{"id":"2012d831-951b-4210-8ba2-c67ac40bfc43","arxiv_id":"2505.10237","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"The level scheme of 202Po is extended with 57 new gamma-ray transitions, a 9.0(5) keV fixed 8+ to 6+ transition energy, and three new M1 sequences, with PBPOP shell-model calculations explaining the missing 12+ E2 decay.","lead":"This paper maps the excited states of the nucleus 202Po up to very high spin, adding 57 new gamma-ray transitions and fixing the energy of a fully converted isomer decay at 9.0 keV. It tests shell-model calculations near the doubly magic lead-208 region and explains a long-standing missing decay.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The shell-model 'explanation' of the missing 12+→10+ E2 is not testable in these data: at 5.3 keV the E2 branch is invisible in γ-ray spectra, so B(E2)≈0 is not supported; the spin-27 chain is less fragile than the reader's concern suggests.","rationale":"I read the paper's central claim as twofold: an experimental level scheme extending to 27ℏ and a shell-model account of key decay patterns. The experimental spin chain is supported by the DCO data; the reader's concern about non-dipole character conflates multipole order with electromagnetic character, and the text's 'multipolarity could not be determined' most plausibly refers to E/M character, not the dipole order used for spin. The genuinely load-bearing weakness is in the shell-model transition-rate interpretation. With the 10+ state only 5.3 keV below the 12+ state, the absence of an observed 12+→10+ E2 gamma is expected from energy and conversion physics, so the near-zero B(E2) is not validated by these data. The same valence-space calculation also gives zero M1 strength for four experimentally observed negative-parity M1 transitions, showing that transition-rate predictions are not a reliable pillar here. This overstatement affects an advertised conclusion but does not overturn the level scheme itself, so the appropriate outcome remains CONDITIONAL rather than ACCEPT or REJECT. The one check that would settle the issue is a lifetime/branching-based B(E2) limit for the 12+→10+ transition; without it, the 'explanation' should be reframed as an untested prediction.","tokens_in":29133,"tokens_out":23418,"duration_ms":233878,"concrete_test":"Take the adopted half-life of the 12+ isomer and the measured 143.0/436.4 keV E1 intensities to derive an upper limit on the total 12+→10+ E2 width, using an internal-conversion coefficient for a 5.3 keV E2 (e.g., from BrIcc). Compare the resulting B(E2;12+→10+) upper limit with the PBPOP prediction (≈0) and with a standard collective value of order 100–300 e2fm4. If the limit does not exclude the standard value, the Sec. V claim that the configuration change explains the missing E2 should be downgraded to an untested prediction; if the limit does exclude it, the concern is resolved in the paper's favor.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim's weakest pillar is the advertised shell-model explanation of the missing 12+→10+ E2 decay (abstract and Sec. V). Table I places the 10+ state at 3044.2 keV and the 12+ state at 3049.5 keV, a spacing of only 5.3(6) keV. At such low energy, an E2 gamma is unobservable with the HPGe array and internal conversion is large; the failure to see a 12+→10+ γ ray therefore carries essentially no information about B(E2) unless conversion-electron or lifetime data are added. The paper reports no such data, no intensity-balance constraint, and no upper limit on the converted branch, so the near-zero PBPOP B(E2;12+→10+) is presented as if it explained a puzzling experimental fact, when the non-observation is largely a phase-space and observability artifact. The fragility of transition-rate predictions in this valence space is independently visible in Table V: PBPOP gives B(M1)≈0 for the observed negative-parity M1 transitions 18−→17−, 19−→18−, 20−→19−, and 21−→20−, whose relative intensities are 8.2, 3.7, 1.4, and 1.1 (Table I). The 27ℏ spin extension is less vulnerable than the reader's statement suggests: the DCO ratios 0.51(9), 0.58(9), and 0.52(6) for 195.4, 211.3, and 267.5 keV are consistent with stretched dipole order, and the unresolved point is electric/magnetic character, not spin.