What are chemical and nuclear reactions?
Now we examine in some detail the physics involved in nuclear weapons. First we take a look at the structure of an atom. All matter is made up of atoms. Atoms consist of a small dense positively charged core called the nucleus which is surrounded by a cloud of negatively charged electrons. The nucleus is made up of electrically neutral particles called neutrons and positively charged particles called protons (see Figure 1). The number of protons in the nucleus is equal to the number of electrons, making the atom electrically neutral. For example, the nucleus of a hydrogen atom is made up of a single proton and has no neutrons. The oxygen nucleus (O-16) consists of eight protons and eight neutrons. The uranium nucleus (U-235) has 92 protons and 143 neutrons. Heavier atoms have a larger excess of neutrons over protons than lighter ones. The protons and neutrons in nuclei are held together by strong nuclear forces which are stronger than any other force that acts between them, such as gra
