Patent GB-1117919-A (GB)
Title: Improvements relating to the analysis of unknown material
IPC: G21H5/02
Filed: 1965-12-08
Abstract: 1,117,919. Support means for twin samples. KAMAN AIRCRAFT CORP. [9 Dec., 1964], No. 51997/65. Heading H5R. [Also in Division G1] A method of quantitative analysis of samples activated by nuclear bombardment e.g. neutrons, protons, deuterons, alpha particles or high energy photons, involves the investigation of at least two samples (one unknown, one reference), which are arranged to be moved together to obtain uniform irradiation during the bombardment process. In the determination of the oxygen content of an unknown sample, a reference sample of known oxygen content is utilized. The samples are irradiated by neutrons, which changes some of the oxygen into an unstable isotope of nitrogen (N<SP>16</SP>). This has a half life of a few seconds, allowing a rapid measurement cycle. The decay of this isotope back to oxygen produces γ- and #- radiation which can be measured and counts for the samples are obtained in turn. The counting rate is proportional to the weight of oxygen in a sample, and thus the weight of oxygen in the unknown sample may be determined. Equal amounts of unknown and reference samples are contained in respective capsules 68, (Fig. 7, not shown). The capsules are loaded into the apparatus and propelled by compressed air to positions where they are located side by side in a sample supporting and receiving head 16, situated adjacent the target 14 associated with a neutron generator 12. The head has provision (a motor and gearing system) for rotating the capsules about their own axes and about an axis perpendicular to the plane in which the two capsules are located (Figs. 2, 3, not shown). This provides substantially uniform irradiation. After the irradiation period, the unknown sample capsule is ejected by compressed air along a tube 22, to the detector head 24 which includes a sodium iodide scintillation detector, feeding a pulse height discriminator. During the first count, the detector output is gated to counter 42. After this first measurement period, the compressed air system is again operated to eject the unknown sample carrier from the detector head 24 to a sample loading port, where a new unknown sample capsule may be substituted. At the same time the reference sample is propelled along a tube 20 to the detector head for evaluation, this time the count being made, for the same time period, on a counter 40. The counts stored in counters 40, 42 may be compared when desired using computation means 44, and the results, percentages of oxygen are printed out. Special arrangements, especially by accurate time intervals between operations prevent overirradiation of one of the capsules or extra pick-up of radiation by the detector. For example, the sample loading port and detector head are sufficiently spaced apart to prevent unknown sample radio-activity affecting the reference sample count. Further, irradiation period completed, both capsules may be ejected from the vicinity of the target, the reference sample capsule being held in its tube 20 by a stop while the other goes on for evaluation. The detector head 24 may be a rotating head similar to the sample receiving head 16 or one involving rotation about a single axis. The timing control circuitry is described (Fig. 6, not shown) as is the air valve construction in the head 16 (Fig. 4, not shown) and gearing mechanisms (Figs. 2, 3 and 5, not shown).