HHomeBackground Color:He
LiBeNeptunium Pictures PageBlack White GrayBCNOFNe
NaMgNeptunium Technical DataAlSiPSClAr
KCaNeptunium Isotope DataScTiVCrMnFeCoNiCuZnGaGeAsSeBrKr


Atomic Weight 237[note]
Density 20.45 g/cm3
Melting Point 644 °C
Boiling Point 4000 °C
Full technical data

Traces of neptunium have been found in uranium minerals like this sample, but not enough that you could ever see it. Neptunium is highly radioactive and has only a few exotic applications in nuclear research.

Scroll down to see examples of Neptunium.
The Elements book Mad Science book Periodic Table Poster  Click here to buy a book, photographic periodic table poster, card deck, or 3D print based on the images you see here!
Neptunium Smoke detector element

Smoke detector element.
The main listing for this sample is under americium, because that is the active ingredient in these small radioactive buttons used in ionization type smoke detectors. This sample had been in my collection for five years before reader Michael Okun pointed out an interesting fact: Americium-241 decays (with a half-life of 452 years) into Neptunium-237, which has a much longer half-life of 2.1 million years. That means neptunium is building up in my existing americium sample, and has been for years.

Michael calculates you get about a trillion new atoms of neptunium every year in a typical smoke detector, and very few of them decay. Much like fine wine, the sample gets better the longer you keep it! (Actually I hate wine, why not drink your grape juice before it goes sour, that's what I say. But anyway, it makes a good analogy, for those people who do think wine tastes better the older it gets.)

If someone has a really old smoke detector, like 20 or 30 years old, I'd love to get it. You know you're supposed to replace those things, they don't last forever, so I'd be doing you a service by taking it off your hands.

Unfortunately even 50 trillion atoms of neptunium still isn't much, only about 20 nanograms. On the other hand, the americium in the button only weighs about 260 nanograms to start with, so after only 50 years it would already be almost 10% neptunium, not too bad for such an exotic element. And when my collection has been gathering dust in a museum for about 500 years, this button will reach a milestone: It will be more than half neptunium. They'll have to move it from the americium shelf to the neptunium shelf and get a new, fresher smoke detector button to replace it. Gosh I hope someone remembers to do that, maybe I can get the Clock of the Long Now people to set an alarm or something.

Source: Hardware Store
Contributor: Theodore Gray
Acquired: 20 September, 2007
Text Updated: 21 September, 2007
Price: $10/smoke detector
Size: 0.075"
Purity: <1%
Neptunium Poster sample

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Poster sample.
This mineral, Aeschynite, appears in my Photographic Periodic Table Poster representing neptunium, because this highly unstable element can't reasonably be photographed. The rock probably contains on the order of a few atoms of neptunium at any one time, as part of the complex decay chain of the uranium that makes up a much larger fraction of the sample. In no meaningful way is neptunium itself visible in the sample, but sadly that's about the best you can do with an element like this. The sample photograph includes text exactly as it appears in the poster, which you are encouraged to buy a copy of.
Periodic Table Poster
Source: SoCal (Nevada), Inc
Contributor: Theodore Gray
Acquired: 20 September, 2005
Text Updated: 4 May, 2007
Price: $29
Size: 1.5"
Purity: 0%
Neptunium Sample from the Everest Set

Sample from the Everest Set.
Up until the early 1990's a company in Russia sold a periodic table collection with element samples. At some point their American distributor sold off the remaining stock to a man who is now selling them on eBay. The samples (except gases) weigh about 0.25 grams each, and the whole set comes in a very nice wooden box with a printed periodic table in the lid.

Radioactive elements like this one are represented in this particular set by a non-radioactive dummy powder, which doesn't look anything like the real element. (In this case a sample of the pure element isn't really practical anyway.)

To learn more about the set you can visit my page about element collecting for a general description and information about how to buy one, or you can see photographs of all the samples from the set displayed on my website in a periodic table layout or with bigger pictures in numerical order.

Source: Rob Accurso
Contributor: Rob Accurso
Acquired: 7 February, 2003
Text Updated: 29 January, 2009
Price: Donated
Size: 0.2"
Purity: 0%
Neptunium Photo Card Deck of the Elements

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Photo Card Deck of the Elements.
In late 2006 I published a photo periodic table and it's been selling well enough to encourage me to make new products. This one is a particularly neat one: A complete card deck of the elements with one big five-inch (12.7cm) square card for every element. If you like this site and all the pictures on it, you'll love this card deck. And of course if you're wondering what pays for all the pictures and the internet bandwidth to let you look at them, the answer is people buying my posters and cards decks. Hint hint.
Source: Theodore Gray
Contributor: Theodore Gray
Acquired: 19 November, 2008
Text Updated: 28 October, 2017
Price: $35
Size: 5"
Composition: HHeLiBeBCNOFNeNaMg AlSiPSClArKCaScTiVCrMn FeCoNiCuZnGaGeAsSeBrKr RbSrYZrNbMoTcRuRhPdAg CdInSnSbTeIXeCsBaLaCePr NdPmSmEuGdTbDyHoErTm YbLuHfTaWReOsIrPtAuHgTl PbBiPoAtRnFrRaAcThPaUNp PuAmCmBkCfEsFmMdNoLrRf DbSgBhHsMtDsRgCnNhFlMcLvTsOg
The Elements book Mad Science book Periodic Table Poster  Click here to buy a book, photographic periodic table poster, card deck, or 3D print based on the images you see here!