Pith. sign in

REVIEW 3 major objections 6 minor 35 references

Electron-impact ionization of Si IV-VIII relevant for inertial confinement fusion

T0 review · 3 major / 6 minor · reviewed 2026-08-11 · deepseek-v4-flash

Pith's one-line read This paper derives electron-impact ionization rates for Si5+–Si7+ by fitting a four-parameter formula to three collision theories and to measurements, then shows that the best theory depends on the electron temperature.

desk verdict Useful, incremental atomic data paper with clean analytic fits but an extrapolated high-temperature tail that needs benchmarking. read the letter →

arxiv 2412.05317 v1 pith:SK3FK4NF submitted 2024-12-02 physics.atom-ph physics.plasm-ph

classification physics.atom-phphysics.plasm-ph PACS 34.80.Kw
keywords electron-impactionizationsiliconionsratecoefficientsinertialconfinementfusionCoulomb-Born-ExchangeBinary-Encounter-DipoleDistorted-Wavesemi-empiricalcross-sectionfit
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper aims to give plasma modelers practical, accurate electron-impact ionization rate coefficients for the silicon charge states Si5+, Si6+, and Si7+, which matter in inertial-confinement-fusion capsules. It computes cross sections with three standard approximations—Coulomb-Born-Exchange, Binary-Encounter-Dipole, and Distorted-Wave—fits each to a four-parameter semi-empirical formula, and integrates the fits analytically over a Maxwellian electron distribution. Comparing those rates with measured cross sections, the authors find that agreement improves as the ion charge increases and that the best approximation shifts with temperature: Coulomb-Born-Exchange near the threshold, Distorted-Wave in the mid range, and Binary-Encounter-Dipole at the highest energies. If correct, the fitted parameters provide fast-to-evaluate rates across $10^{5}$–$10^{8}$ K for collisional-radiative modeling of hot plasmas.

What carries the argument

The load-bearing object is the semi-empirical cross-section formula $$\$\sigma$(E)=\frac{A\ln(E/E_i)}{E/E_i}\sum_{p=0}^{N}\frac{B_p}{(E/E_i)^p}, \quad B_0=1,$$ which vanishes at the ionization threshold and falls logarithmically at high energy. Its four parameters are fixed by fits to measured or calculated cross sections. Because every term can be written as $\ln(t/b)/(t/b)^p$, the Maxwellian average is performed analytically, giving the rate coefficient as a finite sum of generalized integro-exponential functions $E_p^1(b)$ with $b=E_i/(k_BT_e)$; the recurrence relation for these functions makes evaluation fast and stable. Configuration interaction, included through the atomic-structure code's super-configurations, modifies the low-energy cross section noticeably for Si$^{3+}$ and barely for the higher charges.

What would settle it

Measure the single-ionization cross section of Si$^{5+}$, Si$^{6+}$, or Si$^{7+}$ at several incident-electron energies above 5 keV—where no measurement currently anchors the fit—and compare with Eq. (2) evaluated using the tabulated parameters; a deviation larger than the experimental uncertainty would falsify the high-temperature rates in Figs. 9–11, since the Maxwellian average at $10^8$ K is dominated by electrons in that unmeasured range.

Watch

Extended reading notes

Core claim

The authors' central claim is that, for the silicon ions Si5+, Si6+, and Si7+, the reliability of electron-impact ionization rates computed by any of the three methods—Coulomb-Born-Exchange, Binary-Encounter-Dipole, and Distorted-Wave—increases with ion charge, and that the best method for a given calculation depends on the electron temperature. Near the ionization threshold Coulomb-Born-Exchange is closest to experiment; at the highest energies Binary-Encounter-Dipole has the best high-energy slope; and Distorted-Wave is the best compromise in between. Because the Maxwellian rate coefficient integrates over all incident energies, the recommended method shifts with temperature. The paper supports the claim by fitting measured and calculated cross sections for each ion to the four-parameter form, evaluating the rate coefficient analytically, and comparing the resulting rates with measured ones; it also reports that fitting the cross section before averaging reproduces measurements better than fitting the rate directly.

