Geochemical Journal, Vol. 55 (No. 4), Pp. 209-222, 2021

Geochemical Journal, Vol. 55, pp. 209 to 222, 2021 doi:10.2343/geochemj.2.0630

10Be/9Be ratios of phenakite and beryl measured via direct Cs sputtering: Implications for selecting suitable Be carrier minerals for the measurement of low-level 10Be

ATSUNORI NAKAMURA,1* ATSUYUKI OHTA,1 HIROYUKI MATSUZAKI2 and TAKASHI OKAI1

1Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan 2Micro Analysis Laboratory, Tandem Accelerator (MALT), The University Museum, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan

(Received December 23, 2020; Accepted April 29, 2021)

Preparing Be carrier solutions with low 10Be/9Be ratios is essential for the applications of in-situ-produced cosmogenic 10Be in geochronology. This is because commercially available Be carriers are non-negligibly contaminated by 10Be. Recently, in-house Be carriers have been successfully applied to samples that contain small amounts of in-situ-produced 10Be. The first step in preparing in-house Be carriers is selecting suitable Be-bearing minerals that contain less 10Be. Here, we present a simple method for selecting appropriate raw minerals for in-house Be carriers. That is, measuring the 10Be/ 9 10 9 Be ratios of Be-bearing minerals by direct Cs sputtering. Analyses of the Be/ Be ratios of phenakite (Be2SiO4) and beryl (Be3Al2Si6O18) obtained from a mineral collection at the Geological Survey of Japan indicate that phenakite gener- ally contains more 10B, interfering isobar of 10Be, than beryl. In addition to the necessity of finding raw materials that contain low 10Be, our results indicate that it is preferable to select a starting material with a low B concentration. Frag- ments of Be-bearing minerals from target samples were directly packed, and showed effective beam currents. Therefore, we anticipate that the direct packing method can also potentially be used to measure 10Be in Be-bearing minerals for geological applications. The measurement background of accelerator mass spectrometry was evaluated using a B-removed Be carrier solution. While B is partly adhered to hydroxide gel, we demonstrate that the hydroxide gel wash reduces B in a Be carrier solution. To highlight the 10Be/9Be ratios of Be-bearing minerals against commercially available Be solutions, we also investigated the 10Be/9Be ratios of commercially available Be solutions.

Keywords: 10Be, cosmogenic nuclide, phenakite, beryl, beryllium carrier solution

measurement of 10Be/9Be ratios using accelerator mass INTRODUCTION spectrometry (AMS). The 10Be concentrations are calcu- Lowering the measurement background of 10Be allows lated from the measured 10Be/9Be ratios and the amount us to broaden its applications in geochronology, and is of added 9Be. If a large amount of 10Be exists in the car- crucial for measuring in-situ-produced 10Be at geologi- rier, this overwrites the 10Be concentrations of the sam- cal settings with small amounts of nuclide accumulation. ples. This phenomenon cannot be corrected accurately by Although several challenges are associated with lower blank subtractions. The propagated uncertainties for 10Be background measures, preparation of in-house Be carrier concentrations in the samples are much smaller when the solutions from Be-bearing minerals has significantly im- 10Be/9Be ratios of the blanks are well below those of the proved the detection limit of measurements (Balco, 2011). samples. Therefore, Be carriers with low 10Be/9Be ratios Commercially available Be (9Be) carriers typically con- are required to measure low-level 10Be concentrations. tain a non-negligible amount of 10Be contamination, and Fortunately, the 10Be component of Be carriers was are, thus, less ideal for analysis (Middleton et al., 1984; recognized early in the development of 10Be analysis us- Bierman et al., 2002; Merchel et al., 2008; Balco, 2011; ing AMS (Middleton et al., 1984). However, in the 1980s Corbett et al., 2016). In laboratory procedures, a known and 1990s, a commercially variable Be carrier was the amount of Be carrier is added to samples to facilitate the only available solution for Be analysis (Balco, 2011). Subsequently, scientists developed a fusion method to prepare an in-house Be carrier from deep-mined beryl *Corresponding author (e-mail: [email protected]) (Stone, 1998) and an HF dissolving method for an in- Copyright © 2021 by The Geochemical Society of Japan. house Be carrier from phenakite (Merchel et al., 2008,

209 2013). For slightly more than a decade, in-house Be car- STUDY DESIGN riers have been successfully applied to samples that contain small amounts of in-situ-produced 10Be. These carri- Before presenting the 10Be/9Be ratios of the minerals, ers are used to date rocks with exposure ages of only a we first evaluated the background of AMS at the Micro few hundred years (e.g., Schaefer et al., 2009), to obtain Analysis Laboratory, Tandem accelerator (MALT), the remarkably fast denudation rates on steep landscapes (e.g., University of Tokyo, using an in-house Be carrier pre- Derrieux et al., 2014), to measure muon-produced 10Be pared at Purdue Rare Isotope Measurement (PRIME) labo- at deep depths (e.g., Braucher et al., 2011, 2013), and to ratory, Purdue University. Since preliminary measure- determine burial ages (e.g., Granger et al., 2015). Fur- ments indicated that the carrier contained a considerable thermore, in-house Be carriers have been successfully amount of 10B for measurements at MALT, we repeated used to measure in-situ-produced 10Be at unique settings the hydroxide wash to remove B from the carrier solu- such as the Greenland Ice Sheet Project Two (GISP2) tion. A hydroxide gel wash is a commonly used method bedrock core (Schaefer et al., 2016) and marine sediment to reduce B and other soluble elements from solution (von cores proximal to ice sheets (Bierman et al., 2016; Shakun Blanckenburg et al., 1996; Ochs and Ivy-Ochs, 1997; et al., 2018). Gosse and Phillips, 2001; Simon et al., 2013). However, Before conducting chemical procedures to prepare an to the best of our knowledge, the B reduction rate has not in-house Be carrier, suitable Be-bearing minerals that been reported with actual experimental data. This study contain only trace amounts of 10Be are required as the documents the sequential removal of B and reports the raw material. However, whether the occurrence of such efficiency of the hydroxide gel wash method. We then minerals is rare or common among available Be-bearing analyze the 10Be/9Be ratios of the Be-bearing minerals, minerals remains uncertain. Once the appropriate Be-bear- demonstrating the implications of selecting the appropri- ing minerals are located, Be is extracted from the min- ate minerals for an in-house Be carrier. Finally, we show eral following one of the well-documented procedures the 10Be/9Be ratios of commercial Be carrier solutions and (Stone, 1998; Merchel et al., 2008, 2013). Preliminary discuss possible origins of 10Be in the solutions. measurements of 10Be/9Be from the selected Be-bearing minerals prevents processing whole minerals that yield MATERIALS AND METHODS high 10Be/9Be ratios. In addition to the expense and time- consumption of processing a Be-bearing mineral with high Preparation of in-house Be carrier 10Be/9Be ratios, researchers are spared the difficulty of The ‘low-level Be carrier’ (2017.11.17-Be, bottle extracting from minerals that do not dissolve easily such number 20) was provided by PRIME lab, Purdue Univer- as beryl and phenakite (Langmyhr and Sveen, 1965). Here, sity, and is referred to hereafter as the original carrier. we present the details of 10Be/9Be measurements from Be- The carrier solution was made from phenakite. The con- bearing minerals without chemical treatment as a simple centration of Be was 1074 ± 8 µg/g (e.g., Lesnek et al., pioneer method for selecting appropriate Be-bearing min- 2020) and the recommended value of 10Be/9Be was 5 ± 1 erals. This study is motivated by the research of Merchel × 10–16. We prepared four targets with minimal treatments et al. (2013), who briefly reported a test measurement of to avoid possible contamination. In small quartz vials, untreated phenakite fragments before preparing an in- 300 µg of Be aliquots were evaporated, converted to BeO, house Be carrier solution. Our research revisits the method mixed with Nb at an approximately 1:1 molar ratio, and and provides details of pressing mineral fragments into pressed into Cu cathodes. cathodes and analyzing the resultant beam currents over sputtering time. We selected samples of phenakite and Boron removal from the in-house Be carrier beryl stored in the mineral collection at the Geological The direct evaporation procedure revealed high 10Be/ Museum, Geological Survey of Japan (GSJ), National 9Be ratios of 6–10 × 10–15 due to 7Be tails from the reac- Institute of Advanced Industrial Science and Technology tion of 10B(p,α)7Be (see results sections below). There- (AIST), to demonstrate an appropriate and cautious man- fore, we conducted hydroxide washes to remove B from ner for selecting minerals for in-house Be carrier prepa- the carrier solution. Thirty grams of the original carrier ration. Phenakite (Be2SiO4) is a rare mineral compared (2017.11.17-Be, bottle number 20) was transferred to a to beryl (Be3Al2Si6O18) and is difficult to obtain. How- 50 mL polypropylene tube. The hydroxide precipitate ever, phenakite has the advantage of not containing Al. washing procedure consisted of two stages (Fig. 1). The 26 2+ Given that in-situ-produced Al is often measured along- first wash precipitated Be(OH)2 from the Be solution at 10 side in-situ-produced Be, Al needs to be removed when a pH of 8 after adding 30% NH4OH. This was followed preparing an in-house Be carrier from beryl (Stone, 1998). by centrifugation, and the supernatant solution was de- Conversely, we show that phenakite tends to contain more canted. The second wash consisted of mixing the Be(OH)2 10B, which is an isobar of 10Be. gel with deionized (DI) water using a vortex mixer, fol-

