{"id":"7f19f2a0-9fed-4176-8799-153d07064d3e","arxiv_id":"2412.10259","paper_version":5,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"New mass measurements establish 149Tm as the first proton-unbound thulium isotope, locating the proton drip-line at Z=69.","lead":"New mass measurements of the lightest thulium isotopes show that thulium-149 is the first thulium that cannot hold a proton, setting the proton drip-line for this element. The result also tests whether the N=82 nuclear shell closure survives at the limits of nuclear stability.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 'first unbound Tm isotope' claim depends on 150Tm being bound, which rests entirely on an unexplained 2.9 sigma 149Er mass shift; until that mass is independently confirmed, the central drip-line location is not secure.","rationale":"The reader's weakest_assumption identifies exactly the load-bearing point: the revised 149Er mass. My pass confirms it. The measured 149Tm Q-value is sufficiently large that the basic fact of 149Tm proton unboundness is not in question; even if the extrapolated 149Tm isomer correction were removed or changed, the sign stays positive at high significance. The 'first' and 'last bound' claims, however, require 150Tm to be proton-bound, and that conclusion is a 2 sigma result whose sign flips to marginal when the AME2020 149Er mass is used. The authors acknowledge that the discrepancy's cause is unknown and request a third measurement; this is an explicit limitation in the manuscript and should carry weight in the verdict. I find no independent reason to reject the measurement itself, and the N=82 shell-gap analysis is not the vulnerable step. The paper's 'first unbound' wording is sequence-relative (150 bound, 149 unbound), so the known 147Tm proton emitter does not by itself contradict it, but it underscores that the drip-line is non-monotonic and the adjacent-pair transition is the operative claim. Thus the same CONDITIONAL verdict remains appropriate.","tokens_in":18495,"tokens_out":11192,"duration_ms":685219,"concrete_test":"Perform an independent high-precision mass measurement of 149gEr and 149mEr (e.g., Penning-trap mass spectrometry at ISOLTRAP or SHIPTRAP, or Schottky mass spectrometry at ESR) with uncertainty of 20 keV or better, and compare the resulting mass to both the TITAN value (-53584 +/- 47 keV for 149gEr) and AME2020 (-53742 +/- 28 keV). If the independent value agrees with AME2020 within 1 sigma, recompute S_p(150Tm) with that value; if it becomes <= 0 at 1 sigma, the paper's claim that 150Tm is proton-bound and hence 149Tm is the first proton-unbound isotope is not supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"To establish 149Tm as the first proton-unbound Tm isotope, the paper must show both that 149Tm has S_p < 0 and that 150Tm has S_p > 0. The 149Tm unboundness is robust: Q_p = +378 +/- 52 keV from the new 149Tm mass and AME2020 148Er, so this leg holds even under plausible isomeric corrections. The 150Tm-bound leg, however, is a 2 sigma result computed as S_p(150Tm) = -Q_p with Q_p = ME(150Tm) - ME(149Er) - ME(1H) = -202 +/- 99 keV, and it only becomes positive after replacing the AME2020 149Er mass (-53742 +/- 28 keV) with the new TITAN value (-53584 +/- 47 keV). The two measurements differ by 158 +/- 55 keV (2.9 sigma). The paper itself states: 'The cause of our discrepancy in our measurement of this single mass is unknown, but may warrant a third measurement' (Section III). If the AME2020 149Er mass is correct, S_p(150Tm) shifts by roughly +158 keV and becomes consistent with zero or negative at 1 sigma, so 150Tm could be the first unbound isotope encountered from stability. The 'last proton-bound isotope is 150Tm' and the 'transition between 149 and 150' claims therefore stand or fall with a single unconfirmed mass, not with the directly measured 150Tm mass alone. This is the most load-bearing weakness: the headline result is conditional on an unexplained mass discrepancy that the authors explicitly flag.