Miguel Roteta

α-particle emission probabilities in the decay of 235U

235U decays by α-particle emission to 231Th. The decay scheme of this nuclide is very complex, with more than 20 alpha branches. Recommended values for Pα of this nuclide are based on measurements carried out in 1975. This work presents the results of new measurements made with Si detectors and sources of enriched uranium in the frame of the EUROMET 591 cooperation project. The use of improved measurement techniques and numerical analysis of spectra allowed a new set of Pα values for 13 lines with improved uncertainties to be obtained.

Standardization of 134Cs by three methods.

The nuclide 34Cs decays by beta-emission followed by gamma-deexcitation to 134Ba with a half-life T(1/2) = 2.065 a. It has been standardized by three methods: liquid scintillation counting (LSC), 4pi beta-gamma coincidence counting and 4pi gamma counting. In the LSC measurements, the CIEMAT/NIST method was used to calculate the efficiency. For the coincidence measurements, a conventional 4pi beta (proportional counter)-gamma(NaI) system was used. For the 4pi gamma standardization, a well-type Nal(Tl) detector was modeled with the Monte Carlo package PENELOPE, and the counting efficiency obtained by calculation. Results of the three methods agree within 0.65%.

An evaluation of the influence of γ—γ angular correlation on the coincidence-summing corrections in γ-ray spectrometry

Abstract The effect of angular correlation on coincidence-summing corrections has been evaluated for three detectors (planar Ge, coaxial Ge and well NaI), at different measurement geometries and for some selected radionuclides. For the detectors and nuclides studied, it can be concluded that the effect of angular correlation on coincidence-summing corrections can be neglected if the radioactive source is measured either in contact with the detector or at large distances.

Standardization of 110mAg by liquid scintillation and 4πβ–γ coincidence counting

Abstract The nuclide 110m Ag is a β–γ emitter with a very complex decay scheme, including more than 50 γ-rays. It has been standardized by two methods: liquid scintillation counting (LSC) and 4πβ(pc)-γ coincidence measurements. In the LSC measurements the CIEMAT/NIST method was used, with 3 H being used as a tracer for efficiency calculations. In the 4πβ(pc)-γ standardization, Monte Carlo calculations have been made to determine the optimal measurement conditions. Results obtained with both methods for the activity concentration of the solution are in good agreement.

Point source preparation by polypyrrole-based conductive thin film production and radionuclide labelling

Abstract A new method for radioactive point source preparation by radiolabelling of polypyrrole-based conductive thin films is presented. First, the polypyrrole is prepared onto an ITO glass in an electrolytic cell and then the radioactive material is incorporated locally into a small area as a droplet in which electrochemically activated redox reactions are induced, resulting in a strong, chemical bond of radioactive ions to the functional groups of the prrrolic conductive surface. This procedure leads to radiolabelling yields greater than 98% and sources with very low self-absorption and 10% or 17% better energy resolution than VYNS or electrodeposited conventional sources.

Standardisation and precise determination of the half-life of (44)Sc.

The half-life of the positron-emitter (44)Sc has been determined by following the decay rate with two measurement systems; an Ionisation Chamber and a HPGe detector. The combination of seven results gives a value of T1/2=4.042 (25)h, about 2% higher than the recommended value of T1/2=3.97 (4)h (Browne, 2011) and with a lower uncertainty. This radionuclide has also been standardised by coincidence counting, and liquid scintillation counting techniques. A (44)Ti/(44)Sc generator developed at CIEMAT was used to obtain the (44)Sc solutions used in all measurements.

Measurement of the half-life of 68Ga

The half-life of the positron-emitter (68)Ga has been measured by following the decay rate with two systems based on ionization chamber and Ge detectors. The decay rate was measured for periods of time up to 10 half-lives. The combination of the 6 results obtained with both systems gives a value of T1/2=67.845(18) min, in good agreement with recommended data and with an uncertainty lower than any other previously reported value.

Preparation and characterisation of a (226)Ra spiked slag as reference material for radioactive control of steelworks.

One of the issues of the European Research Project MetroMetal is to develop reference materials in order to provide SI-traceable radioactivity monitoring in foundries. For this purpose, a protocol for preparing a set of identical standard slag samples, containing known activity concentrations of (226)Ra, has been developed. This paper describes the preparation of the raw material, the characterisation in terms of its mineralogical, chemical and radiological features, the spiking procedure and the homogeneity testing of the spiked samples.

Standardization of Ga-68 by coincidence measurements, liquid scintillation counting and 4πγ counting.

The radionuclide (68)Ga is one of the few positron emitters that can be prepared in-house without the use of a cyclotron. It disintegrates to the ground state of (68)Zn partially by positron emission (89.1%) with a maximum energy of 1899.1 keV, and partially by electron capture (10.9%). This nuclide has been standardized in the frame of a cooperation project between the Radionuclide Metrology laboratories from CIEMAT (Spain) and CNEA (Argentina). Measurements involved several techniques: 4πβ-γ coincidences, integral gamma counting and Liquid Scintillation Counting using the triple to double coincidence ratio and the CIEMAT/NIST methods. Given the short half-life of the radionuclide assayed, a direct comparison between results from both laboratories was excluded and a comparison of experimental efficiencies of similar NaI detectors was used instead.

Standardization of Sn-113.

The radionuclide (113)Sn is a quasi-monoenergetic gamma emitter often used in the efficiency calibration of gamma spectrometers in the energy region around 390keV. This paper presents the results of the standardization of this radionuclide by three methods: integral (4π-γ) counting with a well-type NaI(Tl) detector, liquid scintillation counting applying the CIEMAT-NIST method and 4π coincidence counting (conversion electron-X) with a digital coincidence system.