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Questions tagged [half-life]

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1answer
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How to model mass diffusion with half life

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 ^...
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3answers
76 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 ...
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Are particle decay times universal constants?

Basically what the title says. For neutrinos, for example.
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500 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 ...
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0answers
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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 ...
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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 ...
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1answer
65 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 ...
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1answer
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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 ...
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51 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 ...
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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 ...
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6answers
125 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 ...
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3answers
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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-...
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1answer
84 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 ...
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3answers
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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.
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3answers
53 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 ...
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2answers
127 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 ...
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2answers
54 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 ...
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3answers
81 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 ...
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2answers
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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}-...
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2answers
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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 ...
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2answers
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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 ...
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2answers
132 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 ...
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1answer
53 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 ...
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5answers
253 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 ...
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0answers
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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 ...
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1answer
151 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?
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1answer
182 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 ...
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1answer
192 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 ...
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0answers
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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 ...
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1answer
879 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 ...
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2answers
363 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 ...
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1answer
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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?
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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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1answer
158 views

Radioactive decay with Curies

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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1answer
159 views

How to Calculate Instantaneous Decay

If I want to calculate the number of moles/sec decayed of a substance, and I know the number of moles of isotope and the half life, would I then use the following? $$N/s=N_0e^{1/\tau_{1/2}}$$ Where $...
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2answers
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Why is radiometric dating only considered a use of alpha and beta radiation?

I was told that a use of both alpha and beta decay is in radiometric dating. Why is radiometric dating not also considered to be a use of gamma radiation?
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1answer
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Radiocarbon Dating; 200 year old wood sample what accuracy may I expect? [closed]

We have an old family house whose age is relatively unknown. By other non-scientific estimates I'd put it 150 to 200 years old. A lot of the beams / columns etc. are wooden. Would it be possible to ...
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1answer
60 views

Kaon beam decay, find momentum [closed]

I don't know how I should solve this exercise: a Kaon has a mean lifetime of 12,4ns. The question is: What momentum should a Kaon beam have, so that after 50m 50% of the original radiant intensity ...
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2answers
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What sets the half life of unstable nuclei/nucleons?

A chemist friend asked me what sets the half life for free neutrons, unstable nuclei, etc. He said in chemistry half lives of molecules can often be calculated based on concentrations and molecular ...
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1answer
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What is the most recent date that can be measured using carbon-14 dating?

With carbon-14 dating, what is the most recent date which can be accurately determined, and why? Is there an accepted time range, within which, accurate results can be attained using carbon-14 ...
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2answers
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Why does a short lifetime of a nucleon excitation imply a broad mass distribution?

In this Coursera lecture by Mercedes Paniccia on inelastic scattering of electrons off hadrons, at 1:45 she says that At moderate $q^2$, inelastic processes produce excited states of the nucleon, ...
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5answers
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How do we know that radioactive decay rates are constant over billions of years?

A friend and I recently discussed the idea that radioactive decay rates are constant over geological times, something upon which dating methods are based. A large number of experiments seem to have ...
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2answers
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Why is beryllium 8 ($ ^8_4 Be $) such an unstable element?

And by unstable I mean a half life of $ 6.7 \cdot 10^{-17} s$. And what is exactly the criterion used to say an element is stable of unstable? Where do we draw the line?
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1answer
157 views

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 ...
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2answers
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Why is a neutron in free state unstable?

A neutron is a neutral particle which is merely some times more massive than an electron. What makes it so unstable outside the nucleus that it has a half life only of about 12 min?
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Why do nuclei decay so fast and slow?

Why do nuclei like Oganesson (also known as Ununoctium, this is the 118th element on the periodic table) decay in about 5 milliseconds? This is weird that they decay. In comparison, why do elements ...
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1answer
728 views

Does a smaller half-life mean that the rate of energy/radiation release is faster?

I had a discussion with someone about using radioactive elements as sources of energy on board long interplanetary voyages. Actually we were talking about going to the moon, and what our source of ...
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1answer
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Half life of potassium

I'm working on half life of potassium using potassium nitrate with GM Counter. When I increase the mass (1 g) to get more counts number of counts decrease as compared low mass (.5 g). With large mass ...
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3answers
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Is a radioactive-powered hand warmer possible? Can it be made to work safely?

So my knowledge of radioactive isotopes is limited to a series of youtube videos. I assume this idea is very dangerous and should never be attempted, but my curiosity still thrives. I own a tritium ...
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2answers
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What are the units of the half life in exponential decay?

I have tried to look up how to determine the units of the half life of an exponential decay, but I keep reading its 'time'. I am well aware it's time. I'm not aware of the specific units of time, is ...