If it's the kind of cell I'm thinking of, the gas pressure inside is very low, and even small leaks will noticeably affect the gas content. Helium can be particularly hard to keep out. How quickly this becomes a problem will heavily depend on the sensitivity of your measurement, and the exact construction of the cell. If it's a commercially manufactured cell, the supplier may be able to provide useful data, and perhaps offer a replacement if the cell doesn't meet its specifications. If you constructed it yourself, you'll  need to review the literature on cells of similar construction, and keep track of the status of your own cells over their lifetime.

Thanks for your answer

The cell was constructed in our lab and with no optical measurement for Ne pressure but they tried to fill the cell with 10 torr of Neon. If we assume that it was fabricated well and there is no leakage in our spherical cell. Is there any relation for walls leakage?

It's well-known that helium can get through glass. It is predictable enough to construct calibrated helium leaks, which are glass elements with a known leak rate. It depends on glass type, wall thickness and temperature.

However, which pressure is increasing? You initially measured a pressure of 10 torr, now it increased by a factor of 100, which is about 30% higher than normal atmospheric pressure. You'd never get such pressure increase from storage in normal conditions, so first try to determine exactly what you are measuring - partial pressure of one component (the neon or the rubidium), were all measurements performed at similar temperatures,... Rb partial pressure can be highly dependent on temperature (when the cell gets too cold for relatively high partial pressures, it will deposit on the walls).

This pressure is gotten from pressure broadening effect on Rb absorption in cell with 80 degree of Celsius temperature. So My measurement shows that initial pressure was higher than normal atmospheric pressure. Do you have any suggestion about how we can make sure about it's pressure? 

Thanks in advanse

It's hard to give specific recommendations, much will depend on the equipment you have available. If at all possible, see if the concentration of neon in your cell can be measured directly, for example by absorption spectroscopy.