What is Radioactive decay: Definition and 215 Discussions

Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha decay (𝛼-decay), beta decay (𝛽-decay), and gamma decay (𝛾-decay), all of which involve emitting one or more particles or photons. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the usual electromagnetic and strong forces.Radioactive decay is a stochastic (i.e. random) process at the level of single atoms. According to quantum theory, it is impossible to predict when a particular atom will decay, regardless of how long the atom has existed. However, for a significant number of identical atoms, the overall decay rate can be expressed as a decay constant or as half-life. The half-lives of radioactive atoms have a huge range; from nearly instantaneous to far longer than the age of the universe.
The decaying nucleus is called the parent radionuclide (or parent radioisotope), and the process produces at least one daughter nuclide. Except for gamma decay or internal conversion from a nuclear excited state, the decay is a nuclear transmutation resulting in a daughter containing a different number of protons or neutrons (or both). When the number of protons changes, an atom of a different chemical element is created.

Alpha decay occurs when the nucleus ejects an alpha particle (helium nucleus).
Beta decay occurs in two ways;
(i) beta-minus decay, when the nucleus emits an electron and an antineutrino in a process that changes a neutron to a proton.
(ii) beta-plus decay, when the nucleus emits a positron and a neutrino in a process that changes a proton to a neutron, also known as positron emission.
In gamma decay a radioactive nucleus first decays by the emission of an alpha or beta particle. The daughter nucleus that results is usually left in an excited state and it can decay to a lower energy state by emitting a gamma ray photon.
In neutron emission, extremely neutron-rich nuclei, formed due to other types of decay or after many successive neutron captures, occasionally lose energy by way of neutron emission, resulting in a change from one isotope to another of the same element.
In electron capture, the nucleus may capture an orbiting electron, causing a proton to convert into a neutron in a process called electron capture. A neutrino and a gamma ray are subsequently emitted.
In cluster decay and nuclear fission, a nucleus heavier than an alpha particle is emitted.By contrast, there are radioactive decay processes that do not result in a nuclear transmutation. The energy of an excited nucleus may be emitted as a gamma ray in a process called gamma decay, or that energy may be lost when the nucleus interacts with an orbital electron causing its ejection from the atom, in a process called internal conversion. Another type of radioactive decay results in products that vary, appearing as two or more "fragments" of the original nucleus with a range of possible masses. This decay, called spontaneous fission, happens when a large unstable nucleus spontaneously splits into two (or occasionally three) smaller daughter nuclei, and generally leads to the emission of gamma rays, neutrons, or other particles from those products.
In contrast, decay products from a nucleus with spin may be distributed non-isotropically with respect to that spin direction. Either because of an external influence such as an electromagnetic field, or because the nucleus was produced in a dynamic process that constrained the direction of its spin, the anisotropy may be detectable. Such a parent process could be a previous decay, or a nuclear reaction.For a summary table showing the number of stable and radioactive nuclides in each category, see radionuclide. There are 28 naturally occurring chemical elements on Earth that are radioactive, consisting of 34 radionuclides (6 elements have 2 different radionuclides) that date before the time of formation of the Solar System. These 34 are known as primordial nuclides. Well-known examples are uranium and thorium, but also included are naturally occurring long-lived radioisotopes, such as potassium-40.
Another 50 or so shorter-lived radionuclides, such as radium-226 and radon-222, found on Earth, are the products of decay chains that began with the primordial nuclides, or are the product of ongoing cosmogenic processes, such as the production of carbon-14 from nitrogen-14 in the atmosphere by cosmic rays. Radionuclides may also be produced artificially in particle accelerators or nuclear reactors, resulting in 650 of these with half-lives of over an hour, and several thousand more with even shorter half-lives. (See List of nuclides for a list of these sorted by half-life.)

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  1. eneacasucci

    I Gamma radiation decay intensity (IAEA nuclide chart)

    I was looking at the gamma radiation data from IAEA's website: (https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html) and was confused by the absolute intensity listed in the page. I Googled it and it seems to be the probability of emission but why it doesn't add up to 100%? For example...
  2. S

    What causes the radioactive decay of an unstable nucleus?