Load-bearing premise

The high-temperature rates rest on the unverified assumption that the four-parameter formula, calibrated on measured cross sections only up to roughly 1500 eV, keeps describing the ionization cross section correctly at the much higher electron energies that dominate a $10^8$ K electron distribution.

Editorial extensions

If this is right

  • Rate coefficients for Si5+, Si6+, and Si7+ can be evaluated at any temperature between 10^5 and 10^8 K directly from the tabulated parameters, making the results drop-in inputs for collisional-radiative models of inertial-confinement-fusion plasmas.
  • The paper's temperature rule gives a concrete selection prescription: for Si5+ and Si6+, Coulomb-Born-Exchange below about 3×10^6 K, Distorted-Wave up to about 20 million kelvin, and Binary-Encounter-Dipole above; for Si7+, Distorted-Wave at low and very high temperatures and Coulomb-Born-Exchange between roughly 2 and 7 million kelvin.
  • Configuration interaction matters mainly at low energy and for the lowest charge state studied, so the simpler calculations are adequate for the higher ions.
  • Fitting the cross section before Maxwellian averaging reproduces the measured rates better than fitting the rate directly with Chebyshev polynomials, indicating that the choice of fitting target affects accuracy.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The tabulated rates at the hottest temperatures are extrapolations: the Maxwellian average at 10^8 K is dominated by electron energies far above the measured range used to set the parameters, so a direct numerical integration of an un-fitted high-energy cross-section calculation would bound the extrapolation error.
  • The temperature ranking of the three methods is a ranking against current measurements; if experimental uncertainties shrink, the crossover temperatures could move even if the ordering holds.
  • A composite rate that switches from Coulomb-Born-Exchange at low temperature to Distorted-Wave in the middle and Binary-Encounter-Dipole at the top would likely track experiment better than any single method, but the paper does not propose such a hybrid.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

3 major / 6 minor

Summary. The paper presents Flexible Atomic Code (FAC) calculations of electron-impact single-ionization cross sections for Si3+ through Si7+ using the Coulomb-Born-Exchange (CB), Binary-Encounter-Dipole (BED), and Distorted-Wave (DW) methods. The cross sections are compared with crossed-beam measurements and with other calculations, and are represented by the four-parameter semi-empirical formula of Eq. (2). Integrating Eq. (2) over a Maxwellian distribution leads to the analytic rate-coefficient expression Eq. (5) in terms of generalized integro-exponential functions. Rate coefficients for Si5+, Si6+, and Si7+ are presented up to 10^8 K and compared with the Chebyshev/Clenshaw fit of Zeijlmans van Emmichoven et al. The authors conclude that agreement with experiment improves with ion charge and that the preferred method depends on the temperature range, with application to inertial-confinement fusion modeling.

Significance. If the rates are accurate, Eq. (5) together with Tables 3-6 provides a computationally cheap and analytic source of ionization rate coefficients for the silicon charge states most relevant to ICF modeling, which is of genuine practical value. The analytic integration leading to Eq. (5) is correct and is a clear strength; the parameter tables are complete and enable immediate use. The paper also usefully clarifies the implementation of the Clenshaw algorithm for the ZvE rate formula. However, the validation of the high-temperature part of the rates is currently indirect and needs strengthening before the central ICF-related claim can be accepted.

