Lantern Mantle (Thorium)

[Go-Figure]

Hi there,
I guess everyone here already did this spectrum and probably many of you even posted it.
Still, here's mine.
Lantern mantles. I received them inside little transparent plastic bags and I have no plan to ever getting out of them, so no direct skin contact, just in order to avoid risk of accidental ingestion or inhalation.
I was surprised by the read on the geiger: 22000 CPM (background 50-60 CPM), with plastic in between blocking a good share of alphas.
The first time I recorded the mantleìs spectrum I didn't even subtract the background and the result wasn't that different from the one I post here. It's one of the most active things I tested so far.

Every time I record a spetrum with Thorium the last Tl208 peak at 2.6 MeV is off by more than 50 keV. That's simply because my last calibration point is at 662 keV (Cs137).
This time I decided to use the mantle itself for calibration, so unsurprisingly the peaks (Th232 progeny) are all where they should be. At 2.6 MeV the error is far less than usual.
Is this cheating? Well...

Below you see two "views" with different zoom in the X-axis, for both I attach both counts per bin and energy per bin. In the first view you can't see the higher energy peaks, but the others are more clear.

Massimo

[Sesselmann]

Massimo,

As you have discovered Th232 is a good source for multi peak calibration. Some detectors suffer from a bit on non linearity, this can be due the the choice of resistors in the voltage divider or the voltage applied. When the resistance is too high, you will see that the 2614 keV pulse does not reach full potential, this is due to current limiting. Often the solution can be as simple as lowering the voltage and increasing the preamplifier gain, however if this doesn't work you may have to rework the VD.

A simple way to check the linearity of your probe is to plot the Th232 peaks on a spreadsheet as a scattergram, expected peak energy on the Y axis and arbitrary units on the X axis. It will look something like;

Y Value,| X Value

0, 0
238, 8.19
338, 11.63
583, 20.07
911, 31.36
1588, 54.674
2614, 90

If your probe is linear you will see that all the points fall on a straight line.

Steven

[cicastol]

Hi,
nice spectrum, 228Ac 1588 KeV peak is also reinforced by the double escape peak (1592KeV) .

[Go-Figure]

Thank you both.

Massimo