210 A. Nakamura et al. Fig. 1. Boron removal method by hydroxide gel washing. The washing procedures of hydroxide precipitate consist of two stages.

The first stage is precipitating Be(OH)2 at pH 8, centrifuging, and decanting the supernatant solution. The second stage is mixing the Be(OH)2 gel with DI water using a vortex mixer, centrifuging, and decanting the supernatant solution. These procedures were repeated three times. The supernatant solutions at each step were measured using ICP-MS.

Fig. 2. Photographs of the measured Be-bearing minerals. The minerals were selected from the mineral collection stored at the GSJ. (a) Phenakite-1. (b) Phenakite-2. (c) Phenakite-3. (d) Beryl-1. (e) Beryl-2. (f) Beryl-3.

lowed by centrifuging and decanting the supernatant so- used were of ultra-pure grade supplied by Kanto Chemi- lution. The second wash was conducted without convert- cal Co., Inc. 2+ ing Be(OH)2 to soluble Be . The precipitate was dis- We measured the supernatant solutions at each step solved using 60% HNO3. We developed this two-stage using inductively coupled plasma mass spectrometry washing method based on previous studies (Stone, 1998; (ICP-MS), Agilent 7900. Be, Na, Mg, and Ca were meas- Bierman et al., 2002). Here, we refer to the first and the ured using the He collision mode, and B was measured 2+ second stages as ‘Be to Be(OH)2 wash’ and ‘Be(OH)2 using the no gas mode. wash’, respectively. We repeated these hydroxide washes The six-times washed Be(OH)2 precipitate was finally three times (Fig. 1). Accordingly, we washed the hydrox- adjusted to a Be concentration of 300 µg/g in 2% HNO3, ide precipitation six times. The volume of the precipitate henceforth referred to as the washed carrier. The concen- and the supernatant were 7.5 and 42.5 mL. All chemicals tration of Be was measured using inductively coupled

10Be/9Be ratios of phenakite and beryl measured via direct Cs sputtering 211 Table 1. Origins of the minerals measured in this study

Mineral ID Mineral Designated IDa Origin Phenakite-1 Phenakite GSJ M34694 Sao Miguel de Piracicaba, Minas Gerais, Brazil Phenakite-2 Phenakite GSJ M19353 Brazilb Phenakite-3 Phenakite GSJ M20371 Volin, Ukraine Beryl-1 Beryl GSJ M34270 Minas Gerais, Brazil Beryl-2 Beryl GSJ M15589 Teofilo Otoni, Minas Gerais, Brazil Beryl-3 Beryl GSJ M37194 Fukuoka mine, Nakatsugawa, Gifu, Japanc

a Designated ID attached as a mineral collection stored at the GSJ. b No other information is attached. c The mine is identified.

Table 2. Laboratory preparation and ICP-MS data of the supernatant solutions of the gel wash procedures

Sample ID Washing step Wash type Be ± B ± Na ± Mg ± Ca ± (ng/g) (ng/g) (ng/g) (ng/g) (ng/g)

2+ PLW-1 1 Be to Be(OH)2 82.7 1.1 9.99 0.50 47.1 2.8 69.5 22.9 1250.9 262.7 PLW-2 2 Be(OH)2 to Be(OH)2 550.1 7.2 3.01 0.15 6.4 0.4 25.5 8.4 250.5 52.6 2+  PLW-3 3 Be to Be(OH)2 30.2 0.4 2.15 0.11 7.2 0.4 n.d. 36.6 7.7   PLW-4 4 Be(OH)2 to Be(OH)2 293.4 3.8 0.65 0.03 n.d. n.d. 10.4 2.2 2+   PLW-5 5 Be to Be(OH)2 27.6 0.4 0.87 0.04 n.d. n.d. 12.9 2.7  PLW-6 6 Be(OH)2 to Be(OH)2 129.7 1.7 0.42 0.02 7.5 0.4 n.d. 28.2 5.9

All uncertainties are 1σ. n.d.: not detected.

