Generally any high Z material can be used for gamma shielding, there are no specific needs for the material to be electrically conducting. Look up half value layer (HVL)

https://radiopaedia.org/articles/half-value-layer

False. High Z and high density is important to attenuate gamma radiation, conductivity is only important when it comes to measure radiation intensity and energy.

True. The need for conductivity or a method to leak the charge varies with the intensity of the radiation and the purpose of the shielding. The higher the intensity, the more charge is built up. Very high charges have a potential for harm to personnel and equipment. Small charges may be sufficient to interfere with sensitive electronic equipment.

Since there is no such thing as a perfect insulator because an insulator can always become electrically conductive, the question is biased. All materials can block gamma radiation in some degree, either they are considered conductors or insulators (i.e. quasi-insulators). It is a tricky question indeed...

Maybe we could answer to this question more precisely if Mr.Yasser can give us more details about his experiment. Are we looking for shielding against nuclear bomb or against normal background gamma radiation? 

Conductivity is probably not an issue in ordinary laboratory systems but charging/discharging is an important issue for space systems where good insulators can be charged by radiation belt electrons. This has been the source of many anomalies and problems, particularly in geostationary orbit. Also EMP can be produced by X-ray and gamma-ray flashes.

For all the material used for gamma shielding, i never came across the problem of conductivity of charges, which may be accumulated on the material.This may be since all the materials practically used for gamma shielding have sufficient conductivity. Therefore you are not required to worried about the conductivity of material while considering high Z material as shielding.

Anyhow, charging problems with gammas do only occur when electrons are knocked out of the surface. WIthin then bulk material, gammas genreate electron/hole pairs which will normally recombinate more or less.

Another issue are alpha- or beta-active samples which can cause serious problems with charges, e.g. if you try to weight them while components of the balance you use are charged up. 

Materials become charged when electrons leave the surface of the material and when electrons from photo and Compton reactions enter the material. These external photons can be substantial for photons above 1 MeV. Hot cell windows irradiated with gamma only can shatter if no leakage method is provided.

Most counting laboratories do not have a problem with shield charging when non-conductive materials are included. Charge build up is easily leaked away as dose to the material is usually low. Nevertheless, surprises do occur in experimental configurations, particularly when there is low humidity. 

Most charging problems are seen in accelerators when targets build up substantial charges. See attached from an electron accelerator.

In our laboratory we have large 25 tons iron shielding and couple of standard Pb shields. For years we have a large problem with static electricity,because as soon as somebody touch iron shield, HV on detector go OFF. 

We made grounding(leak out) for our shield and anti-static floor  to avoid similar problems.  So I understand that conductivity and charging can be big issue in laboratories.

Generally speaking, FALSE  for Low level activity as in NORM analysis.

But for high level, you may have a problem of static electricity on the shielding that must be get rid of it either by grounding the shield or isolating the detector from the shield.   

From discussion, i understand that the use of either high energy radiation or high dose of less one will be responsible for ejection of large No. of electrons, thus the recombination rule  between ejected electrons and atoms become so difficult. As a result, electrostatic charge will be accumulated on surface. At this moment the need for leakage is necessary, isn't it?

It will be smart to do it. Yes :)

It can`t harm :)

Yes, its a matter of the amount of charges. For high doses you need a safe leakage. But of course pmma is able to shield betas or electrons, and you need a leakage in both cases.

Yes I believe so. Also you will have more stable spectrum. 

False.  Water and plastic make perfectly good shields.

Gamma rays can also be shielded by concrete of sufficient density and thickness.

Absolutely.

Concrete contains moisture that aids charge movement by ion formation. Most concrete is well grounded so there is little charge build up.

There is good charge movement in water. Water in a reactor is well grounded.

Plastics make good shields under the right conditions. Charge buildup in plastics can cause electrostatic problems. Large charge buildup can be hazardous. See photo above.

No