I found an answer from www.quora.com

Why can an electron not exist inside the **nucleus**? - Quora

Electrons are orbiting around the **nucleus i.e.** out side the **nucleus**, it is an
experimental fact. ... Why does the **nucleus of an atom** stay together and the
electron stay orbiting around it ... **One** of the applications is to **prove** that electron
can not exist inside the **nucleus**. ... [**math**]P = {2 \over **3**} {q^2 a^2 \over 6 \pi \
epsilon_0**[/math**].

For more information, see Why can an electron not exist inside the **nucleus**? - Quora

I found an answer from en.wikipedia.org

**Atomic nucleus** - Wikipedia

The **atomic nucleus** is the small, dense region consisting of protons and neutrons
at the center ... The **diameter** of the **nucleus** is in the range of 1.7566 fm (1.7566×
10^{−15} m) for ... In principle, the **physics** within a **nucleus** can be derived entirely
from ... power is required to accurately compute the **properties of nuclei** ab initio.

For more information, see **Atomic nucleus** - Wikipedia

I found an answer from en.wikipedia.org

Semi-empirical **mass** formula - Wikipedia

In **nuclear** physics, the semi-empirical **mass** formula (SEMF) is used to
approximate the **mass** and various other properties of an **atomic nucleus** from its
**number** ...

For more information, see Semi-empirical **mass** formula - Wikipedia

Density \rho = \frac{\text{ mass }}{\text{ volume }} = \frac{m}{V}

Given that

Radius of nucleus R = R_0 A^{\frac{1}{3}} where, R_0 - constant and A - mass number of nucleus

Step 1: demonstrating that the density of nuclear substances is constant

Volume of the substance(sphere) V = \frac{4}{3} \pi r^3 where, r - radius of nucleus

V = \frac{4}{3} \pi (R_0 A^{\frac{1}{3}})^3

V = \frac{4}{3} \pi R_0^3 A

Density of nuclear substance \rho=\frac{m}{V}=\frac{A}{\frac{4}{3}\pi R_0^3A}

\rho = \frac{3 A}{4 \pi R_0^3 A}

\rho = \frac{3}{4 \pi R_0^3}

\frac{3}{4 \pi R_0^3} is constant

Hence, the density of nuclear matter is independent of A. It is nearly constant.