What is Alpha decay: Definition and 54 Discussions

Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of +2 e and a mass of 4 u. For example, uranium-238 decays to form thorium-234. Alpha particles have a charge +2 e, but as a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms – the charge is not usually shown.
Alpha decay typically occurs in the heaviest nuclides. Theoretically, it can occur only in nuclei somewhat heavier than nickel (element 28), where the overall binding energy per nucleon is no longer a maximum and the nuclides are therefore unstable toward spontaneous fission-type processes. In practice, this mode of decay has only been observed in nuclides considerably heavier than nickel, with the lightest known alpha emitters being the lightest isotopes (mass numbers 104–109) of tellurium (element 52). Exceptionally, however, beryllium-8 decays to two alpha particles.
Alpha decay is by far the most common form of cluster decay, where the parent atom ejects a defined daughter collection of nucleons, leaving another defined product behind. It is the most common form because of the combined extremely high nuclear binding energy and a relatively small mass of the alpha particle. Like other cluster decays, alpha decay is fundamentally a quantum tunneling process. Unlike beta decay, it is governed by the interplay between both the nuclear force and the electromagnetic force.
Alpha particles have a typical kinetic energy of 5 MeV (or ≈ 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the speed of light. There is surprisingly small variation around this energy, due to the heavy dependence of the half-life of this process on the energy produced. Because of their relatively large mass, the electric charge of +2 e and relatively low velocity, alpha particles are very likely to interact with other atoms and lose their energy, and their forward motion can be stopped by a few centimeters of air.
Approximately 99% of the helium produced on Earth is the result of the alpha decay of underground deposits of minerals containing uranium or thorium. The helium is brought to the surface as a by-product of natural gas production.

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  1. R

    Show that the minimum in alpha-decay spectrum is caused by interference of peak

    This problem set considers (beta-delayed) alpha decay of ##{}^{20}Na##. I'm currently stuck in the following exercise and was hoping some of you could help me in the right way. Thanks in advance! The problem is: c) The experimental spectrum of ##{}^{20}Na## can be found below. Apart from peaks...
  2. Petr Matas

    B Prevalence of nuclear decays accompanied by gamma emission

    Some alpha or beta decays produce an excited daughter nucleus, which typically immediately emits one or more gama rays to reach a ground state. This is the case for beta decay of Co-60 or Na-24 for example. While the table of cobalt isotopes on Wikipedia mentions the gamma emission, the one for...
  3. L

    Calculation on spontaneous fission and effect from alpha decay

    Summary:: Help needed on how to calculate on spontaneous fission and effect from alpha decay Heat from alpha decay from Pu-238 is used to generate direct current. At the beginning (1977) it generated 470W, how large is the effect now? And if the efficiency between the electricity and heat...
  4. Kosdon3200

    I What are these directional energetic particles?

    In addition to the usual alpha and beta particles visible in my condensation cloud chamber, I see occasional tracks that seem highly energetic -they easily penetrate the entire width of the cloud chamber (10-12 inches) going in one side and out the other. More mysteriously, their orientation is...
  5. Stephen Bulking

    Reaction energy of an α decay

    I tried momentum conservation, which gives: -pα = pdaughter <=> 2mKα = 2mKdaugther (squaring two sides) Using the given mass ratio, I found Kdaughter to be 0.0864MeV Adding the two Kinetic energy of the product particles and converting it to Joules, I got A But I don't understand why adding the...
  6. K

    Determining # of Beta Decays from Alpha Decay

    Alpha particle has two protons and neutrons so mass = 4. 4x = 238 -206. x = 1/4(238-206) = 8 Alpha decays. How would I determine the number of Beta decays? Since the mass doesn't change here.
  7. haushofer

    I Alpha decay: why Helium nuclei?

    Dear all, in my teaching of nuclear physics at high school level I noticed that I never really wondered about why alpha decay consists of helium nuclei. So I consulted a lot of lecture notes online, but couldn't find a satisfying answer. The texts I used in the past are "concepts of modern...
  8. I

    Weird readings of a Geiger counter in my basement

    Hi everyone! I'm new to this forum, so I hope my question fits into this category. Yesterday I wanted to check if I could measure any radiation from Radon in my basement with my Radiascan-701 Geiger counter which features a pancake-style probe that should be able to handle alpha, beta and...
  9. A

    Alpha Decay and Total Kinetic Energy

    Since we are looking for K total, I summed the given kinetic energy for lead and the typical kinetic energy of an alpha particle: 0.12 + 5 = 5.12 MeV. My answer is definitely wrong, but I don't how I should approach the problem.
  10. D

