{"id":"81a1cd12-80b0-4418-b8ca-fe1772f70b15","arxiv_id":"2507.01262","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"New spectroscopy of 257Db reveals a high-K isomer, a new 249Md alpha branch, and suggests the 257Db ground state is 9/2- rather than 9/2+.","lead":"This paper reports new alpha, gamma, and conversion-electron measurements on the decay of dubnium-257, including the first sighting of a short-lived high-spin isomer and a new decay branch in mendelevium-249. The data suggest a change in the parity of the dubnium ground state, with consequences for how proton orbitals are ordered above element 100.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The parity-change claim rests on treating all 80-150 keV electrons as a single 145 keV transition; a mixed electron group would undercut Fig. 17.","rationale":"The reader's weakest_assumption identifies two dependencies: the prior 7/2- ground-state assignments and the single-transition interpretation of the electron group. I focus on the latter because it is more directly testable with the data already in the paper and because the parity-change argument cannot survive if the 80-150 keV electrons are not predominantly one transition. The single-transition assumption is load-bearing: the conversion coefficient of 21(+28,-11) is used to support an M1/E2 assignment, but with only 48 electrons and 3 gamma rays, the statistical power is marginal, and the broad energy range (80-150 keV) is suspicious given other transitions shown in Fig. 17. The concrete test I propose—a likelihood comparison of one- versus two-transition models—would settle whether the electron group is actually a single transition. If it is not, the central parity change is unsupported. If it is, the 9/2- proposal still depends on the prior assignments and on the Geant4 fits, which lack error bars, but the single-transition issue is the most vulnerable point. For these reasons, the reader's CONDITIONAL verdict remains appropriate; I do not see grounds to accept the parity change as established, nor to reject the paper outright given the new data on the isomer and 249Md branch.","tokens_in":16357,"tokens_out":3643,"duration_ms":43149,"concrete_test":"Extract the 48 electron events of Fig. 7 (80-150 keV) and perform a binned maximum-likelihood fit with the GABRIELA response for: (i) a single 145 keV E2/M1 transition; (ii) two transitions at 145 and 85 keV with free intensities; (iii) a flat background alone. Use the Akaike information criterion and check whether the single-transition model is preferred. Independently, recompute the conversion coefficient from the 48 electrons and 3 gamma rays with the same geometric efficiency and compare to the expected LMN coefficients; if a two-transition model is preferred or the coefficient deviates by more than 3 sigma, the parity-change argument loses its foundation.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The proposed 9/2-[505] assignment for the 257Db ground state (Section IV.B, Fig. 17) requires that the 48 electron events in the 80-150 keV range observed in coincidence with 257Db alpha decays (Fig. 7) all be LMN conversion electrons of a single 145 keV transition in 253Lr. The conversion coefficient is then claimed to be 21(+28,-11), 'consistent within less than 2 sigma' with M1/E2 LMN values of 4.95/6.4. But the electron energy distribution is broad (80-150 keV) and only three gamma rays at ~145 keV are observed; the decay scheme itself (Fig. 17) includes other transitions (66, 85, 60 keV) that could contribute to the same electron group through summing or incomplete detection. If the electron group is a mixture of transitions, the inferred conversion coefficient, the placement of the 145 keV transition as the 11/2- (or 9/2-) band-head decay, and hence the parity change lose their quantitative foundation. The paper's own Geant4 simulations are fitted to the alpha spectrum, not an independent test; no error bars are shown on simulated spectra, so the exclusion of the 9/2+ scenario in Fig. 16(a) is not statistically quantified.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript reports a combined alpha-gamma-electron spectroscopy study of 257Db produced in the 50Ti + 209Bi fusion-evaporation reaction, using the GABRIELA setup coupled to SHELS. It presents three main experimental findings: (i) the first observation of a high-K isomer in 257Db with t1/2 = 0.71(+0.29,-0.18) ms and an excitation energy of at least 1.1 MeV; (ii) a previously unreported alpha-decay branch from the 1/2- state in 249Md at about 8350 keV with t1/2 ~ 1.1 s, constraining its excitation energy to 48-78 keV; and (iii) the first observation of internal conversion electrons in 253Lr following the high-spin alpha decay of 257Db, with a highly converted 145 keV transition and 48 electron events in the 80-150 keV range. On the basis of these data and Geant4 simulations, the authors propose that the