Nuclear physics iGCSE???? – Flashcards
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basic structure of an atom?
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neutron proton electron
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isotope?
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atoms with the same number of protons but different number of neutrons
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most isotopes are:
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unstable
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mass number?
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no of protons and neutrons
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atomic number?
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no of protons
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unstable isotopes cause?
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radioactivity
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what is 'radioactive'?
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radioactive isotopes decay into other elements, giving out radiation
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what are radioactive isotopes?
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unstable radioactive isotopes undergoing radioactive decay and spitting out high energy particles
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alpha particles are blocked by?
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paper skin
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beta particles are blocked by?
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thin sheet of any metal thin aluminium
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gamma rays are blocked by?
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thick lead very thick concrete
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radioactivity is a _____ _____ process?
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totally random
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natural radioactive decay?
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when a nucleus decays and it spits out 1 or more of the 3 types of radiation in the process the nucleus will often change into a new element
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how can stable nuclei be made unstable?
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by firing neutrons at them when stray neutrons hit a stable nucleus the will usually be absorbed - this generally turns it into an unstable isotope of the same element
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nuclear radiation is?
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dangerous
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alpha particle:
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helium nuclei big, heavy, slow moving dont penetrate into materials stopped quickly strongly ionising (bash into a lot of atoms + knock electrons off them before they slow down, creating a lot of ions)
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beta particle:
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an electron inbetween alpha and gamma in terms of properties quite fast, quite small penetrate moderately moderately ionising for every beta particle emitted, a neutron tunes to a proton in the nucleus
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gamma particle:
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EM wave penetrate a long way into materials cannot be stopped (v hard) weakly ionising (they pass through, rather than colliding with atoms - eventually they do hit something an do damage)
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half life:
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time taken for half the radioactive atoms now present to decay time taken for the activity/count rate to fall by half
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each time a decay happens:
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it means more reactive nucleus has disappeared, and an alpha, beta or gamma particle is given out
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the older a sample becomes:
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the less radiation it will emit
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why do we use half life?
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because radioactive decay activity never reaches zero
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short half life:
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activity falls quickly because lots of nuclei decay quickly
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long half life:
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activity falls more slowly because most of the nuclei dont decay for a long time
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uses of radioactive materials?
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1-tracers in medicine 2-tracers in industry 3-radiotherapy 4-sterilisation of food + surgical equipment 5-thickness control in industry + manufacturing 6-radioactive dating of rocks + archaeological specimens 7-generating power from nuclear fuel
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tracers in medicine?
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certain radioactive isotopes can be injected or swallowed into the body, and their progress around the body can be followed using a detectors, with a computer to convert the reading to a TV display showing where the strongest reading is coming from
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tracers in medicine: half life? radiation?
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always short half life gamma emitters
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tracers in medicine: example
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iodine 131 absorbed by thyroid gland gives out radiation which can be detected to indicate whether or not the thyroid gland is taking in the iodine as it should
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isotopes in the body: which radiation source, why?
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gamma so radiation passes out of the body to be detected
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isotopes in the body: half life, why?
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short half life (few hours) so radioactivity inside patient quickly disappears
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tracers in industry?
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used to find leaks
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tracers in industry: half life? radiation? why?
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short half life -so as not to cause a hazard if it collects somewhere gamma emitter -so that the radiation can be detected even through metal or earth
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tracers in industry: method?
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squirt isotope in go along outside of pipe with detector find areas of extra high radioactivity this will indicated where it's leaking out
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radiotherapy?
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treatment of cancer
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radiotherapy: radiation? why?
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gamma rays -high doses of gamma rays will kill all living cells ->so are easily used to treat cancers
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radiotherapy: method
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gamma rays directed carefully correct dosage to kill cancer cells but not too many normal cells
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radiotherapy: 'however'
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fair bit of damage is done to normal cells makes patient feel ill
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sterilisation of food + surgical equipment: radiation? strength?
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gamma rays v strong
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sterilisation of food + surgical equipment: how used in food industry?
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food is exposed to high dose of gamma rays kills all microbes so keeping food fresh for longer
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sterilisation of food + surgical equipment: how used in medical industry?
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medical instruments exposed to high dose of gamma rays kills all microbes (sterilised)
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irradiation?
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use of radiation to kill microbes/ sterilise
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irradiation advantages over boiling:
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doesnt involve high temps (so) fresh food + plastic instruments can be totally sterilised without being damaged
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radiation and food?
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food is safe to eat. food is not radioactive
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sterilisation of food + surgical equipment: half life? why?
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reasonably long - months doesnt need replacing often
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thickness control in industry + manufacturing
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radiation directed through product being made (usually continuous sheet of paper, cardboard, metal) detector is on other side connected to control unit when amount of radiation detected goes down means product is coming out too thick so controller unit pinches rollers up a bit - making it thinner same applies if the reading goes up - too thin
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thickness control in industry + manufacturing: radiation? why?
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beta -> cardboard, paper gamma -> metal product being made must partially block the radiation
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thickness control in industry + manufacturing: half life? why?
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long half life (years) otherwise strength would gradually decline
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radioactive dating of rocks + archaeological specimens
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accurately work out the age of rocks, fossils etc
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radioactive dating of rocks + archaeological specimens: method
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by measuring the amount of radioactive isotope left in a sample and knowing its half life - you can work out how long its been around for
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generating power from nuclear fuel:
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uranium
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generating power from nuclear fuel: method of producing electricity
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purify uranium ^sets up a chain reaction where each decay causes another one this increases rate of reaction so generates lots of heat use that to produce electricity (heat water -> steam -> turns turbine -> turns generator -> generator produces electricity)
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radioactive decay always gives out energy in the form of?