plasma atomic emission spectrometry (ICP-AES) ing experiment. Instead, our strategy was to chip off the (Thermo iCAP 6300 Duo). We prepared three targets from outer parts of the minerals carefully with a clean ham- this washed carrier. In 15-mL polypropylene tubes, 300 mer. After chipping off the outer parts of the minerals, µg aliquots of Be were precipitated as Be(OH)2. Thereaf- two to three medium-sand-sized fragments from the min- ter, they were centrifuged, rinsed with DI water, centri- erals’ very inner parts were pressed into back-packed cop- fuged, converted to BeO, mixed with Nb at an approxi- per cathodes with Nb powder. First, we dropped a min- mately 1:1 molar ratio, and pressed into copper cathodes. eral grain and a volumetrically equal amount of Nb powder into the cathode hole and then pressed the sample with Direct pressing procedure to measure 10Be/9Be ratios of a stainless rod. The mineral grains were occasionally fur- Be-bearing minerals ther crushed within the cathode by this procedure. We Six Be-bearing minerals were selected from the min- then repeated this procedure for two to three mineral frag- eral collection stored at the Geological Museum, Geo- ments. Finally, a small amount of Nb powder was pressed logical Survey of Japan (GSJ), AIST (Figs. 2a–f). We into the cathodes from the back to increase the samples’ measured three phenakite samples and three beryl sam- hold ability and avoid piercing due to long Cs sputtering. ples. The origins of the minerals are listed in Table 1. Phenkaite-1 was pressed into two cathodes for duplicate Phenakite-1, Beryl-1 and Beryl-2 originate from Minas measurements. Gerais, Brazil, which is the most common source of pegmatitic phenakite and beryl in the world. Phenakite-2 Commercially available Be carrier solutions from Brazil was selected for its relatively large size. We measured 10Be/9Be for three commercially avail- Pheankite-3 originated from Ukraine. Beryl-3 from Ja- able Be solutions (1000 ppm): Merck Be standard solu- pan was selected as the specific mine. All the minerals tion, Merck Be ICP standard, and Scharlau Be standard except for Beryl-1 showed a euhedral shape. Beryl-2 and solution for ICP. The lot numbers corresponding to these Beryl-3 were a light-green color and are classified as aq- solutions were HC55561807, HC55561405, and uamarine in gemology. The collected depths in the mines 17775401, respectively. Multiple targets were prepared were unknown for all minerals. from the same bottle of each solution (n = 5, 5, and 9). Minerals were wrapped in Al foil and covered with The number of repetitions was large for the Scharlau Be clean plastic bags. We preferred not to pretreat the valu- standard solution for ICP because the solution showed able mineral specimens with acids for this rapid screen- slightly larger apparent 10Be/9Be ratios as compared to

212 A. Nakamura et al. the other solutions and because we preferred to conduct additional measurements. In small quartz vials, 300 µg aliquots of Be were evaporated. Thereafter, converted to BeO, mixed with Nb at an approximately 1:1 molar ratio, and pressed into copper cathodes.

AMS measurements We measured targets using AMS at MALT (Pelletron 5UD, NEC) with 07KNSTD (Nishiizumi et al., 2007). In general, the accuracy of the measurements relies on assuming that the isotope fractionation by Cs sputtering between samples and standards is similar. This was a valid assumption for the samples prepared from solution because both samples and standards yielded the same chemical compounds, namely BeO mixed with Nb. Even though this was not the case for the directly pressed minerals, the difference in isotope fractionation between Be-bearing minerals and BeO is likely small. From the analogy of the isotope fractionation of boron crystals and boron oxides (Middleton et al., 1994), the difference in isotope fractionation between Be-bearing minerals and BeO is a maximum of several percent, which does not affect our conclusions. We operated the ion source with the Cs res- ervoir temperature of 90°C and the cathode voltage of 6 kV. To detect 10Be, we used an absorber cell with a gas ionization counter, which allows the monitoring of energy loss (∆E) and residual energy (Er) (Matsuzaki et al., 2000). Blank subtraction was not applied because all the samples were regarded as blanks. We also did not correct for B because (1) uncertainty propagation for B correc- tion is difficult and, (2) the scope of this study did not include providing absolute 10Be/9Be ratios of the minerals. Instead, we provide the raw 10Be/9Be ratios with ∆E- Er spectra.

RESULTS Concentrations of B, Be, Na, Mg, and Ca in supernatant solutions of the gel wash procedures Figure 3 and Table 2 show the results of the gel wash experiment. The concentration of B in the supernatant solution was 9.99 ± 0.50 ng/g at step 1, and gradually Fig. 3. Concentrations of B, Be, Na, Mg, and Ca in the decreased to less than 1 ng/g from step 2 to step 6 (Fig. supernatant solutions of the gel wash procedures. The horizon- 2+ 3a). Concentrations of Be in the supernatant solutions of tal axis indicates the washing steps. Be to Be(OH)2 wash and 2+ Be(OH) wash are repeated alternatively. (a) B. (b) Be. (c) Na. the Be(OH)2 wash were higher than those in the Be to 2 (d) Mg. (e) Ca. Error bars show 1σ measured uncertainties. Be(OH)2 wash (Fig. 3b). Concentrations of Na, Mg, and Ca decreased for the first few steps (Figs. 3c and d). n.d.: not detected.

10Be/9Be ratios of the original and the washed in-house Be carrier the ellipse on the detector spectrum were attributed to 10 9 10 The measured Be/ Be ratios of the original carrier Be. The ∆E-Er spectrum of the original carrier indicated varied between 6.1 × 10–15 and 1.3 × 10–14 (Table 3, Fig. a significant amount of isobaric 10B in the original car- 4). These values were apparent ratios, and all counts in rier. A tail of 7Be from the reaction of 10B(p,α)7Be at the

10Be/9Be ratios of phenakite and beryl measured via direct Cs sputtering 213 gas cell entrance overlapped the 10Be ellipse on the detector spectrum (Fig. 5a). The measurements obtained from the washed carrier were consistent and showed 10Be/9Be ratios of 9–11 × 10–16, an order of magnitude lower than those of the original carrier. The ∆E-Er spectrum of the washed carrier showed significantly less 10B(p,α)7Be reactions (Fig. 5b).

10Be/9Be ratios of Be-bearing minerals The 10Be/9Be ratios of the three phenakite samples varied between 1.3 × 10–14 and 1.5 × 10–13 (Table 4, Fig. 10 9 6). The ∆E-Er spectra revealed the measured values to be Fig. 4. Be/ Be ratios of the original and washed ‘low-level 10 9 Be carrier’ (2017.11.17-Be). Open circles and solid circles show apparent Be/ Be ratios caused by the reactions of 10 7 10Be/9Be ratios before and after the B removal procedures by B(p,α) Be (Figs. 7a–c). 10 9 hydroxide gel washing. Error bars show 1σ measured uncer- The measured Be/ Be ratios of the three beryl sam- tainties. ples ranged from 1.2 × 10–15 to 4.2 × 10–15 (Table 4, Fig.

