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5/12/2009 - Marwell Wildlife Park

The Ramsay Family!

Went to Marwell Wildlife Park today with the family. Alex (my older Son) is almost six so this was an early birthday treat.

Marwell, located near the south coast (about 10 miles from Southampton) is an excellent treat for all the family.There are loads of animals to see (obviously) but also a road train and small gauge railway to ride (see above)!

My younger son Ben really wanted to see ‘Melman' from ‘Madagascar' so we did our best for him!

Alex wanted to see the Tiger so we got a good view of him (I am glad the fence was in place!).

Here is Ben with the train - I think he wanted to take it home!

The 'Boys'

Now for some of my favourite creatures seen at Marwell!

And this ..

And finally this (kinda how I feel when deep into bunker shielding calculations).

27/11/2009 - Worker Overexposure / Public Overexposure

This is taken from the IAEA event log.

Two incidents for you to consider this time.

The Incident - unnoticed public exposure (27/10/2009)


(Peru). In the date Octobre 27th, while a radiography operation was being carried out a member of the public entered the controlled area and stayed at 3 meters of the radiation source for 3 minutes and then left the place, as he was warned by another worker.

The radioactive source was Ir-192 having 171 GBq and the dose recieved by the member of public was 0.12 mSv. The oepration was stoped and a report was sent to the Technical Office for National Authority (Regulatory Body). Currently an investigation is being followed by regulatory body. The event has been preliminary rated Level 0.

Ionactive Comment

Ok, so 0.12 mSv is not a significant exposure. On a recent trip to Scotland (flying) I recorded 5.5 μSv/h at 35,000 feet. So the public exposure is equivalent to perhaps 22 hours of flying. However, that is not really the point here - the control of the work area is appalling. Whilst the resulting exposure was small it could have been so much worse. I'm amazed that someone could have remained in the exposure area for 3 minutes before anyone realised that anything was wrong.

Suppose the member of pubic had been only 1m from the source - their exposure would have then been more like 1mSv (the public dose limit in most parts of the world). Let us take that further, suppose the member of public had been only 10cm from the source - then we are looking at around 108 mSv - way over employee annual occupational dose limits (which are set at 20 mSv per year in most parts of the world, and 50mSv in some states in the US). This assumes that the exposure time was still three minutes.

And it gets worse ....

The Incident - worker overexposure (12/11/2009)


(US). During industrial radiography operations, a radiographer approached the camera, believing the source to be in the shielded position. The radiographer did not have his survey meter, but was wearing an alarming ratemeter and a pocket dosimeter. The radiographer was attempting to put the safety plug on the end of the camera when he realized the source was not in the shielded position.

The radiographer did not contact the Radiation Safety Officer or secure the area, as procedure required, but instead, with the assistance of another radiographer, he put the source back into the shielded position.

Both radiographers' personal monitors were sent for emergency processing. One received a whole body dose of 55.7 mSv (5.57 rem) for November, which made his annual occupational dose 67 mSv (6.67 rem). The other radiographer did not exceed the occupational dose limit. The dose limit is 50 mSv (5 rem).

Ionactive Comment

We know less about this incident (e.g. source type, distance from source and exposure time). However, like the first example involving public exposure, there seems to be a break down in procedural control.

We have been working with a company recently on the design and build of a number of radiography bays - this engineered approach to safety must always be the goal to achieve. What the two examples show are the dangers of Site Radiography - here you are only relying on procedures and local shielding to restrict exposure. That said, suitably qualified and experienced persons should have no trouble in undertaking site radiography in a safe manner - we work with industrial radiographers who do this every day - their work practices are exemplary.

So what has gone wrong here? - the example show that these incidents are not restricted to certain areas of the world - Peru and the US both have issues (and I am not discounting the UK either).

19/11/2009 - The Gamma Ray Constant

Ionactive Gamma Ray Constant Resource

Been a mad few days - I wanted to feature this earlier but had no time (but it has been uploaded for a few days). This is the latest Ionactive resource produced for us by the ever innovative Grallator Limited. Unlike most of our resource which is designed to be accessible to the masses (in terms of no pre-knowledge assumed), this resource is really designed to be a little more thought provoking - perhaps for those that already practice Health Physics.

Gamma Ray Constant Expression

I remember from way back using an equation of the following form (I think this was from my MSc in Radiation Protection):

The terms in the above expression have the following meaning:

  • Dose Rate - μSv/h
  • M - is the activity of the source (MBq)
  • E - is the energy of photons (MeV)
  • f - is the fraction of total photons of a particular energy E
  • r2 - accounts for the inverse square law (m)
  • 6 - is the constant that wraps up everything together

A few questions can then arise:

  • Is this expression any good - how far does it meet reality?
  • How does the result compare to computer models or simulation
  • If there are differences, how do they impact on real-world dose rate predictions in the work place
  • What is the dose rate calculated in (air / tissue / combination of both)?
  • What is the distance r - from centre of source to surface or middle of measurement point?
  • Does any of the above really matter?

