Would Hypothryoidsim make you immune to radiation poisoning?

I agree with tha above posters. Radioiodine produced by, for example, the accident at Chernobyl is able to spread for a certain area around the site of the occurence. To combat this, folks who might be in danger of exposure are given Lugol's solution (essentially a bunch of iodine). This saturates the thyroid with iodine, temporarily blocking any further iodine uptake. A person who has a non-functional thyroid would also have this "benefit".

However, as previously stated, direct exposure to radiation in your environment would not be lessened by your hypothyroidism.

No. The relationship between the thyroid and radiation is that in some nuclear incidents a large amount of radioactive iodine would be released into the atmosphere. Iodine tends to accumulate in the thyroid, but if you take an iodine pill the thyroid would become saturated with iodine and the radioactive stuff would just be passed in the urine.

That is just one possible avenue for radiation poisoning. If you stand in front of an x-ray machine all day or fell into the reactor core of a nuclear power plant, all the iodine in the world wouldn't help you. Those are gamma radiation sources and only lead shielding will help there.

Your sensibility to radiation poisoning remains basically unchanged. Bone marrow, for example, remains sensible and could lead to leukemia. Thyroid gland still captures the isotopes unless it is surgically removed.

Just lie under an X-Ray for a few days and find out