558 Sir ]3. Rutherford on Collision of 



§ 12. Summary. 



1. The production of high-speed hydrogen atoms due to 

 close collisions between a particles and atoms of hydrogen 

 has been studied using the a. particles from radium C as 

 a homogeneous source of radiation. In such close collisions, 

 where the nuclei approach within a distance of about 

 3 x 10 ~ 13 cm., the number and distribution of the H atoms 

 are entirely different from those calculated on the assumption 

 that the nuclei are to be regarded as point charges repelling 

 each other according to the law of inverse squares. 



2. The H atoms produced by swift a particles of range 

 7 cm. are shot forward mainly in the direction of the 

 a particles and are nearly uniform in velocity. 



3. The distribution with velocity of H atoms becomes 

 more and more heterogeneous with decrease of velocity of 

 the a particles. For « particles of range less than -1 cm. of: 

 air, the distribution and absorption of H atoms are in fair 

 accord with the simple theory although the observed 

 numbers are greater than those calculated on the theory. 



4. The number of swift H atoms produced by « particles 

 of range 7 cm. is 30 times greater than the theoretical 

 number. The number falls off rapidly for ranges of 

 a particles between 3 and 2 cm. On an average 10 5 

 of, particles give rise to one swift hydrogen atom in traversing 

 one centimetre of hydrogen. 



5. It has been calculated that all a particles of range 7 cm. 

 projected within a perpendicular distance p= 2*4 x 10 ~ 13 cm. of 

 the centre of the hydrogen nucleus give rise to swift H atoms. 

 The corresponding apsidal distance is about 3'5 x 10" 13 cm. 



6. As observed by Marsden, hydrogen atoms are emitted 

 by the radioactive source. The number observed is small, 

 and it is difficult to decide whether these H atoms arise from 

 the radioactive transformation or from occluded hydrogen 

 in the source. 



Discussion of results. 



On the nucleus theory of the atom, the charged nucleus 

 is supposed to be of such small dimensions that it may 

 be regarded as a point charge for distances of the order 

 of 10~ n cm. The correctness of this point of view in the 

 case of hydrogen is strongly supported by the remarkable 

 success of Bohr and those who have followed him in 

 explaining by its aid the finer points of the hydrogen 



