46-FO-2, Soviet nuclear test nº28. Semipalatinsk, 1956

Описание: After the test of the first soviet two-stage thermonuclear (2ST) bomb, the RDS-37 in 1955, great part of the testing program of 1956 went into improving this new technology, with emphasis in developing thermonuclear charges that could fit as warheads for the R-7 missile. Efforts were done to optimize the dimensions and necessary fissile mass of such charges. The primary of this new generation of H-bombs was developed based on the design of the RDS-4.

In August 24, 1956, at the P-5 site of the Semipalatinsk Polygon, was tested a primary unit meant to be used in new designs of 2ST bombs. The device was indeed assembled as a 2ST bomb without the secondary unit. It was placed inside a case surrounded by boxes with different chemical elements inside them (to study the nuclear reactions of the explosion through isotopes production). The test was the nº28 in the official lists, and was referred as the experiment 46-FO-2 (FO is from Физический Опыт, physics studies) (codenamed Joe-23 by the US). The device was lifted and placed 93 meters high in a tower. The explosion yielded 27 kt, around the expected (30 kt). Could be relevant to say that some source refers to it as successful, and other seems to refer to it as unsuccessful (see discussion in link A). Also could be relevant to say that after the test, the same year, four (or five? link A) thermonuclear bombs were tested, some or all of them using this new primary. In at least two of the experiments (test nº30 and nº33), the secondary failed to ignite. The exact same primary unit was tested again the next year at Novaya Zemlya (test nº43).

About the identification (edited): this explosion is the same as the one portrayed in the excerpts in links B and C (see comparison in link D). The identification is not sure, but is the most likely:
Explosion in links B and C are portrayed as a test that match the description given in literature (a a small device encased in a big structure and mounted on a 100 m tall tower (no other tower shot by the USSR were conducted in towers taller than 30 m)).
Except for the joe-1 and 2, no other soviet nuclear test had a yield and altitude of detonation to produce a mushroom cloud with such shape and incandescence duration (consider the videos in B and C, because the footage in this video is clearly slowed). Compare it to 90-120 m tower shots by the US. Also, compare this explosion to    • Soviet nuclear test, RDS-5 near-ground bur...  ,    • Soviet nuclear test. Low altitude airburst...  , and    • Soviet ground nuclear tests  





Ref http://militaryrussia.ru/blog/topic-788.html

Ref (Link A): https://pfc-joker.livejournal.com/66030.ht...

Excerpt came from here:    • USSR 1000 ton of TNT test  

Video showing the preparations of test nº28 (link B):    • Joe 23 nuclear test  

Video with a short later scene of the explosion (link C): https://vkvideo.ru/video-14225254_163087163

Link D, comparison between the explosions: https://postimg.cc/vxh8CcnR

Image of the mushroom cloud: https://sonicbomb.com/g1.php?img=USR/img/j...

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