Deflection of Ag-atoms in an inhomogeneous magnetic field

Kheswa, Bonginkosi Vincent (2011-12)

Thesis (MSc)--Stellenbosch University, 2011.

Thesis

ENGLISH ABSTRACT: In the current design of the high temperature gas cooled reactor, a small fraction of coated fuel particles will be defective. Hence, 110Ag may be released from the fuel spheres into the coolant gas (helium) and plate out on the cooler surfaces of the main power system. This poses a radiation risk to operating personnel as well as general public. The objectives of this thesis were to design and construct an apparatus in which silver-109 atoms may be produced and deflected in an inhomogeneous and homogeneous magnetic field, compare experimental and theoretical results, and make a recommendation based on the findings of this thesis to the idea of removing silver-110 atoms from the helium fluid by deflecting them with an inhomogeneous magnetic field onto target plates situated on the inner perimeter of a helium pipe. The experimental results for the deflection of the collimated Ag- atoms with the round-hole collimators showed a deflection of 1.77° and 2.05° of the Ag- atoms due to an inhomogeneous magnetic field when the target plate was positioned 13 and 30 mm away from the magnet, respectively. These values were considerably greater than 0.01° and 0.02° that were calculated for the average velocity of atoms, v = 500 m/s. The case where Ag- atoms were collimated with a pair of slits and the target plate positioned 13mm away from the magnet showed the following: An inhomogeneous magnetic field changes the rectangular shape of the beam to a roughly elliptical shape. The beam of Ag- atoms was not split into two separate beams. This was caused by the beam of Ag- atoms consisting of atoms travelling at different speeds. The maximum deflection of Ag- atoms was 1.16° in the z direction and 1.12° in the x direction. These values were also significantly greater than 0.01 mm calculated at v = 500 m/s. This huge difference between the theoretical and experimental results raised a conclusion that the size of each Ag deposit depended mostly on the exposure time that was given to it. It was noticed that the beam of Ag- atoms was not split into two separate beams, in both cases. The conclusion was that the technique of removing Ag- atoms from the helium stream by means of an inhomogeneous magnetic field may not be effective. This is due to the inability of the inhomogeneous magnetic field to split the beam of Ag- atoms into two separate beams in a vacuum of ~10-5 mbar. It would be even more difficult for an inhomogeneous magnetic field to split the beam of Ag- atoms in helium, due to the Ag- atoms having a shorter mean free path in helium compared to a vacuum.

AFRIKAANSE OPSOMMING: In die huidige ontwerp van die hoë temperatuur gas afgekoelde reaktor, is 'n klein fraksie van omhulde brandstof deeltjies foutief. 110Ag kan dus vrygestel word vanaf die brandstof sfere in die verkoelingsgas (helium) wat dan op die koeler oppervlaktes van die hoofkragstelsel presipiteer. Hierdie 110Ag deeltjies hou 'n bestraling risiko vir die bedryfpersoneel sowel as vir die algemene publiek in. Die doelwitte van hierdie verhandeling is eerstens om 'n apparaat te ontwerp en konstrueer wat silwer-109 atome produseer en nie-homogene en homogene magnetiese velde deflekteer,. Tweedens om die eksperimentele en teoretiese resultate met mekaar te vergelyk. Derdens om 'n aanbeveling te maak gebasseer op die bevindinge van hierdie verhandeling rakende die verwydering van silwer-110 atome uit die helium vloeistof deur hulle met 'n nie-homogene magneetveld te deflekteer op die teikenplate binne-in 'n helium pyp. Die eksperimentele resultate vir die defleksie van die gekollimeerde Ag-atome met die ronde gat kollimators toon ‘n defleksie van 1.77° en 2.05° van die Ag-atome as gevolg van ‘n nie-homogene magneetveld wanneer die teikenplaat 13mm en 30mm, onderskeidelik, vanaf die magneet geposisioneer is. Hierdie waardes is aansienlik groter as die teoretiese defleksies van 0.01° en 0.02o wat bereken is vir ‘n gemiddelde snelheid van 500 m/s vir die atome. Die geval waar Ag-atome met 'n paar splete gekollimeer is en die teikenplaat 13 mm weg van magneet geposisioneer is, is die volgende resultate verkry: 'n nie-homogene magneetveld verander die reghoekige vorm van die bondel na 'n rowwe elliptiese vorm. Die bondel Ag-atome is nie volkome twee afsonderlike bundels verdeel nie. Dit is omdat die bondel van Ag-atome bestaan uit atome wat teen verskillende snelhede beweeg. Die maksimum defleksie van Ag-atome is 1.16° in die z-rigting en 1.12° in die x-rigting. Hierdie waardes is ook aansienlik groter as 0.01° bereken teen 500 m/s. Hierdie groot verskil tussen die teoretiese en eksperimentele resultate dui daarop dat die grootte van elke Ag neerslag grootliks afhanklik is van die blootstellingstyd wat daaraan gegee is. Daar is vasgestel dat die straal van Ag-atome in beide gevalle nie in twee afsonderlike bondels verdeel nie. Die gevolgtrekking is dat die tegniek van die verwydering van Ag-atome uit die helium stroom deur middel van 'n nie-homogene magneetveld nie effektief is nie. Dit is te wyte aan die onvermoë van die nie-homogene magneetveld om die bondel Ag-atome te verdeel in twee afsonderlike bondels in 'n vakuum van ~ 10-5 mbar. Dit sou selfs nog moeiliker vir 'n nie-homogene magnetiese veld wees om die bundel Ag-atome in helium te verdeel, weens die korter gemiddelde beskikbare pad van Ag-atome in helium wanneer dit met 'n vakuum vergelyk word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/17891
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