Battle Relic: Luminous Marker Disk, US Army, World War Two
Introduction: Battle Relic # 13 is not about one specific and unique item, but describes a feature of a mass produced and widely distributed little device used by Allied forces in World War Two. This file focuses on the question: "Are the Luminous Markers, Type I, really radioactive; even today?".


 

  
Item Description
These markers consist of a transparent Plexiglas circular front (the 'window') which is attached to a black metal circular back.
The 'window' has a 'bubble' in the center containing a yellowish-white powder.
There are several variations of the device, such as unmarked British-made disks and types that can be attached to equipment by means of a pin-back, a clip or grommets.
The disks were originally designed to mark roads and were produced for the US Corps of Engineers.
The powder inside the disk could be charged by holding it close to a light source.

Stories

In several publications, mostly on-line discussion forums, the story has it that the light emitting disks, used in World War Two to mark routes, equipment and even soldiers, still release a dangerous amount of radiation.
So far, we were not able to find convincing results of a valid radiation test of these markers.
Actually, we were under the impression that after more than sixty-six years the radiation must have decreased dramatically.
This assumption was supported by our modest experiment of looking at one of these markers in a blacked-out room.
It did not show any more brightness than a white sheet of paper.
Incidentally, the marker disks have been the subject of some other controversy in the past.
Because the American-made markers have the warning "POISON INSIDE" stamped on their backs, it was assumed that they were in fact deadly capsules with poisonous powder inside the Plexiglas bubbles, issued to secret operators in the Office of Strategic Services (the predecessor of today’s Central Intelligence Agency).

The persistent online remarks about the danger of these gadgets, often associated with US paratroopers on D-Day, triggered our wish to end the assumptions.
 
There has never been any doubt that these markers were radioactive, though.
Some time ago, we took these photographs inside the Baugnez ’44 Museum near Malmédy in Belgium.


(click to enlarge)
 

These pictures show several disks, their metal container and the instruction for use.
The instruction sheet reads:
 
DIRECTIONS FOR STORAGE, HANDLING, AND DISPOSAL OF RADIOACTIVE LUMINOUS MARKERS, TYPE I

1. AS MANY AS 3 LUMINOUS MARKERS MAY BE WORN ON THE CLOTHING INDEFINITELY WITHOUT HARM TO PERSONNEL.

2. ONE BOX OF 24 MARKERS MUST NOT BE CARRIED ON THE PERSON FOR PERIODS IN EXCESS OF 8 HOURS IN ANY ONE DAY.

3. PERSONNEL EXPOSED MORE THAN 8 HOURS PER DAY MUST MAINTAIN THE FOLLOWING TABU-LATED DISTANCES FROM QUANTITIES OF THE MARKERS:

        NO. OF BOXES (24 PER BOX)                          DISTANCE FROM PERSONNEL
                       2 TO 50                                                      2 TO 50 4 FEET
                      50 TO 300                                                 50 TO 300 8 FEET
                     300 TO 1000                                            300 TO 1000 20 FEET

4. RADIOACTIVE MATERIAL FOGS FILM. – IN QUANTITIES OF 100 BOXES OR LESS A SEPARATION OF AT LEAST 100 FEET MUST BE MAINTAINED BETWEEN FILM AND MARKERS.
FOR GREATER QUANTI-TIES THE DISTANCES MUST BE IN PROPORTION TO THE QUANTITY.

5. PERSONNEL SHOULD BE CAUTIONED AGAINST TEMPERING WITH THE MARKER OR IN ANY WAY EXPOSING THE LUMINOUS COMPOUND. BROKEN OR DAMAGED BUTTONS SHOULD BE DISPOSED OF BY BURIAL OR BY CAREFULLY WRAPPING, MARKING THE PACKAGE AND RETURNING TO THE DEPOT FOR SALVAGE AND DISPOSAL. IF ANY LUMINOUS COMPOUND ACCIDENTALLY COMES IN CON-TACT WITH THE BODY CONSULT A MEDICAL OFFICER.