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper presents a high-spin gamma-ray spectroscopy study of 202Po using the 195Pt(12C,5n) fusion-evaporation reaction at two beam energies with a 16-clover HPGe array. The authors report an extended level scheme reaching roughly 8 MeV and J=27ℏ, with 57 newly assigned transitions, revised placements of 8 previously known transitions, and new multipolarity determinations from DCO and IPDCO measurements. A central experimental result is the determination of the unobserved 8+→6+ transition energy as 9.0(5) keV using parallel 502.5- and 511.5-keV decays from the 2203.2-keV 7− state, which removes the earlier uncertainty in the excitation energies of all levels above the 6+ state. Three new M1 sequences are proposed, and the results are compared with PBPOP shell-model calculations. The paper claims that the calculations reproduce the level structure and explain the missing E2 decay of the 12+ isomeric state by a configuration-change mechanism.","tokens_in":29640,"tokens_out":5579,"duration_ms":56802,"significance":"The experimental part of this work is a substantial and credible contribution to the spectroscopy of the transitional N=118 nucleus 202Po. The 9.0(5)-keV energy inference is elegant and well supported by coincidence data, and the systematic DCO/IPDCO analysis provides useful multipolarity information for many weak transitions. The paper is also careful in several places: it identifies the 600.5/55.5-keV ordering ambiguity, states when multipolarities could not be determined, and notes the suppression of calculated high-spin energies. The shell-model comparison is useful for interpreting configuration changes, but the central theoretical claim about the missing 12+→10+ E2 decay is overstated because the experimental non-observation is not sensitive to B(E2) at the relevant transition energy.","major_comments":[{"comment":"The claim that PBPOP 'explained the missing E2 decay of the 12+ isomeric state' is not supported by the data. Table I places the 10+ state at 3044.2 keV and the 12+ state at 3049.5 keV, a spacing of only 5.3(6) keV. An E2 transition of this energy would be almost fully internally converted and is not observable with the present HPGe setup, so the absence of a 12+→10+ gamma ray carries essentially no information about B(E2). No conversion-electron measurement, lifetime limit, or intensity-balance constraint is presented. The near-zero calculated B(E2) should be presented as a prediction, not as an explanation of an observed decay branch.","section":"Sec. V and Abstract"},{"comment":"Table V shows that the PBPOP calculation gives B(M1) values of 0.0, 0.0, 0.0, and 0.0 μN² for the newly identified negative-parity M1 transitions 18−→17−, 19−→18−, 20−→19−, and 21−→20−, respectively. These are the same transitions that define the main new negative-parity M1 sequence, with relative intensities 8.2, 3.7, 1.4, and 1.1 in Table I. The text notes this discrepancy but does not quantify it or explain how the model can simultaneously 'explain the overall level scheme' and predict zero strength for a prominent measured cascade. This inconsistency needs a substantive discussion or a softening of the theoretical claims.","section":"Sec. V, Table V"},{"comment":"The extension of the level scheme to J=27ℏ rests on the 195.4-, 211.3-, and 267.5-keV transitions being stretched dipoles. Their DCO ratios, 0.51(9), 0.58(9), and 0.52(6), are consistent with stretched dipole character, but no IPDCO information is available, and the text states that the multipolarities of these transitions could not be determined. A non-dipole admixture or an unstretched assignment would change the spin sequence. The abstract and conclusions should therefore state explicitly that the 25ℏ–27ℏ assignments are tentative and based on DCO-only evidence.","section":"Sec. IV.C, Table I, Abstract"}],"minor_comments":[{"comment":"The sentence reporting the DCO calibration values reads 'about 0.5(1.0) and 1.0(2.0) for pure dipole and quadrupole transitions'; the parenthetical notation is implausible as written and should be corrected to the intended uncertainties, e.g., 0.5(1) and 1.0(2), with a clarifying statement about the gating selection.","section":"Sec. III"},{"comment":"The level scheme is very dense, and the spin labels, especially for the parallel and yrare sequences, are difficult to read in the printed version. Consider presenting the scheme in separate panels or with a larger font for level energies and spin assignments.","section":"Fig. 1"},{"comment":"The multipolarity column embeds footnote letters such as 'f E2' and 'g M1', which is confusing. It would be clearer to place the gating-transition footnotes as standard table footnotes separate from the multipolarity entries.","section":"Table I"},{"comment":"The text acknowledges that the ordering of the 600.5-keV and unobserved 55.5-keV transitions is uncertain and that