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heat
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radioactive decay inside the earth is responsible for much of the....?
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heat down there - centre of the earth
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radioactivity of naturally occurring unstable isotopes which are all around us:
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air food building materials rocks beneath our feet
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radiation from space, known as? comes from>
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cosmic rays mostly from the sun
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radiation due to human activity? how much?
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fallout from nuclear explosions dumped nuclear waste represents tiny proportion of total background radiation
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when in high altitudes - radiation levels?
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increase more exposure to cosmic rays
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when underground in mines - radiation levels?
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increases rocks around
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Alpha decay
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Two protons and two neutrons are lost from a nucleus when it emits an alpha particle. This means that: The atomic mass number decreases by 4 The atomic number decreases by 2
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Beta decay
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In beta decay, a neutron changes into a proton plus an electron. The proton stays in the nucleus. The electron leaves the atom with high energy as a beta particle. The nucleus has one more proton and one less neutron when it emits a beta particle. This means that: The atomic mass number stays the same The atomic number increases by 1
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Alpha decay example:
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219 215 4 Rn --> Po + a 86 84 2 radon decays into polonium when it emits an alpha particle
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Beta decay example:
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14 14 0 C --> N + e 6 7 -1 beta decay of carbon-14 into nitrogen:
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Nuclear fusion:
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the joining of 2 smaller nuclei to form 1 bigger nuclei - releasing a lot of *energy*
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nuclear fission:
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the splitting up of an atomic nucleus
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how is energy released in stars?
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by nuclear fusion
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how do stars form?
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when enough dust and gas from space is pulled together by gravitational attraction
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how may planets be formed?
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when smaller masses may also form and be attracted by a larger mass to become a planet
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when is a star stable and why?
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during the main sequence of its life cycle because the forces within it are balanced
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the stars life cycle is determined by?
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the size of the star
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2 commonly used fissionable substances?
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uranium 235 plutonium 239
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for fission to occur?
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the uranium 235/plutonium 239 must fist absorb a neutron
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how does fission occur?
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the uranium 235/plutonium 239 must fist absorb a neutron the nucleus undergoing fission splits into 2 smaller nuclei releases 2/3 neutrons + energy starts chain reaction
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when an atom splits in two?
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it will form 2 lighter new elements these new nuclei are usually radioactive - because they are isotopes
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whats a problem with fission?
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the new nuclei formed are usually radioactive, which is a big problem with nuclear power, as it produces huge amounts of radioactive material - which is difficult and expensive to get rid of safely
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fission gives out?
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a lot of energy ( a lot more energy than you get with a chemical bond)
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nuclear processes energy vs chemical processes?
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nuclear processes release much more energy than chemical processes this is why nuclear bombs are so much more powerful than ordinary bombs - which rely on chemical reactions
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star cycle: stars smaller than the sun
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protostar main sequence star red giant white dwarf black dwarf
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star cycle: stars bigger than the sun
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protostar red super giant supernova neutron star / black hole
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expanded life cycle of a small star:
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1- stars form, dust + gas 2- gravity brings dust together. gravitational energy converts to heat energy (temp rise) 3- when temp high enough, hydrogen nuclei undergo fusion -> forms helium nuclei - produces heat + light *STAR IS BORN* enters stable period main sequence star = 10 billion years 4- eventually hydrogen begins to run out. swells into -> *Red giant* (red as surface cools) 5- cools and contracts -> *White dwarf* 6- finally light fades completely -> *Black dwarf*
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expanded life cycle of a big star:
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1- stars form, dust + gas 2- gravity brings dust together. gravitational energy converts to heat energy (temp rise) 3- when temp high enough, hydrogen nuclei undergo fusion -> forms helium nuclei - produces heat + light *STAR IS BORN* enters stable period main sequence star = 10 billion years 4- eventually hydrogen begins to run out. swells into -> *Red super giant* (red as surface cools) 5-glow bright, more fusion, expand and contract -> EXPLODE *Supernova* 6- exploding supernova throws layers of dust + gas into space leaving very dense core -> *neutron star* 6- if this star is big enough, it will become -> *Black hole* 7- dust and gas thrown off forms into second generation stars - like our sun
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safety precautions in schools:
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never allow skin contact -use tongs keep source at arms length -far away from body as poss keep source pointing away from body -avoid looking directly at it always keep source in lead box -put back asap
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extra safety precautions for industry:
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wearing of full protective suits -to prevent tiny radioactive particles lodging on the skin/fingernails/being inhaled use of lead lined suits + lead/concrete barriers, thick lead windows -prevent gamma escape use of remotely controlled robot arms -in highly radioactive areas
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alpha, beta + gamma will? (damage)
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enter living cells collide with molecules causing ionisation
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what does ionisation do?
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damage/destroy molecules
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lower dosages?
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minor damage without killing cell - leads to mutant cells -cancer
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higher dosage?
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kills cells completely causes radiation sickness
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which radiation are most dangerous outside the body? whY?
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beta and gamma they can get into delicate organs whereas alpha cannot penetrate skin
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which radiation is most dangerous inside the body? why?
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alpha does a lot of damage in a very localised area (small area) whereas gamma and beta pass straight out the body without doing much damage
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which radiation is deflected by electric and magnetic fields?
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alpha (deflected less than beta and in an opposite direction) beta
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how are stars able to maintain their energy output for millions of years?
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forces withing star are balanced and have vast amounts of hydrogen
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why did the early universe contain only hydrogen but now contains a large variety of different Elements?
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fusion in stars formed elements up to iron from original hydrogen
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what elements are made in a supernova and how?
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elements heavier than iron made in a supernova due to very high amounts of heat and energy
