface roughness of the graphite sample. The roughness is reflected by unsuccessful graphite compression with an Arbor press (hammering with a press-pin). We continue to check the surface condition and data related to such irregular results.
The frames in the right-hand side of Figure 6 show histograms corresponding to temporal evolution for each standard in the left frames. It can be seen that the arithmetic mean of the histogram for C6 (labelled as
4.2. Inter-laboratory comparison testing
Comparison of the results obtained in different laboratories on the same samples is fundamental to objectively assessing accuracy and system performance. Comparison tests were carried out twice, in 2010 and 2012, with another AMS facility, the JAEA-AMS-MUTSU, of the Aomori Research and Development Center, JAEA [35,36]. This facility has provided high-quality 129I-and 14C-AMSs for environmental science studies, especially for marine transport properties of radio-isotopes, as well as for radiocarbon dating. The typical properties of the AMS system are as follows: a 3 MV Tandetron Cockcroft–Walton accelerator manufactured by High Voltage Engineering Europa, and the simultaneous injection system with the separator-combiner.
In the comparison test performed in 2012, the samples of the HOxII, C5, and C1 were prepared in the MUTSU, distributed to the TONO, and measured in both facilities. The measurement condition such as the duration time or the beam current was taken as the normal condition in each facility. Figure 7 shows results obtained in 2012. For the data analysis, the algorithm used in the TONO was employed. It can be seen for the C5, that there was no significant difference between data obtained in both facilities. The results of the C1 analyzed in the TONO are much lower than that for the MUTSU. This is mostly due to the fact that during 14C counting, 13C ions for the simultaneous injection also entered the accelerator continuously, thus the counting rate (or its possibility) of 13C coming into the ionization detector is much higher for the simultaneous injection than for the sequential injection, in spite of filtering by the combination of magnetic and electrostatic analyzers. Consequently, the measurement of quite low concentration samples is suitable relative to use by the TONO. The detailed results and discussion for the series of comparison tests will be summarised in a JAEA report in the future.
5. 10Be measurement
5.1. System configuration and method
The configuration for our 10Be-AMS operation is fundamentally standard, and is based on that used in the MALT [18,37,38]. Samples are made from the solid oxide of beryllium, BeO, for its positive electron affinity to produce negative ions. Since the amount of the rare isotope 10Be is distributed according to the abundance of oxygen isotope ratios, i.e., 16O : 17O : 18O=99.76: 0.04: 0.20, respectively, the 10Be16O is selected for injection into the accelerator to ensure high extraction efficiency of 10Be from the sample. The terminal voltage, usually set at 4.7 or 4.8 MV, is made preferably as high as possible within the range of around 8 MV so as to increase the stripping efficiency from negative ions to 3+ (in our AMS system, the terminal voltage is limited to the specification of 5 MV). In addition, the higher ion energy is also preferred for ensuring the good performance of the discrimination between 10Be and 10B for the heavy ion detector as described below (details in Section 5.2). One of the most significant features of 10Be measurement is the simultaneous injection of 9Be17O with mass the same as 10Be16O for counting the abundance of 9Be isotopes. For this purpose the current of 17O5+ is measured to avoid uncertainty in the amount of beryllium hydroxide 9Be16OH contamination in the sample . The abundance isotope is detected with a Faraday cup behind the analyzing magnet as shown in Figure 5.
The mathematical formula used for obtaining the measured isotope ratio (
The boron ions 10B3+ has the same charge-to-mass ratios as the 10Be3+, thus it remains on the beamline regardless of the magnetic and electrostatic filters, and results in the entry into the ionization chamber, with respect to the isobar problem as mentioned in Section 3. Usually a gas or solid absorber technique has been used to discriminate between them. Therefore, optimization of the absorber is fundamental in the 10Be measurement.
