Deflection of Ag-atoms in an inhomogeneous magnetic field

[摘要] ENGLISH ABSTRACT: In the current design of the high temperature gas cooled reactor, a small fraction ofcoated fuel particles will be defective. Hence, 110Ag may be released from the fuelspheres into the coolant gas (helium) and plate out on the cooler surfaces of the mainpower system. This poses a radiation risk to operating personnel as well as generalpublic.The objectives of this thesis were to design and construct an apparatus in whichsilver-109 atoms may be produced and deflected in an inhomogeneous andhomogeneous magnetic field, compare experimental and theoretical results, and makea 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 magneticfield onto target plates situated on the inner perimeter of a helium pipe.The experimental results for the deflection of the collimated Ag- atoms with theround-hole collimators showed a deflection of 1.77° and 2.05° of the Ag- atoms due toan inhomogeneous magnetic field when the target plate was positioned 13 and 30 mmaway from the magnet, respectively. These values were considerably greater than 0.01° and 0.02° that were calculated for the average velocityof atoms, v = 500 m/s. The case where Ag- atoms were collimated with a pair of slitsand the target plate positioned 13mm away from the magnet showed the following:An inhomogeneous magnetic field changes the rectangular shape of the beam to aroughly 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 differentspeeds. 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 calculatedat v = 500 m/s. This huge difference between the theoretical and experimental resultsraised a conclusion that the size of each Ag deposit depended mostly on the exposuretime that was given to it. It was noticed that the beam of Ag- atoms was not split intotwo separate beams, in both cases.The conclusion was that the technique of removing Ag- atoms from the helium streamby means of an inhomogeneous magnetic field may not be effective. This is due to theinability of the inhomogeneous magnetic field to split the beam of Ag- atoms into twoseparate beams in a vacuum of ~10-5 mbar. It would be even more difficult for aninhomogeneous magnetic field to split the beam of Ag- atoms in helium, due to theAg- atoms having a shorter mean free path in helium compared to a vacuum.

[发布机构] Stellenbosch University