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About Binding Blocks

The Binding Blocks project aims to enthuse and engage the public and young people with nuclear physics research. Activities centre on an 8m-long representation of the Nuclide Chart, built using over 25,000 LEGO® bricks. 

The project engages target audiences through a range of programmes:

  • Nuclear Masterclasses for A-level (or equivalent) students. Offered in person and online, these introduce the key concepts of nuclear physics before focussing on applications including nuclear astrophysics, fusion, and medical physics.  
  • A school loans scheme comprised of a curriculum-linked LEGO® workshop for A-level (or equivalent) students. 
  • Teacher CPD programmes (run in conjunction with the National STEM Learning Centre)
  • Exhibitions targeted at family audiences centred around the building of the LEGO® chart.  

The project is funded by the Science and Technology Facilities Council (STFC) and the University of York. 


Frequently Asked Questions

How many Lego™ bricks are used to create the whole nuclear chart?

There are 26,437 bricks used.

What do the different colour Lego™ bricks represent?

Black bricks indicate the nuclide is stable.

The rest of the bricks indicate which decay mode that nuclide decays by.

Light blue and dark blue represent ß- decay and neutron emission respectively.

Red, yellow and orange represent ß+ decay, alpha decay and proton emission respectively.

Green indicates the nuclide undergoes spontaneous fission.

How many different nuclides are there?

There are 254 stable nuclides. They are all found naturally on Earth. There are also 85 unstable (or radio active) nuclides also found naturally on Earth. This means there are 339 nuclides found on Earth in total.

Nuclear physicists have also been able to create 556 more unstable nuclides with a half-life longer than one hour, and over 2400 with a half-life shorter than one hour.

This means there are over 3300 different nuclides that can exist in the universe.

What does the height of the towers represent?

Each block represents the mass excess per nucleon in the nucleus.

Mass excess is the difference in mass between the actual nucleus and its mass number in atomic mass units.

So a taller tower means each nucleon has more mass each than a shorter neighbouring tower.

Why does the Nuclear Chart start tall, become short, then become tall again with increasing Z and N?

Think of the nuclear binding energy per nucleon graph...

For nuclei lighter than iron (Fe), the binding energy per nucleon is increasing as you increase nucleon number.

By fusing to create a heavier nucleus, you have increased binding energy per nucleon and energy is released, this is nuclear fusion.

The energy released when fusing originates from it’s mass (E=mc2) and this decreases the overall mass of the resulting nuclei. The towers become shorter.


For nuclei much heavier than iron (Fe), the binding energy per nucleon is always decreasing as you increase nucleon number.

By splitting heavy nuclei up into lighter nuclei, you have  increased binding energy per nucleon and energy is released, this is nuclear fission.

The energy released when fusing originates from it’s mass (E=mc2) and this decreases the overall mass of the resulting nuclei. The towers become shorter.

What stops a nuclide existing outside the ranges given by the nuclear chart?

The edges of the graph are called the proton drip line (on the side where you can't add any more protons), and the neutron drip line (on the side where you can't add anymore neutrons).

(Reminder): Binding energy is the energy required or released to fuse individual protons and neutrons into the desired nuclide.

For nuclides on these drip lines, the binding energy of the nuclide and the binding energy of a nuclide with one extra proton or neutron are the same.

This means the energy required to remove the added proton or neutron is zero. If an extra proton or neutron was fired at the nuclide, it simply drips off the nucleus like a drop of water.