Level: Introductory, Intermediate
Nuclide charts contain information on the basic nuclear properties of known nuclides – both stable and unstable. In these charts, the vertical and horizontal axes represent the number of protons and neutrons respectively in the nucleus. It can be seen that stable isotopes (represented by the black boxes in the figure) lie within a relatively narrow range indicating that the neutron to proton ratio must have a certain value or range of values to be stable. Radioactive nuclei (coloured boxes) mostly lie outside this range. The plot also shows that for low atomic numbers, the neutron to proton ratio is unity. At higher atomic numbers, this value increases indicating a higher ratio of neutrons to protons in heavy atoms. The extremities of the coloured regions above and below the region of stability are known as the proton and neutron “driplines” beyond which nuclei are extremely unstable (i.e. if a nucleon is added it will “drip” out again). As nucleons are successively added to a nucleus on the stability line, the binding energy of the last nucleon decreases steadily until it is no longer bound and the nucleus decays.
Nuclei with even numbers of protons and neutrons are more stable than nuclei with other combinations of neutrons and protons (there are some notable exceptions to this, for example, the nuclide Be 8 which is highly unstable with a half-life of 67 x10-18 s). For uneven numbers of protons and neutrons, there are only very few stable nuclides. The stability of nuclei is extremely significant for special numbers of protons and neutrons. These (magic) numbers are 2, 8, 20, 28, 50, 82 and 126 and correspond to full shells in the shell model of the nucleus. The element tin with the proton number Z = 50, for example, has 10 stable isotopes, more than all other elements. When the proton and neutron numbers both have magic values, the nucleus is said to be “doubly magic”. Doubly magic, stable nuclides are for example He 4, the alpha particle, as well as the nuclide Pb 208, which is reached in several decay processes, for example in the decay chain of Th 232.
Each nuclide is represented by a box containing element symbol, mass number and the half-life. An important characteristic of the charts is the use of colour to denote the mode of decay, half-life, or some other property. If the nuclide has one or more metastable states, the box is subdivided into smaller boxes for each state. The inset shows the nuclide box for cobalt 60 (Co 60). The ground state is a ß- emitter (indicated by the colour blue) with a half-life of 5.27 years. The metastable state Co60m decays by both isomeric (gamma) transition and to a lesser extent by ß- decay (indicated by the small blue triangle) with a half-life of 10.47 minutes.
Which data is used in the Nuclide Explorer?
The data used by the Nuclide Explorer is from the JEFF3.1 and ENDF/B-VII.1 radioactive decay datafiles . Supplemetary information has been taken from the NUBASE 2003  and for A≥266 from M. Gupta et al. , (see also the Karlsruhe Nuclide Chart, 7th Edition).
 G. Audi et al., Nuclear Phys. A 729 (2003) 3-128. (http://amdc.in2p3.fr/web/nubase_en.html).
 M. Gupta et al., Nuclear Data Sheets 106, (2005) 251.
For a more detailed discussion see the Nucleonica Database
Overview of the Nuclide Explorer
The structure of the Nuclide Explorer navigational interface and its configuration controls are shown in the figure below. There main features correspond to: Main Chart, Select a Nuclide, Select a Database, Statistics, Show decay, Select Colour Theme / Main Decay Mode, Filter Decay Mode. These are discussed in the following sections.
The main chart window above shows the complete island of nuclides. Clicking anywhere on the nuclide island will result in zooming to a section of the nuclide chart centred on the selected nuclide. The zoom level can be changed by clicking on the + and - buttons. The full chart can be restored by clicking on the chart icon.
Select a Nuclide
In order to select a specific nuclide, there are the following options:
1. Zoom to a specific area by clicking on a nuclide in the chart.
2. In the element list box, type the first letter of the chemical symbol. The element list box will then show a list of elements which have this as the starting letter. The element can then be selected directly with the mouse or by repeatedly pressing the same letter until it appears in the box. Thereafter, the mass list box contains all the isotopes of the selected element for which there is data in the database.
Select a Database
The user can choose the data to be viewed in the Nuclide Explorer. Currently JEFF3.1 and ENDF/B-VII.1 radioactive decay datafiles can be viewed.
