Recoil 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... 

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... 

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)...

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. 

True Np Activity. To determine the magnitude of the contribution of fission product activity to the Np peak, the special foil package of Fig. 12.5 is included for the irradiation. The enriched uranium metal foil is a source of recoil fission fragments which are captured by the aluminum catcher foil. In principle, the source uranium foil (1.46 a/o should... 

The target consists of thin Th metal strips sandwiched with thin A1 foils to act as catchers for the recoiled atoms during Irradiation. 

---