In $\beta$ Decay It Is Found That Both the Direction of the of the Ejected

Multiple Choice

In $\beta$ decay it is found that both the direction of the ejected electron (with respect to the recoil direction of the parent nucleus) and the magnitude of the electron's velocity are variable. From these facts, we can infer that another particle (the neutrino, as it turns out) is needed to preserve the conservation of

A) energy.
B) momentum.
C) all of the above.
D) none of the above.