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports precision mass measurements of neutron-deficient thulium and erbium isotopes performed with the TITAN MR-TOF-MS at TRIUMF, including first measurements of 149Tm and 150Tm. Combined with new measurements of 149gEr and 149mEr that deviate from the AME2020 values by about 150 keV, the authors derive a positive proton-emission Q-value of +378±52 keV for 149Tm and a negative Q-value (i.e., positive S_p) of -202±99 keV for 150Tm. They conclude that 149Tm is proton-unbound and 150Tm is proton-bound, placing the thulium proton drip-line at N=80, and they further use the new masses to evaluate the N=82 neutron shell gap at Z=69.","tokens_in":18759,"tokens_out":16492,"duration_ms":114059,"significance":"If the main claim is correct, the paper resolves a long-standing experimental gap: the location of the proton drip-line in the thulium chain is pinned down by direct mass measurements, and the extracted Q-value for 149Tm provides an input for proton-emission half-life calculations. The 149Tm unboundness leg is robust: the Q-value of +378±52 keV is more than 7σ away from zero and relies only on the well-established 148Er mass and the new 149Tm mass. The paper also provides useful data on neighbouring Er and Tm isotopes, including transparent uncorrected values in Table II that allow future reanalysis. However, the companion claim that 150Tm is proton-bound is only a 2σ result and is conditional on an unexplained ~150 keV discrepancy in the 149gEr mass relative to AME2020, which the authors themselves flag as needing a third measurement.","major_comments":[{"comment":"The conclusion that 150Tm is proton-bound (S_p = 202±99 keV) is load-bearing for the paper's central claim, and it is only a 2σ effect that depends entirely on the TITAN value of the 149gEr mass, ME = -53584(47) keV, rather than the AME2020 value of -53742(28) keV. Using the AME2020 149gEr mass, the same 150Tm mass yields S_p = 44±99 keV, which is within 1σ of zero and does not exclude 150Tm being proton-unbound. The authors state that the cause of this single-mass discrepancy is unknown. I request a quantitative sensitivity analysis of the drip-line conclusion to the 149Er mass, or an independent mass measurement, and a clearly caveated statement that the 'first proton-unbound' conclusion is provisional pending confirmation of the 149gEr mass.","section":"Section III, 'Last Proton-Bound Isotope Determined from 149m,149gEr and 150gTm'"},{"comment":"The abstract states that the measurements 'provide the first experimental confirmation that 149Tm is the first proton-unbound nuclide in the Tm chain,' and Section III repeats that 149Tm is 'the first proton-unbound isotope in the thulium chain.' This is inconsistent with the introduction, which notes that 147Tm is a known ground-state proton emitter. The wording must be clarified, for example by specifying 'first proton-unbound isotope beyond the N=82 shell closure' or 'the drip-line transition between 149Tm and 150Tm.' As written, the headline claim is internally inconsistent with the known status of 147Tm.","section":"Abstract and Section III, first paragraph"},{"comment":"The statement 'the present measurements demonstrate that 149Tm is the first proton-unbound nucleus, rather than 148Tm or 150Tm' and the conclusion that '150gTm is the last proton-bound Tm isotope' need to be reconciled with the prior constraint that the drip-line lies between A=148 and A=151. If 148Tm is proton-bound (as implied by that constraint and by 147Tm being unbound), then 148Tm would be more neutron-deficient than 150Tm, so 150Tm cannot be the last proton-bound isotope in an absolute sense. The authors should state explicitly which isotopes around the drip-line are known to be bound or unbound and should avoid absolute 'first' and 'last' language unless it is precisely defined.","section":"Section III, '149Tm: The First p-Unbound Isotope' and Introduction"}],"minor_comments":[{"comment":"Typo: 'Additonally' should be 'Additionally.'","section":"Section IV, Conclusion"},{"comment":"The text lists the excitation energy of 152Tm as -100±250 keV; a negative excitation energy is unphysical and is likely a typo for 100±250 keV.","section":"Section II.B"},{"comment":"The paper says 149Tm and 150Tm represent 'first-time measurements,' but 150Tm was already measured in experiment 1 (Ref. [15]) and is included in Table I (Expt. 1). Please rephrase to reflect that these are first high-precision measurements or first-time measurements in this analysis.","section":"Section II.B"},{"comment":"The