Table 3. Laboratory preparation and 10Be/9Be ratios of the original ‘low-level Be carrier’ (2017.11.17-Be) and the washed carrier

Sample ID Sample type Preparation Analysis time 9Be3+ current Number of countsc Apparent 10Be/9Be ± 1σ (min)a (µA)b (10–14)d Original-1 Low-level Be carrier Direct evaporation 75 3.934 335 1.093 ± 0.065 Original-2 Low-level Be carrier Direct evaporation 75 3.352 160 0.613 ± 0.051 Original-3 Low-level Be carrier Direct evaporation 75 2.128 116 0.700 ± 0.067 Original-4 Low-level Be carrier Direct evaporation 100 2.154 291 1.250 ± 0.078 Washed-1 Washed low-level Be carrier B removal 90 2.930 25 0.091 ± 0.018 Washed-2 Washed low-level Be carrier B removal 90 3.537 38 0.114 ± 0.019 Washed-3 Washed low-level Be carrier B removal 90 3.888 35 0.096 ± 0.016

a Reported analysis time is the total analysis time of all AMS runs for a given sample. b Beam currents of 9Be3 were measured at the high energy side of the accelerator and averaged over all AMS runs. c 10 Number of counts in the ellipse for the Be gate on the ∆E-Er spectrum. d All counts in the 10Be gate are attributed to 10Be.

10 Fig. 5. ∆E-Er spectra of the original and washed ‘low-level Be carrier’ (2017.11.17-Be). The ellipses show the regions for Be. (a) Before the B removal procedures (Original-1). (b) After the B removal procedures by hydroxide gel washing (Washed-3). The spectra of these two samples are presented here because they exhibit similar beam currents. The spectra are overlaid plots of AMS runs for 30 minutes. 9Be3+ beam currents during this period are 3.533 µA and 3.460 µA for Original-1 and Washed-3.

214 A. Nakamura et al. Table 4. Laboratory preparation and 10Be/9Be ratios of the Be-bearing minerals

Sample ID Mineral ID Preparation Analysis time 9Be3+ current Number of countsc Apparent 10Be/9Be ± 1σ (min)a (µA)b (10–14)d Phenakite-1-1 Phenakite-1 Crushing 90 0.953 164 1.769 ± 0.143 Phenakite-1-2 Phenakite-1 Crushing 90 1.194 155 1.335 ± 0.111 Phenakite-2 Phenakite-2 Crushing 65 1.175 1152 14.533 ± 0.550 Phenakite-3 Phenakite-3 Crushing 65 0.837 686 12.151 ± 0.546 Beryl-1 Beryl-1 Crushing 80 0.797 28 0.420 ± 0.080 Beryl-2 Beryl-2 Crushing 80 0.968 10 0.124 ± 0.039 Beryl-3 Beryl-3 Crushing 80 0.836 14 0.200 ± 0.054

DISCUSSION Efficiency of B removal from the gel wash procedure Although B concentrations reduced remarkably through the washing steps, the reduction was not as rapid as for Na, Mg, and Ca (Fig. 3a). This indicates that B is partly adhered to the Be(OH)2 gel and that this adsorption occurs more easily than for the other elements. The concentration of B in the original carrier solution was estimated to be 29.6 ± 1.3 ng/g. The results demonstrate that the washing procedure removed 88 ± 1% of B in the original carrier, and ~10% of B was not removed due to adsorption. ‘Be(OH)2 wash’ is beneficial for the removal of NH4NO3, which is produced through neutralization; however, Be is slightly lost as the supernatant solution in Fig. 6. 10Be/9Be ratios of the Be-bearing minerals. Open rhom- the ‘Be(OH)2 wash’ (Fig. 3b). This is likely because the buses show 10Be/9Be ratios of phenakite samples. Solid rhom- pH slightly decreased when we mixed the Be(OH)2 gel buses show 10Be/9Be ratios of beryl samples. Error bars are 1σ with DI water, but we note that the recovery of Be was measured uncertainties. more than 99% after six times of washing. The recommended 10Be/9Be ratio of 5 ± 1 × 10–16 was successfully determined at the PRIME Lab, Purdue Uni- versity. This level of blank values is routinely obtained 6). The reactions of 10B(p,α)7Be were much lower for the at the PRIME Lab due to the successful reduction of in- beryl samples than for the phenakite samples (Figs. 7d– terference of 10B by applying a gas-filled magnet (Caffee f). et al., 2015). In contrast, the original carrier showed high 10Be/9Be ratios of 6-13 10–15 at MALT because of the 10Be/9Be ratios of commercially available Be carrier so- × significant interference of 10B at the detector (Fig. 4, Fig. lutions 5). The variation in the 10Be/9Be ratios for the four target Figure 8 shows the 10Be/9Be ratios of the commer- carriers most likely arises from differing B evaporation cially available carrier solutions. The ratios for the Merck degrees during the procedures. Conversely, the washed Be standard solution (n = 5), Merck Be ICP standard so- carrier measured significantly lower 10Be/9Be values (Fig. lution (n = 5), and Scharlau Be standard solution (n = 9) 4). The significantly lower interference of 10B on the ∆E- were 1.084 ± 0.184 × 10–14, 1.117 ± 0.081 × 10–14, and E spectrum (Fig. 5) is consistent with the degree of B 1.447 ± 0.194 × 10–14 (arithmetic mean, 1SD). Error- r removal observed by ICP-MS measurements. The mean weighted means and associated 1σ uncertainties were 10Be/9Be ratio of the three washed carrier samples was 1.059 ± 0.058 × 10–14, 1.126 ± 0.047 × 10–14, and 1.432 ± 1.00 ± 0.12 × 10–15 (arithmetic mean, 1SD). The weighted 0.045 × 10–14 for the three solutions, respectively (Table mean was 1.00 ± 0.10 × 10–15. Although the ratios are 5, Fig. 8). The ∆E-E spectra showed interference from r twice as high as the recommended value, we stress that the 10B(p,α)7Be reactions, but the dominated counts in our measurements have updated the background record the gate were 10Be (Fig. 9).

10Be/9Be ratios of phenakite and beryl measured via direct Cs sputtering 215 Fig. 7. ∆E-Er spectra of the Be-bearing minerals. (a) Phenakite-1-1. (b) Phenakite-2. (c) Phenakite-3. (d) Beryl-1. (e) Beryl-2. (f) Beryl-3. The ellipses show the regions for 10Be. The spectrum for Phenakite-1-2 was similar to that of Phenakite-1-1. The spectrums are overlaid plots of AMS runs for 30 minutes. 9Be3+ beam currents during this period are 0.956 µA, 0.977 µA, 0.743 µA, 0.832 µA, 1.027 µA, 0.887 µA for Phenakite-1-1, Phenakite-2, Phenakite-3, Beryl-1, Beryl-2, and Beryl-3, respectively.

