Archive for March, 2010

Are Mobile Phones Safe?

March 28, 2010
Incidence of Cancer of the Brain and CNS 1975 -2006

Incidence of Cancer of the Brain and Central Nervous System 1975 -2006

The Safety of Mobile Phones was our topic at Protons for Breakfast this week. During the week an e-mail was forwarded to me from someone attending the course. They wrote:

I wondered if Michael might have comments on the article at the link? Cell Phone Dangers — What They Don’t Want You to See

Well I do have comment. This is a terrible and pernicious web site. It contains misinformation in its most hateful forms. If you read this you might think we are in the middle of an epidemic. I honestly can hardly bear to look at this site but I will give you three quotes from the site:

  • Here [in a now deleted You Tube video] Dr. Charlie Tia, a preeminent Australian neurosurgeon discusses what he believes is a contributing factor to this exponential increase in brain tumors among children: excessive exposure to electromagnetic fields (EMF), and electromagnetic radiation (EMR) from mobile phones and other electrical and electronic equipment and appliances
  • Few people realize this, but brain cancer has now surpassed leukaemia as the number one cancer killer in children.
  • Australia has seen an increase in pediatric brain cancers of 21 percent in just one decade. This is consistent with studies showing a 40 percent brain tumor increase across the board in Europe and the U.K. over the last 20 years.

The implication of this is that mobile phones are killing our children NOW! Is it true? If you look at the site you will see that he gives no references whatsoever– that’s a clue as to the amount of attention he has paid to the site. But even so the site leaves even me feeling worried. Looking at this you maybe you find yourself asking “Is this really happening?” or “Why didn’t Michael tell us about this?” Well I didn’t tell you about this because its just complete nonsense. Please don’t take my word for it, please look at the statistics yourself and make up your own mind.

Australian statistics

Australian statistics are not so readily available for analysis, but they are summarised here (very long pdf). Surprisingly, they show an increasing trend of incidence for all cancers. I do not know the origin of this, but since it occurs for all cancers, this trend is likely to be an artefact of cancer diagnosis techniques or increased longevity. The Australian data is in contrast to the US where cancer statistics are readily available for all types of cancers dating back to 1975 – before there was any widespread use of mobile phones.

US statistics

US statistics are available from the National Institute of Health (NIH) cancer web site and from the Surveillance, Epidemiology and End Results (SEER) Program web site which has intensively monitored selected populations to garner detailed data sets. Warning: These are BIG web sites and you will not find exactly what you want easily – it took me hours to find and extract the data I was looking for i.e. the data which most closely corresponded to that mentioned in the pernicious web site. This is data for the incidence of Leukaemia and Brain Tumours.  What do the US data show?

Well the data for Brain Tumours and cancers of the central nervous system is shown at head of this piece. The data for Leukemia – mainly a cancer of childhood – is shown below. Please make up your own mind whether there is an” exponential increase in brain tumours” or whether there is a “change in the ratio of brain tumours to leukaemia” or whether there is evidence of “a 40% increase in brain tumours”.

Incidence of Leukemia per 100,000 population 1975 - 2006

Incidence of Leukemia per 100,000 population 1975 - 2006

In contrast to these basically static graphs, mobile phone use went from zero to its current widespread use during this period. If exposure to mobile phones is a significant contributing factor to these diseases we would expect to see a rising trend in these graphs versus time. I don’t see any such trend.

So what?

I don’t claim – and neither does anyone else – that this data is ‘proof’ that mobile phones are ‘safe’. The data above indicate that there is no current evidence of harm. But a link between mobile phone use and cancer may exist and we should continue to look for it. We should continue to compile these statistics (which is an expensive undertaking) and we should go further. For example, we can look at each tragic case behind each dot on the graph above to see if there are common factors about the use of mobile phones or other exposure to microwave radiation.

I have written this blog comment because websites such as the one mentioned at the start spread only alarm and fear and offer no insight into what is really happening. The authors of such sites should be ashamed of themselves.

Balloon Pictures

March 25, 2010
A picture from 'space'

A picture from 'space'

I read a  simple inspiring story this evening from the BBC about a man, Robert Harrison, who launched his camera into ‘space’ – well 21 miles high – on a balloon. He took stunning pictures of the Earth that were just mind blowing. I love his straight-forwardness and I feel inspired. All of a sudden water rockets seem so terrestrial. Mmmmm…

What is the ‘source’ of internal heat in the Earth?

