10/3/2011 - James L Acord – Nuclear Artist, my thoughts and memories
It was with some shock that I noted yesterday on my Twitter feed that James L Acord (Jim) had died in January 2011. It is beyond the scope of my writing skills, my memories and even my ‘right' to describe in words what this man was about. Indeed, I only met him on a small number of occasions during 1998 when he was artist in residence at Imperial College London (I was at that time the Radiation Protection Adviser - RPA for the College). Furthermore, whilst I met him a couple more times in the early 2000's when he was working on an artistic project to transmute radioactive Technetium to stable Ruthenium (an artistic statement perhaps on alchemy, the beauty of nuclear process and perhaps the ultimate if technically challenging goal to deal with nuclear waste), I had really lost touch with him.
So who was Jim?
I think ultimately that question is best left by visiting the following website: http://jameslacord.com . I understand this website has been set up in his memory and provides a growing knowledge base of who he was and what he was about.
Perhaps in summary, the following could be said of Jim. Jim was an artist, a sculpturer who was also fascinated by the whole process of the nuclear age. Indeed, in his mind he was very clear that art and science were very similar in explaining concept and representing the past, present and future. In one talk I attended he showed a picture of the THORP facility (if I recall correctly) at Sellafield and commented on the artistic beauty of the engineering (even the colour coordination of the bright yellow crane against the background of the blue cherenkov radiation from the ponds). He apparently began to think about nuclear process and specifically uranium when carving granite. He moved on to playing around with fiestaware which was a type of bright orange pottery incorporating a uranium glaze (which gave it its colour). Since he wanted to combine his art with radioactive materials he planned on extracting the uranium (panning if you will), but this caused issues with the authorities in the US.
Jim gets a license to hold hold / use radioactive materials in the US
It is at this point that his credibility in nuclear circles was elevated massively because having applied for a personal license in the US to hold and work with radioactive materials (as a ‘person' not a legal entity), he had to pass all the exams. He studied all the required material, and from my memory could talk competently about nuclear process, fission - and he really knew the physics, and could explain and write it down. Indeed, art never playing second best to the science, he would comment on the artistic beauty of the equations and used this as part of his art and talks.
Jim - the talks!
Jim was a great talker and a great lecturer. I have come across the following site where you can watch four videos as part of the The Influencers 2010 series (http://theinfluencers.org/james-acord/video/1 ). I have to say, with the greatest respect to Jim and all of his friends that might read this blog that my memory of his presentations has somewhat faded. However, looking at the videos (and I really do encourage you to watch them), he does seem a little more fragile and a little less confident than I remember him - however, I met him 10 years before this video series so who I am I to criticise!
Notwithstanding my previous comment, they are made with genuine affection, all the hallmarks which make him such a fantastic speaker and his clear ability to describe his life history and aims and objectives are clearly present.
Meeting Jim at Imperial College
I met Jim at Imperial College during 1998 when he was an artist is residence and working with the Arts Catalyst - the work he did can be found at this website http://www.artscatalyst.org/projects/detail/atomic_london . I was phoned up one day, Jim being on the other end of the phone, he said ‘ Hi, I understand you are the radiation officer for Imperial College, we need to talk! '. Not knowing much about the guy I went over to see him in the physics block of the College - shock hands and he began to explain what he wanted to do (much of which is described in the above video). He turned around to get a Geiger counter out of his bag and it was at this point I noticed the tattooed number on his neck. Not knowing what this was at the time (it was actually his US radioactive materials license), I thought I was sharing the room with a US convict! That feeling soon passed and I spent several sessions with him trying to understand what he was about.
Art and science
I have to concede that in the early days of our meetings I am not sure that I ‘got it' - I have never been particularly arty. However, what I did soon realise and accept, was the battle that he was facing - convincing the authorities that what he was doing was not a frivolous use of ionising radiation. I think I probably still have some reservations about what he was doing - but not because he was not competent to do it, but because I needed (as a RPA) to play things by the book and the whole concept of Justification (for use of ionising radiation) did not extend to art. Well, to be more exact, you can use ionising radiation perhaps as part of art (e.g. if you use an x-ray image that has been taken and apply the resulting image in an arty way), but using radioactive materials in art was not justified.
That said, and still playing things by the book, I very much respected what he was trying to do - I felt then that it was not frivolous, but it still did not fit in with the expectations of the regulators or regulatory framework. As you will note below, he began to work outside of the regulatory framework out of frustration - I think this is a pity.
