Actinium

解説アクチニウム，Ac．原子番号89の元素．電子配置[Rn]6d17s2の周期表3族アクチノイド元素．ギリシア語の“光線”を意味するακτινοσから名づけられた．1899年，A. Debierne，1902年，F. Gieselによりウラン鉱石中から独立に発見された．現在，知られている同位体核種は，206～236の範囲に核異性体を含めて35種．質量数227の核種がもっとも長寿命で半減期21.77 y．主としてβ崩壊して227Thになる．天然には，この核種が235Uからはじまるアクチニウム系列の中間に存在する．トリウム系列中にも半減期6.15 h のβ崩壊核種228Acが存在する．単体は，フッ化物AcF3を1100 ℃ 以上の高温でLi蒸気で還元すると得られる．銀白色の金属．密度10.07 g mL－1．融点1050 ℃，沸点3200 ℃．第一イオン化エネルギー498.7 kJ mol－1(5.17 eV)．化学的性質は希土類元素，とくにランタンに似るが，より塩基性である．酸化数3．

説明Actinium-227 occurs in uranium ore and is a decay product of uranium-235. It is found in equilibrium with its decay products. It is prepared by bombarding radium atoms with neutrons. Chemically, the metal is produced by reducing actinium fluoride with lithium vapor at 1,100℃ to 1,300℃. AcF3+Li→Ac + 3LiF The element was discovered independently by A. Debierne and F. Giesel in 1899 and 1902, respectively. It is used in nuclear reactors as a source of neutrons.

天然物の起源Actinium-227 occurs in uranium ore and is a decay product of uranium-235. It is found in equilibrium with its decay products. It is prepared by bombarding radium atoms with neutrons. Chemically, the metal is produced by reducing actinium fluoride with lithium vapor at 1,100°C to 1,300°C. AcF3+Li→Ac + 3LiF The element was discovered independently by A. Debierne and F. Giesel in 1899 and 1902, respectively. It is used in nuclear reactors as a source of neutrons.

来歴The name Actinium derives from the Greek, aktis or akinis for “beam or ray” because in equilibrium with its decay products, actinium is a powerful source of alpha radiation. The discovery has been credited to the French chemist Andre-Louis Debierne in 1899. It was independently discovered by German chemist Friedrich Oskar Giesel in 1902, who called it emanium. It is thought that Debierne’s original preparation actually consisted of two thorium isotopes, 227Th and 230Th, but there was confusion in those early discoveries in radioactivity and Debierne’s claim prevailed and his name of actinium has been retained to this day. The longest half-life associated with this unstable element is 21.77 year 227Ac.