INTRODUCTION TO NUCLEAR WEAPONS EFFECTS

Haldilal

लड़ते लड़ते जीना है, लड़ते लड़ते मरना है
Senior Member
Joined
Aug 10, 2020
Messages
9,160
Likes
28,016
Country flag
INTRODUCTION TO NUCLEAR WEAPONS EFFECTS
  • OBJECTIVES
    • Given the damage criteria for a target, find the required nuclear yield for a specified miss distance or find the maximum allowable miss distance for a given yield that will acheive that level of damage.
    • For a specific effect, choose the nuclear weapon burst type which will maximize that effect.
    • Describe and prioritize passive defensive measures based on a qualitative discussion of the sequence and relative hazard of nuclear weapons effects.
  • WHY LEARN ABOUT THEM?
    • Nuclear weapons will be around.
    • All current nuclear capable countries will maintain an arsenal for deterrence while the development of a nuclear capability is being aggresively pursued by many third world countries.
    • You need to know how they can be used.
    • It is impossible to understand nuclear policy without knowing their capabilities and limitations.
    • You need to know how to defend yourself against them.
    • All branches of the military have either systems or procedures for passive defense.
  • HOW THEY WORK
    • Fission bombs: Splits the nucleus of a heavy atom into smaller ones
      • Energy released is the difference in the total binding energy of nucleus
      • Neutrons initiate fission and are released by fission, creating the chain reaction
    • Fusion bombs: Joins smaller nuclei to make a larger one
      • Energy released is the difference in total binding energy of nucleus
      • Nuclei are joined by extreme heat and pressure (created by fission bomb)
  • FISSION BOMB MECHANIZATION
  • THE RMONUCL EAR (FUSION) BOMB MECHANIZATION
  • WHAT HAPPENS AFTER IT GOES OFF
    • BLAST WAVE
      • The rapid heating of gases to millions of degrees creates intense shock wave
      • The reflection of the blast wave off the ground creates constructive interference called the Mach Stem Effect.
    • THERMAL RADIATION
      • X-rays from the detonation heat the surrounding air, creating a fireball.
      • The fireball gives off intense thermal (infrared) radiation (heat).
    • NUCLEAR RADIATION
      • Neutrons are emitted from the fission/fusion reaction directly (prompt)
      • Gamma rays are emitted from the decay of fission products and air- secondary reactions of the nuetrons with the surrounding air
  • MORE THINGS THAT HAPPEN
    • ELECTROMAGNETIC PULSE: Large scale voltage spike caused by ionization of surrounding air
    • FALLOUT: Radioactive particles (from bomb and surrounding material) falling back to ground from mushroom cloud
  • DAMAGE CRITERIA- HOW THINGS ARE DAMAGED BY NUCLEAR EFFECTS
    • Structures
      • Diffraction loading - shattering effect
      • Drag loading - wind pressure pushes it over
      • Fire - applies to combustible materials only
  • People
    • Diffraction loading - internal damage due to pressure
    • Drag loading -
      • direct - thrown about
      • indirect - hit by flying objects
    • Burns
    • Radiation
      • somatic - immediate (up to months)
      • genetic - lifetime effects (cancer)

RADIATION

  • OBJECTIVES
    • Be able to list the four basic radiation particles and typical sources of each
    • Know the fundamental units describing radiation: roentgen, rad and rem
    • Know the difference between radiation and contamination
  • BASIC RADIATION FORMS: FOUR TYPES
    • Alpha
      • Helium nucleus (2 protons, 2 neutrons)
      • +2 charge
      • Strong ionization potential, low penetrating distance
    • Beta
      • electron (or positron)
      • -1 (or +1 charge)
      • Short penetration distance
      • Very common decay mode
    • Gamma
      • high energy light
      • neutral charge
      • Very long penetration (stopped best by lead)
      • Product of most decay modes
    • Neutron
      • neutral charge
      • long penetration (stopped best by water)
      • comes from fission
  • UNITS
    • Exposure - Roengten = the quantity of gamma rays that will producea charge of 2.58 x 10-4 coulomb in 1 kg of dry air.
    • Absorbed dose - Rad = the absorption of 100 ergs of ionizing radiation per gram of absorbing material (1 roentgen deposits 94 ergs in 1 gm of body tissue)
    • Biological dose - Rem = number of rads x RBE
RBE = relative biological effectiveness
    • Alpha = 10 - 20 (internal, depends on organ)
    • Beta = 1
    • Gamma = 1
    • Neutron = 1 external, 4-10 (internal)
  • Metric: 1 Gray (Gy) = 1 J/kg
  • FORMS
    • Radiation:refers to exposure and is an external hazard, reduced by shielding
    • Contamination: refers to radioactive particles if particles get inside body, they can cause great damage by exposure of internal organs (lungs, intenstines, ...)
    • Initial radiation: defined as radiation received in the first minute after detonation primarily from neutrons and gammas from the fission reaction and its by-products
    • Residual radiation: anything received after first minute decay of fission products
    • Fallout: radioactive cloud (radiation) return of particles to ground (contamination)
  • HOW MUCH IS HARMFUL?
    • <30 rem: no noticeable effect.
    • 200 rem: makes you sick, slight chance of death.
    • 600 rem: makes you very sick, >50% chance of death (1-6 weeks).
    • >1,000 rem: almost always lethal in 1-2 weeks.
    • >5,000 rem: immediate incapacitation, death in 1-2 days.
DAMAGE PREDICTION

