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Old lead

Posted: 04 Jan 2018, 17:48
by pilgrim
Hi all,
a friend of mine provided me some old lead pipes, coming from an old house of the WWII times; so this lead has about 70 years and at least 3 half-life.
I'm trying to build a lead castle with it, but the gross weight it's about 70/75 kg, not enough to make a "serious" shielding.
So my aim is to make a kind of lead liner, only 1 / 1,5 cm thick, then cover it with the classic lead foil 1.5mm thick, to obtain a greater thickness; the internal old lead liner should reduce the outer lead radioactive emission.

I melted a bit of this old lead into an ingot of about 2kg, to compare it with the classic lead (recycled lead seals).
With a GM Counter with LND7317 I made some measures:
Background: 40±1,3 CPM
Old lead ingot: 35±1 CPM
Leas seals : CPM 40±1,3 CPM
So the "old lead" seems to be significantly less active.
Then I tried to make some spectra :
These are the 2 spectra overlapped, light blue is the “new” one, brown is the old one.
As you see there is no voltage drifting

This is the old lead spectrum
This is the new lead spectrum
151,4 vs 145,8 CPS.
Do you think the old lead is really less active and the future lead castle will give really a lower background?

Re: Old lead

Posted: 04 Jan 2018, 23:45
by luuk
Hi Daniel,

It is very difficult to compare two materials if you don’t have a good lead castle :-) to eliminate the background special if you take a long measurement to get enough counts to compare.
Than you need two exactly(100%) the same size(dimension) and weight of lead, under exactly the same angle, and distance with your detector even the slightest difference can influence the outcome.

Re: Old lead

Posted: 05 Jan 2018, 01:32
by pilgrim
Hi Luuk,
thank you for your suggestion.
Maybe I can melt the lead seals into the same ingot to make the comparison you mean.
If I'll do it, I will sure post some other spectra.

Re: Old lead

Posted: 06 Jan 2018, 22:51
by cicastol
Hi Pilgrim, the term "old" should be referred to lead aged at least more than 10* t1/2 210Pb (22y) , you can't take advantage of the low 210Pb content in amateur setup where background continuum is dominated by cosmic interactions ,you get only a little bit of lower background under 500keV ,and probably with your's lead there is no difference at all.

Re: Old lead

Posted: 06 Jan 2018, 23:59
by pilgrim
Hi Cicastol, thank you for the reply.
So you think this lead is quite useless...
By now I have it and I think I will continue with the project, but without great expectations ;-).

Re: Old lead

Posted: 07 Jan 2018, 07:48
by MaxGaspa
pilgrim wrote: So you think this lead is quite useless...
You never know!

The amount of time from the production date is only one parameter to understand if your lead is useful or not. The other parameter is the initial concentration of Pb210.

The reduction factor of Pb210 has to applied to the initial concentration, in "new" lead that concentration may vary from few tenth of Bq/kg (in "special" pure new lead as the "LC2 lead") to 50000 Bq/kg in lead from soldering (due to the process used for adding tin). As far as I know the average value for common new lead is few hundreds of Bq/kg. So there is the possibility that your old lead is worse than common new lead. Especially in cheap lead used in the past for pipes, the production steps may use coal for the reduction processes of the minerals. Coal has an important content of Uranium. So if your lead contains residual Uranium the Pb210 content may be greater than expected.

So the only way to know is a direct measurement of the Pb210 concentration (not easy in an amateur lab) or using very very old (ancient roman) lead. Even ancient roman lead was carefully measured before using it by the INFN (an Italian research lab using ancient roman lead)

The contribution of Pb210 to you background comes from the progeny, Bi210. The soft beta and gamma radiation from Pb210 is self-absorbed by the shield but the energetic beta ray form Bi210 (up to > 1 Mev) is causing bremmstrahlung and X ray fluorescence. The bremmstrahlung continuum peaks at 170 kev that is not enough for pair production, the well known X ray peaks are close to 80 kev.

Usually the "old" or "pure" lead is used as internal lining (one to few cm) to avoid the Bi210 induced radiation.