major comments (3)
  1. [Sec. 3.2, Figs. 10-11] The curves labeled 'Our exp. fit' are obtained by fitting Eq. (2) to the same Thompson et al. and Zeijlmans van Emmichoven et al. measurements that were used to construct the ZvE rate fit; the comparison is therefore between two fitting formulas for the same data set and does not validate either against independent data. This circularity weakens the statement in Sec. 4 that 'our results show a better agreement with experiment than ZvE ones'.
  2. [Sec. 3.2, Eq. (4), Tables 3-6, Figs. 9-11] The rate coefficients at 10^8 K are dominated by electron energies far above the fitted cross-section range. At 10^8 K, kBT is approximately 8.6 keV, while the measured and fitted cross sections cover at most roughly 100 to 1500 eV. The functional form of Eq. (2) determines the high-energy tail through A ln(E/Ei)/(E/Ei), but A is constrained by near-threshold and peak data only. The paper provides no test against high-energy experimental data or an independent asymptotic high-energy theory, so the high-temperature portion of Figs. 9-11 is an unvalidated extrapolation. Because the abstract and conclusion claim reliability up to 10^8 K for ICF applications, this is a load-bearing gap.
  3. [Sec. 2, Figs. 1-8] The manuscript does not state whether indirect ionization channels (inner-shell excitation followed by autoionization) are included in the FAC cross sections. The text discusses indirect processes in earlier work and cites Ref. [20], but the present FAC calculations appear to be direct-ionization-only; if so, comparisons with the measured total cross sections of Crandall et al. and Thompson et al. are not complete, and the conclusion about increasing reliability with ion charge rests on an unstated assumption. Please clarify and, if indirect contributions are omitted, quantify their expected importance for each ion.
minor comments (6)
  1. [Sec. 4] The conclusion says the paper treats 'Si3+ to Si10+', but the calculations and rate fits cover Si3+ to Si7+ only; please correct the ion range.
  2. [Sec. 3.2] 'Zeijlamns van Emmichoven' appears to be a typo for 'Zeijlmans van Emmichoven'.
  3. [Table 1] For Si+ and Si2+, the FAC ionization potentials differ from NIST by factors of up to about 90 for Si+, which is far outside the stated accuracy of FAC for these ions; a sentence explaining this limitation would be useful since the table is presented without comment.
  4. [Figs. 5-8] In the version provided, the axis labels appear garbled (e.g., '/s32/s33/s34'); please ensure the figure files render correctly.
  5. [Figs. 9-11] The label 'Our exp. fit' is potentially confusing because the curve is not an experimental measurement but a fit to measured cross sections; consider renaming it, for example to 'fit to measured cross sections'.
  6. [Sec. 3.3] The claim that the ZvE coefficients reproduce rates to within 1 percent is quoted but not verified; a brief check or statement of provenance would be useful.

Circularity Check

1 steps flagged · score 4.0 of 10

Central theory rates are independent, but the 'Our exp. fit' benchmark is a fit to the same measurements as the ZvE comparison, making the claimed 'better agreement' a fit-vs-fit statement rather than a prediction test.

  1. fitted input called prediction [Section 3.3, after Eq. (9) and in reference to Figs. 10-11]
    "In practice, we fit the cross section, and then integrate it over the Maxwellian distribution, which introduces the dependence with respect of the temperature. In the ZvE approach, the fitting procedure is applied directly to the rate. As a consequence, our results show a better agreement with the experiment than ZvE ones."

    The 'Our exp. fit' curves in Figs. 10-11 are obtained by fitting Eq. (2) to the measured cross sections of Zeijlmans van Emmichoven et al. (and Thompson et al. for Si5+) and then integrating over the Maxwellian distribution. The ZvE 'exp. fit' is a Chebyshev fit to rate coefficients derived from those same measured cross sections. Both curves are therefore parameterizations of the same experimental dataset. The statement that the paper's results 'show a better agreement with the experiment' is a comparison of two fitting functions applied to identical data, not an independent test: the agreement of 'Our exp. fit' with the experiment is forced by construction because the parameters were chosen to reproduce those data.

full rationale

The main physical content of the paper—the BED/CB/DW cross sections computed with the Flexible Atomic Code and the resulting rate coefficients—is independent of the experimental silicon data. Those theory curves are genuinely compared to measured cross sections, and the conclusion that theory improves with increasing ion charge rests on that comparison. The semi-empirical formula Eq. (2) is openly a fitting ansatz from the authors' prior work (Ref. [17]) and is re-fit to silicon data in Tables 3-6; using a previously published fitting form is not circular. The one partially circular element is the comparison of 'Our exp. fit' with ZvE's experimental fit: both are derived from the same Thompson/ZvE measurements, so the paper's claim of 'better agreement with the experiment' is a fit-vs-fit statement, not a prediction test. The extension to 10^8 K relies on the assumed extrapolation of Eq. (2) beyond the measured energy range; this is a validation/correctness risk rather than a circularity, since the high-temperature tail is not identical to the fitted low-energy data by construction. Overall, the central theory calculation retains independent content, but the experimental-fit benchmark used for comparison is partly self-referential.

