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The 3He(d, p)4He reaction at 0° as an analyser for tensor polarized deuterons
Nuclear Physics Al65 (1971) 505-507;
@ North-Holland Publishing Co., Amsterdam
Not to be reproduced by photoprint or microfilm without written permission from the publisher
THE 3He(d, p)4He REACTION AT O” AS AN ANALYSER FOR TENSOR POLARIZED DEUTERONS W. GROEBLER, V. KONIG, A. RUH, R. E. WHITEt, P. A. SCHMELZBACH, R. RISLER and P. MARMIER Laboratorium fiir Kernphysik, Eidg. Technische Hochschule, Ziirich, Switzerland Received 21 January 1971 Abstract: The tensor analysing power T20 of the jHe(d, p)4He reaction has been measured at 0 = 0” between 2 and 11.2 MeV. This reaction shows excellent properties as an analyser for tensor polarized deuteron beams. E
NUCLEAR
RE&T!ON_s
3He(i, p); E = 2-l 1.2 MeV; power T,,(E, 0”)
measured
analysing
The use of tensor polarized deuteron beams from an accelerator to induce nuclear reactions makes it desirable to monitor the beam polarization continuously during the experiment. The reaction serving as analyser should not only possess over an extended energy range a large cross section (r and high analysing power Tkq, yielding a large figure of merit oT& but should also show a smooth variation over the entire energy range without sharp resonances. It is the purpose of this note to draw attention to the merits of the 3He(d, p)4He reaction as analyser tihich fulfils at 0” all the conditions mentioned above. Furthermore this reaction has an exceptionally high Qvalue which facilitates the detection of the emitted protons. In this paper measurements of the analysing power T2,, at 0” in the energy range 2 to 11.2 MeV are reported. Since at 0” all analysing powers Tkqare zero except Tz,-,, the differential cross section of a reaction induced by a polarized beam can be written as ‘) ~(0’) = o,(O”)[l ++?2,,Tzo (3 cos’ a-l)], where ~~(0”) is the cross section at 0” for an unpolarized incident beam. The incident . . beam polarlzatlon 320 is referred to its spin-symmetry axis. The angle a is measured between the deuteron spin-symmetry axis and the incident beam direction. This expression shows that the 3He(d, p)4He reaction at 0” can be used as analyser for all positions of the spin-symmetry axis except in a small angular range around 54.7” where the term 3 cos’u- 1 is zero. In the present experiment the 3He target was set up at the end of the Faraday cup of the scattering chamber described in ref. “). At this position the 3He target and the 7 On leave from the University of Auckland, New Zealand. 505
506
W. GRtiEBLER
et al.
proton detector at 0” form a polarimeter permanently controlling the beam polarization during experiments. The 3He cell had a diameter of 12 mm, a gas pressure of 5 atm and a 6 pm Havar entrance window. The deuteron beam was stopped completely by a stainless steel wall 0.4 mm thick at the end of the cell, but which however absorbed only a small fraction of the energy of the emitted protons. A surface-barrier detector was set up on the beam axis at a distance of 12 cm from the target centre having an angular resolution of k2.5”. Since the proton detector had a depletion layer only sufficiently thick to stop protons up to 12 MeV, aluminium absorbers of 0.2 and 1 mm thickness respectively were placed in front of the detector for low and high beam energies. The spin-symmetry axis lay along the direction of the incident beam and the experimental method described in ref. ‘) was used to determine the analysing power. Briefly, this method consists in switching the sign of the beam polarization jZO every few seconds, the ratio of two observed yields being used to determine T,,. TABLE 1 The analysing power TzO of the 3He(d, p)4He reaction at 0” Ed (MeV) 1.95hO.15 2.28f0.13 2.9OkO.11 3.15f0.10 3.51 *IO.10 4.10&0.09 4.67&-0.07 5.01 hO.07 5.23 kO.07 5.78 50.07 6.31 AO.06 6.49 &0.06 7.39hO.05 8.45kO.05 9.3oi-0.04 9.5OkO.04 10.54&0.04 11.17*0.04
Tzo -0.561 kO.022 -0.696~0.020 -0.919*0.017 -0.969+0.016 -1.028f0.015 -1.183~0.013 -1.237+0.012 -1.291f0.011 - 1.291 kO.009 -1.278&0.010 -1.270~0.011 -1.252&0.018 -1.218f0.011 -1.141~0.010 -1.095~0.040 -1.064~0.015 -1.003*0.010 -0.949 *0.009
The results at 6.49 and 9.30 MeV are absolute calibrations
from ref. ‘).
