mersenneforum.org  

Go Back   mersenneforum.org > Fun Stuff > Lounge

Reply
 
Thread Tools
Old 2020-08-10, 03:02   #221
Dr Sardonicus
 
Dr Sardonicus's Avatar
 
Feb 2017
Nowhere

23×181 Posts
Default

Quote:
Originally Posted by ewmayer View Post
I hate such later hagiography where the role of the actual other 'lesser' scientists who made the discoveries get written out in favor of the Big Names. In this case, Joliot-Curie, Enrico Fermi and Leo Szilard, who approached the by-then-elder-statesman Einstein because they figured someone of his stature would be more likely to catch the president's ear.
Yes, this is the story I learned. WRT discovering the potential of uranium, the name Lise Meitner also comes to mind.

You might be amused at a misdiagnosis by Dr. Einstein in this regard, mentioned, e.g. here:
Quote:
In 1932, the great physicist claimed that "there is not the slightest indication that nuclear energy will ever be obtainable. That would mean that the atom would have to be shattered at will."
Dr Sardonicus is offline   Reply With Quote
Old 2020-08-13, 23:35   #222
ewmayer
2ω=0
 
ewmayer's Avatar
 
Sep 2002
República de California

101101001111002 Posts
Default

Re. the Shinkolobwe mine, my memory got mixed up re. the natural fission reactor - it's actually at Oklo, Gabon, a couple W African statelets NW of the Shinkolobwe mine:
Quote:
The natural nuclear reactor formed when a uranium-rich mineral deposit became inundated with groundwater that acted as a neutron moderator, and a nuclear chain reaction took place. The heat generated from the nuclear fission caused the groundwater to boil away, which slowed or stopped the reaction. After cooling of the mineral deposit, the water returned, and the reaction restarted, completing a full cycle every 3 hours. The fission reaction cycles continued for hundreds of thousands of years and ended when the ever-decreasing fissile materials no longer could sustain a chain reaction.
...
A key factor that made the reaction possible was that, at the time the reactor went critical 1.7 billion years ago, the fissile isotope U235 made up about 3.1% of the natural uranium, which is comparable to the amount used in some of today's reactors. (The remaining 96.9% was non-fissile U238.) Because U235 has a shorter half-life than U238, and thus decays more rapidly, the current abundance of U235 in natural uranium is about 0.70–0.72%. A natural nuclear reactor is therefore no longer possible on Earth without heavy water or graphite.

The Oklo uranium ore deposits are the only known sites in which natural nuclear reactors existed. Other rich uranium ore bodies would also have had sufficient uranium to support nuclear reactions at that time, but the combination of uranium, water and physical conditions needed to support the chain reaction was unique, as far as is currently known, to the Oklo ore bodies.
Note that the U235/U238 isotopic ratio at the time of Earth's formation was a global constant, due to whatever primordial supernova(e) which created the heavy elements incorporated into the Earth having mixed said elements more or less uniformly throughout the presolar nebula.

Getting back to the question of the % of U and Pu atoms which fissioned in the Hiroshima and Nagasaki A-bombs - this would fit better in the Science subforum, but by way of continuity:

Hiroshima: Wikipedia says: "[Little Boy] contained 64 kg (141 lb) of enriched uranium, although less than a kilogram underwent nuclear fission."

For the Nagasaki A-bomb, Wikipedia says "6.2 kg of Plutonium-239, [of which]about 1 kg fissioned", thus more than 10x more efficient than Little Boy.

Modern fission weapons (most often used as the initial small 'trigger' stage of a fusion bomb) achieve significantly higher efficiencies even than Little Boy via use of fusion boosting, so we could conceivably be talking of on the order of half the atoms of fission core undergoing fission.

