Neutron poor nuclei

NEUTRON-POOR NUCLEI (BELOW THE BAND OF STABILITY)... 

Some of the neutron-poor nuclei, especially the heavier ones, increase their neutron-to-proton ratios by undergoing alpha emission. Alpha particles are helium nuclei, fHe, consisting of two protons and two neutrons. Alpha emission also results in an increase of the neutron-to-proton ratio. An example is the alpha emission of lead-204. 

Neutron-Poor Nuclei (Below the Band of Stability) 26-16 Nuclear Fusion... 

Figure 22-1 A plot of the number of neutrons, A/, versus the number of protons,Z, in nuclei.The stable nuclei (green dots) are located in an area known as the band of stability. All other nuclei in the white, pink, and blue regions are unstable and radioactive. No nuclei exist in the large gray shaded region. Most unstable, radioactive nuclei occur outside the band of stability. As atomic number increases, the N/Z ratio of the stable nuclei increases. Unstable nuclei above the band of stability are referred to as neutron-rich nuclei (Woe shad/ng) those below the band of stability are called neutron-poor nuclei (pinkshading). Unstable (radioactive) nuclei decay by alpha emission, beta emission, positron emission, or electron capture. Lighter neutron-poor nuclei usually decay by positron emission or electron capture, either of which converts a proton into a neutron. Heavier neutron-poor nuclei usually decay by alpha emission, which decreases the neutron/proton ratio. Neutron-rich nuclei decay by beta emission, which transforms a neutron into a proton. Decay by alpha emission is by far the most predominant mode of decay for nuclei with atomic numbers beyond 83 (bismuth).

Neutrons may escape more easily from a nucleus than protons because they do not have to overcome the so-called Coulomb barrier, an energy wall which only affects the charged protons. This favors the production of neutron-poor daughter nuclei, i.e., the light isotopes of an element. 

Lutetium is a silvery white metal, relatively stable in air. There are few applications for lutetium. The availability is poor and the price high. If the Lu atom is activated by thermal neutrons its nucleus emits a pure 3-radiation. In this form the metal can be used as a catalyst for cracking and polymerization. ... 

For exposures equivalent to about 20 neutrons per Fe seed nucleus (r 0.5), the seed nuclei are converted principally to elements of atomic mass A from 70 to 85 with very little synthesis of nuclei beyond the neutron magic number N = 50. At about 50 neutrons per Fe seed nucleus, the Fe seeds have been flushed to nuclei between the magic numbers N = 50 and N = 82. And at exposures of 130 neutrons per Fe seed nucleus, the greatest crmnm occur between N = 82 and Pb. Finally for higher exposures the Fe seeds are predominantly converted to Pb nuclei. A recent discovery of lead stars shows that a high neutron to seed ratio is possible for metal-poor stars (Van Eck et al. 2001). 

Mossbauer hyperfine spectra are useful in the determination of nuclear parameters, especially those of the excited states. Their significance stems from the fact that the structure of the nucleus is still poorly understood. Comparison of the parameters as measured with the values estimated from theory is used to discover the validity or inadequacy of the nuclear model. The rare-earth elements are popular for this type of work because of the proliferation of Mossbauer resonances, making it feasible to study the effects of successive proton or neutron addition over a range of nuclei. Although theory and experiment are sometimes in accord, gross differences are not unusual. 

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