@aargee,
Whilst you are on the right track, some of the detail is a little misleading in your post.
In the UK there is no such thing as a 'red your dead' badge, it is a passive cumulative dose badge and provides no instant indication of overdose. Other equipment, namely personal electronic dosimeters are fitted with an alarm set at a safe/unsafe threshold point and these do alert to the presence of excessive ionising radiation. Some also contain a digital display of CPS, uSv/h or accumulated dose in uSv since last reset.
I was required to be badged as I work with open source X-Ray which has the potential to illuminate me with backscatter or by accident. In the UK there is no requirement to be badged when operating X-Ray equipment that uses licenced containment as the unit is considered inherently safe with very low leakage as a detailed in the licence. The operators of X-Ray mail scanners are not required to be badged as a result. This is a key requirement for manufacturers as badging costs a significant sum per year.
For those unaware, an X-Ray dosimeter badge is just a piece of X-Ray film (and a scintillator layer) that has two attenuators in front of it. There are three zones recorded...
1) no attenuation (Alpha & soft X-Ray sensitive),
2) Aluminium attenuator (Beta & Hard X-ray)
3) Steel or Lead attenuator (Gamma & very high energy Hard X-Ray)
Every 3 months the badge 'film' is sent to Harwell in the UK for exposure. The level of radiation exposure is calculated from the relative exposures of the X-Ray film behind each attenuator. A very simple and effective method to measure accumulated dose.
It is true to say that no real time warning is provided to the wearer of the badge if overexposure occurs. You find out only when Harwell send back the badge report. That is why we also use real time dosimeters suited to the task. Note it is essential to use the appropriate dosimeter type for the type of X-Ray generator in use. Many will not respond correctly to pulse X-Ray as produced by many EOD open sources like the Golden X-Ray series. As already stated, a dosimeter often contains an alarm that is pre-set at a specific level so as to warn the wearer of any issues in good time.
Whilst it is true that the wearer of a badge may be taken off of Radiographic duties if the badge has recorded a cumulative dose that is considered excessive (but still safe) it is also an important indicator that equipment used by that person was either poorly deployed or indeed faulty in terms of containment. Sadly in the industrial arena it is possible to receive a radiation dose that is lethal when working with powerful sources like Isotopes or radiotherapy sources. The badge user in such cases will be aware of the dose well before the badge is developed as radiation sickness onset is pretty fast, in some cases a matter of hours. The badge then gives Harwell an idea of how much of a dose has been received and what, if any treatment is possible. Red your dead is a pretty nasty term but in truth you can kill yourself and be a dead man (women) walking until the full effects of the radiation(massive cell damage) take effect.
Before the readership charge off into the distance screaming that X-Ray machines are deadly, I must point out that industrial X-Ray in steel production is very hazardous but the sort of X-Ray found in your average Faxitron, Mail scanner or even a Dentist is far less hazardous due to the lower keV involved. You would have to try very hard to do yourself serious harm with a tube running at 35kVp or even 120kVp when it is properly contained. Medical Radiographers need to take precautions when operating open source X-Ray generators as they can be illuminated by back scatter and reflections within the room. They do many X-Ray exposures a day so do not wish to accumulate a large dose of radiation over a period of time. The body can deal with accumulated doses below a known threshold and a Radiographer can return to duty after a period of 'rest' if their dose is considered excessive in one particular monitoring period. They are NOT removed from radiotherapy duties for life.
There is NO 'safe' dose of radiation. Anyone who thinks so is kidding themselves. Radiation levels should be minimised wherever possible. But bear in mind that flying in an aluminium airframe at 33000 ft provides quite a decent dose of background radiation and cabin crew are exposed to this daily without being badged. It is not considered hazardous to their health. The hazard knowledge of radiation exposure on humans comes from early mistakes made by inventors and sadly the post mortem of accidents involving radiation. Much has been learnt from what were basically many mistakes over the years. Chernobyl was a major contributor of dose data as so many were exposed to differing levels of radiation. My condolences to the families of brave people who worked on containment of the fire and fallout in the early stages of the event. They died a truly horrible death due to massive overdoses of radiation. Some died within hours of exposure.
Please do not leave this post thinking that X-Ray is some sort of deadly death ray and so unsafe to operate in appropriate environs. I wish to grow old and have used open source and cabinet X-Ray for many years. On no occasion has my badge given an indication above background ! My employer takes the view that if your reading exceeds expected background levels an investigation into why ensues.
Cabinet X-ray equipments remain the safest form of X-Ray equipment that you can obtain. The containment must meet international standards in order to be sold in a country as a licenced equipment.
BUT
I strongly advise against building an X-Ray machine unless you are highly experienced in such as a job and have all of the correct equipment for testing its leakage. Even then I still recommend a commercial licenced cabinet that may be trusted as safe to use. When I see people firing up X-Ray tubes or abusing a vacuum tube to produce uncontrolled, non contained X-Ray, I cringe. Not because the radiation levels are so high as to cause death, but because I am indoctrinated with safe working practices and such experiments are very unwise and foreign to me. Remember - there is NO 'safe' level of radiation.
Some trivia for readers..... soldiers used to be equipped with NBC suits that included a small radiation cumulative dose recorder. The unit could only be read by a field deployable analyser. the reason...... HQ could determine how many soldiers were likley to fall due to radiation sickness and how many woudl still be in fighting condition. The soldiers could not tell if they had received a fatal dose so would just keep on going until they dropped
That is the hard truth behind military 'red your dead' thinking. Thankfully the world has not seen a need to use such equipment since WWII. Long may that remain the case.
I am happy to answer questions on dosimeters and badges etc as I am a long term user of such.
I attach a picture of some HARWELL Radiation Dosimeters and a BICRON micro Sievert survey meter that I own
Aurora