How do they measure distance in Personal Radiation Detectors?

Question

since u can see those detectors they have specified only their range then how can we know about their distance.... how will it measure radiation and at what distance (eg) RAD DATECTOR PRD 1250

source:www.nukepills.com

Answer 1

It appears that this device uses scintillation as its operating principle. Scintillation was used in early photo multipliers (Night scopes - Vietnam era) where a single light photon strikes a phosphor coated surface causing several photons to be emitted from the phosphor which in turn strike another coated plate and so on.  

The PRD 1250 uses a similar technique except  instead of a photon triggering the avalanche of photons (light amplification), ionizing radiation initiates the avalanche.

In essence the ionizing radiation strikes a material that causes it to glow or flash(scintillation).  A sensitive light detector sees these flashes and converts them into electric pulses that a circuit can process.

Simply put this is a fancy light detector sealed in a light tight box where radiation passing through the box sides strikes a material that causes a flash of light.  The light detector sees the flash and generates a beep if the number and intensity of flashes rise above a preset level.

Scintillation counters and Light amplification tubes are directional in nature becoming more directional as the number of amplification plates increase. The PRD 1250 appears to be directional in its sensitivity as well but may not have multiple plate series (light amplification) due to its small size. (It may rely upon sensitivity of the light sensor diode instead.)

What ever directional capability this unit has it would  indicate  a stronger signal as its oriented toward a point source.  The idea here would be to indicate a general direction where a stronger signal is comming from so you can run the other way.   This limited directional capability would be of little use if you were in a cloud of radiation that supplied radiation from all around you.

As noted radiation like light spreads out over a larger area the further away you are from the source.  (Think of a candle in a dark room, its brighter the closer you get to the candle)  The PRD1250 would beep at a rate relative to the strenght of radiation. The closer you get to a strong source the faster it will beep.  Although thios would not give a specific feet distance from the source you would get some idea as to intensity of the radiation source (the faster the rate of beeps the stronger the source) . If you weren't contaminated you would expect the rate of beeps to decrease the further away you get from the source or shielded from the source.      

Answer 2

Remember, Radiation Detectors measure overall dosage (and for the film badges, cumulative).

Essentially the intensity of radiation follows the inverse square law. Essentially every time you double the distance between you and a source of radiation, your cut the radiation received by 75%.

Good Luck!

Answer 3

Personal radiation detectors will only detect the radiation that actually hits the detector, and if it is worn close to the body that is a good indication of the dose the body has received.  

These devices do not measure distance from a source.  Neither do they measure rate (time of exposure or rate).  They only measure total dose irrespective of time.

To get an idea of distance from a source, you would have to know the strength of the source at the time of the exposure, the total time of exposure, and the total dose received.  Then you can make an estimate of your distance from the source.

The PRD only gives you total dose.

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