5.2. Optimization of the rare isotope detector
For the development of the 10Be-AMS, discrimination between the 10Be and 10B isotopes was accomplished by optimization of gas pressures in the ionization chamber and the absorber gas cell (hereinafter simply the gas-cell) attached in front of gas ionization chamber. Figure 8 shows the configuration of the rare isotope detector for the 10Be-AMS in our system. Ionization chamber consists of the cathode electrode (plate), grid, and anodes that are multiple (five)
As mentioned in Section 3.2, the
We investigated experimentally the discrimination function of the detector system through observation of the variation of the
The width of the 10Be peak defined by
5.3. Test measurements, Long-term reliability
We completed the development of the 10Be measurement technique last fiscal year (2012), confirming high stability and reliability of the 10Be/Be ratios in numerous test measurements. Even after we started to perform requested 10Be measurements in 2013, data quality has been continuously checked for every routine measurement using standards. Three typical standards are the ICN standards mention in the Section 5.1, S5-1, S5-2, S6-2, and a blank sample. The blank sample (hereafter BLK) is made from a quantified standard for atomic absorption spectrometry (No.020-07481) produced by Wako Pure Chemical Industries for which a 10Be/Be ratio of ~2×10-14 is expected . As shown in Section 5.1, S5-1 is used to obtain the normalization constant given by the measured ratio of S5-1 divided by its nominal ratio. With respect to the data quality of the S5-1 standard, the relative precision, in terms of the relative standard deviation
Figure 11 shows the quality of measurements from October 2011 to December 2013. The left column shows the evolution of the 10Be/Be ratios using the S5-2, S6-2, and BLK standards. The 10Be measurements have been conducted at intervals ranging from around a few months to half a year. All 10Be/Be ratios for both S5-2 and S6-2 agree with the nominal values within 3
The frames on the right-hand side of Figure 11 are histograms corresponding to the left-hand frames. It can be seen that the value of
5.4. Comparison test
We performed a comparison test with the AMS system in the MALT using beryllium samples made from an ice core. The samples measured in our system were originally prepared as spares for the 10Be measurements that had already been performed in the MALT accelerator in 2010. In this test, therefore, the samples measured at both facilities are produced by the same process for the comparison.
Figure 12 and Table 2 show the results of the comparison test. Almost all of the measured 10Be/Be ratios are consistent with the values obtained by the MALT AMS system. There is a significant difference between samples B and H (indicated by the arrow) taking into consideration their uncertainties, which could be due to unknown systematic errors. For the results of the 10Be/Be ratio measured in the MALT AMS system, two data sets are depicted for different data processing methods: one method is used at Hirosaki Univ. Japan, and the other is our method. The algorithms used for drawing the 10Be/Be ratios for both methods are almost the same In the calculation in the normalized constant, S5-1 and/or S5-2 were used atHirosaki Univ., but only S5-1 was used in the TONO.
In the calculation in the normalized constant, S5-1 and/or S5-2 were used atHirosaki Univ., but only S5-1 was used in the TONO.
On the other hand, the average uncertainty for the TONO (unc) is approximately 78% of that for the MALT (unc2). This is due to the fact that the total counts of the 10Be signal for the TONO were three times larger than that for the MALT because of longer measurement time at the TONO. It should be mentioned that the average count rate is 70 cps at the TONO but is 250 cps at the MALT AMS system, a reflection of the different specifications of their respective ion sources. Actually, the ion current for the MALT AMS system can provide a few times larger current than for the TONO.
6. 26Al measurement
6.1. Development and test measurements
Tuning up of the system and the test measurements for the routine 26Al-AMS operation started in March of 2013, after the development of routine 10Be measurements was finished. We plan to complete the development of the routine 26Al-AMS operation in the middle of fiscal year 2014, confirming the long term stability and reliability of the operation through statistical analysis of accumulated data.
For the 26Al measurements, Al2O3 powder is chosen as the sample material (mixed with silver powder), and fundamentally no isobar problems occur because 26Mg does not form negative ions. Therefore, the development of the 26Al-AMS procedure is more straightforward than the 10Be-AMS procedure. The configuration for 26Al-AMS is listed in Table 1.
Figure 13 shows the observed 26Al3+ peak in the
We have performed test measurements using 26Al standards, in order to investigate measurement stability. For the test measurements, the series of standards prepared and distributed by Nishiizumi have been used , as well as the 10Be measurement mentioned in Section 5.3. Typical standards, 01-4-1 and 01-5-1 (S4-1 and S5-1, respectively), especially the former have been employed to compute the normalization constant that is given by the measured ratio of a standard S4-1 divided by its nominal ratio. The blank sample (BLK) was made from a quantified standard for atomic absorption spectrometry (No.016-15471) supplied by Wako Pure Chemical Industries.
The left column on Figure 14 shows the results of the two test measurements carried out between routine 14C- and 10Be-AMS operations. Concerning the isotope ratio for the S4-1 standard, only the precision is meaningful (in other words, the accuracy has little meaning), since the arithmetic mean of the points obtained in the same batch (or on same date) is already normalized to the nominal value. A long-term precision can be drawn from the statistical dispersion of the data points displayed on the same figure, which will be mentioned in the below description related to the histogram. All data points for the S5-1 standard are consistent with the nominal value within 3
The histograms in the right-side frames in Figure 14 present the data distributions shown as data points in the left-side frames. The long-term precision of the S4-1 standard can be indicated by the statistical dispersion of their points in Figure 14a labelled as
7. Research and development: Baseline fluctuation of the 10Be pulse trace
As described in Section 5.2, we saw that discrimination between 10Be and 10B in the 10Be-AMS is strongly dependent on the gas pressure of the gas-cell (
The peak width is a reflection of the statistical dispersion of the pulse height of signal traces detected from the ionization chamber. Figure 15 shows pulse traces observed by the
Figure 16 shows both the variation of the standard deviation of the fluctuation (σ in Figure 15) and the energy loss of 10B in the area of
In general, if the incident frequency can no longer be ignored comparing the reciprocal of the time scale for the pulse width, a high counting rate induces pulse pile-up, and deteriorates the time resolution of the ionization chamber. Our investigation, by measuring the 10B current shows that the average frequency of the 10B incident is on the order of a megahertz, which is comparable to the reciprocal of the pulse width. In fact, the amount of 10B entering toward the ionization chamber is expected to be over 106 times larger than that of 10Be . The mechanism for the baseline fluctuation, however, is independent of the signal pile-up, but can be due to the effect of the charge accumulation in the ionization chamber, as qualitatively described below.
