Stealth technology, small cargo hold, and a propulsion bus with high acceleration You get the idea. A warship's payload section can include anti-spacecraft weaponsorbital bombardment weapons for revolt suppression type spacecraft as wellweapon mountsweapon control stations, combat information centerarmorpoint defenseweapon heat radiators and heat sinksand anything else that can be used to mission-kill enemy spacecraft. Pirate ships and privateers might forgo defenses if they only expect to be engaging unarmed cargo ships.

A more detailed discussion of fission weapon design is aided by introducing more carefully defined means of quantifying the dimensions and time scales involved in fission explosions.

These scale factors make it easier to analyze time-dependent neutron multiplication in systems of varying composition and geometry. These scale factors are based on an elaboration of the continuous chain reaction model. It uses the concept of the "average neutron collision" which combines the scattering, fission, and absorption cross sections, with the total number of neutrons emitted per fission, to create a single figure of merit which can be used for comparing different assemblies.

The basic idea is this, when a neutron interacts with an atom we can think of it as consisting of two steps: If the interaction is ordinary neutron capture, then no neutron is emitted from the collision.

If the interaction is a scattering event, then one neutron is emitted. If the interaction is a fission event, then the average number of neutrons produced per fission is emitted this average number is often designated by nu.

By combining these we get the average number of neutrons produced per collision also called the number of secondariesdesignated by c: In computing the effective reactivity of a system we must also take into account the rate at which neutrons are lost by escape from the system.

This rate is measured by the number of neutrons lost per collision. For a given geometry, the rate is determined by the size of the system in MFPs. Put another way, for a given geometry and degree of reactivity, the size of the system as measured in MFPs, is determined only by the parameter c.

The higher the value of c, the smaller the assembly can be. An indication of the effect of c on the size of a critical assembly can be gained by the following table of critical radii in MFPs for bare unreflected spheres: C is the degree of compression density ratio.

This scaling law applies to bare cores, it also applies cores with a surrounding reflector, if the reflector is density has an identical degree of compression.

This is usually not the case in real weapon designs, a higher degree of compression generally being achieved in the core than in the reflector. An approximate relationship for this is: Fission explosives depend on a very rapid release of energy.

We are thus very interested in measuring the rate of the fission reaction. This is done using a quantity called the effective multiplication rate or "alpha". The neutron population at time t is given by: The more familiar concept of "doubling time" is related to alpha and the time constant simply by: The time constant goes to infinity at criticality.

Alpha is determined by the reactivity c and the probability of escapeand the length of time it takes an average neutron for a suitably defined average to traverse an MFP. If we assume no losses from the system then alpha can be calculated by: The "no losses" assumption is an idealization.

It provides an upper bound for reaction rates, and provides a good indication of the relative reaction rates in different materials. For very large assemblies, consisting of many critical masses, neutron losses may actually become negligible and approach the alphas given below.

The factor c - 1 used above is the "neutron number", it represents the average neutron excess per collision. In real systems there is always some leakage, when this leakage is taken in account we get the "effective neutron number" which is always less than c - 1.

When the effective neutron number is zero the system is exactly critical. Ideally the value of alpha should be determined by "integral experiments", that is, measured directly in the fissile material where all of these effects will occur naturally.

Calculating tau and alpha from differential cross section measurements, adjusted neutron spectrums, etc. In the table below I give some illustrative values of c, total cross section, total mean free path lengths for the principal fissionable materials at 1 MeVand the alphas at maximum uncompressed densities.

Compression to above normal density achievable factors range up to 3 or so in weapons reduce the MFPs, alphas and the physical dimensions of the system proportionately.

In real fission weapons unboosted effective values for alpha are typically in the range doubling times of 2. All nations interested in nuclear weapons technology have performed integral experiments to measure alpha, but published data is sparse and in general is limited to the immediate region of criticality.

Collecting data for systems at high densities requires extremely difficult high explosive experiments, and data for high alpha systems can only be done in actual nuclear weapon tests.

Some integral alpha data is available for systems near prompt critical. The most convenient measurements are of the negative alpha value for fast neutron chain reactions at delayed criticality.This iteration of the BMP family is technically excellent in the application of available technologies and features, especially when compared to its predecessor, the BMP-1, but some view the BMP-2 is nothing more than a "rehash" of the old and obsolete BMP-1 design.

Back to Solid State Lasers Sub-Table of Contents. Q-Switching What is Q-Switching? A Q-switched laser is a type of (or modification to) a pulsed laser which shortens it output pulse width, boosts peak output power, and improves the consistency of the output from pulse to pulse.

Subscribe now and save, give a gift subscription or get help with an existing subscription. I provide advice about how to write novels, comic books and graphic lausannecongress2018.com of my content applies to fiction-writing in general, but I also provide articles specifically about superhero stories..

Here are a few tips to help you write better origin stories for characters in superhero novels and comic books. This iteration of the BMP family is technically excellent in the application of available technologies and features, especially when compared to its predecessor, the BMP-1, but some view the BMP-2 is nothing more than a "rehash" of the old and obsolete BMP-1 design.

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Tankograd: BMP-2