When the Statistics check box is activated, it shows the total number of nuclides in the selected database. In the example shown here, the JEFF3.1 database has been selected. The statistics shows the total number of ground and metastable states.
Activating the "Show decay" checkbox allows the user to see the decay scheme (or the daughters) highlighted on a background nuclide chart.The example below shows the day tree for Th-228. The parent Th-228 is shown highlighted with a red border (optional). It can also be seen in the Statistics that the total number of nuclides in this decay tree is 17.
Select Colour Theme / Main Decay Mode
Select Colour Theme
You can select the colour theme (e.g "Standard") by using the drop-down menu in the combobox in the "Select colour theme" control on the left side of the window. Note that if the colour theme "Karlsruhe" has been selected, the basic nuclear data is from the Nucleonica database i.e NOT from the Karlsruhe Nuclide Chart. Selecting the "Karlsruhe" colour theme means that the colour scheme used in the Karlsruhe Nuclide Chart is used ( i.e. the colour denotes a particluar mode of decay: an alpha emitter is yellow, beta- emitter is blue etc.).
Below the drop-down menu, there is a panel listing the decay modes and the colours used to describe these modes. This panel can be regarded as a legend for the nuclide chart (in the diagram ß- decay is represented by the colour blue, ß+/ec by red, etc.).
The Main Decay Mode The checked boxes on the left of the legend have a particular meaning. If the main decay mode of a ground state or a metastable state is for example an alpha emitter, then the box shown in the nuclide chart (or sub-box in the case of a metastable state) will have this colour. Hence a nuclide "box" in the chart will have a colour indicating the main mode of decay of the ground state and a colour indicating the main decay mode for each metastable state.
What is the main decay mode? The main decay mode of a nuclide or metastable state refers to the decay mode with the highest branching ratio. Most nuclide ground states and metastable states have a single main decay mode which is then indicated by a particular colour. However, it can arise that a nuclide ground state or metastable state can have two or three decay modes with the same branching ratio. The checked boxes in the legend will show a nuclide ground state and metastable states with a single colour. In the event that a nuclide or ground state has more than one main decay mode the following rule is used: the mode which appears first in the following list is used to determine the colour.
Filter Decay Mode
The filter decay mode window can be activated by checking the Filter decay Modes button. The default values are such that all modes are checked. These can be de-activated by unchecking the boxes individually or by unchecking all boxes simultaneously by pressing the "None" button. Thereafter, individual buttons can be checked. With all boxes checked, all nuclides will be shown in the nuclide chart. Below the chart, the total number of ground states, metastable states and the total number of ground + metastable states is given. This feature is very useful for finding the total number of alpha, beta, etc. emitters.
If only alpha is checked the nuclide chart will show only nuclide ground states and metastable states which have alpha emission as the main decay mode. If both alpha and ß- are checked, then the nuclide chart will show all nuclides which have a main decay mode of alpha or ß- emission. Mathematically this can be expressed as . If all boxes are checked, then the Nuclide Explorer shows all
As mentioned aboved, the nuclides shown in the chart will have a single colour referring to the main decay mode. Nuclides - both ground states and metastable states - can have subsidiary decay modes in addition to a main mode. These subsidiary modes can be accessed through the "Filter decay mode" button. To see all nuclides which have a particular decay mode - either as main mode or as subsidiary mode - the user should use the frame "Filter decay mode", select the mode or modes of interest and press the "Update" button. The results are shown in the nuclide chart. Consider the following example. In the main filter both alpha and ß- have been checked. In the "Filter decay mode" box, both SF and ß+ are checked. What is then seen in the Nuclide Explorer is: all nuclides which have either alpha or ß- as main mode (i.e. ) and in addition have either SF or ß+ as subsidiary modes (i.e. ).
Expressed mathematically, the Nuclide Explorer shows the result:
Nuclide chart based on half-life, etc.
A number of other chart colour schemes are available based on the decay mode, half-life, spin & parity, and binding energy.
On right-clicking on a nuclide a context menu appears which offers direct access to nuclide specific information and applications.