Prof.Dr.Tarek Elnimr

L 1Presented to the

Biology Departments in Faculty of

Scienceson February 15 ,

2009

THE ATOMThe nucleus structure

protons and neutrons = nucleons Z protons with a positive electric charge

(1.6 10-19 C) neutrons with no charge (neutral) number of nucleons = mass number A

The extranucleus structure Z electrons (light particles with electric

charge) equal to proton charge but negative

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Particle Symbol Mass Energy Charge (kg) (MeV)----------------------------------------------------------Proton p 1.672*10-27 938.2 +Neutron n 1.675*10 -27 939.2 0Electron e 0.911*10 -30 0.511 -

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AXNZ

SYMBOL OF ELEMENT

MASS NUMBER (the number of protons and neutrons)

ATOMIC NUMBER (the number of protons)

53I78

131Example:

131I or I-131

The number of neutrons

Definitions

04/12/23 VII.5

Isotope: Nuclides of same atomic number Z but different N (and A) same element

Nuclide: Species of atom characterized by the constitution of its nucleus (in particular N, Z)

Radionuclide: Nuclide of measurable half time

Radioactive decay : the process by which an unstable nucleus is transformed into a more stable daughter nucleus by emitting nuclear particles.

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Isotopes I Atoms having the same atomic number are called isotopes

A=131 A= 127 Z= 53 Same Z= 53N= 78 N= 74

Examples:i. lH11H21H3Hydrogen(Protium) Deuterium

Tritium(p= 1, e = 1, n = 0) (p=1, e = 1, n =

1) (p =l, e= l, n=2)

ii. 6C12, 6C13 and 6C14

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Isotones Atoms having the same number of neutrons are called isotones

X YA=131 A= 127 N= 53 Same N= 53Z= 78 Z= 74

Examples : i4Si30,15P31 and i6Si32; 19K39 and 2oCa40 ; 1H3 and

2He4; and 6C13 and 7N14

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Isobars Atoms having the same mass number are called isobars

I XeA=131 A= 131 Z= 53 Same Z= 54N= 78 N= 77

Examples:i. 18Ar40,19K40 and 20Ca40;ii. 52Te130,54Xe130and 56Ba130.

Since isobars are the atoms of different elements, they will have

different physical and chemical properties

Nuclear Isomers

Nuclear isomers (isomeric nuclei) are the atoms with the same

atomic number and same mass number but with different

radioactive properties. They have same number of electrons protons and neutrons.

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IsomersSimilar atoms having different internal energy are called isomers

Tc TcA=99m A= 99 Z= 43 Same Z= 43N= 56 N= 56

i

RADIOACTIVE OR METASTABLE

STABLE

Examples,i. 92U235 and 9oTh231ii. 19K39 and 9F19iii. 29CU65 and 24Cr55

Examples

i. N3-, O2-, F-, Ne, Na+, Mg2+, Al3+, CH4, NH3, H2O and HF have 10 electrons each.

ii. P3-, S2- , Cl , Ar, K+ and Ca2+ have 18 electrons each.

Example Naturally occurring boron consists of two isotopes whose atomic weights are 10-01 and 11-01. The atomic weight of natural boron is 10-81. Calculate the percentage of each isotope in natural boron.

Solution. Let the % of isotope with at. wt. 10-01 =x

.-. % of isotope with at. wt. 11.01 = (100 - x)Now since, At. wt. = 100x ´10.01+ (100 - x) ´11.0110.81 = 100x ´10.01+ (100 - x) ´11.01x = 20Hence % of isotope with at. wt. 10.01 = 20% of isotope with at. wt. 11.01 = 100 -20 = 80

Part 2: Radiation Physics 26

Ques-tions?