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Radiation Readings Rendlesham Forest 28 December 1980 – C J Pearson
Main types of radiation: Alpha, Beta, Gamma.
Alpha: Travels a couple of feet in air and is stopped by skin or paper
Beta: Travels a few meters in air and is stopped by aluminium, Perspex
Gamma: Travels hundreds of meters in air and is stopped by concrete, lead
Gamma is slowed down by water and anything that has this property is known as a moderator. In a reactor the moderator is water.
Radiation is in itself a form of energy and depending on the type depends on its power. Gamma is the most powerful and Alpha is the weakest. Radiation is caused by the forceful removal or addition of parts of an atom. This makes the atom unstable. It vibrates in an unstable fashion and this causes energy waves to be given off. This is known as radioactivity and radioactive decay. The atom tries to become stable again, usually by losing the extra bits it has picked up. These it gives off at high speed, sometimes further ripping atoms to bits in its path. If it comes into contact with the body in Alpha – externally nothing happens, unless some enters the body in which case the tough outer layer of skin on a human is not there. The soft innards become damaged and illness begins. In Beta radiation if it hits the skin it can, depending on its energy, cause Beta burns. It’s like heavy sunburn. Gamma passes straight through the body, only slowing a small amount because we are mostly water. This moderates the speed of the Gamma wave and gives its energy up as heat, ionising as it goes. Gamma radiation is so powerful it can further disrupt other molecules as it passes, and then causes them to become unstable and then also radioactive. As the atom tries to become stable it decays. When it has lost half of its radioactivity this is known as one half-life. Each radioactive element (isotope) has a different half life. Some are as small as 7 second’s, others like Uranium 238 have a half-life of billions of years. In Chernobyl and Hiroshima the doses of radiation were so high it was impossible to measure accurately. The victims dose was estimated by taking blood samples from the victims. These samples were then measured for radioactivity of the sodium (a metal) in their blood. From this an exposure level at time of explosion was estimated by counting the half-lives the sodium went through until it had decayed away to nil radioactivity.
Radiation Meter Used:
The meter used was a AN/PDR-27 but it also had a following model letter. I think it was an F but this is not certain. The model numbers ran from I think- A through T.
These were, despite previous reports, accurate measuring devices. The reason for this was that unlike many meters of the type, this one had two GM tubes. A GM tube is like a strip light bulb. It has a charge on the outside and a wire running through the middle, which is charged in the opposite pole. The tube is sealed and is filled with a gas. This is called a quenching gas. When a radioactive particle passes through the tube at high speed it causes ionisation in the tube, which causes a spike in energy. This changes the polarity of the particles in the gas and they are drawn to the wire in the middle. This effect’s the resistance of the wire and a voltage change is detected in the current. This is what is read on the dial. The gas then resists change and quenches the reactions. This is what happens in layman’s terms. The more radiation the more the voltage changes and the more the needle deflects. Change the scale and you change the voltage change detectable. The AN/PDR-27 has two GM tubes, one for very low, to low, measurement and one for medium to high readings. The medium to high tube is in the main body of the meter. The low range one is in the silver probe. The tube in the body is for high levels of gamma radiation measurement. The body is made from cast aluminium and so only gamma can pass through the body of the meter. The probe end is open to air usually. The probe end has a sliding sheet of metal which, when in place will ensure that any beta radiation is stopped, therefore only gamma will be measured. Remove the metal sheet and both beta and gamma can be detected. There is one odd thing about this meter. When in very high areas of gamma radiation the meter can become compromised and the meter reads very low readings. This meter was used for detection of very low to very high radiation readings in an area and was also used to measure radiation exposure casualty victims and. This would normally be in the form of radiation from contamination on the casualty. This meter gave measurement in millroentgen/phr ( milliroentgens per hour). Because it was designed to measure gamma exclusively in the high ranges as well as the low ranges an alternative unit is the millrem. Millirems and milliroentgens are interchangeable when measuring exclusively for gamma radiation. The international unit of radiation now is the Sievert. Sieverts are further split up into millisievrts and further into microsieverts written as microsieverts per hour = uSv/hr.
