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Polarization in neutron-deuteron elastic scattering at 1.0 MeV
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Nuclear Physics 45 (1963) 253---254; ( ~ North-Holland Publishing Co., Amsterdam Not to be reproduced by photoprint or microfilm without written permission from the publisher
P O L A R I Z A T I O N IN N E U T R O N - D E U T E R O N ELASTIC S C A T r E R I N G AT 1.0 MeV A. F. BEHOF, G. P. LIETZ, S. F. T R E V I ~ O and S. E. D A R D E N t
Department of Physics, University of Notre Dame, Notre Dame, Indiana tt Received 28 March 1963 Abstract: The neutron polarization produced in the scattering o f I MeV neutrons by deuterons has been remeasured for a c.m. scatter/rig angle o f 110 °. A polarization PI = 0.0134-0.021 was measured at this energy and angle.
Several measurements of the neutron polarization produced in n-d scattering in the energy region near 1 MeV have yielded conflicting results. Ferguson and White 1) measured a polarization of 0.10+0.03 (Basel Convention) at 0cm = 80 °. This result is in agreement with the polarizations o f approximately 0.09 +0.05 measured in this laboratory 2) for 0cm = 70 °, 110° and 140°. Recently, Elwyn et al. a) performed a high-precision experiment, and for a neutron energy of 1 MeV obtained polarizations of magnitude 0.01 or less at all angles. These authors 3) also report a private communication, according to which Beghian et al. **¢ measured a polarization o f 0.045+0.040 at 1.175 MeV for 0am = 85 °. In view of the disagreement in these results, the polarization has been remeasured in this laboratory at 0¢~ = 110 ° using a different technique 4), which previously has been used only at higher energies. Neutrons were produced by bombarding a 75 keV thick lithium nitride target with 3 MeV protons from the Notre Dame electrostatic accelerator. The neutrons from the Li7(p, n)Be 7 reaction emitted at a laboratory angle of 50 ° were scattered from a deuterated toluene scintillator and detected by two plastic scintillators, positioned to the right and the left of the scatterer. An electromagnet was used to invert the spin of the neutrons before scattering 5). The recoil-deuteron pulses were detected in fast coincidence with those from the neutron detectors, using a technique similar to that employed by Walter and Kelsey 4). The background was measured to be about 20 Yo of the foreground counting rate by inserting a 100 ns delay in one channel of each coincidence circuit. Using a hydrogenous scintillator in place of the deuterated toluene, an instrumental asymmetry L / R = 1.004+0.0075 was measured. With the deuterated scintillator an asymmetry L / R = 1.008+0.013 was measured for 0am = 110 °. An estimate of the multiple t Alfred P. Sloan Research Fellow. tt Work supported in part by the Office of Naval Research. tit Note added in proof; This work has since been published in Nuclear Physics, Voi. 42, No. 1. 258
254
A.F. BEHOF et aL
scattering correction was made and it was found to be small compared to the uncertainty in the measurements. Using a value 6) o f P1 = 0.31 for the incident neutrons, a polarization P2 = 0.013+__0.021 results. This value agrees with those of Elwyn et aL, and Beghian et al., but is in disagreement with that of Ferguson and White, and with the value previously measured at this laboratory. It is not clear why the value of the polarization measured previously at this laboratory is large. Possibly the extensive numerical analysis required to evaluate the data led to some systematic error. Since the technique used in the present measurement is quite direct and the analysis is free from extensive calculations, the result appears to be more convincing. The authors would like to thank the Neutron Physics Group of the University o f Wisconsin for the loan of the deuterated toluene scintillator. References 1) 2) 3) 4) 5) 6)
A. T. G. Ferguson and R. E. White, Nuclear Physics 33 (1962) 477 S. E. Darden, C. A. Kelsey and T. R. Donoghue, Nuclear Physics 16 (1960) 351 A.J. Elwyn, R. O. Lane and A. Langsdorf Jr., Phys. Rev. 128 (1962) 779 R. L. Waiter and C. A. Kelsey, Nuclear Physics (to be published) C. A. Kelsey, G. P. Lietz, S. F. Trevino and S. E. Darden, Phys. Rev. 129 (1963) 759 H. R. Striebel, S. E. Darden and W. Haeberli, Nuclear Physics 6 (1958) 188
Nuclear Physics 45 (1963) 253---254; ( ~ North-Holland Publishing Co., Amsterdam Not to be reproduced by photoprint or microfilm without written permission from the publisher
P O L A R I Z A T I O N IN N E U T R O N - D E U T E R O N ELASTIC S C A T r E R I N G AT 1.0 MeV A. F. BEHOF, G. P. LIETZ, S. F. T R E V I ~ O and S. E. D A R D E N t
Department of Physics, University of Notre Dame, Notre Dame, Indiana tt Received 28 March 1963 Abstract: The neutron polarization produced in the scattering o f I MeV neutrons by deuterons has been remeasured for a c.m. scatter/rig angle o f 110 °. A polarization PI = 0.0134-0.021 was measured at this energy and angle.
