Were the radiation readings significant?


According to the manufacturers of the instrument that was used to take radiation readings in Rendlesham Forest in December 1980, the measurements were ‘of little or no significance’. From the evidence of the real-time tape recording made during the investigation, it can be shown that the readings are simply background levels and do not support the claim that anything unusual happened in Rendlesham Forest. Onsite checks made within a few years of the incident revealed no unusual radiation at the site.

Setting out the case

In his book Open Skies, Closed Minds published in 1996, Nick Pope described the radiation readings taken by Col Halt’s team at the supposed UFO landing site in Rendlesham Forest as ‘the most tangible proof that something extraordinary happened there’. To justify such a claim, it is essential that the readings are shown to be beyond reproach.

My original conclusion, based on telephone discussions with the UK’s National Radiological Protection Board (NRPB), was that the figures reported in paragraph 2 of Col Halt’s memo, i.e. from 0.05 to 0.1 milliroentgens, were simply background levels of radiation. (As a technical aside, the correct units should have been milliroentgens per hour – the use of incorrect units seems to betray an unfamiliarity with radiation monitoring).

The subsequent release of Col Halt’s real-time tape recording of events confirmed that the peak figure obtained was simply a random burst, not a steady level. For much of the time scarcely anything was being picked up by the geiger counter. On the tape we hear them describing the readings at the site as ‘minor’ and ‘three to four units’, i.e. 0.03 to 0.04 mR/h. They got these readings as they approached the site and then as they checked each of the supposed landing marks. Confirmation that this was only background radiation comes from the fact that the same levels were also recorded over half a mile away from the supposed landing site, after they had crossed two fields beyond the forest (read the transcript here).

The geiger counter operator, Sergeant Monroe Nevels, never wrote up a report on his findings. Inquiries in 1984 by US journalist Chuck de Caro for a CNN documentary elicited the information that the Disaster Preparedness office at the air base had no records of the event at all (see Point 1 on this page). So Col Halt’s memo and tape are all we have to go on.

The highest reading mentioned on the tape is ‘seven tenths’, i.e. 0.07 mR/h; this was a ‘spike’ obtained briefly at the centre of the site, not a steady level. In his memo, Halt reports a peak figure of 0.1 but we do not know where that was obtained, or whether it was just a rough value recalled from memory. The figure of 0.07 mentioned on the tape is only twice the general reading. Such a random jump could easily have been caused by natural sources, or even an accidental movement of the meter, and hence is not significant.

Yet, as is clear from Nick Pope’s quotation above, my conclusion has not been universally accepted. Pope’s own researches led him to claim that the radiation levels recorded were 10 times higher than normal, and similar claims have been made by others.

Resolving the issue

Thanks to the influence and contacts of the British physicist Professor Frank Close the matter was resolved more definitively in 1997 for a television discussion programme produced by London Weekend Television (called Strange But True – Live) on which Professor Close and I were to appear along with Nick Pope and Col Halt.

My earlier inquiries had shown that the radiation monitor used by Halt and his team would have been of the type known as an AN/PDR-27. On behalf of Frank Close, NRPB contacted the American manufacturers of the AN/PDR-27, who stated that Halt’s peak measurement of 0.1 mR/h was the ‘bottom reading on the lowest range’ of the monitor and was ‘of little or no significance’. They noted further that these instruments are designed to be used to monitor workplace fields or radiation levels after sizable nuclear incidents and are therefore not suitable for environmental monitoring at background levels. On the basis of this information from the manufacturers, NRPB concluded that using such an instrument to establish a level of 10 times background is not credible.

This, therefore, is the official view of NRPB and of the makers of the radiation monitor, which Frank Close publicly demonstrated to Nick Pope and millions of viewers on live TV on 1997 June 27 (see video clip). To confirm the matter I subsequently wrote to NRPB to ensure that there was no misunderstanding. In a letter to me dated 1997 July 7 Michael Clark of the NRPB stated: ‘We are convinced of the correctness of our interpretation.’

Nick Pope’s ‘investigation’

Nick Pope, however, had contacted not the NRPB but the Radiation Protection Services department of the UK government’s Defence Evaluation and Research Agency (DERA). Pope has described his inquiries as ‘the first and only official investigation into this aspect of the case’. [Now that the official Ministry of Defence file on the case has been released, we can see for ourselves the results of this ‘official investigation’ – a handwritten memo amounting to fewer than 150 words.]

In his book, Nick does not say who it was that he spoke to at DERA Radiation Protection Services, but I found that it was actually a man named Giles Cowling. When I tracked Cowling down, via his colleague Ron Brown, they sounded surprised that their opinion had been published in Nick’s book. Rather than regarding it as an ‘official investigation’ Cowling described his discussions with Nick Pope as a ‘private conversation’. Perhaps this is why Pope did not name his source or quote him directly.