March 25, 2010

At the Protons for Breakfast session the other night, someone asked me ‘What is the ‘source’ of internal heat in the Earth?‘. I knew that William Thomson (Lord Kelvin) had made estimates of the age of Earth based on its current temperature and arrived at an estimate well short of what we now believe. I had heard the difference had been ‘explained’ by radioactive decay but I had never looked into problem.  Well I looked around on the web, found the appropriate Wikipedia page, and sketched in the answer. The answer turns out be that indeed the weak radioactivity of the rocks within the Earth is responsible. I wrote:

The internal heat is partly left over from the Earth’s creation, but there is a substantial contribution from the decay of radioactive elements. There are many long-lived radioactive elements that heat each kilogram of rock only minutely. For example, Wikipedia tells me that even though Uranium 238 is present only as an impurity in most rocks, the heating from it is estimated to be 0.000 000 000 003 Watt per kg (3 x 10-12 W/kg) of rock. Not much! But there is a lot of rock! The mass of the Earth is 6 x 1024 kg so that amounts to a whopping 18 x 1012 Watts! If we divide this by the surface area of the Earth (5.1 x 1014 metres squared) we arrive at 0.035 Watts per square metre. Since there are three or four other significant long-lived isotopes with similar heating effects, this in line with the figure of around 0.1 Watts per square metre I mentioned in the talk.

Well I was pleased that these numbers sort of tied together. But I wondered if the heating really could be that great. So I made some further order of magnitude calculations and actually it does sort of tie up. Let me explain what I did. I calculated three quantities and then multiplied them together to get a fourth.

  • The first quantity I calculated was the probability per second that a nucleus of an atom of uranium would decay.
  • The second was the number of Uranium atoms in each kilogram of rock.
  • The third was the energy released when each nucleus of uranium decays
  • I then multiplied them together to work out the average amount of energy realsed into each kilogram of rock per second.

Lets look at each of these in turn

Decay Probability

The half life of Uranium 238 – the most common isotope of Uranium is an astonishing 4.468 billion years! This is close to our estimate of the age of the Earth, and so very roughly only about half of the Uranium 238 atoms that originally existed on Earth have decayed. Converting to seconds by multiplying by the number of seconds in a minute, the numbe rof minutes in an hour, the number of hours in a day and the number of days in a year I find the following stupendous number 4.468 x 10^9 x 60  x 60 x 24 x 365 = 1.41 x 10^17 seconds. The probility of decaying in that many seconds is 0.5, so very roughly the probability of decay per second is 0.5÷1.41 x 10^17 or 3.57 x 10^-18 per second.

Number of uranium atoms in each kilogram of rock

Wikipedia tells me that Uranium is present as impurity at a level somewhere between 2 parts per million and 4 parts per million in the Earth’s crust. If we assume that concentration is typical of the whole Earth, then we just need to work out how many atoms there are in a kilogram of rock, and we will then know roughly  how many Uranium atoms there are. Well the interior of teh Earth has a complex structure and contains many different types of rocks. The most common rocks are silicates (SiO2) of magnesium, iron, and aluminium. Calculating the average molecular weight of this mixture is 40 and of 1 mole ‘average Earth’ of atoms would have a mass of 40 grams. So in 1 kg of ‘average Earth material’ there are roughly 25 moles of atoms. Now 1 mole of a substance 6.023 x 10^23 of its microscopic constituents, in thsi case atoms and so 1 kg of ‘Average Earth material’ contains roughly 25 x 6.023 x 10^23 = 1.5 x 10^25 atoms. And we know that approximately 2 out of every million of these atoms will be uranium. So the number of uranium atoms per kilogram of ‘average Earth rock’ is roughly 3 x 10^19 per kilogram.

Energy release

Each radioactive decay of a Uranium 238 nucleus (about 99.3% of naturally occurring Uranium) emits an alpha particle with an energy of 4.27 MeV (Million electron volts). To convert this to joules of energy I need to multiply by the number of joules per electron volt of energy which is 1.6 x 10^-19 joules. Thus we find that each decay releases 4.27 x 10^6 x 1.6 x 10^-19 = 6.83 x 10^-13 joules. This is energy of the alpha particle emitted from the nucleus of uranium 238. The alpha particle bashes into the neighbouring atoms and sets them moving – i.e. it heats them.

Bringing it all together

If we multiply (the probability per second that a uranium nucleus will decay) by (the number of such nuclei in a kilogram of average Earth rock) we find out the average number of radioactive decays per second per kilogram of ‘Average Earth rock. The sum is (3.57 x 10^-18 per second) x (3 x 10^19 per kilogram) = 107 decays per second. This seems reasonable, but perhaps a bit on the high side (based on my experience of measuring radioactivity of rocks – I genrally just get a few counts per second). If we now multiply this number by the amount of energy released in each decay we find the energy released into the rock per second is (107 per second)  x (6.83 x 10^-13 joules) = 7.3 x 10^-11 joules per second (Watts). Looking back up the page I see that originally I took my estimate of heating by Uranium to be 3 x 10^-12 Watts per kg of rock and this estimate is around 20 times bigger.