high-spin ground state of 257Db has negative parity, 9/2-[505], rather than the previously suggested 9/2+[624], with the 1/2-[521] state at 59-89 keV; this revision affects Nilsson-level systematics above Z = 100.","tokens_in":16561,"tokens_out":6227,"duration_ms":65971,"significance":"The experimental material is valuable. The correlation plots in Figs. 2, 5, 7, and 12 support the claimed new isomer, the new alpha branch, and the coincidence pattern, and the measured half-lives and energies are broadly consistent with previous work. If the parity change is correct, the paper provides a rare experimental constraint on single-proton Nilsson states near Z = 105, with implications for the ordering of h9/2 and i13/2 intruder orbitals and for hexadecapole deformation trends. The paper also gives new quantitative constraints on the relative energies of the 1/2- and 7/2- states in 249Md, 253Lr, and 257Db. However, the central parity assignment is not yet established at the level claimed: it rests on the single-transition interpretation of a broad electron group and on Geant4 simulations whose feeding intensities are adjusted to reproduce the same data. The manuscript itself acknowledges the assumption that the 7/2- assignments of 253Lr and 249Md are correct, and the present data do not provide an independent, statistically quantified test of the 9/2- scenario.","major_comments":[{"comment":"The parity-change conclusion depends on identifying all 48 electron events in the 80-150 keV range as LMN conversion electrons of a single 145 keV transition in 253Lr. The text itself says \"If one assumes...\" and the resulting conversion coefficient 21(+28,-11) overlaps M1/E2 predictions at less than 2 sigma, but the electron energy distribution is broad and the decay scheme in Fig. 17 contains other low-energy transitions (66, 85, 60 keV) that could contribute to the same detector group. The authors should demonstrate, for example by simulating the response to a mixture of transitions or by fitting the electron-energy distribution, that the single-transition assumption is justified; otherwise the 145 keV placement and the derived 9/2- parity lose their quantitative foundation.","section":"Section III.A and Section IV.B (Figs. 7 and 17)"},{"comment":"The Geant4 simulations are used to rule out the previous 9/2+[624] interpretation (Fig. 16) and to support the new 9/2- scenario (Fig. 18), but the feeding intensities fed into the simulation are extracted from the same measured alpha spectrum (Table I, Section III.A) and no uncertainties are attached to the simulated spectra. The agreement in Fig. 18 is therefore a fit, not an independent validation, and the statement that the 9/2+ scenario \"cannot account for the double-humped structure\" is not quantified. The authors should provide a statistical comparison (for example chi-square or likelihood with bin-by-bin errors, including systematic uncertainties from implantation depth and detection efficiencies) and show the sensitivity of the conclusion to the fitted feeding intensities.","section":"Section IV.B, Figs. 16(a) and 18"},{"comment":"The proposed assignment explicitly assumes the previous 7/2-[514] ground-state assignments for 253Lr and 249Md: \"The scenario proposed here ... assumes that the previous 7/2- assignments ... is correct.\" This is a load-bearing external input: if either assignment were incorrect, the relative-parity argument and the preferred 9/2-[505] assignment would not follow. The paper does not assess how the conclusion would change if, for example, the ground state of 253Lr or 249Md had spin 9/2- or 5/2-. A sensitivity discussion, or at least an explicit statement that the conclusion is conditional on these assignments, is needed in the interpretation section rather than only as an embedded caveat.","section":"Section IV.B"},{"comment":"The deduced 48-78 keV excitation energy of the 1/2- state in 249Md depends on the assumption that the 7/2+[633] band head in 245Es lies below the 5/2- member at about 30 keV (deduced from systematics) and on excluding the possible 5/2- feeding branch from the simulation because of low statistics. These choices affect the band structure and the subsequent energy constraints in 253Lr and 257Db. The authors should at least indicate the range of excitation energies allowed if the 5/2- branch were present at the few-percent level, or justify the exclusion more quantitatively.","section":"Section IV.A (Fig. 14)"}],"minor_comments":[{"comment":"The phrase \"the first observation the internal decay in 253Lr\" is grammatically incomplete; it should read \"the first observation of the internal decay in 253Lr.\"","section":"Abstract"},{"comment":"There is a typo in \"to ensure the highest detection efficiency possile [14]\"; it should be \"possible.