- Nuclear model of atom electron proton neutron

PARTICLECHARGE RELATIVE MASS -1 (NEGATIVE ) 1/2000 TH (NEGLIGIBLE) PROTON+1 (POSITIVE) 1 UNIT NEUTRON NO CHARGE 1 UNIT ELECTRON Slide 19

PLUM PUDDING MODEL OF ATOM A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it… I did an experiment that proved this idea was wrong. I called it the “Rutherford Alpha particle scattering experiment” Ernest Rutherford, British scientist: -_-_ -

++ GOLD LEAF ATOMS ALPHA PARTICLES - The Rutherford Scattering Experiment

Differences between Thompson’s PLUM PUDDING model and NUCLEAR model of atom Plum pudding modelNuclear model Positively charged with electrons spread out inside Nucleus positively charged Most mass inside nucleus Mostly empty space Electrons orbit around nucleus

ELEMENT SYMBOLS An atom is represented by a symbol which will tell you:- 1.What element it belongs to. 2.Mass number (total number of protons + neutrons inside nucleus). 3.Atomic or Proton number (number of protons inside nucleus).

Li 7 (Mass number) 3 (Atomic or Proton Number) 3 protons 4 neutrons Nucleus of Lithium atom Since all the atoms are neutral:- number of electrons orbiting around the nucleus = the number of protons inside nucleus so the number of electrons in this atom is 3.

Mg protons 12 neutrons Nucleus of Magnesium atom N o of electrons = 12

Al protons 14 neutrons Nucleus of Aluminium atom N o of electrons = 13

There are 3 types of radiation α (alpha particle) Helium nuclei 2 protons and 2 neutrons β (beta particle) fast moving electron γ (gamma rays) electro magnetic waves All 3 types come from the nucleus of the atom!!

Radioactive substances have atoms with unstable nuclei This means that there are an unequal number of protons and neutrons inside the nucleus

NUCLEUS OF UNSTABLE ATOM α β γ 2 PROTONS 2 NEUTRONS FAST MOVING ELECTRON ELECTRO MAGNETIC WAVES Radiation is emitted when an unstable nucleus breaks down or disintegrates

Type of radiation Relative Mass Relative charge Alpha particle 4+2 Beta particle 1/2000 th Gamma rays no massno charge

Radiation Symbol of alpha particle He or α

Radiation Symbol of beta particle e or β 0 0

Radiation Symbol of gamma ray γ

NUCLEAR EQUATIONS Nuclear equations have to balance, just like chemical equations!!!!!!!!!!!!!!

+ 8 P 11 N 2p 2n 6p 9n Alpha Emission: nucleus emits 2 protons and 2 neutrons X X Element X turns into element Y and emits an alpha particle YHe Y +

+ 3 P 5 N4p 4n Beta Emission: neutron turns into proton and electron. The electron is emitted from nucleus but the proton stays behind X X Y β β Y + 4N 1P1e

+ 11 P 13 N12P 12N Gamma Emission: often occurs after alpha and beta emission. There is no change in mass or atomic number. Na Mg e e + 12 N 1P1e + γ Example shows beta decay with gamma emission

Penetrating Powers of Radiation    Sheet of paper Few mm of aluminium Few cm of lead  particles cannot pass through paper  particles cannot pass through aluminium  particles cannot pass through lead

HALF LIFE TIME TAKEN FOR ½ THE RADIOACTIVE ATOMS TO DISINTEGRATE OR TIME IT TAKES FOR THE RADIATION TO FALL TO ½ ITS ORIGINAL LEVEL

Number of popcorn remaining Time (s) HALF LIFE OF POPCORN = 10s Example of half life using pan of popcorn ‘popping’

Question on half life of pop corn Number of popcorn remaining Time (s) HALF LIFE OF POPCORN = 20s The half life of popcorn is 20s. A sample contains 32 popcorn at the start. How many will be remaining after 60s? s 20s 20s 4 4 ANSWER = 4

Number of nuclei remaining Time (years) The half life of Americium is 433 years. A sample contains 480 nuclei. 1. How many will be remaining after approximately 1300 years? 2. How long will it take to become harmless? nuclei 2.6 x 433 years = 2598 years Question on half life

Radioactive tracer in medicine to find brain tumours

Abnormalities with organs e.g. lungs

BREAK IN PIPE UNDERGROUND γ SOURCE USED AS RADIATION WILL NOT BE ABSORBED BY EARTH Industrial Radioactive tracer: finding break in underground pipe RADIATION/FAULT IN PIPE DETECTED

