Alpha rays - alphathene

A nucleus particle beam of ^4He emitted by the alpha decay of a radioactive nuclide. A nuclide that emits alpha rays changes to a nuclide with an atomic number reduced by 2 and a mass number reduced by 4. In early research, it was confirmed that there are three types of radiation from natural radioactive materials, which were named alpha rays, beta rays, and gamma rays. They were named by E. Rutherford. The energy of alpha rays observed in nature is several MeV, with a maximum of 9 MeV, and their range in the atmosphere is about 10 cm. The spectrum of alpha rays is a line spectrum, unlike beta rays. When alpha rays pass through a material, they generate many ions and excited atoms and molecules, but their tracks are linear, and most of them pass through a thin film. However, some are scattered by the atomic nucleus (Rutherford scattering) and change their course significantly. Rutherford, who first noticed this, published the planetary model of the atom in 1911. Alpha rays are used in a variety of fields, including cancer treatment for brain tumors and malignant melanoma, measuring the thickness of thin films, and even in luminous paint. Helium nuclei that are accelerated by accelerators such as cyclotrons rather than by alpha decay, or that are produced in nuclear reactions such as ⁶ Li(n,α)T, are not called alpha rays, but are called alpha particles.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

放射性核種のα崩壊によって放出される⁴Heの原子核粒子線．α線を放出した核種は原子番号を2，質量数を4減らした核種に変化する．初期の研究において，天然の放射性物質からの放射線には3種類あることが確認され，α線，β線，γ線と命名された．命名者はE. Rutherford(ラザフォード)である．自然界で観測されるα線のエネルギーは数 MeV で，最大でも9 MeV，大気中の飛程は約10 cm である．α線のスペクトルはβ線とは異なり，線スペクトルである．α線が物質を通過する際には多くのイオンおよび励起した原子や分子を発生させるが，飛跡は直線的で，薄膜ならば大半が通過してしまう．しかし，一部は原子核によって散乱されて(ラザフォード散乱)進路を大きく変更する．このことに最初に気付いたRutherfordが，1911年に原子の惑星模型を発表した．α線は，脳腫瘍，悪性黒色腫などのがん治療，薄膜の厚さ測定，さらには夜光塗料など，さまざまな分野で利用されている．α崩壊ではなく，サイクロトロンなどの加速器によって加速されたヘリウム核や，⁶Li(n,α)Tなどの核反応で生成するヘリウム核はα線とはよばず，α粒子という．

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