{"id":"2645a93e-8ec7-447a-8d03-ccbf09dd085a","arxiv_id":"2506.11689","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":5.0,"correctness_risk":"low","formal_verification":"none","parameter_count":0,"one_line_summary":"AMS measurements show a consistent 129I/127I ratio of about 2e-13 across three commercial NaI powders and a 210Pb/Pb ratio of 3.6e-15 in Pb3O4, meeting SABRE's carrier purity requirement.","lead":"Researchers measured trace amounts of radioactive iodine-129 and lead-210 in materials used to build dark matter detectors. They found that the choice of sodium iodide powder barely changes iodine-129 levels, and that a lead oxide (Pb3O4) could be pure enough to serve as a lead carrier for these detectors.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The quoted 210Pb/Pb ratio for Pb3O4 rests on low count statistics with no reported procedural blank; until the machine/chemistry background is quantified, the central value is an upper limit, though the carrier-suitability conclusion is conservative.","rationale":"The reader's weakest assumption identifies batch-to-batch representativeness of Pb3O4, which is a fair scope caveat; the paper itself only claims the investigated powder is a potential carrier. The more directly testable weakness is the missing procedural blank for the 210Pb channel. The Pb3O4 signal is small (Feldman-Cousins statistics for <20 counts), and Section 4's assertion of a machine background below 1e-14 is not accompanied by blank counts. A blank equivalent to even a few 210Pb events would change the central value, although it would push it downward and thus keep the suitability conclusion intact. The 129I conclusion is an overgeneralization in the abstract but is qualified in the body and does not affect the measured ratios. These are addressable reporting and verification items rather than demonstrated errors, so the conditional acceptance remains appropriate.","tokens_in":8629,"tokens_out":11682,"duration_ms":115706,"concrete_test":"Measure a procedural blank under identical conditions: process a lead carrier with independently known 210Pb/Pb < 1e-15 (e.g., aged lead) through the same AMS protocol and report the blank-equivalent 210Pb/Pb ratio and counts. If the blank-equivalent ratio exceeds roughly 1e-15, subtract it from the Pb3O4 measurement and recalculate; if it is below about 3e-16, the quoted central value and suitability claim stand.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most consequential quantitative claim is the 210Pb/Pb ratio of (3.6 +1.7/-1.4) x 10^-15 for Pb3O4 (Table 4). This value is based on very low counting statistics (the paper applies Feldman-Cousins for <20 counts), and the statement in Section 4 that 'a machine background at VEGA ... significantly lower than 10^-14' is not supported by an explicit procedural blank or background counts. Without a measured blank, the detector counts assigned to 210Pb cannot be separated from ion-source memory, scattering, or chemical contamination. The quoted central value is therefore not fully established as a material property; it is an upper limit. This does not break the suitability conclusion: if background is present, the true Pb3O4 ratio is even lower, so the conclusion that it is below 1e-14 is conservative. However, the specific numerical ratio, its uncertainty, and any comparison to other carrier candidates are not established. The related overgeneralization of the 129I result from three powders to 'the choice of NaI powder' is a scope issue, but it is qualified in the body ('assessed here') and does not undermine the reported measurements.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports accelerator mass spectrometry (AMS) measurements of two radioimpurities relevant to NaI(Tl) dark matter detectors: 129I/127I in three commercial NaI powders and 210Pb/Pb in three lead compounds (Pb3O4, PbO2, and PbO). For 129I, the authors demonstrate that both unprocessed NaI and chemically converted AgI are viable AMS targets, and they measure a consistent ratio of (2.0 ± 0.3) × 10^-13 across the three powders, in agreement with the DAMA/LIBRA value. For 210Pb, they characterize negative molecular ions PbO^- and PbO2^-, select PbO2^- with charge state 3+ at 0.9 MV, and report a 210Pb/Pb