MEASUREMENT OF THE n=2 DENSITY OPERATOR FOR HYDROGEN ATOMS PRODUCED BY PASSING THROUGH THIN CARBON TARGETS Gerald Gabrielse, H. Berry

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Gerald Gabrielse, H. Berry. MEASUREMENT OF THE n=2 DENSITY OPERATOR FOR HYDRO- GEN ATOMS PRODUCED BY PASSING PROTONS THROUGH THIN CARBON TARGETS. Journal de Physique Colloques, 1979, 40 (C1), pp.C1-338-C1-339. ￿10.1051/jphyscol:1979172￿. ￿jpa- 00218452￿

HAL Id: jpa-00218452 https://hal.archives-ouvertes.fr/jpa-00218452 Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE CofIoque C1, suppl6rnent au no 2, Tome 40, fkvrier 1979, page Cl-338

MEASUREMENT OF THE n3DENSITY OPERATOR FOR HYDROGEN ATOMS PRODUCEDBY PASSING PROTONSTHROUGH THIN CARBON TARGETS* ** Gerald Gabrielse and H. G. Berry Department of , , Chicago, Illinois 60637 and Argonne National Laboratory, Argonne, Illinois 60439, U.S. A.

R6sum6. Nous avons mesurd les 616ments de la matrice d'excitation de 1'6tat n=2 de Ithydro- gPne aprss passage 2 travers une cible mince de carbone aux Bnergies comprises entre 20 et 1000 KeV par nucldon.

Abstract. We report measurements of the n=2 densify operator and the probability for n=2 production, for hydrogen atoms produced by passing 20 to 1000 keV protons through thin carbon targets.

A beam, collimated by a 3/16" collimator, the beam direction. The field plate assembly was then passed through a grid used to monitor the beam current and stepped up beam by approximately .ll mm, and the Ly a then passed a second foil which was 1/4" in diameter. The intensity measurements repeated. grid sampled only the beam which would pass through the second foil, since the collimator was smaller than foil 2. The alignment of collimators and foils was verified by a darkened grid pattern which could be seen centered on foil 2 when it was held up to a light following a run. The second foil was mounted upon a stainless steel '.*, I field plate which measured 4"x 2" and was machined to a 3- - \ tolerance of ,002". Two similar 1/8" stainless plates, con- - - taining 3/8" holes to pass the beam,were mounted down- 2 beam from the foil plate using 3/4' long plexiglass spacers . % located near the four corners of the plates. The foil plate , - was grounde&and a voltage applied to the second and third plates via two resistors. The sole purpose of the third Z plate was to minimize the fringing field due to the hole in the second plate. We were able to reverse kilovolt poten- tials with a time constant of microseconds, and a digital voltmeter continuously monitored the potential difference , 15 between the foil plate and plate 2. We used electric DISTANCE FROM FOIL (mm) fields of 140 and 250 volfs/cm. l'""l""l""'"'a~"l We measured the intensity of Lyman a photons emitted perpendicular to the beam axis,between the foil plate and field plate 2. More piecisely, we measured the number of Ly a photons which passed through two vertical slits of width to allow a usable count rate and so that the high frequency fine structure interference oscillations wouM be irveraged out, leaving only the Lamb shift inter-

ference oscillations as modified by the electric field. An .TIME AFTER EXCITATION (ns) EMR photomultiplier (model 541F-08-18) with a cesium' Fig. 1. Unpolaized Ly a radiation intensity as a function telluride pholocathode detected the 1215 h Ly a photons of distance and time from the foil surface as observedduring a measurement. with a quantum efficiency of about 5%. A Ly a intensity measurement was made with an We measured the movement of the foil caused electric field parallel, I(F,t), and antiparallel, I(-F,t), to by the ion beam and the electric fields we applied, by

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979172 reflecting a laser beam from the foil's surface ontoascreen The results were fit directly to four of these five We found that reversing our electric fields changed the foil parameters using a non-linear least squares fitting progam position by less than .04 mm, (about .4 of a channel). The which is detailed elsewhere.' Included in this analysis ion beam moved the foil surface downbeam from the beam- are the finite time-resolution of the observing system, the off position by less than .16 mm. Although this limit is hyperfine structure of the transition and affects of cascad- nearly 2 channels, we measured the foil position automat- ing. The alignment of the 2p state as defined by the ratio ically during every run and hence were insensitive to small of the density mairix components ppO and p was taken beam-induced displacements, P' from the measurements of Winter and ~ukow.2 The final The hydrogen n=2 density operator has 16 inde- results, consisting of average values of many measurements, pendent components in general, assuming unpolarized spins. for the five density matrix components are shawn in Fig. 2. The axial symmetry of the beam-foil interaction about the beam direction (taken to be the positive 9 axis) requires that average values of all but the q=O tensor components be We choose to show Fig. 2 in units of inverse veloc- zero. The reflection symmetry of the interaction in all ity because any molecular phenomena would depend upon planes which contain the beam axis, requires that the non- the time spent near the foil surface and, if present, would vanishing components be average values of tensas which thus be periodic in l/v. The density matrix elements we transform identically under parity transformations and rota- plot are proportional to the tensor components of thedensity tion of 180° about ?. As a result, the proton-target inter- operator except for p2p0 and p We plot these matrix 2pl' action produces a n=2 density operator for t=O, which has elements rather than tensor components, because p is 2~1 ody the 5 non-zero components. nearly constant over the measured energy range. The other ATOMIC K INETlC ENERGY (MeV) striking feature of the measured density operator is the in- creased relative probability of 2s excitation at the highest energies. The vector components, pR and p1 indicate SPO spo' that the bound leads the proton and is moving faster, consistent with conclusions based upon earlier more qualitative measurements.

References * Work supported in part by the U. S. Department of Energy and National Science Fbundation. * * Present address: Department of Physics, FM-15, Univer- sity of Washington, Seattle, Washington 98195.

1. G. Gabrielse, Ph.D. Thea's, to be published. 2. H. Winter and H. Bukow, Z. Physik, 277, 27 (1 976). 3. A. Gaupp, H. Andr6,and J. Macek, Phys. Rev. Lett. -32, 268 (1 974).

INVERSE ATOM VELOCITY (a.~:'). Fig. 2. The n4density matrix elements, normalized to unit probability for ~2 production, as functions of inverse velocity of the hydrogen atans.