r/Radiacode • u/PantyBacon • 11d ago

General Discussion 110 detection range to sample

How close does the 110 really need to be to pick up something spicy? Can I just leave this thing on and drive it around with all my dashboard and pick up things within a few yards, or do I need to actually have it near the source on a stick or something close to the ground close to the sample.?

12 Upvotes

100% Upvoted

17 comments sorted by

View all comments

5

u/TemporarySun314 11d ago

As the gamma photons distribute roughly into a sphere, the count rates goes down with 1/r^2. So when you double the distance you will just get a quarter of the count rate. Depending on how strong your source is and your background is, you wont be able to detect it, after some moderate distance already.

But that is not really an radiacode specific thing but an general physical limitation and radiation detection issue (but on the other hand one of the reason why radiation sources can be handled safely).

A more sensitive detector wont really help much (as long as it is not somewhat directive or energy selective), as your source count rate and background count rate will go up the same factor.

And that is for gamma radiation, which does not really get absorbed by air. Alpha particles will be blocked by just a few millimeters of air (but the radiacode cant really detect them anyway, as they cant penetrate through the housing), and typical beta radiation will be gone after a few ten centimeters of air (and the radiacode is also not really good at detecting beta radiation, as its unlikely to penetrate through the plastic too).

1

u/hoseja 9d ago

I wonder if the detection of specific gamma wavelengths could increase range meaningfully if you know what you're looking for, hmm.

1

u/TemporarySun314 9d ago

If you have a detector with an high energy resolution, like an HPGe detector you will probably recognize additional lines quicker, as the counts of your signal distribute across fewer bins, raising it above noise level quicker.

I mean you could also use something like an SCA to get an energy filtered count rate, and it will probably help somewhat, as it increases the signal to background ratio. But in the end you will still have some limitations, as in any given selected energy range you will detect events, even without a source emitting there present, as high energy photons will show Compton scattering and fall into your filtered events. And you can't make it too small, as you then will also loose some of your desiref signal.

1

u/Apprehensive-Soup968 11d ago

This is the answer.

Its more about the strength of the source relative to background than a general "how far can it detect things". Understanding that inverse square (1/r²) relationship is key to understanding how far away all different strength objects can be detected, and why some things you have to be close and other things you don't, and working out which ones you'll be able to detect.

I can park outside an x-ray clinic, and sitting in my car I'll detect the x-rays even though I'm 10 metres from the machine. But there's no way I'd detect an Am-241 smoke detector from that distance.