Tag Archives: Nuclear Fallout

America Disarms Most Powerful Nuclear Bomb Ever Created

The US is burying the Cold War hatchet and doing so in style. It is dismantling the most powerful nuclear bomb ever created, believed to be over 500 times more powerful than the one dropped on Hiroshima. It was designed and armed in 1962, but, thankfully, never used. Named enigmatically as B53, it was to be carried by B-52 bombers and was capable of ripping apart even underground bunker facilities, should the Cold War have heated up.

The B53 at the Pantex Plant (Courtesy: Associated Press)

The B53

The B53 was a monster. It weighed in at 10,000 pounds (or 4.5 tonnes) and could release 9 megatons of TNT energy (or 38 PJ, 1 PJ = 1015 J a million billion joules)!! It formed a formidable arsenal, consisting of 340 individuals of its kind, built for B-47, B-52 and B-58 bomber planes. It used highly enriched Uranium (oralloy). It was meant to be used as a bunker buster a surface blast would send shockwaves that would shatter the Earth, enabling the underground parts to be exposed. Multiple strikes(!)  would eliminate technical facilities or even the leadership bunkered underground.


The disassembling process for the B53 arsenal began in 1980’s, but a few of them kept their place in the stockpile. In 1997, it was decided to retire them from the arsenal. The process took longer than expected, because the technology was old and most of the experts are either old or deceased. It took place at the Pantex plant at Amarillo, Texas, the only plant for disarmament in the US.

The disarmament is considered complete when the 300 pound explosive the fuse is separated from the highly fissile nuclear material. This nuclear material is known as the pit and is not heavy enough to detonate on its own (technically, it is of sub-critical mass). These pits are stored at the plant, then sanitized’ and disposed off.

The Pantex plant has served as a disarmament facility for a number of nuclear bombs. It will continue to do so!

Japan’s Nuclear Problem Update: How Radiation From Fukushima Affects America’s West Coast

The reach of atmospheric winds is long. The latest demonstration of this comes from the ruined Japanese power plant Fukushima. Sea water around Fukushima, rich in neutrons from the nuclear matter, was causing a spike in the amount of atmospheric sulfur over the Californian coast. Sulfur is a toxic element in itself and forms oxides which are just as toxic. It is also a major contributor of acid rain.

Fukushima after the disaster

What happened?

This is what was happening at Fukushima. On 13th March, 2011, two days after the deadly tsunami wrecked Fukushima, engineers began pumping seawater into the power plant, so as to keep the nuclear core cool, since the cooling system was not functioning due to loss of power. Lightly radioactive seawater was drained out of the power plant. Neutrons streamed out of the water, knocking against chlorine atoms, converting them into a radioactive isotope of sulfur. The sulfur combined with oxygen in seawater, especially since the warm water provided enough thermal energy for the chemical reaction. A part of this sulfur dioxide bubbled through the water and entered the atmosphere as a gas and another part dissolved in the sea water. Further, when the water hit the hot core, it instantly vaporized, again releasing large amounts of hot elemental sulfur into the atmosphere. Both air currents and ocean currents carried the sulfur rich air or water to the western shores of America.

The observed data and extrapolation

The sulphur peak in the atmosphere was noticed on March 28, 2011, 15 days after the pumping started. According to a study conducted by chemists at the University of California, San Diego, – the first quantitative study of the disaster – about 400 billion neutrons were released per square meter of the cooling pools of liquid in the power plant. This rate stayed constant from 13th March to 20th March. The mechanism of producing radioactive sulphur is well understood from cosmic ray studies, but this is the first time such a process is being noticed near the surface. The study measured 1501 atoms of radioactive sulfur in sulfate particles per cubic meter of air, much much higher than normal levels.

For the levels of sulphur noticed at California to be correctly correlated with sulphur levels over Fukushima, the team calculated that the levels of sulfur ought to be 365 times that over California.

As always, even disasters provide opportunity for science to study different processes. Thiemens, the Dean of the Division of Physical Sciences at UC San Diego, says

We’ve really used the injection of a radioactive element to an environment to be a tracer of a very important process in nature for which there are some big gaps in understanding.

Maybe in this case, it’s just too inhumane to say that every cloud has a silver lining.

News via UCSanDiego

Radiation Risks: How much is too much?

Many people are scared stiff by the possibility of an explosion at the Japanese nuclear reactor. They believe that a nuclear fallout will affect life as we know it. Since, the radiation of radioactive substances takes a long time to die down to zero, and these substances can be carried by strong wind currents across large distances, the consequences might be catastrophic. Well, this is only partially correct.

First point to note – radiation from a radioactive source NEVER goes to zero. There is always something there, no matter how feeble. This is not a bad thing. This means that we already live in a bath of weak radiation. Radiation comes from various sources, like radon gas (the main source!), cosmic rays (which bombard atoms in the atmosphere), elements in soil and even food. This is completely harmless. Even we are radioactive just stand in front of a Geiger-Muller counter and hear the clicks due to the disintegration of atoms in your body! All of this constitutes the background. The crucial point here is that once the radiation from a source is close or below the background, it is harmless.

Sources of background radiation
Sources of background radiation and relative contribution

Next point, radiation flux decreases as inverse-square of the distance. Taking into account various ionization phenomenon, the decrease is even faster; making the decrease a power law in distance with some power higher than 2. This essentially means that radioactive samples high up in the atmosphere will have negligible effects on life on the ground.


Getting Quantitative:

For measurements, we need units. The standard units are the following:

  1. Gray (Gy): Unit of measurement of the amount of radiation incident on any body per unit area per unit time. 1 Gy = 1joule/1kg.
  2. Sievert (Sv): Unit of measurement of radiation incident on a human body per unit area, per unit time. 1 Sv = 1 Gy . W, where W=weight factor

The presence of the weight factor (W) in the definition of Sievert measures the damage done to a human body due to different types of radiation. For example, W=1 for electrons, muons, x-rays etc. These are less harmful than neutrons at 50 keV, which have W=10. Alpha particles from a close enough source can have W=20. (Higher weight=more damaging.) Weight factors also take into account the portion of the human body receiving the radiation. Bones have W=0.01, whereas gonads may have W=0.2.

1 Sv is a very high dose, so units like ‘rem’, (1 rem=0.01 Sv) or milli-Sievert (Sv) (1 mSv = 0.001 Sv) are used.


How much is safe?

There are Threshold Limit Values (TLV) lists available. These recommend that a person on average receive no more than 50 mSv per year, i.e. 5 rem. Over a five year period, a person shouldn’t receive more than 20 mSv (or 2 rem) per year. These estimates vary with location of a person and his/her occupation. Check values here.

These values are slightly misleading because it misses the important point that a large dose (say 50 mSv) delivered all at once much more damaging than the same amount of radiation spread over a long period of time, like a year.

A normal person, not working in or near a nuclear power plant, receives less than 10% of the allowed dose. So don’t worry about the radiation. It’s just not that dangerous.