Gummite, Uranium Ore from Australia

[Go-Figure]

Hello there,
This weekend I tested a 9.62 grams sample of Gummite from Australia. It doesn’t fluoresce under UV light but it certainly looks good nevertheless. Enlarge to have a better look.

21000 CPM was the Geiger counter verdict, not bad but nothing too hot.

As usual the potential danger in handling samples like these is the accidental internal exposure for inhalation or ingestion of dust and little fragments that can break apart from the ore. As can be seen in the photo just a few days were enough for a small amount of dust to deposit at the bottom of the plastic bag.

According to the seller this sample was hot enough to give a dose rate at contact of 5 μSv/h, but that was actually an overestimation, we are more in the region of 1 μSv/h, as can be read in the PDS display that I used to record a preliminary 2 hour spectrum just to get a sense of what to exptect.

This preliminary test was done on July 2, when temperature was several degrees down compared with the last time I calibrated the PDS, so I had to adjust calibration substantially because in my first attempt was off by a long way. The result has “Uranium” written all over it.

Quantitatively the sample at contact gave five times as many counts as the background, so I decided I didn’t need any shielding for the measurement with the GS 2’’x2’’.
So here’s my unshielded background. Just 12 hours were enough.

07 - Background - Stanza Fondo - 12 Hours - 0.040 Gauss - No Shield - 11-07-20.png (46.44 KiB) Viewed 7940 times

And finally I tested the sample for 8 hours. All expected Uranium peaks are there, including Pb210 at 46 keV which not always shows up so clearly.
The most prominent peak in terms of counts is, as always, the 77 keV peak from Pb214, and this is among the reasons why I avoid using lead shielding when not necessary, sometimes that peak is “dismissed” as just XRF, while it’s actually the strongest peak in basically all Uranium spectra regardless of the shielding which, when present, merely reinforces it.
Just north of it the 92 keV Th234 peak is visible, which allows to identify its “brother” at 63 keV despite the fact it’s only visible as a small bump in the result.
The rest is all pretty straightforward, with the exception of the 35 keV peak which I found several times in Uranium spectra but I still cannot identify.

Not visible here, there’s another clear Bi214 peak around 2200 keV, which I cut out just in order to have more “room” to label the other peaks in such a “crowded” spectrum.

There’s a good linearity across the board, it only starts to be a bit off in the 1764 keV Bi214’s peak, but the rest is pretty much dead on.

Results from the quantitative analysis are a bit different from that of PDS, but just because the sample was not as close to the crystal as it was with the PDS

In summary, another nice Uranium ore that was fun to test and that 35 keV still remains a mistery to me…

Until next time.

Massimo

[Mike S]

Excellent work as usual Massimo!

I learn a lot from the spectra you share along with your process and equipment details. Please keep sharing.

According to the seller this sample was hot enough to give a dose rate at contact of 5 μSv/h, but that was actually an overestimation, we are more in the region of 1 μSv/h, as can be read in the PDS display that I used to record a preliminary 2 hour spectrum just to get a sense of what to expect.

I wonder if the seller was using a beta sensitive detector and that incorrectly increased their measured dose rate?

Mike S.

[cicastol]

Excellent work as usual Massimo!

I learn a lot from the spectra you share along with your process and equipment details. Please keep sharing.

According to the seller this sample was hot enough to give a dose rate at contact of 5 μSv/h, but that was actually an overestimation, we are more in the region of 1 μSv/h, as can be read in the PDS display that I used to record a preliminary 2 hour spectrum just to get a sense of what to expect.

I wonder if the seller was using a beta sensitive detector and that incorrectly increased their measured dose rate?

Mike S.

Maybe , Massimo dose rate estimation with PDS take account only for gamma and is not corrected for source-detector geometry, way far off from real, estimating a real whole contact skin dose rate accounting for Alpha, beta, and gammas can be a little trickier , in literature betas are normally 2-3 times gammas dose rate in Uranium ore.
5uSv/h contact skin dose rate could be much more in ballpark.

[Go-Figure]

Yeah, this is the dose rate from gamma only. On the other hand, when talking about external exposure what you want is dose rate from penetrating radiation, we know alphas is not penetrating at all, while beta is absorbed by the top layer of skin, it can damage your skin (skin burn), but cannot affect internal organs if not inhaled or ingested.
When I take measurements that include particulate radiation (beta and alpha) i only report them in count rate. External dose is not really defined for alpha and there are very, very few instances where beta dose becomes more than negligible.

A few references:

https://www.ncbi.nlm.nih.gov/books/NBK158792/
In general, external exposures are from material emitting gamma radiation, which readily penetrate the skin and internal organs. Beta and alpha radiation from external sources are far less penetrating and deposit their energy primarily on the skin's outer layer. Consequently, their contribution to the absorbed dose of the total body dose, compared to that deposited by gamma rays, may be negligible.


https://www.env.go.jp/en/chemi/rhm/basi ... 03-10.html
In the case of external exposure, α-particles do not have any effect as they stop at the horny layer on the surface of the body (the penetrating distance of α-particles is about several tens of micrometers). β-particles pass through the skin (their penetrating distance is about several millimeters) and can cause burn-like symptoms when doses are very high, but do not reach deep into the body. γ-rays reach important organs deep inside the body. Thus, the major concern in the case of external exposure is with γ-rays.


https://www.ncbi.nlm.nih.gov/books/NBK232435/
Beta particles are electrons and typically penetrate into the tissue only a centimeter or so. Their limited range means that they can damage internal organs only when ingested or inhaled, but they can be an external hazard to exposed skin if they are present in sufficient concentrations.

[cicastol]

According to the seller this sample was hot enough to give a dose rate at contact of 5 μSv/h, but that was actually an overestimation, we are more in the region of 1 μSv/h, as can be read in the PDS display that I used to record a preliminary 2 hour spectrum just to get a sense of what to exptect.

If you are talking about contact dose rate as per ICRU you are dealing also with shallow dose equivalent Hp(0.07) , so betas should be always accounted for.

[Go-Figure]

According to the seller this sample was hot enough to give a dose rate at contact of 5 μSv/h, but that was actually an overestimation, we are more in the region of 1 μSv/h, as can be read in the PDS display that I used to record a preliminary 2 hour spectrum just to get a sense of what to exptect.

If you are talking about contact dose rate as per ICRU you are dealing also with shallow dose equivalent Hp(0.07) , so betas should be always accounted for.

Well, if I wanted to measure the shallow dose equivalent for the assessment of the dose to the skin and to the hands and feet I should account for beta but that's not what I am after here.
Besides, "At contact" here means at contact with the body of the device, a few millimiters away from the crystal.
When talking about external esposure I am referring to gamma radiation, for the reasons mentioned above, after all the Total Effective Dose Equivalent (TEDE) doesn't include the shallow dose equivalent, being the sum of the deep dose equivalent (for external dose) and the committed effective dose equivalent (for internal dose).

I don't know for sure and I might well be wrong, but I suspect the seller simply put a Geiger counter close to the sample and read the display, as they all do.