RESUMO
In recent years, aberration correction has slowly become standard in high-end conventional transmission electron microscopy (50-200 kV). However, the integration of correctors to low voltage transmission systems (5-25 kV) has proved to be difficult. The hexapole corrector based on permanent magnet technology seems to be a promising solution for the correction of the primary spherical aberration. Especially if the compact dimensions and low complexity are to be preserved. However, the high importance of chromatic aberration with respect to the microscope resolution still remains a serious obstacle. It must be taken into account when the design is made. The following presented concept is intended exclusively for STEM mode to avoid additional chromatic deterioration caused by electron passage through the sample. The design of the key segment (transfer lens doublet) is discussed in detail, including its compensation systems, which guarantees proper alignment.
RESUMO
This paper presents polymer graphite (PG) as a novel material for the scanning tunneling microscopy (STM) probe. Conductive PG is a relatively modern nanocomposite material used for micro-pencil refills containing a polymer-based binding agent and graphite flakes. Its high conductivity and immunity against surface contamination, with a low price, make it seem like a highly suitable material for electrode manufacturing in general. For the tip production, three methods were developed and are further described in the paper. For the production, three commercially available polymer graphite rods were used. Each has been discussed in terms of performance within the tunneling microscope and within other potential applications.
RESUMO
BACKGROUND: Despite a pronounced technical process attained in radiotherapy of malignant neoplasms, no remarkable improvement in the treatment results has been achieved. The reason for this stagnation is the interaction between tumor cell and photon radiation. Tumor resistance against photon bombardment can be broken down by applying high linear energy transfer (LET) radiation-based treatment. The discovery of californium-252 ((252)Cf) nuclide, a source of gamma neutron radiation, established a precondition for using neutrons in tumor brachytherapy. The design of a remote afterloading device using (252)Cf sources remains an unsolved problem. MATERIAL AND METHODS: The afterloading device has been designed as a stationary radiator which is composed of three mutually interconnected units: 1. the control and drive unit consisting of a control computer and a motor-driven bowden system carrying the (252)Cf source; 2. the source which is housed in a watertight concrete vessel-storage strong room, situated in the ground at a depth of 25 cm beneath the patient's bed; 3. the afterloading application module installed in the irradiation room. RESULTS: Remote afterloading allows simple, inexpensive and highly efficient radiation protection and work safety for the operating personnel. The sources may be moved arbitrarily during treatment with a position accuracy of 0.5-1.0 mm within a distance of 520 cm from the source storage position in the strong room to the application position. Both afterloading systems' unused indexer outputs are protected electronically and mechanically against any unintentional movement of the source outside the application tubes. CONCLUSION: The technologic concept of the present automatic afterloading device for neutron brachytherapy represents a possible option from the range of conceivable design variants, which - while minimizing technologic and economic requirements - provides the operating personnel with optimum protection and work safety, thus extending the applicability of high LET radiation-based treatment methods in clinical practice.
