ABSTRACT
We investigate the capability of a fast-ion luminescent probe to operate as a pulse height ion energy analyzer. An existing high sensitivity system has been reconfigured as a single channel ion detector with an amplifier to give a bandwidth comparable to the phosphor response time. A digital pulse processing method has been developed to determine pulse heights from the detector signal so as to obtain time-resolved information on the ion energy distribution of the plasma ions lost to the wall of the TJ-II stellarator. Finally, the potential of this approach for magnetic confined fusion plasmas is evaluated by studying representative TJ-II discharges.
ABSTRACT
ZnO:Ga is a promising, high time resolution candidate for use as a fast-ion-loss detector in TJ-II. We compare its ionoluminescence with that of the standard fast-ion-loss detector material, SrGa(2)S(4):Eu (also known as TG-Green), when irradiated by H(+) ions with a range of energies E≤60 keV using a dedicated laboratory setup. It is found that ZnO:Ga is a reasonably good candidate for detecting low energy (E<60 keV) ions as it has excellent time resolution; however, its sensitivity is about 100 times lower than TG-Green, potentially limiting it to applications with high energy ion loss signals.
ABSTRACT
A mobile luminescent probe has been developed to detect fast ion losses and suprathermal ions escaping from the plasma of the TJ-II stellarator device. The priorities for its design have been flexibility for probe positioning, ease of maintenance, and detector sensitivity. It employs a coherent fiber bundle to relay, to the outside of the vacuum chamber, ionoluminescence images produced by the ions that impinge, after entering the detector head through a pinhole aperture, onto a screen of luminescent material. Ionoluminescence light detection is accomplished by a charge-coupled device camera and by a photomultiplier, both of which are optically coupled to the in-vacuum fiber bundle head by means of a standard optical setup. A detailed description of the detector, and the first results obtained when operated close to the plasma edge, are reported.
ABSTRACT
A systematic evaluation of activity concentrations of 3H, 63Ni and 14C by using the CIEMAT/NIST method has been carried out over time intervals of 4, 2.4 and 2.3 years, respectively. It proves that the CIEMAT/NIST method can compensate, with no need for additional checking sources or procedures, for count losses and quench parameter reduction in long-term measurements with LSC spectrometers and allows one to obtain very accurate activity concentration values by using a quench curve close to the nuclide measurements. If this requirement of the method is not fulfilled, significant discrepancies, up to 5.6% for 3H, 1.5% for 63Ni and 0.35% for 14C, can be obtained in only 1-year time difference.
ABSTRACT
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%.
ABSTRACT
The accepted value for the 49V half-life is either 330+/-15 days, based on a few old measurements with large dispersion, or 338+/-5 days, from a more recent measurement. Methods of study have included proportional counting and Nal X-ray detection. A new direct measurement of the 49V half-life has been carried out for over 2.5 half lives using liquid scintillation counting, as an additional contribution due to the scarce measurements of this radionuclide. A half-life value of 328.6+/-3.3 days was determined on the basis of an overall uncertainty analysis of 0.99%.
ABSTRACT
The nuclide 110Ag is a beta-gamma emitter with a very complex decay scheme, including more than 50 gamma-rays. It has been standardized by two methods: liquid scintillation counting (LSC) and 4pibeta(pc)-gamma coincidence measurements. In the LSC measurements the CIEMAT/NIST method was used, with 3H being used as a tracer for efficiency calculations. In the 4pibeta(pc)-gamma 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.
ABSTRACT
The stability of 110mAg samples for liquid scintillation measurements has been studied in four commercial scintillators: Insta-Gel Plus, Ultima-Gold, HiSafe II and HiSafe III. Samples using 15 ml of cocktail with four different levels of carrier, 0.0, 1.5, 3.0 and 6.0 microg of AgNO3, were prepared and their total count rate and spectral behaviour monitored for two months. Only samples in HiSafe III were completely stable for the full term studied.
ABSTRACT
Phosphor screens find application in many fields because of their ability to convert incident radiation to wavelengths that are readily measured by modern detectors. While the response of such screens in the X-ray region has been widely studied, much work still remains to be done regarding their response in the vacuum ultraviolet and soft X-ray regions, where the response is predicted to be non-linear owing to the presence of elemental absorption edges. Here, an experiment using synchrotron radiation to determine the response of thin Y(3)Al(5)O(12):Ce (1-21 mg cm(-2)) and Y(2)O(3):Eu (2.64 mg cm(-2)) powder phosphor screens in the spectral range 20-900 A (13.8-620 eV) is reported. Also, a custom-built camera is described which permits simultaneous collection of the forward- and backward-emitted light and that enables measurements to be made at various positions across the screens and at several screen/incident beam angles. Finally, features in the response spectra are identified, and efficiencies across the spectral range indicated for different screen thicknesses and operating modes are plotted, before a curve of the intrinsic radiant efficiency of Y(3)Al(5)O(12):Ce is produced. The results are discussed in the context of other measurements.
