[DoctorOetker]

I was hoping this would be an artists project page describing the passive imaging of radiation (i.e. not a simple X-ray scan).

Imagine a planar array where each pixel gathers counts like an MCA (multichannel analyzer), mounted in some lead pinhole camera obscura.

This would give an extremely wide range of channels didactically illustrating the presence of calcium in gypsum (dryboard etc), visually show backscatter, etc.

Such pictures of modern and old city scenes would be mesmerizing to watch, partially seeing into buildings, the ground, ...

[defrost]

Takes a while to do an entire continent this way, luckily when you start in the 1970s it's all over by now.

* https://www.ga.gov.au/bigobj/GA13928.pdf

* https://www.ga.gov.au/bigobj/GA18007.pdf

Visualising full 256 channel multispectral data can be tricky, the approach taken above was to take the raw data and process it to create a false colour RGB image representing the strength and interaction between natural background potassium, thorium, and uranium.

[DoctorOetker]

Thank you for this reference! I had been looking for such data for a long time.

[defrost]

It's been kicking about in geoscience collections, mining company archives, etc. for a while.

Russians, South Africans, USAians, et al all run crews - we (Australia) have done Australia, Mali, other African regions, all of Fiji (many islands), India in May 1998 (the Pokhran-II nuclear test sites as they happened), and elsewhere.

The data is one thing, processing raw spectrometer data is a whole other thing - calibrations, corrections, dead time, etc.

See: Grasty / Minty GUIDE TO THE TECHNICAL SPECIFICATIONS FOR AIRBORNE GAMMA−RAY SURVEYS https://www.ga.gov.au/bigobj/GA7667.pdf

[DoctorOetker]

Do you know of similar maps for Europe?

[defrost]

This is a different kind of radiometric data that is available:

  The EUropean Radiological Data Exchange Platform (EURDEP) consists of data exchange mechanism and presentation website for radiological monitoring data which is collected and shared by 39 participating countries in almost REAL TIME.

* https://remon.jrc.ec.europa.eu/About/Rad-Data-Exchange

Certainly useful for a mapping European normal background, the details under the hood could be a pain (types and formats of data, etc), it's historic and ongoing chronological data for distributed fixed points.

Their interactive public play map is normalised(?) raw total counts, _not_ a spectrum of gamma events bucketed by energy - ideally they are also recording and sharing full spectrum data at some stations in their network .. and making that publically available.

Of possile interest:

* https://www.abc.net.au/news/2022-08-10/hedley-marston-marali...

* https://www.wakefieldpress.com.au/product/fallout/

[defrost]

Know of .. yes.

Off hand, I'm not familiar with any public facing portals for downloading raw data.

Bear in mind, these are "snapshot" static, historic, broad area spectrum maps - they're not live, they won't show new leaks, changes, etc.

They are, however, "training data" for forming a kernel of a NASVD - Noise Adjusted Singular Value Decomposition - a bundle of all the major features of typical regular environmental radiation for some locale.

If you fly about or have an instrument taking live readings and subtracting a normalised background kernel .. you get the faint trace "weird arse stuff" lighting up instead of being buried.

Finland's the home of the NASVD author, the country used to run "find a barrel of waste" in a forrest compitions back in the day, they're adjacent to some radiometrically filthy submarine docks and pens just over a border.

The game goes thus - fly at about 70m/sec about 80m above the deck in some kind of frame carrying 30 to 40 litres of doped crystal packs .. and pick out a signature in near real time from one second spectrum windows.

They have data, I don't know about portals.

https://www.helsinkitimes.fi/finland/finland-news/domestic/2...

Can confirm, though, Cresco STOL's make a good platform: https://www.youtube.com/watch?v=1_MO5Wfomks

[jareklupinski]

currently trying to make a flip-dot display (think https://theartistbreakfast.com/works/spectral-flashbacks-ser...) but with some kind of radiation detector behind each pixel that will flip the dot when something passes through

i made a small 3x3 proof of concept using more expensive geiger tubes, and their really long 'z-axis' lengths made 'traces' happen very often, like a persistent cloud chamber

trying to find a reliable semiconductor (read:cheaper) method i can scale to an arbitrary number of pixels, but something seems to happen in between the bench and the wall :(

[DoctorOetker]

How many pixels would you aim for?

