Resonance effects in nuclear dichroism - an inexpensive source of tensor-polarized deuterons

Transcription

1 Resonance effects in nuclear dichroism - an inexpensive source of tensor-polarized deuterons 1 H. Seyfarth, R. Engels, F. Rathmann, H. Ströher Institut für Kernphysik, Jülich Center for Hadron Physics, Forschungszentrum Jülich, Jülich, Germany V. Baryshevsky, A. Rouba Research Institute for Nuclear Problems, Bobruiskaya Str. 11, Minsk, Belarus C. Düweke, R. Emmerich, A. Imig Institut für Kernphysik, Universität zu Köln, Zülpicher Str. 77, D Köln, Germany K. Grigoryev, M. Mikirtychiants Institut für Kernphysik, Forschungszentrum Jülich and Petersburg Nuclear Physics Institute, Gatchina, Russia A. Vasilyev Petersburg Nuclear Physics Institute, Gatchina, Russia

2 Introduction Dichroism as an optical effect E eo eo 2 o opt. axis birefringent, uniaxial crystal like Turmalin or filter foils I nucl = 0 m=0 Nuclear (spin) dichroism m=0 σ ±1,tot, σ 0,tot m=-1 m=+1 m=-1 m=+1 ρt unpolarized d beam I -1 = I 0 = I +1 = 1/3 σ ±1 > σ 0 I +1 + I -1 < 2I 0 p zz < 0 σ ±1 < σ 0 I +1 + I -1 > 2I 0 p zz < 0

3 3 Calculations V. Baryshevsky and A. Rouba Proc. 11 th Int. Conf. on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2007), September 10-14, 2007, Forschungszentrum Jülich, Germany (SLACeConf C070910, 346 (2008); arxiv: v2 [nucl-th]) Important: interference terms in the interactions Δσ = σ ±1 σ 0 (b) nuclear p-c, n-c and Coulomb p-c (NNC) nuclear n-c and Coulomb p-c (NC) nuclear n-c and p-c (NN) Total=NNC+NC+NN deuteron energy (MeV) p zz = - (2ρT/3) Δσ p zz <0 p zz >0 carbon foil of 100 mg/cm 2 (ρt = C-atoms/cm 2 ) pzz ~ 0.01 Relativistic energies: G. Fäldt, J. Phys. G: Nucl: Phys 6 (1980) 1513: Δσ=1.87 fm 2 calculated L.S. Azhgirey et al., Particles and Nuclei, Letters (JINR Dubna) 5 (2008) 728: Δσ=7.18 fm 2 exp., 3.87 fm 2 calc.

4 Measurements 4 Performed with unpolarized deuteron beam from Van-de-Graaff tandem accelerator operated by Institut für Kernphysik of Universität zu Köln (J. Jolie, H. Paetz gen Schieck, J. Eberth, and A. Dewald, Nucl. Phys. News 12, 4 (2002)) d beam MeV Target foils D1 D2 D3 Θ p =24.5 Θ p =0 thickness labelled mg/cm 2 as empty Au 5.0 Au5 Au 9.7 Au10 C C36 C C58 C C94 C C129 C C153 C C165 C C mm 3 bar 3 He d + 3 He 4 He + p E d = f(e beam, d tgt ) Θ p =24.5 σ(e d, θ p )=σ o (E d,θ p ) [1+1/2 p zz (E d ) A zz (E d,θ p )] data known data known measured to derive

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7 7 What is expected? 0 r(e d ) for p zz = Target primary beam energy mean deuteron energy in the cell center Au MeV MeV C MeV MeV C MeV MeV

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11 The tensor analyzing powers A zz of the polarimeter reaction d+ 3 He 4 He+p for proton emission under 0 and 24.5 with the fit functions 11 A zz (0 º) P.A. Schmelzbach, W. Grüebler, V. König, R. Risler, D.O. Boerma, and B. Jenny, Nucl. Phys. A264, 45 (1976). S.A. Tonsfeldt, PhD Thesis, University of North Carolina, A zz (24.5 º) M. Bittcher, W. Grüebler, V. König, P.A. Schmelzbach, B. Vuaridel, and J. Ulbricht, Few-Body Systems 9, 165 (1990) S.A. Tonsfeldt, PhD Thesis, University of North Carolina, 1983.

12 The experimental result 12 ~14.4 MeV, p zz <0 ~15.4 MeV, p zz >0 theoretical prediction for the nuclear spin dichroism,i.e., p zz, for a fixed deuteron energy within a carbon target of 100 mg/cm 2

13 13 C MeV 7.31±0.05 MeV C MeV 7.34±0.06 MeV MeV

14 14 Interpretation of the surprizing result Only crude first ideas???

