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11/11/2009 - Cosmic radiation exposure when flying
Ionactive - Cosmic Radiation vs Industrial Radiography

I know everything that needs to be said about cosmic radiation exposure when flying has probably been said. As far as the UK is concerned, any exposures received by someone ‘working' (which could be cabin crew or indeed myself when flying on business) is not covered under the UK Ionising Radiations Regulations 1999 (IRR99). IRR99 is quite specific about what is covered (i.e. a practice, work in a radon atmosphere or work involving naturally occurring radioactive materials). There are limits, conditions and exemptions for all three. Nowhere in IRR99 is there any regulation of exposures to cosmic radiation

Cosmic Radiation Exposure - Regulation

Internationally we have directives and guidance where cosmic radiation is noted. The EU Directive 96/29/Euratom (Laying down basic safety standards for the protection of health of workers and the general public against the dangers arising from ionizing radiation) does have something to say about cosmic radiation. For example it defines sources of natural radiation as  'ionizing radiation from natural terrestrial or cosmic origin' but goes on to say in Article 2 that ‘cosmic radiation prevailing at ground level' does not apply.

Whilst the directive does not consider radiation exposure to frequent flyers (I guess one can debate if they are working or not - I certainly work when I fly), it does consider exposure to Aircrew in a specific Article (Article 42 - ‘Protection of Aircrew').

In the UK this EU requirement has been translated into the ‘Air Navigation Order 2005' in Section 85 ‘Protection of air crew from cosmic radiation'. This section more or less repeats the Directive noted above and require appropriate measures to:

  • (a) assess the exposure to cosmic radiation when in flight of those air crew who are liable to be subject to cosmic radiation in excess of 1 milliSievert per year
  • (b) take into account the assessed exposure when organising work schedules with a view to reducing the doses of highly exposed air crew; and
  • (c) inform the workers of the health risks their work involves.

Item (c) above is very interesting because when I questioned some cabin crew members on a recent BA flight (including the Captain) the impression I got was ‘...told to get on with it...' ‘... in this climate, no one is going to rock the boat...', ‘...what is cosmic radiation?...'.

The order also goes on to require that for pregnant air crew members, the conditions of exposure to cosmic radiation when in flight are such that the equivalent dose to the foetus will be as low as reasonably achievable and is unlikely to exceed 1 mSv during the remainder of the pregnancy (interesting that this UK legislation uses the word achievable and not practicable, but this is an aside).

So, there is some protection mechanisms in place - but how far they are implemented in a practical sense, particularly with pressure on reducing cabin crew numbers in current economic climate, is interesting.

Cosmic Radiation Exposure - Radiation Safety Training Aid

In training and at other times we often quote ‘minutes of flying time' to be equivalent to some type of radiation exposure back on land - as if to reassure the worker or member of public that everything is fine. I do this, for example, when looking at the exposure from an airport based whole body security scanner and comparing with what you will receive in a flight once you are on your hols.

There is a lot of data out there that describes likely radiation exposure when flying. For example, the UK Department for Transport (DoT) has the following Web Publication ‘Protection of air crew from cosmic radiation: Guidance material'. However, not to take this material ‘as read' I was interested to see what I might measure during my recent flight to Scotland (Heathrow to Edinburgh airport).

Real cosmic radiation measurements at 35,000 feet 

There are a number of problems doing this which include suitability of instrumentation (i.e. measuring high energy cosmic radiation) and flight time (i.e. short so sampling time is not so good). Furthermore, with such a short flight (between 55 minutes and 1 hour 10 mins depending on direction / tail wind etc), much of the flight is ascending and descending with a relatively short duration at cruising altitude. However, the aircraft I was on (an Airbus 319 or similar) had a very nifty and detailed in-flight information display so I could check altitude and correlate with dose rate readings.

Cosmic Radiation Dose Rate  - Ground Level

The measuring device I had available for use was an EPD Mk2.3 - great for personal dosimetry but not the most ideal device in the world for this sort of experiment. I let the crew know what I was doing and dutifully took the battery out for takeoff and landing (which again does little for the measurement statistics - but there is little to measure anyway during this time at low altitude).