of 10Be measurements at MALT. The lowest 10Be/9Be als obtained in our analysis indicate that phenakite typi- value of 9.1 ± 1.8 × 10–16, obtained after 90 min of meas- cally contains more B than beryl (Figs. 6 and 7). The ∆E- 10 9 7 urement time, is the lowest Be/ Be ever measured at Er spectra show slight offsets between the tails of Be MALT. We inferred that the 10Be/9Be ratios of the washed and the ellipses’ centers for the 10Be gate. (Fig. 7). This carrier were derived from a slight interference of the 10B indicates that most of the counts are from tails of 7Be due present in the samples. In addition, these values may con- to the reactions of 10B(p,α)7Be. These reactions generate tain 10Be originating from the carrier itself as well as 10Be high 10Be/9Be ratios, particularly for the phenakite sam- originating from possible cross-talk at the ion source. ples. Based on the above observations, the true 10Be/9Be Similar background values have been reported for ratios of the phenakite samples may be at least an order similar types of AMS at SUERC (NEC, 5MV) (Maden et of magnitude lower than the observed values. Since the al., 2007; Nelson et al., 2014). Employing degrader foil counting rate did not increase instantaneously during the techniques (Müller et al., 2010; Steier et al., 2019) or a measurement time, we suspect B is contained in the min- gas-filled magnet (Caffee et al., 2015) may further re- eral lattice rather than in fluid inclusions. The lowest 10Be/ duce the background. However, we need to account for 9Be ratio, 1.24 ± 0.39 × 10–15, obtained from Beryl-2, was the tradeoff between the degree of interreference and beam equivalent to that of the washed carrier solution. efficiency. Although we cannot strictly exclude the possibility that we accidentally selected three phenakites with high B 10Be/9Be ratios of Be-bearing minerals concentrations, it is likely a general trend that phenakite The 10Be/9Be measurements of the Be-bearing miner- contains more B than beryl. In several previous studies,

216 A. Nakamura et al. Beam currents of directly pressed Be-bearing minerals Our analyses indicate that direct pressing provides an easy means of selecting Be-bearing minerals that contain less 10Be and B. This is a rare study reporting the details of the measurements of directly packed minerals in cathodes. Previously, Merchel et al. (2013) briefly tested direct pressing before preparing their in-house phenakite carrier. Even though our targets were prepared by pressing the mineral fragments directly, we observed enough beam currents to conduct the measurements. Overall, the beam currents of 9Be3+, currents measured after the accelerator, typically showed peaks at 15–30 min, and then decreased toward the end of the measurements for targets prepared from solutions (Fig. 10a). Conversely, the Be-bearing minerals’ currents remained at approximately 1 µA, which is approximately 1/4 of the targets prepared from the solutions (Fig. 10b). The beam currents of phenakite and beryl were similar, although any given volume of phenakite contained three times more BeO than the same volume of beryl. This trend relates to the finding that beam currents do not decrease linearly with in- creasing matrix proportion (Fink et al., 2000; Hunt et al., 2006; Rugel et al., 2016). Figure 11 shows photographs of the targets after the measurements. The grain size of the minerals or the volu- metric ratio of minerals and Nb appears to have no apparent effect on beam currents. For example, Phenakite1- 2 provided a 1.7 times larger beam current than Phenakite3 at the end of the measurement, whereas the two photographs of the targets show no obvious differences (Figs. 10b, 11c and 11e). The beam currents for Phenakite1-1 and Phenakite-1-2 increased with the measurement dura- Fig. 8. 10Be/9Be ratios of the commercially available carrier tion. This increase most likely resulted from the fact that solutions. (a) Merck Be standard solution. (b) Merck ICP stand- the mineral grains were covered by Nb at first, and it took ard solution. (c) Scharlau Be standard solution for ICP. Error time to sputter out enough Nb to expose the mineral bars are 1σ measured uncertainties. Thick lines and dashed grains. lines show error-weighted means and associated 1σ uncertainties. Origin of 10Be in commercially available carrier solutions high B concentrations in Be-bearing minerals have been The reason for Be carriers from different suppliers 10 9 reported. Swanson et al. (1959) noted 10–100 µg/g of B yielding similar Be/ Be ratios was established early in 10 in phenakite from Minas Gerais, Brazil. Lee and Erd the Be methodology development (Middleton et al., (1963) showed 200–600 µg/g of B in phenakite and no 1984). They suggested the possibility that all carriers are detectable B in beryl from the Mount Wheeler area, Ne- extracted from a common ore. Until now, a large portion 10 9 vada, USA. Oftedal (1964) recorded 1000 µg/g of B in of the Be/ Be ratios of commercially available Be solu- –15 phenakite from Kragerø, Norway, whereas there was no tions occurred in a small range from the middle 10 to –14 B in beryl from Tørdal, Norway. The higher B concentra- early 10 (e.g., Bierman et al., 2002; Merchel et al., 10 9 tion in phenakite might be attributed to the fact that B is 2008; Corbett et al., 2016). Lower Be/ Be ratios were an incompatible element (Sunde et al., 2020). It can also limited to particular vendors and particular lot numbers be attributed to the relatively late occurrence of phenakite (Merchel et al., 2008). Our results from commercially 10 9 crystallization compared with that of beryl (Cern´ˇ y, 2002). available carrier solutions show Be/ Be ratios of ap- –14 From these observations, we inferred that the B in the in- proximately 10 , similar to previous studies (Fig. 8). house Be carrier (2017.11.17-Be), which was prepared The Scharlau Be standard solution for ICP shows slightly 10 from phenakite, possibly originated from phenakite itself. larger B interferences (Fig. 9), resulting in marginally

10Be/9Be ratios of phenakite and beryl measured via direct Cs sputtering 217 Table 5. 10Be/9Be ratios of the commercially available Be carrier solutions

Sample ID Solution Apparent 10Be/9Be ± 1σ (10–14) Merck-1 Merck Be standard solution 1.113 ± 0.131 Merck-2 Merck Be standard solution 0.856 ± 0.194 Merck-3 Merck Be standard solution 1.366 ± 0.227 Merck-4 Merck Be standard solution 1.044 ± 0.156 Merck-5 Merck Be standard solution 1.040 ± 0.080 Arithmetic mean 1.084 Standard deviation 0.184 Error-weighted mean 1.059 1σ uncertainty of the error-weighted mean 0.058

Merck-ICP-1Merck Be ICP standard 1.228 ± 0.212 Merck-ICP-2Merck Be ICP standard 1.008 ± 0.182 Merck-ICP-3Merck Be ICP standard 1.079 ± 0.172 Merck-ICP-4Merck Be ICP standard 1.133 ± 0.073 Merck-ICP-5Merck Be ICP standard 1.136 ± 0.076 Arithmetic mean 1.117 Standard deviation 0.081 Error-weighted mean 1.126 1σ uncertainty of the error-weighted mean 0.047

Scharlau-ICP-1 Scahrlau Be standard solution for ICP 1.289 ± 0.153 Scharlau-ICP-2 Scahrlau Be standard solution for ICP 1.235 ± 0.145 Scharlau-ICP-3 Scahrlau Be standard solution for ICP 1.630 ± 0.183 Scharlau-ICP-4 Scahrlau Be standard solution for ICP 1.447 ± 0.228 Scharlau-ICP-5 Scahrlau Be standard solution for ICP 1.782 ± 0.233 Scharlau-ICP-6 Scahrlau Be standard solution for ICP 1.375 ± 0.098 Scharlau-ICP-7 Scahrlau Be standard solution for ICP 1.649 ± 0.095 Scharlau-ICP-8 Scahrlau Be standard solution for ICP 1.308 ± 0.131 Scharlau-ICP-9 Scahrlau Be standard solution for ICP 1.310 ± 0.124 Arithmetic mean 1.447 Standard deviation 0.194 Error-weighted mean 1.432 1σ uncertainty of the error-weighted mean 0.045

Fig. 9. ∆E-Er spectra of the commercially available carrier solutions. (a) Merck Be standard solution (Merck-5). (b) Merck ICP standard solution (Merck-ICP-5). (c) Scharlau Be standard solution for ICP (Scharlau-ICP-6). The spectra of these three samples are presented here because these three samples exhibit similar beam currents. The spectra are overlaid plots of AMS runs for 25 minutes. 9Be3+ beam currents during this period are 3.700 µA, 4.128 µA, and 3.763 µA for Merck-5, Merck-ICP-5, and Scharlau-ICP-6, respectively.

