What is Radioactivity: Definition and 116 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. Kairos

    I Radioactivity in quantum physics

    In a block of 1 kg of radioactive material that has reached its half-life, are the atoms in a superposed disintegrated/undecayed state (50-50), or are they all individually determined (50% disintegrated and 50% undecayed) before observation ?
  2. walkeraj

    I Praseodymium, other Elements, and their Magnetic Properties vs. radioactivity

    Question: Does the magnetic properties of an element, like Praseodymium, vary with radioactivity? That is, in general, does radioactivity (perhaps beta decay or alpha decay) subtly or otherwise alter the electronic structure enough to alter magnetic properties? The case for beta decay may be...
  3. O

    I Half life and radioactivity clarification

    As I understand, half life's are where unstable nuclear isotopes Undergo radioactive decay, where they emmit either aplha beta or gamma during this decay. I'm looking for some clarification on whether when an atom undergoes decay, does it then change into another element/ isotope of an...
  4. A

    B Source radioactivity estimate from a radiation detector

    If I have a source of radioactivity that is concentrated instead of evenly spread out, like a "tablet" source instead of a evenly distributed aerosol/dust on ground for example then is it possible to even estimate the total number of disintegrations (Becquerels per second) by measuring the...
  5. 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...
  6. F

    Radioactivity and the Periodic Table

    Hello, The periodic table organizes all known chemical elements (total of 118) based on their atomic number and properties. My understanding is that the first 92 elements are commonly found in nature while the other 26 are either highly radioactive and/or artificially made. Radioactive elements...
  7. J

    Understanding radioactivity levels of different isotopes

    Homework Statement:: Understanding radioactivity levels of different isotopes Relevant Equations:: None Hi, This isn't a homework problem but is an introductory question. Could someone explains what makes one isotope more radioactive than another isotope assuming you have the same amount of...
  8. 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...
  9. I

    Radioactivity Question, Is this method correct?

    Homework Statement Show using your expression for \lambda that if at a time t1 the amount is y1, then at a time t1 + ##\lambda## the amount will be ##\frac{y1}{2}##, no matter what t1 is.Homework Equations y = y0 ##e^{kt}## From previous question: half life ##\lambda =-ln2/k## The Attempt at...
  10. Igor 77

    A Radioisotope-induced radioactivity in a protein molecule

    Dear Forum Members, I am a molecular biologist. One of my projects is focused on the identification of a protein that interacts with a known organic molecule. Namely, I try to chase a transmembrane protein that is known to transport one organic acid. If possible, I would like to get an idea on...
  11. S

    B Is Radioactive Decay Truly Random?

    How can radioactive decay be random if we can calculate aproximately when it will happen . For example we know that an isotope will decay every 2 years by calculating the half life . Doesnt that mean that the decay is systematic rather than random because we can calculate when its guna happen ...
  12. O

    Radioactivity level in the coolant water

    Hi, Can anyone give me a source from which I can obtain the radioactivity level in the coolant water circulating in the primary circuit? Thanks in advance.
  13. S

    I Could a Smoke Detector Serve as a Sail for Spacecraft Propulsion?

    Looking at a humble smoke detector - a metal plate with some alpha source on one side. I guess the fission products / apha etc emitted in one direction are absorbed into the metal, and the opposite direction go into space. So there should be a minute net force ? Would that be useful as a "sail"...
  14. A

    I Super strong magnetic field's effect on radioactivity

    Is it possible that a super strong magnetic field, like those from a magnetar, could increase the instability of a radioactive atom and therefore decrease the half life? Thanks for your response in advance.
  15. 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...
  16. S

    I Is Consuming Wild Boar in Sweden Risky Due to High Radioactivity Levels?

    Recent news story about wild boar in Sweden running about 18,000 bec/kg. I was trying to put this in perspective as to what the risk was for untamed porkchops. This is a non trivial conversion. Please feel free to correct me: The primary radiation source is Cesium 137 -- it's a gamma...
  17. ORF

    Biology: Does radioactivity help fungi to grow?

    Hello Does radioactivity help fungi to grow? The article is 10 years old, I do not know if there is something newer... https://www.scientificamerican.com/article/radiation-helps-fungi-grow/ Thank you for your time. Regards, ORF
  18. A

    B How are activity and decay constant different?

    What's the difference between activity of a radioactive sample and the decay constant. Both are measured in second inverse. Please distinguish among the two?
  19. C_Pu

    I How Do Silicon Radiation Detectors Work in Detecting Beta and Gamma Radiations?

