Spectrum of Allanite-Ce

[sgt_bear]

Hello

A mineral named Allanite-Ce got my attention since the seller mentioned "radioactive", but it was not uranium, radium or thorium related, so i decided to look it up on the internet.

The compositon of Allanite-Ce is:
http://webmineral.com/data/Allanite-(Ce ... fzV7YjathE
Calcium 3.91 %
Cerium 27.35 %
Yttrium 4.34 %
Aluminum 9.88 %
Iron 6.81 %
Silicon 13.71 %
Hydrogen 0.16 %
Oxygen 33.84 %

After seeing this info I decided to aquire the mineral, since the seller confirmed 2000cpm with his ludlum model 3. Of course there is no possibility to confirm if the mineral is really Allanite-Ce of just labeled as. To confirm i guess xrf would be the only option.

The mineral looks is around 100g, 3x5cm and looks like this:

mineral1.png

Here is a aprox. two hour spectrum of the mineral with the energies of the peaks.

spectrum.png

points.png

Im not really sure what i'm seeing here, and i wonder where the radiation comes from.
If we look at the element compositon of the mineral, the only radioactive element i found is Cerium which has 3 stable (Ce136,138,140) and 1 radioactive isotope (Ce142).

If i look up isotope data for Ce-142 there are no energies listed. No sample spectrum or anlaysis was found for this mineral or cerium at all.

Some ideas about the peaks:
Nr 1 some x-rays?
Nr 2 xrays or Ba-133 (81kev) ??
Nr 3 ???
Nr 4 @ 240keV maybe Pb-212 @ 241keV ?
Nr 5 @ 340kev maybe Ac-228 @ 328/338 keV?
Nr 6 ???
Nr 7 ???
Nr 8 @ 600keV mabye Tl-208 @ 583keV or Bi-214 @609keV?
Nr 9 @ 730keV maybe Bi-212 @ 727keV?
Nr 10 @ 930keV mabye Bi-214 @ 934keV?
Nr 11 @ 1650keV maybe Ac-228 @ 1587keV?
Nr 12 ??
Nr 13 ??
Nr 14 ??


I've attached a zip with the theremino files if someone wants to look at the spectrum in the theremino software.

What do you think about this rather unsual spectrum? Any ideas what else the peaks could be?

[Zagros]

Hello,
The spectrum you obtained is typical from Thorium.
Is easy to find allanite samples associated to some Thorium minerals.

[Peter-1]

Hello,

I have a small sample of Allanite. Now i measured > 10 hours and realize that it is not only a series from the thorium decay products, but also from the uranium radium decay.

Allanit-001.jpg

Allanit-002.jpg

Spektrum.jpg

Spektrum-2.jpg

Peter

[Geoff]

Most minerals with dominant REE content will substitute U and Th into the structure. In fact, if you scroll down farther on webmineral you can see that it is considered a radioactive mineral.

Capture.PNG

[Geoff]

Interestingly, there is a form of allanite with Be substituting for Al, creating a natural neutron source. This special type of allanite has the highest known naturally occurring amount of plutonium. The mineral used to have it's own name, but it was discredited and is now just allanite.

[stamasd]

Interesting. I was going to say that it looks like a cousin of monazite, but AFAIK monazite never has Be or Pu.
Even more interesting, apparently allanite can be found in specimens from the Franklin mine in NJ. I have somewhere some rock samples that I collected last summer from there. I never thought of checking those with a GM counter. I'll look for them and check them out.

[sgt_bear]

Most minerals with dominant REE content will substitute U and Th into the structure. In fact, if you scroll down farther on webmineral you can see that it is considered a radioactive mineral.

I know that it was radioactive, i found it because of this (have a ebay watchlist on all radioative rocks), but if you say all REE minerals have U or Th, i guess it will be hard to find any minral that has other isotopes than U,Th and Ra ?

[stamasd]

Well considering that U Th and Ra (and their daughters) constitute the overwhelming majority of natural radioactivity, that would be very hard to do indeed.