A chart of nuclides from ENSDF
The Evaluated Nuclear Structure Data File is the evaluated, recommended nuclear structure and decay data for every known nuclide, kept by the National Nuclear Data Center at Brookhaven for the international Nuclear Structure and Decay Data network. It is published as one text file per mass number, in the fixed 80-column format of the ENSDF manual. This page reads those files as they are — the release on this site was built from the NNDC distribution by the same reader that runs when you open a file — and draws every nuclide with an adopted data set by its neutron number N and proton number Z.
What the chart shows
Each cell is a nuclide’s ground state, or, strictly, its lowest known level. The colour is its half-life by default; Colour by, on the chart’s toolbar, also colours by the main decay mode, the Q-values and separation energies of the adopted data set, the energy of the first 2+ level of the even-even nuclides, and the date the adopted data set was entered. Stable nuclides are drawn darkest on the light theme and lightest on the dark one. The double lines trace the magic numbers 2, 8, 20, 28, 50, 82 and 126. A notch in a cell’s top right corner means the nuclide has isomers. Hover over a cell for its half-life and decay modes, and point at a legend entry to pick out one class.
The states of a nuclide are its ground state and the levels the evaluators flag as metastable (the MS field), together with any excited level that lives at least 1 µs. The second rule is needed: in this release the 3.19 h isomer of 90Y and the 258 s isomer of 90Rb carry no flag, and both decay by β⁻ as well as by IT. Isomers are named m, m1, m2 … after the evaluators’ flags.
The decay chain
The decay modes of each state come from the adopted data set: %B-=100, %EC+%B+=56.3 20, %A<1E-4. Following the ENSDF convention, a β-delayed mode such as %B-N is part of %B-, so the branch that ends at the plain β⁻ daughter is what is left after the delayed ones are taken out.
Where a branch lands in the daughter is worked out from the decay data sets. The cascade in the data set is followed from the levels the decay feeds — the direct β, ε or α feeding of each level, then down through the γ rays leaving it in proportion to their total transition intensities — until it reaches the ground state or an isomer. That is how 234Th is seen to feed 234mPa (99.85 %), 99Mo to feed 99mTc (87.6 %) and 137Cs 137mBa (94.7 %). Which level of a decay data set is which isomer is decided by the evaluators’ own cross-references (XREF), not by energy alone: 212Pb feeds a picosecond level of 212Bi at 238.6 keV that lies within a keV of the 25-minute isomer. An isomer with no IT data set decays through the γ cascade of the adopted level scheme.
Checked against the ICRP Publication 107 decay data of Radionuclide Decay Chains: of 1508 nuclides, 1470 give the same daughters and branching fractions to within 2 % (absolute) or 10 % (relative), with isomers shorter than a minute passed through as ICRP does. The rest differ because the evaluations have moved on since 2008 — 50V, 93Zr, 232Pu — or because ICRP treats a very long-lived nuclide such as 209Bi or 130Te as stable.
On the grid, the first of the two layouts, the chain is drawn with Z across and the mass number A down: α decay steps down a row and two columns to the left, β⁻ one column to the right, electron capture one to the left, and an isomer stands above the ground state it decays to. The share on each arrow is of the decays of the nuclide it leaves; the table gives the share of the first nuclide’s decays that passes through each member. The settings beside the view tabs serve both views, since the chart draws the same chain: the smallest branch to draw and the shortest half-life to draw. The Chain box on the chart’s toolbar draws the chain over the chart, or leaves it off; On chart, on the chain’s bar, shows the chain on the chart, and ticks the box if it is off. By default every nuclide is drawn and only isomers living less than a second are left out; with a half-life from 1 ms up to 1000 years, every member that lives less — nuclide or isomer, but never the one the chain starts from — is left out, and the chain goes straight on to where it decays, each share the product of the branches on the way. An arrow that jumps over left-out members is marked “via” them: with members under a year left out, 238U goes to 234U via 234Th and 234mPa, 226Ra to 210Pb via 222Rn … 214Po, and 210Pb to 206Pb via 210Bi and 210Po. What goes through an isomer’s IT stays in the nuclide and joins the plain arrow: with members under an hour left out, 137Cs goes to 137Ba by one arrow of 100 %, 94.7 % of it through 137mBa. The note under the drawing lists what was left out. Where arrows would cross a box or run on top of each other, they bend; where labels have no room, the gap between the rows widens.