caption refers to 'purple ×' and 'blue triangle' markers, but the figure is likely to be rendered in grayscale in print; consider also using different marker shapes or adding text labels to ensure the distinction is clear.","section":"Figure 3 caption"},{"comment":"For 149gTm and 150gTm, the AME2020 mass excesses are extrapolated values (marked with #), but the TITAN-AME difference column is left blank; adding these differences (or a note explaining the blank) would improve readability.","section":"Table I"}],"recommendation":"major_revision","confidential_remarks":"The paper is within scope for a nuclear physics journal and reports valuable first mass measurements. The main concern is not the 149Tm unboundness, which is robust, but the conditional nature of the 150Tm-bound conclusion that depends on the unresolved 149Er mass discrepancy. I believe major revision is appropriate: the authors need to either obtain an independent confirmation of the 149Er mass or substantially weaken the claims about the precise drip-line location. The 'first proton-unbound' terminology also needs correction in the abstract and conclusions."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe headline: this is a solid, honest mass-spectrometry paper that reports the first masses of 149Tm and 150Tm and a direct measurement of 149gEr, closing a gap in the Tm chain. The claim that 149Tm is proton-unbound is on firm ground: Q_p = +378 ± 52 keV, more than 7σ from zero, and it doesn't depend on the disputed Er mass. The weaker leg is the companion claim that 150Tm is proton-bound. That's a 2σ result, and it depends entirely on the ~150 keV shift they see in the 149Er mass relative to AME2020. If the AME value is right, S_p(150Tm) would be within 1σ of zero or negative, and the drip-line would sit at 150, not 149.\n\nThe paper does several things well. It's transparent about the discrepancy—they say the cause is unknown and a third measurement is warranted. Table II gives the uncorrected data, which is exactly what you want for future re-analysis. The isomeric corrections are handled carefully, and the N=82 shell-gap result is a nice byproduct. The self-citation to their Yb paper is used as a consistency argument, not circular derivation.\n\nThe soft spots are real but not disqualifying. The 149Er mass is load-bearing for the \"first unbound\" claim, and 2σ is not enough to hang a drip-line location on. The two-component fit of the 149g+mEr peak may be fragile, though they seem to have done due diligence with shape calibration. The isomeric corrections for 149,150Tm use extrapolated excitation energies from NUBASE, but again, Table II lets you check the sensitivity.\n\nFor a reviewer: I'd ask them to either secure the 149Er mass with an independent measurement or reframe the conclusion to say the drip-line lies between 149 and 150, conditional on the revised Er mass. As it stands, the \"149Tm unbound\" claim is solid, but the location claim is not airtight.\n\nThis paper deserves a serious referee. It's new data, honestly analyzed, with a clear caveat. I'd send it out.","headline":"Solid new mass measurements with a load-bearing caveat: the drip-line location hangs on an unexplained 149Er mass shift.","tokens_in":19492,"tokens_out":4064,"would_cite":true,"duration_ms":34670,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["21.10.Dr","27.60.+j"],"model":"deepseek-v4-flash","headline":"Precision mass measurements establish 149Tm as the first proton-unbound thulium isotope, placing the Z=69 proton drip-line at N=80.","keywords":["proton drip-line","thulium isotopes","MR-TOF-MS mass measurement","one-proton separation energy","149Tm","N=82 shell closure","149Er mass"],"falsifier":"A third, technique-independent measurement of the $^{149g}$Er and $^{149m}$Er masses would settle it: if the new value agrees with the 2020 Atomic Mass Evaluation rather than with this paper's heavier value, then $^{150}$Tm's separation energy falls back into the $1\\sigma$-of-zero band and the claimed boundary at $N=80$ loses its experimental support, while $^{149}$Tm would still be unbound if its own mass and the $^{148}$Er mass hold.","tokens_in":18245,"feed_emoji":"⚛️","tokens_out":19551,"duration_ms":191398,"temperature":0.7,"pith_summary":"The paper aims to settle where the proton