Thursday, 15 January 2015

Radiation: The danger is in the dose.

By Mark Williams

After a slight reshuffle, Gunth passes the baton on to a new team of hitchhikers. This time, Mark attempts to pin down that invisible ubiquitous threat, radiation. - with footnotes!

Today, whilst checking my own ionising radiation exposure, I was reminded of when I visited a school to talk about radiotoxicity. I borrowed a friend’s outreach exercise, which uses the banana equivalent dose (BED) as a visual way of depicting radiation exposure using one of your five-a-day. After a short description of a bananas radioactive content, students were asked questions such as, what is the BED for taking a plane journey from London to New York? What about doing nuclear research for a year? What about living in the south-west of England for a year[1]?

One banana contains, on average, about 0.5 g of potassium. Right now you contain about 160 g of potassium which, along with sodium, control the electric potential across the synapses of every nerve cell in your body. However, potassium contains ~117 ppm of a radioactive isotope, potassium-40. That gives us 15.5 Bq per banana[2], Becquerels are the SI (or standard) units for activity. One Becquerel is equivalent to one decay per second. (Oh, and before you throw all your bananas out, half a pint of orange juice contains about 0.5 g of potassium too, so carries roughly the same activity.)[3]

The point of this yard-stick is that it highlights the ubiquity of ionising radiation. It is everywhere, and everyone is irradiated all the time. Your exposure is affected if you fly a lot, it will change depending on your local geology, and it will change if you work with radioactive material. So what are we exposed to on average in the UK? And how might this change if say, we lived near a recent nuclear incident zone? The average Brit has an annual exposure to ionising radiation comprised of 84.5% natural background radiation[4], 15% medical[5], 0.2% occupational and 0.2% from nuclear fallout[6], the remainder (<0.1%) is from discharge[7]and consumer products.[8]At this point it may be helpful to relate ionising radiation to UV-rays, that is the radiation we receive from the sun (and certain beds) that both age and burn the skin at high doses, but is also an important factor in helping to prevent skeletal disease and vitamin D deficiency.

Our background dose, radiation from our geology, food, atmosphere and the furthest reaches of space, has been present a lot longer than we have; our bodies have evolved to handle this steady dose. So what about an elevated exposure? What about Fukushima? Currently, your lifetime risk of getting cancer in the UK is approximately 45% for men, and it’s about 5% lower for women.[9]In Japan it’s 41% for men, but for those from the Fukushima province – lifetime risk is increase by 1%[10], totalling ~41.4% for men. This is certainly significant, but it is probably lower than most would have expected. For an excellent analysis of nuclear accidents in context, read our previous article.

This blog has previously stated the importance of demystifying the jargon, highlighting that a misunderstanding from poor communication can lead to feelings of a separation from science. The BED is one way we can try to do this, it is not an official scientific unit of measure, but it can help to explain the ubiquity of radiation - to highlight that its presence in life is normal.

So, what do you think? Feedback I got from the school kids was pretty mixed, some (OK, most) went away talking about telling their parents to stop buying bananas… I’ll explain it better next time, I thought.




