Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session BE: Mini-symposium on Nuclear Moments I |
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Sponsoring Units: DNP JPS Chair: Tadanori Minamisono, Fukui University of Technology Room: Ritz-Carlton Hotel Amphitheatre |
Monday, September 19, 2005 7:00PM - 7:30PM |
BE.00001: Exotic structure of unstable nuclei from the nuclear moment study Invited Speaker: The structure of unstable nuclei is often rather different from that of stable ones, including the disappearance of the magic structure, halo structure, new types of cluster structure, {\it etc.} For even-even nuclei, the in-beam spectroscopy is very useful to reach such exotic structures, while the nuclear moment is one of the most powerful probes to directly investigate the ground-state structure of odd-$A$ and odd-odd nuclei. For instance, the systematic study of the nuclear moment in Na isotopes has played a crucial role in determining where the $N=20$ magic structure disappears. Namely, this disappearance was considered to be restricted to some of $N\ge 20$ isotopes from a naive comparison of experiment with the $sd$-shell calculation about the ground-state spin and the separation energy. On the other hand, it has been recently clarified that the disappearance completely occurs at $N=19$ from comparison of the magnetic dipole and electric quadrupole moments between a recent experiment and the Monte Carlo shell model calculation. Along this line, several experimental data for other nuclei are being accumulated now. As for the moment of the excited state, it is pointed out, for instance, that the $g$ factor and the quadrupole moment of the $2^+_1$ state carry much information on the collectivity: the former tells us the proton- and neutron-contribution to the rotation, and the latter is related to the intrinsic shape. Around $^{132}$Sn, a recent shell-model calculation has succeeded in reproducing both the $E2$ transitions and the $g$ factors in this region, showing a certain deviation from simple collective models. In this talk, I would like to give an overview about how the nuclear moment clarifies exotic structure of unstable nuclei as exemplified above. [Preview Abstract] |
Monday, September 19, 2005 7:30PM - 7:45PM |
BE.00002: Electric quadrupole moment of $^{25}$Na. Kensaku Matsuta, Takashi Nagatomo, Hiroki Fujiwara, Shinichi Kumashiro, Ryohei Matsumiya, Masako Ogura, Mototsugu Mihara, Mitsunori Fukuda, Sadao Momota, Yoichi Nojiri, Takashi Ohtsubo, Masahiro Ohta, Atsushi Kitagawa, Mitsutaka Kanazawa, Masami Torikoshi, Shinji Sato, Tadanori Minamisono, Kei Minamisono, T.J.M. Symons, G.F. Krebs, J.R. Alonso Among the many Na isotopes, whose electric quadrupole moments $Q$ are known, the precision of the $Q$ moment of $^{25}$Na ($I^{\pi }$=5/2$^{+}$, $T_{1/2}$=59.1s) has been extremely poor, which prevents us from the quantitative discussion of nuclear structure of the Na isotopes. In the present experiment, the $Q$ moment of $^{25}$Na has been determined precisely by means of $\beta $-NMR technique. Polarized $^{25}$Na nuclei were produced through the projectile fragmentation process in the $^{26}$Mg on Be collisions at 100$A$ MeV. The NMR/NQR were observed on the $^{25}$Na nuclei implanted in NaCl and/or TiO2 single crystals, by means of the asymmetric emission of $\beta $ rays. As a result, the absolute values of the magnetic and the $Q$ moments were precisely determined to be 3.6832(3) $\mu _{N}$ and 1.0(4) mb, respectively. The obtained $Q$ moment is much precise than the old value --64(44) mb. The present $Q$ is reproduced well by the shell model value --2.7 mb. [Preview Abstract] |
Monday, September 19, 2005 7:45PM - 8:00PM |
BE.00003: Magnetic moments of neutron-rich nuclei $^{30}$Al and $^{32}$Al Daisuke Kameda, Hideki Ueno, Koichiro Asahi, Akihiro Yoshimi, Tomohito Haseyama, Hiroshi Watanabe, Yoshio Kobayashi, Go Kijima, Hisanori Miyoshi, Kenzi Shimada, Go Kato, Daisuke Nagae, Shoken Emori, Masahito Tsukui The magnetic moments of the ground-state $^{30}$Al and $^{32} $Al have been measured by means of the $\beta$ ray-detected nuclear magnetic resonance ($\beta$-NMR) technique with spin polarized radioactive nuclear beams produced from projectile fragmentation reactions. The fragmentation processes that involved large numbers of removed nucleons, 10 and 8, from the $95$~MeV/u $^{40}$Ar projectile were