Measurement of the analysing powers iT11, T20, T21 and T22 in elastic deuteron-proton scattering

Nuclear Physics A180 (1972) 593-599; Not to be reproduced by photoprint

MEASUREMENT

@ North-Hoiland Pablishi~g Co., Amsterdam

or microfilm without written permission from the publisher

OF THE ANALYSING POWERS

ik, T2i,, T21 AND T22 IN ELASTIC DEUTERON-PROTON SCATTERING R. E. WHITE?, W. GKOEEILER, V. KGNIG, R. RISLER, A. RUH, P. A. SCHMELZBACH and P. MARMIER Laboratorium,fiir Kernpbysik, Eidg. Technische Hochschule, Zirrch, Switzerland Received

17 May

1971

Abstract: The analysing powers iTli, TzO, T,, and T,, for the elastic scattering of polarized deutetons

by protons have been measured at deuteron energies of 6,8,10 and 11.5 MeV with the polarized deuteron beam from a tandem accelerator. The measurements cover the c.m. angular range from 40” to 155” and show small but non-zero analysing powers at all energies. E

NUCLEAR

REACTIONS

H(d, d), Ed = 6, 8, 10, 11.5 MeV; measured ~2oV3),

TzI(@,

iT,,(@),

Td@.

1. Introduction

The presence of spin-dependent effects in nucleon-deuteron scattering at low energies is now well established. Accurate measurements of the analysing power iT,, for the scattering of polarized protons by deuterons (p-d scattering) are available for O-20 MeV protons. Measurements of iT,, for n-d scattering and for d-p scattering have also been made in this range but at fewer energies. These measurements have recently been reviewed by Haeberli “), while further results are given in refs. ‘*‘). Small but non-zero values are found for all iiri 1, usually less than 10 p/, and positive in all cases. By comparison, very little is known about the analysing powers T,, , Tzl and Tz2 in d-p scattering. Apart from angular distributions for T,, and T,,measured by scattering 21.7 MeV polarized deuterons from protons, the data at low energies are scattered and have large uncertainties ‘). Some recent measurements of iT,, , T,, and T,,at 12.2 MeV from 100” to 155” made by Griffith et al. at the University of Birmingham are reported in a review article in ref. “). The subject of nucleon-deuteron scattering has also been extensively reviewed recently ‘*“). Most calculations to date have not included spin-dependent effects and phase-shift analyses have in general assumed unsplit phases. This is largely a result of the complexity involved in a full treatment of this system and the Iimited range of t On leave from Physics Department,

University of Auckland, Private Bag, Auckland, New Zea-

land. 593

594

R. E. WHITE et al.

parameters

studied experimentally.

hope of providing

a suitable

The present measurements

experimental

were undertaken

basis for a complete

phase-shift

in the analysis.

2. Method The method used to evaluate the analysing powers has been described in detail previously ’ - ‘). It should be noted that the formulae and results in those papers were given in terms of tensor moments (T,,) while the present results are for analysing powers Tkqdefined according to the Madison Convention “). With the definitions used in refs. 5-7) one finds that all the Tkqequal the corresponding (T,,)except that T21

=

-CT,,).

Briefly, the measurement of a chosen T,,at a particular angle ~9is made by first choosing a suitable orientation for the beam spin alignment axis s. Data are recorded for two states of beam polarization, positive and negative for a tensor polarized beam or polarized and unpolarized for a vector polarized beam, and by using pairs of detectors, at 0 and - 8. By suitably combining the yields for 0 and - 0 and the two beam polarization states it is then possible to evaluate the Tkqwithout knowledge of the cross section for an unpolariked beam. Also the combinations of yields used are chosen to minimise errors in the Tkqdue to uncertainties in the orientation of s or due to differences in the 8 and - 0, or left and right detector geometry.

3. Experimental

procedure

A polarized beam “) from the ETH Tandem accelerator was used to bombard a hydrogen-gas target. For most of the measurements the target was cylindrical, 16 mm in diameter, with 2.5 pm Havar windows and was operated at 1.5 atm pressure. For measurements at angles forward of 20” lab a special target cell with entrance and exit windows 30 mm from the target centre was used with 2.5 ,um Havar windows. Here the pressure was 0.8 atm. Scattered deuterons and recoil protons were recorded in eight solid state detectors arranged in pairs to the left and right of the beam at four scattering angles “). To measure a chosen T,,the desired direction of s was set using a Wien filter. The beam polarization was switched automatically between the two desired states, following the accumulations of a preselected integrated beam charge, by switching on and off the appropriate r.f. transition unit. The switching interval was 5 to 10 sec. Particles were accepted in an angular interval of +0.5” lab, the detector collimation being similar to that described in ref. “). For measurements at angles less than 20’ the vertical extent of the detector window was restricted so that a range of azimuthal angle equal to that allowed at 20” was maintained. This range gives negligible errors in the measured Tkq. The beam was collimated by 2 mm circular apertures and was generally 0.2 to 0.5 nA. The beam polarization was in all cases calibrated by scattering from 4He using values of the analysing powers previously measured at the ETH

