CONTEMPORARY ADVANCES IN PHYSICS, XXVIII 593 



the "initial" or mother nucleus. It is not clear from the litera- 

 ture whether this hypothesis has been fully tested in the manner of 

 Meitner's tests aforesaid, but presumably it was adopted in calculating 

 the ^j^-values from the electron-energies, so that the agreements 

 between hv and ( Ui — Uj) support it.^^ 



The search for interrelations among the energy-levels, the different 

 hp-values and the different f/-values belonging to individual trans- 

 formations has of course already begun. Rutherford and Ellis find 

 that the frequencies of many of the lines in the gamma-ray spectrum 

 of RaC can be fitted by assigning various integer values to p and q and 

 constant values to £i and £2 in the formula pEi -\- qE^; while H. A. 

 Wilson finds that if the tZ-values or the /zj'-values are added together 

 in pairs, an amazing number of the pairs are equal to integer multiples 

 (the integer multipliers ranging from 16 to 54) of the amount 0.385 

 MEV — this even if the two members of a pair are taken from different 

 spectra ! 



The Quantum-Mechanical Theory and the Crater 

 Model of the Nucleus ^^ 

 Anyone who is acquainted with the contemporary atom-model in 

 its present or in its earlier stages, with its congeries of charged particles 

 revolving in or jumping between definitely-prescribed and quantized 

 orbits, governed by attractions and repulsions both classical and 

 unimaginab' 2 — any such person will probably be looking for a nucleus- 

 model of the same variety but built on a very much smaller scale, 



" I learn by letter from Dr. Ellis that in the case of RaC, some at least of the 

 gamma-rays which agree with the ([/,-C/,)-values of the long-range alpha-particles 

 are definitely proved in this fashion to proceed from nuclei of atomic number 84 

 (that of RaC') as distinguished from 83, 82 or 81; the proof is especially strong for 

 the most intense gamma-ray, of photon-energy 0.607 MEV. Perhaps this is the most 

 powerful evidence that the long-range particles come from RaC rather than RaC. 



The half-periods of RaC and ThC' are exceedingly short, 10~^ sec. and 10~^^ sec. 

 respectively; had it been otherwise, objection might be made to Gamow's contention 

 on the ground that atoms in states, from which they are liable to depart by emitting 

 radiation, generally do depart from those states and emit that radiation within a 

 period of the order of 10~^ or 10"* sec. There is no a priori certainty that this 

 principle applies to nuclei, but if it does it may suffice to explain why the long-range 

 particles are observed only from these very short-lived nuclei, why they are so 

 scanty even in these cases (nearly always the photon is emitted before the alpha- 

 particle gets ready to leave, so that the latter nearly always leaves with low energy 

 instead of high), and why the fine-structure of other alpha-ray spectra is related to 

 energy-levels of the final instead of the initial nucleus (Gamow). Incidentally it 

 strengthens the case for ascribing the long-range particles to the C-products insterd 

 of the C-products. 



^2 Quantum mechanics was first applied to the nucleus-model here to be described, 

 independently and almost simultaneously, by Gurney and Condon and by Gamow. 

 Rather than by all three names together, it seems preferable to denote this model 

 thus interpreted by a neutral descriptive term, such as "crater model" (an allusion 

 to the aspect of the graph obtained when the curve of Fig. 12 is coupled with its 

 mirror-image in the yz-plane). 