Dose rate on the ground was not surprisingly shown to be 0.0 μSv/h. I also had a Berthold LB124 device in my hand luggage which showed 0.05 μSv/h (about what I would expect for the London area).

When I was able start measuring on the plane the EPD still showed 0.0 μSv/h which was at about 10,000 Feet (using non SI units here - because I want to!). At about 26,000 feet the EPD showed 1μSv/h and at 35,000 feet (cruising altitude) it read 2 μSv/h.

If you look at the above DoT guidance, and accepting that radiation dose rates will vary with average solar activity & latitude etc, then my results using the EPD look a bit lower than expected. The EPD did peak at 3 μSv/h but I did not get a picture of that.

Getting up from my seat and moving to the overhead locker I turned on my Berthold LB125 portable Gamma Spectrometer. I was not able to calibrate this with its own Cs-137 source during the flight (obviously!) but had calibrated earlier in the day (at 0415 in fact). You can see from the image below that the dose rate recorded is just over 5 μSv/h (for 35,000 feet). The picture quality is very poor as I took this picture in the locker area so as not to worry the passengers!

Radiation Dose Rate at 35,000 feet - from Berthold

So, for my flight up to Scotland, and accounting for the takeoff and landing etc, I could derive an exposure of perhaps 3-5 micro Sv. The DoT guidance states 5 to 6 μSv/h effective dose at 35,000 feet for temperate latitudes and average solar activity. So, let me settle at say 4 μSv for the flight. I also had to do the journey in reverse and this took longer (tail wind in wrong direction), but assuming all the variability averages out then I can assume 4 μSv back to London as well.

So for the trip to and from Scotland I received 8 μSv. Now, regardless of the law (and specifically IRR99), I was ‘working' even if it is not recognised that I was working with ionising radiation. So where am I going with all this?

Type Testing a Radiography Bay

In a future blog entry I am going to describe a whole load of measurements that were taken around a newly built open topped industrial radiography bay. For the purposes of this blog let me just state that we popped a 370GBq (10Ci) Ir-192 in the middle of the new bay, setup for a panoramic shot using an 18mm wall thickness steel pipe, and performed a whole load of dose rate measurements around the bay at ground level and at height.

The bay was also ‘stressed' by placing the source outside the steel pipe, with and without its collimator and at various positions around the bay interior. For each of these positional changes additional dose rate measurements were taken. All the time I was monitoring the bay (using instrumentation) I was also looking at my EPD.

In general dose rates were acceptable - meeting the design constraints I had specified some months ago. However, as predicted, dose rates from sky-shine were found to be significantly above background (e.g. 4-5 μSv/h) in some places during the stress tests. This would be unacceptable for ‘enclosure radiography' on a long term basis with other employees not involved with radiography working just outside the confines of the bay. The stress tests were not ‘typical' working procedures (e.g. they simulated a collimator being left off). When this was taken into account, annual exposures to the most critical person around the bay was shown to be less than 300 micro Sv/h (a project dose constraint), with a maximum μSv-in-any-one-hour of less than 1.

The above values can be shown to be ALARP and will no doubt be acceptable to the HSE should they choose to visit the facility in the future.

Ionactive Radiation Exposure during Bay Test

This for me is where things get interesting. The tests were undertaken using site radiography conditions with all the required notifications being made. During two days of tests, where dose rates were at times significantly greater than background, my total exposure as recorded by the EPD was .... 3 μSv.

This result was not unexpected, and accounting for the bay ‘stress tests' which are not part of normal radiography work, would be lower still during routine use of the bay. So how did I achieve such a modest exposure? I did this by complying with some of the following - something every employer would expect, what the HSE would expect, and what the law expects:

  • Followed the principles of ALARP
  • Used radiation protection principles of minimising time, maximising distance and shielding
  • The testing process was risk assessed and followed local rules
  • Those operating the sources were fully qualified industrial radiographers
  • Used a variety of radiation monitors
  • And so on....

