Pith. sign in

REVIEW 4 major objections 6 minor 25 references

A liquid krypton TPC can hunt double positron decay nearly free of background by tagging four 511 keV gammas, with a 60 kg device already able to set world-best limits.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

T0 review · grok-4.5

2026-07-31 09:44 UTC pith:Y7HG2PTR

load-bearing objection Clean concept paper: LKr TPC plus four-gamma topology can make β+β+ look background-free in MC; 85Kr and hardware assumptions are the real gates, not the topology math. the 4 major comments →

arxiv 2607.28360 v1 pith:Y7HG2PTR submitted 2026-07-30 physics.ins-det nucl-ex

On a Liquid Krypton TPC for double positron decay searches

S. Torelli , A. Sim\'on Est\'evez , F. Monrabal Capilla This is my paper
classification physics.ins-det nucl-ex
keywords liquid krypton TPCdouble positron decay0νβ+β+four-gamma taggingtopological selection78Kr511 keV annihilationbackground-free search
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Double positron decay leaves two positrons plus four 511 keV annihilation gammas in collinear pairs—a topology ordinary backgrounds cannot fake if those gammas are tagged. This paper proposes a liquid krypton time projection chamber as the right tool: dense enough to contain the gammas, sparse enough to keep their clusters separate from the main track, cheaper than xenon, and richer in the candidate isotope 78Kr. Simulations of a compact 60 kg natural-krypton detector show that selecting one high-energy track plus tagged 511 keV photons suppresses 208Tl and 214Bi backgrounds to well below one event per decade in the cleanest channels, yielding half-life sensitivity above 10^23 years in about 1.5 years for both the neutrinoless and two-neutrino modes. A ton-scale detector, especially if enriched in 78Kr, could push the reach to 10^29–10^30 years while remaining essentially background-free. The result matters because it offers a scalable path to a Majorana-neutrino test that does not rely on heroic energy resolution or statistical background subtraction.

Core claim

A liquid krypton TPC that reconstructs one high-energy double-positron track together with four tagged 511 keV annihilation photons can perform a virtually background-free search for 0νβ+β+ and 2νβ+β+. Already a 60 kg natural-krypton chamber of 31.5 cm drift reaches half-life sensitivities ≳10^23 y in ~1.5 years; a ton-scale 78Kr-enriched detector could reach 10^29–10^30 y.

What carries the argument

Four-gamma topological tagging (signatures S1–S5): isolate a single track above 550 keV, then match geometric angles between energy deposits to the Compton scattering angle expected for a 511 keV photon born at that track, and require collinear pairs aligned with the main track. This selection, plus a narrow energy ROI, drives external gamma backgrounds to ≲1 event per 10 years for the cleanest channels.

Load-bearing premise

That radioactive 85Kr can be stripped from natural krypton far enough that pile-up does not cripple the TPC, and that any leftover 85Kr events still fail the four-gamma collinear topology.

What would settle it

Operate a ~60 kg liquid-krypton TPC with the proposed charge readout and tagging algorithm for 1–2 live years; if the cleanest signatures return background rates far above the simulated <0.1 events per 10 years, or if 85Kr pile-up cannot be reduced to operable levels, the background-free claim is false.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • A 60 kg natural-Kr prototype can already surpass existing 78Kr and 106Cd limits on 2νβ+β+ and set the strongest 0νβ+β+ bound.
  • Ton-scale natural Kr could reach ~10^27 y in a few years; 78Kr enrichment opens 10^29–10^30 y.
  • Signatures that demand four extra tracks stay robust even as mass and external background grow.
  • Better gamma containment in larger volumes shifts efficiency toward the cleanest signature, aiding scale-up.
  • The same collinear four-gamma topology can be reused for other β+β+ isotopes if a suitable dense tracker exists.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Industrial 85Kr depletion that works for this TPC would also supply cheaper enriched 78Kr feedstock for other rare-event experiments.
  • The Compton-angle plus collinearity tagger could transfer, with modest retuning, to multi-gamma Compton cameras in medical or nuclear imaging.
  • If LKr electron diffusion is confirmed roughly half that of LXe, coarser than 3 mm pixel pitch may still suffice and cut readout cost.
  • A null result at 10^27 y would still tightly constrain the nuclear matrix elements that enter β+β+ half-life predictions.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