The series. The other layout, chosen in the Layout menu on the chain’s bar, draws the same chain the way Radionuclide Decay Chains draws its chains: a circle for each state, with the mass number over the atomic number before the symbol and the half-life below, α decay straight down, β⁻ a step to the right and electron capture a step to the left, so that a decay series runs down the page as a column with short steps across. Across is Z − N, and each row is one mass number, as on the grid. Every arrow is labelled with its decay mode over its share, an isomer stands above the state it decays to, and spontaneous fission is an arrow out to the side. Arrows bend round circles in their way as they do round boxes. The settings, the table and the notes are the same in both layouts; the SVG and PNG files and the buckets of the Inventory tab follow the layout chosen, and the page remembers it.
Parents. The chain can also run the other way. Set it to parents, beside the view tabs, and it gathers every nuclide and state whose decays come to the one chosen, directly or through others — its parents, their parents and so on — and draws them the same way and by the same settings, the chosen nuclide at the foot of the arrows. Only the branches that lead to it are drawn: 226Ac comes to 226Ra by its 17 % of electron capture, and its β⁻ branch to 226Th, which never gets there, is left out. The share on an arrow is still of the decays of the nuclide it leaves; the table gives the share of each member’s decays that reaches the chosen one. The half-life setting works as it does going down, and a short-lived member that nothing drawn decays to is not drawn at all: with members under a year left out, 226Ra has 230Th, 234U, 238U (via 234Th and 234mPa) and 238Pu above it, and 242Pu, 246Cm and a few more above them. A stable nuclide has parents too. The Nuclide tab lists those that decay straight to the state on show, each with the share of its decays that lands there, as the file gives it.
Going up and going down agree: for every member above a nuclide, the share of its decays that reaches the nuclide is the nuclide’s share in that member’s own decay chain, and every arrow is the same arrow — checked for every pair in this release, at every setting.
Moving the start. A click on a box in the chain, or on a member in the table, opens that member in the panel and leaves the chain as it is, so that the members of one chain can be looked through in turn; the chart, too, picks out the member and still draws the same chain. The Nuclide tab then offers Start the chain here, which draws the chain from that member instead, or, with the chain set to parents, End the chain here, which draws that member’s parents. A nuclide chosen on the chart, or found by the search, starts a chain of its own straight away.
What the file does not say. A few radioactive ground states have no decay mode in the adopted data set — in this release 127Te and 128La, whose percentage is given only in a comment — and a few give only a minor mode (251Fm lists its 1.8 % α but not the electron capture). For those the page adds the β⁻ or electron-capture branch the Q-values leave open, when only one of the two is, and marks it as inferred: a dashed arrow with a *. An excited state with no decay mode is taken to decay by γ emission.
Levels, radiation and data sets
Levels lists the adopted levels with their spins, half-lives and decay modes, and under each the γ rays leaving it with their relative intensities, multipolarities and final levels. Radiation lists what the decay data sets give for the state you are on: γ rays, α particles, β⁻ and β⁺/ε branches and delayed particles, per 100 decays of the parent where the data set’s normalisation allows it, and as relative intensities where it does not. X-rays and conversion electrons are not records in ENSDF and are not shown. Data sets lists every data set filed under the nuclide, and the history of its adopted one.
