Talk:Polonium-210

Decimal separator

The half-life is specified as 138.376 days. I have 2 questions.

• Is the half-life about 138000 days or about 138 days? The use of "point" or "comma" as thousands separator is ambiguous as they are also used as decimal separators.
• Has the half-life really been measured to 6-digit precision? In Isotopes of polonium it is given as 138.376(2). 6-digits are also given in the article Polonium. 6-digit precision is highly unlikely, given the stochastic nature of radioactive decay. In any case, an experimentally determined estimate for the uncertainty should be included with the value, with citation. Petergans (talk) 07:20, 30 July 2019 (UTC)

@Petergans:

• Commas are used for thousands separators and points for decimal. This is standard for English and is consistent within the article and Wikipedia's Manual of Style.
• I cannot comment on whether the precision is accurate, but is supported by ref 1 (doi:10.1088/1674-1137/41/3/030001). The uncertainty is ±0.002 days.

Hope it answers you! ~~Ebe123~~ → report 09:08, 30 July 2019 (UTC)

This web page http://www.nuclearsafety.gc.ca/eng/resources/fact-sheets/polonium-210.cfm%7C[1] should be reliable. It gives the half-life as "about 140 days" Petergans (talk) 09:03, 31 July 2019 (UTC).

https://www.chemistryworld.com/news/polonium-210-a-deadly-element/3003225.article says 138 days. I think the Royal Society of Chemistry is a decent source. I wonder where 138.376 is from? Ewen (talk) 09:41, 31 July 2019 (UTC)

http://nucleardata.nuclear.lu.se/toi/nuclide.asp?iZA=840210 states 138.376 days Ewen (talk) 09:44, 31 July 2019 (UTC)

Nuclear Data Center at KAERI; Table of Nuclides http://atom.kaeri.re.kr/nuchart/?zlv=1 another source for 138.376(2) days Ewen (talk) 10:12, 31 July 2019 (UTC)

{{NUBASE2016}} also gives 138.376 days, and is the most recent data collection that I know of; it is used for half-lives of isotopes of other elements. Petergans, I note that you believe this value is erroneous for being too precise; could you please explain why you believe this even though several reliable sources agree on the 6-digit precision? I don't doubt the reliability of the source you provided, though I wonder if there is one that suggests that 138.376 days is incorrect. Otherwise, it's not clear to me how we decide which value is more correct. ComplexRational (talk) 14:29, 31 July 2019 (UTC)

@Petergans: Your objection to the 3-decimal place figure sounds like original research, and the sources back up the six-digit figure. you gave a counterexample of the more abundant isotope C-14, but isn't the C-14 figure limited because of the longer half-life rather than the abundance? Ewen (talk) 14:29, 31 July 2019 (UTC)

I checked http://atom.kaeri.re.kr/nuchart/?zlv=1 and it cites the half life of C-14 as 5.70 ky (0.03) (edit: 0.003) as well as 138.376 d (0.02) for Po-210. That looks like KAERI are happy with both those levels of precision. Ewen (talk) 14:34, 31 July 2019 (UTC)

(edit conflict) Ewen makes a valid point: that per OR, the decision shouldn't be ours to make. I will also comment that precision is harder when the half-life is longer (e.g. the half-life of ²⁰⁹Bi is estimated to the nearest 10¹⁷ years), but we have many figures from NUBASE (or our isotopes pages) where at least five significant digits, of which at least three are after the decimal point, are given on a comparable timescale (e.g. ²⁰³Hg = 46.595 d; ²²⁸Th = 1.9116 y). ComplexRational (talk) 14:41, 31 July 2019 (UTC)

Thank you, @ComplexRational:. NUBASE is quite a resource! Ewen (talk) 15:03, 31 July 2019 (UTC)

You are welcome. It is indeed very helpful. ComplexRational (talk) 18:09, 31 July 2019 (UTC)

I did a back-of-the-envelope calculation comparing C-14 and Po-210. A commonly cited figure for C-14 is 5730 years, published 22 years after the isotope's discovery. That would mean less than 0.3% of the decay curve was measured. For Po-210 we can measure practically all the decay curve. That explains the extra precision. Ewen (talk) 15:08, 31 July 2019 (UTC)

