Radiation and Reason: a fresh look at the effect of radiation on life

29 October 2012

Professor Wade Allison, Oxford University, presented his Radiation and Reason talk to the Branch at the Institute of Physics on 17 October 2012.

Radiation and Reason Cover

There is a widespread belief that nuclear energy is inexorably dangerous, and this phobic attitude stems from the events leading to the nuclear bombings on Hiroshima and Nagasaki in 1945 and the Cold War era. 

The fear of an imminent annihilating holocaust has been present in the human mind ever since and accidental events at nuclear plants at Chernobyl and more recently, Fukushima, have corroborated this. 

The panic not only affects lay persons but extends to governmental institutions, which the media use as a fertile ground to instil more fear. But is radiation such a deadly influence that has to be avoided at all costs? Are these fears based and justified on solid empirical data?

Everything is made of atoms. Atoms have a nucleus, 100,000 smaller than the atom, heavy, electrically charged, stable and unchanged. Only 1 nucleus in a million has changed since the formation of the earth 6,000 years ago. 

This change is denominated radioactive decay. Every nucleus remains completely isolated because of its small size and by the intense repulsive force of its electric charge. There exists natural radioactivity within the Earth since its formation, and this radioactivity and heat that contributes to earthquakes, volcanoes and tsunamis.

On March 11 2011 a magnitude-9 earthquake struck the northwest coast of Japan and generated a tsunami that completely devastated a wide coastal area. This resulted in significant loss of life ->20,000 persons died- and socio economical loss.

Neutrons exist only inside a nuclear reactor that is 'on' at the time or inside a nuclear weapon at the moment of explosion. As soon as the earthquake was detected, all nuclear reactors were switched off and the neutrons were absorbed. 

By the time the tsunami struck there was only radioactive decay in the reactors. This generated immense heat that was damaging, in the absence of sufficient cooling water to keep both the temperature and pressure down. At high temperature, the nuclear fuel containers made of zirconium reacted with water, releasing hydrogen. This exploded when outside, but these explosions were no worse than the destructive fires. So the damage here was chemical, not nuclear.

Interestingly, radiation exists ubiquitously in nature and is successfully used in medicine for the treatment of malignancies. The average monthly dose received from natural sources is ~0.2 mSv. A CT scan dose is 5-10mSv. PET and SPECT scans are also within that range and these dosages are innocuous unless the number exceeds of >10 monthly.

In radiotherapy, dosages of >50,000Sv are given to tumours, spread over several weekly treatments, and despite some protection, peripheral non-carcinogenic tissues also receive some radiation, but they withstand it. 

At Chernobyl, 27 of the 42 the fire-fighters receiving doses above 4,000mSv died in a few weeks whereas none of the 140 died with a dose below 2,000mSv. 

There were some cases of child thyroid cancer from radioactive iodine, the majority of them treatable. The effects of radiation on the body affect the double stranded DNA molecule. 

The DNA can repair itself. But oxygen radicals also damage the DNA molecule. The radiation damage can be acute (Acute Radiation Syndrome) or more prolonged.

There have been no radiation-related casualties at Fukushima yet and the chances of occurring are remote. The more devastating blows in the region have been economic, social and psychological.

In summary Professor Wade Allison regards nuclear energy as safe, affordable and in the long run, effective and more economical. There are risks posed to humankind and the planet, but these are originating from:  CO2 waste from fossil fuels, biological waste, climate change, financial crises and other economic concerns. 

New safety levels for human radiation exposure are suggested: 100 millisievert in a single dose, 100 mSv in total in any month; 5,000 mSv as a total of whole-of-life exposure. Education, information and general understanding will play an important and decisive role in demystifying the nuclear phobia that currently afflicts our society.