Assumptions & free parameters 4 free parameters · 4 assumptions · 0 invented entities

The central claim rests on four fitted parameters per ion/method, on the validity of FAC's implementations, and on the assumed functional form of the cross section. No new physical entities are introduced.

free parameters (4)
  • A (prefactor in Eq. 2) = per ion and fit: e.g., Si5+ experiment A=9.709e-18 cm^2; values in Tables 3-6
    Scale factor fitted to measured or calculated cross sections; central to the cross-section magnitude.
  • B1 = e.g., Si5+ experiment B1=-0.414451; Tables 3-6
    Shape coefficient fitted to the energy dependence of the cross section.
  • B2 = e.g., Si5+ experiment B2=-0.003916; Tables 3-6
    Second shape coefficient in the polynomial expansion.
  • B3 = e.g., Si5+ experiment B3=-0.000030; Tables 3-6
    Third shape coefficient; B0 is fixed to 1 so the cross section vanishes at threshold.
assumptions (4)
  • domain assumption The cross sections computed by the Flexible Atomic Code (FAC) with CB, BED, and DW methods are correct for Si3+-Si7+.
    All computed cross sections come from FAC (Refs [10,11]); no independent verification of the numerical results is provided.
  • ad hoc to paper The semi-empirical formula sigma(E)=A ln(E/Ei)/(E/Ei) * sum Bp/(E/Ei)^p (Eq. 2) can represent the true cross section over the whole energy range.
    The form is taken from the authors' prior paper [17]; its suitability for silicon ions is not derived or tested against high-energy data.
  • domain assumption Free electrons follow a Maxwell-Boltzmann distribution.
    Used in Eq. (4) to convert cross sections to rate coefficients; appropriate for the stated plasma conditions, but not justified quantitatively.
  • standard math The generalized integro-exponential function recurrence (Eq. 7) is correctly applied.
    Analytic evaluation of the rate integral relies on this recurrence; standard but not machine-checked here.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Electron-impact ionization of Si IV-VIII relevant for inertial confinement fusion." pith.science (2026). https://pith.science/paper/SK3FK4NF

@misc{pith2026241205317,
  author       = {Pith},
  title        = {Pith review of: Electron-impact ionization of Si IV-VIII relevant for inertial confinement fusion},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/SK3FK4NF}},
  note         = {Machine review of arXiv:2412.05317}
}
abstract

In this work, we investigate the ionization of silicon by electron impacts in hot plasmas. Our calculations of the cross sections and rates rely on the Coulomb-Born-Exchange, Binary-Encounter-Dipole and Distorted-Wave methods implemented in the Flexible Atomic Code (FAC), and are compared with measurements and other theoretical values. We use a semi-empirical formula for the cross section, which involves a small set of adjustable parameters. Configuration interaction is taken into account and is shown to affect the cross section at low energy, in particular for Si$^{3+}$. The rate coefficient is then expressed in terms of these parameters and is represented in a large temperature interval, up to 10$^8$ K. As expected, the agreement with measurements improves for increasing ion charges, confirming the applicability of our approach to hot plasma studies such as inertial-confinement fusion, and its reliability.

Figures

Figures reproduced from arXiv: 2412.05317 by the authors.

