Radioactive ion source

The steady-state distribution is independent of the ionic concentration. However, the rate of approach to the steady state depends on the ionic concentrations and other properties of the system. The net result can be summarized as follows for the atmosphere. Ions are steadily generated by cosmic rays and radioactive decay processes. These attach to particle surfaces where they are neutralized at a rate equal to their rate of formation. The particle charge distribution is determined by the steady state relationship between particles separated by one charge. In the atmosphere, the equilibration process takes about 30 min. The rate of equilibration can be increased by increasing the ion concentration using a bipolar ion generator. Radioactive ion sources such as are often used in electrical aerosol instrumentation (Chapter 6). 

Ionization of a radioactive ion source and mobility characterization of ions 5... 

Despite the attractiveness of radioactive ion sources in IMS, use of Ni, Am, or T sources is discouraged today due mainly to regulatory issues as well as financial, organizational, and technical reasons. Radioactive sources require special permits and licensing procedures, and general licenses for alpha-emitting sources with appropriate... 

A variety of methods has been developed to produce ions nnder atmospheric pressure conditions that can be introduced into an IMS. Some of these methods are universal and can be employed for several applications, while others are limited to specific types of compounds (like surface ionization) or to certain types of samples (gaseous, liquid, or solid). Some require expensive and large systems (like MALDI), while others are particularly suitable for handheld devices (like the radioactive ion sources). Some are useful for studies of macromolecules, mainly of biological interest (like ESI and MALDI), while others can only be nsed to detect volatile... 

One of the large shibboleths in expanded use of mobility methods was the ever-present radioactive ion source, and this pattern of design and nse of IMS is changed. The... 

PTR-TOF-MS An alternative mass analyzer is the TOF-MS.The first PTR-TOF-MS instrument with a radioactive ion source was developed by Blake et al. in 2004 [14]. PTR-TOF-MS instrument with a hollow cathode ion source has been reported [15], and its schematic drawing is shown in Figure 28.5. TOF-MS can simultaneously collect the entire mass spectrum, and consequently, PTR-TOF-MS has a potential for rapid and selective online detection of trace components. In combination with a high-resolution TOF-MS, PTR-TOF-MS can provide more precise molecular weight information, and therefore, isobars can be identified. 

Figure 3.9 Diagram of a radioactive ion source and drift tube. The radioactive source is a thin metallic strip impregnated with which delivers a particles. The a particles interact with...

A further important property of the two instruments concerns the nature of any ion sources used with them. Magnetic-sector instruments work best with a continuous ion beam produced with an electron ionization or chemical ionization source. Sources that produce pulses of ions, such as with laser desorption or radioactive (Californium) sources, are not compatible with the need for a continuous beam. However, these pulsed sources are ideal for the TOF analyzer because, in such a system, ions of all m/z values must begin their flight to the ion detector at the same instant in... 

Static eliminating devices that ionize the atmosphere around the device are available. Static eliminators are divided into two main groups silent (corona) discharge eliminators, such as inductive eliminators, or high voltage eliminators which initiate an impact ionization of the air by applying strong electrostatic fields, and radioactive eliminators that provide a multitude of ions from independent ion sources (9). 

Purification of the radioactive tracer was modified to include a fractional sublimation before a single extraction—recrystallization cycle to conserve the tracer material. Microgram samples were prepared in melting point capillaries for assay by mass spectroscopic analysis (Table III), made by direct probe injection of the sample into the ion source (18). The probe was heated rapidly to 200°C, and mass spectra were obtained during vaporization of the sample. Tri-, tetra-, and pentachlorodibenzo-p-dioxins vaporized simultaneously with no observed fractionation. 

The use of radioactive ionization sources in areas subject to explosion or fire is undesirable because of the potential for area contamination with radioactive material which could be disseminated in the event of an explosion or fire. With proper precautions, however, electrical ionizing systems can be safely and effectively utilized while processing electrostatically sensitive energetic materials. Ions are generated electrically by corona discharge... 

Personnel working in some programs at the Los Alamos National Laboratory (LANL) may handle radioactive materials that, under certain circumstances, could be taken into the body. Employees are monitored for such intakes through a series of routine and special bioassay measurements. One such measurement involves a thermal ionization mass spectrometer. In this technique, the metals in a sample are electroplated onto a rhenium filament. This filament is inserted into the ion source of the mass spectrometer and a current is passed through it. The ions of the plutonium isotopes are thus formed and then accelerated through the magnetic held. The number of ions of each isotope are counted and the amount of Pu-239 in the original sample calculated by comparison to a standard. 

As explained above, the continuous radioactive source used in our IMS also produces small, and sometimes troublesome, amounts of impurities within the ion source. In an effort to eliminate this problem, we are presently exploring the use of other source designs by which less radiation damage is done to the source gas. One of these alternative ionization methods is based on the photoemission of electrons from the back side of a gold foil. This ion source offers an attractive advantage for the study of negative IM reactions in that it can be shut off during most of the IMS duty cycle. 

The study of the 0 decay of 0.59s 145Cs was conducted at the TRISTAN mass separator on-line to the high flux reactor at BNL. A detailed description of the TRISTAN facility can be found in reference [GIL81]. The radioactive samples were produced by fissioning a uranium target integrated in a positive surface ionization source.[PI084] In this experiment, the usual Re surface ionizer was replaced with a Ta ionizer. The lower work function of Ta ensured no independent production of Ba from the ion source at a low power operation ( 1200°C). 

The use of a 3He++ beam of 303 MeV/amu has already been mentioned as an advantage in certain cases, especially for nuclei far from stability. Such a beam is also advantageous in that it produces less induced radioactivity in the SC vault. However, the 3He++ beam has not so far been produced with sufficient intensity to make its frequent use an interesting proposition compared to 600 MeV protons. Improvements have been made to the r.f. system and to the SC s ion source which should now permit an intensity gain of a factor 3 or 4 to be achieved, but so far this has not been tested. If the 3He++ intensity rises to the proton intensity (i.e. > 1013 ions/sec), this beam could become the preferred Isolde production beam of the future. 

A solid or liquid sample can be introduced to the analyzer by thermal desorption. The resultant vapors are swept through the inlet by the carrier gas and ionized by a radioactive 63Ni source. Discreet packets of ions are then pulsed down the flight tube under a controlled potential. The arrival of the ions at the detector is inversely proportional to the mass of the molecule. Thus, the smaller ions arrive at the detector first, and the larger ions arrive later. At that point the signal is amplified and read out via an appropriate computer interface. Both commercially available instruments are capable of generation and detection of both positive and negative ions. 

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