So What? Well I just wanted to show that starting with estimates of the half life of Uranium and the energy released in each decay, I could sort of explain the amount of heat produced per second. The big uncertainty here is in the actual concentration of Uranium in the Earth. Given this uncertainty, I feel that my calculations do sort of tie up, and  I feel more confident now in repeating what I have heard, that the reason the Earth is hot inside is because of the radioactive decay of long lived isotopes.

One more thing…

It is hard to imagine how this tiny heating – a few millionths of a millionth of a watt per kilogram – could ever get anything hot! Indeed the heating rate would be infinitesimally slow – roughly 10^-13 of a degree per second. At that rate it would  have taken about 1.5 billion years to have heated up the interior of Earth to our current estimate of around 5000 °C. However the heating rate is sufficient to slow down the cooling of a previously hot body, which is what we believe has happened. OK. I feel I have done this problem to death now! Time to move on!

Atmospheric CO2: Looking at the data

March 23, 2010
C13/C12 Isotope Ratio. The systematic decline in this ratio is due to the distinctive isotopic ratio of fossil fuel derived CO2

C13/C12 Isotope Ratio. The systematic decline in this ratio is due to the distinctive isotopic ratio of fossil fuel derived CO2

It might seem there was very little left to say about the rise in atmospheric CO2 due to anthropogenic emissions. But the other day my colleague Martin sent me a link to two presentations at the Scripps Institute ‘Home of the Keeling Curve‘, and I found out there was plenty left to say. Scientists there presented data which actually evaluated the things I have heard people chat about for years.

  • The first topic covered was changes in the isotopic composition of the carbon dioxide in the atmosphere. This change unambiguously links the rise in CO2 to anthropogenic emissions – in case anyone really doubted that.
  • The second topic covered was the corresponding decline in the oxygen concentration of the atmosphere caused by burning all that CO2.

Isotopic Composition

Carbon is made primarily from two stable isotopes: C12 with 6 protons and 6 neutrons, and C13 with 6 protons and 7 neutrons. The heavier C13 comprises only about 1% of natural carbon. As was first observed in 1961, plants preferentially build their cells from C12 based molecules. Thus fossil fuels, which are derived from plants, have a slightly reduced  ratio of C13 to C12. Thus if the increase in the atmospheric CO2 that we have observed is really due to the emissions from fossil fuels then we should observe a corresponding decline in the ratio of C13 to C12 in the atmosphere. The Figure at the head of this article shows the data, and more detailed graphs are available at the Scripps site which explains the different curves and dots on the graph.What I found pleasing was just to encounter this data that I have heard people chat about for years.

Oxygen Depletion

Graph showing the depletion of atmospheric oxygen due to fossil fuel burning

Graph showing the depletion of atmospheric oxygen due to fossil fuel burning

One natural consequence of the reaction C + O2 → CO2 is that the amount of oxygen in the atmosphere must be decreasing. Its a small effect but once again the people at Scripps have measured the effect and made calculations to determine that the effect observed is in line with the observed CO2 emissions. The relevant data shown above and can be found several slides into this pdf presentation.

And so…

And so it is 10:48 p.m. and time for bed. But I feel the need to comment, that what I really admire about the data in these presentations is that they are so basic. Somehow people have scrabbled together enough funding to keep the measurements going for long enough for someone to recognise their profound importance. This is IMHO really admirable science. Goodnight.

Informa World

March 18, 2010

My son woke me up at 5:30 a.m. this morning with the charming news that he was about to be sick – a promise he fulfilled shortly thereafter. After another episode of vomitting he seemed as right as rain and we settled down to a day at home. He did his music practice and watched some ‘worthy’ television and I answered e-mails, refereed papers and tried to write a thing or two. In the middle of all this he looked over my shoulder at my computer screen and said ‘What’s that?’

What he was talking about was an e-mail from Informa World telling me of new articles available in the latest edition of the Journal of Modern Optics: Volume 57 Issue 4. What puzzled him was the titles of the articles. When we read them together they did indeed sound amazingly abstruse and jargon laden. His reaction to them really made me realise just how opaque this kind of information is for normal people. I offer them here for you complete and unexpurgated for you to form your own opinion. Enjoy 🙂

Original Articles

  • Exact quasi-soliton solutions and soliton interaction for the inhomogeneous coupled nonlinear Schrödinger equations
  • A curvelet transform approach for the fusion of MR and CT images
  • Designing of omni-directional high reflectors by using one-dimensional modified hybrid Fibonacci/Cantor band-gap structures at optical telecommunication wavelength band
  • Controlling entanglement dynamics of two qubits coupled to a common reservoir via a coherent field
  • A single-mode single-polarization monolithically silica waveguide ring resonator used in microoptic gyro
  • A new approach to the analytic soliton solutions for the variable-coefficient higher-order nonlinear Schrödinger model in inhomogeneous optical fibers
  • Effect of a spoke surface error on a phase mask in a computational imaging system
  • Omnidirectional reflection band extension using Fibonacci photonic heterostructures containing negative-index materials
  • Experimental measuring of the coherence length of a single photon generated via a degenerated optical parametric oscillator far below threshold
  • Ultrashort pulse compression by using one-dimensional inhomogeneous photonic crystal

