Recoil Separation from Targets

The recoil energy of an EVR is close to the energy of the compound nucleus. Let hi and Ahi be the energy (in MeV) and mass number of the heavy ion (projectile), while Ecn and Acn are the same quantities for the compound nucleus. Then, from the law of momentum conservation, it follows that 

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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. 

Direct searches for superheavy elements in the U+ U reaction were undertaken at the unilac by several groups. All these efforts remained without positive evidence. The data are summarized in Figure 13. The curve labeled chem [106] was obtained with off-line chemical separations [107] and an assay for a-and spontaneous fission activities here, the 10 picobam level was reached for half-lives between several days and years. Attempts to detect short-lived nuclides were less sensitive. The curve labeled gas holds for an on-line search [108] for components volatile at room temperature. wheel [106] refers to fission track detection in the unseparated product mixture deposited on a rotating catcher, rec [109] to implantation of recoil atoms in a surface barrier detector, and JET to on-line transport from target to detector with a gas jet [91,110],... 

Fission gas recoil. Another interesting example of recoil separation in the (n,fisslon) reaction is the separation technique for krypton fission products from a uranium foil target (202). The target, an enriched uranium film (0.3 mg/cm ) deposited on a 1.6-cm diameter platinum plate, was mounted as shown in Fig. 1 at one end of a vacuum-tight recoil chamber... 

There are good prospects for using some simpler dedicated modifications or varieties of the above separators to help future studies of TAE chemistry. Such equipment will mainly serve to separate the recoils from the projectiles to avoid the technical and principal problems due to the heat and ionization produced in the target chamber by the heavy ion beam. A broader spectrum of recoil energies is allowed and so also thicker targets. An ultimately efficient separation from the... 

Chapter 3 is devoted to step-by-step discussion of the history of a newborn radioactive nucleus, which is included in a molecule and then fed into a chromatographic column. It considers the production reaction, recoil-enhanced separation from the target, the conditions of thermalizing the recoils, halogenation and the transportation by gas or aerosol flow. Some non-trivial peculiarities of the delivery by aerosol flow are mentioned. 

This involves breaking of a covalent chemical bond when a radioactive atom, formed by neutron activation, recoils as a y ray is emitted. When the active hot atom formed is separated from the large excess of inactive target nuclei, its formation is demonstrated by its radioactivity. Separation is possible since the hot and die inactive nuclei are in different oxidation states. 

A schematic plan view of the new on-line separator located on beam line C is given in figure 2. The beam from the accelerator enters the He-jet recoil chamber through a thin Ni window (2mg/cm2), bombards the target and is then stopped in a beam-stopper composed mainly of iron, lead and polystyrene in order to prevent from both neutron and y background. 

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