[1]For more information on the differences in exposure dependent on where you live in the U.K, see this article: http://www.sciencedirect.com/science/article/pii/S0265931X14002598
[2] We start with 0.5 g of potassium, but since we only consider the radioactive K-40, we multiply first by 0.000117 and then by 1/40th of a mole. 1.25 billion years (the half-life of K-40) is 3.9446x1016 seconds, so we write:
decays per second (Bq) = 6.1x1017 /  3.9446x1016 = 15.5 Bq.
[3] 1 Becquerel is 1 disintegration/decay per second. The Grey is the absorbed dose, and the Sievert details the equivalent dose, in other words the actual dose a person receives. Having these different definitions is important when assessing our radiation exposure, but the conversion is not simple, we must know the type of radiation as well as the locality (a banana ingested, inhaled(?!)  and held, all carry the same Becquerel but very different Sievert values).
[4]Background radiation comes from space, namely stars, like our sun.
[5]X-rays are a form of high energy radiation, and therefore ionising. CT scans also use x-rays, but in (much) larger quantities. These operations are localised and only effect the organ being examined. See herefor a nice infographic
[6]There have been many tests of nuclear weapons across the globe; these release radioactive material into the environment.
[7]The UK reprocesses its nuclear waste. The effluent is treated and then discharged into the Irish Sea.
[8]All of this data has been taken from J S Hughes et al. 2005 Review of the radiation exposure of the UK population
[9]Source: http://www.cancerresearchuk.org/cancer-info/cancerstats/incidence/risk/statistics-on-the-risk-of-developing-cancer
[10]WHO: http://apps.who.int/iris/bitstream/10665/78218/1/9789241505130_eng.pdf



Monday, 10 November 2014

Series 2 Episode 1 - Fusion & Wind

The nuclear hitchhiker team is back with a brand new series.

This month we discuss:

  • Lockheed Martin and the state of fusion. (1m 40s)
  • The UK's energy mix. (11m 33s)
  • A stumble through fast reactors. (36m 37s)
  • A collaboration between Manchester University and Warsaw Technical (39m 52s)


Thursday, 2 October 2014

A Comment on Nuclear Ethics

By Mark Williams



After a long absence due to us all writing up our dreaded theses, we're back! This week, Mark Williams discusses the nature of ethics within nuclear and questions whether we are doing enough within the community to educate and inform the wider public.


After a day of discussion around the ethics of nuclear, one thing seems to be clear: people want to know more about the risks, and they want dialogue with experts in the form of an open forum.Earlier this month in Manchester University’s School of Chemistry, 3 invited speakers, who have a range of expertise in energy mix economics, nuclear legislation and ethical studies, discussed their findings to a group of nuclear researchers. Rather than preaching to the choir about the benefits of nuclear, this was more of a critical assessment of how industrial and political actions can affect public perception. Dialogue ranged from the cyclical privatisation/nationalisation of energy markets to the building of another fence around Sellafield. Analysis ranged from the extensive engineered barriers to minimise radiation exposure to workers, to the perceived tarnishing impact of being born in a prefecture with a nuclear contaminant history.

Are Sellafield's security measures
symbolic of a loss of public transparency?
Take tightening security at Sellafield, for example; “anywhere with an electrified fence sandwiched between two razor sharp fences is going to make passers-by believe there is something very dodgy going on inside,” said one speaker. Interestingly, 25 years ago people were being shown around the site by tour guides; all visitor facilities have now been closed off, however. Is this a required security precaution in the light of increased terror alerts post-9/11, or is it a considerable loss of public transparency?

What of the people of the Fukishima prefecture? Parents in the region worry for their children’s future marital eligibility, but are these anxieties a result of their misunderstanding of the radiation risks? More likely it is the societal objectivity of a ‘contaminated’ community based upon a fairly global misunderstanding of radiation risks.

I’m concerned for a nuclear-curious public who have very limited public access to the nuclear industry. Politicians have been strongly in favour of nuclear since January 2008, with Gordon Brown stating “more than ever before, nuclear power has a key role to play as part of the UK’s energy mix” in the government white paper of that year. Then, just months after Fukishima, the current government said “we need […] a new generation of nuclear stations.” But with lacklustre incentives to entice private sector investment and the retraction of proposed carbon cost hikes to curb gas and coal [2011 white paper], nothing has been built and projections predict new build to be connected to the grid no earlier than 2025.

The talk subsequently focused on what can be done about public engagement. Other countries successfully engage with the public via open forums to discuss nuclear plans with respect to waste disposal (France) but little action takes place in the U.K. Perhaps some responsibility lies with nuclear specialists and researchers to try to engage the public in an unassuming, honest way, as opposed to allegedly acting like a fenced-off community, which people should be wary of.