This richly animated and colourful resource aims to answer some of the above. In time this resource will probably feature on our You Tube Channel: IonactiveConsulting

Until then you can watch it on our own video player in our resources section:


Gamma Ray Constant -  Radiation Protection Video Resource


Some screen shots


Absorption and the inverse square law

13/11/2009 - Overexposure of Radiographer

This is taken from the IAEA event log.

The Incident (26/05/2009)


On May 26, 2009 after performing RT with Ir-192 source of 60 Ci radiographer noted that all used films were highly exposed. The unused films were also found exposed. The source guide tube was inspected during which the source assembly fell on the ground.

The radiographer picked up the source assembly by hand and put it back into the projector. Erythema appeared on his both hands in three days after the event. In two weeks, blistering appeared on hands which developed into open wounds.

The incident was reported to Pakistan Nuclear Regulatory Authority (PNRA) on July 12, 2009. Inspectors from PNRA visited the radiographer on July 14, 2009 and found healing wounds and black spots on his palm and finger tips. The victim has been sent for further medical investigation and treatment. The dose to the hands (extremities) was estimated to be between 25~30 Sv.

Investigations revealed that the worker violated the procedures under work pressure and safety tools were not properly used. In addition, the radiographer also did not use personal dosimeter and radiation monitor during the activity. Further the incident occurred due to faulty gamma projector and drive cable which caused the source to disconnect and stuck in the guide tube.

Weaknesses were observed in management oversight, work supervision and safety culture of the organization.
Work stoppage notice was served immediately to the company. Further enforcement actions are being taken against the company involved in the incident.

Due to overexposure of the worker resulting in acute health effects, the incident is rated at level 3.

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

Ionactive Comment

It is not for us to pass judgement on the case illustrated above without knowing the full details. However, the whole point of posting these incident reports is to understand what might have happened and generally help to stop this occurring again by understanding the issues.

The catalogue of errors is quite amazing leading to deterministic effects to the hands which are clearly severe. The report does not comment on the whole body dose but that would also be significant (see similar blog entry below).
The individual picked up the source assembly by hand. This is such a ‘no no' and illustrates a complete lack of training and awareness of what he was working with. Whilst the lack of monitoring equipment and dosimetry is bad enough, as is the noted lack of management and work supervision, the fact that the individual could not practice the basic principles of time, distance and shielding is appalling.

The source was 60Ci (2.22 TBq) of Ir-192 (a medium energy gamma emitter). Dose rates from this source would be in the order of 260 mSv/h at 1m and in the region of 2600 Sv/h at 1cm (this is an approximation as it is difficult to predict exposures accurately very close to the source). Assuming his hands were exposed to a dose rate of this magnitude then we can see that 30Sv to the hand would be delivered in about 42 seconds. As it happens since the hands were actually touching the source the localised dose rate would be even higher, so it is quite possible that the 30Sv equivalent dose could be delivered in a matter of seconds. The threshold for deterministic effects to the hands, i.e. onset of reddening of the skin, is about 3 Gy (3 Sv equivalent dose for gamma rays).

If we assume that individual took 10 seconds to put the source back on the projector, and further assume that this was the duration of ‘significant' whole body exposure, then the whole body dose (assuming average distance between source and trunk of the body of 30cm) would be in the region of 8mSv. I think this is probably an underestimate - but in any case this dose is insignificant compared to the clinically observed harm from the localised hand exposure.

Share good practice

We work with a number of industrial radiography firms in the UK - they undertake both site radiography and enclosure radiography. Some of them work with sources of this type - and some work with even higher activity sources and use radioactive sources of higher energy (e.g. Co-60). In all cases they are well trained, highly experienced and want to work safely. Industrial radiography has got itself a bad name in the past, and the event described above does nothing to dispel that - in my experience I have seen nothing but best practice - let us hope that this can be shared more widely to avoid these incidents altogether.

Pressure of work is no excuse.

Radiation Injury

The picture that follows is from the IAEA. It shows a deterministic injury to the hand of someone who picked up and held an Ir-192 source. It is not a picture of the injury that is described above - it does however clearly show you what can happen.

The above picture shows a severe radiation injury to the hand of an individual involved in an Algerian accident who picked up a lost 925 GBq (25 Ci) Ir-192 source in 1978. Note that this source is only 42% of the activity of the source in the above noted incident.

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...)

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