15 15 A possible application: production of tensor-polarized deuteron beams upper edge of MeV resonance upper edge of 14.4 MeV resonance

16 16 The Three Princes of Serendip, (in our case 12 princes from Jülich, Minsk, Köln, and Gatchina) whose heroes were always making discoveries, by accidents and sagacity, of things they were not in quest of.

17 Complementary measurement under consideration: Transmission of 13.5 to 16.5 MeV deuteron beams through a 20 mg/cm 2 carbon foil Energy loss in the foil ΔE d ~ 1 MeV 17 primary beams p zz = + 1, p z = 0 (100% m=±1) unpolarized beam (2/3 m=±1, 1/3 m=0) p zz = 2, p z = 0 (100% m=0) E out E in dashed lines: with the possibly artificial resonance at 16.1 MeV E in (MeV) MeV resonance removes m=0 m=±1 m=0 deuterons from the beam

18 18 moveable target frame or target wheel Au3 Au2 Au1 empty diaphragms dia1 dia2 dia3 d(e in,i in,p zz,p z ) d(i det ) detector p zz =+1, p z =0 carbon1 p zz = 2, p z =0 p zz and p z 0 (?) carbon2 I dia1 I dia2 I dia3 shielding carbon3 ΣI dia I det

19 D1 I o (E 0 ) Δt I(E 0 -ΔE,ρΔt) I o (E in ) n=1 n=n out I(E out,ρt) T=n out Δt σ ±1 results in p zz <0 σ 0 results in p zz >0 appropriate choice of the function parameters σ i (E 0 ), E 0,i, and Γ i. allows one to fit the measured distribution by

20 D2 Fit by 12 Gaussian-distributed cross Sections 6 p zz <0 6 p zz >0 16.1, 16.7, and 17.5 MeV possibly caused by uncertainties in the target thicknesses

21 D3 a) D. von Ehrenstein et al., Phys. Rev. Lett. 27, 107 (1971); b) P.L. Jolivette, Phys. Rev. C 9, 16 (1974); c) J. Jänecke et al., Phys. Rev. 175, 1301(1968); d) H. Vernon Smith, Jr., and H.T. Richards, Phys. Rev. Lett. 23, 1409 (1969); e) L. Meyer-Schützmeister et al.,phys. Rev. 147, 743 (1966). For each of the resonances σ(e)de= σ(e o ) Γ

22 D4 α emission forward L. Meyer-Schützmeister et al.,phys. Rev. 147, 743 (1966); H. Vernon Smith, Jr., and H.T. Richards, Phys. Rev. Lett. 23, 1409 (1969); P.L. Jolivette, Phys. Rev. C 9, 16 (1974) α emission backward D. von Ehrenstein et al., Phys. Rev. Lett. 27, 107 (1971) 13 C(p,γ) 14 N F. Riess et al., Nucl. Phys. A175, 462 (1971) 14 N(γ,p) 13 C R. Kosiek, K. Maier, and K Schlüpmann, Phys. Lett. 9, 260 (1964) Agreement in the peak positions accidental?

23 D5 A first crude attempt of interpretation present work E o (MeV) 14.4± ±0.03 σ(e 0 ) (b) 1100± ±40 Γ (kev) 520± ±250 p zz ± ±0.016 E*( 14 N) (MeV) 22.6± ±0.03 earlier (d,α) experiments D. von Ehrenstein et al., Phys. Rev. Lett. 27, 107 (1971): E*( 14 N) (MeV) ~22.6 ~23.5 dσ/dω (μb/sr) ~19 ~6 P.L. Jolivette, Phys. Rev. C 9, 16 (1974): E*( 14 N) (MeV) 22.6± dσ/dω (μb/sr) The giant resonance in 14 N spreads around 22.5 MeV with a width (FWHM) of 3.5 MeV M. Goldhaber and E. Teller, Phys. Rev. 74, 1046 (1948): dipole vibration of the bulk of protons against that of neutrons φ=30 MeV, ε=2.4 fm, and R 0 =R e =3.13 fm ћω= 22.3 MeV

24 Extension of the vibrational model to 2 orthogonal vibrations in a deformed nucleus D6 The tentative use of the quadrupole moment of the 14 N ground state of b yields R long =R fm=3.20 fm and R short =R fm=3.06 fm d (I=1) m=±1 m= C (I=0) 14 N*(I=1) R long R short These modified values of R 0 yield Ћω (R long )=22.1 MeV Creation of the compound state leads to the removal of deuterons in the m=±1 state from the beam and Ћω (R short )=22.6 MeV Creation of the compound state leads to the removal of deuterons in the m=0 state from the beam excitation energy (MeV) vibrational model spin-projection quantum number m ±1 0 p zz <0 >0 resonance energy E*( 14 N) (MeV) 22.6± ±0.03 present experiment p zz produced by the resonance -(0.375±0.014) +(0.228±0.016) The simple picture would allow a first interpretation. Is it, however, valid?