drip-line lies in the thulium chain ($Z=69$): the neutron count at which thulium nuclei stop being able to hold a proton and become proton-unbound. Because very small proton-emission energies imply extremely long tunneling lifetimes, the boundary often cannot be observed directly as a decay; it has to be inferred by weighing the parent and daughter nuclei. The authors use a multiple-reflection time-of-flight mass spectrometer to weigh $^{149}$Tm, $^{150}$Tm, and two states of $^{149}$Er, and they find that $^{149}$Tm is proton-unbound while $^{150}$Tm is proton-bound, putting the drip-line at $N=80$. If this is right, it gives nuclear mass models a firm experimental anchor in a region where their predictions disagree, and it also shows that the $N=82$ neutron shell closure persists at this proton-rich edge.","feed_headline":"149Tm is first proton-unbound thulium isotope, mass data show","feed_subtitle":"Weighing 149Tm, 150Tm and 149Er fixes the Z=69 drip-line at N=80 and tests mass models.","key_machinery":"The carrying instrument is a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS), which sends bunched ions bouncing between electrostatic mirrors and turns their flight times into mass ratios; mass-selective retrapping suppresses contaminants and lets the weak $^{149,150}$Tm peaks be fit. The physical identity doing the work is the one-proton separation energy, $$S_p = M(Z,N) - M(Z-1,N) - M({}^1H),$$ with $Q_p = -S_p$; a nucleus is proton-unbound when $S_p \\le 0$. In the crowded $A=149$ spectrum, a hyper-exponentially modified Gaussian line shape calibrated on a strong $^{149}$Dy peak separates the low-lying ground state of $^{149}$Er from its dominant 741.7 keV isomer, so the daughter mass entering $S_p$ can be extracted directly from a tail.","core_discovery":"The paper's central claim is that $^{149}$Tm is the first proton-unbound isotope in the thulium chain, with a proton-emission $Q_p = +378 \\pm 52$ keV, and that $^{150}$Tm is the last proton-bound isotope. The argument rests on measured masses for both thulium isotopes together with revised masses for $^{149g}$Er and $^{149m}$Er, which the authors find to be about 150 keV heavier than the 2020 Atomic Mass Evaluation. That revision is what makes $^{150}$Tm look bound: using the old $^{149}$Er mass instead, the $^{150}$Tm separation energy would be within $1\\sigma$ of zero. The new masses also give a $^{150}$Tm proton-emission $Q$-value of $-202 \\pm 99$ keV and fix the empirical $N=82$ shell gap at $Z=69$, supporting the continued existence of that shell closure toward the drip-line.","pith_inferences":["A third, independent mass measurement of $^{149g}$Er would settle the one unexplained 150 keV discrepancy; if it returned the 2020 evaluation value, $^{150}$Tm would no longer be clearly proton-bound, although $^{149}$Tm would remain unbound on the present data.","The alternating bound and unbound pattern seen between $^{149}$Tm and $^{150}$Tm suggests the one-proton separation energy can oscillate with neutron number; a similarly precise remeasurement of $^{147,148}$Tm could reveal whether that pattern continues below $N=80$.","If the revised $^{149}$Er mass survives scrutiny, the mass surface in this region may need systematic re-evaluation, because a single 150 keV shift at $N=81$ can change the proton-bound character of a neighbouring odd-$Z$ isotope."],"forward_implications":["The proton drip-line for $Z=69$ is now fixed at $N=80$ by experiment, rather than left to model interpolation.","The $Q_p = +378 \\pm 52$ keV value for $^{149}$Tm can be used to compute its ground-state proton-emission partial half-life for the expected $11/2^-$ state, since only the $0^+$ ground state of $^{148}$Er is energetically open.","The $\\approx 150$ keV shift in the $^{149}$Er masses would, if confirmed, propagate into one-proton separation energies and alpha-decay chains that use those masses as anchors.","The $N=82$ shell gap measured at $Z=69$ remains sizeable, consistent with the neighbouring $Z=70$ result and with the persistence of magicity at the proton drip-line."],"supporting_citations":[{"why":"Provides the previous Schottky mass value for 149mEr that this work finds to be about 150 keV too light.","marker":"[14]"},{"why":"Provides the companion Yb mass data and the mass-selective