ANALYSXNG

595

POWERS

‘*6

but reduced by a factor of 0.92. This factor is based on the results of recent measurements made here “) using the ‘%(d, cc1)r4N* reaction for which is known absolutely lo), and is in agreement with the results of similar measurements made elsewhere “1. Several difficulties arise in these measurements associated with the laboratory kinematics of the scattering as can be seen from fig. 1. After scattering, the deuterons are confined to a 30” cone and their energy varies quite rapidly with angle. For each angle two deuteron energies are possible. The low-energy deuterons were not observed

E2ute ‘k T,, 20

Fig. 1. Kinematics

of elastic deuteron-proton

scattering.

in the measurements presented here and the corresponding cm. angular range was covered by recording the recoil protons which emerge between 0” and 90”. Below 25” the deuterons and the protons have very similar energies at a given angle and special measures were required to separate them. Initially this was achieved by operating the detectors at such a bias that only the deuterons stop in the depletion layer so that the proton group appears at a much reduced pulse height. This method was successful but at the very low biases required, both the pulse height and resolution deteriorated. As a result the separation of the groups was not always as complete as desired and the background was at times as high as 30 % rather than the more normal value of 10 % or less. In later measurements the separation was achieved by reducing the deuteron energy sufficiently with aluminium foils so that the deuteron groups lay below the proton group. This method yielded better spectra with lower backgrounds. Results from the two methods agree excellently. This reflects the fact that when the Tk4are small the values obtained for the T,,are

R. E. WHITE

596

at al.

not very sensitive to the details of the background treatment as long as the spectra from a given detector for the two beam polarization states are treated in the same way. The backgrounds in a given detector for the two states were observed to be very similar or identical as would be expected since switching of the polarization state occurs while the beam is still neutral and in a region well removed from focussing and collimating elements. Since for small T,, the yield ratios used in their evaluation are very near unity, subtraction of these very similar backgrounds in numerator and denominator changes the ratios and the associated Tkqvery little, normally considerably less than the s~tisti~l error in the Tkq. 0’

30*

60.

’

’

-

,

I

I

0”

30°

6Q0

90°

0,05--

-0,05

so’

120°

150*

ISOb’

30’

SO’

0’

30’

60’

SO’

i2O0

150.

180”

90°

120”

150’

180’

6,OdMeV

/

21,7 MeV

/

OCTI

BClll

Fig. 2. Tensor analysing powers iT 11 and TzO for elastic deuteron-proton scattering. Open circles show points at which deuterons were recorded. The dots represent measurements in which the recoil protons were detected. Crosses refer to 12.2 MeV data of ref. 2). The data at 21.7 MeV is from ref. 16).

ANALYSING

POWERS

597

6,Ob MeV o,05 1

t

t’

0'

30.

SO'

90'

120.

1’ ’ ’ ’ i 8,00 MeV

1

I

I

I

Il.50 MeV

QO5

21,7 MeV

'50* 0,05

Bcm

/

0,05

qo5

1

t

40

T22Q0 -905

T22

-0,005 0'

30'

60'

90'

120.

150' SO'

Bern

Fig. 3. Tensor analysing powers T11 and Tzz for elastic deuteron-proton scattering. Open circles show points at which deuterons were recorded. The dots represent measurements in which the recoil protons were detected. Crosses refer to 12.2 MeV data of ref. 2). The data at 21.7 MeV is from ref. 16).

In order to compare these two methods and oheck the initial measurements, most points in the angular range 20” to 25” lab were measured twice or in some cases three times. The agreement was excellent in almost all cases. 4. Results The results are shown in figs. 2 and 3. Solid dots indicate points where recoil protons were recorded while open circles correspond to scattered deuterons. Errors shown are statistical only. The accuracy claimed for some points is quite high but several factors apart from the reproducibility of the results support the correctness of these errors. We have examined other possible sources of error carefully and find that errors due to uncertainties of a few degrees in the orientation of s [refs. 5P‘)I are

598

R. E. WHITE

et al.

negligible compared to the statistical errors. The same applies to errors due to a 5 7: difference in the detector geometry for 0 and -8. The observed detector yields for 8 and - 0 with an unpolarized beam differed by less than this amount. As stated above, the problem of background treatment for such small Tkq is not as serious as might be expected. In cases where the background was unusually large, the points were often rejected. Finally, errors due to finite detector geometry are also negligible with such small Tkq and their relatively slow angular variations. Uncertainties in the beam polarization, whose value was checked every 12 h at least, could produce changes in the maximum values of the Tkq of at most kO.003. It,is also possible to apply certain checks to the data which can indicate poor background treatment or similar errors. These consist of forming appropriate ratios of the left and right detector yields for the two polarization states. These ratios should equal unity within the statistical uncertainty of the data. In the case of T,, , for example, this ratio is (L( +)+R( -))/(L( -)+R( +)), where L( +) indicates the left or + 8 detector yield for a positive beam polarization. For T,, such a check is not reliable since the appropriate ratio is (L( + )+L( -))/R( + )+ R( -)) and a difference in detector geometry or in the background treatment left and right will cause a departure from unity. Such checks were applied wherever possible and were satisfied in 79:4 of the cases considered. Points which violated these checks badly were often not consistent with the trend of the data and were rejected.

