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Questions tagged [half-life]

Half-life is the time required for an attenuating quantity to reduce to half of its initial value. It is proportional to the mean lifetime, whose inverse is the decay constant. It is a constant for exponential decay.

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Which exact element makes Spent Nuclear Fuel dangerous?

I understand that beta and gamma emissions are what makes the decay of a radioisotope dangerous. However, U-238, which is what SNF is mostly made of, doesn't emit gamma or beta particles frequently ...
BigBox989's user avatar
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Confidence level on excluded lifetime of decay

Could someone help me understand the ideas behind setting confidence levels on decay lifetimes. Like what Super K has been doing on the proton. Given the count rate of the decays is a poisson ...
Jasper amirante's user avatar
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Would a muon placed in a confinement smaller than most electron wavelengths decay slower?

We know that between two perfect mirrors certain photon frequencies become disallowed. The casimir effect is often even described as a lack of virtual photons of certain frequencies within quantum ...
Sven Heinz's user avatar
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Exponential decay of relativistic muons

I am working on an exercise that models the exponential decay of muons. The problem asks to calculate the percentage of surviving muons after $ 50 \mu s $ in two situations: Stationary muons. Muons ...
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Why does critical mass for radioactive isotopes seem to have little relation to half-life?

I understand that too short a half-life and flash point, becomes kind of meaningless, if the element generates too much heat, so this only applies to longer half-lives. Also, as I understand it, flash ...
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Possible electron capture decay of $^{148}\mathrm{Gd}$?

While the nuclide $^{148}\mathrm{Gd}$ is only known to undergo $\alpha$ decay, with a half-life of $86.9$ years, I noticed that it has higher energy than its isobar $^{148}\mathrm{Eu}$: $m_{^{148}\...
Jianing Song's user avatar
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2 answers
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Derivation of mean life of a radioactive nucleus

How can the mean life of a radioactive nucleus be derived? Consider R.dt number of nuclei decaying in the time interval t and t+dt. Then, isn't the lifetime of those R.dt number of nuclei is t? But, I ...
Vinay5101's user avatar
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Does antimatter have the same half-life as ordinary matter?

Antimatter is just ordinary matter but with opposite electric charge. Scientists have created only a handful of antihelium-4 in the LHC. I am wondering if the half-life of, say, antiRadium-226 is ...
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What do we actually mean by carrier lifetime in perovskite materials and where do charge carrier reside during that time?

During time-resolved photoluminescence studies in perovskite materials, one sometimes says that it has a microsecond carrier lifetime. What do we actually mean by that? Where does the excited electron ...
Balpartap Singh's user avatar
8 votes
2 answers
510 views

Is there a sharp definition of an unstable nuclide?

This may be a somewhat philosophical question, but here goes. Wikipedia claims that several nuclides (e.g. hydrogen-5) have half-lives shorter than $10^{-22}$ seconds. This is on the same order of ...
tparker's user avatar
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Why does Lamb shift renormalization not affect decay rate?

As a preface, I know there are "more" correct ways to calculate the Lamb shift and decay rate through full blown QED, but this is what's most familiar with me, so I would appreciate an ...
Electric to be's user avatar
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Why is the relaxation of coherence rate half the spontaneous emission rate?

Consider a two-level atom of which the lower and upper levels are denoted, respectively, a and b. If spontaneous emission from the upper to the lower level is the only source of relaxation, then the ...
Nicolas Schmid's user avatar
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If the time at which a single atom decays is random, why do groups of atoms behave in predictable ways? [duplicate]

Why do groups of atoms decay at predictable rates even though a single atom’s decay point is completely unpredictable? I’m having trouble wrapping my head around this. From my reading, it seems that ...
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Decay rate with specific helicity in rest frame and lab frame

Consider a two-body decay, such as the pion decay: $\pi^+\to \mu^+ + \nu_\mu^{}$. In the Standard Model, as there only exits left-handed massless neutrinos, the helicities of final particles are known....
Jihong Huang's user avatar
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Difference between endpoints and kinetic energy in a beta minus decay

I want to understand the difference between the Q value and Endpoint energy and Kinetic energy of a beta minus decay. I understood that the Q value is the overall energy of the reaction given by Q ...
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How is rate of radioactive decay constant?

If I understand correctly, the rate of radioactive decay depends on the amount of the radioactive element. How then can it be constant, if it depends on concentration?
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Nuclear decay formula derivation

I don't understand why the nuclear decay formula is derived with logarithms. if $t=T_{1/2}$ then $N=N_0\cdot\frac{1}{2}$ if $t=2T_{1/2}$ then $N=N_0\cdot\frac{1}{2^2}$ if $t=3T_{1/2}$ then $N=N_0\cdot\...
Lid's user avatar
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What is the half-life of deuterium if protons decay?

