Nuclear physics studies the building blocks and interactions of atomic nuclei. The field is the basis for applications like nuclear power, nuclear bombs, nuclear medicine, and radiocarbon dating. Atoms consist of a nucleus containing protons and neutrons, surrounded by orbiting electrons. Radioactivity occurs when unstable atomic nuclei decay by emitting particles like alpha and beta particles or gamma rays. Nuclear fission and fusion can release energy as nuclei split or combine.

1. Nuclear Physics

4. All matter is made up of elements (e.g. carbon, hydrogen, etc.). The smallest part of an element is called an atom. Atom of different elements contain different numbers of protons. The mass of an atom is almost entirely due to the number of protons and neutrons.

5. X A Z Mass number Atomic number Element symbol = number of protons + number of neutrons = number of protons

6. A = number of protons + number of neutrons Z = number of protons A – Z = number of neutrons Number of neutrons = Mass Number – Atomic Number X A Z

7. Most of the isotopes which occur naturally are stable. A few naturally occurring isotopes and all of the man-made isotopes are unstable. Unstable isotopes can become stable by releasing different types of particles. This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides.

8. Radioactivity Radioactivity means that atoms decays. The reason for this decays is that they are instable. A atomic nucleus is instable when he is to heavy or when a balance is missing between the protons and the neutrons. Every atom which has got a higher number of nucleons (protons and neutrons togehter) than 210 is instable.

10. An alpha particle is identical to that of a helium nucleus. It contains two protons and two neutrons. Alpha Decay The center of the atom contains a tight ball of neutrons and protons, which is held together by the strong nuclear force, unless it is too large. Unstable nuclei may undergo alpha decay, in which they emit an energetic helium nucleus.

11. Alpha Decay unstable atom more stable atom alpha particle X A Z Y A - 4 Z - 2 + He 4 2

12. Alpha Decay Ra 226 88 Rn 222 86 He 4 2

13. Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton and an electron.

14. Beta Decay As a result of beta decay, the nucleus has one less neutron, but one extra proton. The atomic number, Z, increases by 1 and the mass number, A, stays the same.

15. Beta Decay Po 218 84  0 -1 At 218 85

16. Beta Decay X A Z Y A Z + 1 +  0 -1 Po 218 84 Rn 218 85 +  0 -1

17. Gamma Decay Gamma rays are not charged particles like  and  particles. Gamma rays are electromagnetic radiation with high frequency. When atoms decay by emitting  or  particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x 10 -12 J).

20. Gamma

22. Gamma-Ray Burst over 40 Seconds http://www.rssd.esa.int/Integral/integ_images.html

23. Nuclear Fission When atoms are bombarded with neutrons, their nuclei splits into 2 parts which are roughly equal in size. Nuclear fission in the process whereby a nucleus, with a high mass number, splits into 2 nuclei which have roughly equal smaller mass numbers. During nuclear fission, neutrons are released.

24. Nuclear Fission There are 2 types of fission that exist: 1. Spontaneous Fission 2. Induced Fission

25. Spontaneous Fission Some radioisotopes contain nuclei which are highly unstable and decay spontaneously by splitting into 2 smaller nuclei. Such spontaneous decays are accompanied by the release of neutrons.

26. Induced Fission Nuclear fission can be induced by bombarding atoms with neutrons. Induced fission decays are also accompanied by the release of neutrons. The nuclei of the atoms then split into 2 equal parts.

27. The Fission Process A neutron travels at high speed towards a uranium-235 nucleus. U 235 92 n 1 0

28. The Fission Process A neutron travels at high speed towards a uranium-235 nucleus. U 235 92 n 1 0

29. The Fission Process A neutron travels at high speed towards a uranium-235 nucleus. U 235 92 n 1 0

30. The neutron strikes the nucleus which then captures the neutron. The Fission Process U 235 92 n 1 0

31. The nucleus changes from being uranium-235 to uranium-236 as it has captured a neutron. The Fission Process U 236 92

32. The uranium-236 nucleus formed is very unstable. The Fission Process It transforms into an elongated shape for a short time.

33. The uranium-236 nucleus formed is very unstable. The Fission Process It transforms into an elongated shape for a short time.

34. The uranium-236 nucleus formed is very unstable. The Fission Process It transforms into an elongated shape for a short time.

35. It then splits into 2 fission fragments and releases neutrons. The Fission Process 141 56 Ba 92 36 Kr n 1 0 n 1 0 n 1 0

36. It then splits into 2 fission fragments and releases neutrons. The Fission Process 141 56 Ba 92 36 Kr n 1 0 n 1 0 n 1 0

37. It then splits into 2 fission fragments and releases neutrons. The Fission Process 141 56 Ba 92 36 Kr n 1 0 n 1 0 n 1 0

38. It then splits into 2 fission fragments and releases neutrons. The Fission Process 141 56 Ba 92 36 Kr n 1 0 n 1 0 n 1 0

39. Fission Process An induced nuclear fission event. A slow-moving neutron is absorbed by the nucleus of a uranium-235 atom, which in turn splits into fast-moving lighter elements (fission products) and free neutrons.

40. Nuclear Fission Examples U 235 92 + Ba 141 56 + n 1 0 3 n 1 0 + Kr 92 36 U 235 92 + Cs 138 55 + n 1 0 2 n 1 0 + Rb 96 37

41. Energy from Fission Both the fission fragments and neutrons travel at high speed. The kinetic energy of the products of fission are far greater than that of the bombarding neutron and target atom. E K before fission << E K after fission Energy is being released as a result of the fission reaction.

42. Energy from Fission mass difference, m = total mass before fission – total mass after fission This reduction in mass results in the release of energy. total mass before fission > total mass after fission

43. Energy Released The energy released can be calculated using the equation: E = mc 2 Where: E = energy released (J) m = mass difference (kg) c = speed of light in a vacuum (3 x 10 8 ms -1 ) E m c 2

44. Energy from Fission The energy released from this fission reaction does not seem a lot. This is because it is produced from the fission of a single nucleus. Large amounts of energy are released when a large number of nuclei undergo fission reactions.

45. Nuclear Fusion In nuclear fusion, two nuclei with low mass numbers combine to produce a single nucleus with a higher mass number. H 2 1 + He 4 2 + n 1 0 H 3 1 + Energy

46. The Fusion Process H 2 1 H 3 1

47. The Fusion Process H 2 1 H 3 1

48. The Fusion Process H 2 1 H 3 1

49. The Fusion Process H 2 1 H 3 1

50. The Fusion Process

51. The Fusion Process

52. The Fusion Process

53. The Fusion Process

54. The Fusion Process ENERGY He 4 2 n 1 0

55. The Fusion Process ENERGY He 4 2 n 1 0

56. The Fusion Process ENERGY He 4 2 n 1 0

57. The Fusion Process ENERGY He 4 2 n 1 0

58. Nuclear Fusion The electrostatic force caused by positively charged nuclei is very strong over long distances, but at short distances the nuclear force is stronger. As such, the main technical difficulty for fusion is getting the nuclei close enough to fuse. Distances not to scale.