4 major / 6 minor

Summary. The manuscript proposes a single-phase liquid-krypton TPC for 0νβ+β+ and 2νβ+β+ searches that exploits the four collinear 511 keV annihilation photons plus a high-energy double-positron track. After arguing that LKr is preferred over LXe (abundance, cost, interaction length for cluster separation), the authors define five topological signatures (S1–S5) based on Compton-angle tagging of 511 keV photons and collinearity with a HE track (E>550 keV). GEANT4 simulations of a 60 kg natural-Kr cylinder (31.5 cm diameter/drift, 3 cm Cu vessel) yield selection efficiencies and 208Tl/214Bi background rates (Tables 1–3); a multichannel Feldman–Cousins construction then projects 0ν half-life sensitivity ≳10^23 y in ~1.5 y in a virtually background-free regime, with a ton-scale 78Kr-enriched detector claimed to reach 10^29–10^30 y. Appendix A addresses atmospheric 85Kr via centrifuge “light cut,” a 1992 enrichment citation, and qualitative pile-up rejection arguments.

Significance. If the topological rejection and operational premises hold, the work opens a distinctive, potentially background-free channel for Majorana-neutrino searches that is complementary to conventional 0νββ programs and could set world-best 78Kr limits already at the 60 kg scale. Strengths include a concrete multi-signature analysis with an explicit multichannel Feldman–Cousins construction, transparent efficiency/background tables, and a clear physics motivation for LKr over LXe. The concept is falsifiable by future prototype data and is of genuine interest to the instrumentation and rare-event communities. The result remains a forward MC projection rather than a demonstrated measurement; its impact therefore hinges on the credibility of the 85Kr mitigation and external-background assumptions.

major comments (4)
  1. [Appendix A; Figs. 5–6; Tables 1–3] Appendix A is load-bearing for any real exposure yet supplies only a 1992 citation of 4×10^3 85Kr depletion for 98% 78Kr plus qualitative arguments (second S1, ~30 cm spatial containment, S1 threshold >1 MeV). Natural Kr activity is ~147 kBq/kg; without a stated residual specific activity for the commercial “light cut” and without an end-to-end pile-up Monte Carlo folded through the S1–S5 selection of Tables 1–3, the zero-background premise and the sensitivity curves in Figs. 5–6 are not quantitatively supported. A residual activity ≳ few Bq/kg would invalidate the virtually background-free claim before enrichment or ton-scale arguments apply. Either provide a quantitative residual-activity target and pile-up MC, or clearly condition the sensitivity projections on an as-yet-undemonstrated purity.
  2. [Section 3 (detector setup and background model)] Section 3 states that a 3 cm copper vessel “sufficiently suppresses the external background, at a level to make it negligible compared to the internal one,” and only internal Cu 208Tl/214Bi (activities taken from Ref. [4]) are simulated. No external-gamma campaign (cavern rock, lab gammas, cosmogenic activation, or vessel outer surfaces) is shown. For a concept claiming virtually background-free operation this assumption is central; it should be justified with at least an order-of-magnitude external flux estimate or a shielding calculation, or the claim should be restricted to internal backgrounds only.
  3. [Section 3; Table 2; Fig. 4] The ROI analysis assumes 1% energy resolution (σ) at 802 keV, citing LZ LXe performance [16]. No LKr charge-readout resolution measurement or simulation (including recombination, attachment, and the proposed ~3 mm pixel/wire pitch) is provided. Because the ±3σ ROI cut directly sets the residual 2ν and continuum-gamma leakage in Table 2 and Fig. 4, the resolution must be motivated for LKr or varied as a systematic; otherwise the background-free conclusion is resolution-dependent in a way that is not quantified.
  4. [Tables 1–3; Eqs. (2)–(5); Section 3] Several background entries in Tables 1–3 are 90% CL upper limits from zero MC survivors (e.g., S1 208Tl/214Bi). The simulated exposures (1601 y 208Tl, 504 y 214Bi) are large, but rare multi-site topologies that pass Compton tagging and collinearity can be under-sampled. The paper should state the effective number of trials after preselection, confirm that the zero-event limits remain valid under modest changes of Δθ and collinearity cuts, and propagate these upper limits (rather than treating them as exact zeros) through the multichannel Feldman–Cousins sensitivity so that the “virtually background-free” statement is statistically transparent.
minor comments (6)
  1. [Section 2] Electron diffusion in LKr is taken from LXe data [9] and a simulation paper [10]; state explicitly that no LKr measurement exists and quote the factor-of-two transverse reduction claimed in [10] when justifying the ~3 mm pitch.
  2. [Section 3, Eqs. (1)] The Compton tolerance Δθ<0.06 and HE threshold E>550 keV are free analysis parameters; a short scan (already alluded to for Δθ) should be shown or tabulated so readers can judge robustness.
  3. [Section 3 (end)] Truth-level tagging efficiency is quoted as 17% (S1–S3) / 40% (S1–S5) versus lower analysis efficiencies; clarify whether the gap is dominated by containment, barycenter approximation, or algorithm simplicity, and whether ML improvements are expected to close it without increasing false tags.
  4. [Figure 4] Figure 4 y-axes and legends are hard to read in grayscale; ensure line styles distinguish 0ν, 2ν, 214Bi, and 208Tl without color.
  5. [Abstract; throughout; Appendix A] Typographical/notation issues: “we’ll show” in abstract; inconsistent spacing in Q_val and m_e; “T opology” in Fig. 4 labels; Ref. [25] is a 1992 Atomnaya Ehnergiya note—give the English translation citation fully.
  6. [Section 3] The assumed 2ν half-life of 10^24 y used to normalize 2ν background should be referenced or flagged as a benchmark value, since it directly enters the “<<1 ev/(10 y)” claim.

