RESUMEN
In the framework of a BIPM 238Pu comparison exercise, a new design for a-radiation counting sources was developed. These sources are constructed with a gold-coated Vyns film stretched over a stainless-steel disk. To improve the crystallization of the radioactive salt, the physical properties of the gold-coated polymer surface which receives the radioactivity deposit is modified. A pad of polystyrene micro-spheres (Estapor K-007) mixed with a wetting agent (Tween 20) is directly electrosprayed before the radioactive drop is deposited. After hot air-drying, the source is finally sealed with a thin Vyns film covering the entire radioactive spot. This new design makes it possible to create 238Pu sources that are easy and safe to handle, homogeneous and stable during ageing.
RESUMEN
In the framework of R&D studies for the improvement of radioactive source efficiencies prepared on thin films for 4pibeta-gamma coincidence counting, a comparative study on two drying methods has been undertaken in our laboratory (BNM-Laboratoire National Henri Becquerel, France). The standard method of evaporation at atmospheric pressure and a method based on freeze-drying using commercial equipment are compared. The preliminary results of this study obtained with 65Zn sources are presented and a significant improvement of the detection efficiencies to the electron emission for freeze-dried sources is shown. In the course of validation of this method, other radionuclides were studied and, up to now, the results confirm the better crystallization homogeneity achieved for freeze-dried sources.
RESUMEN
The EUROMET project 428 examines efficiency transfer results for Ge gamma-ray spectrometers when the efficiency is known for a reference point source geometry. For this, different methods are used, such as Monte Carlo simulation or semi-empirical computation. The exercise compares the application of these methods to the same selected experimental cases to determine the usage limitations versus the requested accuracy. For carefully examining these results and trying to derive information for improving the computation codes, this study was limited to a few simple cases. The first part concerns the simplest case of geometry transfer, i.e., using point sources for 3 source-to-detector distances: 2, 5 and 20 cm; the second part deals with transfer from point source geometry to cylindrical geometry with three different matrices. The general conclusion is that the deviations between the computed results and the measured efficiencies are mostly within 10%. The quality of the results is rather inhomogeneous and shows that these codes cannot be used directly for metrological purposes. However, most of them are operational for routine measurements when efficiency uncertainties of 5-10% can be sufficient.
RESUMEN
Method of electrodeposition on rotating disk cathode (RDE) is applied for preparation of Np, Pu and Am alpha-standards. Phenomenon of critical current density is experimentally observed which is in perfect accord with Hansen's theory of electrodeposition. Influence of deposit calcination regime on quality of alpha-sources is studied, and comparison is made of uniformity of deposits obtained in various deposition systems. Standards with energy resolution better than 9 keV can be reproduceably obtained by optimized RDE electrodeposition technique.