Last fiddled with by ewmayer on 2020-08-13 at 23:36
ewmayer is offline   Reply With Quote
Old 2020-11-23, 08:47   #223
Nick
 
Nick's Avatar
 
Dec 2012
The Netherlands

158210 Posts
Default

Today (23 November 2020), the Dutch city of Haarlem is 775 years old!
(The district of Harlem in New York City was named for our Haarlem, but is much younger.)
Nick is offline   Reply With Quote
Old 2020-11-23, 22:06   #224
kladner
 
kladner's Avatar
 
"Kieren"
Jul 2011
In My Own Galaxy!

22·43·59 Posts
Default

Quote:
Originally Posted by Nick View Post
Today (23 November 2020), the Dutch city of Haarlem is 775 years old!
(The district of Harlem in New York City was named for our Haarlem, but is much younger.)
Happy Birthday, Haarlem!
kladner is offline   Reply With Quote
Old 2020-11-26, 12:54   #225
AJensen89
 
Nov 2020
Florida

3 Posts
Default

Today (26.11.2020)
The most interesting what happened this day:

1949 India becomes a sovereign Democratic republic.
1922 Lord Carnarvon and Howard Carter, archeologists, open King Tut's tomb, undisturbed for 3,000 years.
1789 George Washington proclaims this a National Thanksgiving Day in honor of the new Constitution. This date was later used to set the date for Thanksgiving.
AJensen89 is offline   Reply With Quote
Old 2020-11-27, 01:57   #226
Dr Sardonicus
 
Dr Sardonicus's Avatar
 
Feb 2017
Nowhere

23·181 Posts
Default

Quote:
Originally Posted by AJensen89 View Post
Today (26.11.2020)
The most interesting what happened this day:
<snip>
1789 George Washington proclaims this a National Thanksgiving Day in honor of the new Constitution. This date was later used to set the date for Thanksgiving.
Currently, Thanksgiving Day in the USA is the fourth Thursday in November.

Thus, it can occur as early as November 22 (as it did in 2018), and as late as November 28 (as it did in 2019).

Not a religious holiday, but even so, a "moveable feast," in a manner of speaking...
Dr Sardonicus is offline   Reply With Quote
Old 2020-12-30, 21:24   #227
Dr Sardonicus
 
Dr Sardonicus's Avatar
 
Feb 2017
Nowhere

23×181 Posts
Default

When I was a kid, I heard that a fire, the Iroquois Theater Fire, was the reason that exits from public buildings open outward. It turns out it also led to a related invention - "panic bars." They are described in a hardware company piece, How the Deadliest Fire in U.S. History Saved Countless Lives.

I just ran across a mention of the fire in an "On this day" listing. It happened on December 30, 1903.
Dr Sardonicus is offline   Reply With Quote
Old 2021-01-12, 14:42   #228
TommyJ
 
Dec 2020

2·5 Posts
Default January 12

January 12, 1907 - Sergei Korolev, designer of Soviet rocket and space systems, academician, founder of practical cosmonautics, was born.
I think this event is quite important.
January 12, 1955 - the beginning of construction of the Baikonur cosmodrome. This is the first and also the world's largest cosmodrome.
January 12, 2005 - Deep Impact spacecraft launch.
Spacecraft from NASA, designed to study comet Tempel 1. For the first time in history, the spacecraft dropped a probe on the comet, which rammed its surface, having previously photographed it at close range.
TommyJ is offline   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Official "Faits erronés dans de belles-lettres" thread ewmayer Lounge 39 2015-05-19 01:08
Official "all-Greek-to-me Fiction Literature and Cinema" Thread ewmayer Science & Technology 41 2014-04-16 11:54
Official "Lasciate ogne speranza" whinge-thread cheesehead Soap Box 56 2013-06-29 01:42
Official "Ernst is a deceiving bully and George is a meanie" thread cheesehead Soap Box 61 2013-06-11 04:30
Official "String copy Statement Considered Harmful" thread Dubslow Programming 19 2012-05-31 17:49

All times are UTC. The time now is 07:41.

Mon Jan 18 07:41:25 UTC 2021 up 46 days, 3:52, 0 users, load averages: 1.66, 2.05, 2.12

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.