Measuring Nuclear Weapons Illuminating Time to Determine Yield

Source: HQDA FM 3-12 "Operational Aspects of Radiological Defense"
Text in Square Brackets added by Cornelius Seon [76576,1330]

"As a field expedient, [nuclear weapon] yield may be estimated from the 
measurement of the illumination time of the burst, especially during hours of 
darkness or poor visibility [or out in space]. However, this method should be 
used ONLY if it is impossible to obtain cloud parameters [such as in Space] 
..., since this method only gives a yield estimate on the order of a factor of 
10. Techniques for measuring illumination time time will vary, depending on 
the situation, but under NO circumstances should the observer attempt to look 
directly at the fireball, since this can result in permanent damage to the 
eyes." [For the purposes of this file, Illumination Time is defined as that 
duration which occurs between the VISUAL start of an un-restrained Nuclear 
Reaction, and its VISUAL termination. Part of the problem with using 
Illumination Time to measure yield, is the fact that the reaction has already 
started, and has been continuing for some duration prior to its illumination, 
since the reaction starts when the device reaches Critical Mass, and the 
reaction continues after it loses illumination until it finally falls below 
Critical Mass. Another problem, is that in space - since it lacks an 
atmosphere which would "dampen" the fireball  - there will be some lingering 
glow which will steadily falloff as the surrounding vacuum "cools" the 
remaining mass. This can be misinterpreted as part of the illumination, but it 
is not. Rather, it is residual Infra-Red Radiation which is broadcast by the 
mass as it cools. Finally, there is the problem of the lack of gravity. Within 
a Gravitational Well, such as on a planet, especially when aided by an 
atmosphere, the fireball is contained in the shape of the mushroom cap. What 
escapes in a perfect globe, is the Blast Wave and the broadband radiation 
products of the blast itself. outside of a gravitational well, and an 
atmosphere, the fireball itself will continue to expand in the same manner as 
the Broadband Radiation [there would be NO Blast Wave in space - that effect 
is a function of the atmosphere], but at a slower rate, which is determined by 
the mass of the device itself. Further, it will dissapate as it expands, so a 
device will have to be really huge in order to have any effect as a weapon 
over any great distance, other than as a Radiation Weapon.

Nuclear Burst Illumination Time Yield Measurement Table
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ILLUMINATION      YIELD IN YIELD                                       
TIME              KILOTONS INCREASE                                    
[SECONDS]         +/- 2 KT [KT]     KILOTONIC YIELD GRAPH              
-----------------------------------------------------------------------
LESS THAN 1               1        1 #                                 
        1               2.5      1.5 ##                                
        2                10      7.5 ###                               
        3                22       12 #####                             
        4                40       18 ######                            
        5                60       20 ########                          
        6                90       30 #########                         
        7               125       35 ###########                       
        8               160       35 #############                     
        9               200       40 ##############                    
       10               250       50 ################                  
       12               325       75 ##################                
       14               475      150 ######################            
       16               700      225 ##########################        
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