(15分)有關粒子及電磁波的輻射有害程度

Alpha、Beta及Gama粒子的速度由低至高，學校老師利用這特點進行以下解說：「一個粒子移動速度愈低，代表愈容易碰上另一粒ion，因此它的電離力ionizing power高及穿透力penetrating power低。」
這句解釋的因果關係是否正確?又是否都適用於解釋3者的電離力和穿透力?


這個因果不正確. 其實行得愈快先愈容易撞另一粒atom, 不過係依個case唔關行得快唔快事微觀上, 原子atom入面大部分地方都係空嘅(space), 入面nucleus直徑得atom嘅十萬分一左右, 啫係如果atom係大球場, nucleus就只係大球場入面嘅一粒米咁上下。係依個情況下, gamma係光子, 無charge(電荷), 好細機會可以同d 粒子(質子同電子)有interaction, 自然難ionise, 同埋撞唔到直接穿過, penetrating power自然高。
而相對上, beta同alpha有charge又大粒d, 同atom入面嘅particle多d interaction(因為入面嘅質子同電子都係帶電), 所以就ionisationpower高d.alpha ge penetratingpower 細, 係因為佢size相對電子(beta)大好多, 較容易被阻隔. 除此之外, mass ofalpha>> mass of beta, 所以 KE of alpha>> KE of beta, 所以撞埋去, alpha比到多d energy, ionise 到嘅機會都高d



在維基百科查閱「微波通訊」，當中提及「只有高能微波才會變得有害和危險。」
但電磁波在真空的速度均為光速，無法用老師的解說方法解釋其電離力及穿透力的高低，該如何去解釋？
為什麼高能微波較低強度微波有害？能量高低跟波長及頻率有任何關係嗎？ 波長短嘅, 能量就高d, 電磁波(microwave)同gamma都係光速, 但microwave波長長過gamma好多, 所以microwave係無gamma咁勁。 高能微波勁d係因為第一, 波長短, 能量高, 啱啱講過第二, 散射(diffraction)少, 能量散失(energy loss)少, 密度(intensity)高, that’s why你見wiki話佢有90%咁高效率 基本上, 波長係同頻率成反比, 即係波長長, 頻率就會低左 希望解答到你, 有咩唔明歡迎再問

2012-02-29 00:02:30 補充：
樓上講得啱, microwave係ionise唔到野嘅, 我所講嘅只係比較gamma同microwave之間嘅能量差別

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Alpha, beta and gammma fall into the category of "ionizing radiation". That is, they cause ionization when passing through matter.

The ionization power is, in fact, depends mainly on the charges possessed by the particle and the speed of the particle.

Alpha, because of its low speed, could spend more time near an atom. This provides a greater chance for the alpha to "tear off" an orbital electron from the atom by electrostatic interaction, thus causing ionization.

Beat, on the other hnad, moves at high speed. In so doing, it only spend a short interval of time (as compared with alpha) near an atom. The chance of causing ionization is therefore proportionally reduced.

Gamma rays carries no charge. It cannot cause ionization by direct electrostatic means. Gamma rays ionize matter by processes of photoelectric effect, inverse Compton scattering or pair-production. It is thus a weak ionizing radiation.

During ionization, the radiation (alpha, beta or gamma) loses energy. Radiation with strong ionization power therefore loses energy much faster than radiation with weak ionization power. The radiaion disappear when all its energy has been lost. Hence, radiation with strong ionization power has the least penetration and vice versa.

Microwave is NOT ionizing radiation. It cannot cause ionization when passing through matter, and hence is not as dangerous as ionizing radiation. Based on up-to-date scientific knowledge, the only established health effect of microwave on human body is skin heating. Microwave with high intensity (高能微波) heats up the human body similar to the effect of heating foodstuff in a microwave oven.




2012-02-28 23:14:26 補充：
Just wish to correct a mistake in the sentence:
"Gamma rays ionize matter by processes of photoelectric effect, Compton scattering or pair-production".
I have mistyped "inverse Compton scattering" in the answer.