In ordinary cases, electrons (negative charges) and ions (positive charges) produced by the ionization caused by the incident ion colliding with atoms in the ionization chamber drift toward the anode and cathode, respectively, in the applied electric field, and finally lose their charge at the electrodes. In the present case, it should be noted that the time interval of the 10B incident is much shorter than the time scale for the ions-loss on the order of milliseconds for the ordinary condition as mentioned above. This can lead to the charge accumulation in the space; the positive charge reaches a certain level so as to provide a balance between production rate and loss rate. The substantial positive charge lowers the anode potential through the inefficiency of the Frisch-grid playing a role in shielding the charges [44,45]. If some instability exists inherently in the relationship between the enhancement of the charge and the ion loss system, the anode potential, therefore, can fluctuate around its equilibrium value. Volumetric ion-electron recombination would be a candidate system for causing an instability so as to enhance the fluctuation of positive charge. This kind of degradation of the performance of the ionization chamber caused by the residual positive charge is not just related to the 10Be measurement, but to more general measurements of rare isotopes accompanied by the isobar problem. Indeed, an effect of remaining charge was mentioned in a paper for improving the discrimination of 36S in 36Cl-AMS . Therefore, it can be said that the investigation of the nature of pulse trace presented here has been conducted as a preparatory activity in the development of the 36Cl-AMS operation.
The AMS system operating at the Tono Geoscience Center (TGC) has not only continued to contribute reliable routine AMS measurements, but also made steady progress in developing multi-nuclide AMS in order to provide geochronological dating methods applicable to the entire Quaternary timescale.
Our versatile AMS system, based on the 5 MV PelletronTM tandem accelerator, is designed for AMS analysis of most radio-isotopes including 10Be, 14C, 26Al, 36Cl, and 129I. The AMS system is in good condition after fifteen years of operation, ensured by regularly scheduled maintenance. Total measurement time has been increasing for the last 15 years, and reached 15,000 hours this year. The average annual number of samples measured is 800, and the grand total number of samples will exceed 12,500 within a few months.
In the 14C-AMS operation, the long-term reliability of routine measurements has been continuously verified by measuring standard samples such as C1, C5, and so on, produced by the IAEA, and HOxII produced by the NIST and by comparative testing with other AMS facilities. Almost all the relative standard deviations of the isotope ratios of HOxII in percent modern carbon are less than 0.25% for each measurement, and the average isotope ratio of C1 lies around 0.15 pMC. The comparison tests were carried out twice, in 2010 and in 2012, with the AMS facility at the JAEA-AMS-MUTSU. The results showed that there was no significant difference in the data obtained from the facilities.
With respect to the 10Be-AMS operation, we completed the development of 10Be measurement capability last year, confirming both high stability and reliability of the 10Be/Be ratios obtained from numerous test measurements. Then, routine measurements started since the beginning of fiscal year 2013. The detection limit of the isotope ratio can be less than 7 × 10-15, estimated by using samples made of commercial high-purity BeO powders. For the development of 10Be-AMS, discrimination of 10Be from 10B was accomplished by optimization of gas pressure in the gas cell located in front of gas ionization chamber. We also performed a comparison test with the AMS system at the MALT in the University of Tokyo using beryllium samples taken from an ice core. Measured 10Be/Be ratios were consistent with the values obtained by the MALT group, confirming the reliability of our measurements.
We have now entered into the development of 26Al-AMS. This development and the test measurement have progressed and have shown satisfactory results. We have performed system tuning and test measurements using 26Al standard samples. Almost all measured ratios of 26Al/Al are consistent with nominal values, within the range of their uncertainty and routine measurements of 26Al will start in the near future.
We have also conducted investigations for improving the heavy ion detection system based on the
We would like to express our gratitude to Prof. Matsuzaki of the University of Tokyo for his continuous academic and practical advice. We would like to offer our special thanks also to Dr. Horiuchi of Hirosaki University for providing unknown beryllium samples and measurement data. Special thanks to Mr. Hanaki of the facility administrator for his management support and constant encouragement. We also thank the staff members of the AMS laboratory for their help and support.
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- In the calculation in the normalized constant, S5-1 and/or S5-2 were used atHirosaki Univ., but only S5-1 was used in the TONO.