Designation of Radiation Areas and their respective limits:
Uncontrolled radiation area - less than 2.5uSv/hr
Supervised Radiation area - 2.5uSv/hr to 7.5uSv/hr
Controlled radiation area - 7.5uSv/hr or more
I stress this is brief description of radiation. The idea is to give a brief description to enable further understanding of events by everyone, not just those familiar with radiation safety practice. For those who wish to delve further there is IRR’s 1999. Which are available from the internet.
Halt’s tape – Radiation Readings Dec 28 1980.
The radiation readings have created perhaps the biggest argument over the years. Were they low or high? This is a difficult question to answer due to the fact that we have only a verbal representation of these readings. Because of this, it is important to be able to plot these on the meter used and then work out what the readings were in modern day units. Once this is done we can say what they mean.
This is the meter’s lowest scale. It reads from 0 to 0.5 milliroentgens per hour. This is further divided up into smaller markings on the scale above the blue measure, into 50 smaller markings.
Now as per several websites and as per the Halt memo the readings on the night were recorded as 0.07 milliroentgens per hour. Now it is important that this is plotted on the scale so that we can see what it would look like. This next picture is the common assumption of where the needle was shown in red:
The actual verbal reading given was 7 tenths on the point five scale. As this was taken from the recording live at the scene as it were, it is considered more valid than the readings later written. Because 7 tenths written as a decimal is 0.7. Not 0.07 which is 7 hundredths. This is the system where in the number 123.45 is represented as, 1(hundreds), 2 (tens), 3(units) decimal, 4(tenths), 5(hundredths) – 123.45
The misconception of the needle being at the 0.07 mark on the dial – as above comes from the fact that there are 10 markings from 0 to 0.1 – so 7 tenths puts the needle at seven, from the ten available from 0 to 0.1 There is however a slight problem with this theory. There are also 10 markings in the next section from 0.1 to 0.2 and so on up the scale. 50 in total. As we read scales from the 0 mark, if the needle were to stop on the 0.2 marking, the needle would have 20 markings from 0 to 0.2. We would not be able to say 20 tenths. It would be referred to (if at all) as 1 twentieth. However whenever we say readings like this we always say the amount, out of the amount available. If the needle were where the Halt memo says it was, it would have to be written or said as 7 out of the total available, (this would enable plotting/reporting easily by parties after the event). The total in this case would be 50. So the verbal report would have been 7 fiftieths. So in order to get the verbal reading of 7 tenths out of the ten available we have to look at the scale and see where it divides up into 10 equal markings. And it does. After we do this we can see that 7 tenths fits on the scale easily. Using the prominent markings shown below. REMEMBER although the report is 7 tenths and the debumkers would have you believe it meant 0.07 as per the Halt memo, the Halt tape though transcribed by everyone is as follows:
Lt Col Halt: Can you read that on the scale?
Sgt Nevilles: Yes Sir. We’re now on the 5 tenths scale (0 to 0.5 and therefore clearly understood that tenths means one place after the decimal point) and we are reading about . . er. . third , fourth, make(mark) over.
Look familiar?
This gives us a reading of the 7th marking out of the ten available which puts us at 0.35 milliroentgens per hour after reading off the scale below the markings.
However before any of this to help confirm the above we get at 01:25 hours on the Halt tape:
Sgt Nevilles: We’re getting right at half a millirem.
That’s here.
