Pulsar star. The neutron star retains most of its angular momentum, and since it has only a tiny fraction of its progenitor's radius (and therefore its moment of inertia is sharply reduced), it is formed with very high rotation speed. A beam of radiation is emitted along the magnetic axis of the pulsar, which spins along with the rotation of the neutron star. The magnetic axis of the pulsar determines the direction of the electromagnetic beam, with the magnetic axis not necessarily being the same as its rotational axis. This misalignment causes the beam to be seen once for every rotation
External beam radiotherapy treatment. This means that rather than radiation entering the patient through only a small number of fixed angles, it can enter through many angles. This can be beneficial for some treatment sites where the target volume is surrounded by a number of organs which must be spared radiation dose. The intensity of the X-rays produced in an megavoltage linac is much higher in the centre of the beam compared to the edge. To counteract this a flattening filter is used. A flattening filter is a cone of metal (typically tungsten); after the X-ray beam has passed through the flattening filter