Transmutation using a neutron source
In the video he speaks of wanting to use the Imperial College reactor to undertake transmutation. He says that he was promised its use and the ‘authorities' backed down. I think it is more than likely that those responsible for the facility at the time would never have agreed to such a use (even if they ‘got' his concepts), rather I suspect someone else at the institution probably made this ‘promise' but with no actual influence or control over use of the reactor (and therefore they probably should not have made the promise in the first place). Anyway, I digress.
It is sad, but perhaps inevitable that Jim turned to using the Am-241 out of smoke detectors in the US because his license had been revoked (I believe the fees and compliance work to keep that license going had become too much for him). In the video there is an image of him smashing the casing of the detector to extract the source (the source looks like it is intact) - I think this image is a a pity but typically has his hallmark arty tones - (and makes a statement about his frustrations perhaps?).
However, what is interesting is that he wanted to build a neutron generator to make that transmutation - if now only symbolically because any resulting neutron flux would be so low as to be practically useless. He used the Am-241 to provide alpha particles, emeralds (which are rich in Beryllium and so would produce an alpha-n reaction) to produce neutrons and beeswax to moderate the neutrons to thermal energies. This was never in his mind (as far as I know) when I met him as he was still hopeful that some entity would give him access to a neutron source (i.e. a reactor or accelerator). He claims indeed to have produced some plutonium from this set-up (which in theory is possible if looking at this from an atomic level).
Our chats about life and the nuclear age
However, what he did after we met is in some senses less important than what we discussed during our meetings. We took several long walks into Knightsbridge, found a nice coffee shop and would chew the fat about the nuclear age, politics, art and science. What was very clear is that he, perhaps unlike my typical (and perhaps wrong?) view of the art world, was pro-nuclear for the right reasons. Even the artistic statements he wanted to make about the Hanford site in the US, and the fact that this site would be ‘contaminated for 1000's of years', were not said in disgust, but rather accepting the natural consequence of the early nuclear age. This is then reflected in his views on transmutation - dealing with radioactive waste.
However, I think the biggest influence that Jim had on me has to some extent been illustrated in my own website, and perhaps some of my own training styles and methods. Certainly when I started Ionactive, and this website, the ‘nuclear sites' were ‘serious', ‘blue and grey', perhaps dark and mysterious to some. I use the phrase ‘nuclear sites' in both its contexts - i.e. physical nuclear plant behind security fences, and the websites that are also related to nuclear matters. Therefore when you look around www.ionactive.co.uk you see brightness, yellow (!), a radiation protection blog that talks about curry (I do have a life outside radiation protection), the training of the Police / Fire Service in CBRN matters by someone ‘outside the establishment' and so on.
I think circumstances after 9/11 did not help what Jim wanted to do - rightly so control of radioactive materials, their security and justification for use have been tightened up. He was therefore facing an ever uphill struggle to complete his mission. Some of his followers talk about his battle with the bureaucratic processes, as if those processes were unjust. I think they are wrong - they are there for a reason - health, safety, environment, security - does robust mean bureaucratic?
Final thoughts ...
Make what you will of James L Acord - there is much information available on the web and in the links provided above. I found him an incredibly friendly, interesting and engaging person - it was a pleasure to meet him, if only for such a short period of time some 10 years ago.
7/3/2011 - Overexposure to Radiation Worker
This is taken from the IAEA event log.
Overexposure to Radiation Worker (US)
On January 13, 2011, the licensee received a dosimetry report which stated that one of their employees received a year-to-date exposure of 55 mSv (5.5 rem) which was above the statutory limit of 50 mSv (5 rem). The overexposure was received in December 2010 during the emergency repair of a cyclotron unit over a period of several days.
However, the affected employee's real-time dosimeter indicated a much lesser exposure, calling into question the measurement indicated on the permanent dosimeter. Massachusetts subsequently performed an onsite inspection in February 2011 and determined that the affected employee did receive an exposure of 55 mSv (5.5 rem).
The licensee attributes the overexposure to misinterpretation of existing policy which restricts workers when year-to-date exposures approach limits and over-reliance on real-time dosimeters. The licensee implemented several corrective actions to include application of administrative correction factors to readings of job-specific dosimeters to obtain more conservative real time results; modifying the permanent dosimeter exchange frequency to obtain more current year-to-date exposure totals; and revision to existing policy.
