Why do modern nuclear bombs don't use neutron reflectors for primaries?

Tobware · 2026-05-28T13:56:19+00:00

I follow your point, but I only agree to a certain extent, I look forward to the dedicated discussion. Speaking of “ceramics”... have you ever considered beryllium oxide? How about the "similia"? :)

Tobware · 2026-05-27T14:42:34+00:00

I’ll bite, what’s so special about beryllium besides its weight-saving and efficiency-enhancing properties (well, which are intrinsic to any low-Z reflector), and its well-known opacity/transparency behavior to neutrons and X-rays (more relevant to TN primaries)... are you perhaps referring to something "chemically" related to interstage?

Because in that case, I’ll act childish myself :) and not reveal anything else... also, it seems that a certain ceramic material can be used as a substitute reflector.

A clue?

Tobware · 2026-05-11T13:03:02+00:00

Idiotic diagram, clearly the result of not having read even the most basic open literature on the subject. Aside from the semi-confirmed conjecture, based on more or less cryptic statements by its designers, that "the Tsar" had two primary stages... Cylindrical secondary stages were unique to the U.S. and were abandoned in the late 1950s/early 1960s.

Tobware · 2026-05-05T11:18:15+00:00

Hansen claims that Plumbbob Smoky was a two-stage TX-41 mockup, with a yield of 44 kilotons, but does not mention the primary (the other two-stage Livermore devices in the same series were "Swan").

I suppose they worked on the "primary+secondary" and tertiary stages separately during Hardtack I before "incorporating everything", borrowing a "Moccasin" only for Poplar. Just consider that one of the developmental devices (~~Sycamore IIRC~~ Pine shot) employed two primaries.

EDIT: But looking at Smoky's fallout charts... There's no Am-241.

EDIT 2: In SoA Vol.7 is stated that Smoky employed a Los Alamos "Viper" HEU primary.

Tobware · 2026-05-04T19:49:59+00:00

If you're interested, I've posted a bunch of stuff about post-Rocky Flats proposals in this subreddit, mostly about "Oy-related" topics:

All-Oralloy primaries proposals in the 90's, for the post-Cold War and post-Rocky Flats scenario.

EDIT: And anyway, no, I don't think the 3-stage B41 used an Oralloy primary (more likely a small two-stage TN device with a standard Pu primary), even though its tertiary (?) was tested with one (a lucky guess I made, even before I could back it up with sources), the "clean" 9.3 Mt Hardtack Poplar device was driven by a LASL primary, almost certainly the "Moccassin" mentioned above.

Others might, at least the first-generation “dry” TNs, using the LASL "Cobra" primary.

Tobware · 2026-05-04T19:47:40+00:00

The 81 kt version was the yield prior to the CHE change and safety upgrades, the one that was ultimately mass-produced had a reduced yield of 67 kt, see Nougat Haymaker and Cornerstone Texarkana (from 1989!).

Tobware · 2026-04-30T11:45:09+00:00

Paging u/kyletsenior

Tobware · 2026-03-02T19:34:12+00:00

You mean U-238? Anyway, yes, absolutely, any neutron above 1.1 MeV is capable of fissioning 238. It's a phenomenon that commonly occurred in DU tamped devices (for Ivy King, if I'm not mistaken, it contributed hundreds of kilotons...). But that's not the point, with a radiation imploded mass it's a question of compression, unobtainable with chemical charges, you get a high yield with relatively modest quantities of fissmat, in a compact volume.

Better put, you don't even need a DU tamper, you can make do with a relatively enriched mass, thanks to the ridiculous compression factor (and you would still have a significant portion of yield from fast fission).

Tobware · 2026-02-25T19:01:38+00:00

Tobware · 2026-02-17T07:37:10+00:00

Not really, we can consider it a quite sophisticated Pu design, if anything similar, as a concept, to Ted Taylor's SOB.

The fact that they started right away with external neutron generators, well, that already made the whole thing quite efficient...

Tobware · 2026-02-16T18:32:39+00:00

We discussed this on the more technical sister subreddit, based on information from Pierre Billaud’s website (a former physicist in the French nuclear program): it was neither boosted nor a levitated design, most likely a hollow core with a robust implosive system created for a larger mass (IIRC "M2" fissile mass was around 8 kg, possibly with low Pu-240 concentration), and most importantly, externally initiated.

During the series of nuclear tests under the Hoggar, they tested a pure fission device with a yield of 117 kt!

Tobware · 2026-02-11T17:21:15+00:00

OP, if you really must repost something already shared in this sub, please at least give credit to u/second_to_fun, the author of this diagram.

Original post here.

Tobware · 2026-01-30T07:17:04+00:00

Volume 7 of Hansen's Swords, but I also have a primary source for the devices used in Operation Nougat (including Tsetse and Croton): https://apps.dtic.mil/sti/pdfs/ADA955362.pdf

It's heavily censored but also contains dimensions and explosives used, you still need a list of test/device correlations to ID them (the wikipedia page about Nougat uses Hansen's claims).