A far as I know the usefulness of the pure lead is negligible in an amateur lab where very low radioactivity measurements are difficult or impossible. So use your lead for building the shield and post the final background in your final shield. Just to know.

Re: Old lead

Posted: 07 Jan 2018, 08:05
by pilgrim
From bad to worse! :-(
Thank you Max for your detailed explanation.
I'll build it, by now it's a personal challenge :-).
I don't know when, but I will surely post the background spectrum once finished, hope within few months.

Thank you all again.

Re: Old lead

Posted: 11 Jan 2018, 07:48
by pilgrim
I couldn't help trying to assembly a castle with the lead ingots, to make the test Max suggested.
As you see the castle it's quite teetering and full of fissures, but it works respectably : with a 2"x2" NaI probe, it gives a background of 8.3 CPS against about 166.5 CPS on the outside.
Here you can see the calibration with Cs137
Cs137, 30min calibration.Lead ingots castle, 60Kg.NaI(Tl) 2x2 @ 900V 2.png
And the background after an 8h acquisition.
Background 8h.Lead ingots castle, 60Kg.NaI(Tl) 2x2 @ 900V 2.png
Here there’s a comparison between the two backgrounds, taken in different days.
Background 8h.Next to the castle NaI(Tl) 2x2 @ 870V.png
I don't know if it's enough to judge if this lead is more o less radioactive than the standard lead...

Re: Old lead

Posted: 07 Jul 2018, 09:49
by Alain
Hi Daniel,

As other members already said, you will hardly see any difference in normal background environment. But I should be careful with old sewer pipes! In case of old house and dry syphones, radon gas can easily find it's way from the underground sewer system to the surface through the house pipes. And you can expect a lot of radon in this air, believe me! When radon decays, one of its progeny is also unwanted Pb-210, which sticks to the internal walls of the pipes and contaminates them. Although most of this Pb-210 readily oxidize in air and water, some part of it can stays in the metalic form and when you melt such pipes, both Pb (stable and radioactive) would mix together and become inseparable. So if using such pipes, I would try at least to scratch-off a surface layer of the internal part of pipes, but that is not so easy to do (you can, for example, cut-open pipes with some shears, then roll-off and straighten this lead sheets/stripes and then try to scratch a surface layer with some sharp object until your lead shines). When melting, try to remove as much as possible of oxide layer and other dirt, which floats on the top of melted lead (a yelowish-bluish "skin").

One more remark about spectra comparison in Theremino, which is not so uncommon: it would be better to see the actual shielding effect from both spectra, if you turn off the function "Max" (a button on the right upper corner of the screen). If you have turned on (as in your case), the program automaticaly "zooms" both spectra to their maximum peak to fit the best on display, thus disable the real comparison about amplitude or even give totaly wrong impression (look the right side of the spectrum - line with lead castle appears like the background is even higher than without shield, which is not the case).

Regards, Alain

Re: Old lead

Posted: 07 Jul 2018, 13:15
by pilgrim
Hi Alain,
thanks for your reply.
Just few days ago I melted all the ingots into 9 rings and a bottom and believe me, only God knows how much oxide and dirt I removed!
But now the shield is almost ready, only the liner is missing.
Before melting the lead I made a comparison with a standard lead ingot and an "old" lead ingot, and actually the difference is tiny :
With a Geiger counter (LND 7317) :
Pb new = 10287 ± 102 => 43 ± 1.2 CPM (2σ -> 95%)
Pb old = 9604 ± 98 => 40 ± 0.8 CPM (2σ -> 95%)
With a 2"x2" scintillator probe + Ratemeter
Pb new = 14884 ± 122 => 1488 ± 24.4 CPM (2σ -> 95%)
Pb old = 13904 ± 118 => 1390 ± 23.6 CPM (2σ -> 95%)
These days I will work on the liner, I've already find the copper sheet (2000x400x0.6mm), now I'm looking for the tin, then, finally, I will be able to take some spectra.

Thank you again for your reply and suggestions.