Detector Mica fission track

For long-lived y-active nuclides obtained with sufficient yield, which is the case for lighter homologs of TAEs, the profiles can be revealed by spectrometric measurements from outside the column. The profiles of short-lived a-activities can be measured only when the column is a channel formed by surfaces of electronic particle detectors. Such measurements are done in real time of course, they also work well for s.f. nuclides. The latter can also be registered in open columns made of the materials which can serve as solid-state track detectors of fission fragments (fused silica, mica) see Sect. 1.2.2. 

The situation becomes much more complicated when the radionuclides used undergo a decay or spontaneous fission, i.e., if non-penetrating radiation needs to be detected. If these radionuclides are long-lived, the colunm is cut into small sections, the substances adsorbed on its inner surface are washed off with appropriate solutions, and the resulting solutions are analyzed. In the case of short-lived radionuclides, e.g., transactinide elements, semiconductor or track detectors (mica, quartz) placed inside the column are used. They allow single decays to be determined at each point of the column. In principle, other methods may be used to determine the distribution of substances in the column, e.g., photospectrometry and X-ray fluorescence. 

Behind the column, mica solid-state detectors were positioned. They were kept at lower temperatures in order to adsorb the RfCl4 molecules. It was assumed that the produced isotopes of Rf decay at least partly by spontaneous fission. Mica is known to be well suited for identification of latent fission tracks. In a series of experiments that accumulated a total beam dose of 4 x 10 beam particles 65 fission tracks were detected along the mica detectors. These fission events were assigned to a spontaneously fissioning isotope of Rf, presumably Rf. Later, this assignment was questioned since additional measurements proved that this isotope has a half-life of only 20 ms, too short for a chemical study. It was therefore concluded that Rf with a half-life of 3 s and an assumed small fission branch was the isotope that labeled the separated molecule. 

The detection techniques applied in those early attempts were often surprisingly simple searches for spontaneous fission activities. The whole product mixture was collected on a catcher foil and exposed to mica, glass or polymer sheets to produce tracks of spontaneous fission events. By quickly rotating the catcher between detector foils during bombardment, this technique allows the detection of short-lived nuclides down to millisecond half-lives [88],... 

The fact that mica (and fused silica) can serve as solid state track detector (SSTD) of fission fragments was reported shortly before the final stage of development of the method for element 104 [12-14], In the dielectric solids, fission fragments produce tiny tracks visible by electron microscopy. Mica and silica are very resistant to active chemical reagents and elevated temperatures. The tracks proved to stay in hostile conditions of real experiments for a reasonably long time. Thanks to this, after the end of bombardment (EOB), the mica sheets could be etched with hydrofluoric acid to enlarge the tracks to micrometer size they were distinct in appearance and were searched out by scanning the surface of the detectors with an... 

In addition to NAA, neutrons are widely used in prompt radiation analysis for the determination of concentration and spatial distribution of elements in different matrices. For example, a track-etched detector (LR-115, Makrofol KG, CR 39, mica) placed on the polished surface of a sample is irradiated with fast or thermal neutrons then etched with a suitable chemical to deduce the concentration profiles from the track distributions. This method can also be used for the detection of suspended and dissolved U, Th, and Pu in water by (n,f) reactions N in polymers by the N(n,p) C reaction B and Li in semiconductors or glasses by the B(n,a) Li and Li(n,ot) H reactions, respectively. For the detection of fission fragments the use of mica is recommended. 

During the experimental studies of chemical properties of transactinides early approaches exploited the possibility to detect spontaneous fission in thermochromatographic columns by mica or quartz track detectors at temperatures below 400°C, while more modern setups employ Si detectors to register a decay or spontaneous fission at room temperature and below (liquid nitrogen). Then, the technique, however, is limited to the study of highly volatile atoms or compounds. 

---