Several measurements of the neutron polarization produced in n-d scattering in the energy region near 1 MeV have yielded conflicting results. Ferguson and White 1) measured a polarization of 0.10+0.03 (Basel Convention) at 0cm = 80 °. This result is in agreement with the polarizations o f approximately 0.09 +0.05 measured in this laboratory 2) for 0cm = 70 °, 110° and 140°. Recently, Elwyn et al. a) performed a high-precision experiment, and for a neutron energy of 1 MeV obtained polarizations of magnitude 0.01 or less at all angles. These authors 3) also report a private communication, according to which Beghian et al. **¢ measured a polarization o f 0.045+0.040 at 1.175 MeV for 0am = 85 °. In view of the disagreement in these results, the polarization has been remeasured in this laboratory at 0¢~ = 110 ° using a different technique 4), which previously has been used only at higher energies. Neutrons were produced by bombarding a 75 keV thick lithium nitride target with 3 MeV protons from the Notre Dame electrostatic accelerator. The neutrons from the Li7(p, n)Be 7 reaction emitted at a laboratory angle of 50 ° were scattered from a deuterated toluene scintillator and detected by two plastic scintillators, positioned to the right and the left of the scatterer. An electromagnet was used to invert the spin of the neutrons before scattering 5). The recoil-deuteron pulses were detected in fast coincidence with those from the neutron detectors, using a technique similar to that employed by Walter and Kelsey 4). The background was measured to be about 20 Yo of the foreground counting rate by inserting a 100 ns delay in one channel of each coincidence circuit. Using a hydrogenous scintillator in place of the deuterated toluene, an instrumental asymmetry L / R = 1.004+0.0075 was measured. With the deuterated scintillator an asymmetry L / R = 1.008+0.013 was measured for 0am = 110 °. An estimate of the multiple t Alfred P. Sloan Research Fellow. tt Work supported in part by the Office of Naval Research. tit Note added in proof; This work has since been published in Nuclear Physics, Voi. 42, No. 1. 258
254
A.F. BEHOF et aL
scattering correction was made and it was found to be small compared to the uncertainty in the measurements. Using a value 6) o f P1 = 0.31 for the incident neutrons, a polarization P2 = 0.013+__0.021 results. This value agrees with those of Elwyn et aL, and Beghian et al., but is in disagreement with that of Ferguson and White, and with the value previously measured at this laboratory. It is not clear why the value of the polarization measured previously at this laboratory is large. Possibly the extensive numerical analysis required to evaluate the data led to some systematic error. Since the technique used in the present measurement is quite direct and the analysis is free from extensive calculations, the result appears to be more convincing. The authors would like to thank the Neutron Physics Group of the University o f Wisconsin for the loan of the deuterated toluene scintillator. References 1) 2) 3) 4) 5) 6)
A. T. G. Ferguson and R. E. White, Nuclear Physics 33 (1962) 477 S. E. Darden, C. A. Kelsey and T. R. Donoghue, Nuclear Physics 16 (1960) 351 A.J. Elwyn, R. O. Lane and A. Langsdorf Jr., Phys. Rev. 128 (1962) 779 R. L. Waiter and C. A. Kelsey, Nuclear Physics (to be published) C. A. Kelsey, G. P. Lietz, S. F. Trevino and S. E. Darden, Phys. Rev. 129 (1963) 759 H. R. Striebel, S. E. Darden and W. Haeberli, Nuclear Physics 6 (1958) 188