The length of the half-life is immaterial. The issue concerns the precision of the original measurements and the stochastic nature of radioactive decay. We need to find a primary publication as secondary sources are clearly contradictory. Petergans (talk) 22:44, 31 July 2019 (UTC)

I haven't yet found any primary publication in which the half-life is directly measured, but there are two things I can say already. Many of the secondary sources do seem to agree on 138.376, with some even quoting it as the "accepted value" (e.g. page 7 of {{Thoennessen2016}} quotes the present/presently accepted half-life as 138.376 ± 0.002 days). Also, given that the initial measurement was in 1898 (longest studied and discovery paper harder to find), and that the isotope ²¹⁰Po is mass-produced unlike most radionuclides that are made one atom at a time, I am less inclined to believe that the value is erroneous and instead it seems that the measurement only becomes more precise after 100+ years of studying this nucleus. If I do find a primary publication, though, I'll let you know. ComplexRational (talk) 23:57, 31 July 2019 (UTC)

The problem is that literature values are contradictory in regard to precision. In a quick search I found 3 reports that contain a low-precision value and chose the one which was presumably prepared by an expert.

From the WP page List_of_radioactive_isotopes_by_half-life:

isotope	half-life
	days	106 seconds
phosphorus-32	14.29	1.235
vanadium-48	15.9735	1.38011
californium-253	17.81	1.539
chromium-51	27.7025	2.39350
mendelevium-258	51.5	4.45
beryllium-7	53.12	4.590
californium-254	60.5	5.23
cobalt-56	77.27	6.676
scandium-46	83.79	7.239
sulfur-35	87.32	7.544
thulium-168	93.1	8.04
fermium-257	100.5	8.68
thulium-170	128.6	11.11
polonium-210	138	11.9

This table gives values with the number of significant figures that are warranted by the precision with which the values have been obtained. This value for polonium-210 should be used in the absence of a citation of a primary source that says otherwise. Petergans (talk) 10:04, 1 August 2019 (UTC)

I bet most people are simply rounding the value off when 6-figure precision is not needed. It seems quite strange to advocate for an unreferenced value at List of radioactive isotopes by half-life when there are much more precise referenced values around. Radioactive decay is stochastic, but since the half-life is defined simply as the time period it takes for the probability of a radioactive atom to decay to reach 50%, that is no objection to its being measured with great precision (like this for ²¹Na, with six digits indeed, even if the uncertainty affects the last two). As for ²¹⁰Po, you may look at the source list from the BIPM's table of radionuclides (²¹⁰Po alone here): there the half-life is given as 138.3763(17) days. Primary-source determinations should be somewhere in those references. Double sharp (talk) 10:23, 1 August 2019 (UTC)

Those other sources do look rounded, especially the one that says 140 days; everything else gives at least three significant digits, if not six or seven. Even though decay is stochastic, a large enough data set can enable precise measurements; no one would provide an arbitrary estimate of six significant digits. Additionally, if all the primary sources were published no later than 1989 (as suggested by the ²¹⁰Po data sheet above), can we really consider them more reliable than the nuclide table or atomic mass evaluation published c. 2016 that includes the last 30 years of data? ComplexRational (talk) 11:24, 1 August 2019 (UTC)

@Petergans: no, the length of the half-life will affect the precision. With a longer half life there will be fewer observations to go on, inter alia. Po-210 has a half life 15,000 times less than C-14. This means, for the same number of atoms, over the same time period (shorter than the half life), roughly 15,000 times more data can be collected for Po-210 than for C-14. Call "stochastic" all you like, but if an atom is 15,000 times more likely to decay, then it's easier to collect the data. Ewen (talk) 10:15, 1 August 2019 (UTC)

The precision of the value of a half-life depends only on instrumental factors. For an exponential decay, the value, x(t), of a measured decay count at time t is given by

x(t)= a e^-kt

where a is the rate at t=0 and k is the decay constant which is simply related to half-life. The values of the parameters a and k are determined, along with error estimates, by non-linear least-squares fitting of a set of experimental data values. The precision depends only on the precision of the experimental data. This is a property of the instrument used to collect the data. To a lesser extent, the greater the number of data points collected, the greater the precision of the calculated parameters. Petergans (talk) 13:15, 4 August 2019 (UTC)