successfully utilized to produce the polarized $^{30}{\rm Al}$ and $^{32}{\rm Al}$ fragments. A single-crystal corundum sample was employed as a stopper of the projectile fragments. The stopper temperature was maintained below $100$~K to preserve the spin polarizations during the $\beta$ decays. The quadrupolar splitting in the crystal was avoided by employing the ``magic angle'' technique. The magnetic moments have been successfully obtained, as $|\mu(^ {30}{\rm Al})|=(3.010\pm0.007)\mu_{\rm N}$ and $|\mu(^{32}{\rm Al})|=(1.959\pm0.009)\mu_{\rm N}$. Shell model calculations within the {\it sd} valence orbits using the USD interaction reproduced the both magnetic moments within $6$~\%. The border of the ``island of inversion'' will be discussed in comparison with the magnetic moments of $N=19$ isotones. [Preview Abstract] |
Monday, September 19, 2005 8:00PM - 8:15PM |
BE.00004: Ground-state nuclear moments of neutron-rich {\it p}- and {\it sd}-shell nuclei Hideki Ueno, Akihiro Yoshimi, Tomohito Haseyama, Hiroshi Watanabe, Daisuke Kameda, Go Kijima, Koichiro Asahi, Hisanori Miyoshi, Kenzi Shimada, Go Kato, Daisuke Nagae, Shoken Emori, Masato Tsukui We have been conducting a series of experiments at RIKEN for the measurement the nuclear moments in the light unstable nuclei based on the $\beta$-NMR method with the spin-polarized radioactive-isotope beams. So far the measurements have been carried out in the region of neutron-rich {\it p}-shell nuclei. The obtained experimental nuclear moments have been shown quite effective in discussing the effect of neutron excess on their nuclear structure, where we discussed the deviation of magnetic moments from the Schmidt value and the isospin dependence of the effective charges. To extend the observation into the neutron-rich {\it sd}-shell region, the ground-state magnetic moments of $^{30}$Al and $^{32}$Al were measured. Important issue in this region is to understand what causes the manifestation of the ``island of inversion''. Microscopic studies of such nuclei close to the ``island of inversion'', as well as those inside it, would offer a clue to this question. The obtained $\mu$ moments, $|\mu_{\rm exp}{\rm (^{30}Al)}|$ = 3.010(7) $\mu_{\rm N}$ and $|\mu_{\rm exp}{\rm (^{32}Al)}|$ = 1.959(9) $\mu_{\rm N}$, are in agreement with shell model calculations within the {\it sd} valence space, although a reduction in the energy-gap between the {\it sd} and {\it pf} states is predicted for $^{32}$Al in recent theoretical studies. Recent progress in this region will be presented. [Preview Abstract] |
Monday, September 19, 2005 8:15PM - 8:30PM |
BE.00005: Ground-state magnetic moment of $^{35}$K P.F. Mantica, T.J. Mertzimekis, A.D. Davies, D.E. Groh, S.N. Liddick, B.E. Tomlin Spin-polarized $^{35}$K fragments were produced at the NSCL using a single-proton pickup, two-neutron removal reaction from an $^{36}$Ar primary beam at an energy of 150 MeV/A incident on a $^{9}$Be target. The polarized $^{35}$K nuclei were implanted into a KBr crystal placed at the center of a beta-NMR magnet for magnetic moment analysis. The new value of the $^{35}$K magnetic moment improves on the precision of the previously measured value by an order of magnitude. The isoscalar magnetic moment of the T = 3/2 mirror pair $^{35}$K-$^{35}$S was found to compare well with the systematic variation of isoscalar moments extracted for heavy, T = 1/2 mirror pairs. Work supported in part by the NSF Grant Nos. PHY-01-10253 and PHY-99-83810. [Preview Abstract] |
Monday, September 19, 2005 8:30PM - 8:45PM |
BE.00006: Magnetic Moment of the extremely proton rich nucleus $^{23}$Al Takashi Nagatomo, Kensaku Matsuta, Yoshiki Nakashima, Mototsugu Mihara, Ryohei Matsumiya, Mitsunori Fukuda, Akira Ozawa, Takuma Yasuno, Kazunari Yamada, Takashi Ohtsubo, Takuji Izumikawa, Daisuke Shinojima, Hideki Tanaka, Takayuki Yamaguchi, Shin-pei Nakajima, Hisashi Maemura, Takeshi Suzuki, Toshiyuki Sumikama, Kanenobu Tanaka, Koichi Yoshida, Sadao Momota, Yoichi Nojiri, Tadanori Minamisono, Isao Tanihata We have studied the spin parity of $^{23}$Al through the measurement of the magnetic moment by the $\beta $-NMR method. The experiment was performed at RIKEN/ RIPS. The polarized $^{23}$Al nuclei were produced through the 135-$A $MeV $^{28}$Si and Be collisions, and were separated by the RIPS separator and RF deflector. The NMR was observed by the $\beta $-ray asymmetry change. From the resonance frequency, we determined the $g-$factor of $^{23}$Al as $\vert g\vert (^{23}$Al) = 1.56(9). From the comparison between the present result and the shell model calculation, it was found that $^{23}$Al had the normal spin parity of 5/2$^{+}$. The magnetic moment was determined as $\vert \mu \vert (^{23}$Al) = 3.89(22) $\mu _N $. The level inversion between $d_{5/2} $ and $s_{1/2} $ states was not seen in the structure of $^{23}$Al. [Preview Abstract] |
