Neutron-rich nuclei

The pattern of nuclear stability can be used to predict the likely mode of radioactive decay neutron-rich nuclei tend to reduce their neutron count proton-rich nuclei tend to reduce their proton count. In general, only heavy nuclides emit a particles. 

The magic numbers which impart stability to a nucleus are 2, 8, 20, 28, 50, 82 or 122. The isotope, 39K, has a magic number equal to its number of neutrons, so it is probably stable. The others have a larger neutron-to-proton ratio, making them neutron-rich nuclei, so 40K and 41K might be expected to decay by beta emission. In fact, both 39K and 41K are stable, and 40K does decay by beta emission. 

Hamilton, J.H. Fission and Properties of Neutron-Rich Nuclei. World Scientific Publishing Company, Inc., River Edge, NJ, 1998. 

There are several hundred radionuclides that have been used as radiotracers. A partial list of the properties of these nuclides and their production methods are shown in Table 4.1. The three common production mechanisms for the primary radionuclides are (n,y) or (n,p) or (n,a) reactions in a nuclear reactor (R), charged-particle-induced reactions usually involving the use of a cyclotron (C), and fission product nuclei (F), typically obtained by chemical separation from irradiated uranium. The neutron-rich nuclei are generally made using reactors or... 

Knowledge of fission and its consequences is important for the nuclear power industry and the related fields of nuclear waste management and environmental cleanup. From the point of view of basic research, fission is interesting in its own right as a large-scale collective motion of the nucleus, as an important exit channel for many nuclear reactions, and as a source of neutron-rich nuclei for nuclear structure studies and use as radioactive beams. 

We discuss RPA calculations of the Gamow-Teller properties of neutron-rich nuclei to study the effect of B"delayed fission and neutron emission on the production of Th, U and Pu chronometric nuclei in the astrophysical r-process. We find significant differences in the amount of -delayed fission when compared with the recent calculations of Thielemann et al. (1983). 

We mentioned in the Introduction that neutron-rich nuclei around A=100 and A 150 are produced by fission. The PAC method was used to measure... 

Nuclear Structure Studies of Neutron-Rich Nuclei R. L. Gill... 

To define more accurately the boundaries of the mass regions that could be accessed with the proposed He-jet coupled mass separator system, production cross sections for both neutron-deficient and neutron-rich nuclei far from stability have been estimated for 800-MeV proton reactions. The spallation-product cross sections were estimated through use of the Rudstam systemstics [RUD66]. For estimation of the fission-product cross sections, however, there is no established, similar approach. Thus, an empirical approach was taken in... 

Proton-Rich and Neutron-Rich Nuclei Produced by Heavy Ions... 

Recent nuclear-structure studies of proton-rich and neutron-rich nuclei, performed at the GSI on-line mass separator, are surveyed and an outlook is given towards a continuation of such investigations with heavy-ion beams of higher energies. 

In conclusion thre first half-life measurements of light neutron rich nuclei using the MSU Reaction Product Mass Separator has resulted in the measurement of eight half-lives,two of which represent first time measurements and three of which are second measurements.The RPMS coupled with fast beam switching has proven to provide a very clean environment in which to study the decays of neutron rich nuclei. 

In recent years there has been a rapid increase in our knowledge of the atomic-mass surface far from the valley of 0 stability [BEN80,CER8l]. However, even with these advances there remain more than 60 neutron-rich nuclei with A < 70 for which the only known information is that they are stable with respect to neutron emission. It is clear that more detailed information about these exotic nuclei is essential. Especially important are the measurements of ground state atomic masses, since the ground state mass is one of the most fundamental properties of a nucleus. 

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