Circularity Check

0 steps flagged

No circularity: sensitivities are forward GEANT4/Feldman–Cousins projections from external inputs, not fits or self-definitional claims.

full rationale

The paper’s load-bearing chain is a detector-concept Monte Carlo study: GEANT4 generation of 0ν/2ν signal and 208Tl/214Bi backgrounds in a 60 kg LKr geometry, topological tagging of HE track + 511 keV photons (signatures S1–S5), ROI energy cuts assuming 1% resolution from an external citation, copper radioactivities taken from NEXT-100, and a multichannel Feldman–Cousins construction of half-life sensitivity. None of these steps equates the claimed T1/2 to a fitted input by construction; analysis thresholds (E_HE > 550 keV, Δθ < 0.06, ±3σ ROI) are free cuts whose efficiencies are measured on independent MC samples, not definitions of the signal. There is no uniqueness theorem, no self-citation that forces the central claim, and no renaming of a known empirical pattern as a first-principles result. The 85Kr depletion premise (Appendix A) is a soft operational assumption supported by a 1992 external enrichment citation and qualitative pile-up arguments; that is a feasibility/correctness risk, not circularity under the stated rules. The derivation is therefore self-contained against its stated external benchmarks.

Axiom & Free-Parameter Ledger

6 free parameters · 7 axioms · 2 invented entities

The claim chain is a detector-concept MC study. It inherits standard particle data and GEANT4 transport, assumes noble-liquid TPC performance numbers (resolution, diffusion, light), fixes analysis thresholds by hand, treats vessel radio-purity and 85Kr depletion as enabling premises, and invents no new particle—only a detector architecture and event taxonomy.