The affected employee had been temporarily removed from potentially high exposure operations during the licensee's investigation, and was re-instated on March 3, 2011.
The incident log for the above event can be read at the following link: IAEA News (You may need to log in as a guest).
As always we do not know all the details in this case. My only comment here is where was ‘ALARP' (as low as reasonably practicable) - or with respect to ionising radiation work in the US - ALARA (as low as reasonably achievable). The following part of the above report is interesting: ‘misinterpretation of existing policy which restricts workers when year-to-date exposures approach limits'. This may well be the case, but it might imply that ‘working up to limits' is acceptable or normal practice perhaps? In the UK you can be found in contravention of radiation protection legislation even when no dose limit has been breached - if it is shown that you did not follow the ALARP concept to restrict exposure. This is partly achieved by using dose constraints which are set far below the limit and are meant to be challenging. It appears that a similar procedure failed in the case highlighted.
I should add that I personally feel that in some cases the concept of ALARP in the UK is taken far beyond its remit - that is, that ‘acceptable doses' (perhaps as accepted by the regulators or members of the public) are far lower than the ALARP concept would require (disproportionally, so that doses are within the negligible region and not the ALARP region).
Finally, it is also worth noting that the effective whole body dose limit in Boston (US) is 50mSv/year (5rem / year). In most of the rest of the world the effective whole body dose limit is now 20mSv/year (as recommend by the International Commission on Radiological Protection - ICRP). There is scope in the ICRP recommendations for up to 50mSv/year, but that the 5 year average dose does not exceed 100mSv.
6/3/2011 - A beta beef curry
OK, a quick blog entry here (I have to get on with part 4 of the RDD article), but thought I would just drop this curry into the mix: a ‘beta beef curry’ (get it??).
This was going to be made with lamb – but the shop had run out so I changed the meat to beef (which sounded more in keeping with the ‘beta’ too). In making the change I decided to buy a piece of brisket beef joint. Your mum, or grandmother, will tell you that brisket is used for pot roast – or in any case with a very slow cooking method. I thought I would try this cut of meat in a curry – also employing a long period of cooking. I think the results are great – and it is good value too, a 500g piece of brisket beef was about £4.
You have to spend a bit of time preparing the beef. Removing the fat layer is a bit of a pain but necessary. You need a really sharp knife so do be careful (keep the cobra larger for later, after this process is complete). Once the fat is removed (there will be a little wastage) you then need to cut the joint into bite size pieces - ensuring that you cut across the grain.
Next you need to marinade the meat in the following. To do this just bung the following ingredients into a plastic dish. You will note there is no ginger or tomatoes in this recipe; it indeed has more of a Caribbean ambience, particularly with the Allspice.
1 Tablespoon of oil
2 Chopped onions
2 Tablespoon of medium curry powder
3 Bay Leaf (I used dried)
A large handful of Lemon Thyme.
1 Teaspoon of Allspice (this took about 6 Allspice which I then ground to a powder)
2 Tablespoon of crushed garlic
You then add the meat and give it a really good stir.
I then put the lid on, gave it a good shake and left in the fridge. I left it two hours, but I guess that overnight would be even better.
You then get a pan, bung the meat and all the ingredients in and fry for about 5 minutes – warning – the smell will be heavenly but powerful! During the 5 minutes drop in some chopped mushrooms and some chopped green chilli (I used about 2 tablespoon of chopped chilli).
Then pour in 500 ml of vegetable stock – I cheated and bought some nice stuff from Waitrose (I saved on my meat after all), but you could use a stock cube and water.
You then bring to the boil, turn down to simmer and then put a tight lid on the pan.
You now need to let that cook for 2 hours – checking every now and again to ensure nothing is burning, and adding a little liquid if you need. What you will find during this process is that the liquid will thicken and become darker. Towards the end of the cooking drop in some chopped yellow pepper (or whatever else you fancy!).
I served mine with some couscous rather than rice (see top picture).
Tip: after about 1.5 hours check the meat – it should start to become tender. After the 2 hours the meat should be ‘melt in the mouth’ – seriously, it will be the best beef you have tasted.
So there you have a ‘beta beef curry’.
19/2/2011 - Radiological Dispersal Device (Dirty Bomb) – notes for Media and Public (3 of 4)
Dirty Bomb - dispersal of radioactive material.