    A philosopher whose work I'm using in a paper uses a radium atom's decay as an example of a "spontaneous power," or an uncaused event. My professor, though, says "quantum fluctuations" cause radioactive decay. What are these fluctuations, and do we know what causes them? It's a college paper, so...
  3. cpspolly

    Question about radioactive decay

  4. U

    Understanding the determination of Radon activity

    When we want to determine the radioactivity of a nucleus, we usually determine the counts detected using say a Geiger counter. The count rate is then usually used as the disintegration rate i.e. the activity of the nucleus. However, say now we wish to measure the activity of Radon 222 using...
  5. P

    I Radioactive decay question for K --> Ca

    As I understand 40K decays into 40Ca over a period of ##1.248(3)×10^9## yrs. Assuming this is the natural rate of decay, is there any way to shorten the period of decay (increase the rate of decay), for example, under extreme pressure or heat? Thanks:biggrin:
  6. rpthomps

    I Are the daughter particles Ionized when the parent particle beta decays?

    I was wondering if the resulting daughter element is ionized after the parent undergoes beta(or any other kind) of radioactive decay,
  7. BWV

    I How do hidden variables supposedly explain radioactive decay?

    If individual atoms are indistinguishable from one another, then how can you tell if atom A will experience radioactive decay before identical atom B? ISTM there would have to be some underlying structure beyond electrons and quarks and unique to each atom / particle to be able to do this...

    Poisson's Distribution application in Radioactive decay

    Summary:: I have been provided with the table in which N and occurence are given. I have been asked to calculate the 1. Total count 2. mean count 3. mean count. Now, assuming our distribution described by Poisson's we need to calculate the tasks. The Poisson's distribution is given by...
  9. Dukon

    A What is the cause of radioactive decay?

    A prior closed post inquired as to precisely what determines the time of any given decay. I wasn't able to comment during that thread, but most responses were about probability and other aspects of the problem. I did not see however any mention of quantum fluctuations as possibly participating...
  10. D

    B Exact cause of radioactive decay?

    I recognize that radioactive decay is a spontaneous process in which an unstable atomic nucleus breaks into smaller, more stable fragments, but exactly what is it that causes an atom to decay at a particular time rather than at some other time?
  11. P

    Calcualtion of electric potential and radioactive decay

    This is just a representative diagram to visualize Surely a very tough one for me to solve. The number of nickel atoms are not mentioned. if the number of decays are ##3.78∗10^8## and with each decay depositing 100keV. The total energy deposited is ##100keV∗3.78∗10^8=6.048∗10^6## I have to...
  12. N

    Does radioactive decay exhibit stimulated emission?

    If you have a lump of the same species of radioactive isotopes, why can't the photons emitted from the radioactive decay of one nucleus cause spontaneous emission from other atoms? I presume it doesn't, because if it did, there would be a geometric effect of radioactive decay, which is not...
  13. B

    Why didn't radioactive decay probabilities cause the same uproar as QM

    It is equally puzzling why we are confined to probability amplitudes for RD as in QM measurements. Newtonian determinism is undermined in both, so why were there still Newtonian determinists around when QM hit the scene? We still have deterministic equations for both ofc but they are limited to...
  14. D

    B Is Radioactive Decay Uncaused/Causeless?

    I know that it has a cause! It happens to make the nucleus more stable. But some say it has no cause. I am confused actually.
  15. jdou86

    Statistics of radioactive decay

  16. A

    I Nuclear Fusion: Radioactive Decay?

    Radioactive decay modes always release energy; but why can't nuclear fusion of light elements be a mode of radioactive decay? I guess because although such processes are exothermic, we need an inaccessible fairly high amount of energy to overcome the electrostatic repulsion barrier. But now...
  17. A

    B Radioactive decay, Stability and Halflife

    As it's written in the following article, nuclear binding energy is always a positive number; thus it takes energy to disassemble a nucleus into its nucleons. ...The binding energy is always a positive number, as we need to spend energy in moving these nucleons, attracted to each other by the...
  18. Zeynaz

    The safety of radioactivity in Medicine

    The question also considered 99m-Tc which has a 6h of half-life. And 99Tc has about 2.2E5 years. My argue was, “the half life of 99Tc is greater than the lifespan of a person. So ionization energy that is released has minimal effect to the person compared to Tc-99m which decays (and releases...
  19. J

    I Why is Uranium-236 less stable than Uranium-235 and Uranium-238?

    Why is Uranium-236 less stable than Uranium-235 and Uranium-238?
  20. Bheshaj

    I Radioactive decay constant

    What is the significance of the radioactive decay constant?
  21. dRic2

    B Thought experiment -- A radioactive decay detector and randomness

    Take one radioactive element and put a detector all around it so that you can immediately detect whenever it will undergo radioactive decay. Have a clock connected to the detector to note the "exact" instant at which the atom decays. Let's say that after 3min after the clock started counting the...
  22. R

    Physics question about half life / radioactive decay

    Homework Statement You have 0.0625 grams of an unstable element and 0.9375 grams of the stable daughter product. How many half-lives has it undergone? Homework Equations N=No (1/2)^(t/(t1/2)) In which N represents the final activity for a period of time No is the original activity t...
  23. J

    Vector Plasma vs. Variable Radioactive Decay

    Could there be a connection between Robert Zimmermann's work (McMaster Univ. Toronto) on Vector Plasma, and Jenkins and Fischbach's (Perdue Univ.) work on variations in the rate of radioactive decay for elements on Earth in relation to solar activity? Only looking for a confirmation that their...
  24. JesW87

    B Is radioactive decay truly random?