So, all credit to myself and all those involved in the project - 3 μSv for all the testing.

Then, I got back in the plane and received 4 μSv in just under an hour on the way back home

Final thoughts

So what am I saying? I am not trying to change anything or point out a significant flaw in radiation protection. However, when you look at this in black and white it does amaze me that my radiation exposure through flying is significantly more than I receive from the radiation protection related job I undertake. In the last 12 months I have flown perhaps 70 hours - this being modest compared to many business personnel. If I use the average 4 μSv /h I came up with above (based on mostly domestic flights), then that is near 300 μSv/year. That is considerably more than I receive from all the work I do for clients.

I fully accept that exposure to natural radiation and occupational exposure cannot and should not be added together. However, with respect to ‘natural radiation exposure' there is nothing quite as tangible as sitting on a plane and staring at your EPD as the dose rate increases and the total exposure clocks up over a number of flying hours. That is something you simply do not get when sitting in your house in Cornwall (where you may or may not be ‘working').

Furthermore, when talking to cabin crew a few weeks ago one of them told me ‘why worry about radiation when there is dry atmosphere, frequent time zone changes and shift work to contend with?'. This might be true - but other similar factors can also be applied to a typical nuclear / radiation worker (e.g. manual handling, shift work, work with chemicals and so on).

In my humble opinion (!) the control of radiation exposure to cabin crew is just not controllable - at least to the ‘standards' (note: I did not say limits) that are accepted in the workplace when firmly back on land. HPA data shows that the average nuclear worker in the UK receives an effective dose of < 1mSv a year. Those working in medicine receive more. Clearly those that work on long haul flights as cabin crew, spending many working hours at 35,000 feet or above, are near the top (if not at the top) of the ‘occupational exposure league table'.

We must remember that the ALARP principle in the UK requires that reasonably practicable methods are used to restrict exposure. With ALARP the ability to pay is not to be taken into account - simply that the resource spent in saving dose are proportional to the actual dose saved.

Now I think I know why the UK Air Navigation Order 2005 (as noted above) sticks with ALARA - as low as reasonably achievable , societal and economic factors being taken into account. Quite simply, with the UK nuclear industry you CAN control doses to < 1mSv for the average employee, in air transport you CANNOT control doses to a similar level without significant impact on societal and economic factors. Therefore you do not fit Cabin Crew into the IRR99 framework. Something does not seem quite right somehow..... (But it is not unexpected...)

8/11/2009 - Unintended exposure of a worker

This is taken from the IAEA event log.

The Incident (29/09/2009)


The French Nuclear Safety Authority (ASN) has rated at level 2 on INES the accidental exposure on the 29 September 2009 of a radiographer of the ABC Company (HORUS holding) during a welding test using gamma radiography at the Flamanville NPP operated by EDF. Through violation of the working procedures, the worker entered the controlled area and remained in during several seconds while the high activity source was not yet in its safe store position.ASN was first quickly informed by EDF. Later on, ABC declared the event as "significant incident" according to French technical guidelines.

The worker received a dose of 5 mSv due to this incident. The medical officer in charge of monitoring the worker was informed. He did not consider it necessary to conduct a medical examination after the incident.

This accidental exposure has been caused by the non-compliance with basic radiation protection procedures. Based on a misinterpretation of the actions performed by the radiographer operating the radioactive source, the exposed worker, who was observing from the distance, believed the exposure was completed. He then entered the controlled area while the radiation source was still exposed without waiting for the formal confirmation of the end of operations and without any survey meter to check the end of the exposure.

A joint inspection by ASN and the Labour Inspectorate was carried out on 29 October 2009. Deviations from radiation protection approved standards were confirmed. The corrective actions implemented by ABC and Horus were considered as satisfactory. ASN will ensure the follow-up of the implementation of these actions.

ASN has rated this incident at level 2 on INES (October 2008 version) due to the non respect of the comprehensive set of safety rules to access the controlled area which has led to a significant unintended exposure of a worker.

