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Physics · 术语表

什么是 The three historic radiations？

又称： alpha radiation · beta radiation · gamma radiation · attenuation

Definition 19.7 High School Physics · 第 19 章 — The Nucleus and Radioactivity

Three radiations, named before anyone knew what they were:

alpha ( $\alpha$ ): a helium nucleus ${}^{4}_{2}\mathrm{He}$ ejected whole — heavy, doubly charged, stopped by a sheet of paper or centimetres of air;
beta ( $\beta^-$ ): an electron ${}^{\;0}_{-1}\mathrm{e}$ created in the nucleus and ejected — light, fast, stopped by millimetres of aluminium;
gamma ( $\gamma$ ): electromagnetic radiation, far more energetic than light — never quite stopped, only attenuated: a centimetre of lead absorbs half.

dies in paper, - in millimetres of aluminium; is only thinned, even by lead. — $\alpha$ dies in paper, $\beta^-$ in millimetres of aluminium; $\gamma$ is only thinned, even by lead.

示例

Example 19.11 (An alpha decay)

Radium-226, the Curies’ radium, is an $\alpha$ emitter: ${}^{226}_{88}\mathrm{Ra} \to {}^{A}_{Z}\mathrm{Y} + {}^{4}_{2}\mathrm{He}$ forces $A = 226 - 4 = 222$ and $Z = 88 - 2 = 86$ ; element $86$ is radon, so ${}^{226}_{88}\mathrm{Ra} \to {}^{222}_{86}\mathrm{Rn} + {}^{4}_{2}\mathrm{He}$ — the radioactive gas of unventilated cellars.

Example 19.12 (A beta-minus decay)

Carbon-14 sits above the band ( $8$ neutrons against $6$ protons): ${}^{14}_{6}\mathrm{C} \to {}^{14}_{7}\mathrm{N} + {}^{\;0}_{-1}\mathrm{e}$ . Check: $14 = 14 + 0$ , $6 = 7 - 1$ ; a neutron became a proton plus the ejected electron — the weak interaction at work.

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