Radioactivity

Questão	Responda
Discover of Radioactivity	In 1896 French physicist, Henri Becquerel, discovered image of a key on a developed film. Remembering film had been in a drawer under a key, on top of that had there had been a packet of uranium salts. Which must have sent some form of radiation that passed through paper but not metal. young researcher Marie Curie asked to investigate found salts always gave out radiation, no matter what was done to them, used word radioactivity to describe properties of uranium. Discovered new radioactive elements polonium after native county Poland. Died from Leukemia from work after winning Nobel prizes
What stops radiation	Ernest Rutherford found: alpha radiation stopped by paper Beta radiation went through paper
Radioactive puzzle	Hard to figure out why some substances were radioactive, atoms with an unstable nucleus are radioactive. Can become stable by emitting alpha, beta or gamma radiation. Impossible to tell when unstable nucleus will decay (when it emits radiation). It's a random event that occurs with no influence
Origins of background radiation	Geiger counter clicks without near any radiation. Radiation from radioactive substances: In environment (in the air, ground, building materials) from space (cosmic rays) from devices like x-ray tubes Some from present radioactive substances like nuclear weapons testing or nuclear power stations. Mainly due to naturally occurring substances in the Earth. For instance radon gas, radioactive, and is a product of uranium decay in rocks in certain areas.
Discovery of nucleus	Ernest Rutherford discovered alpha and beta radiation consisted on different types of radiation. Realised alpha particles could be used to probe the atom. Asked two researchers Hans Geiger and Ernest Marsden to investigate. Used a thin metal foil to scatter a beam of alpha particles. Deduced nucleus at centre of atom positively charged
Discovery of nucleus experiment	-Apparatus was in a vacuum chamber in order to prevent air molecules absorbing the alpha particles -There was a fixed thin metal foil -Detector moved at different positions, at each point number of spots of light observed in a certain time counted. -Detector consisted of microscope focused on small glass plate, each time an alpha particle hit the plate spot of light was observed Measured number of alpha particles deflected per second through different angles, found: -Most of the alpha particles passed through metal foil -Number of alpha particles deflected decreased greater the angle of deflection -About 1 in 10000 alpha particles were deflected greater than 90 degrees
Results of discovery of nucleus experiment	-At centre of every atom positively charged as knew alpha particles alpha particles so would repel -Nucleus smaller than atom as most alpha particles passed straight through -Most of the mass in an atom is located in the nucleus From this able to deduce proportion of alpha particles that would be deflected at a given angle. Used theory to estimate diameter of the nucleus, found 100,000 times smaller than the atom
Acceptation of Rutherford's nuclear atom model	quickly accepted because: Agreed exactly with Geiger and Marsden experiments Explains radioactivity in terms of change of that happen to an unstable nucleus when it emits radiation predicted existence of the neutron, which was later discovered
No plum pudding model	Before 1914 scientists didn't know structure of an atom. Knew atoms contained electrons which were tiny negatively charged particles, didn't know how positive charge arranged in an atom. Different models one was plum pudding mode: -Positively charged matter in the atom evenly spread -Electrons buried inside
Ions	Atoms have the same number of protons and electrons so have no charge. However atom can become an ion if it loses or gains electrons so unequal number of protons to neutrons
Isotopes	These are atoms with the same number of proton so that the are of the same element but different number of neutrons. Number of protons and neutrons in an atom is its mass number
Alpha particle emissions	Alpha particles consists of two neutrons and protons. Relative mass of 4 and charge of 2+. Same as helium. When an unstable nucleus emits an alpha particles atomic number goes down by 2 and mass number by 4
Beta particles emissions	This is an electron created and emitted if an atom has too many neutrons compared to protons. Neutron in nucleus changes into beta particle which is immediately emitted at high speed and a proton Relative mass of beta particle basically 0 and relative charge is -1. When a unstable atom emits a beta particle mass number stays the same as neutron just changed into proton but atomic number increases by 1 because one more proton
gamma radiation emission	Gamma radiation emitted by some nuclei after beta and alpha particles have been emitted. Gamma radiation is uncharged and has no mass. So number of protons and neutrons in a nucleus is unchanged
