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  • 天同
    Lv 7
    7 years ago
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    (a) There is a separation of 20 cm between the source (放射源) and the GM tube (彌勒管). Alpha particles has a range in air of only a few centimetres. They cannot reach the GM tube even if alpha particles are emitted by the source.

    (b)(i) The magnetic field is from B to A.

    Such direction of magentic field would deflect beta particles downward (try to use Fleming's Left Hand Rule). This gives a reading on the GM tube when it is placed at Q.

    (ii) It is the background radiation (本底輻射)

    (iii) The source emits beta particles and gamma rays.

    Beta particles carry -ve charges and hence are deflected by the magnetic field of the coils to move downward, giving a reading on the GM tube at Q.

    Gamma rays carry no charge. It is undeflected by magnetic field, thus giving a reading on the GM tube at P.

    (iv) The readings each include background radiation. Adding the readings in fig.h and i doubles the background radiation.

    (v) Move the whole set-up (GM tube abd coils) to a few centimetre distance (within ~ 5 cm) from the source. Move the GM tube along the vertical line above P. A reading above background should be observed if alpha particles are present.

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