  • USE OF DAMAGE CRITERIA TABLE
    • Targets separated by effects:
      • Diffraction: shattering effect of blast wave. Directly proportional to peak overpressure.
      • Drag loading: pressure caused by wind. Directly dependant on dynamic pressure (or maximum wind speed)
      • Fires/Burns: depend on thermal radiation exposure. Measured in cal/cm2.
      • Radiation: only applies to initial (first minute) dose. Measured in rad (assumes only external exposure, so all RBEs are 1. In other words, rads = rems)
    • Damage criteria are divided into three levels
      • Light: minor damage. Function essentially unimpaired.
      • Moderate: some degredation of function, some fatalities.
      • Severe: total degredation of function. Structures destroyed, near certain death.
  • USE OF SCALING LAWS
    • Blast Effects:
      • Graphs available for 1 kt only.
      • Yield, W1/3 scaling applies to:
        • height of burst, h
        • ground distance, d
        • slant range, r
      • Peak overpressure, dynamic pressure can be found for any h, d, W as follows:
        • scale height of burst, h to 1 kt: h1 = h/W1/3
        • scale ground distance the same way.
        • Use graph to find value of peak ovverpressure or dynamic pressure.

EXAMPLE: BLAST EFFECTS

Given 1 1000 kt bomb detonated at 2000 feet, find the peak overpressure at 3000 feet from ground zero:

STEP 1: scale height of burst and ground distance to 1 kt

h1 = 2000 ft/ (1000)1/3 = 200 feet

d1 = 3000 feet / (1000)1/3 = 300 feet


STEP 2: use graph to find magnitude of effect:


EXAMPLE: BLAST EFFECTS

Given a 1000 kt (1 Mt) bomb detonated at 2000 feet, find the ground distance to which 200 psi overpressure will extend.

STEP 1: scale height of burst

h1 = 2000 feet/ 10 = 200 feet

STEP 2: use graph

STEP 3: scale back to 1 MT

d = d1 x W1/3

d = 260 feet x 10 = 2600 feet.

  • USE OF BLAST EFFECT GRAPHS: HELPFUL HINTS
    • Interpolate between lines. For instance, if your are halfway between the 100 and 200 psi lines, then use 150 psi for your answer.
    • Use whichever one of the three possible graphs for peak overpressure that fits the valules your are using. There is some overlap, so you will be most accurate using the curve that has the biggest separation between the lines
    • If the height of burst isn't given, then you can solve for the optimum hieght of burst, which is where the curve extends the furthest to the right. Note that this is also just below the top of the Mach Stem Region.

  • CRATER SIZE PREDICTION: FOR BURIED TARGETS
    • Crater diameter can be predicted from a simple formula: Diameter (feet) = 80 W0.3 (W in kt)
    • Damage effects are predicted by relationship to the crater size.
Example:
Small heavy underground structures will be severly damaged only if they are within 1.25 apparent crater radii of a nuclear blast, find the maximum miss distance for a 150 kt earth penetrating warhead.

Crater size: D = 80 (150)0.3 = 270 feet

Result: 1.25 x 270/2 = 170 feet. Therefore if the 150 kt bomb is exploded withing 170 feet (horizontal distance) it will severely damage the underground structure.

  • THERMAL EFFECTS PREDICTION: GRAPHICAL METHOD
    • There is only one graph for thermal effects, using slant range and yield as entering arguments.
    • Slant range is found be geometry (using right traingle)
    • Slant range, r2 = d2 + h2.
    • Curve set up in miles (because thermal effects extend farther than blast or radiation).
    • The curve doesn't go below 3 cal/cm2 because that exposure is insignificant.
    • Likewise, beyond 50 is excessive (for people).
    • Scaling, if desired, is linear. THERMAL EFFECTS PREDICTION A 10 kt bomb gives off 10 times the thermal exposure.

