红水银（Red Mercury）一直传闻是前苏联在冷战时代研制出来，把纯水银和氧化汞锑放在核反应堆内辐照二十天，即制造出这种呈红色的廉价但辐射度极高的物料。据说，红水银每立方分米（即十厘米乘十厘米乘十厘米）的质量高达二十点二公斤，只需把棒球大小的份量制成肮脏弹，已足以造成灾难性破坏。但由于至今仍没有有力证据证明红水银存在，科学家对红水银到底是甚么莫衷一是。有科学家质疑，以如此高能量密度的辐射物，稳定性不足，难以制造炸弹。所有相关讨论都与苏联相关连，故部份专家认为是有心人士散播的谣言。

Red mercury is a hoax substance of uncertain composition purportedly used in the creation of nuclear bombs, as well as a variety of unrelated weapons systems. In reality, no such substance exists.

It is purported to be mercuric iodide, a poisonous, odorless, tasteless, water-insoluble scarlet-red powder that becomes yellow when heated above 126 °C, due to a thermochromatic change in crystalline structure. However, samples of "red mercury" obtained from arrested would-be terrorists invariably consisted of nothing more than various red dyes or powders of little value, which may have been sold as part of a campaign intended to flush out potential nuclear smugglers.