The device used is a gamma radiographer containing a high activity radioactive source of Ir 192 (1,73 TBq)

The incident log can be read at the following link: IAEA News (You may need to log in as a guest).

Ionactive Comment

As always we provide analysis for general information and interest only - we may not always have all the relevant facts.

Let us assume that ‘several seconds' is 3 or more - so let that be 3 seconds. Assuming the 5mSv dose suggested above is ‘whole body' (effective dose) then that is quite a considerable exposure based on the limited duration. It is true that the dose rate contributing to the entire exposure is unlikely to have been constant throughout as the worker may have entered the area after the exposure had commenced (so dose rates would have increased with decreasing distance to the source, and decreased if he was moving away from the source).

Since we do not have detailed information we will assume that the worker was static during the exposure. The dose rate from a point source of Ir-192, of activity 1.73 TBq, will be in the order of 202 mSv/h at 1m. This assumes the source is not collimated or otherwise shielded. The dose rate per second is therefore about 0.056 mSv/s - so not enough to produce the exposure in the individual over the understood exposure duration (at distances of 1m or more).

For an exposure of 5mSv in about 3 seconds, a dose rate of around 1.67mSv/s would be required (6000 mSv/h). This implies that the distance from the exposed source would be somewhat less than 20 cm (18.3cm actually). This is shown in the graphic below.

The area of interest is shown in this expanded graphic:

Therefore this implies (noting our assumptions above) that the individual would have been very close to the source indeed - probably right over the source projector or within the region of the actual object being radiographed.

7/11/2009 - Radiation Risk Calculator

Radiation Risk Calculator

Came across this interesting site located at

This site claims to provide a risk calculation service which will determine your additional cancer risk, i.e. over and above that risk that you receive from exposures from everyday life (cosmic, radon etc), from a number of medical diagnostic procedures. In fact the site goes further than just x-rays because it also considers a number of nuclear medicine procedures (i.e. whole body PET scan).

I have not verified the data, and comparisons with everyday exposures are from a US perspective (but references are given for you to explore if you wish). For example, the site states that average US exposure is 6.2 mSv/y (all sources) whereas the UK is around 2.7mSv/year (UK Ref: HPA-RPD-001) - therefore you need to take that into account when looking at risk comparisons.

Taking a quote directly from the site is informative:

While the need for education in this area has clearly been established, there are no widely available resources that provide information to both patients and health care providers about the increased risk of cancer from medical imaging. is an educational website that focuses on estimating this risk. One of the site's main features is a web based calculator that allows users to track their imaging history and estimate their personal risk, while providing answers to frequently asked questions.

The site plays is quite straight and there is no particular attempt to either provide reassurance or enhance concern (which is good). We would emphasise (to anyone who tries out this resource) that the whole point of using any of these diagnostic procedures is to ensure the benefit of the procedure clearly outweighs the risks. So the early detection of breast cancer using mammograms is still shown to save more lives when compared to 'lives lost' through cancer which might be attributed to the actual radiation exposure.

Calculation Method

The calculation methodology adopted appears to be fairly standard and relies on published data in the literature - in other words the calculator is not creating risk values from first principles, rather it is a database of pre-defined values which are selected on the basis of your inputs (e.g. age, type of procedure etc). The key reference used is: Biological Effects of Ionizing Radiation (BEIR) VII Phase 2 Report - typical data is shown in the table below (from

The above data is then converted into a % attributable risk of cancer for males and females against age. As one will expect the risk tends to be higher in the young where there are more years ahead of them (to realise a potential radiation induced cancer).

The calculator also uses data from ‘Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog (Mettler FA)'. Some typical data from this publication is shown below (the link in this paragraph will take you to the actual report).

A risk Calculation

Using the risk calculator is straight forward. In the example below I have selected a chest x-ray, selected gender and entered age and number of scans, and then pressed calculate. You can also build an x-ray risk report by adding the risks from a number of separate procedures together.