ratio for Pb3O4 of (3.6 +1.7/-1.4) × 10^-15, which meets the stated SABRE criterion of 1 × 10^-14 when 1 mg of lead carrier is added to 1 kg of NaI(Tl). The paper concludes that Pb3O4 is a potential lead carrier for SABRE and that commercial NaI powders are indistinguishable from an 129I perspective.","tokens_in":8865,"tokens_out":7055,"duration_ms":64610,"significance":"If the results hold, the paper provides a useful technical capability: direct atom counting of 210Pb at the low ratios required for dark matter detector radiopurity, and a convenient AMS method for 129I using unprocessed NaI powder. The study is also of practical value to the SABRE collaboration by identifying a candidate 210Pb-clean lead carrier. Strengths include the use of external calibration standards with fixed nominal ratios (Woodward iodine, Kuni standard, ERISS-derived lead references), a systematic characterization of charge-state yields, and the use of Feldman-Cousins confidence intervals for low-count data. The main weakness is the absence of a reported procedural blank or machine-background measurement for 210Pb, which undermines the specific quoted ratio as a material property, although the conservative character of the suitability conclusion mitigates the impact.","major_comments":[{"comment":"The 210Pb/Pb ratio of (3.6 +1.7/-1.4) × 10^-15 for Pb3O4 is derived from very low counting statistics (Feldman-Cousins applied for <20 counts), yet no procedural blank or dedicated machine-background measurement is reported. The statement in Section 4 that 'a machine background at VEGA ... significantly lower than 10^-14' is unsupported by explicit data, so the measured counts cannot be unambiguously assigned to 210Pb in the sample; contributions from ion-source memory, scattering, or chemical contamination are not quantified. The authors should either provide a measured blank/background sample (e.g., a lead-free matrix or a known much-lower-ratio material) and subtract it, or explicitly present the Pb3O4 result as an upper limit. The suitability conclusion is conservative—if background contamination were present, the true Pb3O4 ratio would be even lower—but the specific central value and its uncertainty are not established as a material property and should not be used for quantitative comparisons or activity-budget calculations.","section":"Section 3.2 and Section 4"},{"comment":"The abstract claims that 'the choice of NaI powder has a negligible influence on the 129I contribution to low-background dark matter experiments,' and Section 2.2 states that 'there is no distinction in quality between different NaI powders.' This overgeneralizes the evidence, which consists of only three specific powders: astro-grade and growth-grade from Sigma-Aldrich and one ANU in-house powder from May and Baker. The conclusion in Section 4 is properly qualified with 'assessed here,' but the abstract and Table 1 caption are not. Please restrict the conclusion to the investigated powders or add a clear scope limitation in the abstract, since manufacturers and production batches may differ.","section":"Abstract and Section 2.2"}],"minor_comments":[{"comment":"The phrase 'the required lower activity limit' is misleading; the condition is an upper bound on the 210Pb/Pb ratio (1 × 10^-14). It should read 'the required maximum (upper) activity limit.'","section":"Abstract"},{"comment":"For the PbO2 row, the quoted 210Pb atoms per g Pb, (2.3 ± 6.5) × 10^7 at/g, is inconsistent with the isotopic ratio (7.9 ± 2.2) × 10^-15; error propagation gives (2.3 ± 0.6) × 10^7 at/g. This appears to be a misplaced decimal. Please correct and recheck all derived quantities in the table.","section":"Table 4"},{"comment":"There are two typos: 'seculiar equilibrium' should be 'secular equilibrium', and 'In oder' should be 'In order'.","section":"Section 3.2"},{"comment":"The paper states that the measured 210Pb/208Pb ratios of the reference samples were used to normalize the results, but it does not report the measured values or their agreement with the nominal ratios. One or two sentences with the measured reference ratios would strengthen confidence in the normalization.","section":"Section 3.1 and Table 2"}],"recommendation":"major_revision","confidential_remarks":"The paper is technically sound in its AMS methodology and the 129I part is convincing. The main issue is the unsupported machine-background claim for 210Pb; asking for either an explicit blank measurement or clear upper-limit language is appropriate. The 129I generalization is a wording issue. The manuscript fits the scope of NIM B as a technical radiopurity measurement. I see no grounds for rejection, but the load-bearing 210Pb value needs the requested support."