[en] In 1999 the Tandem Accelerator operated 3228 hours beam on the target. The acceleration potential on the terminal electrode ranged between 1.5 MV and 8.5 MV. The accelerator operation proved to be very stable, without any discharge inside the tank. The accelerator is provided with two ion sources, i.e. a classical duoplasmatron type source and a sputtering HICONEX 834 source. Both sources have been employed to get 28 types of ions, mainly heavy ions. A table shows the way the ion beams were used with the tandem accelerator in 1999 year. The accelerated ions were p, ⁷ Li, ⁹ Be, ^10,11 Be, ¹² C, ¹⁴ N, ¹⁶ O, ¹⁹ F, ²⁸ Si, ³² S, ³⁵ Cl, ⁴⁰ Ca, ⁴⁸ Ti, ⁶³ Cu. A new ion source has been constructed for the tandem accelerator quite recently. It is a high-intensity sputtering source with spherical ionizer, and an inflection magnet at 90 angle aimed to be applied in mass spectroscopy (AMS). The research domains of interest and the corresponding time percentage of accelerator were: Nuclear Spectroscopy (45.6%); Nuclear Reactions (1.5%); Atomic Physics (2.5%); Applications of Nuclear Techniques (17.4%); Accelerator Mass Spectrometry tests (3.3%). About 30% of the accelerator time was used to make same improvements, repairs of the accelerator's malfunctions and routine maintenance, among which: - The introduction of a chiller system with 2 freezing compressors in order to chill the distilled water required for the accelerator; - Tracing and repairing of the faulty area located in the first acceleration tube, which evidenced a high level of radiations; - The tracing technology according to which the acceleration gapes are sequential in short-circuit of two small balls in service, by means of two selsyn type motors. After short-circuiting the faulty point, the radiation field came back into its initial normal value; - During 1999, the accelerator tank was opened twice for routine maintenance works, namely, the drive motor and alternator greasing, the change of the stripping foils. The stripping foils fabricated by the tandem accelerator group, are very high quality foils and provide the accelerator operation for a very long time; - Also during 1999, a new system of dosimetric monitoring of the tandem accelerator and the target rooms, with the possibility of recording on computer, was installed. (authors)

[en] Thickness control in the manufacturing process of various foils of materials like metal, plastic, paper, cellulose, rubber, etc is one of the industrial applications of nuclear techniques. This control is based on the measurement of the exposure rate variation or absorbed dose rate due to the fluctuating thickness of material circulating or placed between radiation source and detector. The exposure rate or the absorbed dose rate is converted into a proportional electrical current. The higher the ionization current stability of ionization chambers (for a constant exposure rate or a constant adsorbed dose rate), the smaller the variations of the exposure rate (or absorbed dose rate) that can be detected, and so, the smaller the thickness variations of the adsorbent material interposed between radiation source and detector that can be determined. (authors)

[en] The problem of radiation dose measurement arises in research and in practical activity whenever the evaluation of radiation effects based on radiation energy absorbed in matter is required. Among the great number of known methods, the free air ionization chamber method and cavity ionization chamber method are most viable because these detectors represent reference standards for national metrology and ionization radiation dosimeter laboratories. These detectors are based on the electronic equilibrium principle and Brag-Gray equation for exposure rate determination and/or absorbed dose in different materials, including the air. For development of the above methods, we used a hardware configuration - Keithley electrometer - and the particular software - Keithley 2000 and test point method. They allowed us to measure some characteristic parameters of radiation detectors of ionization chamber type. Experimental data obtained with the two ionization chambers are in agreement with the standards required for these products and also with existing data in the world. Both detectors are reference standards for national metrology laboratories. These two measuring methods, are suitable for the determination of the exposure, exposure rate, dose, dose rate and activity for gamma, X and beta radiation. (authors)