Final Comments

Overall this is a nice piece of online resource. Like everything on the web, one must be cautious when using any online data or information. The right thing to do is to question your medical practitioner about any medical radiation exposure you are about to receive - and get them to explain the risks to you - for your own specific case.

However, talking to family members and friends who have undergone such procedures, does reveal that many practitioners (radiologists / x-ray operators) are not always geared up to explain the key concepts. It is not that they do not know the answer, it is more likely that they are not often asked the question and so do not have a strategy to answer simply.

7/11/2009 - Know your Schrodinger from your Bohr ?
Ionactive Consulting Radiation Protection Training Resource - C-14

Or your Dirac from your Curie?

Solvay Physics Conference of 1927

Well the Solvay Physics Conference of 1927 gives you insight into to some of the most famous scientists of that period. The resource below, brought to you by, provides a fascinating near 3 minute ‘home video' taken by Irving Langmuir.

Some of those shown in the video include: Ervin Schrodinger, Niels Bohr, Werner Heisenberg, Auguste Piccard, Paul Dirac, Max Born, Wolfgang Pauli, Louis de Broglie, Marie Curie, Hendrik Lorentz and Albert Einstein.

Apparently it was at this time that Einstein was quoted as saying "God does not play dice" in response to Max Born's statistical interpretation of the wave function (the Bohr model of the atom, itself a quantum physics-based modification of the Rutherford model, would never be quite the same!).

It is great to see such resource available for the masses, and meets Ionactive's objective of providing free radiation Protection / Physics online.

6/11/2009 - X-rays 'top scientific invention'

Ionactive Training Resource - X-ray Tube

Earlier on in the week we spotted that the public had voted the X-ray machine as the best invention, this being ahead of the Apollo 10 space capsule and Stephenson's Rocket. The story came to light on the BBC website and can be found here.

We now have our x-ray tube animation on YouTube which can be accessed directly below.

Ionactive X-Ray Tube Training Resource

This resource is also available for playback via a WMV file which can be found on our Radiation Protection Video (x-ray) page.

The resource looks at the major parts of the x-ray tube and considers Bremsstrahlung:

Ionactive Training Resource: Bremsstrahlung

 ... and Characteristic x-rays:

Ionactive Training Resource: Characteristic x-ray

It might also interest you to know what other inventions were in the top 10. The list was as follows:

  • 1st place - X-ray machines
  • 2nd place - Penicillin
  • 3rd place - DNA double helix
  • 4th place - Apollo 10 capsule
  • 5th place - V2 Rocket Engine
  • 6th place - Stephenson's Rocket
  • 7th place - Pilot ACE Computer
  • 8th place - Steam Engine
  • 9th place - Model T Ford
  • 10th place - Electric Telegraph 

Other X-ray Tube Resource

Please note: the resource below is provided for your interest only - Ionactive does not endorse this material.

For some much older x-ray tube resource, but no less useful, why not watch this 1940's X Ray Physics Documentary By William D Coolidge! This should play directly from the player below.

I would love to have an ion chamber radiation dose rate monitor in William D Coolidge's lab - might be quite interesting!

It is then time for a 'do not try this at home' (and I mean it). Check out this chap below measuring doserates from an x-ray tube - neither sensible or clever under the circumstances illustrated, but interesting none the less.

I could not quite make out the scale in the above video, but I think the instrument read 1R/h at one point. For our purposes that would give you an ambient dose equivalent of something near 10 mSv/h - not a trivial dose rate by any means!!

And finally, if you cannot find an x-ray machine it appears that you just go and make one yourself. Please note I do not condone this at all, what you see in this video below is potentially dangerous if not fatal - and that is from high voltage as well as radiation. However, I kind of get the impression that this chap knows what he is doing (even though I believe it to be wrong - there are no obvious safety interlocks for example). If I read the monitor correctly then the dose rate at the point of measure is 50R / h (for our purposes about 0.5 Sv/h).

That is all folks!

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This is the company blog of Ionactive Consulting Limited, a Radiation Protection Adviser consultancy. Visit here often to read our views on radiation protection and related matters. You can contact our director and RPA directly at

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