    241Cm alpha decay to 237Pu

    I understand that In general, the branching ratio for a particular decay mode is defined as the ratio of the number of atoms decaying by that decay mode to the number decaying in total. But I can’t get this specific branching ratio.
  11. S

    Kinetic Energy for particles (alpha decay)

    Homework Statement Many heavy nuclei undergo spontaneous "alpha decay," in which the original nucleus emits an alpha particle (a helium nucleus containing two protons and two neutrons), leaving behind a "daughter" nucleus that has two fewer protons and two fewer neutrons than the original...
  12. S

    I Am I understanding the Geiger-Nuttall law correctly

    Geiger–Nuttall rule relates the decay constant of a radioactive isotope with the energy of the alpha particles emitted. Roughly speaking, it states that short-lived isotopes emit more energetic alpha particles than long-lived ones. - wiki I am trying to understand why there is an inverse...
  13. S

    Energy released through alpha decay

    Homework Statement The radioactive isotope radon-222 may decay spontaneously by emitting an alpha particle. The daughter nucleus is an isotope of polonium. The atomic masses of these isotopes are: Rn-222 : 222.0157 u Po : 218.00896 u He : 4.00260 u A sample of radon-222 contains 3.0 x 107...
  14. H Tomasz Grzybowski

    A Mechanism of α decay - truth about structure of nuclei

    α decay probably implies that heavy enough nuclei which undergo this decay, consist relatively loosely bound α particles and extra neutrons. I haven't found any theory which views nuclei in this way. I value truth in science, and would like to know it, also regarding stucture of nuclei and...
  15. L

    Compute the energy of the emitted alpha for Na20 decaying to an excited state

    I think I got this right, I just want a second opinion to know if my concepts are correct 1. Homework Statement 20Na decays to an excited state of 20Ne through the emission of positrons of maximum kinetic energy 5.55 MeV. The excited state decays by ##\alpha## emission to the ground state of...
  16. Farang

    Calculating pressure / energy difference confusion

    Homework Statement The electron density per area, ##N## for a gas layer of thickness 10 cm can be determined $$n = k \times p \times 2.47 \times 10^{19}$$ For each adjacent sets of pressure data using Matlab, calculate the average energy in keV, the pressure difference in hPa, the energy...
  17. K

    B Alpha decay produces electron surplus?

    Hi! I recently learned about the Alpha decay, where the atomic Nukleus emittes Alpha-Particles. I was wonderin if a material, which emittes such Alpha Particles has a surplus of electrons and so a negativ electronic charge after the decay. Because it loses Protons but stays with the...
  18. M

    Charged Particle in Magnetic field calculation

    Homework Statement Basically having a problem when trying to theoretically calculate the mass of alpha particle in a charged field. r is the unknown radius of curvature m = mass of an alpha particle (6.646 *10^-27 kg) v = velocity of an alpha particle immediatly after decay (1.381 *10^7 m/s)...
  19. S

    Alpha decay in elements under 35

    For a chemistry paper I'm writing, I have to include an example of alpha decay using only elements up to number 35, however, I can't find one that would actually work. Does anyone know of any that could be used?
  20. A

    Nuclear Physics and energy levels

    Homework Statement A unknown nuclide emits four alpha particles with energies 8.54, 7.04, 6.38, and 5.10 MeV a) what are the nuclear energy levels of this nuclide b) What are the possible gamma ray energies that should be observed[/B]Homework EquationsThe Attempt at a Solution I was trying...
  21. A

    I Alpha decay and magnetic fields

    How is the alpha decay of a given nucleus affected by the presence of an external electromagnetic field? It's probably an easier question that I think but I've been unable to find a treatment of the tunneling of the alpha particle using WKB method in the presence of a magnetic field.
  22. I

    Alpha decay ##Q##-value, recoil energy, momentum

    Homework Statement Calculate the ##Q##-value for ##^{230}Th\to \; 226Ra + \alpha##. Also calculate the kinetic energy and the velocity of the daughter nuclei. Homework Equations Alpha decay ##Q = (m_X-m_X'-m_\alpha)c^2## Kinetic energy ##T_\alpha = \frac{Q}{1+\frac{m_\alpha}{m_{X'}}}##...
  23. Kara386