    Before you report this, yes I do know there was already another post like this one, but I don't feel like it fully answered the question. Note that I really don't know anything about quantum anything, but I'm trying to do some reading up on "randomness" and the consensus seems to be that this...
  25. A

    B Radioactive decay characteristics as measured by a dosimeter

    If I put a dosimeter 1 meter away from a gamma sample that starts decaying at the moment I switch on the dosimeter then how would I measure the dose level received by the dosimeter, would it gradually decrease over the first half life or would it stay the same throughout the first half life...
  26. Krushnaraj Pandya

    Radioactive decay question

    Homework Statement Consider nucleus A decaying to B with decay constant D1, B decays to either X or Y (decay constants D2 and D3). at t=0, number of nuclei of A,B,X and Y are J,J,0 and 0. and N1,N2,N3 and N4 are the number of nuclei of A,B,X and Y at any instant. My question is, what is the...
  27. C

    I Why is radioactive decay so rare?

    Hi all, I'm just curious about the weak force and how it works. If quarks and electrons both have weak iso-spin and are constantly whizzing about next to their neighbour's (especially so inside a nucleon), what prevents say, the up quarks from emitting a W- boson everytime they are near a down...
  28. H

    [Poisson Stats] Error on half-life for radioactive decay

    Hi there, not sure whether this is in the right section but: I've made two runs of a radioactive decay experiment where I've got a log(N) vs. time plots. From this I've got the decay constants and hence the half-life. I've averaged these two half-lives ( = 160 secs) and now I'm trying to work...
  29. Q

    I Radioactive decay caused by WIMPS?

    I read from various sources that Non-baryonic matter (primarily WIMPs) is the best candidate to explain a number of cosmological phenomena. Why would the phenomenon of radioactive decay not be attributed to these abundant (over 1/4 of the mass-energy of the universe) particles? I'm not trying to...
  30. J

    Don't understand this question regarding radioactive decay

    1. Create and solve differential equations for the number of different amounts of isotopes, which change through time in the decay chain X -> Y -> Z, where X and Y are radioactive atoms, and Z is a stable atom. 2. Make a mathematical analysis of how the different amounts of isotopes from 1 mg...
  31. A

    B Quick Question about emitted radiation and Geiger counter accuracy

    Hi everyone. I read from: https://www.nucleonica.com/Applet/NaturalRA/Button5/page5.html that inside the human body, 4400 of K40 atoms disintegrate every second through radioactive decay. Of this decay, 11% (480) results in gamma radiation, and 50% of that 11% (240) escapes the body. My...
  32. Pushoam

    The amount of radioactive substance after 38 days

    Homework Statement Homework Equations The Attempt at a Solution Is there anyway to choose the correct option without solving it? ## \lambda = \frac { 0.693 } { t_{\frac 1 2}} ## [/B] ## N = N_0 e^{- 0.693 {\frac { t } { t_{\frac 1 2 }}}} ## ## N = 10.24 e^{- \frac { 0.693 * 38 }...
  33. Z

    Relation of EM radiation equation to radioactive decay

    Hello, I am a Mechanical Engineering student but I am a TA for an electricity and magnetism course, and I had a student ask a question that's a little bit outside my understanding. The question was related to the equation for a radiating electric field from an accelerating charged particle...
  34. ubergewehr273

    A question about radioactive decay

    Homework Statement Two species of radioactive atoms are mixed in equal numbers. The disintegration constant of first species is ##\lambda## and that of second species is ##\frac \lambda {3}##. After a long time, the mixture will behave as a species with mean life ________. Homework Equations...
  35. S

    I Twin paradox in SR and its applicability to radioactive decay

    Hi, thanks to a different thread/question on this forum I've come to appreciate time dilation ..somewhat. And from that I wondered if, given the range of locally measured times aboard any and all particles in the universe, given their different trajectories and histories since the big bang...
  36. P

    Radioactive decay of Uranium 238

    Homework Statement Analyzing a rock sample, it is found that it contains 1.58 mg of 238U and 0.342 mg of 206Pb, which is the stable final product of the disintegration of 238U. Assume that all 206Pb found comes from the disintegration of 238U originally contained in sample. How old is this...
  37. E

    I Radioactive decay of Carbon 14

    Alright, a very simple question here. I am reading about nuclear decay of Carbon 14 into Nitrogen 14. I understand how one electron is released and subsequently one neutron turns into a proton, but I am curious about how many electrons are left with the Nitrogen atom. I want to believe five, as...
  38. Alfredo Tifi

    A Reversibility of radioactive decay process?

