Expression, purification, crystallization and preliminary diffraction studies of the mammalian DAG kinase homologue YegS from Escherichia coli.

yegS is a gene encoding a 32 kDa cytosolic protein with unknown function but with strong sequence homology to a family of structurally uncharacterized eukaryotic non-protein kinases: diacylglycerol kinases, sphingosine kinases and ceramide kinases. Here, the overexpression, crystallization and preliminary diffraction analysis of Escherichia coli YegS are reported. The crystals belong to space group P2(1), with unit-cell parameters a = 42.4, b = 166.1, c = 48.5 A, beta = 96.97 degrees. The presence of a dimer in the asymmetric unit was estimated to give a Matthews coefficient (VM) of 2.5 A3 Da(-1) and a solvent content of 50.8%(v/v). Single-wavelength diffraction data were collected to a resolution of 1.9 A using synchrotron radiation.

Neutron measurements in the Vandellòs II nuclear power plant with a Bonner sphere system.

In some Spanish nuclear power plants of pressurised water reactor (PWR) type, albedo thermoluminescence dosemeters are used for personal dosimetry while survey meters, based on a thermal-neutron detector inside a cylindrical or spherical moderator, are used for dose rate assessment in routine monitoring. The response of both systems is highly dependent on the energy of the existing neutron fields. They are usually calibrated by means of ISO neutron sources with energy distributions quite different from those encountered at these installations. Spectrometric measurements with a Bonner sphere system (BSS) allow us to determine the reference dosimetric values. The UAB group, under request from the National Coordinated Research Action, was in charge of characterising the neutron fields and evaluating the response of personal dosemeters at several measurement points inside the containment building of the Catalan Nuclear Power Plant Vandellòs II. The neutron fields were characterised at five places using the UAB-BSS and a home made unfolding code called MITOM. The results obtained confirm the presence of low-energy components in the neutron field in most of the selected points. Moreover, we have found no influence of the nuclear fuel burning on the shape of the spectrum.

Characterisation of the IRSN CANEL/T400 facility producing realistic neutron fields for calibration and test purposes.

The new CANEL/T400 facility has been set-up at the Institute for Radiological Protection and Nuclear Safety (IRSN) to produce a realistic neutron field. The accurate characterisation of this neutron field is mandatory since this facility will be used as a reference neutron source. For this reason an international measuring campaign, involving four laboratories with extensive expertise in neutron metrology and spectrometry, was organised through a concerted EUROMET project. Measurements were performed with Bonner sphere (BS) systems to determine the energy distribution of the emitted neutrons over the whole energy range (from thermal energy up to a few MeV). Additional measurements were performed with proton recoil detectors to provide detailed information in the energy region above 90 keV. The results obtained by the four laboratories are in agreement with each other and are compared with a calculation performed with the MCNP4C Monte-Carlo code. As a conclusion of this exercise, a reliable characterisation of the CANEL/T400 neutron field is obtained.

Characterization of Bonner sphere systems at monoenergetic and thermal neutron fields.

The Institute for Radiological Protection and Nuclear Safety (IRSN) and the GFR, Universitat Autónoma de Barcelona (UAB) use Bonner spheres (BS) for neutron spectrometry at workplaces. The two systems, equipped with similar cylindrical 3He proportional counters, were simulated with the MCNP Monte-Carlo code to determine the response to neutrons of different energies for each polyethylene sphere. The BS systems were characterized at monoenergetic and thermal neutron fields. Measurements were performed at the Physikalisch-Technische Bundesanstalt (PTB) and at the National Physical Laboratory (NPL) standard laboratories, and with the newly characterized IRSN 'SIGMA' thermal neutron facility. The energy distribution of the reference neutron fluence was folded with the response functions for comparison purposes with the experimental data. In almost all cases related to monoenergetic neutrons, a good agreement between the experimental and the calculated count rates was found, and some discrepancies of a few per cent were observed in the thermal region.

MITOM: a new unfolding code based on a spectra model method applied to neutron spectrometry.