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Useful, careful AMS work. The headline results are real: three commercial NaI powders give a consistent 129I/127I ratio around 2e-13, agreeing with DAMA/LIBRA, and the paper is the first to show that unprocessed NaI powder works directly as an AMS target. The 210Pb story is more conditional. The Pb3O4 ratio is low enough to justify cautious optimism as a carrier, but without a procedural blank the central value is effectively an upper limit, not a firmly established material property. The stress-test note gets this right.\n\nWhat is genuinely new: the PbO2- molecular ion data, the charge-state yield systematics across terminal voltages, and the first comparison of Pb3O4, PbO2, and PbO as carrier candidates. The methods are largely adapted from prior group work, but the new data and the unprocessed-NaI demonstration are real contributions. The normalization scheme is clean—external standards (Woodward, Kuni, ERISS-derived references) are used, with no circular fitting.\n\nSoft spots: the absence of an explicit procedural blank for 210Pb is the main one. The statement in Section 4 that the VEGA machine background is \"significantly lower than 1e-14\" is asserted, not demonstrated. This matters for the specific numerical ratio and for any comparison to other carriers, but not for the suitability conclusion, which is conservative—if background is present, the true Pb3O4 ratio is even lower. A smaller issue is that the abstract's claim that NaI powder choice has \"negligible influence\" goes beyond the three powders tested; the body is properly qualified with \"assessed here.\" Also check Table 4: the \"210Pb atoms/g Pb\" column and the PbO2/PbO atom uncertainties look off—likely typos, but they should be fixed before publication.\n\nWho this is for: AMS practitioners and NaI dark matter collaborations (SABRE, COSINE, ANAIS). It deserves a serious referee. The fixes are minor: add a procedural blank or explicitly label the Pb3O4 value as an upper limit, soften the abstract's 129I claim, and clean up Table 4.","headline":"Sound AMS measurements; the 129I data are solid, the 210Pb carrier ratio is a useful upper limit pending a blank, and the paper deserves review with minor revisions.","tokens_in":9455,"tokens_out":2125,"would_cite":true,"duration_ms":20904,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Commercial NaI powders show a consistent $^{129}$I content, and a Pb$_3$O$_4$ sample meets the $^{210}$Pb limit for use as a lead carrier in dark matter detectors.","keywords":["accelerator mass spectrometry","NaI(Tl) detectors","dark matter","iodine-129","lead-210","radioimpurity","lead carrier","radiopurity"],"falsifier":"Take additional Pb$_3$O$_4$ from the same and different suppliers and measure $^{210}$Pb/Pb with the same protocol, both as powder and after the carrier-preparation chemistry; if any batch exceeds $1 \\times 10^{-14}$, the carrier claim fails. Likewise, measure $^{129}$I/$^{127}$I in a commercial NaI powder from a supplier not tested here; a ratio outside $(2.0 \\pm 0.3) \\times 10^{-13}$ would overturn the uniformity claim.","tokens_in":8469,"feed_emoji":"⚛️","tokens_out":12428,"duration_ms":100972,"temperature":0.7,"pith_summary":"The paper aims to establish that two radioimpurities that can mimic dark matter signals in sodium-iodide scintillation detectors can be measured reliably by accelerator mass spectrometry: iodine-129, which is intrinsic to the sodium iodide, and lead-210, which must be tracked in any stable lead carrier used to process detector material. The authors measured a consistent $^{129}$I/$^{127}$I ratio of $(2.0 \\pm 0.3) \\times 10^{-13}$ in three commercially available NaI powders, including unprocessed powder as an AMS target for the first time, and