5. Discussion Few measurements of the deuteron analysing powers are available for comparison with the present results. However measurements of iT,, at 8 MeV [ref. “)I agree within statistics with those in fig. 2 while measurements at 11 MeV [ref. ‘“)I and at 12.2 MeV [ref. “)I agree very well with the 11.5 MeV results in fig. 2. These data have been omitted from the figure for the sake of clarity. Some earlier results for T2 o and T22 [refs. i2-i4)] are in general agreement with the values found here but they are of low accuracy. Recent measurements at backward angles for T2 ,, and T22 [ref. ‘)I are shown in figs. 2 and 3 and agree well with the present results. The data of Arvieux et al. ’ “) at a deuteron energy of 21.7 have been included in figs. 2 and 3 to provide a more complete picture of the trends in the Tkqwith energy. These results show that the deuteron analysing powers Tkq are non-zero at all energies studied and have variations with angle which are slightly energy-dependent. Calculations of spin-dependent parameters in a theoretical treatment of the threenucleon system are still in an early stage. Some predictions based on various approximate treatments exist for the proton polarization in proton-deuteron scattering ‘*‘) but similar calculations for the deuteron analysing powers or polarizations have not been reported.

ANALYSING

POWERS

599

Quite good fits to low-energy proton iT,, values and to the deuteron iT,, , T,, and T,, at 21.7 MeV have been obtained in a phase shift analysis using split phases but with no channel-spin or angular momentum mixing ’ “). However, calculations of T,, and T,, at 12.2 MeV reported in ref. ‘) and based on a recent phase-shift analysis, again using only split phases 17), a gree only qualitatively with the measurements at 11.5 MeV and those at 12.2 MeV. A phase-shift analysis which allows for channel spin mixing and orbital angular momentum mixing as well as using split phases has recently been completed in this laboratory. A full account of this analysis is being prepared for publication. References 1) W. Haeberli in The three-body problem in nuclear and particle physics, ed. J. S. McKee and P. M. Rolph (North-Holland, Amsterdam, 1970) p. 188 2) Proc. of the third Int. Conf. on polarization phenomena in nuclear reactions, eds. H. H. Barschall and W. Haeberli (Univ. Wisconsin Press, Madison 1971 3) J. Taylor, G. Spalek, Th. Stammbach, R. A. Hardekopf and R. L. Walter, Phys. Rev. Cl (1970) 803 4) J. D. Seagrave in The three-body problem in nuclear and particle physics, eds. J. S. McKee and P. M. Rolph (North-Holland, Amsterdam, 1970) p. 41; also ref. 2, and Few body problems, light nuclei, and nuclear interactions, eds. G. Paic and I. Slaus (Gordon and Breach, 1968) 5) V. Konig, W. Grilebler, P. A. Schmelzbach and P. Marmier, Nucl. Phys. Al48 (1970) 380 6) W. Griiebler, V. Konig, P. A. Schmelzbach and P. Marmier, Nucl. Phys. Al34 (1969) 686 7) W. Griiebler, V. Konig, P. A. Schmelzbach and P. Marmier, Nucl. Phys. A148 (1970) 391 8) W. Grilebler, V. Kijnig and P. A. Schmelzbach, Nucl. Instr. 86 (1970) 127 9) V. Kbnig, W. Griiebler, A. Ruh, R. E. White, P. A. Schmelzbach, R. Risler and P. Marmier, Nucl. Phys. Al66 (1971) 393 10) B. A. Jacobsohn and R. M. Ryndin, Nucl. Phys. 24 (1961) 505 11) S. E. Darden, Phys. Rev. Lett. 25 (1970) 1673 12) P. Extermann, Nucl. Phys. A95 (1967) 615 13) P. G. Young, M. Ivanovich and G. C. Ohlsen, Phys. Rev. Lett. 14 (1965) 831 14) P. G. Young and M. Ivanovich, Phys. Lett. 23 (1966) 361 15) J. Arvieux, R. Beurtey, J. Goudergues, M. Mayer, A. Papineau and J. Thirion, Nucl. Phys. A102 (1967) 503 16) J. Arvieux, Nucl. Phys. .4102 (1967) 513 17) C. J. Clews and N. Berovic, Phys. Lett. 33B (1970) 347