---
title: "Californium (Cf) — element 98"
description: "Californium is element 98, symbol Cf, most stable isotope 251. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/californium/
site: "At One Place"
---

# Californium (Cf)

**Californium — element 98: Cf**

[251] · Actinide · period 7

Californium-252 is one of the few practical portable neutron sources: a single microgram emits around 2.3 million neutrons a second by spontaneous fission, which is enough to start a reactor, find gold in ore, or spot water and oil in a borehole. Worldwide production is a few tens of milligrams a year, split between Oak Ridge and Dimitrovgrad, and the price has been quoted around $27 million per gram, making it one of the most expensive substances routinely sold. It is the heaviest element of which weighable quantities have ever been prepared.

## Properties

- **Atomic number:** 98
- **Symbol:** Cf
- **Mass number of most stable isotope:** [251]
- **Category:** Actinide
- **Period:** 7
- **Block:** f-block
- **Electron configuration:** [Rn] 7s² 5f¹⁰
- **Electrons per shell:** 2, 8, 18, 32, 28, 8, 2
- **Melting point:** 1,173 K — 899.9 °C — 1651.7 °F
- **Electronegativity:** 1.3 (Pauling)
- **Oxidation states:** +3
- **Discovered:** 1950 by Stanley Thompson, Kenneth Street Jr., Albert Ghiorso and Glenn Seaborg

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁰
- **Noble gas shorthand:** [Rn] 7s² 5f¹⁰
- **Shells:** K: 2 · L: 8 · M: 18 · N: 32 · O: 28 · P: 8 · Q: 2

## What it is used for

- Neutron sources for starting up nuclear reactors
- Portable neutron activation analysis, including gold and silver assay
- Detecting metal fatigue and water in oil wells
- Cancer brachytherapy with neutrons

## Hazards

- Powerful neutron emitter; requires substantial shielding well beyond what alpha emitters need
- Bone-seeking if ingested

> No stable isotope; the mass given is the mass number of californium-251, the longest-lived at 898 years. Boiling point and density are omitted: no measured values exist.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 96 | Curium | Cm | [247] |
| 97 | Berkelium | Bk | [247] |
| 98 | Californium ← | Cf | [251] |
| 99 | Einsteinium | Es | [252] |
| 100 | Fermium | Fm | [257] |

## Common questions

### What is the atomic number of californium?

98. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for californium?

Cf.

### What is the electron configuration of californium?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁰, or [Rn] 7s² 5f¹⁰ in noble-gas shorthand.

### What is the melting point of californium?

1,173 K — 899.9 °C — 1651.7 °F

## Related pages

- [Curium (Cm)](https://atoneplace.net/element/curium/)
- [Berkelium (Bk)](https://atoneplace.net/element/berkelium/)
- [Einsteinium (Es)](https://atoneplace.net/element/einsteinium/)
- [Fermium (Fm)](https://atoneplace.net/element/fermium/)

## Sources

- Official vendor product documentation — At One Place (/about/)