an alternative level at 2282.7 keV cannot be discarded. This ambiguity should be indicated graphically in Fig. 1 with dashed levels/transitions so that readers can immediately see which part of the scheme is not uniquely determined.","section":"Sec. IV.B"},{"comment":"The statement that the first 10+ state 'has more contributions from the proton orbitals' is vague; it would be more informative to quote the average occupancies from Table II, which show that the 10+ state has <Lp> = 8.415 and <Ln> = 2.211, whereas the 12+ state is essentially purely neutron dominated.","section":"Sec. V"}],"recommendation":"major_revision","confidential_remarks":"The experimental level-scheme work is solid and within the scope of the journal. The main concern is the overstatement of the shell-model explanation for the missing 12+→10+ E2 decay, which is not actually tested by these data, and the unaddressed zero B(M1) predictions for the observed negative-parity M1 cascade. Both issues are fixable by reframing the claims and adding caveats."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First thing to know: this is a solid, old-fashioned high-spin gamma-ray spectroscopy paper. The new data are real: 57 new transitions, a revised 202Po level scheme up to about 8 MeV and 27 hbar, and a clever, convincing determination of the unobserved 8+ to 6+ energy at 9.0(5) keV using the parallel 502.5/511.5 keV decays from the 7- state at 2203.2 keV. That inference is the cleanest part of the paper and it resolves the absolute excitation energies above the 6+ state. The three new M1 sequences are also well supported by coincidence and DCO/IPDCO data where statistics allowed.\n\nThe experimental analysis is careful and the authors are appropriately transparent about limitations. They state plainly that the multipolarities of the 195.4, 211.3, and 267.5 keV transitions - the ones that carry the level scheme to 27 hbar - could not be measured, and an ordering ambiguity remains for the 600.5/55.5 keV pair. The DCO ratios for those top transitions are consistent with stretched dipole, so the spin chain is plausible; the caveat is E/M character rather than spin. The 22-24 hbar region is on firmer footing.\n\nWhere the paper is weaker is the shell-model narrative. The claim that PBPOP 'explains the missing E2 decay of the 12+ isomer' is not supported by these data. The 12+ and 10+ states are separated by only 5.3(6) keV; at that energy an E2 gamma-ray is unobservable with an HPGe array and internal conversion dominates. The non-observation carries essentially no information about B(E2), so the near-zero calculated B(E2) is not tested. The authors should add conversion-electron or lifetime data, or soften the claim to a prediction. Similarly, Table V shows the calculated B(M1) values for the observed negative-parity M1 chain are near zero, which is in tension with the experimental intensities. The paper notes this, but it undercuts the 'explained the overall level scheme' summary. The energy systematics and the 8+ isomer purity are reproduced well; the transition rates are not.\n\nNet: the experimental content deserves publication, and the authors have been honest about its limits. The shell-model discussion needs revision, not rejection. I would send this to a competent referee. It is for nuclear structure specialists, mainly those working around Z=82, N=126. I would cite it for the level scheme, not for the B(E2) story.","headline":"A careful experimental level-scheme paper with a genuinely new 9.0(5) keV inference; the shell-model 'explanation' of a missing E2 should be read as speculative.","tokens_in":30156,"tokens_out":2236,"would_cite":true,"duration_ms":20691,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["21.10.-k","23.20.Lv","25.70.-z","27.80.+w"],"model":"deepseek-v4-flash","headline":"202Po's level scheme is extended to 27ℏ and 8 MeV with 57 new transitions, and the unobserved 8+→6+ energy is fixed at 9.0(5) keV.","keywords":["202Po","high-spin level scheme","gamma-ray spectroscopy","isomeric states","M1 sequences","shell model","PBPOP interaction","E2 decay hindrance"],"falsifier":"Measure the multipolarities of the 195.4, 211.3, and 267.5 keV transitions with higher statistics DCO/IPDCO or conversion-electron spectroscopy; a non-dipole assignment for any of them would lower the 27$\\hbar$ spin. Independently, detect the 9.0 keV $8^+\\to 6^+$ transition directly with low-energy photon or conversion-electron detectors; a measured energy different from 9.0(5) keV would break the parallel-loop