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,

The AtomLab # 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.

AXZ N

• # protons + # neutrons = mass number = A

• # protons = atomic number = Z

• # neutrons

Structure of the Nucleus

AAl

13 14

27

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, C6

12

Decay of Radionuclides

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

815

816

817

2659 60 62

27 29

67673029

Units of Radioactivity

• 1 curie (Ci) = 3.7 X 10 10 dps • = 2.22 X 10 12 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 10 -11 Curie• 1 kilobecquerel (kBq)= 2.7 X 10 -8 Curie

• 1 Ci = 3.7 X 10 10 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 = Aoe- 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”