A Nice Description of a
Nuclear Explosion…
INTRODUCTION TO NUCLEAR
WEAPONS
INTRODUCTION TO NUCLEAR
WEAPONS
OBJECTIVES
• Distinguish between tactical and strategic nuclear
weapons – yields, intended targets, delivery
methods.
• Describe how fission and fusion reactions are
achieved.
• Identify the critical components of fission and
fusion warheads and then describe the principles of
operation.
• Define critical mass and know what it is dependent
upon.
• List characteristics of nuclear explosions and the
damage mechanisms.
NUCLEAR WEAPONS
CLASSIFICATION
TACTICAL
– Yield < 100 Ktons (15 Ktons min)
– Eliminate personnel
STRATEGIC
– Yield > 100 Ktons
– Used on vast area targets
WPNS OF TERROR
Perspective…
Hiroshima ≈ 15 KT
 Nagasaki ≈ 21 KT

– “small yields”  easy to hide
– Unpredictable
– Dirty Bombs
http://nuclearsecrecy.com/nukemap/
WHAT WOULD DAMAGE
LOOK LIKE IN ANNAPOLIS?
TYPES OF NUCLEAR REACTIONS
FISSION vs FUSION
ENERGY
RELEASE
COMBINES
ENERGY
RELEASE
SPLITS
FISSION
FUSION
TYPES OF NUCLEAR REACTIONS
FISSION vs FUSION
INCIDENT NEUTRON
FISSIONABLE NUCLEUS
NUCLEUS SPLITTING
FISSION PRODUCT (RADIOACTIVE NUCLEI)
FUSION
FISSIONABLE NUCLEUS
FUSIONABLE NUCLEI
ENERGY RELEASE
INCIDENT NEUTRON
NUCLEUS JOINING
CHAIN REACTION
ENERGY RELEASE
FUSION
PRODUCT
FISSION
NUCLEAR vs MOLECULAR
BINDING ENERGY
HELIUM ATOM
+
MOLECULAR
BINDING ENERGY
NUCLEAR
MOLECULAR
BINDING ENERGY
BINDING ENERGY
-
+
-
NUCLEAR FISSION
NUCLEAR FUSION
Deuterium
Tritium
He
Change between
total binding
Energy
+
+
energy (before and
after).
Neutron
CRITICAL MASSES
Neutron generation across subsequent generations of neutron production is
referred to as the neutron life-cycle, and the fissions which occur are
referred to as a chain reaction.
SUPERCRITICAL
When fissile material is densely packed such that neutrons
produced in subsequent generations continuously increase at
an exponential rate  SUPERCRITICAL CHAIN REACTION.
• Principle behind fission weapon.
CRITICAL
Chain reaction that produces same amount of neutrons in
each subsequent generation  CRITICAL CHAIN REACTION.
• Basis for electrical generation from nuke power
plants.
SUBCRITICAL
Neutron population decreases throughout subsequent
generations & produces less than one neutron to carry out
fission  SUBCRITICAL CHAIN REACTION
SUPERCRITICAL FISSION WARHEAD
– Must be reliable and rapid.
– Each reaction produces one or
more neutrons.
– Neutrons cause exponentially
increasing reactions.
FISSION WARHEAD
GUN-TYPE DESIGN
“Little Boy”  Hiroshima
POLONIUMBERYLLIUM
INITIATOR
•
235U
RINGS
& BULLET
BREACH BLOCK &
DETONATOR
GUN BARREL
Forces (2) subcritical masses
together to form supercritical mass.
Simple & Uncomplicated design
•
High production cost
• Low efficiency  “FIZZLE”
•
FISSION WARHEAD
IMPLOSION DESIGN
“Fat Man”  Nagasaki
• USES TAMPER & HE TO
MAXIMIZE EFFICIENCY.
• Subcritical mass
surrounded by high
explosive.
• Implodes inward,
compressing material,
sustaining chain reaction.
• Prevents ‘FIZZLE’ – a
premature end to
reaction.
• TAMPER  Confines
fission material allowing
it to fission longer.
FUSION WARHEADS
• Requires extreme heat & pressure to combine nuclei
• Uses a fission detonation to trigger fusion reaction
–
–
–
–
Fission increases pressure 50Million X ambient pressure
Pressure compresses & heats fusion material
Temp & Pressure increase @ same ratio
Temps reach 1010K  thermal motion of fusion material  very energetic
THERMONUCLEAR FUSION
NUCLEAR WEAPONS
PRIMARY EFFECTS
• Blast & Shockwave - 50%
• Thermal Radiation - 35%
• Nuclear Radiation (Initial
& Residual) – 15%
• Other Effects
– Electromagnetic Pulse
(EMP).
BLAST & SHOCK
PEAK OVERPRESSURE
As wave passes, pressure oscillates.
DIFFRACTION
LOADING
NEGATIVE
PHASE
POSITIVE PHASE
PEAK DYNAMIC PRESSURE
2ND POSITIVE
PHASE
WINDS CAN EXCEED 1000 MPH
DRAG
LOADING
Wind away from explosion
Wind toward from explosion
THERMAL RADIATION
X-RAYS created from extreme heat  produce a giant
FIREBALL
FIREBALL radiates energy rapidly in form of thermal
(IR) radiation (heat) and visible light.
Extends further than any other primary effect 
spontaneous ignition of combustible material
NUCLEAR RADIATION
• After nuclear detonation
– Neutrons emitted immediately
– Gamma rays emitted from decay of fission
products/secondary reactions of the neutrons with
surrounding air
– Radiation effects can be immediate or long –term
(residual).
– Classifications:
• Prompt/initial radiation (within the 1st minute)
• Residual radiation (after the 1st minute)
RESIDUAL RADIATION PRODUCTS
ALPHA (large/heavy)
• Helium nucleus from fusion …skin
can protect you
BETA (small/light)
• Electron or positron…clothing can
protect you
GAMMA (EM Radiation) • High energy photons emitted both
immediately from fission reaction
and later on during radioactive
decay…lead can protect you
• Excess neutrons not used in nuclear
NEUTRON (small/heavy)
reactions…lots of water may protect
you
RADIATION PENETRATION DEPTHS
ADDITIONAL EFFECTS
• FALLOUT  long-term effects
–Environment
–Population
• EMP
–TREE
–BLACKOUT
SUMMARY
• Distinguish between tactical and strategic nuclear
weapons – yields, intended targets, delivery
methods.
• Describe how fission and fusion reactions are
achieved.
• Identify the critical components of fission and
fusion warheads and the describe the principles of
operation.
• Define critical mass and know what it is dependent
upon.
• List characteristics of nuclear explosions and the
damage mechanisms.