Counter fission

Gas-filled detectors are used, for the most part, to measure alpha and beta particles, neutrons, and gamma rays. The detectors operate in the ionization, proportional, and G-M regions with an arrangement most sensitive to the type of radiation being measured. Neutron detectors utilize ionization chambers or proportional counters of appropriate design. Compensated ion chambers, BF3 counters, fission counters, and proton recoil counters are examples of neutron detectors. 

Geiger-Mueller tube proportional counter fission chamber b... 

Fig. 11.5. Diagram illustrating the components of an ESI source. A solution from a pump or the eluent from an HPLC is introduced through a narrow gage needle (approximately 150 pm i.d.). The voltage differential (4-5 kV) between the needle and the counter electrode causes the solution to form a fine spray of small charged droplets. At elevated flow rates (greater than a few pl/min up to 1 ml/min), the formation of droplets is assisted by a high velocity flow of N2 (pneumatically assisted ESI). Once formed, the droplets diminish in size due to evaporative processes and droplet fission resulting from coulombic repulsion (the so-called coulombic explosions ). The preformed ions in the droplets remain after complete evaporation of the solvent or are ejected from the droplet surface (ion evaporation) by the same forces of coulombic repulsion that cause droplet fission. The ions are transformed into the vacuum envelope of the instrument and to the mass analyzer(s) through the heated transfer tube, one or more skimmers and a series of lenses.

Neon is also used in scintillation counters, neutron fission counters, proportional counters, and ionization chambers for detection of charged particles. Its mixtures with bromine vapors or chlorine are used in Geiger tubes for counting nuclear particles. Helium-neon mixture is used in gas lasers. Some other applications of neon are in antifog devices, electrical current detectors, and lightning arrestors. The gas is also used in welding and preparative reactions. In preparative reactions it provides an inert atmosphere to shield the reaction from air contact. 

The fact that neutrons can be detected with reasonably high efficiency and with minimal interferences from other radiations permits the practical determination of fissionable species such as isotopes of uranium and thorium by delayed neutron counting. The known delayed neutron emitter precursors are all short lived and the irradiated samples are counted with 10BF3-filled proportional counters immediately after irradiation without any separation chemistry. 

Examinations of the same and of other lead-bearing samples for spontaneous fission events with large proportional counters in Dubna seemed to confirm these findings, but further measurements [37] of thin samples sandwiched between two plastic fission-track detectors showed that the events were background caused by cosmic-ray induced reactions of lead. Other groups [38] found no evidence for spontaneous fission activities in lead and other samples at a lower detection limit of 10" 3 g/g achieved with the sandwich technique. Even lower limits down to 10"17 g/g can be reached by etching... 

Fig. 6. Large neutron counter with 3He counting tubes for the detection of neutron bursts emitted in the spontaneous fission of superheavy nuclei. Reproduced from R.L. Macklin et al. [43], Copyright (2002), with permission from Elsevier Science.

Californium Assay dnd Analyses. Quality control for the californium feedstock is accomplished by measuring the neutron emission rate of an aliquot of the starting material and by performing analyses for isotopic content and chemical purity. Neutron emission rate is measured in a fission counter (9). Isotopic content is measured by mass spectrometry and chemical purity by spark source mass spectrometry. The completed assembly is leak tested, decontaminated, and assayed before packaging and shipping. 

Very similar, though rather less extensive, studies have been made of decomposition reactions of MnRe(C0)jg (15), Tc2(C0)iq (17), and Re2(C0)jg (13). All the kinetics are consistent with the rather stringent predictions of rate eq 9 for the homolytic fission mechanism and are totally inconsistent with a simple C0-dissociative mechanism. Other workers have studied substitution reactions of Mn2(CO)10 (18) and MnRe(CO)10 (19) and have commented, correctly, that their kinetic results are consistent with the dissociative reaction. This seems to have led to some doubts about the correctness of our conclusion that the reactions of all the decacarbonyls proceed mainly or totally via homolytic fission. These doubts do not arise from the kinetics because the kinetics observed by these workers (18, 19) are equally consistent with the homolytic fission mechanism or, indeed, virtually any first-order activation of the complexes. The conditions under which the reactions were followed were simply not those capable of leading to a kinetic distinction between the various mechanisms proposed. The absence of any homonuclear products of the reactions of MnRe(C0)jg was offered (19) as evidence against the homolytic fission mechanism. This point had been raised before (15, 17) when it was countered by emphasizing the absence of sufficient data on... 

The operation principle of pulse channel for measuring the coimt rate is based on the neutron registration by the detector of ionization fission chamber or neutron counter, pulse transmission from the detector via the communication lines to the preamplifier inlet and their following amplification, formation and processing by means of the auxiliary electronic equipment. 

The mixture is extracted with a counter-current of a solution of TBP in kerosene. Uranium and plutonium are extracted into kerosene as the complexes [U02(N03)2(tbp)2] and [Pu(N03)4(tbp)2], but the other nitrates, of metals such as the lanthanides and actinides beyond Pu, as well as fission products, do not form strong complexes with TBP and stay in the aqueous layer. 

Geiger counter (21.1) half-hfe (21.2) hydrogen bomb (21.4) isotopes (21.1) nuclear fission (21.3) nuclear fusion (21.4) nuclear radiation (21.1)... 

Diastereoselective Acetal Fission Followed by Benzylation (Step 2). Upon treatment with KHMDS and 18-crown-6 in THF at —78 °C, the acetal from the (/f,/ )-bis-sulfoxide is rapidly converted into the alkoxide having the (lS,2f ) configuration. The counter cation of the base is very important for high selectivity. Diastereoselectivity was seen to increase in the order LiHMDS (8% de) 96% de). 

The species extracted into the BLM phase is Pu(N03)4 2TBP(o> which is similar to that reported in the solvent extraction studies [30]. With increase in carrier concentration in the organic membrane, the increase in the amount of plutonium that could be extracted into the membrane is countered by the increase in the viscosity of the carrier solution. These opposing effects resulted in maximum plutonium permeation with about 30% TBP in dodecane [29]. More than 85% transport was observed in about 5 h when 5 mg/L solution of Pu in 2 M HNO3 was used as the feed. Selective transport of Pu(TV) over fission product contaminants, such as Ce-144, Ru-106, and Cs-137, was also observed. 

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