@Petergans: It's not a linear relationship between the precision of the data and the precision of a and k, though. For example, with a very long half life (millions of years, for example) we will measure almost the same values of radioactivity even if we can measure for a long period (in human terms). This would give the value for a with high precision but k would be much less certain. With a faster half life we might be able to measure k more precisely but a would be less certain. Now, a is not such an important property of the isotope so that's no big deal. I suppose you could calculate k if you knew exactly a and the number of atoms in the sample at time zero, but I've not heard of the being done: maybe for the single nucleus samples of superheavy elements? Ewen (talk) 14:44, 4 August 2019 (UTC)

I ran a Monte Carlo simulation using Excel. Keeping the timing and number of measurements constant, the error for k decreases as k increases (it's linear on a log-log plot). The precision for a is pretty constant, actually, and in line with the (simulated, random) error of the measurements. The error of k can be less than the random instrumental error, generally this happens if the measurements are taken for a period more than twice the half-life.

I used to do similar stuff with real data and Michaelis-Menten plots, so I know it's not a given that 1% error in data causes 1% error in every parameter calculated from that data. Ewen (talk) 15:41, 4 August 2019 (UTC)

These issues are discussed in detail in my book https://www.wiley.com/en-gb/Data+Fitting+in+the+Chemical+Sciences%3A+By+the+Method+of+Least+Squares-p-9780471934127. Petergans (talk) 19:20, 4 August 2019 (UTC)

@Petergans: A volume which is sadly lacking from my shelves! I appreciate your expertise, Peter, and I hope you don't think I was trying to "pull rank" on you by mentioning my experience; I was merely hoping to give you a handle on my own background. Incidentally, I would caution that, as you probably know, Wikipedia might reject your arguments as Original Research, which seems odd but it is an encyclopaedia, not the font of all Truth. Anyway, I'm still not clear how the 138.3763(17) day figure is flawed. To me, the precision is not only from the calorimetry but also the timekeeping, and over a period of months with measurements taken with a precision of seconds, the precision of the half life looks okay to me. As I haven't had the benefit of your book, your opposing line of reasoning therein would bear repetition here. Ewen (talk) 21:38, 4 August 2019 (UTC)

The issue for Wikipedia concerns verifiability. The precision of the value "138.3763(17)" is not verifiable as its source contains no experimental details. If the value is accepted, it should be written as 138.376(2) as it is most unlikely that the error value has 2-digit precision. Petergans (talk) 10:57, 5 August 2019 (UTC)

138.376(2) seems to be the widely accepted value anyway. That looks fine to me. ComplexRational (talk) 11:50, 5 August 2019 (UTC)

Hazards

It says:

"Heavy smokers may be exposed to the same amount of radiation (estimates vary from 100 µSv to 160 mSv per year) as individuals in Poland were from Chernobyl fallout traveling from Ukraine. As a result, 210Po is most dangerous when inhaled from cigarette smoke, providing further evidence for a link between smoking and lung cancer."

I can't read the cited Science article; but even if it says that, it doesn't make sense, because it's a non-sequitur; or at least, badly phrased. That there is Polonium in tobacco doesn't provide "evidence for a link between smoking and lung cancer". You'd have to show (a) that most tobacco contains Polonium, and (b) smoking Polonium causes the smoker to get cancer (and not smoking e.g. Benzene, which is also present in tobacco smoke, and also causes cancer).

Does the source make the case better than this summary?

If not, I propose to delete the "evidence" clause.

MrDemeanour (talk) 19:34, 24 June 2023 (UTC)

Deleted the dubious clause.

MrDemeanour (talk) 10:28, 4 July 2023 (UTC)

Prominent Contaminate in Seafood and Tobacco

In the introduction it states that Polonium 210 is a prominent Contaminate in seafood and tobacco, there is no citation and to my knowledge this is a complete fabrication. 66.253.144.35 (talk) 05:38, 21 October 2023 (UTC)

There are several citations for this in the body (section Hazards). ^Complex/_Rational 16:34, 21 October 2023 (UTC)