Patent GB-990920-A (GB)
Title: Improvements in radiometric analysis
Inventor: STARNES PETER EDWARD
IPC: G01N23/12
Filed: 1962-06-12
Abstract: 990,920. Radiometric analysis; weighing apparatus. HILGER & WATTS Ltd. Sept. 11, 1963 [June 12, 1962], No. 22616/62. Headings G1A and G1W. [Also in Divisions B8 and G3] In order to determine the chemical composition of dry powdered material by radio-metric analysis a moving sample carrier and means for forming a layer or ribbon of the powdered material having a substantially constant depth and mass per unit area on the carrier are provided. The analysis may be effected by the use of electrons, neutrons, X-rays, or a combination thereof, and the radiation transmitted, back-scattered, or produced as secondary radiation may be investigated alone or in combination. In apparatus for carrying out the analysis the sample carrier is a circular disc V having a rectangular section groove extending round its circumference. The bottom of the groove is made of material having a low absorption for the radiation used such as the berylium, aluminium, or a rigid organic material. The disc is supported by a shaft A depending from a thrust-race B gimbal mounted on a saddle assembly D. The saddle assembly is carried by knife edges on one end of a balance beam E. A counter-weight I moving freely in a container of oil hangs from a similar saddle H at the opposite end of the beam and weight pans L<SP>1</SP> and L<SP>2</SP> are also provided on the saddles. The centre beam support consists of a double knifeedge assembly F and incorporates conical-ended lateral locating pins to prevent movement about a vertical axis. The fixed support G for the beam carries a dynamometer N and indicator h<SP>1</SP>, h<SP>2</SP>, associated with a clamp h carried by saddle H. The probe O of the dynamometer N is coupled to contact stud Q resting on the beam through circular plates separated by a rubber pad P. The bottom of the shaft A terminates in a universal coupling whose lower element carries a horizontal pin T fitted with two small groovedwheels z<SP>1</SP> and z<SP>2</SP> preferably of polytetrafluoroethylene. These wheels engage with four polished vertical pins mounted in the base of container R. The lower element of the coupling is steadied by a vertically depending open-ended hollow polished steel needle j extending into a lined bush fixed centrally in the bottom of container R. The container R is filled with oil and the arrangement allows a rotational drive to be transmitted from it to the shaft A whilst permitting some vertical movement with low frictional drag. Container R is driven by an electric motor rotating a knurled wheel co-operating with a rubber-faced plate r and in order to jolt the drive between the pins and the wheels z<SP>1</SP> and z<SP>2</SP> to further reduce the effect of friction the shaft U carrying the plate and container is spring mounted and the plate provided with cam-like projections in the path of the knurled drive wheel. Above sample carrier disc V is a plate X mounted on three rollers X<SP>1</SP> and pressed downwards by spring X<SP>3</SP>. The plate carries three spaced arms one of which is attached to a fixed vertical rod by a substantially horizontal restraining spring. The other arms carry, respectively, a shoe Z for smoothing powdered material fed into the sample groove to achieve uniform thickness and a plough positioned beyond the radiation analysis point to loosen the material prior to its being sucked out of the groove. Powder is fed into the groove by a vibrating hopper feeder at a point just prior to the shoe Z and the weight of powder on the carrier, and thus the mass per unit urea of the groove, is maintained constant by using the dynamometer output to control the amplitude of the hopper vibrations. The actual mass of powder on the carrier is determined by putting weights into the balance pans. To avoid transient signals affecting the feed the error signal applied to control the hopper is derived from signals proportional to the dynamometer output and its integral. A suitable radiation source and one or more radiation detectors are fixed below and/or above the groove in the carrier disc between the shoe Z and the plough mentioned above. The connection between the detector system and display means may include an averaging or integrator circuit.