Patent Number: 
Section: claims

1. An x-ray inspection system arranged to inspect at least one object and comprising:a source of radiation;a detector, which in use, is configured to detect the radiation passing through an irradiation zone and generating a periodic output of data therefrom, wherein the period of the output comprises a duration of a measurement pulse and a duration of a reset pulse;wherein the detection is arranged such that radiation is detected when a measurement pulse occurs;processing circuitry arranged to process the output generated by the detector;a speed determiner arranged to determine and output to the processing circuitry the speed at which an object passes the detector; wherein the processing circuitry is arranged to vary the period of the output of the detector according to the output from the speed determiner whilst maintaining the duration of the measurement pulse at a substantially constant period. 2. A system according to claim 1 in which the processing circuitry is arranged to vary the period of the output by controlling the duration of the reset pulse applied to the detector. 3. A system according to claim 1 in which the processing circuitry is arranged to measure the output of the detector at an end region of the measurement pulse. 4. A system according to claim 1 in which the detector comprises a plurality of photo-diodes. 5. A machine readable medium containing instructions which cause a processing circuitry to function as the system of claim 1 when run thereby. 6. An x-ray inspection system arranged to inspect at least one object and comprising:a source of radiation;a detector, which in use, is configured to detect the radiation passing through an irradiation zone and generating a periodic output of data therefrom, wherein the period of the output comprises a duration of a measurement pulse and a duration of a reset pulse;processing circuitry arranged to process the output generated by the detector;a speed determiner arranged, in use, to determine and output to the processing circuitry the speed at which an object passes the detector;wherein the processing circuitry is arranged to vary the period of the output of the detector according to the output from the speed determiner, and is further arranged to vary the period of the output by controlling the duration of the reset pulse applied to the detector. 7. A system according to claim 6 in which the processing circuitry is arranged to maintain the duration of the measurement pulse, during which radiation is detected, at a substantially constant period. 8. A machine readable medium containing instructions which cause a processing circuitry to function as the system of claim 6 when run thereby. 9. A method of monitoring a product comprising: measuring the speed at which the product passes through an irradiation zone in which x-rays generated by an x-ray source are incident; detecting the amount of x-rays that pass through the product using a detector adjacent the irradiation zone and having a periodic output comprising a duration of a measurement pulse and a duration of a reset pulse, radiation being detected when the measurement pulse occurs;wherein the method comprises adjusting the period of the output according to the speed at which the object passes through the irradiation zone, whilst maintaining the duration of the measurement pulse at a substantially constant period. 10. A method according to claim 9 which controls the duration of a reset pulse applied to the detector in order to adjust the period of the output. 11. A method according to claim 9 which reads the output from the detector at an end region of the measurement pulse. 12. A method according to claim 9 which sets the duration of the measurement pulse according to the maximum speed at which the object will pass through the irradiation zone. 13. A computer readable medium containing instructions which when read by a processing circuitry cause that processing circuitry to perform the method of claim 9.