Visualisation of a silicon nucleus. This image represents the nucleus of a silicon atom. The nucleus is made of 28 particles, called nucleons (14 protons and 14 neutrons). Each nucleon is composed of three quarks surrounded by a quantum cloud of virtual particles. Protons have two 'up' quarks and one 'down' quark, neutrons have two 'down' and one 'up'. The nucleons are bound together by the strong nuclear force, the same force which binds the quarks together within each nucleon. The colours in the image reflect the three charges of the strong force; known as red, green and blue. Each nucleon has one quark of each colour" (charge)."