Spontaneous separation of californium and curium. [View all]

[NNadir]

The environmental tragedy now commencing in the United States means that future generations will be even more challenged to address severe environmental issues than they would have been had the United States constitution prevented the installation of an insane administration.

The insanity exists however, and those of us who can in the United States should not abandon our pursuit of knowledge, however much science may be threatened by the anti-intellectual bent of the mob that has seized control of the United States in defiance of Democracy.

If we have learned nothing in the last two decades about addressing climate change, it is that so called "renewable energy" cannot stabilize the atmosphere. This is demonstrated by the incontrovertible fact that the expenditure of trillion dollar sums on this failed technology has had no effect whatsoever on the unrelenting increase in climate change forcing gases.

We're at 406,14 ppm this week, 3.52 ppm higher than last year.

Although we have left a great mess for all future generations, one thing that they may not appreciate is that we have left them is sufficient fully isolated uranium to provide for all of the world's energy demands for many generations to come, as well as technology that can make access to uranium inexhaustible beyond several centuries, with rather less than dire environmental impact. A relatively small amount of uranium is capable of eliminating all the world's energy mines, all of the coal fields, all of the gas fields, fracked and traditional, and all of the world's oil fields.

For the overwhelming bulk of this uranium to be utilized, it will need to be converted to plutonium, utilizing, among other things, existing plutonium inventories (including weapons grade plutonium which must be denatured and rendered impossible to use in nuclear weapons.)

Right now, and for the immediate forseeable future, most of the world's nuclear reactors utilize the thermal neutron spectrum which is many ways undesirable, but it's what we have for now, at least until the fine upcoming generation of nuclear, chemical, and materials science engineers can apply their intellects to change this state of affairs, as we must hope they will.

Continuously recycled plutonium in a thermal cycle, according to one reference, (Ref: Nuclear Reactor Physics, William E. Stacy, Wiley and Sons 2001. pg.234) will consist of an isotopic mixture having roughly 8.17% ²³⁸Pu, 45.10% ²³⁹Pu,
20.54% ²⁴⁰Pu, 18.57%, ²⁴¹Pu, and 7.62% ²⁴²Pu. These figures show - they are probably only valid as a first approximation - that plutonium can be readily transformed into a form totally unsuitable for weapons use, owing to the heat load associated with ²³⁸Pu and ²⁴¹Pu which decays in situ to ²⁴¹Am.

However the transuranium isotope distribution will not be limited to plutonium in this state of affairs (which is less sustainable than fast spectrum fission reactors, which can supply all human energy needs indefinitely.) Among the transuranium elements, working from the same reference, only 51% will be represented by plutonium. Roughly 5% will be neptunium, 9% will be americium, 34% will be curium, with smaller amounts being represented by californium and berkelium.

As I noted earlier in a post here, the accessibility of high oxidation states makes the separation of plutonium, neptunium, and americium from traditional used nuclear fuels, almost all of which are based on oxides of the actinides. Neptunium and americium are the key to generating ²³⁸Pu to eliminate the value of plutonium for weapons diversion.

In the case of americium, however, an intermediate in the production of ²³⁸Pu is ²⁴²Cm. The other curium isotopes will also be present, and what's more, inevitably, this curium will also be contaminated with californium. Because of californium's high rate of neutron production, it is desirable to separate it from other elements both to utilize this spontaneous flux, and to simplify the handling of curium for the recovery of its heat.

Neither californium nor curium however exhibit stable higher oxidation states. This means that while they are easily separated from the lower actinides, they are more challenging to separate from one another; in general (especially since in general only small amounts are produced today), one must resort to procedures like chromatography.

All of this is why I read with interest today a paper detailing a spontaneous separation of curium and californium.

