# Questions tagged [half-life]

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### How to Clearly Define Sample Size in Half-Life Measurements?

I'm curious about how to clearly define the sample size when calculating the half-life of particles. My understanding is that the half life is statistical in nature and that for very small samples, ...
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### How do we know the rate of decay for radiometric dating is constant?

http://www.purdue.edu/newsroom/research/2010/100830FischbachJenkinsDec.html The link above talks about a paper by Sturrock et al. in which slight fluctuations were detected in radioactive isotope ...
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From what I read online - Polonium 210 is the isotope used as the neutron initiator in nuclear weapons. But the half-life of this element 138 days. This raises questions: how do substantial ...
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### What does safety limit mean in radioactive decay? [closed]

What does safety limit mean here?
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I am in the process of writing a model for the diffusion of a chemical in an aqueous medium. Typically, to do this, one would use the diffusion equation $$\frac{\partial}{\partial t}U=\gamma \nabla ^... 3answers 121 views ### Can muonic atoms exist? Would it be possible in the standard model to have atom like systems in which muons (or tauons) take the place of electrons? Why don't we see more of them? For instance it could be related to some ... 2answers 53 views ### Are particle decay times universal constants? Basically what the title says. For neutrinos, for example. 5answers 556 views ### Probability of decay of a nucleus Question: A given sample of radium-226 has a half life of 4 days. What is the probability that a nucleus disintegrates after 2 half lives? Attempt at solution: After time t, the number of ... 0answers 42 views ### Lifetime of up quark I am taking an introductory particle physics course, and from having studied about the breit wigner cross section and propagator terms:$$\frac{1}{(E-E_0)^2+ \frac{\Gamma^2}{4}}$$where E is the ... 0answers 31 views ### A case where entanglement leads to correlation in decay time Half-lives of unstable or metastable states are typically known, but specific decay times are inherently uncertain. On the other hand, quantum entanglement leads to correlations between inherently ... 1answer 66 views ### How would you calculate the half-life of a source with one long measurement? I'm working on a project, and I understand that half life of a source is typically calculated with time intervals (eg 5 sec intervals for 20 minutes) and then using that data to find the decay ... 1answer 21 views ### Why do half lives of Carbon isotopes vary by a great extent? Both Carbon-14 and Carbon-15 decay by the \beta^- mechanism but the half life for C^{14} is approximately 5500 years whereas that if C^{15} is around 2 seconds.What causes this disparity in ... 3answers 56 views ### Half-life and muon decay Imagine that we have a single muon. It has a life span of 2.2 microseconds on average. So normally, after that amount of time, the muon will decay. Now imagine we have two groups of muons. Group A has ... 5answers 853 views ### What is the Half-Life of a Large Chunk of Fissile Material? Uranium-235 has a half-life of about 700 million years and a critical mass of about 52\,kg. That means if you take a large number of U-235 atoms, say a 26 \,kg amount, and put each atom in ... 6answers 129 views ### Does the half-life of an element mean it will never decay completely? Example: Half life of Polonium-194 is 0.7 seconds. If we supposedly take 50g of Polonium, there will surely be a time when no more of this Polonium will be left because if we consider the decay ... 3answers 83 views ### If you take 200 rods of plutonium what would happen due to it’s half-life? [closed] If you take 200 rods of plutonium then stick them together would 100 full rods worth of plutonium be remaining? And after half-life #2 here would be 50 rods worth of plutonium left and then after half-... 1answer 86 views ### Nuclear reaction – What is the asterisk an indication of? I've been observing the two-step decay of iodine-131 and can't quite determine what the asterisk above Xenon-131 indicates. I'm currently unsure as to what precisely the superscript asterisk on Xenon ... 3answers 82 views ### What is the measured decay rate of antineutrons? / What is the measured mean lifetime of antineutrons? Please do not post any "answers" dealing with predicted/theoretical estimates. The question specifically asks for measured / experimental evidence. 3answers 56 views ### Proportionality of rate of decay with the amount of nuclei present in the substance Why is the rate of decay of a substance directly proportional to the amount of nuclei present in the substance? I don't know much about this topic, my teacher introduced us to this concept in class ... 2answers 144 views ### Chemotherapy radiation physics in Grey's Anatomy In the Grey's Anatomy episode "Everyday Angel" airing Thursday 25th, 2018, a patient with growths on each scapula is found to have cancer in these growths. Dr. Jackson Avery is upset that this boy ... 