Penetrating power of radiation	-Alpha particles can't penetrate paper and has about 5 cm range in air -Beta particles are stopped and absorbed by aluminum sheets about 5mm thick and have about 1 m range in air -Gamma radiation is stopped and absorbed by thick lead sheets several cm thick and concentrate more than 1 m thick and has unlimited range in air as the spread out in the air without being absorbed by get weaker as spread out
Absorption tests of radiation	We can use a Geiger counter but must take into account background radiation. So must: -Measure the count rate without radioactive source present, this is background count rate, due to background radiation -Then measure the count rate with the source in place subtracting background count rate giving count rate due to the source alone. -To test absorption of material, place material between tube and radioactive source, measure count rate, can add layers of material until count rate drops to zero -To test air range move tube away from source when zero then this is its range
nature of alpha, beta and gamma particles: Deflection by a magnetic field	Beta particles easily deflected like electrons so radiation consists of negatively charged particles as a beta particles is a fast moving electron. Alpha radiation in opposite direction of beta particles so is attracted to magnetic field. so alpha particles consist of positively charged particles more attractive than beta particles as have +2 charge and has much greater mass. Gamma radiation not deflected as electromagnetic radiation so uncharged.
Nature of alpha, beta and gamma radiation: Deflection by an electric field	Alpha and beta particles passing through an electric filed deflected in opposite directions. Alpha particles attracted towards negative plate as positively charged Beta particles attracted to positive plate as negatively charged Alpha particle deflected to a lesser extent than beta particles even though has +2 charge mass of alpha particle 8000 times that of a beta particle, so deflection of alpha particle is much less.
Nature of alpha, beta and gamma radiation: Radioactivity dangers	Radiation from radioactive substance can knock electrons out of atoms. Atoms are charged because they lose electrons, process known as ionisation. X-rays cause ionisation which in a living cell can damage or kill the cell. damage to genes in cell can be passed on if cell generates more cells so strict safety rules used. Alpha radiation is more dangerous in body than beta or gamma radiation as have greater ionising effect
Activity	Activity of a radioactive isotope is the number of atoms that decay per second. As nucleus of each unstable atom decays number of unstable atoms decrease. Therefore activity decreases. Geiger counter can be used to monitor activity of a radioactive sample. For this must measure count rate, which is number of counts per second
Half-Life	Half life of a radioactive isotope is the average time it takes for: number of nuclei of the isotope in a sample and hence mass of unstable atoms to halve and for the count rate of the isotope in a sample to fall to half its initial value
Random nature of radioactive decay	Radioactive decay is a random process, can't predict when an individual atom will suddenly decay. Can predict how many atoms will decay in a certain time because of the large number, so follow general trend less there are less will decay.
Automatic thickness monitoring	Used when making metal foil. Beta particles emitted as radioactive source through foil detector detects amount that gets through depending on thickness of foil. If thickness of foil increases too much, detector reading drops. The detector sends a signal to the rollers to increase the pressure on the metal sheet making foil thinner.
Radioactive tracers	used to trace flow of substance through a system. Doctors use radioactive iodine to identify if the kidney is blocked. Before test patient drinks water containing small amount of radioactive substance so detector reading goes up and down. if kidney blocked reading stays up as radioactive substance goes into kidney but doesn't flow out.
Why radioactive iodine used in medial processes	Has a half-life of 8 days so lasts long enough for test to be done but decays almost completely after a few weeks. As radioactive sources have 5 half-lives before radioactive emissions relatively unseen Emits gamma radiation so can be detected outside the body Decays into a stable product
Carbon dating	Used to find age of ancient wood and other organic material. Living wood contains a tiny proportion of radioactive carbon has a half life of 5600 years. When a tree dies no longer absorbs. So amount of radioactive carbon in it decreases. To find the age of a sample, need to measure the count rate from the wood compared with count rate of the same mass of a living wood.
Uranium dating	Used to find age of igneous rock. Rocks contain radioactive uranium, which has a half life of 4500 million years. Each uranium atom decays into an atom of lead. Can work out the age of a sample by measuring the number of atoms of uranium and lead. If sample contains 1 sample of uranium for lead sample must be 4500 million years old. As originally been 2 atoms of uranium for each of atom of uranium now present.

Próximo

Descrição

Resumo de Recurso

Semelhante

	Criado por Chima Power aproximadamente 10 anos atrás