STERILIZATION OF SURGICAL EQUIPMENT AND FRESH FOOD

controlRadiation detector Radiation source β Rollers to control thickness of paper CONTROL THICKNESS OF PAPER ( β SOURCE) 200 COUNTS/SECOND CORRECT THICKNESS PAPER TO THICK PAPER TOO THICK 150 COUNTS/SECOND PAPER TO THIN 250 COUNTS/SECOND

control Radiation detector Radiation source γ Rollers to control thickness of paper CONTROL THICKNESS OF ALUMINIUM/STEEL ( γ SOURCE) 200 COUNTS/SECOND CORRECT THICKNESS PAPER TO THICK TOO THICK 150 COUNTS/SECOND TO THIN 250 COUNTS/SECOND

CARBON DATING OF ONCE LIVING THINGS ETC. FOSSILS

ALIVE – RADIATION LEVEL CONSTANT DEAD – ORGANISM STOPS TAKING IN CARBON 14 AND RADIATION LEVEL BEGINS TO FALL RADIATION LEVEL AGE OF DEAD ORGANISM HALF LIFE CURVE FOR CARBON 14

EXAMPLES OF CARBON DATING TO FIND THE AGE OF :- ROMAN SHIP TURIN SHROUD

BUILT 180 A.D. Take piece of wood from local tree Find radiation level of sample wood taken from ship Find radiation level from wood from local tree

RADIATION LEVEL TIME (YEARS) HALF LIFE GRAPH FOR CARBON 14 (finding age of ship) RADIATION LEVEL OF WOOD FROM TREE RADIATION LEVEL FROM WOOD FROM BOAT AGE OF BOAT 1824 YEARS OLD

Turin shroud Cotton plant

RADIATION LEVEL TIME (YEARS) HALF LIFE GRAPH FOR CARBON 14 (finding age of Turin Shroud) RADIATION LEVEL OF COTTON PLANT RADIATION LEVEL FROM CLOTH OF TURIN SHROUD AGE OF SHROUD 1400 YEARS OLD

Finding the age of rocks UraniumLead Approximately years

Rock Uranium Lead

Question: Uranium decays into lead. The half life of uranium is approximately 4,500,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample. 8 8 Answer: The sample was originally completely uranium… …of the sample was uranium Now only 4/8 of the uranium remains – the other 4/8 is lead Now only 2/8 of uranium remains – the other 6/8 is lead Now only 1/8 of uranium remains – the other 7/8 is lead So it must have taken 3 half lives for the sample to decay until only 1/8 remained (which means that there is 7 times as much lead). Each half life is 4,500,000,000 years so the sample is 13,500,000,000 years old. 1 half life later…

Ionisation Powers of Radiation Prolonged exposure to ionising radiation is dangerous to humans. Ionisation is the ability of radiation to remove electrons from atoms which will then change their structure

ATOM IONONIZATION ATOM WITH ELECTRONS DISPLACED

Type of Radiation Ionizing power Alpha particleHigh Beta particleLow Gamma raysExtremely low

Dangers of radioactivity – OUTSIDE BODY OUTSIDE the body  and  are more dangerous as they can penetrate the skin into your body to your organs. Alpha Radiation will ionise atoms in living cells – this can damage them and cause cancer or leukaemia. Gamma Beta

Dangers of radioactivity (INSIDE BODY) INSIDE the body an  radiation is the most dangerous because it has not enough energy to pass out of the body and has the greatest ionization power to damage cells. β and γ are less dangerous because they have enough energy to pass out of the body Gamma Beta Alpha Dangers of radioactivity – INSIDE BODY

PROTECTION OF MEDICAL STAFF PROTECTIVE SUITSTONGS SCREEN/BARRIERARMS LENGTH

PROTECTION OF PATIENT SMALL DOSES FOCUS EXACTLY WHERE NEEDED PROTECTIVE BIB/GARMENT

Deflection of radiation in an electric field β (-) γ α (+) α PARTICLES TAKE LONGER TO BE DEFLECTED BECAUSE THEY HAVE THE MOST MASS

α γ β Deflection of radiation in magnetic field Magnetic field is into page

DISPOSAL OF WASTE IS EXPENSIVE BECAUSE OF:- CONTAINERS/BURYING UNDERGROUND LONG HALF LIFE KEEPING SITE SAFE FROM HUMANS & TERRORISTS

Rocks Underground Cosmic Rays from stars Dumped Nuclear Waste Radon Gas Causes of Background Radiation Hospitals/Factories