With this method the measured analysing power is not very sensitive to the orientation of the spin-symmetry axis of the deuteron beam. The deviation was at the most 4”, a value which affects the observed T,, by less than 1 %. The absolute calibration of the 3He(d, p)4He reaction at Ed = 6.49 MeV and 0” [ref. “)I was used to determine the beam polarization every other run. The variation of the beam polarization during the measurements was less than +2 %. The results are given in table 1 and depicted in fig. 1. Since the target pressure was the same for all measurements the energy spread is larger at lower deuteron energies. The stated errors are of a statistical nature
3He(d, p) REACTION
507
only, except for the energies 6.49 and 9.30 MeV where the errors of the absolute values are indicated (cf. ref. “)). A n estimated uncertainty of 2 % in the absolute values should be added for the other results. At very low energy Galonski et al. “) have calculated TzO to be -0.707 assuming only an s-wave contribution. The analysing power in fig. 1 was therefore tentatively extrapolated to this low energy. The analysing power T, 0 is given in accordance with the Madison convention ‘).
Fig. 1. The analysing power Tao of the 3He(d, p)4He reaction at 0” between 2 and 11.2 MeV. The open symbols denote absolute calibrations of the analysing power 3, with the absolute errors. The solid dots show statistical errors only.
The results show clearly the attractive features of the 3He(d, p)4He reaction at 0 as an analyser for tensor polarized deuterons between 2 and 11.2 MeV, namely a high analysing power coupled with a smooth behaviour without sharp resonances over a wide energy range. The analysing power at higher energies seems to decrease only slowly and one could hope that the usable energy range can be extended. For these reasons we would like to propose that the 3He(d, p)4He reaction at 0” be adopted as an analysing power standard. This analysing reaction is also far superior to the d-a elastic scattering, which was proposed earlier ” “) as an analyser. Although the cross section of the d-cr scattering is larger the figure of merit equals that of 3He(d, p)4He at most over a small energy and angular range. In addition, the 4He analyser has the disadv~~ge that it cannot be used at 0” and at other angles its use depends on the orientation of the spin-symmetry axis. References 1) V. Konig. W. Griiebler, P. A. Schmelzbach and P. Marmier, Nucl. Phys. A148 (1970) 380 2) W. Grtiebler, V. Konig, P. A. Schmelzbach and P. Marmier, Nucl. Phys. Al34 (1969) 686 3) V. K&rig, W. Grtiebler, A. Ruh, R. E. White, P. A. Schmelzbach, R. Risler and P. Marmier, Nucl. Phys., to be published 4) A. Galonski, H. B. Willard and T. A. Welton, Phys. Rev. Lett. 2 (1959) 349 5) Proc. 3rd Int. Symp. on polarization phenomena in nuclear reactions, ed. H, H. Barschall and W. Haeberli (University of Wisconsin Press, 1970) to be published 6) W. Griiebler, V. KBnig, P. A. Schmelzbach and P. Marmier, Nucl. Phys. A148 (1970) 391
@ North-Holland Publishing Co., Amsterdam
Not to be reproduced by photoprint or microfilm without written permission from the publisher
THE 3He(d, p)4He REACTION AT O” AS AN ANALYSER FOR TENSOR POLARIZED DEUTERONS W. GROEBLER, V. KONIG, A. RUH, R. E. WHITEt, P. A. SCHMELZBACH, R. RISLER and P. MARMIER Laboratorium fiir Kernphysik, Eidg. Technische Hochschule, Ziirich, Switzerland Received 21 January 1971 Abstract: The tensor analysing power T20 of the jHe(d, p)4He reaction has been measured at 0 = 0” between 2 and 11.2 MeV. This reaction shows excellent properties as an analyser for tensor polarized deuteron beams. E
NUCLEAR
RE&T!ON_s
3He(i, p); E = 2-l 1.2 MeV; power T,,(E, 0”)
measured
analysing
The use of tensor polarized deuteron beams from an accelerator to induce nuclear reactions makes it desirable to monitor the beam polarization continuously during the experiment. The reaction serving as analyser should not only possess over an extended energy range a large cross section (r and high analysing power Tkq, yielding a large figure of merit oT& but should also show a smooth variation over the entire energy range without sharp resonances. It is the purpose of this note to draw attention to the merits of the 3He(d, p)4He reaction as analyser tihich fulfils at 0” all the conditions mentioned above. Furthermore this reaction has an exceptionally high Qvalue which facilitates the detection of the emitted protons. In this paper measurements of the analysing power T2,, at 0” in the energy range 2 to 11.2 MeV are reported. Since at 0” all analysing powers Tkqare zero except Tz,-,, the differential cross section of a reaction induced by a polarized beam can be written as ‘) ~(0’) = o,(O”)[l ++?2,,Tzo (3 cos’ a-l)], where ~~(0”) is the cross section at 0” for an unpolarized incident beam. The incident . . beam polarlzatlon 320 is referred to its spin-symmetry axis. The angle a is measured between the deuteron spin-symmetry axis and the incident beam direction. This expression shows that the 3He(d, p)4He reaction at 0” can be used as analyser for all positions of the spin-symmetry axis except in a small angular range around 54.7” where the term 3 cos’u- 1 is zero. In the present experiment the 3He target was set up at the end of the Faraday cup of the scattering chamber described in ref. “). At this position the 3He target and the 7 On leave from the University of Auckland, New Zealand. 505
506
W. GRtiEBLER
et al.