free parameters (6)
  • Compton angle tolerance Δθ = 0.06 rad
    Tagging requires |θ_geo − θ_ene| < 0.06; authors scanned 0.04–0.1 and report weak dependence, but the cut is a hand-chosen analysis parameter controlling efficiency vs fake tags.
  • HE-track energy threshold = 550 keV
    Main-track definition uses E > 550 keV for 0ν (above 511 keV photopeak); directly sets which events enter tagging.
  • Assumed energy resolution σ at 802 keV = 1%
    ROI is ±3σ with 1% resolution assumed from LXe-like performance [16]; not measured in LKr for this setup.
  • Assumed 2ν half-life for background = 10^24 y
    2ν background normalization uses T_1/2 = 10^24 y → 0.28 ev/y in 60 kg; scales residual 2ν leakage into ROI.
  • Copper vessel 208Tl/214Bi activities = 0.4e-3 Bq Tl; 2.5e-3 Bq Bi
    Background rates scale from NEXT-like copper radio-purity [4] applied to the full vessel (0.4e-3 Bq 208Tl, 2.5e-3 Bq 214Bi).
  • Collinearity geometric cuts = HE-axis / 1 mm
    Collinearity uses perpendicular distance vs HE major-axis length (0ν) or 1 mm line proximity counts (2ν main-track finder)—hand-set topology parameters.
axioms (7)
  • domain assumption GEANT4 electromagnetic transport adequately models multi-site 511 keV and MeV gamma topologies in LKr for efficiency and background estimates.
    Entire sensitivity tables come from GEANT4 signal and 208Tl/214Bi samples (§3).
  • ad hoc to paper 3 cm copper vessel makes external gamma background negligible relative to internal Cu 208Tl/214Bi.
    Stated explicitly as an assumption when defining the geometry (§3), without a full external-shielding study.
  • domain assumption Electron diffusion in LKr is comparable to or better than LXe (~mm over 50 cm), so ~3 mm charge readout resolves tracks.
    No LKr diffusion measurement; Xe data and a simulation paper are used as proxy (§2).
  • domain assumption Single-phase charge readout (GAMPix/LarPix/DUNE-like wires) can deliver ≲1% energy resolution near 0.8 MeV in LKr.
    ROI width and background rejection after energy cut depend on this (§3, ref [16]).
  • domain assumption Centrifugal bulk separation can deplete 85Kr enough for TPC operation; residual pile-up fails signal topology or S1 trigger.
    Appendix A; without it the quoted live-time exposures are operationally impossible at natural 85Kr activity.
  • domain assumption Only 208Tl and 214Bi (plus 2ν) are relevant high-energy topological backgrounds; lower-energy gammas and 40K are negligible after selection.
    §3 states lower-energy gammas omitted; 40K checked at low pass rate in conclusions.
  • standard math Feldman–Cousins multichannel combination of independent Poisson signature counts yields the quoted average 90% CL sensitivity.
    §3 equations (2)–(5) following standard unified ordering [17].
invented entities (2)
  • Five topological event signatures S1–S5 (HE track + tagged 511s / isolated tracks with collinearity rules) no independent evidence
    purpose: Partition signal-like topologies to combine high-efficiency and ultra-low-background channels in the sensitivity calculation.
    Analysis taxonomy defined in §3 and Figure 3; not a new physical particle, but a paper-specific event ontology the claim uses.
  • 60 kg / ton-scale single-phase LKr TPC concept for β+β+ no independent evidence
    purpose: Proposed detector architecture realizing four-gamma tagging in a containable liquid target.
    Core instrument proposal; independent evidence would require a built prototype, not provided.

pith-pipeline@v1.2.0-daily-grok45 · 16878 in / 4537 out tokens · 76302 ms · 2026-07-31T09:44:14.952792+00:00 · methodology

0 comments
read the original abstract

Double positron decay features the emission of four 511 keV gamma rays from positron alongside the well-known 'double blob' signature which can be tracked with a TPC. Successfully detecting these gammas creates a unique signature that cannot be replicated by any background radiation. This enables a virtually background-free search if the four gammas are efficiently tagged. In this work, we propose the concept of a liquid Krypton Time Projection Chamber designed to search for double positron decay using this four-gamma tagging concept, and we'll show how already a small version of this prototype could set the world best limit on the search of this decay towards a sensitivity of $10^{29}-10^{30}$ y with a ton scale detector.