218 A. Nakamura et al. Fig. 10. 9Be3+ beam currents versus time. (a) Typical 9Be3+ beam currents for samples prepared from solutions. Thin lines show currents for the original carrier. Bold lines show currents for the washed carrier. (b) 9Be3+ beam currents for directly pressed Be- bearing minerals. Thin lines show currents for phenakite samples. Bold lines show currents for beryl samples. Currents are measured at the high energy side of the accelerator.

higher 10Be/9Be ratios than the other two solutions. depth information on Be-bearing minerals, which serve Although we attempted to obtain details regarding the as raw materials. The 10Be/9Be ratios of phenakite and raw materials for commercially available Be solutions, beryl were estimated to be 9 × 10–17 and 3 × 10–16 assum- none were available. Nonetheless, we anticipate that the ing a 10Be production rate of 10 atoms/g/yr and a surface raw material for commercially available Be standard so- exposure age of 100 kyr with no erosion. These ratios are lutions has been the same among typical commercial sup- low enough for our interest. The 10Be production rates in pliers since the 1980s (Middleton et al., 1984). In 2000, phenakite and beryl are unknown, and hence the assump- 75% of globally produced Be originated from Spor Moun- tions are regarded as first-order estimations. In addition tain in Utah, USA, operated by Brush Wellman Corpora- to neutron spallation and muon interactions, 10Be can be tion (changed name to Materion Corporation) (Barton and produced in Be-bearing minerals due to the neutron cap- Young, 2002). By 2011, the rate increased to 90% (Foley ture reactions of 9Be(n,γ)10Be. (Sharma and Middleton, et al., 2017). In this district, mines are open pits, and Be 1989). With these in mind, the assumed 10Be production ore is non-pegmatitic bertrandite in tuff breccia with an rate is, as an example, equivalent to that of quartz at 20°N average grade of 0.265% (Barton and Young, 2002; Foley with an elevation of 1750 m when considering the ‘st’ et al., 2017). These situation lines would permit the scaling model (Stone, 2000; Balco et al., 2008). The as- contamination of the ore with meteoric 10Be and elevate sumed exposure age is equivalent to 7 m/Myr for a steady- the 10Be/9Be ratio of source products for Be solutions. state erosion rate. As a reference, 10Be erosion rates of 2– 6 m/Myr have been reported in Minas Gerais, Brazil Implications for the selection of suitable Be carrier min- (Barreto et al., 2013), one of the main regions in the world erals where Be-bearing minerals are mined. These results in- Previously, in-house Be carriers were provided from dicate that Be-bearing minerals from shallow mines or ‘deep-mined’ or ‘shielded’ Be-bearing minerals minerals without depth information may contain only (Middleton et al., 1984; Stone, 1998; Merchel et al., trace amounts of 10Be. Our results indeed show low 10Be/ 2008). This is a highly preferable approach to avoid 10Be 9Be ratios for beryl samples without depth information. accumulation in raw materials. However, sampling depths In addition to the necessity of finding raw materials that of gem-grade minerals are often difficult to obtain. There- contain low 10Be amounts, our results indicate that it is fore, the direct pressing method provides a simple means preferable to select a starting material with a low B con- for selecting Be-minerals suitable for preparing in-house centration. Once the appropriate Be-bearing minerals are Be carriers. found, Be can be extracted from the mineral using the The method presented in this paper will allow labora- fusion method (Stone, 1998) or HF dissolution (Merchel tories to prepare in-house Be carriers without obtaining et al., 2008, 2013). In addition to the procedures described

10Be/9Be ratios of phenakite and beryl measured via direct Cs sputtering 219 Fig. 11. Photographs of the measured cathodes where Be-bearing minerals are directly pressed. (a) Schematic cross section of a cathode. Be-bearing mineral fragments and Nb powder are pressed into a cathode. Small amount of Nb powder is further pressed into a cathode from the back to increase the mineral fragments’ hold ability and avoid piercing due to long exposure to Cs sputtering. (b) Phenakite-1-1. (c) Phenakite-1-2. (d) Phenakite-2. (e) Phenakite-3. (f) Beryl-1. (g) Beryl-2. (h) Beryl-3. Photo- graphs of the cathodes taken from the front side of the sputtering surface after measurements were obtained. Samples are con- sumed and show sputter pits. White fragments are the packed mineral fragments. Dark gray parts are pressed Nb powder. in these studies, we recommend repeatedly conducting bearing minerals using the direct pressing method. Ob- gel washes to remove B and measure the concentrations taining the rough exposure ages of the Be-bearing miner- using ICP-MS. While B can be reduced by volatilization als using the direct Cs sputtering method before conduct- 10 via the procedure with HF and HClO4, (Stone, 1998; ing conventional Be measurements is useful. Assuming Merchel et al., 2008, 2013), selecting minerals with low a 10Be production rate of 10 atoms/g/yr and a surface ex- B concentrations are easier to process for in-house Be posure age of 3 Myr with no erosion, the 10Be/9Be ratios preparation. The presence of low B concentrations in Be of beryl are estimated to be 5 × 10–15. This level of 10Be/ carrier solutions is likely unproblematic for AMS facili- 9Be is detectable by the direct Cs sputtering method. Al- ties, where interference by 10B is negligible. However, though these settings are limited, and the production rates preparing Be carrier solutions with B concentrations as of 10Be in Be-bearing minerals are poorly understood, low as possible is particularly important when conduct- avoiding chemical procedures to extract 10Be from quartz ing 10Be measurements at AMS facilities where the de- is a fascinating application. In addition, we expect that gree of interference by 10B is similar to that of MALT. direct Cs sputtering provides the opportunity for single- Typical chemical treatments for samples and for full pro- grain measurements of 10Be in Be-bearing minerals. cedural blanks probably reduce B concentrations that originate from a Be carrier. Nevertheless, it is better not CONCLUSIONS to add B to samples and blanks. Moreover, B reduction through chemical treatments is not the case for the blanks The first step in preparing in-house Be carriers is the that are minimally processed, which are often termed selection of suitable Be-bearing minerals that contain less machine blanks and used to evaluate the background of 10Be. AMS measurements of direct pressed untreated Be- the AMS itself. bearing minerals are potent tools for selecting suitable Be-bearing minerals for raw materials of in-house Be Geological applications carriers. Our results demonstrate that untreated mineral In contrast to the above-mentioned locations, a de- targets provide effective beam currents. The beam cur- tectable amount of 10Be accumulates in Be-bearing min- rents for Be-bearing minerals are approximately 1/4 of erals at sites where the Be-bearing minerals are long ex- the targets prepared from the solutions. Three measured posed. Thus, for geological applications in some ideal phenakite samples contained more B than the beryl sam- settings, we anticipate that we can measure 10Be in Be- ples. In addition to the necessity of finding raw materials