proton detector at 0” form a polarimeter permanently controlling the beam polarization during experiments. The 3He cell had a diameter of 12 mm, a gas pressure of 5 atm and a 6 pm Havar entrance window. The deuteron beam was stopped completely by a stainless steel wall 0.4 mm thick at the end of the cell, but which however absorbed only a small fraction of the energy of the emitted protons. A surface-barrier detector was set up on the beam axis at a distance of 12 cm from the target centre having an angular resolution of k2.5”. Since the proton detector had a depletion layer only sufficiently thick to stop protons up to 12 MeV, aluminium absorbers of 0.2 and 1 mm thickness respectively were placed in front of the detector for low and high beam energies. The spin-symmetry axis lay along the direction of the incident beam and the experimental method described in ref. ‘) was used to determine the analysing power. Briefly, this method consists in switching the sign of the beam polarization jZO every few seconds, the ratio of two observed yields being used to determine T,,. TABLE 1 The analysing power TzO of the 3He(d, p)4He reaction at 0” Ed (MeV) 1.95hO.15 2.28f0.13 2.9OkO.11 3.15f0.10 3.51 *IO.10 4.10&0.09 4.67&-0.07 5.01 hO.07 5.23 kO.07 5.78 50.07 6.31 AO.06 6.49 &0.06 7.39hO.05 8.45kO.05 9.3oi-0.04 9.5OkO.04 10.54&0.04 11.17*0.04
Tzo -0.561 kO.022 -0.696~0.020 -0.919*0.017 -0.969+0.016 -1.028f0.015 -1.183~0.013 -1.237+0.012 -1.291f0.011 - 1.291 kO.009 -1.278&0.010 -1.270~0.011 -1.252&0.018 -1.218f0.011 -1.141~0.010 -1.095~0.040 -1.064~0.015 -1.003*0.010 -0.949 *0.009
The results at 6.49 and 9.30 MeV are absolute calibrations
from ref. ‘).
With this method the measured analysing power is not very sensitive to the orientation of the spin-symmetry axis of the deuteron beam. The deviation was at the most 4”, a value which affects the observed T,, by less than 1 %. The absolute calibration of the 3He(d, p)4He reaction at Ed = 6.49 MeV and 0” [ref. “)I was used to determine the beam polarization every other run. The variation of the beam polarization during the measurements was less than +2 %. The results are given in table 1 and depicted in fig. 1. Since the target pressure was the same for all measurements the energy spread is larger at lower deuteron energies. The stated errors are of a statistical nature
3He(d, p) REACTION
507
only, except for the energies 6.49 and 9.30 MeV where the errors of the absolute values are indicated (cf. ref. “)). A n estimated uncertainty of 2 % in the absolute values should be added for the other results. At very low energy Galonski et al. “) have calculated TzO to be -0.707 assuming only an s-wave contribution. The analysing power in fig. 1 was therefore tentatively extrapolated to this low energy. The analysing power T, 0 is given in accordance with the Madison convention ‘).
Fig. 1. The analysing power Tao of the 3He(d, p)4He reaction at 0” between 2 and 11.2 MeV. The open symbols denote absolute calibrations of the analysing power 3, with the absolute errors. The solid dots show statistical errors only.
The results show clearly the attractive features of the 3He(d, p)4He reaction at 0 as an analyser for tensor polarized deuterons between 2 and 11.2 MeV, namely a high analysing power coupled with a smooth behaviour without sharp resonances over a wide energy range. The analysing power at higher energies seems to decrease only slowly and one could hope that the usable energy range can be extended. For these reasons we would like to propose that the 3He(d, p)4He reaction at 0” be adopted as an analysing power standard. This analysing reaction is also far superior to the d-a elastic scattering, which was proposed earlier ” “) as an analyser. Although the cross section of the d-cr scattering is larger the figure of merit equals that of 3He(d, p)4He at most over a small energy and angular range. In addition, the 4He analyser has the disadv~~ge that it cannot be used at 0” and at other angles its use depends on the orientation of the spin-symmetry axis. References 1) V. Konig. W. Griiebler, P. A. Schmelzbach and P. Marmier, Nucl. Phys. A148 (1970) 380 2) W. Grtiebler, V. Konig, P. A. Schmelzbach and P. Marmier, Nucl. Phys. Al34 (1969) 686 3) V. K&rig, W. Grtiebler, A. Ruh, R. E. White, P. A. Schmelzbach, R. Risler and P. Marmier, Nucl. Phys., to be published 4) A. Galonski, H. B. Willard and T. A. Welton, Phys. Rev. Lett. 2 (1959) 349 5) Proc. 3rd Int. Symp. on polarization phenomena in nuclear reactions, ed. H, H. Barschall and W. Haeberli (University of Wisconsin Press, 1970) to be published 6) W. Griiebler, V. KBnig, P. A. Schmelzbach and P. Marmier, Nucl. Phys. A148 (1970) 391