Reaction Mechanism of ^4He Photodisintegration and Charge Symmetry

^4He光崩解反应机理与电荷对称性

• 批准号: 13640287
• 负责人: SHIMA Tatsushi
• 金额: $ 2.18万
• 依托单位: Osaka University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640287/
• 关键词: photonuclear reaction; charge symmetry; ^4He; tagged photon; time projection chamber; 標識ガンマ線; レーザー; 逆コンプトンγ線

The photonuclear reactions of ^4He in the energy region below the pion threshold are quite useful to investigate fundamental properties of few-nucleon systems and the nuclear charge symmetry. The present work was aimed to investigate the reaction mechanism of the photodisintegration of ^4He occurring in the energy region from 30MeV to 100MeV by measuring the reaction events precisely. For this purpose, we developed a new experimental method. In this method we used the tagged photon beam at Laboratory of Nuclear Science (LNS) of Tohoku University and a time projection chamber (TPC) filled with a gas mixture of He and CD_4. The photon beam impinged upon ^4He nuclei contained in TPC, and the charged particles were detected by TPC. So TPC served as an active target, and that provided extremely high detection efficiency of -100% and very large acceptance of almost 4π of the solid angle.Since TPC is a kind of drift chambers, an external trigger signal was needed to measure the tracks of the … More charged particles emitted from the reactions. But the LNS tagged photon beam is a continuous beam, it cannot be used as a source of the external trigger. So we installed a trigger counter (TR) made of plastic scintillators in TPC. TR could provide a prompt signal of the particles with the energies down to 1MeV, and the time resolution was 1.1ns(1σ). To study the performance of the measurement system, we made a test experiment at the LNS tagged photon facility We accumulated the raw data of about 400000events during the measuring time of 42300s. By requiring the coincidence between TPC and the photon tagging counter (TAG) in the offline analysis, the background events were efficiently reduced, and 20000events survived. Then we checked the tracks of the particles in the remaining event, and we could select the candidates of the photoreaction events of ^4He, D and ^<12>C, which were main compositions of the counter gas. The present result shows the good performance of our experimental method. More detailed analysis is now in progress. Less

^4He在介子阈值以下能量区的光核反应对研究少核子系统的基本性质和核荷对称是非常有用的。本文旨在通过精确测量^4He在30MeV ~ 100MeV能量范围内发生光分解的反应事件，探讨其反应机理。为此，我们开发了一种新的实验方法。在该方法中，我们使用了东北大学核科学实验室（LNS）的标记光子束和充满He和CD_4混合气体的时间投影室（TPC）。光子束撞击到TPC中包含的^4He核上，TPC检测到带电粒子。因此，TPC作为主动目标，具有极高的检测效率-100%和几乎4π的立体角接受度。由于TPC是一种漂移室，因此需要一个外部触发信号来测量反应释放的更多带电粒子的轨迹。但LNS标记的光子束是连续光束，不能作为外部触发源。因此，我们在TPC中安装了一个由塑料闪烁体制成的触发计数器（TR）。TR可以提供能量低至1MeV的粒子的提示信号，时间分辨率为1.1ns（1σ）。为了研究测量系统的性能，我们在LNS标记光子设备上进行了测试实验，在42300s的测量时间内积累了大约400000个事件的原始数据。通过在离线分析中要求TPC与光子标记计数器（TAG）的一致性，有效地减少了背景事件，使2万个事件存活下来。然后对剩余事件中粒子的轨迹进行了检测，确定了作为反气体主要成分的^4He、D和^<12>C的候选光反应事件。目前的结果表明，我们的实验方法具有良好的性能。更详细的分析正在进行中。少

项目成果

M.Fujiwara, T.Shima: "Electromagnetic Interactions in Nuclear and Hadron Physics"World Scientific Publishing Co. Pte. Ltd.. 709 (2002)

M.Fujiwara、T.Shima：“核与强子物理中的电磁相互作用”世界科学出版有限公司 Pte。

T.Shima et al.: "Photonuclear reaction of ^4He at Eγ=20〜32MeV"Physics Letters B. (in press).

T. Shima 等人：“^4He 在 Eγ=20〜32MeV 处的光核反应”Physics Letters B.（出版中）。

T.Shima et al.: "Photonuclear Reactions of ^3He and ^4He at Low Energies and Few Body Problems"Physica Scripta. T104. (2003)

T.Shima 等人：“^3He 和 ^4He 在低能量和很少的身体问题下的光核反应”Physica Scripta。

T.Shima et al.: "GDR Problem in Photodisintegration of ^4He"Nuclear Physics A. 687. 127c-131c (2001)

T.Shima 等人：“^4He 光崩解中的 GDR 问题”核物理 A. 687. 127c-131c (2001)

T.Shima et al.: "GDR Problem in Photodisintegration of ^4He"Nuclear Physics. A687. 127-131 (2001)

T.Shima 等人：“^4He 光崩解中的 GDR 问题”核物理。