If we where to assume that protons decay and we know the half-life of protons, would it be possible to determine the half-life of deuterium? If $^{1}$H (a single proton) has a half-life of, say, $10^{...
Quinali Solaji's user avatar
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2 answers
687 views

What might be the half-life of observationally stable nuclei with energetically favorable decay modes?

For example, a reaction $${}^{132} \mathrm{Ba} \rightarrow {}^{128}\mathrm{Xe} + \alpha + 22.19\mathrm{keV}$$ would be energetically favorable, contrary that ${}^{132} \mathrm{Ba}$ is observationally ...
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Where could I find an example of a numerical calculation in quantum electrodynamics?

I’ve been reading Student Friendly Quantum Field Theory and I’m discouraged by the fact that I’ve yet to encounter an actual numerical calculation in the book. I feel like I would be able to ...
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Radioactive decay: calculating probability of decay from half life/decay constant

Let's say due to a nuclear reaction a radionuclide of half-life $T_{1/2}$ was created. I am trying to find out what will be the probability of that radionuclide undergoing radioactive decay within ...
uran42's user avatar
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Should I use Ground State-Ground State (GS-GS) $Q$-value for decay heat?

I am calculating the decay heat of sample of an isotope of plutonium at a single point in time. To do so, I am using the formula $$Q = λNE,$$ where $Q$ is the decay heat for a given sample of ...
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Detection the age of fossils using the carbon dating method

The life of carbon-14 isotope is about 5 thousand years. But we still are able to detect traces of it in fossils which are older, more than 10 thousand years. Why?
Nikku's user avatar
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When can a sum of exponential decays be approximated by a single exponential decay?

In my experiment, I have a signal y(t) that should be given by a continuous sum of exponential decays: $y(t) = \int_a^b n_0(E) \exp[-t/\tau(E)] {\rm d}E$ However, I see just a single exponential decay....
Kent's user avatar
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Simulating $e^-\rightarrow e^-\gamma$ scattering in QED

Is there any physical reason/symmetry prohibiting me from studying the $e^-\rightarrow e^-\gamma$ interaction? Because I haven't seen any QFT textbook dealing with such a simple process. It is the ...
schris38's user avatar
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Maximum and Minimum electron energy

I am trying to find the maximum and minimum electron energy for the calculation of the beta spectrum. I understood the minimum energy of the electron is the Q value. What is the maximum energy of the ...
Rhit.B's user avatar
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1 vote
1 answer
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Equation to predict stability, half-life and decay products of atomic nuclei?

Given an atomic nuclei say C-14 or U-233 or anything in-between or outside the range and given the ratio of protons and neutrons in the nuclei, is there a comprehensive equation or set of equations ...
Naveen's user avatar
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1 answer
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Why is water bright in a T2 weighted image?

I am new to study MRI. Please understand if some terminologies I use are wrong. This might be a silly question, but I wonder why water is bright in a T2 weighted image. T2 relaxation is also called ...
Andy Junghyun Kim's user avatar
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Why does Americium-241 not exist naturally?

A few searches says that it's because "the half life is too short with respect to the age of the universe." I don't understand what that means. Note that the half life of Americium-241 is ...
photon's user avatar
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Why is Astatine-210 (At-210) the longest-lived isotope of astatine despite possessing an odd number of neutrons?

I am guessing that isotopes with an even number of neutrons more readily release an alpha particle... When and if At-210 does that, it still has the problem of being 'odd/odd'... But this begs the ...
Kurt Hikes's user avatar
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3 votes
1 answer
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Isotopes half-lives distribution - is it log-uniform?

Decay of single isotope follows exponential law. BUT decay of nuke fallout / spent nuclear fuel will follow hyperbolic law. It is easy to explain if we assume that half-lives are log-uniformly ...
Vashu's user avatar
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Relationship between reactivity and half lives

I understand that after the 4th half life, there will be $\frac{1}{16} = 0.0625$ of the original substance left but I'm not sure how to find the half life according to this graph (since it's not ...
I'm a lightbulb's user avatar
1 vote
1 answer
97 views

Why does the doubly-magic nucleus tin-$132$ have such a short mean lifetime?

Why does the doubly-magic nucleus tin-$132$ have such a short mean lifetime? Only because it is far from valley of stability?
tbb's user avatar
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Does a charged isotope have a different half life than the neutral counterpart?

