Promethium: The Hidden Element Between Neodymium and Samarium and Its Nuclear Battery Legacy

Periodic Videos explains how promethium, element 61 between neodymium and samarium, was inferred from gaps in relative atomic masses and eventually isolated during the Manhattan Project at Oak Ridge using ion exchange chromatography. The video covers the element’s radioactivity, its naming history from earlier proposed names to promethium, and the concept of a nuclear battery that leverages promethium’s beta decay and phosphor based light conversion. It also notes the limited practicality due to its short half life and ends with a few colorful facts about promethium compounds.

• Why an element between Nd and Sm was predicted
• How ion exchange chromatography separated promethium
• The modest discovery paper and the element names
• The promethium battery concept and its limitations

Introduction

This video from Periodic Videos centers on promethium, element 61, which lies between neodymium (60) and samarium (62) in the periodic table. The host explains how the large gap in relative atomic masses between Nd and Sm led early chemists to suspect a missing element, a prediction sharpened by the chemistry of the time. Promethium turns out to be radioactive, with its longest lived isotope bearing a half life around a few years, making early detection challenging.

The Periodic Table Gap and Promethium’s Place

The narrative highlights that most atomic weight gaps are two to three units, but the Nd–Sm gap is six units. This anomaly was a strong cue for a hidden element and sparked multiple claims of discovery before the correct identification. The talk also touches on how valence variations in lanthanides confounded straightforward predictions about chemical behavior, a theme that runs through the early development of the periodic table.

From Early Deductions to Nuclear Realities

The presenter notes that early chemists largely did not know about electrons, and Mendeleev’s era preceded a complete electronic picture. A historical observation is cited where neodymium appears to react with hydrogen in a way that samarium does not, implying an intermediate element with one hydrogen equivalent, a clue contributing to the search for a missing member of the series.

Discovery and Isolation: The Manhattan Project Approach

The video recounts how large scale nuclear research during the Manhattan Project produced sufficient promethium isotopes to allow detection. The actual discovery paper, authored by Marinsky, Glendenin and Koriel at Clinton Laboratories in Oak Ridge, is praised for its restrained tone that contrasts with contemporary announcements. The key feat was the separation of promethium using ion exchange chromatography, a technique that uses a column of acid functionalized plastic beads to separate ions by their affinity to the solid phase. The authors show elution graphs where promethium 61 creates a characteristic peak in radioactivity, enabling identification distinct from adjacent elements like neodymium.

Name and Identity

Promethium carried several proposed names in earlier claims, including illinium and florentium, but settled on promethium. The etymology traces to Prometheus, a mythic figure who stole fire, a symbolic nod to the discovery of nuclear energy and the power associated with fission products.

Promethium in Nuclear Science and Production

The element is formed as a product of nuclear fission pathways, including minor channels during uranium fission. With the expansion of reactor based research, promethium isotopes accumulated in quantities sufficient to contemplate real world uses. The video notes that the longest lived promethium isotope has a lifetime of about 3.7 years, with shorter lived isotopes being more common, which limits practical applications.

Promethium Batteries: A Nuclear Battery Concept

A notable part of the talk is the idea of promethium based nuclear batteries. The beta decay of promethium releases electrons that can be captured by a phosphor material to emit light, which is then converted into electricity by photocells. The envisaged advantage is reduced temperature dependence relative to conventional chemical batteries, making such devices attractive for extreme environments and spaceflight. However the short half life means the energy source would decay too quickly for long journeys, diminishing the practicality of such batteries in the long run.

Colorful Chemistry and Final Facts

The host shares color observations for promethium compounds, noting that promethium hydroxide is brown, promethium chloride yellow, and promethium nitrate pink. These tidbits provide a tangible, memorable glimpse into the chemistry of the element and its compounds.

Historical Footnotes and Legacy

The discovery paper is highlighted as an understated milestone that occurred just before the presenter's birth, emphasizing how scientific achievements were communicated in the early era. The Oak Ridge work on promethium sits alongside broader nuclear chemistry history, including later achievements in synthesizing heavier elements. The narrative also offers a personal reflection on the era of discovery and the quiet ingenuity that accompanied early nuclear science.