Figure 1
Figure 1. Si3+ cross sections comparisons. Our results (using the FAC code): BED, CB, DW. Experiment of Crandall et al. [6], with the shaded area representing the experimental uncertainty. Calculations of Badnell et al. [7]: CCC (convergent close-coupling), TD (hybrid time-dependent). In the DW method, the ionization radial integrals are calculated by summing up partial-wave con￾tributions. This is a time consuming process be… view at source ↗
Figure 2
Figure 2. Si3+ cross section comparisons. Our results with limited CI (using the FAC code): BED, CB, DW. Experiment of Crandall et al. [6], with the shaded area representing the experimental uncertainty. Calculations of Badnell et al. [7]: CCC (convergent close-coupling), TD (hybrid time-dependent). (1)2 (2)8 (3)1 →  (1)2 (2)8 (1)2 (2)7 (3)1 12 10 8 6 4 2 0 Cross section (10-18 cm 2 ) 200 400 600 800 1000 1200 1400 1600 Inci… view at source ↗
Figure 3
Figure 3. Si3+ cross section comparisons. Our results with extended CI (using the FAC code): BED, CB, DW. Experiment of Crandall et al. [6], with the shaded area representing the experimental uncertainty. Calculations of Badnell et al. [7]: CCC (convergent close-coupling), TD (hybrid time-dependent). 4 [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figures from the paper (8 more)
Figure 4
Figure 4. Figure 4: Si3+ cross section comparisons. Zoom in [PITH_FULL_IMAGE:figures/full_fig_p005_4.png]
Figure 5
Figure 5. Figure 5: Si4+ cross section comparisons. Our results with extended CI (using the FAC code): BED, CB, DW. Experimental data are from Thompson et al. [25]. The shaded area represents the experimental uncertainty. As in the previous case, for Si5+ ions experimental data are from T…
Figure 6
Figure 6. Figure 6: Si5+ cross section comparisons. Our results with limited CI (using the FAC code): BED, CB, DW. Experimental data are from Thompson et al. [25]. The shaded area represents the experimental uncertainty . !" #!$ #!" "!$ "!" %&'(()(*+,-'.)/#"0#1 +2 [PITH_FULL_IMAGE:figure…
Figure 7
Figure 7. Figure 7: Si6+ cross section comparisons. Our results with limited CI (using the FAC code): BED, CB, DW. Experimental data are from Zeijlmans van Emmichoven et al. [18]. The shaded area represents the experimental uncertainty . 7 [PITH_FULL_IMAGE:figures/full_fig_p007_7.png]
Figure 8
Figure 8. Figure 8: Si7+ cross section comparisons. Our results with limited CI (using the FAC code): BED, CB, DW. Experimental data are from Zeijlmans van Emmichoven et al. [18]. The shaded area represents the experimental uncertainty . the lower bounds of the error bars very closely. Up…
Figure 9
Figure 9. Figure 9: Rate coefficient of Si5+ as a function of the temperature. The solid lines represent our fits of the experiment (Our exp. fit) and of the BED, CB and DW calculations . 3.5 x10-9 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Rate coefficient (cm 3 s -1 ) 1.0 x10 0.2 0.4 0.6 0.8 8 Tempera…
Figure 10
Figure 10. Figure 10: Rate coefficient of Si6+ as a function of the temperature. The solid lines represent our fits of the experiment (Our exp. fit) and of the BED, CB and DW calculations. The dashed line represents the fit of the experiments made by Zeijlmans van Emmichoven et al. (ZvE ex…
Figure 11
Figure 11. Figure 11: Rate coefficient of Si7+ as a function of the temperature. The solid lines represent our fits of the experiment (Our exp. fit) and of the BED, CB and DW calculations. The dashed line represents the fit of the experiments made by Zeijlmans van Emmichoven et al. (ZvE ex…

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

35 extracted references · 34 canonical work pages

  1. [20]

    Moores D L, Golden L B and Sampson D H 1980 J. Phys. B 13, 385

  2. [1]

    125 , Oxford University Press, Oxford

    Atzeni S and Meyer-ter-Vehn J 2004 The physics of inertial fusion: Beam plasma interaction, hy - drodynamics, hot dense matter , 1st ed., International Series of Monographs on Physics, Vol. 125 , Oxford University Press, Oxford

  3. [2]

    (The Indirect Drive ICF Collaboration) 2024 Phys

    Abu-Shawareb H et al. (The Indirect Drive ICF Collaboration) 2024 Phys. Rev. Lett. 132, 065102

  4. [3]

    Plasmas 21, 056315

    Goncharov V N, Sangster T C, Betti R, Boehly T R, Bonino M J, Collin s T J B, Craxton R S, Delettrez J A, Edgell D H, Epstein R, Follett R K, Forrest C J, Froula D H, Glebov V Yu, Harding D R, Henchen R J, Hu S X, Igumenshchev I V, Janezic R, Kelly J H, Kess ler T J, Kosc T Z, Loucks S J, Marozas J A, Marshall F J, Maximov A V, McCrory R L, McKenty P W, M...

