van der Waals coefficients for helium and neon
The question intregues me so I looked up the $a$ and $b$ values in Wikipedia on the web page Van der Waals constants. This doesn't answer the question, but adds more data to focus the question. 

$$\begin{array}{cc}
\hline
\text{Element} &amp; a\text{ / }\mathrm{L^2 \ bar\ mol^{-2}} &amp; b\text{ / }\mathrm{L\ mol^{-1}}\\
\hline
\ce{He} &amp; 0.0346 &amp; 0.0238 \\
\ce{Ne} &amp; 0.2135 &amp; 0.01709 \\
\ce{Ar} &amp; 1.355  &amp; 0.03201 \\
\ce{Kr} &amp; 2.349  &amp; 0.03978 \\
\ce{Xe} &amp; 4.250  &amp; 0.05105\\
\ce{Rn} &amp; 6.601  &amp; 0.06239 \\
\hline
\end{array}$$

A plot of the Van der Waals $a$ and $b$ values.


So is the b value for He high, or is the b value for Ne low ?!?

I also looked up for each element what was listed for the covalent radius and the Van der Waals radius on each elements individual Wikipedia webpage. 

$$\begin{array}{cc}
\hline
\text{Element} &amp; Covalent\text{ (pm) } &amp; Van~der~Waals \text{ (pm)}\\
\hline
\ce{He} &amp; 28 &amp; 140 \\
\ce{Ne} &amp; 58 &amp; 154 \\
\ce{Ar} &amp; 106±10  &amp; 188 \\
\ce{Kr} &amp; 116±4  &amp; 202 \\
\ce{Xe} &amp; 140±9  &amp; 216 \\
\ce{Rn} &amp; 150  &amp; 220 \\
\hline
\end{array}$$