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proton mass , m p = 1.672 6231 x 10 -27 kg = 1.007 2765 u

proton mass , m p = 1.672 6231 x 10 -27 kg = 1.007 2765 u. neutron mass , m n = 1.674 9286 x 10 -27 kg = 1.008 6649 u. electron mass , m e = 9.109 3897 x 10 -31 kg = 0.000 548 579 90 u. 1 u = 1.660 5402 x 10 -27 kg. 1 u = 931.494 32 MeV. The mass of a nucleus is always less

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proton mass , m p = 1.672 6231 x 10 -27 kg = 1.007 2765 u

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  1. proton mass, mp = 1.672 6231 x 10-27 kg = 1.007 2765 u neutron mass, mn = 1.674 9286 x 10-27 kg = 1.008 6649 u electron mass, me = 9.109 3897 x 10-31 kg = 0.000 548 579 90 u 1 u = 1.660 5402 x 10-27 kg 1 u = 931.494 32 MeV

  2. The mass of a nucleus is always less than the sum of the uncombined masses of the constituent particles. The difference is called the nuclear mass defect. The mass defect can be converted into an equivalent nuclear binding energy using the relationship 1 u = 931 MeV. Divide the binding energy by the number of nucleons to get the binding energy per nucleon. This value is used to determine the stability of that atom’s nucleus.

  3. RADIOACTIVITY the spontaneous uncontrollable decay of an unstable atomic nucleus with the emission of particles and/or rays An unstable atomic nucleus will decay naturally (emit particles and/or rays from the nucleus) until it becomes stable. The danger of radioactive decay products depends on their charge and energy.

  4. Alpha Decay • alpha particle: a “doubly • ionized helium atom” or simply a “helium nucleus” • written a,a ,or He +2 4 2 4 2 • Z > 82 for alpha decay possible • have relatively slow speeds (0.1 c) • can be stopped by a few cm of air or • an ordinary sheet of paper • natural a’s have energy between 4 and 10 MeV • half-lives from 10-6 s to 1010 yr (link)

  5. Beta Decay (link) 0 -1 0 -1 • electron, written e or b • or positron, written e or b 0 +1 0 +1 • occurs primarily in light nuclei • penetrates many meters of air • or thin sheets of metal • high speed (approach speed of light) or

  6. Gamma Decay • high energy photons • (electromagnetic radiation) • written g • penetrates 2 km air or 30 cm lead • short lifetimes • energy range of keV to MeV • have short wavelength (high frequency) (link)

  7. Proton Decay Neutron Decay When balancing nuclear equations, mass number and nuclear charge must be conserved. These equations are generally simpler to write than chemical equations.

  8. The rate of radioactive decay depends on the amount of nuclei present. The equation for the number of radioactive nuclei present at any time t is given by the equation:

  9. N(t) = # radioactive nuclei • present at time t • N0 = number initially present • = the disintegration constant, which is equal to (ln 2)/T1/2, where T1/2is the half-life of the decaying nucleus

  10. Click here, and here,to run simulations of radioactive decay.

  11. Often, the product of a decaying nucleus is also unstable and subsequently decays at some other rate. The amount of each nucleus present depends on the amount of initial nuclei present and on the decay rates of the parent and daughter nuclei.

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