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7/30/2019 Radiation Powrpoint Sea and Charlay

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Nuclei which are less stable then othersmay decay into smaller more stable nuclei The faster the nuclei decay, the moreactive the sourceThe number of decays per second ismeasured in Becquerels (Bq)1 decay per second means 1 Bq


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Radioactive particles are emitted fromunstable nuclei in a random process

Atoms which do this are radioactiveThere are three particles which nuclei mayemit when decaying; Alpha ( ), Beta ( )and Gamma ( )


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Alpha radiation is a release of an alpha particle during nuclear

decayThe alpha particle is a heliumnucleus ( 2 neutrons and 2protons


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Beta radiation involves theemission of high-energy

electrons from thenucleus.It happens when a neutronin the nucleus turns into a

proton, and electron, and aparticle called an anti-neutrino


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Gamma radiation is emittedwhen a nucleus loses

energy.Gamma radiation takes theform of photons (which haveno rest mass, and no

charge).


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You can write down nuclear changes as nuclear equations:The numbers in the top row must be balanced oneach side of equation, because the number of nucleons will not change. (For example, you couldget 231 on the left and 227 + 4 for an alphaemission, and 231 on the left and 231 + 0 on theright for beta emission.)The numbers on the lower row must be balancedon each side of the equation, because the totalelectrical charge will stay unchanged.


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Nucleus loses 2 protons and 2 neutrons.Nucleon number goes down by four.Eg. 238 92 U -> 234 90 Ra + 4

2He


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Neutron goes to a proton.Eg.

23892

U -> 238 93 Np +0

-1 e


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Nucleus doesnt change. The * symbolisesenergy. 238

92 U* -> 238 92 U +Gamma


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Ionising radiation is invisible to the naked eye,but it affects photographic platesThey can also be detected using a Geiger

Muller tubeThe ionizing radiation creates ions andelectrons within the tube

A voltage between the electrodes means a

current can flowThe pulse of current is used to produce aclick noise and add to the total count


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There is always ionising radiation present called background radiationIt is caused by soil, rocks and materialslike concrete, radioactive gases andcosmic rays.


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The activity of a radioactive source is thenumber of ionising particles it emits eachsecondThe activity decreases over time, as thereare fewer nuclei decaying


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A radioactive element is detected by a Geiger Muller tube and counter as having an activity of 400 countsper minuteThree hours later the count is 50 counts per minute.What is the half life of the radioactive element?Write down the activity and progressively halve it:0 400 counts1 half life 200 counts2 half lives 100 counts3 half lives 50 counts3 hours corresponds to three half lives, and 1 hour therefore corresponds to 1 half life


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Gamma rays: can kill bacteria, and is used insterilization of medical equipment, andpreserving food. It can also be used on aweld, with a photographic plate backing it you can see any weaknesses.

Alpha rays: used in smoke alarms.Beta particles: monitor the thickness of paper or metal

Radiotherapy uses high doses of radiation tofry cancer cells. Radiation is also used in X-rays.


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The alpha, beta and gamma rays can alldamage living cellsAlpha rays can damage human tissue,

due to ionisationGamma is dangerous due to its highpenetration power, but can repair cellswhen at ordinary radiation levelsThey can mutate cells, cause damage in

cells and tissues, and also cause issueswith its disposal.


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use forceps to hold radioactive sourcesdo not point it near living tissuestore radioactive materials in lead-linedcontainers and lock them awayCheck the surrounding area for aboveaverage background radiation


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Alpha () Beta () Gamma ()

Description A positively charged particle,identical to a helium nucleus (2protons, 2 neutrons)

A negatively charged particle,identical to an electron

Electromagnetic radiation.Uncharged

Penetration 4 10 cm of air. Stopped by asheet of paper

About 1m of air. Stopped by afew mm of aluminium

Almost no limit in air. Stoppedby several cm of lead orseveral m of concrete.

Effect of electric and magneticfields

Deflected Deflected Unaffected not deflected


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J.J Thomson came up with his plum pudding atomic theory after conducting experiments in 1897. He used a cathode ray tube toidentify smaller than atomic size particles that were negativelycharged. From this, he figured out that atoms were made up of bothpositive and negatively charged particles.


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Click on the picture
https://www.youtube.com/watch?v=VJfIbBDR3e8


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Rutherford designed an experiment to test the plum puddingmodel. It was carried out by his assistants Geiger andMarsden. A beam of alpha particles was aimed at very thingold foil and their passage through the foil detected. Thescientists expected the alpha particles to pass straight through

the foil but something else also happened.Some of the alpha particles emerged from the foil at differentangles and some even came straight back. The scientistsrealised that the positively charged alpha particles were beingrepelled and deflected by a tiny concentration of positivecharge in the atom. As a result of this experiment, the plum

pudding model was replaced by the nuclear model of theatom.


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Ernest Rutherford hypothesised that atomsare mostly empty space but have a densecentral nucleus. He used a gold foilscattering experiment to prove it.


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Possibly the most important use for radioactiveelements is in harnessing the energy their reactions give out to generate electricity. At themoment we do this using nuclear fission of Uranium. We can split up a big (unstable) nucleusby bombarding it with small particles (likeelectrons). In this case of uranium we canbombard it with a neutron which makes it evenmore unstable and eventually there will be fissionwhich creates energy.Fission of U-235 produces two daughter nuclei anda small number of neutrons


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When a uranium-235 or plutonium-239 nucleus is hit by aneutron, the following happens:

the nucleus splits into two smaller nuclei, which areradioactive

two or three more neutrons are releasedsome energy is released

The additional neutrons released may also hit other uranium or plutonium nuclei and cause them to split.Even more neutrons are then released, which in turn cansplit more nuclei. This is called a chain reaction. Thechain reaction in nuclear reactors is controlled to stop itgoing too fast.


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Click the picture
http://www.youtube.com/watch?annotation_id=annotation_696116&feature=iv&src_vid=kHXMiYsFSrU&v=Ezbyg2iNdQs


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The nuclear fuel, usually uranium oxide, isheld in metal containers called fuel rods.These are lowered into the reactor core. A

coolant, usually water or carbon dioxide, iscirculated through the reactor core to removethe heat. Control rods are also lowered intothe core. These absorb neutrons and control

the rate of the chain reaction. They are raisedto speed it up, or lowered to slow it down.


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