User:ANUnuclearhonoursclass/Single Nucleon Transfer

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Single Nucleon Transfer

Single nucleon transfer experiments are a way of studying single particle nuclear wavefunctions while excluding other effects such as collective excitations. They can be used to test nuclear models.

Single nucleon transfer reactions involve a beam of light nuclei such as $^{2}$H reacting with a heavier target nucleus. One of the nucleons from the light nucleus is transferred to the heavier nucleus. This leaves an outgoing beam, and a target nucleus with one extra nucleon. In the case of $^{2}$H, the nucleon transferred is a neutron and the outgoing beam consists of protons. In principle, the transfer of the neutron could be accompanied by any of a multitude of energy transfers. If the original nucleus was left unexcited, any change in properties must be due to the extra neutron. In particular, if the original nucleus was an even-even nucleus and therefore had ground state spin $0^{+}$, the spin and parity of the new nucleus must be exactly those of the single particle state in which the neutron was deposited. The angular distribution of the outgoing proton beam depends on the spin and parity of the neutron lost . Measuring the distribution and energy of outgoing protons thus identifies the spin, parity and energy of single particle states in the target nucleus.

For a deformed nucleus, states with the same angular momentum but different projections onto the symmetry axis have non-degenerate energies. More different energy states may thus be identified using this technique in deformed nuclei than in spherical nuclei. The presence of these extra states and their relative energies provide experimental support for the Nilsson model. As an example, $^{183}$W has 109 neutrons and a deformation parameter of approximately $\epsilon =0.21$ . According to the Nilsson model, the lowest states should be $7/2^{-},1/2^{-},11/2^{+}$ and $3/2^{-}$ . These states are the lowest single-particle excitations in $^{183}$W, however, the observed order is $1/2^{-},3/2^{-},11/2^{+},7/2^{-}$ . Empirical parameters in the Nilsson Model inhibit predictions of this precision, however it does perform better than the shell model, which predicts low energy excitations with spins of $3/2^{-},1/2^{-}$ and $13/2^{+}$ .