placement.","tokens_in":28966,"feed_emoji":"⚛️","tokens_out":8148,"duration_ms":74267,"temperature":0.7,"pith_summary":"This paper reports a high-spin gamma-ray spectroscopy study of $^{202}$Po that extends the level scheme to about 8 MeV excitation energy and angular momentum $27\\,\\hbar$, adding 57 new transitions. It fixes the energy of the unobserved $8^+\\to 6^+$ isomer decay at 9.0(5) keV by finding two parallel decays from a newly placed $7^-$ state, and it identifies three new sequences of $M1$ transitions. Large-scale shell-model calculations with the PBPOP interaction reproduce the positive-parity structure and trace the missing $E2$ decay of the $12^+$ isomer to a near-zero wave-function overlap with the $10^+$ state. The result matters because $^{202}$Po sits at $N=118$, where competing neutron and proton pair break-ups decide which states live as isomers.","feed_headline":"57 new gamma rays map 202Po to spin 27ℏ","feed_subtitle":"A 9.0 keV missing transition and three M1 cascades sharpen the N=118 shell-model test.","key_machinery":"The machinery is a coincidence-based level scheme built from $\\gamma\\gamma$ and $\\gamma\\gamma\\gamma$ data, with DCO ratios and integrated polarization asymmetries assigning spins, parities, and electric or magnetic character to each transition. The load-bearing identity is the energy loop $502.5 + 9.0 = 511.5$ keV that locates the unobserved $8^+\\to 6^+$ transition at 9.0(5) keV. The interpretive mechanism is the PBPOP surface-delta interaction in a $Z>82$, $N<126$ valence space: average orbital occupancies show which states are proton-driven and which are neutron-driven, and the change from $\\pi h_{9/2}$ purity at $8^+$ to $\\nu i_{13/2}$ dominance at $12^+$ suppresses the $E2$ matrix element between them.","core_discovery":"On the paper's own terms, the central discovery is that the level scheme of $^{202}$Po is both larger and different from what was previously known: 57 new gamma-ray transitions, revised placements for 8 known transitions and new multipolarities for 4 of them, three new $M1$ sequences above the $16^+$ and $15^-$ states, and an energy of 9.0(5) keV for the fully converted $8^+\\to 6^+$ transition, deduced from the energy loop formed by the parallel 502.5 keV ($7^-\\to 8^+$) and 511.5 keV ($7^-\\to 6^+$) transitions. The accompanying PBPOP shell-model calculation shows that the $8^+$ isomer is nearly pure $\\pi h_{9/2}^2$, while the $12^+$ isomer is dominated by $\\nu i_{13/2}$; the two wave functions have almost no overlap under the $E2$ operator, which explains why the $12^+$ state decays by $E1$ rather than by an $E2$ to the $10^+$ state. This configurational-change mechanism is the paper's answer to the long-standing anomaly of the missing $12^+\\to 10^+$ decay in $^{202}$Po.","pith_inferences":["If the 27$\\hbar$ assignment holds, the highest observed state at 7898.5 keV would sit near the limit of what fusion-evaporation populates in this mass region; a natural next test is to search for feeding from above and to measure the lifetimes of the $25$, $26$, and $27$ levels.","The parallel-loop method that pins a fully converted transition at 9.0 keV could be applied to other even-even Po and Pb isotopes where the $8^+\\to 6^+$ decay is unobserved, turning inferred gaps into measured ones.","The paper does not claim these $M1$ sequences are shears bands; if future angular-correlation measurements find increasing $B(M1)$ and decreasing transition energies with spin, a shears interpretation would become viable.","The shell model's systematic suppression of high-spin energies suggests that including neutron excitations above $N=126$ would shift the calculated states upward; comparing the present results with such extended-space calculations would quantify the missing core-polarization effect."],"forward_implications":["The 9.0(5) keV $8^+\\to 6^+$ energy resolves the absolute excitation energy of every level above the $6^+$ state, so all previously known and newly added high-spin levels in $^{202}$Po are now anchored to the ground state.","The three new $M1$ sequences above the $16^+$ and $15^-$ states provide band-like structures whose lifetimes can be measured; the shell model already predicts decreasing $B(M1)$ values along the $24^+\\to 23^+\\to 22^+\\to 21^+$ chain.","The near-zero calculated $B(E2;12^+\\to 10^+)$ explains the experimentally missing $E2$ decay, and makes $N=118$ a documented case where the $12^+$ isomer decays by $E1$ because of changed nucleonic configurations rather than by an $E2$.","The shell model predicts a low $B(E2;20^+\\to 18^+)$, so the $20^+$ state may be isomeric; a lifetime analysis can