Sec. 7.10] RADIOACTIVITY 171 



Definition: A rutherford is the quantity of any radioisotope that decays at 

 the rate of 10 6 disintegrations per second. 



The rutherford has been proposed as a new unit of quantity for all radio- 

 isotopes with the exception of the decay products of radium for which 

 the curie applies [3]. Its value was arbitrarily chosen so that 1 rutherford 

 is in the order of magnitude of quantities used in tracer and therapeutic 

 applications. 



REFERENCES FOR SECS. 7.1 TO 7.9 



1. Bateman, H.:Proc. Camb. Phil. Soc, 15, 423 (1910). 



2. Curie, I., Mme., A. Debierne, A. S. Eve, H. Geiger, O. Hahn, S. C. Lind, St. Meyer. 

 E. Rutherford, and E. Schweidler: Rev. Mod. Phys., 3, 427 (1931). 



3. Condon, E. U., and L. F. Curtiss: Science, 103, 712 (1946); Phys. Rev., 69, 672 (1946). 



7.10. Decay Schemes. The decay schemes given below are intended to 

 convey as much essential information as possible about the radiations asso- 

 ciated with radioactive decay of certain isotopes. It must be recognized that 

 the experimental data are not yet complete nor are they always conclusive. 

 Many of the decay schemes therefore are still tentative, and most are incom- 

 plete so far as detailed information, such as conversion coefficients, is 

 concerned. 



The transitions from the unstable states of a nucleus to its ground state 

 proceed from left to right. The first transition is indicated, for example, by 

 70 /3~ 2.9. The first number is the percentage of disintegrations in which 

 the particular transition (fi~ emission) occurs, followed by the type of radia- 

 tion and finally, the energy in mev, except in K capture. Isomeric transitions 

 are indicated in the same manner except that when the internal conversion 

 coefficient is known it is given as the denominator of a fraction before the 

 Greek letter y, the numerator, when given, indicating the percentage of 

 disintegrations in which the particular transition occurs. The conversion 

 coefficient given here is defined by/ = N e /(N e + N y ), where N e and N y are 

 the numbers of conversion electrons and gamma rays associated with the 

 transition which are emitted per transition. When the spin and energy of 

 particular levels are known, these are indicated above or below the vertical 

 bar indicating the level. The ground state of the stable nucleus is indicated 

 by a vertical double bar and designated by the Z, symbol, and A of the stable 

 nucleus. Excited levels of the same nucleus are indicated by a horizontal 

 line connecting the indicated levels. 



The numbers in parentheses in the schemes refer to the numbered references 

 given on page 177. 