Inventory over time
The Inventory tab gives the decay chain on show an initial inventory — an activity (Bq), an amount (mol) or a mass (g) for any of its members; the start of the chain has 1 Bq until you set something else — and follows it over the span of time you choose: each member’s activity, amount or mass, or the energy it gives off as alpha particles, electrons (beta particles, positrons, conversion and Auger electrons) or photons (gamma rays, X-rays, annihilation radiation), or all together. An amount can be typed with an exponent, and with a decimal point or a comma: 6.21E12 and 6,21e12 are the same. For the energies and the power, integrated over time shows instead what has been given off from the start up to each time, in MeV, or in joules for the power. With the chain set to parents, give any of them an amount and follow how the chosen nuclide grows in from it: every nuclide that feeds a member of that chain is a member too, so what each member holds is complete. The chain is taken as it is drawn, so the half-life setting counts: a member it leaves out decays as fast as it is made, in secular equilibrium with the member that feeds it, and what it gives off is counted with that member. Point at a line, a box of the chain (a circle, in the series) or a row of the table and the same member is picked out in all three; the boxes or circles fill, as buckets, to their share of the whole at the time under the cursor, and Run through moves that time from start to end. The values drawn save as CSV, the chart as SVG or PNG.
The decay is worked by the Chebyshev rational approximation of the matrix exponential (CRAM, order 16), which is exact to about 10−14 of the largest value for any span, with members from microseconds to billions of years. The integrated energies come from the same calculation, which counts each member’s decays as the chain decays, so they are as exact as the rest and do not depend on the points drawn. Energy per decay is worked out from the ENSDF decay data sets: the alpha energies with the recoil of the nucleus, the mean beta and positron energies, the gamma rays, and the de-excitation energy of the levels fed that the gamma rays do not carry; X-rays and Auger electrons after electron capture, which ENSDF does not list, are estimated from the K-shell binding energy and the fluorescence yield. Against ICRP Publication 107, with isomers under a minute counted with their parents as ICRP counts them, the total is within 5 % for four nuclides in five and within 10 % for nine in ten. Neutrinos and fission fragments are not counted, and a mass is converted with the mass number as the molar mass.
Another database
The menu offers the releases installed on this site, then those you have opened in this browser, then every release in the NNDC ENSDF archive, back to 2004. The page cannot fetch a release from NNDC by itself — their server does not allow other sites to read its files — so choosing one from the archive shows the file to download, ensdf_YYMMDD.zip (before 2022 a release came in three parts by mass number, _099, _199 and _299, to be opened together), and a button to open it once it is downloaded; dropping it on the page does the same. The page reads it in your browser in a few seconds; nothing is uploaded. Individual ensdf.NNN files, or any ENSDF text, can be opened with Open ENSDF… in the same way. An opened database is kept in this browser and stays in the menu until you choose Forget.
To install a release on the site, run node scripts/gen-ensdf.mjs ensdf_YYMMDD.zip; it writes the data under resources/data/ensdf/ and adds it to the menu. node scripts/gen-ensdf-archive.mjs brings the list of NNDC’s releases up to date.
Links, keys and files
The address follows the nuclide you are on — ensdf.html#99mTc — so a link opens the page there. The arrow beside the search, Back, returns to where you were before you followed a link, clicked the chart or the chain, or searched: the nuclide, the start of its chain and which way it runs, the view and the tab, as you left them. The browser’s own Back and Forward go the same way, and a run of arrow-key steps counts as one move. On the chart, arrow keys step between nuclides, + and − zoom and 0 shows the whole chart. In the decay chain + and − zoom too and 0 shows the whole chain, as do the buttons on the chain’s bar, and a pinch, or the wheel with Ctrl held, zooms about the pointer. A chain opens with the whole of it in view, as ⤢ shows it, and stays whole as the window changes size; once you zoom, the zoom stays while you click about in the chain, and a new chain opens whole again. CSV saves every ground state as a table, PNG the chart as it is on screen; the decay chain saves as SVG, PNG or CSV, the drawing at its own size however it is zoomed. The button at the right end of the toolbar gives the page the whole window, without the site’s header and footer; the kvot mark at the left of the toolbar then goes to the home page, and the switch beside the button changes between light and dark. The page remembers the choice.
Data: Evaluated Nuclear Structure Data File, National Nuclear Data Center, Brookhaven National Laboratory, on behalf of the Nuclear Structure and Decay Data network. The release in use is named in the menu above.
