Slide 1: - Nuclear model of atom electron proton neutron Slide 2: ELECTRON Slide 19 PLUM PUDDING MODEL OF ATOM: 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: -_ - Slide 5: ++ ++ ++ ++ GOLD LEAF ATOMS ALPHA PARTICLES - The Rutherford Scattering Experiment Slide 6: Differences between Thompson’s PLUM PUDDING model and NUCLEAR model of atom Plum pudding model Nuclear model Positively charged with electrons spread out inside Nucleus positively charged
Most mass inside nucleus
Mostly empty space
Electrons orbit around nucleus Slide 7: ELEMENT SYMBOLS An atom is represented by a symbol which will tell you:-
What element it belongs to.
Mass number (total number of protons + neutrons inside nucleus).
Atomic or Proton number (number of protons inside nucleus). Slide 8: 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. Slide 9: Mg 24 12 12 protons
12 neutrons Nucleus of Magnesium atom No of electrons = 12 Slide 10: Al 27 13 13 protons
14 neutrons Nucleus of Aluminium atom No of electrons = 13 Slide 11: 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!! Slide 12: Radioactive substances have atoms with unstable nuclei This means that there are an unequal number of protons and neutrons inside the nucleus Slide 13: 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 Slide 15: Radiation Symbol of alpha particle He or α 4 2 4 2 Slide 16: Radiation Symbol of beta particle e or β 0 -1 0 -1 Slide 17: Radiation Symbol of gamma ray γ Slide 18: NUCLEAR EQUATIONS Nuclear equations have to balance, just like chemical equations!!!!!!!!!!!!!! Slide 19: + 8 P 11 N 2p
9n Alpha Emission: nucleus emits 2 protons and 2 neutrons X X 19 8 15 6 4 2 Element X turns into element Y and emits an alpha particle Y He He Y + Slide 20: + 3 P 5 N 4p
4n Beta Emission: neutron turns into proton and electron. The electron is emitted from nucleus but the proton stays behind X X 8 3 8 4 0 -1 Y β β Y + 4N 1P 1e 1e Slide 21: + 11 P 13 N 12P
12N Gamma Emission: often occurs after alpha and beta emission. There is no change in mass or atomic number. Na Na 24 11 24 12 0 -1 Mg e e Mg + 12 N 1P 1e 1e + γ Example shows beta decay with gamma emission Slide 22: Penetrating Powers of Radiation Penetrating Powers of Radiation Slide 23: 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 Slide 24: HALF LIFE TIME TAKEN FOR ½ THE RADIOACTIVE ATOMS TO DISINTEGRATE
TIME IT TAKES FOR THE RADIATION TO FALL TO ½ ITS ORIGINAL LEVEL Slide 25: Number of popcorn remaining 16
0 0 10 20 30 40 50 Time (s) HALF LIFE OF POPCORN = 10s Example of half life using pan of popcorn ‘popping’ Slide 26: Question on half life of pop corn Number of popcorn remaining 32
0 0 20 40 60 80 100 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? 32 16 8 4 20s 20s 20s 4 4 ANSWER = 4 Slide 28: Number of nuclei remaining 480
0 0 433 433 433 433 433 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? 480 240 120 60 30 16 8 433 433 433 433 433 433 1. 60 nuclei 6 x 433 years
= 2598 years Question on half life Slide 29: USES OF RADIOACTIVITY Slide 30: Radioactive tracer in medicine to find brain tumours Slide 31: Abnormalities with organs e.g. lungs Slide 32: 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 Slide 33: STERILIZATION OF SURGICAL EQUIPMENT AND FRESH FOOD Slide 34: control Radiation 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 Slide 35: 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 Slide 36: CARBON DATING OF ONCE LIVING THINGS ETC. FOSSILS Slide 37: 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 Slide 38: EXAMPLES OF CARBON DATING TO FIND THE AGE OF :-
TURIN SHROUD Slide 39: 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 Slide 40: 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 Slide 41: Turin shroud Cotton plant Slide 42: 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 Slide 43: Finding the age of rocks Uranium Lead Approximately 4500 000 000 years Slide 44: Rock Uranium Lead Slide 45: 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. 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. Slide 46: 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 Slide 47: ATOM IONONIZATION ATOM WITH ELECTRONS DISPLACED Slide 49: Dangers of radioactivity – OUTSIDE BODY OUTSIDE the body and are more dangerous as they can penetrate the skin into your body to your organs. Radiation will ionise atoms in living cells – this can damage them and cause cancer or leukaemia. Gamma Gamma Beta Dangers of radioactivity (INSIDE BODY): 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 Slide 51: PROTECTION OF MEDICAL STAFF PROTECTIVE SUITS TONGS SCREEN/BARRIER ARMS LENGTH Slide 52: PROTECTION OF PATIENT SMALL DOSES FOCUS EXACTLY WHERE NEEDED PROTECTIVE BIB/GARMENT Slide 53: + + + + + + + + + - - - - - - - - - - - Deflection of radiation in an electric field β (-) γ α (+) α PARTICLES TAKE LONGER TO BE DEFLECTED BECAUSE THEY HAVE THE MOST MASS Slide 54: + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + α γ β Deflection of radiation in magnetic field Magnetic field is into page Slide 55: DISPOSAL OF WASTE IS EXPENSIVE BECAUSE OF:- CONTAINERS/BURYING UNDERGROUND LONG HALF LIFE KEEPING SITE SAFE FROM HUMANS & TERRORISTS Slide 56: Rocks Underground Cosmic Rays from stars Dumped
Nuclear Waste Radon Gas Causes of Background Radiation Hospitals/Factories