Original disks

Two disks were borrowed from private collections.
Both are of the American type with 'just' grommets for attachment purposes.
We discovered that varieties with clip and pin back attachments are scarcer and therefore more expensive.

One disk was in mint condition, the other one had a crack running along the Plexiglas 'window' and its powder containing 'bubble'.

(click to enlarge)

Experiment
A radiation expert, working with the Regional Health Aid Organization (abbreviated GHOR or Geneeskundige HulpOrganisatie in de Regio in Dutch) in Eindhoven (The Netherlands) was willing to put these two disks to an Alpha and Gamma meter test.
His job is to measure radiation values in suspected locations before fire fighters or policemen enter the scene of a fire, environmental accident or clandestine narcotics laboratory.

The results are eye-opening!
We suggest viewers to watch this video:
 

 
At the time indication of 0:09 in the video the radiation expert can be heard saying:
"When you are exposed to this amount of radiation for ten hours, you have had your yearly dose!"

Radiation level
We were told that the disks are emitting so called Gamma-rays.
The biological effect of these rays is expressed in "millisievert" (1 mSv = 10−3 Sv) and "microsievert" (1 μSv = 10−6 Sv) per amount of time.
It is advised that an average person should not be exposed to more than 2.4 millisievert of natural background radiation (from cellular phones, electronic devices, etcetera) per year in order to avoid a higher chance of getting cancer.

The experiment included measuring the radiation emitted by the individual disks, by both disks stacked, by the disks inside a plastic container and with a metal (aluminum) sheet over the plastic container.


An Automess 6150 "tempo meter" or "dose meter" was used to conduct this experiment.
After an initial test with only the meter, a measuring probe was attached and the amount of radiation was measured again.
The meter produced a few short beeps, increasing in frequency to end in a constant warning tone indicating a hazardous dose.
The individual disks emitted an amount of radiation between 120 and 140 μSv per hour.
The stacked disks emitted an even higher value than a single disk:
in this case 207 μSv/h .
The radiation expert was able to pinpoint both disks inside the thick plastic container just by hovering the dose meter over it and listen to the increase of bleeps.
A metal plate of a few millimeters thick did not stop the radiation; although it then was of a lower value.

        (click to enlarge)   
     

(click on the thumbnails to enlarge)


The expert went on to explain that he had held the meter in close proximity of the tested disks.
Keeping the disks inside a thick metal box and maintaining a certain distance are remedies against too much exposure to their radiation.
He advised against keeping the disks close to (a) person(s).

CONCLUSION
It has now been well established that the Luminous Markers, Type I, are in fact radioactive; even today.
They emit a dose of radiation which can be hazardous to the health of people.
The advice in the World War Two dated instruction sheet, stating that up to 3 disks can be worn on a person indefinitely without harm, is therefore not true.
We advise viewers who own a device as described here, to keep a safe distance from it and / or to keep it stored in a metal (preferably thick lead) container should one desire to continue owning it.
 
EXHIBITS
Although often associated with American airborne troops deployed in the night before the Normandy invasion on 6 JUN 1944, there are few period photographs to justify labeling the luminous markers as a typical airborne item.
 
In several of the excellent books by Belgian author Michel DeTrez the luminous disks are depicted as in integral part of the individual equipment of the American paratrooper:

(click to enlarge)
   

We did however find these images of Lt-Col Michaelis, executive officer of the 502nd Parachute Infantry Regiment, in the marshalling area prior to the D-Day drops.
He seems to be wearing a luminous disk on his helmet.
Given the results of our experiment, this is a very unadvisable practice.
 

The pictures below may show that "Iron Mike" only carried a disk on his helmet for a limited amount of time.
 

(click to enlarge)

1                                   2                                               3                                                   4             

Picture 1 and 2 were taken in England prior to D-Day, picture 3 was presumably taken during his deployment in Normandy and picture 4 shows Michaelis on his return in England in July 1944. On neither one of these pictures he is seen wearing a disk again.

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