Later we get the 7 tenths reading which is explained above. However and this is where it gets confusing. The manual for this meter says that you approach the area on the highest scale and if you get nothing you work your way down the scales. So you would start on the highest selection 0 to 500 milliroentgens per hour and work your way through until the needle shows a reading. So you would assume (and I have to say if your getting right at half a millrem/milliroentgen I would, as would any radiation monitor) that Nevilles changed scales to 0 to 5.0 To see if it went higher than the, full scale deflection on the 0 to 0.5 scale. So we get Halt asking is that “up to 7 tenths (0.7) or 7 units (7.0) its called on the point 5 scale (0.5). Well clearly 7.0 cannot fit on the lowest scale nor on the next scale up. Which is worrying because that means if it was units it would have to be on the 0 to 50 milliroentgens per hour scale.
Like this.
Before Nevilles can answer Halt makes a plan to survey the area. Neville’s only reply is “right”. Right to what, the plan or 7 units or 7 tenths. Slightly worrying because right after Halt gives his plan Halt says “put the light on it an sweep around it”. So it was dark enough for Halt to miss Neville’s cycling through the scales perhaps, who knows?
Following only the radiation reports through the transcripts we get:
25 30 feet from the site – Minor clicks.
At the site now – still getting clicks.
Can you read that on the scale – 0 to 0.5 scale third, fourth make(mark) over.
Second pod indentation – minor readings (readings none the less).
Third pod marking – getting residual and definitely giving a little pulse.
At the centre now – best deflection of the needle I’ve seen yet. (so the highest so far)
Can you give me an estimation – half a millirem on the 0 to 0.5 scale
From here they move on to between the pod marking and the centre, and then the confusing bit of 7 tenths or 7 units. Strangely no one ever focuses on the half a millrem reading and always argue over the 7 tenths position. Which I hope was not 7 units. If as you should do, Neville’s changed the scale when he reached the half a millirem on the 0 to 0.5 scale 7 tenths (0.7) can be seen plotted here on the next scale up.
0.7 on the 0 to 5.0 scale
A short while later while Halt is examining the “abrasion on the tree” Lt Englund declares that they are getting interest meaning the radiation readings, and Halt says ok lets go on back around and there is a break in the tape.
When the tape is started again there is clicking sounds. It has been reported that this is the Geiger counter clicking. It is not. I have used meters like this for years and it is the sound of the scale being changed. Now if I counted the number of clicks, and I could be sure what scale they were on (which you can’t because the tape breaks between readings) then I would know what scale they could be on. However you cannot be sure. But as the clicking stops Nevilles says “that’s what it gives” meaning the readings. You can tell by his tone he is enlightened. At first we get no verbal reports of note, then picking up and picking up and we hear LT Englund proclaim “astonishing” which means he finds something unusual. Halt says “yeah but your still not going above 3 to 4 units. 3.0 to 4.0. on the next scale up from 0 to 0.5. Shortly afterwards 2 to 3 to 4 units. Now it has to be the next scale up because they have already shown that they are familiar with using units to mean figures, left of the decimal point i.e whole numbers.
Radiation reading conclusions.
The radiation readings need to be converted into modern day units in order that the significance is not lost for the future.
Firstly you have to question the presence of a radiation detection device at all. I know when there is a security breach the first people to turn up are the guards. If there is an intruder the balloon goes up. When you may have a downed aircraft the fire service are called. When you get a big bang the fire service are called. Who in their right mind gathers a “group of experts” and a radiation monitoring device. Unless you expect radiation based on prior knowledge. I mean if you take nothing further from this be amazed at that bit of guesswork.
THE most significant thing you can do is NOT get embroiled in the 7 tenths 7 units argument. We have exact non-disputable higher readings of “right at half a millirem. Remember when measuring gamma only i.e the beta shield is across, it is perfectly acceptable to cross back and forth from millrem to milliroentgens.
I will list the readings as they appear through the Halt tape.
“Minor clicks” – no idea (each radioactive particle that goes through the tube produces the reading. The more particles the more the needle deflects. The same applies with the clicks. No one can translate this legitimately because my reference for minor clicks would depend on my career. If I worked with nuclear weapons most of the time, then minor clicks could mean quite a bit in woodland nowhere near a nuclear weapon. Or they could just be minor clicks. Who knows?