Figures

Figures reproduced from arXiv: 2607.28360 by A. Sim\'on Est\'evez, F. Monrabal Capilla, S. Torelli.

Figure 1
Figure 1. Figure 1: Schematic of the second step in the gamma-tagging sequence for an example of event. [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Schematic of the third step in the gamma-tagging sequence for the same event of [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Graphic representation of the 5 signatures used in the analysis. The green stars are [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Spectra of the HE track for the different topological selection and the cut in the region [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Projected sensitivity curves for the 0νβ+β + decay process using a 60 kg natural Kryp￾ton target. Each curve displays the total sensitivity achieved by combining the different signature. The different signature used are reported in the legend, together with the sensitivity projection form [18]. a range of live times t to project the resulting sensitivity as a function of exposure for each configuration. Un… view at source ↗
Figure 6
Figure 6. Figure 6: Projected sensitivity curves for the 2νβ+β + decay process using a 60 kg natural Kryp￾ton target. Each curve displays the cumulative sensitivity achieved by combining successive signature efficiencies. The different signature used are reported in the legend. The two horizon￾tal limits correspond to the current world-best limits established for 106Cd [19] and 78Kr [20]. A larger version of the detector on t… view at source ↗

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

25 extracted references · 6 canonical work pages

  1. [1]

    Final results of gerda on the search for neutrinoless double-beta de- cay,

    M. Agostini et al., “Final results of gerda on the search for neutrinoless double-beta de- cay,”Physical Review Letters, vol. 125, no. 25, Dec. 2020,issn: 1079-7114.doi:10 . 1103 / physrevlett . 125 . 252502[Online]. Available:http : / / dx . doi . org / 10 . 1103 / PhysRevLett.125.252502

    2020

  2. [2]

    First results from LEGEND-200: searching for 0νββdecay in 76Ge,

    G. Saleh, “First results from LEGEND-200: searching for 0νββdecay in 76Ge,”PoS, vol. EPS-HEP2025, p. 159, 2026.doi:10.22323/1.485.0159arXiv:2603.12884 [hep-ex]

    arXiv 2026

  3. [3]

    The search for neutrinoless double beta decay with Cuoricino and Cuore,

    E. Guardincerri, “The search for neutrinoless double beta decay with Cuoricino and Cuore,” J. Phys. Conf. Ser., vol. 335, A. Di Domenico et al., Eds., p. 012 046, 2011.doi:10.1088/ 1742-6596/335/1/012046

    2011

  4. [4]

    The next-100 detector,

    C. e. a. Adams, “The next-100 detector,”The European Physical Journal C, vol. 86, no. 2, Feb. 2026,issn: 1434-6052.doi:10.1140/epjc/s10052-025-14951-y[Online]. Available: http://dx.doi.org/10.1140/epjc/s10052-025-14951-y

    doi:10.1140/epjc/s10052-025-14951-y 2026

  5. [5]

    Search for Double Beta Decays of 134Xe with EXO-200 Phase II,

    S. Al Kharusi et al., “Search for Double Beta Decays of 134Xe with EXO-200 Phase II,” Nov. 2025. arXiv:2511.13990 [nucl-ex]

    arXiv 2025

  6. [6]

    Phase space factors for double-beta decays,

    S. Stoica and M. Mirea, “Phase space factors for double-beta decays,”Frontiers in Physics, vol. Volume 7 - 2019, 2019,issn: 2296-424X.doi:10.3389/fphy.2019.00012[Online]. Available:https : / / www . frontiersin . org / journals / physics / articles / 10 . 3389 / fphy.2019.00012

    arXiv 2019

  7. [7]

    Neutrinoless double-positron decay and positron- emitting electron capture in the interacting boson model,

    J. Barea, J. Kotila, and F. Iachello, “Neutrinoless double-positron decay and positron- emitting electron capture in the interacting boson model,”Physical Review C, vol. 87, no. 5, May 2013,issn: 1089-490X.doi:10.1103/physrevc.87.057301[Online]. Available: http://dx.doi.org/10.1103/PhysRevC.87.057301

    work page doi:10.1103/physrevc.87.057301 2013

  8. [8]