2answers 55 views ### Link between average lifespan and half time in radioactivity I have learnt that in radioactivity λ=\ln2/t_{1/2}, thus showing the link between λ and radioactive half time. I have also learnt how to apply it in calculations (such as R={R_0}e^{-λt}) etc. Now ... 3answers 84 views ### What happens to a radioactive material's atom when it disintegrates? Suppose you initial had radioactive 2^n atoms (where n is an integer). Now after a number of halflives the number of left out atoms becomes 1. Now what will happen to it will it disintegrate and ... 2answers 128 views ### Half-life of W and Z bosons W and Z bosons should decay through weak interaction. But their half-life is around \tau = 10^{-25} s which is a typical value for particles decaying through strong force (instead of a 10^{-12}-... 2answers 89 views ### What's wrong with the following way to calculate mean lifetime from half-life? So I understand that half-life T_{1/2} is the time for the amount N(0) to reduce by half. Basically,$$N(t)=N(0)2^{-t/T_{1/2}} $$My question is that why can't I use this to directly pull out the ... 2answers 76 views ### What is the reason for radioactivity? In any radioactive series we can observe that the half-lives of a daughter nucleus might be less than that of the parent nucleus. If the reason for radioactivity is gaining stability, why does a more ... 2answers 151 views ### Is there a way to slow down radioactive decay? (with mathematical proof) See http://wtamu.edu/~cbaird/sq/2015/04/27/can-the-decay-half-life-of-a-radioactive-material-be-changed/ It stated that relativistic effect(obviously) and chemical component can slow down the radio ... 1answer 55 views ### Are there radioactive elements that can be seen to diminish/change with the naked eye? That is, after creating a quantity of a radioactive isotope with a half-life of several seconds or minutes, could the sample be seen to change into decay products with the naked eye? (Excluding ... 5answers 268 views ### Half-Life of Radioactive Isotopes [duplicate] Why do radioactive isotopes have a half-life? I know that they decay in order to become stable but why would it take out enough subatomic particles to be half? Or am I approaching this question the ... 0answers 34 views ### Cm-244 metastable state While searching for decay product information for Cm-244, I came across the UCSD Radionuclide Data Sheets, which lists the half life for the metastable isomer Cm-244 (34 ms), rather than the nuclear ... 1answer 162 views ### Width of the J/\psi resonance The J/\psi resonance has a mass of ~3 GeV but its width is only of 100 keV, why is it so narrow compared to the total mass? How can the width of these resonances be calculated? 1answer 196 views ### half-life for electron in excited state Imagine a single atom in which one of its valence electrons is put into an excited state. The electron then decays back into its original state, releasing a photon of a characteristic energy in a ... 1answer 204 views ### Special Relativity Muon Decay [duplicate] When talking about how muons reach earth even though their half-life is very short the explanation of time dilation is given. From earth's frame of reference, the Muon's clock is "slowed down" so is ... 0answers 96 views ### What is the shelf-life of a gravity-powered uranium bomb? Inspired by this Worldbuilding question about making a booby-trap with a very long shelf life. The idea is to suspend one lump of fissile material say 3/4 of a critical mass above another of the ... 1answer 1k views ### Does temperature affect nuclear decay? I'm wondering if the temperature could affect the half-life in an element. For example, Carbon 14 has a half-life of 5,730 years. Is this always true or only true for standard conditions of ... 2answers 399 views ### Why not quarter-life? The number of nuclei left after time t in radioactive decay is given by:$$N(t) = N_0 e^{-t/ \tau}$$Now if we put N(t) as \dfrac{N_0}2, we get half-life. But, if we had put \dfrac{N_0}4, we ... 1answer 1k views ### Stability of elementary particles Are elementary particles stable, like many atoms or molecules are stable if there are no reaction partners nearby? Or can they be observed just for very short instances of time? 2answers 89 views ### Is T_{decay} the time it takes for an amount of radioactive nuclei to decay \it{completely}? My friend told me about this idea. Let there be N_0 atoms of a particular radioactive material. Then the number of atoms at time t, N_t, we already know, is given by:$$N_t = N_0 e^{-t/\tau},\;...
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I want to make sure I am approaching this problem correctly: Element X has a half-life of 100 years. If I have a 128 Curie sample of element X, how long will I have to wait until its radioactivity ...
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### How are billion-year half-lives approximated? [duplicate]

Our life-time is negligible, compared to that of unstable nuclei with half-lives of billions of years. How, then, are these half-lives estimated, if you may never even witness a decay. It's like ...