The Nature of the Blast

Efficiency of explosion Kind and shape of blasts Blast effects, range & damage Thermal effects Radiation effects

The results of the weapons test programs

Blast—40-60% of total energy Thermal radiation—30-50% of total energy Ionizing radiation—5% of total energy Residual radiation (fallout)—5-10% of total energy

Classifications of blasts Surface Blast:

fireball in touch with surfacevaporization of surface structures through blastand firestorm, immediate radioactive fallout

High Altitude Air Blast: fireball > 100,000 ft (>3000m)interrupts satellite based communicationthrough electromagnetic pulse (EMP)

Low Altitude Air Blast:fireball < 100,000 ft (without touching ground)generates shock waves, pressure differenceartificial for large areal damage, sea battle

Subsurface Blast:Underwater burstgenerates surge

Surface Blast – the fireball

Central temperature: ~10,000,000 KImmediate vaporization of material!Central pressure: ~33000 atm

Radiation release & absorption in surrounding matter generates red-glow intense luminosity. Expansion of fireball through internal pressure Fireball rises like hot air balloon

StokesAugust 1957

1500 Foot Balloon19 kt

Fireball expansion

psiatmT

T

p

p

KTatmpKT

constVTVp

000,503300300

000,000,1

101,1,300

;

1

2

1

2

6211

Pressure evolution within the fireball:

tem

pera

tur

e

pressure

Sedov Taylor approximation (valid of first 0.1s) allowed Russians to estimate the power of the Trinity bomb from the expansion time conditions

TNTktE

JTNTkt

mstJtP

PKE

P

P

mtr

mkgKtrKE

10

1018.41

)1(1004.41074.7

][950

/1,1

12

135/814

00

00

5/2

30

5/25

t r

0.1 ms 24 m0.4 ms 42 m0.7 ms 52 m0.9 ms 60 m

Expansion speed

sftskmv

skmTRcc

v ss

/000,240/8015.1

202

5.1;/201

2

Initial expansion speed v (T≈1,000,000 K)

cs is the speed of sound in the vaporized gas is the specific heat ratio of the gasR is the gas constant: 287 [J/kg K]; T is temperature [K]

Cool-down to T≈3,000 after 15 ms due to radiation losses

sftskmv

skmTRcc

v ss

/500,24/8125.1

12

25.1;/11

2

Ideal gas

Fully ionized plasma

The shock front developmentAfter ~10 second the fireball expands with constant rate of ~300 ft/s

After ~ 1minute fireball has cooled and radiation emission ceases!

18 ms

16 ms

6ms 90 ms

109 ms

15.0 s

Analysis of Fire ball

Sedov-Taylor Blast analysis

5/2

5/1

0

tK

ER

Valid as long as shock is super sonic: K≈1Approximation allowed Russian scientists to estimate the power of US Trinity bomb.

Evolution of Mushroom cloud

General Features – the mushroom the emergence of the mushroom shape

Absorption of cool airtriggers fast toroidal circulation of hot gases and causes upwardmotion forming the stem and mushroom.

Condensation of water changes red brownish color ofcloud towards white!

Strong upward windDrags dirt and debrisInto the cloud mixingwith radioactive material

Cloud rises in heightwith ~ 440 ft/s

Model

Dirt

Cloud AltitudeMaximum altitude for cloudrise is reached after ~ 4min. RATE OF RISE OF THERADIOACTIVE CLOUD FROM a I-MEGATON AIRBURSTHeight Time Rate of Rise(miles) (min) (mph) 2.0 0.3 330 3.0 40.7 270 4.0 61.1 220 5.0 102.5 140 6.0 123.8 27

Cloud height & cloud radiusdepend on the magnitude ofthe explosion, increase ofboth radius & height scaleswith explosion yield.

Chimney effect again!

v=wind velocity in m/sg=9.8 m/s2 earth accelerationH=height of heat column in [m]To=outside temperature, KTi=inside temperature in K

i

oi

T

TTHgv 265.0

For typical firestorm:H ≈ 10,000 mTi ≈ 1,000,000 KTo ≈ 300 K

➱ v ≈ 288m/s = 647 miles/hHurricane speeds ~100 miles/hConventional firestorm ~220 miles/h