*FACULTY: MEDICAL LABORATORY SCIENCES (MLS) * COURSE: physics for medical equipments and invistigations MLS- PHY-124 SEMESTER2 * BATCH :11 * U. Ali S.Ahmed * TEL.: 0969266035 Composition of Matter
All of matter is composed of at least three fundamental particles (approximations): Particle Fig. Sym Mass Charge Size Electron e- 9.11 x 10-31 kg -1.6 x 10-19 C ~ Proton p 1.673 x 10-27 kg +1.6 x 10-19 C 3 fm Neutron n 1.675 x 10-27 kg 0 3 fm
The mass of the proton and neutron are close, but they are about 1840 times the mass of an electron. The Atomic Nucleus Compacted nucleus: 4 protons 5 neutrons
Since atom is electri-cally neutral, there must be 4 electrons. 4 electrons Beryllium Atom Definitions A nucleon is a general term to denote a nuclear particle - that is, either a proton or a neutron. The atomic number Z of an element is equal to the number of protons in the nucleus of that element. The mass number A of an element is equal to the total number of nucleons (protons + neutrons). The mass number A of any element is equal to the sum of the atomic number Z and the number of neutronNs : A = N + Z Symbol Notation
A convenient way of describing an element is by giving its mass number and its atomic number, along with the chemical symbol for that element.
For example, consider beryllium (Be): Example 1: Describe the nucleus of a lithium atom which has a mass number of 7 and an atomic number of 3. A = 7; Z = 3; N = ? N = A – Z = 7 - 3 neutrons: N = 4 Protons: Z = 3 Electrons: Same as Z
Lithium Atom Nuclides Because of the existence of so many isotopes, the term element is sometimes confusing. The term nuclide is better. A nuclide is an atom that has a definite mass numberA andZ -number. A list of nuclides will include isotopes.
The following are best described as nuclides: Isotopes Isotopes are atoms that have the same number of protons (Z1= Z2), but a different number of neutrons (N). (A1 ≠ A2)
Helium - 3 Helium - 4 Isobars Isobars are atoms (nuclides are atoms (nuclides) differ in atomic number are atoms (nuclides) differ in atomic number (or number of protons Z1 ≠ Z2) but have the same mass number A1 = A2. An example of a series of isobars would be 40S, 40Cl, 40Ar, 40K, and 40Ca. The nuclei of these nuclides all contain 40 nucleons; however, they contain varying numbers of protons and neutrons Isotones Isotones Two nuclides are isotones if they have the very same neutron numberN , but different proton numbeZr . For example, boron-12 and carbon-13 nuclei both contain 7 neutrons, and so are isotones. Similarly, 36S, 37Cl, 38Ar, 39K, and 40Ca nuclei are all isotones of 20 because they all contain 20 neutrons For the following group of nuclei, Which are isotopes, isobars, isotones?
12 14 14 14 16 B5, C6, N7, O8, O8 14 16 Isotopes - O8, O8
14 14 14 Isobars - C6, N7, O8
12 14 Isotones - B5, N7 The Mass Defect The mass defect is the difference between the rest mass of a nucleus and the sum of the rest masses of its constituent nucleons. Mass Defect • Mass defect (M.D) is another way of saying nuclear B.E. It is simply the nuclear B.E. expressed not as MeV but in mass units (MeV/c2) The Binding Energy
The binding energy EB of a nucleus is the energy required to separate a nucleus into its constituent parts.
2 2 EB = mDc where c = 931.5 MeV/u
The binding energy for the carbon-12 example is:
EB = (0.098940 u)(931.5 MeV/u)
Binding EB for C-12: EB = 92.2 MeV Binding Energy per Nucleon
An important way of comparing the nuclei of atoms is finding their binding energy per nucleon:
Binding energy per nucleon
For our C-12 example A = 12 and: Binding Energy Vs. Mass Number Curve shows that 8 EB increases with nucleon
A and peaks at 6
A = 60. Heavier per
nuclei are less 4 stable. Energy
2 Green region is for most stable 5 100 1 2 250 Binding atoms. 0 Mass number5 0A 0 0 For heavier nuclei, energy is released when they break up (fission). For lighter nuclei, energy is released when they fuse together (fusion). Stability Curve
Nuclear particles are 14 held together by a 0 Stable
N 12 nuclear strong force. 0 10 nuclei 0 A stable nucleus 80 number remains forever, but as 60 the ratio of N/Z gets 40 Z = larger, the atoms decay. Neutron 20 N Elements with Z > 82 20 40 60 80 10 are all unstable. Atomic number Z0 Radioactivity
As the heavier atoms become α β more unstable, particles and − photons are emitted from the β + nucleus and it is said to be γ radioactive. All elements with A > 82 are radioactive.
Examples are: Alpha particles α β− particles (electrons) Gamma rays γ β+ particles (positrons)