Monday, September 19, 2005 8:45PM - 9:00PM |
BE.00007: Magnetic moment of $^{23}$Ne M. Mihara, K. Matsuta, R. Matsumiya, T. Nagatomo, M. Fukuda, T. Minamisono, S. Momota, Y. Nojiri, T. Ohtsubo, T. Izumikawa, A. Kitagawa, M. Torikoshi, M. Kanazawa, S. Sato, J.R. Alonso, G.F. Krebs, T.J.M. Symons The magnetic moment of the \textit{$\beta $}-emitting nucleus $^{23}$Ne ($I^{\pi }$ = 5/2$^{+}$, $T_{1/2}$ = 37.2 s) has been remeasured by means of the \textit{$\beta $}-NMR method. The $^{23}$Ne nuclei were produced in the single neutron pickup and the projectile fragmentation processes using 100$A$-MeV $^{22}$Ne and $^{26}$Mg beams, respectively, impinged on a Be target at NIRS-HIMAC, and were separated by the fragment separator. After selection of the reaction angle and the momentum to obtain polarization, the $^{23}$Ne nuclei were implanted into a NaF single crystal at 15 K. The magnitude of polarization of $\sim $3{\%} for $^{23}$Ne in NaF obtained in the pickup process was much larger than that in the fragmentation process. From the NMR spectra, we obtained the magnetic moment $\vert $\textit{$\mu $}($^{23}$Ne)$\vert _{uncorrected}$ = (1.081 $\pm $ 0.001)\textit{$\mu $}$_{N}$ as the preliminary result. [Preview Abstract] |
Monday, September 19, 2005 9:00PM - 9:15PM |
BE.00008: Nuclear polarization of the ground state of $^{57}$Cu produced through a nucleon pick up reaction at the primary beam energy 140 MeV/nucleon Kei Minamisono, Paul Mantica, Theodore Mertzimekis, Andrew Davies, Jorge Pereira, Josh Stoker, Bryan Tomlin, R. Ranjith Weerasiri, Michael Hass, Warren Rogers In order to measure the magnetic moment of the ground state of $^{57}$Cu($I^{\pi }$ = 3/2$^{-}$, $T_{1/2}$ = 199 ms), which is one proton outside doubly-magic $^{56}$Ni, a polarized $^{57}$Cu beam has been developed at NSCL/MSU. $^{57}$Cu ions were produced through a (p, 2n) reaction process of a 140 MeV/nucleon $^{58}$Ni primary beam on Be target and separated from other products in the A1900 fragment separator. To produce polarization, $^{57}$Cu ions ejected at an angle of 2 degree relative to the normal beam axis were selected. Polarized $^{57}$Cu ions were implanted into a single-crystal NaCl under an external magnetic field $H_{0} \quad >$ 0.1 T. The degree of the polarization was measured by an $H_{0}$ on and off technique with normalization runs without polarization. The degree of the polarization as a function of the momentum of $^{57}$Cu and $H_{0}$ will be discussed. [Preview Abstract] |
Monday, September 19, 2005 9:15PM - 9:30PM |
BE.00009: Bohr Weisskopf effect measurements using NMR-ON Takashi Ohtsubo, Susumu Ohya, Katsuhiko Nishimura, Takuji Izumikawa, Jun Goto, Minoru Tanigaki, Akihiro Taniguchi, Yoshitaka Ohkubo, Yoichi Kawase, Suguru Muto The difference between the point nuclear magnetic structure and the finite magnetic structure is referred as Bohr-Weisskopf (BW) effect (hyperfine anomaly), which depends on the nuclear structure. If the spin and orbital contributions to the magnetic moment have opposite sign, the large BW effect is expected. Recently, we have measured BW effects using NMR-ON and Brute force (12T) NMR-ON method. For Sc isotopes ($A=44, 44m, 46$ and $47$) we determined the BW effects comparing the magnetic resonance frequencies in Fe and the magnetic moments from atomic beam method. We also deduced the large BW effect of $-4.2\%$ between $^{91}$Y and $^{91}$Y$^ m$ in Fe from the precise measurement of the field shift of resonant frequency. Furthermore, we determined the BW effects between $^{95}$Tc and $^{96}$Tc, and $^{106}$Ag and $^{110}$Ag$^m$ comparing resonance frequencies of Brute force NMR-ON and those of the known NMR-ON results in Fe. These results will be discussed in terms of the shell model including core polarization and exchange current effects. [Preview Abstract] |
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