[en] The FN-model Tandem Accelerator in Bucharest was commissioned in March, 1973 but it was put out of service in the years 1977 and 1986 due to the two strong earthquakes that struck Romania. For this accelerator, a seismic protection system was designed and implemented and some technical improvements that allow an improvement of the operation parameters and operational stability were also applied. (authors)

[en] The spherical ionization chamber under pressure is designed for the secondary calibration of alpha, beta and gamma radioactive sources. We can measure very low activity of such sources by placing them inside the ionization chamber and using air or krypton and xenon gases up to a pressure of 10 Atm. The ionization chamber is made of two hemispherical metallic electrodes polarized with 100-500 V d.c. (authors)

[en] The HVEC FN-Tandem accelerator of NIPNE - Bucharest, Romania was subject to numerous improvements among which the most important are the following: 1. Design and implementation of a seismic protection system; 2. A new type of a 10 MV voltage resistive divider was designed, constructed and installed. This new divider ensures a higher stability in the accelerator operation; 3. A new method employing the recoil atoms was elaborated to allow the analysis of the insulating gas composition in the accelerator tank; 4. A reflex mode of operation of the HICONEX 834 type sputtering ion source was introduced to obtain a wide range of heavy ion types with higher intensities and stability. For that purpose two new types of cones containing the sputter material were designed and tested. The numbers of accelerated ion species was increased from 7 to 28; 5. For conditioning the accelerator tube under high voltage, a sequential short-circuiting system was designed and implemented; 6. A new technology for manufacturing stripping carbon foils of longer life was accomplished. Following these improvements the accelerator is now more performing: - The potential on the terminal electrode was increased from 7.5 MV to 8.5 MeV, with the possibility to be raised up to 9 MV. The accelerator conditioning was performed up to 8.8 MV; - The accelerator is more stable - No reversing of column currents or discharges in the tank are present; - As the time of interventions inside the tank dropped drastically the present time of operational beam on target increased by more than 30%; - the service time of charging belt increased by 30% as the screens were reduced from three to two (the charging and the collector ones remained); - The electric resistance on the accelerator gaps is increased from 400 MΩ to 600 MΩ. To extend the work of the machine in the field of Accelerator Mass Spectrometry a new high resolution injector and a new high current sputtering ion source were developed

[en] Available as short communication only. The principal activities for maintaining and improvement of the High Voltage FN - type tandem accelerator in Bucharest are presented. The accelerator operation was cut off long periods of time after the strong earthquakes in 1977 and 1986. Therefore the major improvement was designing, construction, installation and testing of an antiseismic protection system. This system is activated at a seismic action that exceeds 0.05 g, being free of conventional sources of energy. In seismic conditions, the accelerator is free on an elastic suspension, oscillating with its characteristic frequencies. The seismic response capacity of the accelerator column has been increased from 0.1 g to 0.18 g by enlarging the number of tie bars. Another major improvement was the manufacturing and mounting of a new high voltage divider. Some other activities are mentioned, as well. As a consequence, the high voltage was increased to 8.5 MV. The number of delivered ion species was increased three times in the last two years. Schematic diagrams giving the beam time distribution in 1992 - 1993 are given. (Author) 1 Fig., 1 Tab., 3 Refs