  5. [4]

    Ralchenko Yu 2016 Modern methods in collisional-radiative modeling of plasm as, Springer

  6. [5]

    Dolder K 1994 Adv. At. Mol. Opt. Phys. 32, 69

  7. [6]

    Crandall D H, Phaneuf R A, Falk R A, Beli´ c D S and Dunn G H 1982 Phys. Rev. A 25, 143

  8. [7]

    Badnell N R, Pindzola M S, Bray I and Griffin D C 1998 J. Phys. B: At. Mol. Opt. Phys. 31, 911

Show all 35 references
  1. [8]

    Jonauskas V 2020 A & A 642, A185

  2. [9]

    Data and Nucl

    Jonauskas V 2020 At. Data and Nucl. Data Tables 135-136, 101363

  3. [10]

    Gu M F 2008 Can. J. Phys. 86 675

  4. [11]

    Flexible Atomic Code: A software package for the calculation of v arious atomic processes, GitHub, F AC-1.1.4 release, https://github.com/flexible-atomic-code/fac 14

  5. [12]

    Zhang H L and Sampson D H 1990 Phys. Rev. A 42, 5378

  6. [13]

    Fontes C, Sampson D H and Zhang H L 1993 Phys. Rev. A 48, 1975

  7. [14]

    Takagishi K, Ohkura M and Nakazaki S 1995 Comput. Phys. Commun. 85, 293

  8. [15]

    Vriens L 1966 Phys. Rev. 141, 88

  9. [16]

    Kim Y-K and Rudd M E 1994 Phys. Rev. A 50 3954

  10. [17]

    Benredjem D and Pain J-C 2024 J. Phys. B: At. Mol. Opt. Phys. 57, 115001

  11. [18]

    Zeijlmans van Emmichoven P A, Bannister M E, Gregory D C, Haven er C C, Phaneuf R A, Bell E W, Guo X Q and Thompson J S 1993 Phys. Rev. A 47, 2888

  12. [19]

    N IST Atomic Spectra Database (version 5.11), [Online]

    Kramida A, Ralchenko Yu, Reader J and NIST ASD Team (2023). N IST Atomic Spectra Database (version 5.11), [Online]. Available: https://physics.nist.gov/asd [Fri Jun 07 2024]. National Institute of Standards and Technology, Gaithersburg, MD

  13. [21]

    Younger S M 1980 Phys. Rev. A 22, 111

  14. [22]

    Golden L B and Sampson D H 1977 J. Phys. B: At. Mol. Opt. Phys. 10, 2229

  15. [23]

    Golden L B and Sampson D H 1980 J. Phys. B: At. Mol. Opt. Phys. 13, 2645

  16. [24]

    Peart B, Thomason J W G and Dolder K 1991 J. Phys. B: At. Mol. Opt. Phys. 24, 4453

  17. [25]

    Thompson J S and Gregory D C 1994 Phys. Rev. A 50, 1377

  18. [26]

    Lotz W 1968 J. Opt. Soc. Am. 58 236

  19. [27]

    Younger S M 1982 Phys. Rev. A 26 3177

  20. [28]

    Bernshtam V A, Ralchenko Y V and Maron Y 2000 J. Phys. B: At. Mol. Opt. Phys. 33 5025

  21. [29]

    of Comput

    Milgram M S 1985 Math. of Comput. 44 443

  22. [30]

    MacLeod A J 2002 J. Comput. Appl. Math. 148 363

  23. [31]

    Luke Y L 1969 The special functions and their approximations , Academic Press, New York

  24. [32]

    3: More special functions

    Prudnikov A P, Marichev O I and Brychkov Yu A The Meijer G-function Gmn pq (z|(ap); (bp)), section 8.2 in Integrals and series, Vol. 3: More special functions. Newark, NJ: Gordon and Breach, pp. 617-626, 1990

  25. [33]

    Rivlin T J 1974 The Chebyshev polynomials , Pure and Applied Mathematics, 1st ed., New York- London-Sydney: Wiley-Interscience, John Wiley & Sons, pp. 56–12 3

  26. [34]

    Clenshaw C W 1955 Math. Comp. 9, 118

  27. [35]

    Clenshaw C W 1957 Proc. Camb. Phil. Soc. 53, 134 15

Pith tools

Reviewed August 11, 2026 · model on record in the stance chip above.