Precision mass measurements of very short-lived, neutron-rich Na isotopes using a radiofrequency spectrometer

Mass measurements of high precision have been performed on sodium isotopes out to $^{30}$Na using a new technique of radiofrequency excitation of ion trajectories in a homogeneous magnetic field. This method, especially suited to very short-lived nuclides, has allowed us to significantly reduce the uncertainty in mass of the most exotic Na isotopes: a relative error of 5x10$^{-7}$ was achieved for $^{28}$Na having a half-life of only 30.5 ms and 9x10$^{-7}$ for the weakly produced $^{30}$Na. Verifying and minimizing binding energy uncertainties in this region of the nuclear chart is important for clarification of a long standing problem concerning the strength of the $N$=20 magic shell closure. These results are the fruit of the commissioning of the new experimental program Mistral

Accurate mass measurements of 26^{26}Ne, 26−30^{26-30}Na, 29−33^{29-33}Mg performed with the {\sc Mistral} spectrometer

The minuteness of the nuclear binding energy requires that mass measurements be highly precise and accurate. Here we report on new measurements $^{29-33}$Mg and $^{26}$Na performed with the {\sc Mistral} mass spectrometer at {\sc Cern}'s {\sc Isolde} facility. Since mass measurements are prone to systematic errors, considerable effort has been devoted to their evaluation and elimination in order to achieve accuracy and not only precision. We have therefore conducted a campaign of measurements for calibration and error evaluation. As a result, we now have a satisfactory description of the {\sc Mistral} calibration laws and error budget. We have applied our new understanding to previous measurements of $^{26}$Ne, $^{26-30}$Na and $^{29,32}$Mg for which re-evaluated values are reported.Comment: submitted to Nuclear Physics

Accurate mass measurements of short-lived isotopes with the MISTRAL rf spectrometer

The MISTRAL experiment has measured its first masses at ISOLDE. Installed in May 1997, this radiofrequency transmission spectrometer is to concentrate on nuclides with particularly short half-lives. MISTRAL received its first stable beam in October and first radioactive beam in November 1997. These first tests, with a plasma ion source, resulted in excellent isobaric separation and reasonable transmission. Further testing and development enabled first data taking in July 1998 on neutron-rich Na isotopes having half-lives as short as 31 ms

Determination of correction factors for alpha activity measurements in the environment (conditions of high dust loading)

Within the framework of a French national monitoring program to survey the man-made radioactivity in the environment, several power plants and research facilities on the territory use environmental air monitors for unwanted releases of radioactive aerosols. High sensitivity and lack of false alarms are all important for environmental air monitors. The project aims to conduct investigations to improve operation of environmental air monitors, particularly under conditions where a lot of nonradioactive dust may be deposited on the filters (conditions of high dust loading). The dust may increase the frequency with which filters must be changed and can lead to an underestimation of the real activity. This underestimation is due to deteriorated alpha energy resolution and response specificity to the radionuclides of interest. In this study, our objective was to find experimental correction factors for the degraded activity measurements taking into account the alpha absorption in the dust loading. © The Author 2010. Published by Oxford University Press. All rights reserved

Experimental and simulation methods to evaluate the alpha self-absorption factors for radioactive aerosol fiber filters

Air sampling for particulate radioactive material involves collecting airborne particles on a filter in order to measure the radioactivity in the environment or in working areas. The amount of alpha radioactivity collected on the sampling filter is frequently determined by global alpha-particles measurements. Several factors can affect the alpha energy while passing through the filter to reach the detector. The most affecting factor on the alpha spectrum degradation is the absorption of alpha particle energies in the filter fibers. The fibers' density can range from 1 to 9 mg cm-2. The counting losses can accordingly be important, and the global activity in the filter can be underestimated. The complexity of the experiments and the diversity of the filter types, filtration conditions as well as detector types used for survey incite us to formulate a numerical model to simulate the correction factors of the degraded activity. Comparisons between experimental and simulated correction factors for a commonly used filter are presented. The good agreement found between experimental and calculated values validates the method in the studied conditions. © 2009 Elsevier Ltd. All rights reserved

Application of the monte carlo method to study the alpha particle energy spectra for radioactive aerosol sampled by an air filter

An alpha spectrometer including a semi-conductor detector is commonly used for measurements of the emergent alpha particles from an air filter, on which was sampled a radioactive aerosol. The alpha spectrometry and the detection efficiency are necessary input information for real radioactivity measurements. The MCNPX code based on the Monte Carlo method has been applied to simulate the detection process in order to obtain spectrum peaks and determine the detection efficiency for modeled geometry. First simulations with MCNPX have been carried out in order to validate the alpha particle energy spectrometry of an electrodeposited solid source and an initial simulated filter model. Furthermore, to improve our first filter model, the real spatial distribution of radioactive aerosols across the filter thickness, found experimentally, is taken into account in a multi-layer filter model. Such an alpha particle distribution allows achieving an adequate simulation of the filter. Comparison between measured and simulated alpha spectra highlights the good agreement in spectral parameters and in detection efficiency even under different aerosol spatial distributions inside the volume of the filter. © 2009 Health Physics Society

Sorption properties of activated carbons for the capture of methyl iodide in the context of nuclear industry

International audienceIn the present study, some commercially available activated carbons were evaluated towards the methyl iodide (CH3I) capture in the context of nuclear industry. A specific methodology was implemented in order to establish structure-activity relationships between adsorbent characteristics and its adsorption behavior towards CH3I. On the one hand, the investigated adsorbents were characterized by a combination of physico-chemical techniques. On the other hand, CH3I retention performance from batch sorption tests under different conditions (temperature and relative humidity) was studied using an original experimental setup. In this work, two conditions were investigated: (i) T = 35°C, R.H. = 26 % ([H2O] ∼15,000 ppmv); (ii) T = 75°C, R.H. = 30 % ([H2O] ∼130,000 ppmv). Different trends were obtained depending on the investigated scenario. At ambient conditions (i), CH3I adsorption performance was affected after KI/TEDA impregnation because of partial pore blockage phenomena induced by the of impregnants presence within the microporosity. However, TEDA impregnation was found to be required to enhance the trapping stability and to capture CH3I with superior efficiency at higher temperature (ii)