F. Fernández

Experimental and theoretical study of radon levels and entry mechanisms in a mediterranean climate house

Abstract An experimental study has been carried out in an inhabited single-family house. Radon concentration in the different rooms of the house and in its garden soil has been measured with Nuclear Track Detectors. No high differences of radon concentration have been observed between the different rooms of the house, so that the proximity of the room level to the soil seems not to affect the radon concentration. The annual radon concentration obtained indoors and in the soil has been respectively 35 Bq m −3 and 24 kBq m −3 . Since radon generation in the source, entry into indoor air and accumulation indoors depend on several parameters, the effect of a specific parameter on indoor radon concentration is difficult to explain from the radon measurements only. The RAGENA (RAdon Generation, ENtry and Accumulation indoors) model has been adapted to the room in the basement of the house. The mean radon concentration values obtained with the model are compared to experimental results derived from measurements using Nuclear Track Detectors. The use of the model, together with the experimental study, has allowed characterising radon sources, levels and entry mechanisms in the house. The concrete walls have been found to be the most relevant radon source, while the contribution of the soil is negligible in this case. The indoor radon level is given by the balance of the permanent exhalation from concrete and the removal due to ventilation. The indoor radon levels are close to the average value for the Barcelona area which, in turn, is close to the world averaged value.

Secondary neutron production from thick Pb target by light particle irradiation

Abstract Neutron multiplicities from spallation neutron sources were measured by Solid State Nuclear Track Detectors. Light particles as protons, deuterons and alphas in the GeV range were used on Pb targets. For neutron thermalization the targets were covered by 6 cm paraffin moderator. Neutron multiplicity distributions were studied inside and on the moderator surface. Comparison of SSNTDs results were made for thermal-epithermal neutrons with 139 La activation method as well as with Dubna DCM/CEM code. Discussion including previous 12 C results are given.

Simultaneous measurement of radon, radon progeny and thoron concentrations using Makrofol-DE detectors

Abstract In this study we describe the set-up of a new passive integrating system to measure simultaneously 222Rn, 222Rn progeny (218Po and 214Po) and 220Rn concentration indoors. It consists of four Makrofol-DE (polycarbonate) circular foils. Two are enclosed within two diffusion chambers—each one with a different filter membrane—to measure 222Rn and 222Rn+220Rn. The other two foils are kept in direct contact with air and are electrochemically etched at different conditions to obtain the 222Rn daughters. Theoretical sensitivities of each Makrofol-DE foil are calculated using Monte-Carlo technique. The calculations are performed taking into account: (1) the Bethe–Blochs expression for the stopping power of heavy charged particles in a medium, (2) the properties and behaviour of 222Rn, 220Rn and their progeny in the open air and within the diffusion chamber and (3) the etching conditions used to visualise α-particles tracks.

Fast neutron dosimetry with CR-39 using electrochemical etching

Abstract A Monte Carlo method is used in order to calculate the response (tracks⋯cm −2 ⋯ μSv −1 ) of a fast neutron dosemeter, composed of a polyethylene radiator and CR-39 plastic track detector, to monoenergetic neutron beams at normal incidence and taking into account the electrochemical etching conditions. The method is applied to neutrons having energies in the range 0.08–10 MeV. The total number of protons emerging from the radiator is calculated, as well as their energetic and angular distribution. Detection efficiency as a function of proton energy and angle is taken into account. The theoretical calculation is compared with experimental results obtained for Am-Li and Pu-Be sources for protonic equilibrium radiator thicknesses

Semi-automatic evaluation system for nuclear track detectors applied to radon measurements

Abstract A global semi-automatic evaluation system has been set up in our laboratory to scan and count etched tracks in both Makrofol-DE and LR-115 detectors. This methodology is, in principle, fully adaptable to any chemical and electrochemical etched track detector. The main advantage it offers is a considerable reduction of the counting time in comparison with the traditional methods using optical devices — microscope or microfiche reader depending on the track size — and a wide detectable range. In addition, it yields accurate, reliable and quite reproducible results. It has been used to measure the track density in both Makrofol-DE and LR-115 based radon and radon daughter detectors. A detailed description of this method is presented in this paper. Results from a comparison study between this system and ocular counting and from experimental calibration are presented as well. The correspondence between the results of the semi-automatic system and those obtained directly with ocular counting has been found to be rather good.

Application of SSNTD in nuclear physics and especially to the reaction 238U + Ag at 15 MeV/n

Abstract Reactions of 15 MeV/n 238 U on Ag have been studied by means of CR 39 detector. Analysis of 3 pronged events was done and classified as a function of impact parameter. For 4 and 5 pronged events, two and three steps mechanisms were found.

Indoor radon concentration measurements in some Spanish houses and dwellings with plastic nuclear track detectors

Abstract A passive dosemeter, based on Makrofol ED track detectors covered with aluminized Mylar, enclosed in the Karlsruhe diffussion chamber, has been used for radon concentration studies. Detectors have been irradiated, using a 241Am source, at different energies and fluences in order to obtain the electrochemical etching conditions that allow the optimum registration of alpha particles having energies over 3 MeV. Thirty dosemeters have been sent to the NRPB Radon Environmental Chamber for calibration. The sensitivity of the dosemeter has been calculated. Several dosemeters have, also, been exposed in houses and dwellings in the Barcelona and Madrid areas for monitoring. Values for radon concentration in the areas under study are presented.

Measurement of the 214Po concentration in air using Makrofol-DE detectors

Abstract The measurement of the 214 Po concentration in air with Makrofol-DE detectors is useful to estimate the long-term averaged equilibrium factors indoors. To differentiate α-particles emitted by 214 Po from those emitted by 218 Po and 222 Rn, the detector must register only α-particles with energies between 6.2 and 7.5 MeV. The required energy response is obtained only if a removed layer of about 43 μm is achieved in a chemical etching of the detector. The methodology used to determine the etching conditions is described in this paper. The optimum conditions found are: a) chemical etching for 6 h at a temperature of 40°C, using 7.5 M KOH mixed with 50% ethanol as an etchant, and b) electrochemical etching for 1 h at a frequency of 3 kHz and an electric field strength of ∼ 34 kV cm −1 . Several dosimeters have exposed during 2 months in dwellings located in the Barcelona area, Spain. A 214 Po averaged concentration of (13.6 ± 8.6) Bq m −3 was obtained.

High flux neutron production from 12C beams on heavy targets

Abstract Spallation neutrons produced from 12 C ions at 18 and 44 GeV on Cu and Pb targets were studied as well as thermalization in appropriate moderators. The irradiation were performed at the Dubna LHE Synchrophasotron. Results are given for thermal and fast neutrons estimated and compared with different experimental methods.

Calculation of range and energy loss of fast ions with Z ≥ 30 using a corrected Bethe-Bloch formula

Abstract The classical Bethe-Bloch formula is not fully applicable to fast ions with Z ≥ 30 due to the assumptions and approximations utilized in its deduction. Several corrections have been introduced in the Bethe-Bloch equation in order to extend the equation applicability to a wider range of ion charges and energies. A computer code that allows calculation of analytical ranges and energy losses of any fast heavy ion passing through any dielectric absorber, has been developed. A study of the behaviour of the different corrections introduced in the Bethe-Bloch formula has been performed using this code. Range results calculated with the program have been compared with experimental measurements of ranges of several ions with Z ≥ 30 of kinetic energy about 1 GeV/amu using etched track detectors exposed at the Berkeley Bevalac. It was found that discrepancies between the measured and our calculated ranges are of the order of 8%, whereas if the classical Bethe-Bloch expression is used these discrepancies are about 12%.