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The Persian Bomb

World Affairs, Science and Technology, National Security

Lot of folks seem to be exercised over the potential of Iran developing an atomic bomb to loft into Israel or even across the pond to us. Equally dire is the potential for Israel to attack Iran's nuclear facilities. However, we must remember that in politics, local or world, all is not as it seems. In fact, practically nothing is. Actually, all the hoopla is about oil. (Surprise!)

The Iranians are busily working to enrich uranium. Vanilla uranium has an atomic weight of 238: U238. It's actually pretty stable and rather weakly radioactive, not able to sustain a chain reaction which is required for an atomic explosion. However, natural uranium contains a very small amount of U235--less than 1%--which is highly radioactive and the primary fissible material in an atomic bomb. (Modern bombs sometimes employ plutonium [Pu239] to augment the U235 neutron flux. This permits a more compact device.) An atomic explosion occurs when the U235 core is compressed, typically by precisely-timed conventional explosives, increasing the neutron flux (density) to the point where enough U235 atom nuclei are fissioned (busted)  to provide new neutrons needed to sustain the chain reaction/explosion. The explosion terminates when the remaining U235 is scattered, diminishing the neutron flux density below the critical level. (Neutrons are atomic particles with mass but no charge. Thus they can bang into charged particles and isotopes without being deflected.)

NOTE 1: Where plutonium is used, it forms a shell around the uranium, usually in a ball shape. The combination is compressed by the conventional explosive charges, greatly increasing the neutron flux and increasing the yield.

NOTE 2: U235 atoms are fissionable--splittable--because they have fewer neutrons than U238. The latter atoms won't absorb neutrons because they have their full complement. U235 will absorb a neutron, forming U236 which is unstable and breaks up (fissions) spontaneously, emitting more neutrons and incurring a mass-to-energy conversion, the combination creating an uncontrolled chain reaction and explosion.

The real tricks in making a bomb are the super-precision needed in machining the parts, the placement of the conventional explosive charges and especially the complex triggering mechanism for setting off the charges in the proper split-second sequence to create a perfectly spherical shock wave to compress the fissile ball in the center. This is in addition to manufacturing sufficient enriched uranium to build the thing.

One method of making U235 involves selectively getting rid of U238 using rather sophisticated gas centrifuges until the concentration of U235 is high enough. (The U238 atom is heavier than the U235 and so can be separated by centrifuging.)                                


                                                   Gas Centrifuge

Uranium flouride gas (UF6) is spun at high speed. Heavier U238 atoms move to the outside of the spinning chamber, leaving a slightly higher concentration of the lighter U235 in the center which is drawn off. Repeated centrifuge cycles gradually increase the concentration of U235. The process goes on--literally hundreds of cycles--until the resulting product contains mostly U235, as much as 90% pure, although lower concentrations are adequate for a bomb. It takes lots of centrifuges running around the clock to provide enough enriched uranium for one bomb. (To be fair to the Iranians, enriched uranium is also needed for power plant reactors which employ controlled nuclear fission.)

NOTE 3: There is another process for enriching uranium called gaseous diffusion. This is a somewhat more complex process using membranes to separate the uranium isotopes. This process is used almost exclusively in the United States for commercial enrichment.

The reason I went through this long technical explanation is to demonstrate the complexity of the process for building an atomic bomb. Then you have to package it in a deliverable form and find a means to deliver it, no simple tasks. The bottom line is the Iranians are years away from becoming a realistic nuclear threat. The real problem with Iran is its formidable conventional military power which is a real threat to countries like Saudi Arabia and Kuwait, the source of much of the world's oil.

Israel will not attack Iran's nuclear facilities partly because Iran is far away and would be very difficult and costly to attack, but mainly because it's not necessary. Besides, if Iran is attacked, the first thing they will do is mine the Straits of Hormuz to the hilt, stopping the flow of oil via tanker and creating a monumental world economic crisis that will make the present one seem tame. This is in no-one's interest, including Israel but especially the U.S.

In order to successfully attack Iran and neutralize its real or imagined nuclear threat, their conventional military capability, especially naval (which is not insignificant), would have to be neutralized to prevent the closure of Hormuz. Only the U.S. has the capability to do this. That is the dilemma that we and the western world, as well as much of the Middle East, face. Consequently, don't expect anything more than bluster and rhetoric along with ineffective sanctions, at least for the duration.

Five years from now ...? At some point in time, Iran, unless it implodes politically which is at best a remote possibility, will have to be dealt with. It is likely that, again, only the U.S. will have the capability. This is not as implausible as it sounds. Many of the other Middle Eastern countries fear Iran and would like nothing better than to see its teeth pulled. Remember, Iran is Persian, not Arab.

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