220 A. Nakamura et al. that contain lower 10Be, we reveal that it is preferable to Vol. 50 (Grew, E. S., ed.), 147−205, The Mineralogical So- select a starting material with a low B concentration. ciety of America. Bierman, P. R., Shakun, J. D., Corbett, L. B., Zimmerman, S. Compared to beryl (Be3Al2Si6O18), phenakite (Be2SiO4) has the advantage of not containing Al, which otherwise R. and Rood, D. H. (2016) A persistent and dynamic East needs to be removed because 26Al is often measured Greenland Ice Sheet over the past 7.5 million years. Nature 540, 256 260. alongside with 10Be. However, it is likely a general trend − Braucher, R., Merchel, S., Borgomano, J. and Bourlès, D. (2011) that phenakite contains more B than beryl. Because B Production of cosmogenic radionuclides at great depth: a partly adheres to hydroxide gel, we suggest that repeated multi element approach. Earth Planet. Sci. Lett. 309, 1−9. hydroxide gel washes are highly efficient in B removal. Braucher, R., Bourlès, D., Merchel, S., Romani, J. V., Fernadez- Our results further demonstrate that we can measure 10Be Mosquera, D., Marti, K., Leanni, L., Chauvet, F., Arnold, in Be-bearing minerals using the direct pressing method M. and Aumaître, G. (2013) Determination of muon attenu- for geological applications in several settings where the ation lengths in depth profiles from in situ produced minerals are long exposed. This is beyond our study’s cosmogenic nuclides. Nuclear Instruments and Methods in scope, and we recommend it as a potential future research Physics Research Section B: Beam Interactions with Mate- topic. Reproducible measurements of three commercially rials and Atoms 294, 484−490. available carrier solutions show 10Be/9Be ratios of ap- Caffee, M. W., Granger, D. E. and Woodruff, T. E. (2015) The Gas-Filled-Magnet at PRIME Lab: Increased Sensitivity of proximately 10–14, which is similar to previous studies. 10 9 Cosmogenic Nuclide Measurements (abstract). AGU Fall Since the 1980s, the Be/ Be ratios of commercially Meeting Abstracts V31G-09. available Be solutions were within a small range. This is Cern´ˇ y, P. (2002) Mineralogy of beryllium in granitic pegmatites. likely due to a common raw material origin—non- Beryllium: Mineralogy, Petrology and Geochemistry, Re- pegmatitic ore from open-pit mines in one particular dis- views in Mineralogy and Geochemistry Vol. 50 (Grew, E. trict. S., ed.), 405−444, The Mineralogical Society of America. Corbett, L. B., Bierman, P. R. and Rood, D. H. (2016) An ap- Acknowledgments—This work was supported by JSPS proach for optimizing in situ cosmogenic 10Be sample prepa- KAKENHI Grant Number 18K13624 and the GSJ research grant ration. Quat. Geochronol. 33, 24−34. for early career researchers. We thank two anonymous review- Derrieux, F., Siame, L. L., Bourlès, D. L., Chen, R.-F., Braucher, ers for their helpful comments. We thank the Geological Mu- R., Léanni, L., Lee, J.-C., Chu, H.-T. and Byrne, T. B. (2014) seum, GSJ, for permitting us to use the samples from the min- How fast is the denudation of the Taiwan mountain belt? eral collection, T. Sumii for access to the samples, and M. W. Perspectives from in situ cosmogenic 10Be. J. Asian Earth Caffee, D. E. Granger, G. S. Jackson, and G. J. Chmiel for pro- Sci. 88, 230−245. viding the in-house Be carrier, ‘low-level Be carrier’ Fink, D., McKelvey, B., Hannan, D. and Newsome, D. (2000) (2017.11.17-Be). Cold rocks, hot sands: In-situ cosmogenic applications in Australia at ANTARES. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with REFERENCES Materials and Atoms 172, 838−846. Balco, G. (2011) Contributions and unrealized potential con- Foley, N. K., Jaskula, B. W., Piatak, N. M. and Schulte, R. F. tributions of cosmogenic-nuclide exposure dating to gla- (2017) Beryllium. Critical Mineral Resources of the United States—Economic and Environmental Geology and Pros- cier chronology, 1990–2010. Quat. Sci. Rev. 30, 3−27. Balco, G., Stone, J. O., Lifton, N. A. and Dunai, T. J. (2008) A pects for Future Supply (Schulz, K. J., DeYoung, J. H., Jr., complete and easily accessible means of calculating sur- Bradley, D. C. and Seal, R. R., eds.), E1−E32, US Geologi- face exposure ages or erosion rates from 10Be and 26Al meas- cal Survey. Gosse, J. C. and Phillips, F. M. (2001) Terrestrial in situ urements. Quat. Geochronol. 3, 174−195. Barreto, H. N., Varajão, C. A. C., Braucher, R., Bourlès, D. L., cosmogenic nuclides: theory and application. Quat. Sci. Rev. Salgado, A. A. R. and Varajão, A. F. D. C. (2013) Denuda- 20, 1475−1560. tion rates of the Southern Espinhaço Range, Minas Gerais, Granger, D. E., Gibbon, R. J., Kuman, K., Clarke, R. J., Brazil, determined by in situ-produced cosmogenic beryl- Bruxelles, L. and Caffee, M. W. (2015) New cosmogenic burial ages for Sterkfontein Member 2 Australopithecus and lium-10. Geomorphology 191, 1−13. Barton, M. D. and Young, S. (2002) Non-pegmatitic deposits Member 5 Oldowan. Nature 522, 85−88. of beryllium: mineralogy, geology, phase equilibria and ori- Hunt, A., Petrucci, G., Bierman, P. and Finkel, R. (2006) Metal gin. Beryllium: Mineralogy, Petrology and Geochemistry, matrices to optimize ion beam currents for accelerator mass Reviews in Mineralogy and Geochemistry Vol. 50 (Grew, spectrometry. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and E. S., ed.), 591−691, The Mineralogical Society of America. Bierman, P. R., Caffee, M. W., Davis, P. T., Marsella, K., Pavich, Atoms 243, 216−222. M., Colgan, P., Mickelson, D. and Larsen, J. (2002) Rates Langmyhr, F. J. and Sveen, S. (1965) Decomposability in and timing of earth surface processes from in situ-produced hydrofluoric acid of the main and some minor and trace cosmogenic Be-10. Beryllium: Mineralogy, Petrology and minerals of silicate rocks. Analytica Chimica Acta 32, 1−7. Geochemistry, Reviews in Mineralogy and Geochemistry Lee, D. E. and Erd, R. C. (1963) Phenakite from the mount