    M. N. et al.,Xraydb: X-ray reference data for python, version 4.5.8, Oct. 2025.doi:10. 5281/zenodo.4118556[Online]. Available:https://github.com/xraypy/XrayDB

    2025

  9. [9]

    W. .-. Chen et al.,Measurement of the transverse diffusion coefficient of charge in liquid xenon, 2011. arXiv:1109.3300 [physics.ins-det]. [Online]. Available:https://arxiv. org/abs/1109.3300

    Pith/arXiv arXiv 2011

  10. [10]

    A high-fidelity electron transport simulation package in the geant4 toolkit for liquid argon, krypton, and xenon detectors,

    L. Cao, Y. Huang, X. Sun, T. Liu, M. Yang, and J. Ye, “A high-fidelity electron transport simulation package in the geant4 toolkit for liquid argon, krypton, and xenon detectors,” Radiation Detection Technology and Methods, May 2026,issn: 2509-9949.doi:10.1007/ s41605 - 026 - 00681 - 6[Online]. Available:https : / / doi . org / 10 . 1007 / s41605 - 026 - 00681-6

    2026

  11. [11]

    GAMPix: a novel fine-grained, low-noise and ultra-low power pixelated charge readout for TPCs,

    T. Shutt et al., “GAMPix: a novel fine-grained, low-noise and ultra-low power pixelated charge readout for TPCs,” Jan. 2024. arXiv:2402.00902 [physics.ins-det]

    Pith/arXiv arXiv 2024

  12. [12]

    Larpix: Demonstration of low-power 3d pixelated charge readout for liquid argon time projection chambers,

    D. Dwyer et al., “Larpix: Demonstration of low-power 3d pixelated charge readout for liquid argon time projection chambers,”Journal of Instrumentation, vol. 13, no. 10, P10007, Oct. 2018.doi:10.1088/1748-0221/13/10/P10007[Online]. Available:https://doi.org/10. 1088/1748-0221/13/10/P10007

    work page doi:10.1088/1748-0221/13/10/p10007 2018

  13. [13]

    Low-energy calibration, reconstruction software and light-collection efficiency parametrization of the next-white detector,

    G. Mart ´ ınez Lema, “Low-energy calibration, reconstruction software and light-collection efficiency parametrization of the next-white detector,” Ph.D. dissertation, 2018

    2018

  14. [14]

    GEANT4: A Simulation toolkit,

    S. Agostinelli et al., “GEANT4: A Simulation toolkit,”Nucl. Instrum. Meth. A, vol. 506, pp. 250–303, 2003.doi:10.1016/S0168-9002(03)01368-8

    doi:10.1016/s0168-9002(03)01368-8 2003

  15. [15]

    A comprehensive review on compton camera image reconstruc- tion: From principles to ai innovations,

    S. M. Kim and J. S. Lee, “A comprehensive review on compton camera image reconstruc- tion: From principles to ai innovations,”Biomedical Engineering Letters, vol. 14, no. 6, pp. 1175–1193, Sep. 2024.doi:10.1007/s13534-024-00418-8 13

    work page doi:10.1007/s13534-024-00418-8 2024

  16. [16]

    Energy resolution of the LZ detector for high-energy electronic recoils,

    G. Pereira, C. Silva, V. N. Solovov, and LZ Collaboration, “Energy resolution of the LZ detector for high-energy electronic recoils,”Journal of Instrumentation, vol. 18, no. 4, p. C04007, Apr. 2023, Art. no. C04007.doi:10.1088/1748-0221/18/04/C04007

    work page doi:10.1088/1748-0221/18/04/c04007 2023

  17. [17]

    Sense and sensitivity of double beta decay experiments,

    J. J. G´ omez-Cadenas et al., “Sense and sensitivity of double beta decay experiments,” Journal of Cosmology and Astroparticle Physics, vol. 2011, no. 06, p. 007, Jun. 2011.doi: 10.1088/1475-7516/2011/06/007arXiv:1010.5112

    Pith/arXiv arXiv 2011

  18. [18]