    So we are doing Radioactivity lab at second year undergraduate. I am confused about the workings of the silicon radiation detects we are using even though the demonstrators tried to explain. We are detecting beta and gamma radiations by placing sources above a silicon detector that have a small...
  20. wronski11

    Specific and surface activity of nuclear waste

    Dear all, I am looking for more information how specific activity \frac{Bq}{g} and surface activity \frac{Bq}{cm^2} is measured. This is done to determine whether the materials of interest can be treated as harmless and disposed as usual waste. I am interested how the experimental procedure...
  21. JulienB

    Discussing an experiment (radioactivity, Geiger-counter)

    Homework Statement Hi everybody! My homework this week is to discuss the results we obtained in an experiment last week, which was about determining the gamma-rays absorption coefficient of lead ##\mu## with a Geiger-counter and then read from a graph the gamma photon energy of the radioactive...
  22. Y

    I Radioactivity measurements -- finding a fit for lab measurements

    As a part of an experiment in radioactivity, we placed an alpha particles emitting source (Am) and a sensor in a vacuum chamber, and measured the power (number of particles per time unit) for various angles of the sensor. Our goal is to fit a theoretical function to our measurements (power vs...
  23. G

    B Calculating safe levels of radioactivity

    Hello! I am not sure how I would go about calculating the time it takes for a radioactive element to decay to safe levels. I know of the decay formula (N=No*e^(-kt)) and K =ln2/t(1/2). I believe calculating the time until an atom has decayed to safe levels has to do with the activity (Bq) A=kN...
  24. Jeremy Thomson

    Radioactivity of fusion reactor walls vs. fission

    I'm wondering if a fusion reactor would make its walls more radioactive thru neutron activation than a fission reactor, for a given amount of energy. It seems to me that (hydrogen) fusion produces most of its energy as neutrons that are unlikely to absorbed by the sparse near vacuum plasma...
  25. sevenperforce

    Sustained nuclear criticality in liquid vortex

    In 1958, chemical operator Cecil Kelley was killed by a nuclear excursion in a mixing tank. A tank intended to reprocess trace amounts of dissolved plutonium-239 accidentally had dramatically more radioactive material dumped into it. The plutonium, being dissolved in a lower-density fluid than...
  26. ElegantSir

    Calculating Energy from Mass Using E=mc²

    Homework Statement I have the question with a diagram posted in the thumbnail to make things easier. Homework Equations E = mc² The Attempt at a Solution The homework only had a single example for a question like this so I am not 100% sure how to get the answer. So far I've added the 2...
  27. S

    Simple test to determine type of radioactive decay

    Hi Guys Is there a simple test by which one could determine the type of decay a radioactive specimen is undergoing? Thanks sonip
  28. S

    Hello Physics Forums, I'm excited to finally join

    I have often visited and read questions and answers, and really like the subject so figured I'd join and participate. Academically, I come from the Arts world (history). What really got me interested was a project I did a few years ago, which was a market study of radioisotopes. I am endlessly...
  29. C

    Why is the central electrode in a G.M. tube positive?

    Why is the central electrode in a Geiger-Muller tube always positive (and not negative)? Many thanks!
  30. Calpalned

    What Are the Fusion Temperatures and Masses of Tritium for Thermonuclear Fusion?

    (Correct me if I am wrong as I am a novice in the area of chemistry) - If an element has a half-life of 10 years, half of its mass would turn into a daughter element. After another ten years, another half of it would decay, so that after 30 years only 12.5% of the mass of the original element...
  31. Teemo

    Radioactive Decay to a Non-radioactive Isotope

    Homework Statement Magnesium (Z = 12) has isotopes that range from Mg–20 to Mg–31. Only Mg–24, Mg–25, and Mg–26 are not radioactive. What mode of radioactive decay would convert Mg–20, Mg–21, Mg–22, and Mg–23 into stable isotopes most quickly? (A) electron emission (B) alpha particle emission...
  32. A

    How is heat generated in decay?

    I'm trying to tinker with a little home radioactive material, like Americium-241. I'm taking all the precautions for shielding, even though Americium isn't that dangerous behind any surface. So I understand the physics behind WHY radioactive decay generates heat, I'm wondering, though, what...
  33. S

    How to hide from the electromagnetic spectrum/electrical pol

    Hello. I need help! is it possible to create a box/cage (ive seen the faraday cage etc) to give one 100% protection from all/some the electromagnetic spectrums - and from electrical pollution? "Nothing enters and nothing leaves" style, so it but cut out all that comes outside of it, and blocks...
  34. H

    Calculating Q-Value for given Beta- decay

    Hello, I've recently started studying Nuclear physics and would appreciate help from someone who could clarify my doubt. Given Problem: 19O -> 19F + e + v Calculate the Q-value in the given decay using following data: Atomic masses: 19O 19.003576u 19F 18.998403u The problem that I'm having...
  35. 2

    How can metastable isotopes exist?