I have considered

* scanning a linear array of BPW34 photodiodes, in a similar spirit to a scanner to cover a plane, each photodiode going to its own "MCA circuit" (TIA->cheap audio codec like those from Everest Semi). Either direct measurement of generated charge pulses or covering the photodiode with phosphor on aluminum foil or so

* cloud or bubble chamber (cloud chamber is less dense and will generate fewer events, so probably bubble chamber): instead of needing a large 2D or 1D array of parallel circuits, we image and track generated charged particles and use the trajectory starting end (less curved) to determine the source direction!

* consider X-ray crystallography, an incoming straight beam can diffract in many directions on a monocrystal. rotating say a silicon wafer, and measuring the incoming photon energies with one or more photodiode/MCA circuits we can assign a source likelihood distribution by keeping track of the orientation of the monocrystal. akin to sparse sampling but instead of masks its diffraction patterns.

If you have better ideas or variations in mind, let me know!

[jareklupinski]

for resolution, i'm only limited by whatever the bus company is throwing away that day ;) but i'd love to come up with an easy-to-produce design that can work per-pixel for arbitrary spacing

yup after seeing #2 at a museum and learning about the chemistry needing to keep it running, i started looking for something like #1, but i'm not able to get any PIN diode circuit properly reporting events with consistency compared to my GM tubes :(

#3 sounds fun! i'd like to turn this into something i can open-source and hang on a wall, emitting x-rays might make it a hard sell :P

after reading about https://en.wikipedia.org/wiki/Single-event_upset#SEUs_and_ci... , i'm wondering if it's possible to use a suitably dense FPGA in a complicated enough design that any failure must be due to cosmic effects? monitoring ECC might not be enough https://en.wikipedia.org/wiki/ECC_memory#Concept

[DoctorOetker]

For your PIN diodes, what was the depletion region width/thickness of the Intrinsic layer?

Do you have access to a high bandwidth oscilloscope? do you observe the expected exponentially decaying pulses? Sound like you could debug your circuit to find out what is happening.

For higher energies on would want to use a thicker intrinsic region, one approach I have considered would be to use a distant aperture, so that the direction of incoming rays is known, and then tilt the photodiode so that the rays can experience a much longer path in the intrinsic region (so that when a photon generates a high energy electron, the stopping length can be attained without clipping / aliasing the energy resolution as much). Basically tilt the photodiode so that its plane is closer to parallel (or exactly so). There is a trade off between cross section (fewer events) and maximum energy measurable, one can compensate for the lower cross section by having more photodiodes.

all 3 proposals would be passive, including #3, so it wouldn't emit X-rays, just detect them and build up a self-consistent picture that explains the observation statistics for each event (with that energy and time/orientation of the silicon wafer).

[jareklupinski]

i was just using BPW34s :) i have a batch of different photodiodes that i was planning on swapping and comparing but i can't even make these work reliably...

currently limited by my 20MHz scope (and free time...), but i saw the expected pulses after they were drawn out long enough by the amplification circuit to validate it was working on my desk (https://physicsopenlab.org/2020/06/15/cern-diy-particle-dete...), but i think my issue is shielding the diodes without introducing noise?

this guy has to actually shave away some part of the diode to make it work? https://hackaday.io/project/204159-geigerwatch-a-sensitiv-ra...

[DoctorOetker]

sounds like you were nearly there

> this guy has to actually shave away some part of the diode to make it work? https://hackaday.io/project/204159-geigerwatch-a-sensitiv-ra...

Thats because he also wants to measure alpha and beta particles directly, if you are satisfied with high energy photons you wouldn't need to do that