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The (7Li,d) reaction and final spin determinations from analyzing powers

K. W. Kemper, O. Momotyuk (FSU) , N. Keeley (Sacaly), F. Maréchal (Strasbourg) and K. Rusek (Warsaw)

The exciting results from highly predictive structure calculations continues to move upward in mass, with knowledge of the nature of all states in a few select nuclei needed to test these calculations. For example, quantum Monte Carlo calculations now describe the low-lying structure of the mass 9 and 10 nuclei but they also predict the presence of unobserved levels (4). In the nucleus ⁷Li, there are four 5/2- states predicted, but only two are known.(5) Also, there continues to be the speculation that clustering plays an increased role close to the neutron dripline so a full characterization of levels in a few select nuclei will allow these models to be more fully developed.

During numerous runs over the years tremendous selectivity has been observed in reactions such as ⁶Li, ¹²C and ¹⁶O (⁷Li,d). New levels have been observed in the excitation energy range of 8-15 MeV in the final nuclei ¹¹B, ¹⁷O and ²¹Ne. The character of these new states has not been pursued because the measured angular distributions are typically non-descript and with the levels being unbound there has been little hope of determining their final spins with the use of angular correlation techniques because the levels decay by non-spin zero particles. The difficulty with carrying out transfer calculations to match with measured experimental angular distributions is that they require the assumption of a ⁵He cluster transfer which is generally not considered to be a good cluster. However a recent analysis of ⁹Be scattering and breakup by us (6) strongly supports the ground state of ⁹Be having the structure ⁵He+ α and hence also suggests that ⁵He transfer might be possible. We propose to explore whether analyzing power signatures for total spin transfers can be established for the (⁷Li,d) reaction, which will then allow final state spins to be assigned. These data will be taken at the same time as that of (⁷Li,t) but because the cross sections tend to be much smaller, will be more limited in number of angles measured.

The initial work will focus on ¹⁷O where several new levels have been found in ¹²C(⁷Li,d) in the 10-15 MeV region of excitation. Our work also confirms several levels found in an earlier ¹²C(⁶Li,p) report (7). To completely characterize the levels in ¹⁷O at excitation energies of 10-15 MeV, we also will have to carry out ¹⁶O(d, p) and ¹⁴N(⁶Li,t/³He) measurements since previous works have not acquired data for levels above about 7 MeV in excitation. For both the (d,p) and (⁶Li,t/³He) data taking we will fill the polarimeter that we normally fill with Helium gas and use to monitor the beam polarization, with CO2 and N2. By using polarized ⁶Li for the t/³He measurements we should learn the spins of states populated since we early on (8) showed that the analyzing powers are dependent on the total angular momentum transferred in this reaction.

(1) S. C. Pieper, K. Varga and R. B. Wiringa Phys. Rev. C66, 044310 (2002).

(2) S. C. Pieper, private communication.

(3) N. Keeley, K. W. Kemper and K. Rusek Phys. Rev. C64, 031602(R) (2001)

(4) M.J Smithson, D.L. Watson, and H.T. Fortune, J. Phys. G, Nucl. Phys. 12 (1986)
985

(8) K. W. Kemper et al Phys. Lett. B321, 183 (1994)

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	FSU Experimental Nuclear Physics Main			The (7Li,d) reaction and final spin determinations from analyzing powers K. W. Kemper, O. Momotyuk (FSU) , N. Keeley (Sacaly), F. Maréchal (Strasbourg) and K. Rusek (Warsaw) The exciting results from highly predictive structure calculations continues to move upward in mass, with knowledge of the nature of all states in a few select nuclei needed to test these calculations. For example, quantum Monte Carlo calculations now describe the low-lying structure of the mass 9 and 10 nuclei but they also predict the presence of unobserved levels (4). In the nucleus ⁷Li, there are four 5/2- states predicted, but only two are known.(5) Also, there continues to be the speculation that clustering plays an increased role close to the neutron dripline so a full characterization of levels in a few select nuclei will allow these models to be more fully developed. During numerous runs over the years tremendous selectivity has been observed in reactions such as ⁶Li, ¹²C and ¹⁶O (⁷Li,d). New levels have been observed in the excitation energy range of 8-15 MeV in the final nuclei ¹¹B, ¹⁷O and ²¹Ne. The character of these new states has not been pursued because the measured angular distributions are typically non-descript and with the levels being unbound there has been little hope of determining their final spins with the use of angular correlation techniques because the levels decay by non-spin zero particles. The difficulty with carrying out transfer calculations to match with measured experimental angular distributions is that they require the assumption of a ⁵He cluster transfer which is generally not considered to be a good cluster. However a recent analysis of ⁹Be scattering and breakup by us (6) strongly supports the ground state of ⁹Be having the structure ⁵He+ α and hence also suggests that ⁵He transfer might be possible. We propose to explore whether analyzing power signatures for total spin transfers can be established for the (⁷Li,d) reaction, which will then allow final state spins to be assigned. These data will be taken at the same time as that of (⁷Li,t) but because the cross sections tend to be much smaller, will be more limited in number of angles measured. The initial work will focus on ¹⁷O where several new levels have been found in ¹²C(⁷Li,d) in the 10-15 MeV region of excitation. Our work also confirms several levels found in an earlier ¹²C(⁶Li,p) report (7). To completely characterize the levels in ¹⁷O at excitation energies of 10-15 MeV, we also will have to carry out ¹⁶O(d, p) and ¹⁴N(⁶Li,t/³He) measurements since previous works have not acquired data for levels above about 7 MeV in excitation. For both the (d,p) and (⁶Li,t/³He) data taking we will fill the polarimeter that we normally fill with Helium gas and use to monitor the beam polarization, with CO2 and N2. By using polarized ⁶Li for the t/³He measurements we should learn the spins of states populated since we early on (8) showed that the analyzing powers are dependent on the total angular momentum transferred in this reaction. (1) S. C. Pieper, K. Varga and R. B. Wiringa Phys. Rev. C66, 044310 (2002). (2) S. C. Pieper, private communication. (3) N. Keeley, K. W. Kemper and K. Rusek Phys. Rev. C64, 031602(R) (2001) (4) M.J Smithson, D.L. Watson, and H.T. Fortune, J. Phys. G, Nucl. Phys. 12 (1986) 985 (8) K. W. Kemper et al Phys. Lett. B321, 183 (1994) Back to Dr. Kemper's Research Menu