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匿名 發問於 科學及數學其他 - 科學 · 7 年前


1) Can a piece of paper be "charged" by beta radiation (Can the radiation induce the paper and make it positively charged?)? Is there something wrong in my concepts?

2) I found from the Internet that "lead is good for shielding against X-rays, gamma rays because lead has lots of electrons the rays can interact with". Then what about those elements that have high atomic numbers? Are they really good at shielding?

3) Why can hitting a heavy metal target with high-speed electrons produce X-rays?


1 個解答

  • 天同
    Lv 7
    7 年前

    1. Beta ray is "ionizing radiation". It can ionize the substance that it passes through. Hence, in principle, electrons and ions are produced within the substance. But such charges are rapidly neutralized by free electrons and ions present in the air.

    2. X-ray absorption is mainly due to photoelectric effect in which the energy of the incident X-ray photon is absorbed by the orbital electrons of target materials. Hence, the more no. of atoms in a unit volume, the better is the absorption. That is to say, high density materials are good shielding materials for x-rays.

    Leas is commonly used as x-ray shield because of its high density compared with other common metals like iron or copper, and also because of its low cost. In fact, metals/materials with density higher than lead serve as radiation shield better than lead. Depleted uranium (i.e. uranium with most radioactivity removed) is the best shielding material for x- or gamma rays because uranium is the heaviest natural occuring metal. It is used mainly on military purpose because of its high cost.

    3. When a fast moving electron strikes a heavy atom, such as those in a heavy metal target like tungsten, it is under a rapid deceleration. According to classical electromagnetic theory, a charge under rapid acceleration or deceleration would lose its kinetic energy and have it radiated out as electromagnetic waves in the form of x-rays. Such phenomenon is knowned as Bremsstralung (Braking Radiation).

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