為什麼鉛能阻擋伽瑪射線﹖

In fact, any material could absorb gamma rays. It is only the question of how effective the absorption is. Generally, the higher the density of the material, the more effective is the absorption. This is the reason why X-ray or gamma ray shielding usually use materials of high densities, such as lead, concrete or even depleted uranium.

The absorption of gamma rays passing through a shielding material is rather complex, as the degree of absorption depends very much on gamma ray energy.

The three important processes involved are (1) photoelectric effect, (2) comption scattering, and (3) pair production.

Breifly, photoelectric effect involves the complete absorption of gamma ray photon by orbital electrons of the shielding material. This process mostly occurs at low energy gamma ray photons (energy < about 50 keV) .

Compton scattering involves the incomplete absorption of gamma ray energy by orbital electrons. However, the scattered photon is usually of very low energy and would be easily absorbed.This process takes place for gamma ray photon energy from about 50 keV to 1 MeV

Pair production involves the complete absorption of gamma ray photon with the production of elctron-positron pair. This process tkaes place for high energy gamma rays (energy > 1 MeV), such as those emitted by Cobalt-60 .

沒有氧化層的鉛色澤光亮，密度高，硬度非常低，延伸性很強。它的導電性能相當低，抗腐蝕性能很高，因此它往往用來作為裝腐蝕力強的物質（比如硫酸）的容器。加入少量銻或其它金屬可以更加提高它的抗腐蝕
鉛有四種自然的、穩定的同位素：Pb-204（1.4%）、Pb-206（24.1%）、Pb-207（22.1%）和Pb-208（52.4%）。後三種是鈾-238、鈾-235和釷-232經過一系列裂變後的最終產物。這些反應的半衰期分別是4.47×109年、7.04×108年和1.4×1010年。只有204Pb是自然存在的、非衰變產物。
鉛可阻擋放射性同位素的輻射型式有α射線、β射線、γ射線三種，對物質具有穿透能力，故容易偵測。放射性同位素應用於工業上，依工業上所需選擇輻射型式、半生期、最大能量各不同的核種。利用放射性同位素不同的能量、輻射型式、半生期，及對物質的效應不同，且微量的放射性同位素即具有足夠偵測的輻射，故能作為示蹤劑。放射性同位素，有下列三種特性：物質影響放射線強度，放射線能改變物質結構和以微量的放射性同位素為示蹤劑。依這三種特性，使放射性同位素配合適當的偵測儀器來作物質的厚度、密度、種類的測定和其他工業上的廣泛用途，如品質管制等。