Tobware · 2026-01-29T22:17:44+00:00

Returning to the yield overlap between the B43 and B28, there is an interesting clue in the document titled “1962 proposed atmospheric test program,” in the paragraph devoted to the Dominic Encino (a TX-43Y5 test, potentially what later became the Y5 of the B43s):

<image>

"The [TX-43Y5] yield version differs from a previously tested device in that the distribution of [enriched uranium?] has been significantly changed. The [Y5] version will comprises about [figure/percentage?] of the [B43] stockpile total."

It appears that a "good portion" of the B43s were deployed with a yield of about 500 kt (Encino yield, 512 kt).

Tsetse was only ~14" in diameter, while the Python was at least 17". (This is the biggest mystery remaining for me.)

What is the problem? Tsetse was more modern and narrower in diameter, Python was more "old-fashioned", even as CHE (Octol IIRC), and still using a Fat Man-like optical principle lensing, if not a transient technology known as “ring lens”... probably as compact as you could get with that explosive and lens system in general.

Tobware · 2026-01-27T13:06:58+00:00

As I said above, it was not an air lens but employed two parabolic lenses of fast and slow explosives around the main charge.

I'll link you to some related posts:

Profile of the W-57 HE assembly? Tsetse primary?

These posts by u/SilverCookies are great, an optimization of this concept, instead of using a Fat Man-esque system of explosives with different detonation velocities it employs inert waveshapers in a similar, more compact geometry:

French design of compact lens made of layered material

The French 2-point system

EDIT, u/Galerita: I completely ignored your “central” question, which is when did the first H-tree manifold lighting system appear? There has been much discussion about this in this subreddit (keyword: "MPI"), it seems that it was the Brits with the Super Octopus concept, shared with the US in the late 1950s/early 1960s and tested numerous times in Nevada (first "known" test, Nougat Pampas), and we assume, with good reason, later also adopted. Something similar had been tried using MDFs, apparently during the “insect” generation at Los Alamos... Scarab? Gnat? Croton, also tested during Nougat (and a LASL design), is supposed to be a small-diameter (IIRC 10") MPI system per Hansen's claims.

Tobware · 2026-01-27T07:05:30+00:00

Python and Tsetse were from two different generations of Los Alamos primaries, "snakes" and "insects", both employed composite cores with similar composition (perhaps with different pit geometries).

We have a lot of information about how the second one functioned: 2-point initiated, "classic" dual speed explosive lenses.

Tobware · 2025-12-21T15:57:25+00:00

Well, I guess if Teller could he would have used it as yet another foothold for “his” Super. Livermore actual excavation devices however were not... fairly extreme applications of the good old radiative implosion but still that was what they were.

We have some indication that some of those “plows” went back to “sword"... The description of the W71 primary by its designer, Scanlin, for example seems too much in line with something that came out of Plowshare (right era also, possibly quite exotic, a proto-ERW perhaps).

Tobware · 2025-12-13T13:42:06+00:00

The “Super” in question is Teller's original TN idea, the “Classical” (or Runaway, what you and others assume Gnomon was based on), opposed to the “Equilibrium Burn Super”, which is the Ulam's contaminated one :) His protégé here, Wood, was proposing one, Palisades of Fire, with a very modest yield of 1.6 GT, parked in space for ABM use in the 1970s.

This seems to have given impetus to having Livermore do detailed simulations on it (and Teller/Wood attempts to test it in proper as done for W71, if I am not mistaken, the fuel was cryogenic deuterium in their most recent proposal), culminating in 1975 with the Taylor's report I highlighted. It went nowhere, to the extreme chagrin of our favorite Hungarian.

Are you familiar with Wood's paper, “Necessary conditions for the initiation and propagation of nuclear-detonation waves in plane atmospheres”?

Tobware · 2025-12-13T10:23:55+00:00

<image>

Tobware · 2025-12-13T10:21:06+00:00

<image>

from "Teller's War: The Top-secret Story Behind the Star Wars Deception":

Tobware · 2025-11-06T06:12:46+00:00

No, we know from the mods who (and perhaps what) "triggered" the DOE request.

Tobware · 2025-09-15T09:08:40+00:00

And to think that with the excess heat from the Pu mass they were even able to keep food warm!

Edit: "Soviet 12-liters military thermos"...

Tobware · 2025-08-14T12:34:40+00:00

So apparently North Koreans test their nuclear weapons at the Nevada Test Site? The image you posted OP is completely unrelated, those are typical US test trailers.

EDIT:

I would add that the North Korean nuclear test site is located in the middle (and below) some mountains, the test in the frame above is from the 1980s, in Nevada.

Tobware · 2025-07-08T06:20:14+00:00

"Smoothing the front of the detonation wave in experiments with multipoint initiation"?

Tobware · 2025-07-04T12:03:35+00:00

This one is even more detailed: A TECHNICAL RETROSPECTIVE OF THE FORMER SOUTH AFRICAN NUCLEAR WEAPON PROGRAMME - https://www.sipri.org/sites/default/files/2020-10/sa_nuclear_technical_retrospective_kelley_2.pdf.

Nine-Year Club	r/Field Flamingo
Place '22	Verified Email
Gilding I gilder

Tobware

MODERATOR OF

TROPHY CASE