Cosmic Radiation Beechen Cliff Physics

Cosmic Radiation

Beechen Cliff Physics

http://www.hisparc.nl/en/

Cosmic radiation: introductionThe year is 1900 and so far scientists know:

There is high energy radiation coming from radioactive sourcesThis radiation passes through thin gold leaf foil, or thin metal or several cm of leadThey don’t currently know how harmful it can beOne cm of lead approximately halves the intensity of gamma radiationBut there was more that still couldn’t be explained


Cosmic radiation: spontaneous discharge

After 1900 it was noticed that a charged electroscope discharged itself spontaneouslyTo check as to why this happened electroscopes were made more and more isolated from electric fields and the surrounding airThe only thing left that could be causing the discharge was ionisingradiation


Cosmic radiation: spontaneous dischargeThe ionising radiation creates positive and negative charge carriers inside the electroscope which travel towards their opposite chargeThis reduces the charge on the electroscopeEven when 5cm of lead was used to surround the electroscope to reduce the amount of ionising radiation the loss of charge was only reduced by 30%!There must be a type of radiation that can pass through over 5cm of lead.


Cosmic radiation: spontaneous dischargeIn 1900 an Englishman called Wilson took his electroscope into a deep railway tunnel to see if the radiation came from the skyThere was hardly any difference so it seemed unlikely that the radiation came from outer space - so surely the source of this radiation was undergroundIf this was the case then surely the higher you go the amount of discharge should decrease


Höhenstrahlung – Height radiationSo scientists wen up mountains with their electroscopes!The results were unclear and some scientists suggested the radiation may well be coming form the mountains themselvesA new method must be used to get to high altitude to measure the effect on the electroscope


Wulf and HessWith an increase in height comes a decrease in pressure which may influence the rate at which charge carriers are created – new electroscopes had to be designedTheodor Wulf made one that was airtight and had a magnifying window in 1909In 1910 Wulf took his device up the Eiffel tower – at 80m the gamma radiation intenity halves and he was up at 300mHe measured a small decrease in the charge lost, but not as low as he was expecting – further investigation was required


Wulf and HessVictor and Hess in 1911/12 showed with balloon flights that the discharge speed actually increased with altitudeIn 1936 he received a Nobel prize for this workHess performed his measurements up to 5kmUp to 2km the intensity of the radiation did decrease but from 2km upwards the intensity increased – he called this increase Höhenstrahlung – Height radiationKolhörster was a contemporary of Hess and confirmed his results up to 9km in his own measurements


Cosmic RadiationAfter the first world war the German Reneger found a maximum height for radiation before it decreased again up to 30kmRobert Millikan (US) carried out a extensive project into cosmic radiation. He obtained lower radiation intensities at low altitudes up to 1.5km that Hess and KolhörsterThis put fresh doubt in the origins of this radiation and was not resolved after a second set of results were found


Robert A. MillikanHe took his electroscopes to two different lakes on two different mountains measuring the radiation intensity in the air and lake waterThe deeper in the water the slower the rate of dischargeAt the higher altitude lake the electroscope had to go deeper (2m) into the water to get the same discharge speedMillikan realised that the radiation passes through 2m of water the same as 2000ft of air i.e. the same amount of matter


Cosmic RadiationMillikan’s conclusion was there could only be one explanation for the source of the radiationIt comes from outer space: cosmic radiationInitially Millikan thought it was a higher energy gamma radiation which is why they are still sometimes called cosmic rays.Jacob Clay however showed that the radiation should be mostly positively charged particlesFurther research found these to be stripped atomic nuclei such as Hydrogen (proton)These travel at near light speed velocities


Latitude EffectThe Dutchman Jacob Clay measured the discharge speed whilst on route from Genoa to JavaHe determined that there was less radiation nearer the equation than at higher latitudesThis was confirmed in the US by Arthur Compton and the reason was determined to be the Earth’s magnetic fieldThe cosmic radiation must consist of charged particles that are subjected to a Lorentz forceCareful analysis showed these to be positive


