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For mass numbers of 147, 151, and 209+, the beta-stable isobar of that mass number has been observed to undergo alpha decay. (In theory, mass number 143 to 155, 160 to 162, and 165+ can also alpha decay.) This gives a total of 101 stable nuclides with odd mass numbers.
This occurs when an isotope has a nonzero nuclear spin, meaning an odd number of protons and/or neutrons (see Isotope). Nuclides with even numbers of both have a total spin of zero and are therefore not NMR-active. In its application to molecules the NMR effect can be observed only in the presence of a static magnetic field.
To be NMR-active, a nucleus must have a non-zero nuclear spin (I ≠ 0). [8] It is this non-zero spin that enables nuclei to interact with external magnetic fields and show signals in NMR. Atoms with an odd sum of protons and neutrons exhibit half-integer values for the nuclear spin quantum number (I = 1/2, 3/2, 5/2, and so on). These atoms are ...
Spallation does not require high temperature and pressure of the stellar environment but can occur on Earth. Though the lighter products of spallation are relatively rare, the odd-mass-number isotopes in this class occur in greater relative abundance compared to even-number isotopes, in contravention of the Oddo–Harkins rule.
Furthermore, for odd–odd nuclei, there are two unpaired nucleons to be considered, as in deuterium. There is consequently a value for the nuclear magnetic moment associated with each possible l and s state combination, and the actual state of the nucleus is a superposition of these. Thus the real (measured) nuclear magnetic moment is between ...
The nitrogen rule states that organic compounds containing exclusively hydrogen, carbon, nitrogen, oxygen, silicon, phosphorus, sulfur, and the halogens either have (1) an odd nominal mass that indicates an odd number of nitrogen atoms are present or (2) an even nominal mass that indicates an even number of nitrogen atoms in the molecular formula of the neutral compound.
For other isotopes, the isotopic mass is usually within 0.1 u of the mass number. For example, 35 Cl (17 protons and 18 neutrons) has a mass number of 35 and an isotopic mass of 34.96885. [7] The difference of the actual isotopic mass minus the mass number of an atom is known as the mass excess, [8] which for 35 Cl is –0.03115.
Nuclear magnetic resonance (NMR) spectroscopy uses the intrinsic magnetic moment that arises from the spin angular momentum of a spin-active nucleus. [1] If the element of interest has a nuclear spin that is not 0, [1] the nucleus may exist in different spin angular momentum states, where the energy of these states can be affected by an external magnetic field.