Let's say you have a radioactive isotope of an element with relatively short half-life (e.g. <0.5s). If you add or remove electrons from the atom so that is has a positive or negative charge, is ...
MFerguson's user avatar
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Lifetime derived from a measured spectrum when initial and final state have a finite lifetime

Can we infer the lifetime of states from a simple absorption or emission spectrum if both states involved in the transition have finite lifetimes? For example excited state absorption. It seems that ...
Hans Wurst's user avatar
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4 answers
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Why is $\tau=1/k$ the time constant of an exponential decay $f(t)=e^{-kt}$

Some context on why I came up with this question: I have to do a presentation on a paper about the heat equation on the cooling of a metal bar. In this experiment, the general solution for the PDE is: ...
Mikel Solaguren's user avatar
1 vote
3 answers
437 views

Why do things decay in terms of base $e$?

For instance, why do radioactive elements follow some $e^{-x}$ relationship? Why not $\pi^{-y}$ or some other numerical constant as the base? Is there some fundamental reason for Euler's number ...
honeste_vivere's user avatar
14 votes
1 answer
340 views

Why is there a sudden drop-off in half-life of isotopes at around 130 neutrons? Is there a name for this?

Pertaining to the chart of nuclides, there is a region above Bismuth, in which the relatively continuous trend of stability is interrupted by a batch of isotopes all with extremely short half-lives. I ...
Xiphosura's user avatar
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11 votes
3 answers
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How should half-lives be added?

Suppose I have a sample which can decay via two processes and/or decay to two separate products, $$A \to B, A \to C$$ The total half life can be calculated $t= (t_A^{-1} + t_B^{-1})^{-1}. $ I am ...
Jbag1212's user avatar
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General Half-life calculation for an abitrary nucleus

I have been getting back into physics and I was wondering whether there was a generalized half-life equation for any given nucleus composition. For instance for gold isotope 210-AU. Is it possible to ...
Anton von huenerbein's user avatar
1 vote
1 answer
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What is the analogy of cross section for particle decays?

So if two particles are fired at each other the chance they interact is the cross section of the interaction. What is the equivalent term for the chance that a particle decays into certain particles? ...
sputnik44's user avatar
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Conservation of energy with metastable pure states and doubts about energy-time uncertainty relation

Experimentally we know there are metastable states in nuclear physics and molecular physics. For example, the isotope Tantalum-180m ${}^{180m}\text{Ta}$ is long-lived metastable excited state, with a ...
Davius's user avatar
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1 vote
2 answers
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How do physicists know that some of a beta ray/particle's 'missing' energy isn't lost to interference with the electron cloud surrounding the atom?

Enrico Fermi and Wolfgang Pauli ultimately concluded that beta decay resulted in an electron and an electron antineutrino leaving a nucleus... BUT... How does the electron leaving a neutron punch its ...
Kurt Hikes's user avatar
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0 answers
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Experimental results for the measurement of Positron lifetime / Positron decay [duplicate]

It is assumed that the positron, being the antimatter particle of the electron, is stable. I am interested in finding experimental results or experiments which have measured the positron lifetime in a ...
user3728501's user avatar
48 votes
16 answers
10k views

Why is radioactive half-life constant?

Say you have just four radioactive atoms with a half-life of one hour. (I am using a small number of atoms to keep it simple and illustrate my confusion more clearly). So that means one hour from now, ...
Luke B's user avatar
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0 answers
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What is the half-life of isotopes that decay via electron capture, if they are stripped of their electrons?

If an isotope that undergoes decay via electron capture, like 7Be, loses ONE electron, how will its radioactive half life change? What about 2 electrons? And so on and so forth for heavier elements? ...
RadiationPhysicsGirl's user avatar
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Calculation for Decay of a Pseudoscalar to Two Particles [closed]

I am following some of the exercises in Srednicki's textbook on QFT. One of the questions is to consider a theory with a real scalar field $\phi$ and a complex scalar field $\chi$ with $$L=g \phi \...
Tom's user avatar
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3 answers
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Energy as a function of half-life?

How much energy is released in the radioactive substance's decay of one cycle of its half life? I'd like the plot the energy released of a radioactive substance over time. What must I reference to ...
StackQuest's user avatar
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0 answers
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Question on the life-time of a super-symmetric particle [duplicate]

I was watching a random video on SUSY. In the video, they were discussing that SUSY explains dark matter. That DM is probably a SUSY particle. How is this possible? We know that the life of a Top ...
Rick's user avatar
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2 votes
3 answers
79 views

Do unstable nuclei affect each other for decaying?

I am thinking about beta decay. If we graph decayed nuclei count over time, we don't see a linear line. Rather, it would be a curved line. I imagine myself as an unstable nucleus. If I don't care ...
Saeed Neamati's user avatar