\"","section":"Section II"},{"comment":"The half-life for the 253Lr low-spin state is labeled \"2.0(14) s\", whereas the text and Table I give 2.0(1) s; this should be corrected.","section":"Figure 17"},{"comment":"The alpha-decay energies for 257Db are listed as \"extracted from the Monte Carlo simulation\"; the directly measured peak centroids should also be reported, since those are the primary observable quantities and would allow independent checks of the simulation-based corrections.","section":"Section III.A, Table I"}],"recommendation":"major_revision","confidential_remarks":"I support major revision rather than rejection. The new experimental observations are likely solid and the proposed scheme is a plausible reinterpretation, but the central parity claim should be presented as a hypothesis until the single-transition assumption and the simulation-based exclusion are quantified. I would suggest that the authors also soften the abstract's \"requires a revision\" to \"suggests a revision\" unless the requested analyses are added."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You should know this paper gets the headline right: it reports the first high-K isomer in 257Db, a new alpha branch in 249Md, and the first internal transition in 253Lr, all with quoted uncertainties and clearly presented correlation plots. Those results are genuinely new and will be cited. The 8350 keV branch in 249Md was visible in earlier data but not interpreted, and the paper says so, which is honest. The half-lives, alpha energies, and coincidence patterns are measured independently of the simulations, so the experimental core is solid. The paper's bold move is to flip the parity of the 257Db ground state from 9/2+ to 9/2-[505], based on the double-humped alpha spectrum and the 145 keV transition in 253Lr. That interpretation is plausible but not ironclad. The conversion coefficient of 21(+28,-11) is stated to be within 2 sigma of the M1/E2 values of about 5-6, but even the lower bound (10) is above those expectations, and the 48 electron events span 80-150 keV. If that group is a mixture of the 145 keV transition and the 66/85/60 keV transitions in the scheme, the conversion coefficient and the placement of the 145 keV transition as the band-head decay lose their footing. The stress-test note is right to flag this; it is a real caveat, not a manufactured one. The Geant4 simulations are fitted to the same alpha spectrum they are compared against, with no error bars on the simulated curves, so the exclusion of the 9/2+ scenario in Fig. 16 is not statistically quantified. The paper openly says the proposal assumes the 7/2- ground states of 253Lr and 249Md, which is the right thing to do but means a wrong prior would topple the scheme. On the other side, the paper engages fairly with the counterarguments—the conflicting predictions of Chasman and Cwiok on beta4 effects, the tentative 9/2+ assignments elsewhere, and the limits of the statistics. The central interpretation is a hypothesis, not a result, but it is well-argued and testable with more data. This deserves a serious referee, not a desk rejection. If I were refereeing, I would push on the composition of the 80-150 keV electron group, ask for error bars on simulated spectra, and request that the feeding intensities be presented as constraints rather than fitted parameters. The paper is a solid contribution either way. I would bring it to the next reading group for the discussion of how far you can push low-statistics spectroscopy, and I would cite the new experimental data.","headline":"Genuinely new data on 257Db and its decay chain, but the parity-change claim is a plausible interpretation built on a few soft assumptions, not a settled result.","tokens_in":17308,"tokens_out":3883,"would_cite":true,"duration_ms":42648,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["23.60.+e","21.10.Hw","27.90.+b"],"model":"deepseek-v4-flash","headline":"This paper argues that the ground state of $^{257}$Db is the $9/2^-[505]$ Nilsson state, not the previously assigned $9/2^+[624]$ state, based on the first observation of a high-$K$ isomer in $^{257}$Db, a new $\\alpha$-decay branch in…","keywords":["257Db","dubnium-257","high-K isomer","alpha decay","Nilsson states","internal conversion","superheavy nuclei","hindrance factors"],"falsifier":"Measure the multipolarity of the $145$ keV transition in $^{253}$Lr by collecting enough $K$-shell versus $L$-shell conversion-electron ratios to distinguish E1 from M1/E2; an E1 result would contradict the proposed decay from the $9/2^-[505]$ band head to the $11/2^-$ member. A second, independent check is direct atomic spectroscopy of $^{257}$Db: if the ground-state spin and parity turn out to be $9/2^+$, the paper's central revision is refuted.","tokens_in":16126,"feed_emoji":"⚛️","tokens_out":12314,"duration_ms":100393,"temperature":0.7,"pith_summary":"Along the $\\alpha$-decay chain of $^{257}$Db, this paper reports three new observations: a $0.71$ ms high-$K$ isomer in $^{257}$Db, a faster $1.1$ s $\\alpha$ branch from the $1/2^-$ state in $^{249}$Md, and the first internal transition in $^{253}$Lr, a highly converted $145$ keV decay. These data fix the relative excitation energies of the high-spin and $1/2^-$ states in $^{249}$Md, $^{253}$Lr, and $^{257}$Db to within roughly $30$ keV. To explain the double-humped $\\alpha$ spectrum of the $^{257}$Db high-spin state together with the new internal transition, the paper argues that the ground state of $^{257}$Db is the $9/2^-[505]$ Nilsson state, not the previously assigned $9/2^+[624]$ state. If correct, this revises the ordering of single-proton states above $Z=100$ and indicates that non-self-consistent calculations miss essential deformation or charge-density effects.","feed_headline":"New decay data flip the parity of dubnium-257's ground state","feed_subtitle":"A 0.71 ms isomer and a new alpha branch overturn the level scheme above Z=100.","key_machinery":"The load-bearing object is the Nilsson single-proton orbital $9/2^-[505]$, which the paper places at the Fermi surface of $^{257}$Db. The mechanism that carries the argument is the hindrance factor of $\\alpha$ decay: a transition between states of opposite parity and different spin projection would be strongly hindered, so the observation of favoured decays (hindrance factor near $1$) forces the initial and final states to share the same Nilsson configuration. This is combined with Monte Carlo simulations of the detector response that reproduce the energy summing of $\\alpha$ particles with internal-conversion electrons and atomic radiations; the double-humped shape of the measured $\\alpha$ spectrum is the fingerprint that selects among candidate decay schemes. The newly observed high-$K$ isomer, whose decay is seen only in correlation with the high-spin ground state, provides the additional constraint that the ground state must itself be high-spin.","core_discovery":"The central claim is that the accepted $9/2^+[624]$ ground-state assignment for $^{257}$Db cannot accommodate the sum of the measured decays, and that the data instead support a $9/2^-[505]$ ground state, a proton Nilsson orbital from the same $h_{9/2}$ shell that gives the $7/2^-[514]$ ground state of $^{253}$Lr. The evidence assembled is that the $145$ keV highly converted transition in $^{253}$Lr appears only after the high-spin $\\alpha$ decay of $^{257}$Db; that no scenario built on a $9/2^+$ state can reproduce the double-humped $\\alpha$-energy spectrum in Monte Carlo simulations unless an inter-band transition of about $145$ keV is introduced; and that the newly measured chains place the $1/2^-[521]$ state $48$-$78$ keV above the ground state in $^{249}$Md, nearly degenerate ($-24$ to $6$ keV) in $^{253}$Lr, and $59$-$89$ keV above the ground state in $^{257}$Db. With the $9/2^-$ assignment, the favoured $\\alpha$ decay to the $9/2^-[505]$ band head has hindrance factor about $1.2$, the weaker branches to the $11/2^-$ and $9/2^-$ members are consistent with the observed spectrum, and the conversion coefficient of the $145$ keV transition, although imprecise, does not exclude M1 or E2 multipolarity.","pith_inferences":["A direct test would be to search for the $9/2^-[505]$ band head in neighbouring odd-proton nuclei such as $^{255}$Lr or $^{251}$Md; finding it close to the $7/2^-[514]$ ground state, as this scheme predicts, would strengthen the assignment, while a high placement would weaken it.","The technique of using the summed $\\alpha$-plus-conversion-electron spectral shape as a fingerprint, rather than relying only on peak energies, could be applied to other odd-$Z$ superheavy $\\alpha$ emitters that show unexplained double-humped structures.","A model-independent parity measurement of the $^{257}$Db ground state, for example from laser spectroscopy of the hyperfine structure or from angular correlations of oriented nuclei, would settle the $9/2^-$ versus $9/2^+$ question without invoking hindrance-factor systematics.","The conversion coefficient of the $145$ keV transition in $^{253}$Lr is measured with very wide uncertainties; a dedicated run collecting more electron events would discriminate M1/E2 from the much less converted E1 alternative, and with it the proposed decay path."],"forward_implications":["The ground state of $^{257}$Db should be reassigned as $9/2^-[505]$, and future work on the $A=257$ decay chain should adopt the revised level scheme of Fig. 17.","The $1/2^-[521]$ isomer is now placed at $48$-$78$ keV in $^{249}$Md, $-24$ to $6$ keV in $^{253}$Lr, and $59$-$89$ keV in $^{257}$Db; these values become fixed points that nuclear-structure calculations of the $Z>100$ region must reproduce.","If the reassignment holds, the $9/2^+[624]$ orbital is no longer a low-lying proton state in $^{257}$Db, which affects the microscopic configurations proposed for high-$K$ isomers in neighbouring nuclei such as $^{257}$Rf and $^{254}$No.","Confirmation