146 The Birth and Death of the Sun

(1) J)2 + iH1 -- >2He3 + radiation

(2) 3Li6 + iH1 - >2He4 + 2He3

(3) 3Li7 + iHi - »2He4 + 2He4

(4) 4Be9
() 5Bio + 1H1 - »6Cn + radiation

2He4 + 2He4

The available data of nuclear physics permit us to esti-
mate the rate of subatomic energy liberation for each of
the above reactions with the result that they fall into three
distinctly separate types.

The first type includes only the extremely rapid reac-
tions between deuterons and protons (i). Owing to the
small electric charges of both particles involved, this
reaction leads to a very high energy liberation even at
such low temperatures as a million degrees.

The second type contains the slower reactions of both
lithium isotopes (2, 3), the reaction of beryllium (4), and
the reaction of the heavier isotope of boron (6). The
temperatures necessary for these reactions lie in the range
between 3 and 7 million degrees.

Finally, the third type consists of the still slower reaction
of the lighter isotope of boron (5), which requires a tem-
perature only slightly lower than that to be found in the
centres of the main-sequence stars. The reason for so com-
paratively low a rate in this particular case is that the
transformation involves the process of a y-ray emission,
which causes a considerable decrease of its probability. In
fact, it is well known that the emission of y-rays is as a rule
many millions of times less probable than the ejection of a
nuclear particle, so that in order to obtain an appreciable
rate for that kind of reaction it is necessary to intensify
the bombardment by raising the temperature of the gas.*

* The reader raay have noticed that the first reaction on our list (D-H)