# B Conservations in nuclear reactions

1. Mar 25, 2017

### Fiona Rozario

Is the atomic number and mass number conserved in nuclear decays?

2. Mar 25, 2017

### vanhees71

No! Take $\beta$ decay, where within a nucleus a neutron decays to a proton, electron, and antielectron neutrino. The daughter nucleus has the same number of nucleons $A'=A$ but $Z'=Z+1$.

For $\alpha$ decay a nucleus emits a $_2^4\mathrm{He}$ nucleus, i.e., the daughter nucleus has $A'=A-4$ and $Z'=Z-2$.

3. Mar 25, 2017

Staff Emeritus
What decays have you looked it? Are the atomic number and mass number conserved in those decays?

4. Mar 25, 2017

### Fervent Freyja

Usually not, but that depends upon the type of decay...

5. Mar 25, 2017

### Fiona Rozario

So mass number is conserved but not atomic number...

6. Mar 25, 2017

### Staff: Mentor

Right (assuming you count all invovled particles, e.g. including the alpha nucleus in an alpha decay).

The conservation of the sum of mass numbers is equivalent to baryon number conservation. While it is expected that there are processes changing it, it has never been observed.

7. Mar 25, 2017

### Fervent Freyja

In the case of gamma decay, both are conserved (most of the time).