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【正文】 nd the nucleus is assumed to have a positive charge Ze where e is the electronic charge and Z the atomic number. The α particle has a charge of +2e and the force between it and the nucleus is given by Coulomb’s law. Figure shows through situation, with the nucleus situated at the origin. The α particle starts far enough away from the nucleus for the interaction force to be negligible and travels parallel to the χaxis. An important parameter of the motion is the impact parameter, b, which defines the minimum distance between the nucleus and the particle if the particle were mot deflected. Electrostatic repulsion means that the particle is deflected through an angle Θ and it is obvious that the smaller the value of b, the greater is the value of Θ. It is now possible to work out a value for Θ in terms of b and the kiic energy of the particle T. Since the mass of the nucleus is much greater than that of the α particle, the kiic energy and hence the speed of the particle before and after deflection remains the same. However the particle’s direction of motion has changed and the law of conservation of momentum gives an expression for the absolute value of the change in momentum () ? ?21 2 sin / 2p p p m ?? ? ? ? ? （ ） Where m is the mass of the particle, and υ its speed. From Newton’s second law,this change of momentum must be equal to the force acting on the particle, integrated over the whole time that the particle is in the field of the nucleus. Therefore, 02 sin ( / 2 )p m F d t? ?? ? ? ? ? （ ） Figure the direction of F a particular position of the particle, defined by through angle φ, as shown, by symmetry, it can be seen that the integral in () is given by 00 c o sI F dt F dt??????? (since the integral of the ponent parallel to the χaxis, F sinφ, must be zero, by symmetry ). Fig Change in momentum of an α particle during interaction with through nucleus. A change of variables for integration enables () to be rewritten: ? ? ( ) / 2( ) / 22 s in / 2 c o s ( / )m F d t d d??? ? ? ???? ? ??? ? （ ） (see Fig for the changed limits of integration). Finally, (dt/dφ) is equal to 1/ω where ω is the angular speed of the particle about the origin. Since the force acting on the particle is radial, the angular momentum of the particle is the same for any value of φ, and ω must be given by the equation 2mr m b??? Therefore 2( / ) /dt d r b??? Coulomb’s law gives 2202 / 4F Ze r??? so that substituting in () and integrating through right hand side gives an expression for Θ in terms of υ and b 220c ot( / 2) ( 2 / )m Z e b?? ??? （ ） or, in terms of the kiic energy T of the particle 20c ot( / 2) ( 4 / )T Z e b???? （ ） This gives an equation for the scattering angle in terms of the kiic energy and impact parameter of the particle and of the charge on the nucleus, Ze. 介紹 雖然希臘哲學(xué)家德謨克利特曾推測(cè)了在公元前一世紀(jì)原子的存在和道爾頓的原子理論 1807 年奠定了原子的存在 ,在 20 世紀(jì)之交以前。事實(shí)上，當(dāng)時(shí)一所有影響力的學(xué)校的領(lǐng)導(dǎo)德國(guó)物理學(xué)家馬赫認(rèn)為原子模型僅僅是一個(gè)沒(méi)有現(xiàn)實(shí)的基礎(chǔ)上有用的圖片。 原子的存在 這種情況戲劇性的改變由超過(guò) 1897 年和 1912 年之間 15 年的實(shí)驗(yàn)研究。在19 世紀(jì) 70 年代，在真空泵施工技術(shù)的改進(jìn)已使制 造電極管和無(wú)形射線的發(fā)現(xiàn)成為可能，電極管是一電負(fù)電極（陰極）和電正極（陽(yáng)極）組成的。 這些射線后來(lái)被稱為陰極射線。起初，曾經(jīng)有過(guò)很大的爭(zhēng)議的性質(zhì)，而由湯姆孫在 1897 年一系列實(shí)驗(yàn)得出結(jié)論表明，該陰極射線是一個(gè)大概在陰極（圖 ）原子發(fā)射帶負(fù)電荷的粒子流組成。 湯姆森對(duì)由電場(chǎng)和磁場(chǎng)的陰極射線偏轉(zhuǎn)的測(cè)量由粒子的速度來(lái)衡量，也是一個(gè)粒子的電荷比質(zhì)量。到了世紀(jì)之交，這些粒子，被稱為電子，可以測(cè)量到相當(dāng)高的精度。 然而，在不同的實(shí)驗(yàn)需要我們的荷質(zhì)比絕對(duì)的值。實(shí)驗(yàn)最成功的是，油滴被控以某種方式及其在電力領(lǐng)域的宏 觀粒子的運(yùn)動(dòng)情況。油滴質(zhì)量相對(duì)簡(jiǎn)單的測(cè)量啟用了電子電荷來(lái)衡量。著名的實(shí)驗(yàn)由密立根在 1909 年和 1916 年間被做出，并且發(fā)表了測(cè)量結(jié)果為 177。 1019庫(kù)侖，和今天接受的實(shí)驗(yàn)結(jié)果相比
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