Radiation from SpaceThe Sun is the first source of cosmic radiation.We consider the Sun to have low energy particles sent out as cosmic radiation but compared to Earth sources they are still high energyOn Earth radioactive decay provides particles with energies up to several MeVOur Sun produces particles with energies up to 100GeVAt the LHC at CERN create particles up to 3.5TeV


Radiation from SpaceThe radiation from the Sun is very sensitive to the Earth’s magnetic fieldWhy and how so?The field is sufficiently strong to deflect most of the particles to the poles due to the Lorentz forceAt the equator the amount of radiation detected from the Sun is lower than at the polesHigh energy particles are less likely to be deflected by the Earth’s magnetic field and as such are just as likely to be found at the poles or equator


SunspotsLight intensity is fairly constant during a yearMagnetic processes in the Sun and on the surface, however affect the amount of cosmic radiation given offDuring large sunspots huge amounts of particles are given offSunspots are regions on the Sun’s surface where the temperatures are roughly 1000oC below average, around 5000oCThis is why they appear darker on images of the Sun


Sunspots


SunspotsEvery 11 years there is a maximum and minimum number of sunspots – reason unknownThey linked to the Sun’s complex magnetic fieldDuring a sunspot the magnetic field is at its strongestThis means we are most protected from radiation coming from outer spaceBut on the other hand the Sun is most turbulent


SunspotsThe surface solar flares emit large numbers of charged particles with great speed into spaceParticles headed for Earth are deflected by our own magnetic field to the polesHere they collide with nitrogen and oxygen molecules in the upper atmosphereThis creates the polar or northern lightshttp://www.youtube.com/watch?v=FcfWsj9OnsI

http://www.youtube.com/watch?v=FcfWsj9OnsI

http://www.youtube.com/watch?v=FcfWsj9OnsI


SunspotsThese solar eruptions also disturb radio communications and can pose a real danger to satellites and astronauts Because of this repeated 11 year cycle on the Sun – there is a similar cycle on Earth for the amount of cosmic radiation that reaches us.


Solar WindOur Sun emits a constant stream of charged particles, predominantly protons and electronsThese particles move at speeds of up to 700km/sThe Earth’s magnetic field protects us against most of these – however the solar winds increase the sphere of influence of the Sun’s magnetic fieldThe area dominated by the Sun’s magnetic field is called the heliosphere – this is larger than the total size of the solar system


Solar Wind


Further awayOur Sun is not the only star emitting radiation – all stars do soSome of them are far brighter than the Sun (which is actually very average)Bright stars emit particles with much higher energies- they have much bigger heliospheresNovas or supernovas (exploding stars) emit radiation and particles with energies up to 1015eV


Further awayRadiation up to this energy stays within our galaxyOur magnetic field has little effect on these particles – but the Milky Way has its own magnetic field!It is weak but has massive distances to act over so the force is strong enough to deflect particles so they start to spiral around in the galaxy


Further awayThe radiation cannot leave – but we cannot exactly determine its originsSome radiation gets past the Sun’s and Earth’s magnetic field resulting in collisions in the atmosphere creating C-14It is thought that cloud formation is also connected with cosmic radiation


Higher energiesParticles with energies greater than 1015eV regularly reach EarthWhere from?Possibly black holes at the centre of a galaxy or colliding galaxies!When particles have energies of over 1018eV then they can leave out galaxyThey move too fast to be effected by the Milky Way’s magnetic fieldMost obvious miss Earth so we cannot measure them


Higher energiesHowever if higher energy particles can leave our galaxy what can we infer from that?High energy particles hitting Earth may come from distant galaxiesAs they have such high energies they are only slightly deflected meaning we can determine the origins of the high energy particlesWith this we can track down the processes that create these particles


High energy particlesThis is one of the goals of the HiSPARC project:Detect ultra high energy cosmic radiationDetermine where it cam from and how it was created


High energy particlesWhen energies are over 1020eV then they interact with the cosmic background radiation left over from the ‘big bang’After travelling over 100 light years the particles have lost significant amounts of energyMeaning that any particles detected in this energy bracket come from our own cluster of galaxiesThese particles have 10million times more energy than anything created on Earth


Cosmic Radiation Beechen Cliff Physics

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