Velocity filter

In this experiment a week of target bombardment was required to produce a single fused nucleus. The team confirmed the existence of element 109 by four independent measurements. The newly formed atom recoiled from the target at predicted velocity and was separated from smaller, faster nuclei by a newly developed velocity filter. The time of flight to the detector and the striking energy were measured and found to match predicted values. 

In a sector instrument, which acts as a combined mass/velocity filter, this difference in forward velocity is used to effect a separation of normal and metastable mj" ions (see Chapter 24, Ion Optics of Magnetic/Electric-Sector Mass Spectrometers ). However, as discussed above, the velocity difference is of no consequence to the quadmpole instrument, which acts only as a mass filter, so the normal and metastable mj ions formed in the first field-free region (Figure 33.1) are not differentiated. 

Wien analyzer. A velocity filter with crossed homogeneous electric and magnetic fields for transmitting only ions of a fixed velocity. 

A filter that combines both a magnetic and electric field is the so-called Wien filter (or velocity filter). In this case, charged ions pass through a region characterized by uniform magnetic and electric fields at right angles to each other and to the direction of incident ions only those particles for which the module of the Lorentz... 

Gicquel, L. Y. M., P. Givi, F. A. Jaberi, and S. B. Pope (2002). Velocity filtered density function for large eddy simulation of turbulent flows. Physics of Fluids 14, 1196-1213. 

The Wien velocity filter possesses a high sensitivity and allows analysis over a mass range (using a high accelerating voltage V), but with increasing mass the mass resolution decreases.3 For his discovery Wien was honoured with the Nobel Prize in 1911. 

Figure 1.4 Schematic of a Wien velocity filter with EB configuration combination of electric ( ) and magnetic ( ) field (Wien, 1898). (C. Brunnee, Int. ). Mass. Spectrom. Ion Proc. 76, 125 (1987). Reproduced by permission of Elsevier.)...

In older instruments, a velocity filter placed before the magnetic field was used to eliminate v. This was done by combining two opposing forces created by an electric and magnetic field, which would only permit ions remaining on a central trajectory to exit the filter. 

Figure 15.7 Velocity filter SHIP. (Figure also appears in color figure section.)...

In 1981, G. Miinzenberg et al. (1981), working in Darmstadt at the velocity filter SHIP, identified the isotope 262Bh produced in the cold fusion reaction ... 

The mass analyzer works primarily as a velocity filter because the slope in the time-space diagram corresponds to the ion velocity. An ion moving on a line within the light gray and white areas will not be deflected and pass the analyzer, ions with other velocities will be subjected to an orthogonal electrical field and be deflected. Ions of different mass but equal energy are selected according to ... 

The identification of the first transuranium elements was by chemical means. In the early 1960s physical techniques were developed which allowed for detection of nuclei with lifetimes of less than one second at high sensitivity. A further improvement of the physical methods was obtained with the development of recoil separators and large area position sensitive detectors. As a prime example for such instruments, we will describe the velocity filter SHIP (Separator for Heavy-Ion reaction Products) and its detector system, which were developed at the UNILAC. The principle of separation and detection techniques used in the other laboratories is comparable. 

Velocity filter SHIP to separate transactinide fusion products from the projectile beam (reproduced with permission from G. Herrmann, An ew. Chem., Int. Ed. Engl., 1988, 27, 1422). 

Schnitzer and Anbar s experiments are rather similar to those of Baumann, Heinicke, Kaiser and Bethge Both employed plasma ion sources that employed by Schnitzer and Anbar was a hollow cathode duoplasmatron. Also, both used einzel lenses and momentum/charge analysis. But the different lifetimes of the doubly-charged negative ions studied dictated somewhat different analyses. Baumann, et al. used an electric deflection analysis after the magnetic sector, as already seen, whereas Schnitzer and Anbar employed a Wien velocity filter and einzel lens voltage variation prior to the magnetic sector. 

Extraction and acceleration of the negative ions from the duoplasmatron was accomplished with voltages of 5 to 15 kV. After passing through the einzel lens, the ions encounter a 30 cm Wien velocity filter. The ExB field of this filter allows analysis based only on the ion velocity according to... 

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