Neptunium moment

The problem could be stated from another point of view. In an isostructural series the uranium and neptunium compounds tend to be itinerant electron magnets or band magnets (like iron) and their orbital contribution is at least partially quenched. For much heavier actinides we know that the compounds will make local moment magnets with orbital contributions. It is quite possible that in between these two clear cut forms of magnetism that the intermediate case could be dominated by fluctuations, and no recognizable form of magnetism would occur. To state that the... 

Since plutonium is the actinide generating most concern at the moment this review will be concerned primarily with this element. However, in the event of the fast breeder reactors being introduced the behaviour of americium and curium will be emphasised. As neptunium is of no major concern in comparison to plutonium there has been little research conducted on its behaviour in the biosphere. This review will not discuss the behaviour of berkelium, californium, einsteinium, fermium, mendelevium, nobelium and lawrencium which are of no concern in the nuclear power programme although some of these actinides may be used in nuclear powered pacemakers. Occasionally other actinides, and some lanthanides, are referred to but merely to illustrate a particular fact of the actinides with greater clarity. 

Both the paramagnetic and the ordered moment are well below the free trivalent ion values and yet, as Mossbauer measurements show, neptunium is unambiguously in the trivalent state. 

Fig. 14. Plot of hyperfine fields (as measured by Np Mossbauer spectroscopy) versus the moment on Np (as measured by neutron diffraction) for various magnetically ordered neptunium intermetallics. A general, linear relation emerges independent of details of magnetic or crystallographic structure (Dunlap- Lander relation). [Taken from Dunlap and Lander (1974).]...

---