10Be/9Be ratios of phenakite and beryl measured via direct Cs sputtering 221 wheeler area, snake range, white pine county, Nevada. Am. Atoms 123, 235−240. Mineral. 48, 189−193. Oftedal, I. (1964) On the occurence and distribution of boron Lesnek, A. J., Briner, J. P., Baichtal, J. F. and Lyles, A. S. (2020) in pegmatite. Norsk Geologisk Tidsskrift 44, 217−225. New constraints on the last deglaciation of the Cordilleran Rugel, G., Pavetich, S., Akhmadaliev, S., Baez, S. M. E., Scharf, Ice Sheet in coastal Southeast Alaska. Quat. Res. 96, 140− A., Ziegenrücker, R. and Merchel, S. (2016) The first four 160. years of the AMS-facility DREAMS: Status and develop- Maden, C., Anastasi, P. A. F., Dougans, A., Freeman, S. P. H. ments for more accurate radionuclide data. Nuclear Instru- T., Kitchen, R., Klody, G., Schnabel, C., Sundquist, M., ments and Methods in Physics Research Section B: Beam Vanner, K. and Xu, S. (2007) SUERC AMS ion detection. Interactions with Materials and Atoms 370, 94−100. Nuclear Instruments and Methods in Physics Research Sec- Schaefer, J. M., Denton, G. H., Kaplan, M., Putnam, A., Finkel, tion B: Beam Interactions with Materials and Atoms 259, R. C., Barrell, D. J., Andersen, B. G., Schwartz, R., Mack- 131−139. intosh, A. and Chinn, T. (2009) High-frequency Holocene Matsuzaki, H., Tanikawa, M., Kobayashi, K. and Hatori, S. glacier fluctuations in New Zealand differ from the north- (2000) Development of a gas counter for AMS measure- ern signature. Science 324, 622−625. ment of 10Be and 26Al of cosmic spherules. Nuclear Instru- Schaefer, J. M., Finkel, R. C., Balco, G., Alley, R. B., Caffee, ments and Methods in Physics Research Section B: Beam M. W., Briner, J. P., Young, N. E., Gow, A. J. and Schwartz, Interactions with Materials and Atoms 172, 218−223. R. (2016) Greenland was nearly ice-free for extended peri- Merchel, S., Arnold, M., Aumaître, G., Benedetti, L., Bourlès, ods during the Pleistocene. Nature 540, 252−255. D., Braucher, R., Alfimov, V., Freeman, S., Steier, P. and Shakun, J. D., Corbett, L. B., Bierman, P. R., Underwood, K., Wallner, A. (2008) Towards more precise 10Be and 36Cl data Rizzo, D. M., Zimmerman, S. R., Caffee, M. W., Naish, T., from measurements at the 10–14 level: influence of sample Golledge, N. R. and Hay, C. C. (2018) Minimal East Ant- preparation. Nuclear Instruments and Methods in Physics arctic Ice Sheet retreat onto land during the past eight mil- Research Section B: Beam Interactions with Materials and lion years. Nature 558, 284−287. Atoms 266, 4921−4926. Sharma, P. and Middleton, R. (1989) Radiogenic production of Merchel, S., Bremser, W., Bourles, D., Czeslik, U., Erzinger, 10Be and 26Al in uranium and thorium ores: Implications J., Kummer, N.-A., Leanni, L., Merkel, B., Recknagel, S. for studying terrestrial samples containing low levels of 10Be and Schaefer, U. (2013) Accuracy of 9Be-data and its influ- and 26Al. Geochim. Cosmochim. Acta 53, 709−716. ence on 10Be cosmogenic nuclide data. J. Radioanal. Nu- Simon, K., Pedro, J., Smith, A., Child, D. and Fink, D. (2013) clear Chem. 298, 1871−1878. Reprocessing of 10B-contaminated 10Be AMS targets. Nu- Middleton, R., Klein, J., Brown, L. and Tera, F. (1984) 10Be in clear Instruments and Methods in Physics Research Sec- commercial beryllium. Nuclear Instruments and Methods tion B: Beam Interactions with Materials and Atoms 294, in Physics Research Section B: Beam Interactions with 208−213. Materials and Atoms 5, 511−513. Steier, P., Martschini, M., Buchriegler, J., Feige, J., Lachner, Middleton, R. J., Juenemann, D. and Klein, J. (1994) Isotopic J., Merchel, S., Michlmayr, L., Priller, A., Rugel, G., fractionation of negative ions produced by Cs sputtering in Schmidt, E., Wallner, A., Wild, E. M. and Golser, R. (2019) a high-intensity source. Nuclear Instruments and Methods Comparison of methods for the detection of 10Be with AMS in Physics Research Section B: Beam Interactions with and a new approach based on a silicon nitride foil stack. Materials and Atoms 93, 39−51. Int. J. Mass Spectrom. 444, 116175. Müller, A. M., Christl, M., Lachner, J., Suter, M. and Synal, Stone, J. (1998) A rapid fusion method for separation of beryl- H.-A. (2010) Competitive 10Be measurements below 1MeV lium-10 from soils and silicates. Geochim. Cosmochim. Acta with the upgraded ETH-TANDY AMS facility. Nuclear In- 62, 555−561. struments and Methods in Physics Research Section B: Beam Stone, J. O. (2000) Air pressure and cosmogenic isotope pro- Interactions with Materials and Atoms 268, 17−18. duction. J. Geophys. Res. 105(B10), 23753–23759. Nelson, A. H., Bierman, P. R., Shakun, J. D. and Rood, D. H. Sunde, Ø. F., Friis, H., Andersen, T., Trumbull, R. B., (2014) Using in situ cosmogenic 10Be to identify the source Wiedenbeck, M., Lyckberg, P., Agostini, S., Casey, W. H. of sediment leaving Greenland. Earth Surface Processes and and Yu, P. (2020) Boron isotope composition of coexisting Landforms 39, 1087−1100. tourmaline and hambergite in alkaline and granitic Nishiizumi, K., Imamura, M., Caffee, M. W., Southon, J. R., pegmatites. Lithos 352−353, 105293. Finkel, R. C. and McAninch, J. (2007) Absolute calibration Swanson, H. E., Gilfrich, N. T., Cook, M. I., Stinchfield, R. of 10Be AMS standards. Nuclear Instruments and Methods and Parks, P. C. (1959) Standard X-ray diffraction powder in Physics Research Section B: Beam Interactions with patterns vol. 8—Data for 61 substances. National Bureau Materials and Atoms 258, 403−413. of Standards Circular 539, 1−76, U.S. Government Print- Ochs, M. and Ivy-Ochs, S. (1997) The chemical behavior of ing Office. Be, Al, Fe, Ca and Mg during AMS target preparation from von Blanckenburg, F., Belshaw, N. and O’Nions, R. (1996) terrestrial silicates modeled with chemical speciation cal- Separation of 9Be and cosmogenic 10Be from environmen- culations. Nuclear Instruments and Methods in Physics tal materials and SIMS isotope dilution analysis. Chem. Research Section B: Beam Interactions with Materials and Geol. 129, 93−99.

222 A. Nakamura et al.