In part 1 of this blog series we explored the concept of external and internal radiation hazards. We looked at the various factors which affect the magnitude and significance of these effects (particle size, wind, chemical form etc). In part 2 we looked at radioactive source material (Po-210, Cs-137, Am-241, Co-60 etc) and how these might be used to ‘deliver their dose'. We looked at the form of these materials (e.g. metal Co-60 vs. powdered Cs-137) and then explored in basic terms the structure of older sources and more modern types. Finally, accepting that Cs-137 might be the radioactive source material of choice (due to its potential availability, form, and beta / gamma radiations), we looked at some external radiation dose rate properties of a 1TBq source. We discovered that a 1TBq source is not easy to work with, impractical to shield (if you want your dispersion), and not that easy to smuggle into the country (given that it could be ‘seen' be sensitive detectors many m's away).
In part 3 we now look at two scenarios of what might happen if radioactive material was used in an explosive device - a Radiological Dispersal Device (RDD) - or ‘dirty bomb'. The animations you are about to see below are for illustration only; whilst they do show some specific effects (e.g. ballistic effect, wind drift) they are not intended to be an accurate simulation. Rather, they are used to illustrate the key issue of ‘dispersion' (or lack off). What we will then do is make some reasonable illustrative assumptions about activity spread which we can use in part 4, to provide some dose estimates for various groups that might be exposed.
Co-60 RDD Device (or other non-dispersible radioactive material).
The first device uses a 1TBq Co-60 radioactive source. You will note that this source is made of solid cobalt-60 metal which is then encapsulated in steel. As you might imagine this is unlikely to be dispersed with explosive material, instead it will probably fragment into pieces. In fact, we believe that this is the likely result for most modern sources which have ‘Special Form' status (constructed to rigorous ISO standards). So this animation, whilst showing Co-60, could be illustrative of much of the likely radioactive source material available for a RDD.
As you see, the source fragments into pieces and behaves as expected - the source pieces do not ‘float around' they quickly fall back to the ground (i.e. the motion is ballistic). In a real event the size of the fragments and their distribution will be unknown until it occurs, for the purposes of this blog entry we are going to assume that each piece has the same size - therefore it will have the same activity. Seven fragments are observed and these will therefore be assumed to have an activity of 142 GBq (i.e. 1/7 of 1TBq). Most pieces have fallen within 10m of the blast event, with perhaps one piece reaching 20m from the event.
What is very important to note is that this radioactive material is now unlikely to move around - it will not be blown around by the wind, it will not be dissolved in rain water - what you have in effect now is a distribution of 7 sources in an area of perhaps 1km2. Clearly anyone in the vicinity of the blast is going to be badly injured (or worse). However, once this event has occurred the time old radiation protection principles of TIME (minimise), DISTANCE (maximise) and SHIELDING (use if possible) will be all that is needed in the early days to minimise exposure from these small individual sources. We will look at some likely figures in Part 4.
Cs-137 Powder RDD Device (or other dispersible radioactive material).
This device uses a 1TBq Cs-137 radioactive source which comprises CsCl with the physical attributes of a talc powder. In all likelihood this material would still be encapsulated and therefore its dispersion would be mitigated to some degree if blown up. However, for the purposes of the following animation and discussion we assume that significant dispersion will occur. Whilst we are considering Cs-137, the animation applies to any radioactive material that has the physical properties leading to a dispersive release.
This animation clearly shows dispersion. The radioactive material is dragged up by the fire plume, the large air drag on the particles then carries same far (via the wind). Clearly this animation has to make a number of assumptions regarding particle size, wind speed, direction, settling and so on
Some technical considerations.
If you are interested in the maths then please visit our Technical Health Physics Papers - The Mathematics of Radiation Protection. Here, Dr Chris Robbins of Grallator Limited (who has created these fabulous animations for us), discusses radioactive particle transport mathematics. The paper for many will be quite complicated (unless you love your maths) but it does provide some interesting conclusions. For example the paper discusses references that assume that 90% of the original source material might be liberated with a particle size distribution ranging from 1 micron to 150 micron (with the most probable being 100). The smallest size particles can then remain suspended for several minutes (where they are carried far away), whilst the most probable sized particles settle out in about a second (and hence are not dispersed far from the event). In the paper Dr Robbins notes that for the most probable size (100 micron), the likely dispersal range is approximately 40m (with no wind), whilst respirable sized particles (< 10 micron) are likely to settle close by (due to viscous drag effects). However he notes that for a 1m/s wind, respirable particles could travel much further (i.e. 2 km or more). It is important to note that Chris also acknowledges the many assumptions made and how a much more rigorous mathematical approach could be taken (i.e. looking at fluid dynamics, buoyant plume effects and resuspension).
