Atomic Physics at Accelerators: Mass Spectrometry: by Georges Audi (auth.), David Lunney, Georges Audi, H.-Jürgen

By Georges Audi (auth.), David Lunney, Georges Audi, H.-Jürgen Kluge (eds.)

The look for examples of proton radioactivity has led to the invention of a big variety of proton emitters within the area 50 < Z < eighty four [1]. lots of those proton emitters and their daughters also are a-emitters, and every now and then the a-decay chain from the daughter terminates on a nuclide in the direction of balance whose mass extra is understood. This opens up the potential for utilizing a-and proton-decay Q-values to figure out the mass excesses of a big workforce of nuclei hooked up via particle decay. The Q-values are derived from the measured kinetic energies of the emitted protons or a-particles. the place the decay chains are usually not attached to nuclei with identified mass excesses, proton separation energies will be measured every so often and derived in others. For the a-decay ofthe guardian nucleus (Z, A) to the daughter (Z - 2, A - 4), the power and momentum kinfolk used to transform among Q-value, mass (M) and mass extra (ME) are: M(4He)E", (1) M(Z - 2, A - 4)Erecoil, (2) Q", E", + Erecoi\, ME(Z, A) Q", + ME(Z - 2, A - four) + ME(4He). (3) In perform, one makes use of M(4He) ~ four and M(Z - 2, A - four) (A - 4), in order that Equation (3) turns into ME(Z, A) = E", (_A_) + ME(Z - 2, A - four) + ME(4He). (4) A -4 equally, for protons, we have now ME(Z, A) = Ep(_A_) +ME(Z - 1, A-I) +ME(lH).

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Extra info for Atomic Physics at Accelerators: Mass Spectrometry: Proceedings of the APAC 2000, held in Cargèse, France, 19–23 September 2000

Example text

The total mass is thus: M(N, Z) = NMn + ZM H - aA + fJ (N - Z)2 A 3 e 2Z 2 + yA2/3 + ---1/-3' 5 roA (16) where A = N + Z, is the atomic weight, roA 1/3 the nuclear radius, Mn and MH the masses of the neutron and of the hydrogen atom. 58 MeV). The formula of Equation (16) is unchanged if M(N, Z), Mn and MH are replaced by their respective mass excesses (at that time they were called mass defects). 44 MeV in the 16 0 standard, with a value of930 MeV for the atomic mass unit. 3 MeV, and the value of 'u' given in the header of Section 3.

Differences. in the rare-earth region. between the masses and the values predicted by the model of Duflo and Zuker [36]. Open circles represent values estimated from systematic trends; points are for experimental values. THE EVALUATION OF ATOMIC MASSES 27 To be complete, it should be said that the REGULARITY property is not the only one used to make estimates: all available experimental infonnation is taken into account. In particular, knowledge of stability or instability against particle emission, or limits on proton or alpha emission, yield upper or lower limits on the separation energies.

For proton-rich nuclei decay may occur with the emission of a positron Qf3+ = ~A - ~D - 2mec2 or via electron capture, QEC = ~A - ~D. If the decay Q-value is measured and one of the masses (either of the parent or daughter nucleus) is known, the other mass may be deduced using one of the equations above. Decay may occur to either the ground or excited states of the daughter and in the latter case, the excitation energy of the final state has to be taken into account when calculating the mass differences.

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