Patent GB-1093885-A (GB)
Title: Method and apparatus for x-ray analysis
IPC: G01N23/22
Filed: 1965-03-25
Abstract: 1, 093, 885. X-ray analysis apparatus. COMPAGNIE GENERALE DE RADIO LOGIE. March 25, 1965 [March 26, 1964], No. 12782/65. Heading G1A. Non-dispersive X-ray fluorescence analysis apparatus for analyzing a series of samples in sequence employs electronic gating and counting means to count pulses, in a selected amplitude range representing a particular element in a sample, and produced at a rate corresponding to the proportion of that element in a sample. The resolving power of the apparatus may be increased by precisely regulating the X-ray tube supply. Such regulation ensures that the tube voltage can be adjusted accurately to a level so that atoms of the test element are excited but not those of elements of higher atomic number than the test element. General. The X-ray tube 1 and a proportional counter 2, continuously supplied with a flow of argon and methane, are arranged on one side of a large sample carrier turntable 3, on which can be mounted 12 different samples. This apparatus is contained within an evacuable cover 4, which is hinged to base-plate 16 and when the interior is let down to atmospheric pressure, can be lifted by a handle, a shutter 5 being simultaneously caused to cover the X-ray tube exit window to prevent the escape of radiation harmful to an operator Figs. 6, 7 (not shown). The tube is supplied from a device 15 provided with voltage and current controls 28, 29. The output from the detector 2 is applied to an amplitude discriminator 11 provided with controls 25, 26 for setting respectively the lower or gating threshold voltage, and the gate width for pulses, so that only pulses of amplitude corresponding to the test element are counted by a digital counter 12 having a control 27 to pre-set the time interval for counting. The indications of the counter are recorded by a printer 13. The sequence of operations for the testing of a number of samples (up to 12) mounted on the turntable is controlled by a device 6. The operation &c. of the turntable mechanism is described Fig. 5 (not shown). Control sequence. After setting the controls for the X-ray tube, amplitude discriminator &c., and lowering the cover 4, the switch 104, Fig. 3 (not shown) to start the measuring sequence, is closed. This causes the energization of a fan motor (M3) to blow the gas mixture through the detector tube 2. A number of relays are operated in sequence after the closing of the start-cycle switch (K 1 ), including one to actuate pumping down of the enclosure 4. A count is made on the first specimen and printed out on printer 13 (or card or tape perforating unit, display, &c.) which then issues a control signal to switch a first monostable circuit to its unstable state for a period of 1 second. This causes the turntable indexing gear 8, mounted below the apparatus base-plate 16, to be released for rotation by motor M 2  to locate the next sample for testing. Eleven keys are provided, each associated with one of the sample positions in the turntable, which are depressed before the start of the sequence, to pre-select which samples, besides the first one in position 1, are to be tested. If a key has not been depressed, the discriminator is not energized to gate pulses to the counter 12 and a zero count is printed. The cycle is completed when a second monostable circuit is energized and the various components, motors, &c. are shut off and the vacuum in enclosure 4 let down. A recycle switch is provided to keep the cycleterminating monostable circuit inoperative and allow further measurement on the same set of samples. The turntable is arranged to be bodily removable to be replaced by an identical table with a fresh set of samples. Modifications. A special circuit may be provided which has sets of adjustable potentiometers, controlling the various test parameters (X-ray tube current and voltage, count time, and discriminator voltage settings), each set corresponding to a particular sample position on the turntable Fig. 4 (not shown). This allows the testing of different samples for different constituents in a single cycle. A further modification of the apparatus provides for gating of more than one amplitude range through an amplitude discriminator, for counting by separate counters such that two or more elements in a sample may be measured. An example of an application of the apparatus is the determination of the sulphur content of specimens of tyre rubber, the initial calibration of the instrument being carried out on a graphite sample of known sulphur content.