of the $9/2^-[505]$ assignment would imply that non-self-consistent mean-field calculations misorder proton orbitals above $Z=100$, pointing to higher-multipolarity deformation or charge-density effects as the missing ingredient."],"supporting_citations":[{"why":"Supplies the previous $^{257}$Db decay scheme and the $9/2^+[624]$ ground-state assignment that this work reinterprets.","marker":"[7]"},{"why":"Provides the $^{245}$Es level scheme used to place the new $^{249}$Md $\\alpha$ branch and to constrain excitation energies.","marker":"[16]"},{"why":"Supplies the experimental gyromagnetic factor of the $7/2^-[514]$ configuration used in the Monte Carlo simulations.","marker":"[17]"},{"why":"Describes the detector response and simulation procedure that reproduces $\\alpha$ summing with conversion electrons.","marker":"[14]"},{"why":"Reports the same about $8350$ keV $^{249}$Md decay without interpretation; this work identifies it as the $1/2^-$ branch.","marker":"[18]"},{"why":"Provides the $^{251}$Lr data showing inversion of the $7/2^-[514]$ and $1/2^-[521]$ states, used as systematic support.","marker":"[20]"},{"why":"Gives density-functional predictions that the $9/2^+[624]$ orbital may lie farther from the Fermi surface than non-self-consistent calculations suggest.","marker":"[28]"},{"why":"Shows the $\\beta_4$-dependence of single-proton Nilsson energies used to argue that $9/2^-[505]$ can be lowered near $Z=105$.","marker":"[32]"}],"fun_headline_variants":["Parity flip for dubnium-257 ground state","New data flip dubnium-257's ground-state parity","257Db ground state reassigned to 9/2- after decays","High-K isomer in 257Db changes parity assignment","Alpha and gamma spectroscopy revise 257Db level scheme"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The argument assumes that the previously assigned $7/2^-[514]$ ground states of $^{253}$Lr and $^{249}$Md are correct and that all $80$-$150$ keV electron events in $^{253}$Lr come from conversion of a single $145$ keV transition; if either of these gives way, the deduced band structure and the $9/2^-[505]$ assignment lose their foundation.","fun_headline_variants_meta":{"raw":{"variants":["Parity flip for dubnium-257 ground state","New data flip dubnium-257's ground-state parity","257Db ground state reassigned to 9/2- after decays","High-K isomer in 257Db changes parity assignment","Alpha and gamma spectroscopy revise 257Db level scheme"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000745,"raw_usage":{"total_tokens":3379,"prompt_tokens":1058,"completion_tokens":2321,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":674,"completion_tokens_details":{"reasoning_tokens":2238}},"tokens_in":674,"tokens_out":2321,"duration_ms":75114,"temperature":1.0,"reasoning_tokens":2238,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T20:56:12.874661+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the multipolarity of the $145$ keV transition in $^{253}$Lr by collecting enough $K$-shell versus $L$-shell conversion-electron ratios to distinguish E1 from M1/E2; an E1 result would contradict the proposed decay from the $9/2^-[505]$ band head to the $11/2^-$ member. A second, independent check is direct atomic spectroscopy of $^{257}$Db: if the ground-state spin and parity turn out to be $9/2^+$, the paper's central revision is refuted.","supporting_citations":[{"cited_title":"Heßberger, S","cited_arxiv_id":null,"evidence_quote":"Supplies the previous $^{257}$Db decay scheme and the $9/2^+[624]$ ground-state assignment that this work reinterprets."},{"cited_title":"Heßberger, S","cited_arxiv_id":null,"evidence_quote":"Provides the $^{245}$Es level scheme used to place the new $^{249}$Md $\\alpha$ branch and to constrain excitation energies."},{"cited_title":"Briselet, C","cited_arxiv_id":null,"evidence_quote":"Supplies the experimental gyromagnetic factor of the $7/2^-[514]$ configuration used in the Monte Carlo simulations."},{"cited_title":"Chakma, K","cited_arxiv_id":null,"evidence_quote":"Describes the detector response and simulation procedure that reproduces $\\alpha$ summing with conversion electrons."},{"cited_title":"Briselet, C","cited_arxiv_id":null,"evidence_quote":"Reports the same about $8350$ keV $^{249}$Md decay without interpretation; this work identifies it as the $1/2^-$ branch."},{"cited_title":"Huang, D","cited_arxiv_id":null,"evidence_quote":"Provides the $^{251}$Lr data showing inversion of the $7/2^-[514]$ and $1/2^-[521]$ states, used as systematic support."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives density-functional predictions that the $9/2^+[624]$ orbital may lie farther from the Fermi surface than non-self-consistent calculations suggest."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Shows the $\\beta_4$-dependence of single-proton Nilsson energies used to argue that $9/2^-[505]$ can be lowered near $Z=105$."}],"review_version":1}