The Atom Lab # 2

What’s Inside an Atom? An atom is made up of a team of three players: protons, neutrons, and electrons They each have a charge, mass, and a location Protons + Neutrons collectively called nucleons

What is the structure of an atom? Nucleus – center of the atom –Home of Protons and Neutrons –Proton Has a positive (+) charge Has a relative mass of 1 Determines the atomic number Found inside the nucleus

What is the structure of an atom? –Neutron Has no charge (0) Has a relative mass of 1 Found inside the nucleus

What is the structure of an atom? Electron –Has a negative (-) charge –Has a relative mass of 0 (zero) –Determines the ion –Found outside the nucleus

Electrons circle around the nucleus of an atom. Protons are a main part of the nucleus of an atom. Neutrons also hang out in the nucleus of an atom.

How are P, N, e - related? # protons = atomic number = Z # electrons = # protons in a neutral atom # protons + # neutrons = mass number = A –Ex: The atomic number of Hydrogen (H) is 1, so all hydrogen atoms have 1 proton. –Ex: All Oxygen atoms (O) have 8 protons, so the atomic number of Oxygen is 8. Remember all atoms are electrically neutral. Therefore; the number of Protons equal the number of Electrons. Meaning the number of negatively charged particles must equal the number of postively charged particles. –Ex: Helium (He) has 2 protons and 2 neutrons: its mass number is 4. –Ex: Carbon (C) has 6 protons and 6 neutrons: its mass number is12.

A X ZN # protons + # neutrons = mass number = A # protons = atomic number = Z # neutrons Structure of the Nucleus

A Al Structure of the Nucleus

Some 3000 nuclides have been discovered and most are unstable. Unstable nuclei decay by one of the following in order to achieve stability –spontaneous fission –α-particle –β-particle –σ-ray emission –Electron capture Decay of Radionuclides

The stability of a nuclide is governed by the structural arrangement and binding energy of the nucleons in the nucleus. The ratio of the number of neutrons to the number of protons N/Z is an approximate index of the stability of a nuclide. N/Z = 1 in the stable nuclei with low atomic no. Ex, C 6 12 Decay of Radionuclides

Radionuclides may decay by any one or a combination of six processes: –Spontaneous fission –α decay –β- decay –‏β+decay –Electron capture –Isomeric transition

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –Spontaneous fission Fission is a process in which a heavy nucleus breaks down into two fragments typically in the ratio of 60:40. This process is accompanied by the emission of Two or three neutrons with a mean energy of 1.5 MeV. A release of 200 MeV energy appears mostly as heat. Fission in heavy nuclei can occur spontaneously or by bombardment with energetic particles. Spontaneous fission is an alternative to a decay or g emission

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –α decay Usually heavy nuclei decay by α particle emission. The α particle is a helium ion containing two protons and two neutrons bound together in the nucleus. In α particle the atomic number of the parent nuclide is therefore reduced by 2 and the mass number by 4. An example of a decay is

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –β- decay When a nucleus is ‘‘neutron rich’’ it decays by β- particle emission along with an antineutrino. An antineutrino is an entity almost without mass and charge and is primarily needed to conserve energy in the decay. In β- decay, a neutron essentially decays into a proton (p) and a β- particle For example (i.e., has a higher N/Z ratio compared to the stable nucleus)

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –β- decay

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –Positron or β+decay Nuclei that are ‘‘neutron deficient’’ or ‘‘proton rich’’ can decay by β+ particle emission accompanied by the emission of a neutrino which is an opposite entity of the antineutrino. After β+ particle emission, the daughter nuclide has an atomic number that is 1 less than that of the parent. In β+ decay, a proton transforms into a neutron by emitting a β+ particle and a neutrino For example, (i.e., have an N/Z ratio less than that of the stable nuclei)

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –β+ decay

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –Electron capture Electron is captured from the extranuclear electron shells. Thus, transforming a proton into a neutron and emitting a neutrino.

Decay of Radionuclides Radionuclides may decay by any one or a combination of six processes: –Isomeric transition The decay of an upper excited state to a lower excited state A nucleus can remain in several excited energy states above the ground state. All these excited states are referred to as isomeric states and decay to the ground state

Nomenclature Isotopes: Nuclides of the same atomic number. O O O Isotones: Nuclides having the same number of neutrons but different atomic number Fe Co Cu Isobars: Nuclides with the same no. of nucleons that is the same mass no. but different no. of protons Cu Zn Isomers: Nuclides having the same number of protons and neutrons but differing in energy states and spins. 99Tc 99mTc

Units of Radioactivity 1 curie (Ci) = 3.7 X dps = 2.22 X dpm 1 millicurie (mCi) = 3.7 X 10 7 dps = 2.22 X 10 9 dpm 1 microcurie (µCi) = 3.7 X 10 4 dps = 2.22 X 10 6 dpm

1 Becquerel (Bq)= 1 dps = 2.7 X Curie 1 kilobecquerel (kBq)= 2.7 X Curie 1 Ci = 3.7 X Becquerel (Bq) Units of Radioactivity

Decay Equations -dN/dt=λN –λLambda= decay constant. –Defined as the probability of disintegration per unit time for the radioactive atom –-dN/dt = A =disintegration rate –N is the no. of radioactive atoms At = A o e- λt A=λN λ=0.693/t1/2 –t1/2 = the time required to reduce the initial activity of a radionuclide to one half

Problems 1.At 11:00 A.M., the 99mTc readioactivity was measured as 9 mCi on a certain day. What was the activity at 8:00 A.M. and 4:00 P.M. on the same day (t1/2 of 99mTc= 6hr)

Thank You “Instead of giving yourself reasons why you can’t, give yourself reasons why you can”