[en] The operation of FN-Tandem accelerator in 1997 raised no special technical problems of any kind. The accelerator operated very stably to a maximum potential of 8.5. MV on the terminal, delivering a total number of 3104 beam-hour on target. Due to manufacturing of some long-life carbon foils for the charge stripping process by a new technology, as well as to a new voltage divider for 10 MV developed by our team, which was mounted on the accelerator and has been operating with very good results since 1991, during the year 1997 only two openings of the accelerator tank were necessary. The first opening was required to lubricate the drive-motor and alternator bearings and to replace the stripping foils. The second opening was needed for installing a new charging belt which was, at that time, under guarantee testing. We have taken that opportunity to clean for the dust caused by the band operation inside the accelerator, to inspect the charging screens and lubricate the drive-motor and alternator bearings and to replace the stripping foils. To the HICONEX 834 sputtering ion source a new type of symmetrical cone operating in the reflex mode was added and tested in order to get new types of radiogenic ions, highly interesting for applications in the accelerator mass spectrometry (AMS). The new type of cone was also employed and initially tested with the tandem in the Muenchen University (Germany). The cone exhibits the great advantage that it requires a very low quantity of sputtering material, a feature which is very important in AMS. With the new type of cone we succeeded in getting and accelerating aluminium and chlorine ions. The experimental results obtained at FN-Tandem accelerator (Bucharest) with different types of ions are presented. Our Tandem team has also carried out in 1997 a series of works associated to the preparation of the accelerator for the mass spectrometry. In the line, we have constructed the installation platform for the AMS injector as well as some ion-optical elements associated to the injector. An important contribution was the sputtering source with high intensity spherical ionizer constructed according to the design received from Purdue University (USA). The pre-acceleration tubes of AMS injector were mounted and, simultaneously, the voltage resistive divider was made and connected. Now, the new injector installation works along with the installation of the 90 angle inflection magnet manufactured by Danfysik. (authors)

[en] The employment of some of the best quality carbon foils for the charge stripping process is a must for the efficient operation of a tandem accelerator. One of the special quality parameters is the stripping foil service-life i.e., the longer the stripping foil service-life, the longer the accelerator operation period without any intervention. Our tandem operation team has succeeded in developing a technology to manufacture carbon foils with a service-life of about one order of magnitude higher than the classic ones commonly employed. When preparing the carbon foils, we have used an ion deposit procedure according to the method used by Takeuchi (Japan). The deposits which creates the foils are produced by carbon evaporation in vacuum between two graphite electrodes located in a direct current electric arc for a very short period of time. The glass blades, the carbon foils are placed on, are then washed-out by a detergent, degreased by acetone and iso-propylic alcohol and afterwards, a very thin film of 100 ml distilled water, 12 g Betaine-monohydrate and 6.4 g Saccharose is gently manually spread over the deposit surface. The glass blades are then placed on a metal framework at about 15 mm distance away from the electric arc. The electric arc is made up of two 5 mm diameter electrodes with parallel sides which are brought into contact for a very short time and next released to about 2 mm from each other, for only 2 seconds. Meanwhile, a 50 ampere arc current is maintained. Then, there comes a 15-20 second break, a time period long enough to get the cooling down of the electrodes and recovering the vacuum. Next, a new re-striking of the electric arc is carried out under the same conditions. As a current power supply, a welding transformer with direct current outlets supplied by an adjustable voltage transformer, was used. Next, the carbon foil is placed on its support by means of a very thin sub-layer made up of formvar. During the period when both the formvar sub-layer and the carbon foil are deposited, the carbon foil support is placed on a system which allows the foil to be easily inflated by means of a fine air jet. Simultaneously, the carbon foil is dried-up by infrared radiation. (authors)

[en] Thickness control and fluctuation of various foils of material is one of the applications of nuclear methods in industry. This process is based on the measurement of the exposure rate variation (for gamma radiation) or of the absorbed dose rate (for beta radiation) produced by different thickness of materials located between radiation source and detector. Exposure rate and absorbed dose rate variations can be monitored with radiation detectors of ionization chamber type. They convert the exposure rate or absorbed dose rate into a proportional electrical current. The better the ionization current stability of ionization chambers (for a constant exposure rate, or a constant absorbed dose rate), the smaller are the variations of the exposure rate (or absorbed dose rate) which can be put into evidence. Therefore, the variations of the thickness of the absorbent material interposed between the radiation source and the detector that can be determined are smaller. We manufactured three models of radiation detectors of ionization chamber type for industrial applications as follows: CIS-P5M-1000Kr, CIS-P2M-1000Kr and CIS-P8M-70Kr. (authors)