“Still getting clicks” – again no idea but its reading something. Background gives the odd click now and then. Not clicks. And of course if they were doing as the manual said they should, they could well be on the highest scale at this point. But again who knows.
0 to 0.5 scale – third, fourth make(mark) over – 0.35 Millroentgens per hour. This converted into the International units is 3.5 uSv per hour. Interesting because this makes it a supervised radiation area now. Dosimeters must be worn etc. Wonder where those records are?
Minor readings – as it says, but, from their perspective.
Second pod – minor readings – as above
Third pod – residual and a little more excited so clearly more than the above. How much by is anyone’s guess.
Centre – best deflection – estimation etc. . . half a millirem. 0.5 full scale deflection on the 0 to 0.5 scale. This gives us 5 uSv/hr which is well within the supervised radiation area and creeping up towards controlled radiation area limits of 7.5uSv/hr
7 tenths 7 units discussion, which would be back to 0.35 milliroentgens and 3.5 uSv’hr. However if the scales had been changed then it could well mean 7 units recorded which means 7 milliroentgens per hour and this is 70 uSv/hr
2 to 3 to 4 units is a maximum of 4 milliroentgens per hour which is 40 uSv/hr
These readings would obviously be well past both Supervised radiation area, and Controlled radiation area and into Restricted radiation area territory.
Later on as they are following the lights and taking readings (though we never hear a value just clicks) we hear the beta shield has been removed. This obviously shows that the operator knew what the shield did.
Probe with beta shield removed:
As explained previously it does prevent beta radiation entering the probe. So the implication is, that the shield had not been previously removed for the readings we have on tape. The implication is that the readings voiced were gamma alone. I find it odd, that faced with the unknown anyone should choose to take a radiation monitor with them on what is in essence an intruder alert or at worst a downed aircraft. The only logical assumption I can make is that based on prior knowledge the team felt it necessary to take a radiation meter with them in order to assess the danger from a supposed radiological source. Knowing that the levels have exceeded the supervised and perhaps the controlled radiation area limits, they would have also had the forethought to take dosimeters. These would then have been assessed for measurement of exposure. These records will be held somewhere as is the law. Further more, given that these radiological area doses have been exceeded, precautions would have been put in place. Barriers. Personnel would have to be monitored in and out of the area. As per the AN/PDR-27 manuals instructions, this practice was in place in the face of a radiological hazard. These facts are not assumption they are procedure.
A further interesting thing is this - if you are used to radiological incidents or practice scenarios you are used to wearing dosimeters. These days they are electronic real time dose meters - mini GM tubes, but also you wear a neutron track plate and a TLD (thermo luminescent dosimeter) for beta gamma exposure. However you also get an older device in an emergency called a QFD - quartz fibre dosimeter. Remember these are only issued in an emergency exposure situation when you do not have the more common forms of dosimeter. I remember reading somewhere that one of the witnesses found what looked like a small pen like object made of metal. Not something like this then perhaps?
http://en.wikipedia.org/wiki/File:Direct-reading_dosimeter.jpg
Finally if anyone wishes to ask me anything feel free to email/PM as required.
Source for meter pictures: http://www.alpharubicon.com/basicnbc/anpdr27ser.htm
Source for radiological info: IRR1999, personal knowledge.
Handy converter: http://www.convertworld.com/en/equivale ... lirem.html
) 30 R/ 12 h= 2.5 R/ h (or 2500 mR/ h). That is 5 times more than the maximum on the scale they used (again, I don't know if my interpretation of the scale is correct). Since full recovery is expected in the case of 2500 mR/ h that should definitely be applicable to 500 mR/ h. So there would be no threat at all. Thus I won't call UFOs highly radioactive 
). The object and the beings were somewhat translucent which might indicate that the propulsion of the craft could be based on a totally unknown method.