    I viewed the answers to the non repliable post https://www.physicsforums.com/threads/is-radioactive-decay-reversible-in-time.673735/, but I have doubts. In particular, the last claim by nugatory: "the overall decay of the sample is as irreversible as the transfer of heat from a hotter body to a...
  39. AryaUnderfoot

    Radioactive decay of CaCO3

    Homework Statement Archeologists removed some charcoal from a Native American campfire, burned it in O2, and bubbled the CO2 formed into Ca(OH)2 solution (limewater). The CaCO3 that precipitated was filtered and dried. If 4.58 g of the CaCO3 had a radioactivity of 3.2 d/min, how long ago was...
  40. Recycler

    I Radioactive decay initiation

    what conditions must occur randomly to allow a radioactive nucleus to decay spontaneously?
  41. moenste

    KE of alpha particle using integer values of nuclear masses

    Homework Statement (a) Cobalt has only one stable isotope, 59Co. What form of radioactive decay would you expect the isotope 60Co to undergo? Give a reason for your answer. (b) The radioactive nuclei 21084Po emit alpha particles of a single energy, the product nuclei being 20682Pb. (b) (i)...
  42. wolf1728

    Radioactive decay - the difference between "lambda" and "k"

    When reading about radioactive decay, I see two types of decay constants: λ and "k". From what I have interpreted, k = ln (.5) / half-life whereas λ = ln (2) / half-life. Have I defined these correctly? If this is so, the difference between the two is slight. When putting these into equations...
  43. D

    Modern Physics question -- an atom ejecting a relativistic electron

    Homework Statement . An atom at rest can undergo radioactive decay, ejecting an electron at a maximum speed of 0.5c. If the atom in a particle accelerator is observed to produce an electron traveling at 0.75c, at least how fast must the atom itself have been moving? Homework Equations u0 x...
  44. durant35

    I Radioactive decay, macroscopic objects

    Radioactive decay is known to be a pure quantum effect, the particle from the nucleus is in a superposition until we measure it (according to collapse interpretations). In the Sch. cat experiment the radioactive particle gets entangled with a macroscopic object (Geiger counter) and so the...
  45. L

    Radioactive decay, relation between binomial to expon. dist

    You can model the probability for radioactive decay as a Poisson distribution. This is the probability for radioactive decay within a specific time interval. (I probably got some of it wrong here). P(k,μ)=λ^k⋅exp(-μ)/k! Is there a way to use this formula to derive the other formula for...
  46. H

    I Radioactive decay, falling pencils and the uncertainty principle

    Consider an ensemble of identically prepared pencils balanced on its tip. If a pencil is precisely vertical, ##x=0##, and precisely at rest, ##p=0##, then it will never fall. But some pencils in the ensemble would fall, because according to the uncertainty principle, the standard deviation...
  47. S

    I Is radioactive decay independent of the environment?

    Is the rate of radioactive decay fixed or does the environment have any impact eg would the rate of decay be the same in a low or very high gravitational field (in both cases measured from the viewpoint of the radioactive material)?
  48. victorhugo

    Experiment to simulate the radioactive decay of U-235

    Basic high-school homework. I mostly just want feedback on my answers and advice :) The experiment was to: Drop pins into a box. Pick out the one's upside down and count them and these are the ones that underwent decay. Get the ones that weren't upside down and throw them into the box again...
  49. A

    Determine half life from gamma radiation

    I'm working on a lab and the task is to determine the half life of an element studying the beta radiation or the gamma radiation (emitted from the daughter). I have all the data and I'm done with the beta part, that was pretty straight forward. I have no clue how to relate the gamma radiation to...
  50. VjStylz

    Solve Half-Life Problem: Find # Atoms Decaying in 12 Days

    Alright so i have exams in a matter of days and stumbled upon this multiple choice question 7. A radioactive source has 1.6×10^20 atoms of a radioactive isotope, with a half-life of 3 days. How many atoms will decay in 12 days? A. 1.0×10^19 B. 1.2×10^20 C. 4.0×10^19 D. 1.5×10^20 So my first...