    Kinetic energy of alpha particle in alpha decay

    Homework Statement Consider the nuclear decay 21486Rn → 21084Po2- + α. Calculate the Q for this decay, and give the value of the kinetic energy of the alpha particle in the rest frame of the Rn nuclide. The rest mass of the Rn nuclide is 213.9954u, of Po is 209.9829u, of α is 4.00015u and of...
  24. M

    Power produced from alpha decay

    Homework Statement Assume that a 14 kg sample of 240Pu is used to produce electrical power from its α decay. If your device is 60% efficient in producing electrical power, how much power can be produced? (in watts) Homework Equations Q=mass of plutonium-mass alpha-mass daughter; 240 plutonium=...
  25. A

    What is this notation? I haven't seen it before

    X5(p,α)X6 This is an equation/part of a question in my nuclear physics unit, where X5 represents the reactant nucleus and X6 is the product nucleus. The alpha symbol is most likely alpha decay, but I have no idea what it means in conjunction with 'p' like that. The rest of the question is: In...
  26. patrickbotros

    Charge following Alpha Decay

    The following equation is written in my book: 204Pb→4α + 200Hg If an alpha particle is a helium nucleus, why doesn't it have a +2 charge and why doesn't Hg have a -2 charge? Did my text just omit the charge?
  27. S

    Estimating Half-Life of Alpha Decay: Nucleus ##^{252}_{98}Cf##

    Homework Statement Nucleus ##^{252}_{98}Cf## alpha decays with half life time ##t_{1/2}=2.6## years. What is the velocity of the alpha particle after the decay? Estimate the half life time of the nucleus after the decay. Homework EquationsThe Attempt at a Solution Ok, no worries about the...
  28. S

    Q-value and kinetic energy of alpha particle in alpha decay.

    Homework Statement The nuclear masses of parent and daughter nuclei are Mp= 226.025 amu and Md=222.017 amu.Mass of alpha particle is Mα=4.002amu.Find qvalue and kinetic energy of alpha particle emitted for the alpha decay. Homework Equations Q=(Mp -Md-Mα)amu...1 Assuming nucleus to be at rest...
  29. T

    Momentum Formula for Alpha Decay

    [Mentor's note: this thread does not use the standard homework-help template, because it was started in one of the non-homework forums. It was moved here because it had already gotten some help.] Hi everyone. This isn't a homework question, as I am just revising notes for my exams, and after...
  30. LotusTK

    Homework Question - Beta and Alpha decay

    Hi, i am new here. Thought it would be good to sign up as i have just started hitting the books in preparation for my AS Level exams. So this is my first question. I think i may have done this question correctly, but i was just seeing what other people think as i am not 100% sure about it...
  31. M

    Can this diagram make any sense? [counts of alpha decay]

    Hello all you physics folks, this is my first post, so if I screw this up, go easy on me :) Here's the problem I'm working on and that I simply can't get my head wrapped around: I have a table of 10 values of counts per second (cps) of alpha decay of Americium-241, depending on the...
  32. E

    Alpha Decay, Binding Energy and fusion

    Hi there, When an alpha particle is formed inside a nucleus by binding together is this essentially nuclear fusion occurring? Why is this more likely to happen in a large nucleus than a small one? Thanks
  33. A

    Alpha decay potential barrier.

    Homework Statement A nuclei of a atomic number Z decays into a alpha particle (a He nucleus with Z =2) and a daughter nucleus with (Z_{d}). The decay may be described as the tunneling of an alpha-particle through a barrier caused by the Coulomb potential between the daughter and the...
  34. S

    Statement about Forbidden Alpha decay transitions.

    Hi, I'm confused about a statement about the change in final/initial states of the daughter/parent atom in an alpha decay. It is the following; "The spin between the parent (I_i) and daughter (I_f) can change by lh (h being h-bar, l is the orbital angular quantum number of the alpha particle)...
  35. X

    Alpha decay vs 12C emission

    Homework Statement Radium 226 usually decays via three consecutive alpha decays into Pb 214. Show that energetically possibly for radium 226 to decay into 214|86 Pb and 12|6 C but tell why it is highly unlikely. Calculate the lifetime of the direct transition as a function of the possibility...
  36. A

    Why aren't the daughter isotopes of alpha decay charged?