If the above more technical description is of interest then please do go and read the paper by Grallator. Also, why not visit the sites run by Chris and see what he can do for you?
For now we will simplify this all down to some gross assumptions, which do not have the same mathematical rigor, but can give as some dose assessment figures to discuss in part 4 of this blog series.
Data for use in RDD Blog part 4
We will consider that all the activity is made ‘available' for exposure for a number of different scenarios - the main two being ‘ground contamination' (where an external exposure can occur from walking around the contaminated land), and ‘airborne' contamination where internal exposure can occur from inhalation, and external radiation exposure can occur from ‘cloud shine' (i.e. where the body is immersed in a cloud of airborne radioactive material).
For the case of Cs-137, we will consider that activity has only travelled 100m from the event before all is ‘available' for exposure. We will also consider that at this point the activity spread is uniform from the event to the 100m boundary. This is clearly a significant simplification which leads to over and under estimates of exposure - but it is necessary to avoid the otherwise involved mathematics (which has been avoided in this blog article).
It is further considered that the wind has carried the contamination to the East (as shown in the animation) and that if that circular area were seen from above (31400 m2), then a ¼ segment of this - in the direction of the wind - has been contaminated (about 800 m2). Unlike the animation we are going to consider that the radioactive material is all now available near ground level. So in effect, we have taken a small physical mass of Cs-137 powder (10's of g), with an activity of 1TBq, and distributed this in various ways into an area of 800 m2. Again, a gross simplification, but good enough for what this blog article wants to achieve.
So, there we have our two incident types: one involves a fragmented Co-60 source; the other involves the dispersion of Cs-137 powder over an area of 800 m2. In part 4 we will use this basic data to make some dose predictions. By now you may already be considering the external dose rates from the dispersed Cs-137. Remember the dose rate at 10cm from the 1TBq Cs-137 source was 7600 mSv/h. Without any maths at all (!) it is clear to see that external dose rates are going to be considerably less than this at any point from the event - certainly nowhere near dose rates that would lead to early radiation effects - even after several hours' exposure. Indeed, the better the dispersion the less the dose rate will be at any given point. Internal radiation hazards via inhalation or ingestion are a different matter - but before part 4 arrives consider the following for inhaled Cs-137 : 100,000Bq for an effective whole body dose of near 1mSv (approximately!). Now consider if you think an intake of 100,000 Bq is realistic given the dispersion just considered above !!
Part 4 to follow soon.
18/2/2011 - Radiological Dispersal Device (Dirty Bomb) – notes for Media and Public (2 of 4)
Likely sources (and why most are not good)
Ok, we can now begin to look at some likely sources and why most of these are not that good for a RDD / dirty bomb device. At this point I caution that this is from the radiation dose / exposure perspective, as I have noted above I do not believe a RDD is specifically about exposing masses of the population to significant dose - however the thought of that possibility is where the ‘MAD' (disruption) principle comes in.
Basically, radioactive material will emit alpha, beta or gamma radiation (or some combination of these). From an internal radiation hazard perspective, for a given activity, an alpha emitter will give you the highest exposure (if the radioactive material is inhaled or ingested). For example, consider the inhalation of Co-60 dust (if it could be created!) as compared to Po-210 (as was used to kill Alexander Litvinenko - he died 23 November 2006 after being given a Po-210 based substance). For each we consider the activity in Bq (Becquerels) required to given a whole body effective dose of 1mSv. The data is as follows:
Inhalation: 104000 Bq for 1mSv (Co-60)
Inhalation: 303 Bq for 1mSv (Po-210)
So based on the above data, we can use 343 times less Po-210 activity to deliver the 1mSv radiation dose. However, if you were sat on top of a RDD device using 1TBq of Po-210 (or even much greater activity), you would know nothing about it. Furthermore, should that device actually manage to disperse the material far and wide you would have a hard time detecting it - for Po-210 is predominantly an alpha emitter and not easy to detect (certainly in less than perfect monitoring conditions). Therefore, Po-210 is not really the source of choice with respect to MAD - furthermore, getting hold of it in a form that would disperse would be very difficult.
[By the way, if you wonder what the significance of the 1mSv effective whole body dose it - then broadly speaking it carries the same future cancer risk as smoking two packets of cigarettes].