retrapping method used to observe the weakest Tm peaks.","marker":"[15]"},{"why":"Supplies the earlier 147,148Tm masses that bracketed the drip-line region and set the baseline this work extends.","marker":"[19]"},{"why":"Gives the Bayesian model-averaging prediction that 149Tm is the first proton-unbound thulium isotope, which these measurements confirm.","marker":"[30]"},{"why":"Defines the MR-TOF-MS calibration and peak-fitting procedure used to obtain all masses in the paper.","marker":"[41]"},{"why":"Provides the hyper-exponentially modified Gaussian line shape used to separate 149gEr from its dominant isomer in the same peak.","marker":"[42]"},{"why":"Supplies the isomer excitation energies used to correct measured masses for unresolved isomeric states, including extrapolated values for 149,150Tm.","marker":"[50]"},{"why":"Gives the AME2020 procedure for applying isomer corrections and their uncertainties to measured masses.","marker":"[54]"},{"why":"Provides the AME2020 masses used as calibrants and as inputs for one-proton separation energies (1H, 148Er, 155Er).","marker":"[59]"}],"fun_headline_variants":["149Tm is first proton-unbound thulium","Proton drip-line for thulium lands on 149Tm","Mass data pin thulium's proton drip-line","149Tm unbound: thulium drip-line confirmed","Thulium's proton frontier at 149Tm"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is the newly measured $^{149}$Er mass being about 150 keV heavier than the 2020 Atomic Mass Evaluation, because that shift is what makes $^{150}$Tm look proton-bound; the authors themselves cannot explain the discrepancy and call for a third measurement.","fun_headline_variants_meta":{"raw":{"variants":["149Tm is first proton-unbound thulium","Proton drip-line for thulium lands on 149Tm","Mass data pin thulium's proton drip-line","149Tm unbound: thulium drip-line confirmed","Thulium's proton frontier at 149Tm"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000925,"raw_usage":{"total_tokens":3983,"prompt_tokens":983,"completion_tokens":3000,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":599,"completion_tokens_details":{"reasoning_tokens":2920}},"tokens_in":599,"tokens_out":3000,"duration_ms":23057,"temperature":1.0,"reasoning_tokens":2920,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T16:00:36.633378+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A third, technique-independent measurement of the $^{149g}$Er and $^{149m}$Er masses would settle it: if the new value agrees with the 2020 Atomic Mass Evaluation rather than with this paper's heavier value, then $^{150}$Tm's separation energy falls back into the $1\\sigma$-of-zero band and the claimed boundary at $N=80$ loses its experimental support, while $^{149}$Tm would still be unbound if its own mass and the $^{148}$Er mass hold.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the previous Schottky mass value for 149mEr that this work finds to be about 150 keV too light."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the companion Yb mass data and the mass-selective retrapping method used to observe the weakest Tm peaks."},{"cited_title":"Rauth, D","cited_arxiv_id":null,"evidence_quote":"Supplies the earlier 147,148Tm masses that bracketed the drip-line region and set the baseline this work extends."},{"cited_title":"Dickel, M","cited_arxiv_id":null,"evidence_quote":"Defines the MR-TOF-MS calibration and peak-fitting procedure used to obtain all masses in the paper."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the hyper-exponentially modified Gaussian line shape used to separate 149gEr from its dominant isomer in the same peak."},{"cited_title":"Singh, Nuclear data sheets for a = 151, Nuclear Data Sheets 110 (1) (2009) 1–264","cited_arxiv_id":null,"evidence_quote":"Supplies the isomer excitation energies used to correct measured masses for unresolved isomeric states, including extrapolated values for 149,150Tm."},{"cited_title":"Broda, P","cited_arxiv_id":null,"evidence_quote":"Gives the AME2020 procedure for applying isomer corrections and their uncertainties to measured masses."},{"cited_title":"Block, D","cited_arxiv_id":null,"evidence_quote":"Provides the AME2020 masses used as calibrants and as inputs for one-proton separation energies (1H, 148Er, 155Er)."}],"review_version":1}