Welcome to the ISOSPIN smmetry world !


Welcome to the ISOSPIN Symmetry World !
対称性の世界へようこそ！



電磁相互作用によるγ遷移、弱い相互作用によるβ崩壊、強い相互作用で起こ
る(3He,t)反応の結果を比較し、粒子崩壊の始まる直前までの励起状態の鏡対
称性が、27Al-27Si において"観えだした"のです。



"Mirror-symmetry structure of A=27, T=1/2 nuclei studied 
 through strong, weak, and electromagnetic interactions"

   Physical Review C 59 (1999) 90.


 Abstract
     Gamow-Teller (GT) transitions and M1 transitions from or the 
     ground states are analogous in the pair of T=1/2 mirror nuclei, 
     if the excited states hold the mirror-symmetry properties.  
     In order to study the mirror-symmetry structure of 
     the A=27 mirror nuclei 27Al and 27Si, experimental data on GT 
     transition strengths obtained from 27Si \rightarrow 27Al beta-
     decay and from a good-resolution 27Al(3He,t)27Si reaction at 
     150 MeV/nucleon and 0-deg have been compared with M1 transition 
     strengths obtained from gamma-decay in 27Al and
     27Al(\gamma,\gamma') reaction.  Good overall correspondence of 
     transitions is observed for states up to nearly 9 MeV in
     excitation energy, where the particle-decay channel becomes 
     important.  The difference of excitation energies of analog
     states in the mirror nuclei are about 250 keV at this excitation 
     energy.  From a comparison of B(M1) and B(GT) strengths of the 
     analogous transitions, the contribution of the isoscalar and 
     the orbital terms in the M1 operator is found to become prominent 
     in weak M1 transitions.  


(3He,t) (p,p') 反応から知るアイソスピン対称性の世界の登場です。
崩壊による測定と異なり、強い相互作用で起こる原子核反応を使うと、高い
励起状態までの研究が可能です。しかし必要な分解能を200-400 MeV の高い
入射エネルギー領域で、どのように達成できるかが大問題だったのです。
分散整合法で高分解能を達成し、(3He,t)反応と (p,p')反応で観測される
個別状態の１対１対応を調べることを可能としました。その結果、鏡映核
27Al-27Si において、励起エネルギー 15 MeV までのアイソスピン対称性が
確認されました。




"Isospin symmetry-structure study at new high-resolution course 
 of RCNP"

   Nuclear Physics, A687 (2001) 311c-320c.


 Abstract 
     High-resolution (3He,t) reaction at an intermediate incident 
     energy is a new spectroscopic tool.  With the achieved resolution 
     of well less than 100 keV, it is possible to study the fine 
     structures of various excitation modes up to highly excited region.  
     By comparing energies and strengths of individual Gamow-Teller 
     transitions obtained in the (3He,t) reaction with those of M1 
     transitions from M1 $\gamma$ decay as well as from (p,p') reaction, 
     analogous states are identified  for the isospin T=1/2 mirror 
     nuclei 27Al and 27Si.  Good correspondence of GT and M1 states 
     showed the existence of mirror (isospin) symmetry structure up to 
     Ex=15 MeV in these nuclei.  The excitation strengths of analogous 
     states have been compared in detail in the Ex > 8 MeV region,   
     where T=1/2 and 3/2 states are expected to coexist.  Based on the  
     different enhancement of analogous M1 and GT transitions 
     depending on the T=1/2 -> 1/2 or 1/2 -> 3/2 nature of transitions, 
     T values of highly-excited states have been systematically 
     determined for the first time.

次々に明らかにされる対称性の世界。現在改良工事進行中。