The paper is here: Inorg. Chem., 2015, 54 (23), pp 11399–11404 "Spontaneous Partitioning of Californium from Curium: Curious Cases from the Crystallization of Curium Coordination Complexes"

Some text from the paper:

Curium plays a central role in actinide chemistry in that it is isoelectronic with gadolinium, and both trivalent ions possess half-filled f7 shells. This allows curium(III) compounds and complexes to be used as benchmarks for comparisons with gadolinium and other lanthanide analogues as well as with both earlier and later actinides.(1) Given the spherical symmetry of the f⁷ configuration and the general perception that both 4f and 5f orbitals are nonbonding, one might expect that gadolinium(III) would be an excellent analogue of curium(III) if the difference in their ionic radii is excluded. In fact, the electronic characteristics of curium(III) diverge from those of gadolinium(III) in a number of respects...

Actually the "general perception" of 5f is not really valid, but no matter.

A little more on uses for curium:

Curium(III) is perhaps the most luminescent of all 5f-element ions and emits characteristic orange light centered near 600 nm.(7) This property is extraordinarily useful in a wide variety of applications that range from solution complexation studies to the environmental behavior of trivalent actinides to biological probes to understanding energy-transfer processes in f-block materials.(7) Changes in the coordination of curium(III) can cause substantial shifts in the photoluminescence peak position and spectral shape.(7) In contrast, gadolinium(III) compounds, while capable of emitting at visible wavelengths, have low quantum yields even when antennas are utilized for energy transfer and are often used as nonemitting hosts in europium(III)- and terbium(III)-doped materials.(8)

Some remarks on separations:

The separation of middle-to-late actinides from one another has been a key challenge for decades in the development of the chemistry of these elements, their use as targets for the production of super heavy elements (i.e., transactinides), and advanced nuclear fuel cycles for separating lanthanides from actinides. Studies of the stability constants of trivalent lanthanides and actinides with ?-hydroxyisobutyrate show that a monotonic trend exists with lanthanides.(14) However, with diethylenetriamine-N,N,N?,N?,N?-pentaacetic acid, this trend is not preserved; curium binds more weakly, and californium more strongly, than expected.(14, 15) These early studies were already suggestive of a change in chemistry occurring at californium that continues through mendelevium.(14, 15)

We recently communicated a few features of the curium(III) tris-chelate, 2,6-pyridinedicarboxylate (dipicolinic acid, DPA) complex, Cm(HDPA)3, as a part of a comprehensive study that compared middle actinides with californium.(16-18) Herein, we substantially expand on our analysis of this complex as well as elucidate the structure and properties of the bis-chelate complex [Cm(HDPA)(H2DPA)(H2O)₂Cl]⁺.

They ran some crystallizations and to their surprise found that the crystallization process lead to the separation of tiny amounts of californium complexes from curium complexes.

The collection of photoluminescence spectra from groups of crystals revealed that the colorless crystals of DPA that cocrystallize with the bis-chelate luminesce green, as shown in Figure 4. Collection of this luminescence spectrum showed that the green luminescence is superimposable with that of Cf(HDPA)₃, including the fine vibronic structure (see the Supporting Information).(16) Single-crystal X-ray diffraction studies demonstrate that these crystals are ostensibly just DPA. However, it must be kept in mind that crystal structures are averages of the total composition of the crystal and are largely insensitive to trace doping.(31) However, they are clearly doped with low levels of Cf(HDPA)₃, . Dissolution of the crystals followed by energy-resolved liquid scintillation counting of californium in the crystals reveals doping levels of 37(5) ppm. The error on this number represents the deviation in the dopant levels between crystals and supports essentially constant doping levels from crystal to crystal. Crystals were also cut and broken, and the lack of significant variation in the photoluminescence intensity of the interior versus exterior of the crystals reveals a relatively uniform distribution of californium throughout the samples. This level also indicates that californium is concentrated within the DPA crystals because the californium levels in typical 248Cm samples are ?1 ppm (or less).

Here's the picture of the crystals:



Esoteric, I know, but cool. They'll need to know these sort of things in the future if they wish to save themselves from what our irresponsibility has done.

Enjoy the coming week.