Catcher foil

The catcher foil can take the form of a jet of rapidly moving gas, a helium jet. The atoms produced in a nuclear reaction recoil out of a thin target and are stopped in — 1 atm of helium gas in the target chamber. The gas contains an aerosol, typically... 

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 gold "catcher" foil E was mounted on the end of rod F with Scotch tape. Rod F terminated in water-cooled aluminum blocks which served as a Faraday cup for beam measurement. 

The space between the target and the catcher foil was evacuated. 

At the end of bombardment, the Faraday cup rod was removed and the catcher foil torn off. The foil was dissolved in a few drops of 8 M hydrochloric acid containing a little nitric... 

In all nuclear reactions the product nucleus suffers a recoil, which may be marked if nucleons or a particles are emitted (chapter 9). Due to this recoil, a certain amount of the product nuclei are thrown out from the target and may be collected in catcher foils. Stacks of samples and thin monitor and catcher foils are used to obtain as many data as possible. 

The amount of Es available at this time was very small about N = 10 atoms (a 4- 10 g). At a flux density of a particles = 10 " cm s , a cross section (Ta n = 1 mb and an irradiation time of 10 s a yield N

single atoms, the recoil technique was applied (Fig. 14.6). Es was electrolytically deposited on a thin gold foil. The recoiling atoms of Md were sampled on a catcher foil. After irradiation, the catcher foil was dissolved and Md was separated on a cation-exchange resin. In 8 experiments 17 atoms of Md were detected and identified by their transmutation into the spontaneously fissioning the properties of which were known ... 

In these experiments, the recoil technique was modified into a double recoil technique by application of a moving belt (Fig. 14.7). The recoiling atoms generated by the heavy-ion reaction (first recoil) are deposited on the belt and transported along a catcher foil on which the recoiling atoms from a decay (second recoil) are collected. From the activity recorded as a function of the distance, the half-life can be calculated. 

A new technique was used that allowed the atoms of Md to recoil from the very thin target onto a "catcher" foil. Thirteen atoms of Md (ti 1.3 h) were made in 9 h of irradiation and isolated by rapid elution from a colunm of cation exchange resin using a solution of of-hydroxy isobutyric acid. The elution showed 5 atoms of element 101 (identified by the spontaneous fission of the daughter f m) and 8 atoms of the Fm daughter (Fig. 16.7 eqn. (16.10)). The recoil — ion exchange technique used in... 

Mass spectroscopy. In addition to radiochemical separations, in which the different isotopes of one element were isolated, mass separations can be carried out (De Laeter 1988). A sample is introduced into the ion source of a mass separator it is heated, vaporized, ionized, accelerated, separated, intercepted on a catcher foil, and counted. In some cases, the separated ions can be counted directly when the accelerated ions impinge on a detector. In mass separation one has the problem that the separation yield is not known, but one knows that this yield is identical for all isotopes of one element (as long as the precursors have decayed completely). Therefore, if one knows the fission yield of one nuclide, one can determine the fission yields of the other isotopes of this element. It is often possible to determine the same chain yield by identifying more than one isotope. These cases may be used to interrelate the separation yields of different elements. Finally, when sufficient yields are known, one... 

For the investigations on the release of foreign and lattice atoms by diffusion or evaporation from metals and alloys, the activated sample is placed into a vacuum chamber and the released radioactive atoms are collected by catcher foils. The activity of these foils is measured as a function of time at different sample temperatures. Data on the release of alloying elements from metallic compounds and alloys are required not only by solid state physics but also by high-tech industry and fusion technology. 

H FO has also been found satisfactory and hydrogen is the only gaseous product. Aluminum dissolves nicely in 6N NaOH, again with no gaseous products by hydrogen. This method of solution may be useful for aluminum catcher foils or as a preliminary to the solution of small targets clad in relatively large amounts of aluminum. 

Fig. 1 Schematic diagram from Piroda, 1955. The helium atoms (1) strike the gold target with Es-253 on the back side (2), recoiling product atoms are collected on the gold catcher foil (3), symbolically dissolved in crucible (4) and separated on a pre-calibrated ion-exchange column (5) and measured in the detection and recording system (6), and (7)...

Fig. 10.2. The total separation time was reported to be 8 min. The fast separation of berkelium from beryllium foil targets and gold catcher foils has been published [55].

As with Md, the physical separation of the nobelium atoms from the target material can be made using the recoil-atom catcher technique. It is preferable to combine this with the gas jet technique since the atoms are deposited on the catcher foil in nearly a monolayer and can be easily rinsed off the surface with dilute acid without complete dissolution of the foil. Isolation of the No from other actinides produced in the bombardment and from any target material transferred to the foil can be readily made using schemes based on the separation of divalent ions from trivalent ones, e.g. selective elution by solvent extraction chromatography using HDEHP as the stationary organic phase and 0.05 n HCl... 

For the very thin foils containing oxide, the correction technique is given in Appendix D. The correction is based on a direct measurement of the fission contribution to the neptunium peak. The measurement is made by comparing the pure fission activity of an aluminum catcher foil which was activated by recoil fission fragments from a source uranium metal foil with the combined neptunium and fission activity of the oxide foil. From the catcher foil activity, the ratio of fission activity in the neptunium peak region to that above 600 keV is determined, and as all 7 activity above 600 keV arises from fission products, a simple proportion equation yields the fission contribution to the neptunium peak. For metal foils or thick composition foils, an additional experiment for attenuation versus foil thickness is needed. 

The value of 6 can be readily obtained from the measurement of the fast-fission factor. Aluminum catcher foils in contact with uranium foils of two different enrichments will have different gross fission product activations, so that from a plot of gross activity versus enrichment the following factor "F" is determined from the equation... 

---