EXAMPLE

Given a 75 kt warhead, detonated at 300 feet, find the radiant exposure at 2 miles away

STEP 1: compute slant range. In this case 2 miles >> 300 feet, therefore the slant range is essentially the same as ground distance, 2 miles.

STEP 2: read the graph:

Answer: 18 cal/cm2. More than enought to cause 3rd degree burns.
  • RADIATION DOSE PREDICTION: GRAPHICAL METHOD
    • There is one graph for gamma, and one graph for neutron.
    • Dose is the sum of the two exposures.
    • You must calculate slant range, again (in yards)
    • The graphs don't go below 30 rads because that dose doesn't cause any somatic effects
    • Likewise, above 10,000 rads is certain, immediate death in all cases.
EXAMPLE

Given a 200 kt bomb that detonates at 750 feet, find the initial gamma dose at 2000 yards from ground zero.

STEP 1: compute the slant range: (750/3)2 + 20002 = 2100 yards

STEP 2: Use graph:

Answer: about 600 rad, a lethal dose for at least 50% of the population.
  • USE OF DAMAGE PREDICTION: SUMMARY
    • STEP 1: For a specific target, look up the effect that causes the desired level of damage
    • STEP 2: For the specific weapon (yield, height of burst), you can predict how far that level of damage will extend.
    • STEP 2: (alternate) For a given distance (miss distance, CEP, for example) you can predict what yield will be required to do the job. Or for fixed yields, the number of warheads required.
VARIATIONS IN EFFECTS
  • BURST TYPES
    • Air = above surface up to 30 km
    • Surface = if fireball touches the ground
    • High Altitude = above 30 km
    • Underground = if height of burst is negative
    • Underwater = self-explainitory
  • VARIATIONS WITH BURST TYPE
    • HIGH ALTITUDE
      • Blast is less because there is less to heat
      • Excessive slant range minimizes most other effects
      • EMP extends over a great distance
      • Ionizations disrupt communications over large area
      • Best use is therefore as a preemptive strike, to disrupt command and control
    • SURFACE
      • Ground absorbs a lot of energy, so range is reduced for most effects
      • Makes a crater
      • Creates massive amount of fallout, due to contaminated soil thrown into air
      • Very intense EMP is local area, due to asymmetry in ionizations (ground blocks 1/2)
      • Best use is for single targets that need maximum effect to damage (closer to target always has stronger pressures)
      • EMP maximized
    • UNDERGROUND
      • Makes a crater
      • If crater (or void) doesn't break surface there is no radiation or fallout (the way they are tested)
      • Only good for buried targets (would require a penetrating warhead design)
    • UNDERWATER
      • Creates a base surge (sunami-like) of radioactive mist
      • Overpressure greater but shorter duration
      • Overpressure limited near surface by destructive interference (surface cutoff)
      • Deep detonations only good for damaging submarines.
      • Above water detonations are probably more likely to damage surface ships
  • SUMMARY OF BURST TYPES: WHAT THEY ARE GOOD FOR
    • Surface: hard targets
    • Underground: buried targets
    • Underwater: submarines
    • High Altitude: command and control
    • Air: everything else.
  • NUCLEAR ATTACK DEFENSIVE MEASURES
    • SEQUENCE OF EVENTS
      • FIRST EVENT: Bright flash followed by thermal pulse (8-10 seconds duration)
      • SECOND EVENT (15 seconds) : Blast wave, rapid rise in pressure followed by extreme winds (in excess of 600 mph), winds last up to 10 seconds, then reverse direction for 1-2 seconds.
      • THIRD EVENT (first minute): continuous exposure to high radiation
    • NUCLEAR ATTACK DEFENSIVE MEASURES: PRIORITY OF ACTIONS
      • COVER EYES/TURN AWAY: protect against flash blindness.
      • TAKE COVER: any sort of barrier will shield skin from burns.
      • HOLD ON: injuries to personnel are due to tumbling or being hit by flying objects.
      • GET BEHIND SOME SUBSTANTIAL SHIELDING: neutrons and gammas penetrate deeply, so get behind metal (best) or any thick object for first minute or so.
      • FOR SHIPS: expect either the base surge or some sort of sunami (tidal wave) in the next few minutes.
      • PUT OUT FIRES: over half the fatalities are usually due to secondary fires.
      • GUARD AGAINST CONTINUED EXPOSURE/CONTAMINATION: use respiratory protection, anti-contamination clothing and/or wash-down systems.
 

Latest Replies

Global Defence

New threads

Articles

Top