Short Communication

  • Non-diffracting Airy beams in planar optical waveguides: a convenient method for visualization

1975

March 18, 2010
The Jackson 5 in 1975

The Jackson 5 in 1975

Remember 1975? Possibly not, but I was reminded of the summer of that year recently when my good friend from school Richard Leahy sent me a pdf of the Physics_O_level_1975 (pdf). Please feel free to download the paper and have a go. There is no doubt that it requires a level of recall and facility with formulae and abstract manipulations that go way beyond GCSE. I don’t want to go on and on about this, but these days Richard is a fair old whizz with at all kinds of brain imaging. And he was set on this road to making peoples lives better by his education. He didn’t come from a family of academics and neither did I. I don’t have any doubt at all that if we had had the kind of education being offered in schools today, it would have been impossible for us to have achieved we have. The education we had stretched us and we are failing the capable children of today if we fail to stretch our children to achieve what they can.

Take a look at some of the things he can do at his site.

West London Academy

March 18, 2010

Inside West London Academy

Inside West London Academy

Today – Wednesday 17th March – was a busy day. A day that stretched my limits. And a day that has a left me thinking.

The first part of the day was spent visiting the West London Academy to visit my old colleague Florence Wayas who is now Head of Science at the school. I gave a highly improvised version of my temperature talk to four groups of 90+ students from Years 7, 8, and 9. I found the visit very moving.

The school was architecturally beautiful. It was a real pleasure to simply to be inside such a gorgeous building. But academically the school was poor. Indeed I am sure the school barely judged itself on its academic performance. Its challenges were rather more immediate. The sessions involved students with a wide range of both abilities and disabilities – I have never been in a school which coped so seamlessly with 5 wheel chair bound students.

I talked about temperature as I have often done – and indeed hopefully on a few students my talk and the things I showed will have made an impression.  But talking with the teachers and the students certainly left an impression on me. And they made me reflect on an elitist aspect of my current views on education. For these students, whose aspirations were in general so low, the teachers spoke highly of the explicit relevance of a new AQA course they were following. For example Chemistry and Physics were taught in a module called ‘Cook’. The physics was about heat transfer, and the chemistry was about the changes that occurred during ‘cooking’. It didn’t seem to me any more than a knowledgeable teacher could add to regular lessons, but here knowledgeable teachers were thin on the ground. So it seems here the QCDA have a ‘market’ that finds their exams challenging. I still feel that there are many many students who are not fully challenged and it is important to challenge and stretch all students. But I found the work they were doing at this school slightly humbling.

And then I finished up with a presentation of a modified Protons for Breakfast talk on Global Warming. I rather messed up the talk and I really want to sort the talk out so it is the right length. However I did get a couple of experimenst into the talk and they both worked – I will describe them in a future blog. Anyway: I ended the day knackered: returning home 15 hours after I had left it.

My Friend John

March 2, 2010
John's Solar PV Panels

John's Solar PV Panels

My friend John is crazy about reducing his carbon footprint. He has a website describing the sustained endeavours of himself and his partner over many years. I have learned a great deal by talking with him.

The results

John looks at all aspects of his life, including those harder to measure aspects of life associated with consumption and transport. However his headline results concerning electricity and gas consumption are pretty impressive.

  • Over 4 years he and his partner have reduced gas AND electricity consumption by 60%
  • Including the energy they generate through solar photovoltaic panels, their net electricity consumption has fallen by 90%.

And this shows what is possible. We don’t all have to be exactly like them, but if we only paid attention to these issues there are significant saving we could all make.

And lessons for a measurement scientist

John was a scientist at NPL for much of his career, and, now enjoying the blessings of retirement and a secure pension, comes into work in an persistently good mood. And he is up for the challenges of measuring the difficult. John doesn’t mention it on his site, but he spent quite a bit of energy trying to measure how airtight his house was. The measurement is tricky, and the results equivocal – just another day at the office for a measurement scientist! The experiments involved boarding up a window except for a large circular hole to which was attached a fan with a known air throughput. If the house was completely airtight the pressure inside would plummet. From measurements of the actual pressure drop one can assess exactly how leak tight a house is. When John made these measurements his house was so leaky it was hard to measure any pressure drop at all! But fortunately I had lent him one of the most sensitive barometers in existence and he could actually rescue some data.

From his measurement adventure I was reminded of the need for ambition in what one seeks to measure; of the need to borrow and beg to get what one needs; and the need for honesty and humility in the face of unwelcome results. Everyone needs a friend like John


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