    For example, when a radioactive isotope of Uranium undergoes alpha decay, a radioactive isotope of Thorium is formed. Why isn't this daughter isotope charged?
  37. D

    Kinetic energy of daughter nucleus and alpha particle from alpha decay

    Homework Statement In \alpha decay a nucleus X at rest decays to a daughter nucleus Y and an \alpha particle. Conservation of momentum and kinetic energy gives: M_{\alpha}v_{\alpha}+M_{Y}v_{Y}=0 \frac{1}{2}M_{\alpha}v_{\alpha}^{2}+\frac{1}{2}M_{Y}v_{Y}^{2}=Q Where the Q value is the...
  38. T

    Alpha Decay & Ionization: Modeling an Electron's Tunneling

    Hello, I'm trying to figure out if an atom undergoing alpha decay can knock out its orbital electrons. I was hoping someone might give me a hand coming up with a model to figure this out. What I need to figure out is: How far out does an alpha particle tunnel can I use a classical...
  39. M

    Calculating Alpha Decay Energy for A=210, Q=5Mev

    Homework Statement if the decay of nucleuse with A=210, what is the alpha energy emited when the Q of the decay is 5Mev Homework Equations The Attempt at a Solution by energy and momentum conservation: parent=daughter+alpha decay+Q from the question the parent has A=210, in...
  40. E

    Electric Potential Difference involving Alpha Decay question

    Homework Statement A plutonium-239 nucleus, initially at rest, undergoes alpha decay to produce a uranium-235 nucleus. The uranium-235 nucleus has a mass of 3.90x10^-25 kg, & moves away from the location of the decay with a speed of 2.62x10^5 m/s. Determine the minum electric potential...
  41. S

    Alpha decay and its relationship to speed

    I need some explanation to what I must know in order to solve the next problem. A step by step process and mention of the particular concept I must know would be greatly appreciated as I must learn how to do this by june 8. " In the alpha decay of a Uranium-238 nucleus, what is the ratio v/V...
  42. L

    Alpha Decay of Polonium-210 Homework

    Homework Statement Polonium isotope {}_{84}^{210}Po is unstable and emits a 5.30MeV \alpha particle. i. Indentify the daughter nuclide (using a periodic table) ii. Calculate the mass of the daughter nuclide. Homework Equations Mass of neutral {}^{210}Po nuclide is 209.9829u Mass of...
  43. S

    Alpha Decay of Actinium 223

    Homework Statement Find which of the α and β decays are allowed for 223Ac. (Determine the disintegration energy Q for each decay which is allowed, and calculate the binding energy B against each decay which is not allowed.) Homework Equations Q=(Parent mass-Daughter mass-alpha particle mass)c^2...
  44. S

    Kinetic Energy of a daughter Particle in Alpha decay.

    Homework Statement How much kinetic energy does the daughter have when Samarium 148 undergoes alpha decay from rest?Homework Equations Q=(Mparent + Mdaughter + Malpha)c^2=Kd+Kalpha Kalpha=MdQ/(Md+Malpha) The Attempt at a Solution I started with the fact that samarium 148 would become...
  45. J

    Explaining Alpha Decay Energies in 232Th

    Homework Statement I got ask the following question, and i don't know the answer. Why in a rdioactive decay of 232Th by alpha emission, the alpha particle can have energy 4.01 Mev and 3.95 Mev? Homework Equations The Attempt at a Solution I look up this website and i found...
  46. D

    Alpha decay short half lives correspond to large disintegration energies

    Homework Statement i) Explain why in alpha decay short half lives correspond to large disintegration energies. ii) Determine the energy release during the alpha decay of 238U to 234Th. The mass of 238U is 238.0508mu, the mass of 234Th is 234.0436mu, and the mass of 4He is 4.0026mu...
  47. K

    Californium-242 nucleus 242/98 Cf decays via alpha decay

    Hey I'm new to this forum, just want to say hi! I'm not sure if this is the rite place to put this but sry if i posted in the wrong section >.< I'm actually working on an assignment in my natural science course and I'm stuck on this question cause I'm not sure how to use the variables in the...
  48. W

    Half Life / Alpha Decay Question - No IDea

    Half Life / Alpha Decay Question -- No IDea Homework Statement A space rock contains 3.20 g of 147 62 Sm and 0.110 g of 143 60 Nd. 147 62 Sm alpha decays to 143 60 Nd with a half-life of 1.06 1011 yr. If the rock originally contained no , how old is it? Homework Equations ...
  49. W

    Alpha Decay extra electrons

    Alpha Decay "extra" electrons I am sure this question has been asked before, and I have searched many sources for a good answer, but have yet to be satisfied with what i have read. ===================================== Question 1 deals with this version of the decay formula 238/92 U -->...
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