So, what about an alpha emitter with associated beta and gamma radiation? Surely that would provide the ‘significant' alpha radiation dose potential (from internal exposure), but with the added twist that it is more easily detected (due to the beta / gamma emissions) - hence a better MAD prospect? From a detection perspective it is a better prospect, and its inhalation dose per unit activity is near Po-210 (and very far away from the Co-60 data presented above). The problem however is dispersal - remember RDD ‘Radiological Dispersal Device' - the choice candidate would be Am-241 (found in most ionisation based smoke detectors) - but getting this to disperse in a way that not only travels a distance, but also is rendered into a particle size that can be inhaled, would be immensely difficult. Also remember (and this is really important) - the bigger and more elaborate the explosive device is, in order to try and disperse radioactive material, the less worry is the radiation (not only because it may have been dispersed far and wide, but also because the resulting ballistic injury to those nearby make the radiation effects pale into insignificance).
So, whilst alpha emitters, if dispersed, could deliver the highest internal exposure per unit intake, they are an unlikely candidate for a RDD.
Beta / Gamma Emitters - a better choice?
So we turn to beta / gamma emitters. It is true to say that these are the more obvious choice, partly because they are easier to get hold of (although security services around the world continue to make this more and more difficult). It is unfortunate that legacy / orphaned radioactive sources, where control of them has been lost in certain regions of the world, are vulnerable to malicious use. The IAEA and other groups are working closely with member states to find such sources and bring them back under control.
Probably the most widely available vulnerable radioactive material, and this is mainly because of its long history of use in medicine and industrial processes, is Cs-137. It is at this point we need to consider how such a source of Cs-137 might be constructed.
In the early days, certainly going back 30 years or more, many Cs-137 sources were constructed using Cs-137-Cl in a finely powdered form. This powder was then encapsulated - some times in a robust doubly welded sealed capsule (e.g. industrial radiography), but in some cases in capsules with a ‘thin metal window' (e.g. medical radiotherapy machines). The structural vulnerability of some of these sources makes them of particular concern because it is reasonable to conceive that an explosive device might rupture the source spreading the Cs-137 powder, or the powder might even be removed and then placed within an explosive assembly. In summary, it is sources such as these that are more easily dispersible - and because they are beta / gamma emitters they are also easily detected.
However, from an internal radiation dose perspective (e.g. if inhaled), their dose per unit activity is much lower (about 100,000Bq for an effective whole body dose of near 1mSv). So, whilst you can disperse this widely, you are then lowering the potential for internal radiation exposure because its availability in the environment will be at lower concentrations (i.e. Bq/g soil, Bq/m3 of air and so on). Then if you are exposed, the dose per unit intake is much less than that for Po-210.
Of course, unlike the Po-210 (and Am-241), what the Cs-137 does provide (and to an even greater extent the Co-60) is external radiation hazards - that is being irradiated from just being near the radioactive material. [Review part 1 of this blog series if you wish, the external hazard does not require that the radioactive material be near or within the body].
Typical dose rates from a Beta / Gamma Source
The dose rate from a given activity of radioactive material is proportional to that activity. The higher the activity the higher the resulting dose rate (from a given distance from the source). So, with respect to the external radiation hazard, and for a given exposure time, the worst place to be around a RDD with Cs-137 is sitting right on top of it! For example, for a RDD using 1TBq of Cs-137 the dose rate at an average distance of 10cm from the device would be about 7600 mSv/h (without shielding). You would receive a fatal level of radiation exposure in under an hour (your death would be nothing to do with cancer, but full scale failure of vital body systems, taking days or perhaps weeks). That said, I think I would still be more worried about sitting upon such an explosive assembly.
Developing this further, if you were on average 1m from the RDD then the dose rate (unshielded) would be 76 mSv/h and if you were 5m from the RDD the dose rate would be 3mSv/h (unshielded). The important point is that at these much lower dose rates you are not in a danger of ‘death by irradiation' (as you were at 10cm). If you stayed at 5m for one hour, the equivalent risk from ‘death by cigarettes' (i.e. cancer that might take years to become apparent) would be about 6 packets (120 cigarettes). What worries you more at this point - the radiation or the fact that despite being 5m away from this device, if it goes off in the next hour you may well be blown to bits?
