Californium is a synthetic, highly radioactive actinide metal. It is notable for the isotope Cf-252, a strong spontaneous-fission neutron source used in neutron radiography, reactor start-up, and analysis.
Californium (Cf) is a synthetic actinide with atomic number 98 in period 7 (f-block), positioned between berkelium (Bk) and einsteinium (Es). It was first produced at the University of California in the early 1950s and exists only in minute, laboratory-made quantities.
\(^{252}\mathrm{Cf}\) emits a large flux of neutrons due to spontaneous fission (SF), making it a compact, portable neutron source for applications such as reactor start-up, neutron radiography, well logging, and neutron activation analysis. Its neutron emission rate per gram is on the order of \(10^{12}\) n·s−1·g−1, enabling strong signals from very small sources.
\(^{252}\mathrm{Cf}\) has two principal decay modes:
\(^{252}\mathrm{Cf} \;\to\; ^{248}\mathrm{Cm} + \alpha\)
\(^{252}\mathrm{Cf} \;\to\; \text{fission fragments} + \nu\,n\)
where \(\nu\) is the average neutron multiplicity per fission event.The combination of alpha decay and SF yields both intense radiation and useful neutrons.
A commonly cited ground-state configuration is [Rn] 5f10 7s2. In chemistry, Cf(III) is the most stable oxidation state in aqueous solutions, while Cf(IV) can be stabilized in some solids (e.g., CfO2). Lower states like Cf(II) are rare and require strongly reducing conditions.
Important isotopes include:
Californium is produced by multiple neutron captures and beta decays starting from lighter actinides (e.g., curium or berkelium) in high-flux reactors, followed by radiochemical separations. A stylized step in such chains is:
\(\cdots \xrightarrow{(n,\gamma)} \mathrm{Bk} \;\to\; \mathrm{Cf} + \beta^-\)
Because yields are extremely small, only specialized national laboratories can make microgram-scale amounts.
Representative compounds include Cf2O3 (californium(III) oxide), CfO2 (californium(IV) oxide), and trihalides such as CfCl3 and CfF3. In water, Cf(III) forms hydrated complexes like \(\mathrm{[Cf(H_2O)_n]^{3+}}\)
Neutrons interact with materials through scattering and capture, enabling techniques like neutron activation analysis (NAA), where induced radioisotopes reveal elemental composition. A simple capture step is:
\(^{A}_{Z}\!X + n \;\to\; ^{A+1}_{\;\;Z}\!X^{*} \;\to\; ^{A+1}_{\;\;Z}\!X + \gamma\)
The emitted \(\gamma\)-rays are characteristic of specific nuclides, allowing sensitive detection.
Yes. Californium is a radiotoxic heavy metal that emits intense neutron and gamma radiation (directly and via daughters). Handling requires licensed hot cells or glove boxes, heavy hydrogenous shielding (e.g., polyethylene, water) often doped with boron to capture thermalized neutrons, strict contamination control, dosimetry, and compliant waste management.
Beyond research, \(^{252}\mathrm{Cf}\) sources see niche use in industrial radiography, well logging, and historically in certain neutron therapy contexts. However, due to handling hazards and cost, applications are tightly regulated and relatively limited compared with gamma sources like \(^{60}\mathrm{Co}\).