When I presented Cowling with the above information from the NRPB, he wrote to me as follows on 1998 August 21:

In my original discussions with Mr Pope I did indeed state that the readings were around 10 times normal background levels, provided that the instrument was appropriate for measuring background radiation (at the time of our discussions he could not state what the instrument was), calibrated and being used/interpreted correctly. I share the NRPB view that the use of a high-range survey instruments to measure (accurately) environmental levels of radiation is somewhat questionable and this must throw some doubt on the validity of the data reported.

Cowling also confirmed to me by telephone in 1998 August that Nick Pope had not re-checked the facts with him. This was over a year after Professor Close’s TV demonstration that there was nothing significant about the radiation levels at Rendlesham – an opinion with which Cowling, Pope’s own source, now agrees. (See also 2009 Update, below.)

Tim Printy, a former US Navy nuclear engineer familiar with the AN/PDR-27, has made an independent assessment of the radiation readings at Rendlesham, concluding that ‘contrary to what Nick Pope has stated, the levels reported are insignificant even if the maximum reading of 0.07 mR/h was accurate’ – for full details, see this page from Tim’s online UFO review SUNlite.

This was also the view of the Public Affairs Officer on the base at the time the story became public, Captain Victor Warzinski, who explained to an inquirer in 1984 that ‘these reported readings fall within the range of normal background radiation counts. Warzinski’s letter makes it clear that no one on the base at the time regarded the radiation readings as anything out of the ordinary, but Pope’s investigation seemingly never went as far as asking the base for their opinion.

Some on-site checks

In September 1982, less than two years after the event, the site was checked for radiation by researchers from the Swindon Centre for UFO Research and Investigation (SCUFORI). They found nothing unusual. Nor did USAF Major James McGaha when he checked the site unofficially in 1987 while stationed at the base. McGaha emailed me in 1994: ‘There [was] nothing above background. They simply did not know what they were doing. If there were higher levels then you would still see them today, even with a very careful clean-up.’

In 2003, as part of a TV documentary about the Rendlesham case, the Sci Fi Channel made their own check on radiation levels at the site in the hope that, had the area genuinely been contaminated with unusually high levels of radiation, some traces might remain. (Of course, it has never been established why an alien craft should be leaking radiation, or what sort of radiation was involved.)[note] The readings were taken for them by Patrick Davison, an environmental scientist from Mayer Environmental Ltd of Brentford, west London. The Sci Fi Channel’s programme itself was non-commital about the results, but Davison confirmed to me by telephone in 2006 March that he found nothing above background at the site.


If Nick Pope or anyone else is going to continue to use the radiation readings as ‘tangible proof that something extraordinary happened’ in Rendlesham Forest then they are on very shaky ground indeed.

2009 update – Pope tries again (but with no more success)

In a pro-UFO TV programme first broadcast in 2009 called I Know What I Saw,Nick Pope was interviewed about the radiation readings at Rendlesham. In this interview, Pope did not rely on his now-discredited ‘investigation’ discussed above but showed instead this internal memo from the Ministry of Defence files which says in part:‘The value of 0.1 milliroentgens (mr) ... seems significantly higher than the average background of about 0.015 mr.’ In the TV interview, a clip of which can be seen here, Pope described the memo as ‘One of the most important documents to emerge from the MoD’s case files... absolute proof positive that something extraordinary happened’.

The MoD files make it clear that they never undertook any investigation into the radiation levels at Rendlesham so they never established the truth about the readings reported by Halt. The opinion in the MoD memo was based on the same assumptions as Pope’s own cursory ‘investigation’, namely that the figure quoted by Halt was a steady level and taken with an appropriate instrument. As we have seen, both these assumptions are incorrect – it was a random peak recorded by a meter designed to measure much higher levels of radiation. Hence the opinion quoted by Pope is no ‘proof’ at all and would doubtless have been withdrawn had the MoD established the full facts laid out above.

Content last revised: 2023 July.

© Ian Ridpath. All rights reserved

How do the levels of radiation detected at Rendlesham compare with normal everyday exposure?

According to the Health Physics Society in the US, ‘The average person in the United States gets about 365 milliroentgens a year  from natural and medical x-ray exposure, including exposure to natural⁠ radon ⁠gas in the air. This is about 1 milliroentgen a day.’

Even if the radiation levels recorded at Rendlesham were accurate, they averaged no more than about 0.04mR/h. So, 24 hours’ exposure to this would produce a dose of 0.04 x 24 = 0.96mR, i.e. no more than the average for a day as given by the Health Physics Society.

So whatever the witnesses were exposed to out in Rendlesham Forest, it did not include unusual levels of radiation.

Halt’s peak measurement of the radiation at the site was the bottom reading on the lowest range of the monitor

An AN/PDR-27 meter of the type used byHalt et al, shown switched to its lowest range, which Halt referred to on his tape recording as the ‘Point Five scale’. The dial has five major divisions from 0.1 to 0.5 and each of these is subdivided into tenths. All the readings obtained were below 0.1 milliroentgens per hour, i.e. below the first major division on the scale. In the image at right the 0.03 and 0.07 levels are marked. For more about the AN/PDR-27 click here.

Image of the meter dial from http://www.alpharubicon.com/basicnbc/anpdr27ser.htm