concluded that powder choice has negligible influence on the $^{129}$I background. For $^{210}$Pb, they identified PbO$_2^-$ as the preferred molecular ion and measured a $^{210}$Pb/Pb ratio of $(3.6^{+1.7}_{-1.4}) \\times 10^{-15}$ in one Pb$_3$O$_4$ powder, which they conclude meets the limit required when adding 1 mg of stable lead to 1 kg of NaI(Tl) powder. If correct, a suitable lead carrier is available for low-background NaI(Tl) experiments, and $^{129}$I uniformity simplifies powder selection.","feed_headline":"NaI powders share a 129I level; Pb3O4 lead carrier clears 210Pb bar","feed_subtitle":"Three commercial NaI powders match at 129I; one lead oxide passes the 210Pb radiopurity bar for dark matter detectors.","key_machinery":"The central mechanism is accelerator mass spectrometry (AMS), direct atom counting of $^{129}$I/$^{127}$I and $^{210}$Pb/Pb rather than decay counting. For $^{129}$I, the load-bearing target choice is unprocessed NaI powder mixed with silver powder, which delivers stable 5 microampere beams and yields ratios identical to chemically converted AgI; for $^{210}$Pb, the load-bearing choices are the PbO$_2^-$ molecular ion, a terminal voltage of 0.9 MV, and charge state 3+ (29.2% yield), which together give enough efficiency to measure ratios near $10^{-15}$. Reference materials with known ratios normalise the measurements, and the argument rests on the agreement between samples and references at these very low isotopic ratios.","core_discovery":"On the paper's own terms, the central discovery is that the $^{129}$I/$^{127}$I ratio is the same, within uncertainty, across three commercial NaI powders and consistent with the value reported for the crystals used by a long-running dark matter experiment, so no tested powder grade is better than another with respect to $^{129}$I background. It further reports that one commercial Pb$_3$O$_4$ powder carries $^{210}$Pb at a ratio of $(3.6^{+1.7}_{-1.4}) \\times 10^{-15}$, below the $1 \\times 10^{-14}$ target for a 1 mg-per-kg lead addition, while the other two lead oxides tested do not meet that target within uncertainties. The paper also demonstrates that unprocessed NaI works as an AMS target and that PbO$_2^-$ extraction with charge state 3+ yields efficient enough measurement of $^{210}$Pb to characterise candidate carriers, with a machine background below $10^{-14}$.","pith_inferences":["If the $^{129}$I uniformity extends to other commercial suppliers, then the only way to reduce the intrinsic $^{129}$I background further would be to use synthetic or otherwise $^{129}$I-free iodine, not to buy a purer powder grade.","The same PbO$_2^-$ AMS protocol could be applied to screen small environmental or archaeological lead samples for $^{210}$Pb, making the method useful beyond dark matter instrumentation.","An implicit test of the carrier claim is the chemical yield and contamination during the actual NaI processing; a batch with a low starting $^{210}$Pb/Pb ratio could still introduce $^{210}$Pb if the carrier preparation itself is not clean.","If multiple Pb$_3$O$_4$ batches are characterised, a simple procurement rule — accept only ratios below $1 \\times 10^{-14}$ — could be applied, which the paper does not explicitly state."],"forward_implications":["For the three powders tested, the $^{129}$I contribution to detector background is effectively fixed near 1 mBq per kg of NaI, so switching commercial powder grade will not reduce this particular background.","The tested Pb$_3$O$_4$ batch can be used as a $^{210}$Pb-clean lead carrier at the 1 mg-per-kg addition level, provided the measured ratio holds after chemical processing.","Unprocessed NaI powder works as an AMS target, removing a chemical-conversion step and making routine radiopurity screening of iodide materials faster.","The $^{210}$Pb AMS protocol reaches backgrounds below $10^{-14}$, so other candidate carrier materials can now be screened quantitatively at the required sensitivity.","Because the measured Pb$_3$O$_4$ sits near, not far below, the $1 \\times 10^{-14}$ limit, an ideal carrier would be at least ten times purer; the paper reports that aged lead materials are being tested for this purpose."],"supporting_citations":[{"why":"It supplies the earlier $^{129}$I/$^{127}$I measurements used to normalise and cross-check the present results.","marker":"[15]"},{"why":"It provides the previously reported $^{129}$I/$^{127}$I ratio in detector sodium iodide against which the new ratios are compared.","marker":"[19]"},{"why":"It defines the expected $^{210}$Pb activity in NaI(Tl) crystals from which the $1 \\times 10^{-14}$ carrier limit is derived.","marker":"[20]"},{"why":"It demonstrates the earlier $^{210}$Pb AMS work at one of the facilities, establishing the method extended here.","marker":"[9]"},{"why":"It describes the 1 MV AMS facility used for the $^{210}$Pb measurements and its capabilities.","marker":"[13]"},{"why":"It describes the 14 UD tandem accelerator facility used for the $^{129}$I measurements.","marker":"[16]"},{"why":"It provides charge-state yield data at higher terminal voltage that confirm the observed yield trend.","marker":"[21]"},{"why":"It supplies the asymmetric confidence-interval prescription used for low counting-statistics uncertainties.","marker":"[22]"}],"fun_headline_variants":["NaI powders share 129I; Pb3O4 carrier meets 210Pb limit","129I uniform in NaI powders; Pb3O4 clears 210Pb bar","Same 129I in 3 NaI powders; Pb3O4 hits 210Pb target","NaI powders match on 129I; Pb3O4 passes 210Pb test"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The conclusion that Pb$_3$O$_4$ works as a lead carrier assumes that the one tested bottle represents all Pb$_3$O$_4$ and that its radioactive-lead content stays low after chemical processing; the authors note that an ideal carrier would be ten times purer.","fun_headline_variants_meta":{"raw":{"variants":["NaI powders share 129I; Pb3O4 carrier meets 210Pb limit","129I uniform in NaI powders; Pb3O4 clears 210Pb bar","Same 129I in 3 NaI powders; Pb3O4 hits 210Pb target","NaI powders match on 129I; Pb3O4 passes 210Pb test"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000479,"raw_usage":{"total_tokens":2493,"prompt_tokens":1186,"completion_tokens":1307,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":802,"completion_tokens_details":{"reasoning_tokens":1211}},"tokens_in":802,"tokens_out":1307,"duration_ms":9816,"temperature":1.0,"reasoning_tokens":1211,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T04:03:34.245854+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Take additional Pb$_3$O$_4$ from the same and different suppliers and measure $^{210}$Pb/Pb with the same protocol, both as powder and after the carrier-preparation chemistry; if any batch exceeds $1 \\times 10^{-14}$, the carrier claim fails. Likewise, measure $^{129}$I/$^{127}$I in a commercial NaI powder from a supplier not tested here; a ratio outside $(2.0 \\pm 0.3) \\times 10^{-13}$ would overturn the uniformity claim.","supporting_citations":[{"cited_title":"Fifield, M","cited_arxiv_id":null,"evidence_quote":"It supplies the earlier $^{129}$I/$^{127}$I measurements used to normalise and cross-check the present results."},{"cited_title":"Bernabei, P","cited_arxiv_id":null,"evidence_quote":"It provides the previously reported $^{129}$I/$^{127}$I ratio in detector sodium iodide against which the new ratios are compared."},{"cited_title":"Antonello, E","cited_arxiv_id":null,"evidence_quote":"It defines the expected $^{210}$Pb activity in NaI(Tl) crystals from which the $1 \\times 10^{-14}$ carrier limit is derived."},{"cited_title":"Froehlich, Z","cited_arxiv_id":null,"evidence_quote":"It demonstrates the earlier $^{210}$Pb AMS work at one of the facilities, establishing the method extended here."},{"cited_title":"Hotchkis, D","cited_arxiv_id":null,"evidence_quote":"It describes the 1 MV AMS facility used for the $^{210}$Pb measurements and its capabilities."},{"cited_title":"Dracoulis, Nuclear Physics News 9 (1999) 9-19","cited_arxiv_id":null,"evidence_quote":"It describes the 14 UD tandem accelerator facility used for the $^{129}$I measurements."},{"cited_title":"Sookdeo, R.J","cited_arxiv_id":null,"evidence_quote":"It provides charge-state yield data at higher terminal voltage that confirm the observed yield trend."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"It supplies the asymmetric confidence-interval prescription used for low counting-statistics uncertainties."}],"review_version":1}