    I thought I would ask this question in the quantum mechanics section as I presume it has something to do with QM, like the reason why alpha and beta decay do not happen immediately but instead there is a half life for this decay. My understanding is that with alpha decay, the strong nuclear...
  36. K

    Comparing Death Risks: Smoking vs. Driving in Terms of Distance

    Homework Statement Hello All, This question is from my chemistry and health section so it's not really too "chemistry-ish" but rather more mathematical I think. Thanks in advance! Q:// Smoking 1.4 cigarettes per day carries a one in a million chance of death compared with driving 50 km by...
  37. R

    How do the W and Z Gauge Bosons work in the weak nuclear force?

    I've seen explanations that when a neutrino with a W+ Boson comes near a neutron, it affects one of the bottom quarks and changes it to a up quark which effectively turns the neutron into a proton. The neutrino then turns into an electron. Source: (2:20 onwards) I've seen other explanations...
  38. M

    How long does it take for Tc-99m to reach a nearby hospital for a bone scan?

    The question is: The activity of a source of Tc-99m (half-life = 6.01 hours) is counted in an ionization chamber in a radiopharmacy. (b) 44989345 counts are counted in 5.0 seconds. What is the activity of this sample and what is the error on this measurement? (c) A nearby hospital...
  39. M

    Radioactivity and Quantum Zeno Question

    Radioactivity is independent of the time the radioactive element was produced. If i remember correctly (which is a big IF, correct me if I'm wrong) this has to do with the collapse of the wavefunction into a definite state by "measurements" and then slipping back into a wave to evolve again...
  40. nuclearhead

    Idea for an internal scanner using natural radioactivity

    Here is an idea I had for a way to deduce the internal structure of an organic object using it's natural radioactivity. The set-up is an array of gamma ray detectors located circularly around the object. By detecting both the position and direction of the gamma rays (obviously impossible to get...
  41. C

    Exploring the Radioactive Nature of Carbon-14 and Its Nucleus Size

    There are many other particles having a larger nucleus than carbon-14 but they are stable. Why? Why is carbon-14 radioactive even though its nucleus is relatively small? Is that the strong force applied to carbon-14 is relatively small? If yes, why? Is the size of a nucleus proportional to...
  42. Deepak K Kapur

    A question about radioactivity.

    Hi, A radioactive substance which has a half-life of, say 5 years, will 'certainly' decay to half its amount after 5 years ( i am good at maths!). My question is, When radioactivity is a random process, where does this 'certainty' come into picture? Thanks.
  43. F

    Calculating radioactivity after a period of time

    Homework Statement QUESTION A cancer patient is typically given an intravenous dose of Metastron with an activity of 148 MBq. Calculate the activity after 6 months (183 days). PREVIOUS INFORMATION Physical half-life of Metastron = 50.5 days Biological half-life of Metastron =...
  44. W

    Question on Radioactivity, Activity and Age Estimations.

    Hi all, my end of year Physics exam is tomorrow and I need some help on this question and if someone could help I'd appreciate it. Carbon-14 has a half life of 5730 years, and an equilibrium concentration in the Earth’s lower atmosphere of approximately one atom per 8.3 x 1011 atoms of normal...
  45. M

    Derivation for Time to Max Radioactivity Transient Equilibrium

    Hi, I'm having a bit of difficulty deriving the time to max activity for the case of transient equilibrium for a parent-daughter. This is where I want to get to , tm = (1 / (λ1-λ2)) * 1n(λ1/λ2) I believe there is an alternative equation for tm as well expressed in terms of half-life...
  46. B

    Absorbed Radioactivity: Safe Handling of Irradiated Metals

    I need some source material to understand if, the metals which are gone through irradiation process, can exhibit radiation. Though we will be irradiating at a dose rate of ≈ 1M rad/hr, Our Total Integrated dose requirement is 55M rad. The question I have is for the material used to hold the...
  47. C

    Trying to understand causes and effects of nuclear reactions and radioactivity

    I have been reading a lot about nuclear plants and how when things go wrong the whole area becomes inhabitable. I have been trying to understand certain things but i am not sure. I hope my understanding of it are not filled with self-inflicted misconceptions. 1) Uranium crystals found in nature...
  48. U

    Chemical Kinetics Radioactivity

    Homework Statement The mean life of a certain radioactive element is 6 hrs. By what fraction will its initial activity decrease over a time period of 5 hrs. Homework Equations t_{avg}=\frac{1}{k} Initial Activity = kN_{0} Final Activity = kN_{t} The Attempt at a Solution From eqn 1...
  49. K

    Radioactivity - quantum tunnelling

    Can anyone link to a synthetic and understandable explanation of radioactivity through basic quantum mechanics? It does not need to be a comprehensive explanation at all, examples or partial explanations are fine. Online class notes are welcome but so are books suggestions. Thanks in advance