The MITOM code was developed at UAB (Universitat Autònoma de Barcelona) for unfolding neutron spectrometric measurements with a Bonner spheres system (BSS). One of the main characteristics of this code is that an initial parameterisation of the neutron energy components (thermal, intermediate and fast) is needed. This code uses the Monte Carlo method and the Bayesian theorem to obtain a set of solutions achieving different criteria and conditions between calculated and measured count rates. The final solution is an average of the acceptable solutions. The MITOM code was tested for ISO sources and a good agreement was observed between the reference values and the unfolded ones for global magnitudes. The code was applied recently to characterise both thermal SIGMA and CANEL/T400 sources of the IRSN facilities. The results of these applications were very satisfactory as well.

Personal neutron dosimetry in nuclear power plants using etched track and albedo thermoluminescence dosemeters.

Measurement of the personal dose equivalent rates for neutrons is a difficult task because available dosemeters do not provide the required energy response and sensitivity. Furthermore, the available wide calibration spectra recommended by the International Standard Organisation does not reproduce adequately the spectra encountered in practical situations of the nuclear industry. There is a real necessity to characterise the radiation field, in which workers can be exposed, and to calibrate personal dosemeters in order to determine the dose equivalent in these installations. For this reason, we measure the neutron spectrum with our Bonner sphere system and we fold this spectrum with energy-dependent fluence-to-dose conversion coefficients to obtain the reference dose equivalent rate. This reference value is then compared with the personal dosemeter reading to determine a field-specific correction factor. In this paper, we present the values of this field-specific correction factor for etched track and albedo thermoluminescence dosemeters at three measurement locations inside the containment building of the Vandellòs II nuclear power plant. We have found that assigning to each personal dosemeter the mean value of the field-specific correction factors of the three measurement locations, allows the evaluation of neutron personal dose equivalent rate with a relative uncertainty of approximately 25 and 15% for the PADC and albedo dosemeters, respectively.

First Report of Rhizoctonia solani AG-3 on Potato in Catalonia (NE Spain).

During the last 3 years, potatoes (Solanum tuberosum L.) with symptoms typical of Rhizoctonia canker and black scurf have been found in Catalonia; from 21,546 samples submitted to the official diagnostic laboratory (Laboratori de Sanitat Vegetal, DARP, Generalitat de Catalunya), 20% were infected with R. solani. Also, basidia and basidiospores of Thanatephorus cucumeris (A.B. Frank) Donk, the teleomorph of R. solani, have been observed frequently on stems near the soil surface. Previous work (1) has reported R. solani in the same geographic area, but anastomosis groups (AG) were not identified. Isolates (103) were collected from damaged roots, mature or progeny tubers, soil, debris, and weeds (roots and stem of Oxalis latifolia, Diplotaxis eurocoides, Solanum nigrum, Sorghum halepense, and Chenopodium album) in fields where potatoes were cultivated. All isolates were multinucleate, variable in number of nuclei (mean = 12, range = 7 to 19), and with morphological features typical of R. solani (3). Following the procedure of Parmeter et al. (2), all isolates (84) were identified as R. solani AG-3. Thirty-two isolates were evaluated for pathogenicity on potato plants at 20 to 25°C in the greenhouse. Germinated tubers (sprout length 3 cm) free of Rhizoctonia were placed in pea-sand mix (3:1, vol/vol; Compo Sana Universal, Barcelona, Spain) at 5-cm depth and inoculated by placing a 5-mm-diameter plug cut from 1-week-old cultures of each isolate adjacent to the sprouts. Potatoes were harvested 20 days after planting, and both emerged and nonemerged sprouts were examined for lesions and rated using a 0 to 4 scale. The AG-3 isolates caused major damage to roots and shoots (average disease rating 3.4). R. solani isolates were recovered from diseased plants and identified as AG-3. Preliminary field studies in Catalonia (Baix Llobregat and Maresme, unpublished) indicate that disease severity is not dependent on cultivar or related to yield reduction (10 to 65%), but is related to soil and seed contamination with sclerotia and mycelium. This is the first reported occurrence of R. solani AG-3 on potato in Catalonia. References: (1) Cebolla et al. Actas del III Congreso de la SECH, 1989. (2) Parmeter et al. Phytopathology 59:1270, 1969. (3) Sneh et al. Identification of Rhitzoctonia species. American Phytopathological Society, St. Paul, MN, 1991.