As I hope you can see, you do not need to be far away from this device for the radiation effects (from the external hazard) to be entirely survivable. And remember, this device has not yet dispersed its content - as soon as it does that single ‘point source' of radioactive material is going to be spread far and wide (if perfect dispersion occurs). If it is flung far and wide, then the dose rate at any point will be less than has been expressed above (e.g. at 5m away from the unexploded RDD). If it is not flung far and wide, it will still be spread locally - then, those near will be dead or injured from the blast, radiation exposure at this point will still be of secondary concern. It is true that responders (emergency services) and members of the public who enter the local scene post explosion will receive a radiation exposure - we will estimate this in part 4 of this blog series.
The dispersal of Cs-137 as noted above is based on using an old Cs-137 source - using powdered Cs-137 (CsCl). Thankfully, modern sources (say in the last 20 years) are not built that way - many use a ceramic matrix (followed by at least double skin steel encapsulation) to lower dispersal risks. The sources are known as ‘Special Form Sources' - their structural integrity is made to exacting (ISO) standards so that they will not ‘fail' (leak..) in all reasonably foreseeable events (i.e. fire, mechanical damage etc). Iit is true that the whole concept of ‘reasonably foreseeable' was changed post 9/11. ‘Special Form' status is not designed to deal with malicious events (i.e. such sources are not designed to withstand being deliberately placed within explosives which detonate). However, it is reasonable to suggest there whereas a Cs-137 powder it more likely to disperse when used in an RDD, the same cannot be said for a more modern Cs-137 source (or indeed other type of radioactive source), where they meet the modern ISO standards - fragmentation and more local spread is more likely - this will be explored in part 3 of this blog series.
So what sources would be any good?
So where does this leave us? Radioactive materials, of a type that would deliver a significant internal radiation exposure, are just not that ideal for use in a RDD. Radioactive materials that could be dispersed, for example Cs-137 in a powder form, are a better choice for a RDD device. However, this leads us on to make some comments on the feasibility of working with such material. Whilst beta / gamma materials (of significant energy like Cs-137 and Co-60) would be detectable even after some considerable dispersal, their dose rates prior to dispersal are considerable - as has been outlined above.
Even after 9/11 where it has been shown that individuals are willing to die for their cause, working with 1TBq of Cs-137 is not easy. Note above, that the dose rate at 10cm from 1TBq of Cs-137 was 7600 mSv/h - you cannot work around such a source and survive long term. Yes, it is true that you might survive long enough to set the device up - but this is just for 1TBq of activity. As we shall explore in parts 3 and 4 of this blog series, if you want to disperse enough activity into the environment to cause a significant radiation exposure to a significant population, you are going to need more than 1TBq of Cs-137, and the more you have to work with the higher the dose rate. Furthermore, typical Cs-137 sources that ‘might' be available for use in a RDD are likely to be of activities significantly exceeding 1TBq.
So what about shielding the finished device?
What about shielding - could you shield such a device to protect yourself as you set it up, store it and deliver it? Well for the 1TBq Cs-137 source, wrapping the entire source / device in lead of thickness 2cm would lower the dose rate at 10cm to just under 1000mSv/h. So, some considerable lowering of dose rate, but still a significant radiation hazard. I will leave you to do the maths, but consider the mass of a 2cm lead shield built around such a device - hardly portable now?
What about distance from the device?
Furthermore, an unshielded 1TBq Cs-137 source will yield direct line of sight dose rates, assuming we treat as a point source, of some 5 micro Sv/h at 100m. This dose rate, about the same as you will measure from cosmic radiation, flying at 37,000 feet at UK latitude, is detectable by modern radiation detection equipment - such an amount of activity is very hard to hide. Getting a source of this amount of Cs-137, in a dispersible form from inside the UK is very unlikely. Smuggling this amount of activity into the UK, undetected is also a major challenge - but not impossible. Border / port monitoring for illegal transport of radioactive materials does take place.
The bottom line thus far...
The bottom line though is this. Is all this hassle, from the perspective of the terrorist, really worth the effort? Part 2 of this blog series has shown that there are radioactive materials out there which could be used in a RDD. However, none of them are ideal if the aim is making a dispersal device which will deliver a significant dose to many people. In part 3 we will explore the dispersal potential for two types of radioactive sources - solid Co-60 metal and Cs-137 in powder form. We will not look at this rigorously but will provide some basic data that we can look at in part 4 when determining dose estimates from a device if it were constructed and used.
Part 3 to follow soon.
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