Bechtold, V.

Brueckmann, H.

Finken, D.

Friedrich, L.

Hamdi, K.

Seitz, E.

English

KITopen

August 1970Institut für Experim.entelle KernphysikThe Energy Dependence of Charge Exchange ReactionsFavourably Us ed in Lam.bshift Type Ion SourcesV. Bechtol.d, H. Bz'ückrnann, D. Finken, L. F'r-iedi-i.ch ,K. Ham.di, E. SeitzKFK 1265H.---------- :-:-::--=--:--:KERNFORSCHUNGS ZENTRUM KARLSRUHEAugust 1970 KFK 1265Institut für Experimentelle Kernphysik*The energy dependence of charge exchange reactionsfavourably used in Lambshift type ion sourcesV.Bechtold, H.Brückmann, D.Finken, L~FriedrichK.Hamdi and E.SeitzGesellschaft für Kernforschung rn.b.H. Karlsruhe*contributed paper submitted to the"Third International Symposium onPolarization Phenomena in NuclearReac t Lons "Madison, Wisconsin 1970- 1 -AbstractIodine and argon can be favouraply used in Lambshift type ionsources for selective ionisation by charge exchange collisions.The energy dependence of the selectivity of these charge exchangecollisions has been measured by investigating the quenchingeffect and the nuclear tensor polarization. Both reactions showwith increasing energy the sqme monotonous decrease of theselectivity. For production of polarized deuterons at optimumconditions a Lamb-shift ion source is to be operatedbelow 1 keVbeam energy.In Lambshift-Typ Ionenquellen können Ladungsaustauschreaktionenmit Jod und Argon vorteilhaft für eine selektive Ionisation ver-wendet werden. Durch Messung des Quenchingeffektes und der Kern-tensorpolarisation wurde die Energieabhängigkeit der Selektivitätdieser Ladungsaustauschreaktion untersucht. Beide Reaktionenzeigen eine mit steigender Energie monoton abfallende Selektivität.Um optimale Bedingungen zu erreichen, sollte für Lambshift-Quellenfür polarisierte Deuteronenstrahlen eine Primärstrahlenergie unter-halb von 1 keV gewählt werden.~--~------------------------------ 2 -The method which takes advantage of the Lambshift and the 2S - 2Plevel crossing to polarize hydrogen ions is very weIl suitable toproduce either positively or negatively charged ion beams with ahigh phase space density. The procedure makes use of specificcharge exchange reactions to ionize the metastable H(2S) atomsselectively. One of the main features determining the applicabilityof such reactions for sources of polarized ions is the energydependence of the selectivity of these charge exchange processes.We have systematically investigated various reactions with theaspect to determine the selectivity for production of positivelyand negatively charged polarized hydrogen ion beams as a functionof beam energy. Some of the results of measurements with eitherargon or iodine will be discussed because just these two gasesseem to be practicable in polarized ion sources. The argon reactionwas firstly proposed for the production of negatively chargedbeams by Donnally et ale 1). Their measurements seem to exhibita maximum of the selectivity at 1 keV deuteron beam energy.Positively charged polarized beams were firstly achieved by usinghydrogen or helium as charge exchange partners 2). Lateronhalogens were found to be in advantage 3,4). L.D. Knutson hasmeasured 3) the selectivity and the relative cross section foriodine at specific iodine vapour pressures but without checkingthe nuclear polarization. Argon and iodine were investigated atthe Karlsruhe polarized ion source (A-LASKA) 5,6,7,8) by variingthe vapour pressure as weIl as the primary beam enerey.The selectivity is in general a function of the vapour pressurein the charge exchange cell as was shown in 5). This effect isdue to a superposition of secondary reactions and increases withincreasing vapour density. For a reliable comparison of differentreactions we have measured the dependence on the vapour density7,8) at each beam energy and have compared the selectivitiesextrapolated to zero vapour pressure. The quantity d = ~ is ameasure of the selectivity. d is defined as ratio of the twoslopes A and B at zero pressure. A is the slope of the I versusp curve in the case when the primary beam consists of metastableand groundstate atoms. B is the corresponding slope when all the- 3 -100r---=-------~50105d=A/B\\! ,,,\\ ,,,, ,,,....,'tl1 2 3 4 5DEUTERONENERGY (keV)Fig. 1 As a measure of the argon-selectivity the quantityd = AlB is plotted versus the deuteron energy. Thesolid line gives the quantity d extracted from ref. 1.i f33 j;uteronpolarization! -0.8~'H,'-0.6 +- ~ f, '- ,{-_-0.4II-0.2 ~I1 2 [keV]Fig. 2 The deuteron tensor polarization P3~ as a functionof the beam energy obtained by use öf iodine ascharge exchange partner.- 4 -metastable atoms are quenched to the ground state.d is plotted in fig. 1 in a logarithmic scale versus the beamenergy. The dashed line shows that d is decreasing strongly withincreasing energy. At somewhat different experimental conditionsearlier measurements have shown the same monotonous decrease of d inthe energy range between 1 and 5 keV (dashed line). These valuesare not directly comparable and hence not plotted in fig. 1. Forcomparison the quantity d was extracted from the measurements ofreference 1) and is shown as asolid curve in fig. 1 additionally.The selectivity does not seem to exhibit the peak reported at 1 keV.Lambshift type ion sources are also very suitable for theproduction of positively charged polarized beams 2,3,4,7,8). Halogencharge exchange partners are at the time the most promisingcandidates 3,4). Fig. 2 shows as an example the nuclear tensorpOlarization P33 versus beam enerbY which was obtained with thesame experimental set up by using iodine vapour to producepositively charged ions. Contrary to argon the halogens show aselectivity which is almost independent from the vapour pressure 7).Consequently one is able to measure the nuclear pOlarization at themaximum yield. P33 is decreasing monotonously with energy. Thisbehaviour seems to be a general feature which can be explainedqualitatively with the pseudo-crossing theory. The monotonousdecrease was also observed at all the other reactions investi-gated 8).From the measurements it can be concluded that the optimum energyto operate a Lambshift source will depend on the specific geometryused but will surely be in the range between a few 100 eV and 1 keV.- 5 -References1) B.L. Donnally, W. Sawyer,Phys .. Rev. Lett. 15 (1965), 4392) H. Brückmann, D. Finken, L. Friedrich,Phys. Lett. 29B (1969), 2233) L.D. Knutson,to be pub lished in Physical Review A24) H. Brückmann, D. Finken, L. Friedrich,(Nucl.lnstr. Meth in press.)5) H. Brückmann, D. Finken, L. Friedrich,Z.f. Physik 224 (1969), 4866) V. Bechtold, H. Brückmann, D. Finken, L. Friedrich,Z. f. Physik 231 (1970), 987) V. Bechtold, H.Brückmann, D. Finken, L. Friedrich,K. Hamdi, E. Seitz, P. ZieglerThe Karlsruhe polarized ion source,presented at the conference "Third International Symposium onPolarization Phenomena in Nuclear Reactions" Madison/Wisconsin1970 und KFK Report Nr. 12628) V. Bechtold, H. Brückmann, D. Finken, L. Friedrich,K. Hamdi, E. SeitzKFK Report Nr. 1256----------------------------------------------------------------------------------- ------------------------------------- ------------------------------------

The energy dependence of charge exchange reactions favourably used in Lambshift type ion sources

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The energy dependence of charge exchange reactions favourably used in Lambshift type ion sources

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