    Combining hybrid and opaque scintillator techniques in the search for double beta plus decays: A concept study for the nudoubt ++experiment,

    M. B¨ ohles et al., “Combining hybrid and opaque scintillator techniques in the search for double beta plus decays: A concept study for the nudoubt ++experiment,”The European Physical Journal C, vol. 85, no. 2, Jan. 2025,issn: 1434-6052.doi:10.1140/epjc/s10052- 025- 13847- 1[Online]. Available:http://dx.doi.org/10.1140/epjc/s10052- 025- 13847-1

    doi:10.1140/epjc/s10052- 2025

  19. [19]

    New limits on 2β + decay processes in 106cd,

    P. Belli, R. Bernabei, A. Incicchitti, and et al., “New limits on 2β + decay processes in 106cd,”Astroparticle Physics, vol. 10, no. 1, pp. 115–120, 1999.doi:10 . 1016 / s0927 - 6505(98)00034-6

    1999

  20. [20]

    Results of a search for double positron decay and electron-positron con- version of 78kr,

    C. S´ aenz et al., “Results of a search for double positron decay and electron-positron con- version of 78kr,”Nuclear Physics B - Proceedings Supplements, vol. 35, pp. 363–365, 1994, issn: 0920-5632.doi:https : / / doi . org / 10 . 1016 / 0920 - 5632(94 ) 90277 - 1[Online]. Available:https://www.sciencedirect.com/science/article/pii/0920563294902771

    arXiv 1994

  21. [21]

    Half a cen- tury of krypton-85 activity concentration measured in air over central europe: Trends and relevance for dating young groundwater,

    A. Bollh¨ ofer, C. Schlosser, S. Schmid, M. Konrad, R. Purtschert, and R. Krais, “Half a cen- tury of krypton-85 activity concentration measured in air over central europe: Trends and relevance for dating young groundwater,”Journal of Environmental Radioactivity, vol. 205- 206, pp. 7–16, 2019,issn: 0265-931X.doi:https://doi.org/10.1016/j.jenvrad.2019. 04....

    work page doi:10.1016/j.jenvrad.2019 2019

  22. [22]

    Update and improvement of the global krypton-85 emission inventory,

    J. Ahlswede, S. Hebel, J. O. Ross, R. Schoetter, and M. B. Kalinowski, “Update and improvement of the global krypton-85 emission inventory,”Journal of Environmental Ra- dioactivity, vol. 115, pp. 34–42, 2013,issn: 0265-931X.doi:https://doi.org/10.1016/j. jenvrad.2012.07.006[Online]. Available:https://www.sciencedirect.com/science/ article/pii/S0265931X12001816

    doi:10.1016/j 2013

  23. [23]

    Analysis of 85Kr: A comparison at the 10 −14 level using micro-liter samples,

    G.-M. Yang et al., “Analysis of 85Kr: A comparison at the 10 −14 level using micro-liter samples,”Scientific Reports, vol. 3, no. 1, p. 1596, 2013.doi:10.1038/srep01596

    work page doi:10.1038/srep01596 2013

  24. [24]

    Effect of molecular solutes on the electron drift velocity in liquid ar, kr, and xe,

    K. Yoshino, U. Sowada, and W. F. Schmidt, “Effect of molecular solutes on the electron drift velocity in liquid ar, kr, and xe,”Phys. Rev. A, vol. 14, pp. 438–444, 1 Jul. 1976.doi: 10.1103/PhysRevA.14.438[Online]. Available:https://link.aps.org/doi/10.1103/ PhysRevA.14.438

    doi:10.1103/physreva.14.438 1976

  25. [25]

    Radioactivity of 85kr in krypton enriched with a light isotope,

    V. V. Kuz’minov, V. M. Novikov, A. A. Pomanskij, et al., “Radioactivity of 85kr in krypton enriched with a light isotope,”Atomnaya Ehnergiya, vol. 73, no. 6, pp. 499–500, 1992, English translation: Atomic Energy, 73(6), 1010–1011 (1992). 14

    1992