test this prediction.","The revised placements above the $16^+$ state supersede earlier tentative assignments, so future compilations and isomer studies of $^{202}$Po should use the present scheme as the reference."],"supporting_citations":[{"why":"Provides the previous high-spin level scheme of 202Po that this work extends and revises.","marker":"[10]"},{"why":"Supplies the low- and medium-spin states and adopted multipolarities from the beta-decay study of 202At.","marker":"[12]"},{"why":"Gives the generalized-seniority prediction that N=118 is a transition point for Po isotopes, which motivates the study.","marker":"[21]"},{"why":"Demonstrates in 200Po how parallel transitions fix the energy of an unobserved 8+ to 6+ transition, the method used here.","marker":"[22]"},{"why":"Provides the measured half-lives and B(E2) values for the 8+ and 11- isomers used to benchmark the shell-model results.","marker":"[44]"},{"why":"Defines the PBPOP surface-delta interaction with empirically fitted single-particle energies used in the calculations.","marker":"[56]"},{"why":"Establishes that the Z>82, N<126 valence space is sufficient for level schemes and electromagnetic properties in A approximately 200 Po isotopes.","marker":"[58]"},{"why":"Supplies the shell-model diagonalization code used to obtain the calculated spectra and occupancies.","marker":"[59]"}],"fun_headline_variants":["Configurational flip explains missing decay in 202Po","57 new gamma rays, three M1 cascades map 202Po","9-keV transition deduced in 202Po high-spin level scheme","202Po: 57 new transitions, missing E2 explained"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The extension to 27$\\hbar$ depends on the 195.4, 211.3, and 267.5 keV transitions being stretched dipoles, but their multipolarities could not be determined; if any is a quadrupole the implied spins would drop, and the shell-model explanation also assumes no neutron excitations above $N=126$, which the authors note suppresses high-spin energies.","fun_headline_variants_meta":{"raw":{"variants":["Configurational flip explains missing decay in 202Po","57 new gamma rays, three M1 cascades map 202Po","9-keV transition deduced in 202Po high-spin level scheme","202Po: 57 new transitions, missing E2 explained"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000255,"raw_usage":{"total_tokens":1654,"prompt_tokens":1108,"completion_tokens":546,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":724,"completion_tokens_details":{"reasoning_tokens":471}},"tokens_in":724,"tokens_out":546,"duration_ms":5151,"temperature":1.0,"reasoning_tokens":471,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T21:13:29.259912+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the multipolarities of the 195.4, 211.3, and 267.5 keV transitions with higher statistics DCO/IPDCO or conversion-electron spectroscopy; a non-dipole assignment for any of them would lower the 27$\\hbar$ spin. Independently, detect the 9.0 keV $8^+\\to 6^+$ transition directly with low-energy photon or conversion-electron detectors; a measured energy different from 9.0(5) keV would break the parallel-loop placement.","supporting_citations":[{"cited_title":"Frauendorf, Rev","cited_arxiv_id":null,"evidence_quote":"Provides the previous high-spin level scheme of 202Po that this work extends and revises."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the low- and medium-spin states and adopted multipolarities from the beta-decay study of 202At."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives the generalized-seniority prediction that N=118 is a transition point for Po isotopes, which motivates the study."},{"cited_title":"Kesteloot, B","cited_arxiv_id":null,"evidence_quote":"Demonstrates in 200Po how parallel transitions fix the energy of an unobserved 8+ to 6+ transition, the method used here."},{"cited_title":"Kanjilal, S","cited_arxiv_id":null,"evidence_quote":"Provides the measured half-lives and B(E2) values for the 8+ and 11- isomers used to benchmark the shell-model results."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines the PBPOP surface-delta interaction with empirically fitted single-particle energies used in the calculations."},{"cited_title":"Kr¨ amer-Flecken, T","cited_arxiv_id":null,"evidence_quote":"Establishes that the Z>82, N<126 valence space is sufficient for level schemes and electromagnetic properties in A approximately 200 Po isotopes."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the shell-model diagonalization code used to obtain the calculated spectra and occupancies."}],"review_version":1}