An ordinary basement is not a great protection against radiation exposure. The book that has the radiation dose counter that you can make at home tells you to move it around if a basement is your only available shelter after a nuclear blast. It said that corners are usually safer from radiation than the open areas. You should find the safest corner. You can then further fortify that spot into a smaller and safer shelter.
It suggests that you dig into the floor of the basement and use the dirt from it to make your safe corner even safer. Failing that option, you can pile things, the denser, the better. The object is to make a safer space under the pile of things to block more radiation for those inside it.
It would be a lot better if you prepare a better shelter in your basement ahead of time, however. I hope that you will do this.
One principle that you need to be aware of when making a shelter is that of "halving". By building up layers of radiation blocking materials, you can halve the radiation dose received by those protected by the layers. There is a chart in the book that shows you how this works. I believe 18 inches of densely packed earth provides halving of radiation down to 32. If you are receiving a lot of radiation in your shelter area that is still not acceptable and it would be better to have a much thicker protection around you. You can look at the charts and figure out what you want to do.
More dense than earth materials such as concrete provide radiation halving with a smaller thickness than packed earth does. You can plan your shelter with that and your finances and materials in mind.
The blast of a nuclear explosion causes an impact on everything in its path, including the human body. One source said that winds exceeding 800 miles per hour (1287.5 Km./hr.) come after a nuclear blast from a large bomb. I do not yet know what this is from a nuclear power plant accident, but since I plan to post on that as well, I soon will. Sigh.)
If you are very close to a nuclear bomb detonation, the concussion from the blast and winds can be enough to kill you. If you are not that close to a nuclear bomb detonation, you can plan to be in a shelter, in a hammock, which will bounce and swing and lessen the impact. The book I gave a link to the day before yesterday had how to plan a hammock that you can use in your shelter. The hammock can be converted to a chair during the day.
Terrorist nuclear bombs are considered to be quite different than military type ones. Preparedness for them needs to be different because of this. I intend to post about these and about nuclear power plant disaster preparedness.
I have already posted on many subjects such as basic food and evacuation kits, or "go bags", or "bug out bags". If you are new to my blog, please take the time to learn about such matters. It will do little to keep you alive if you make a shelter to keep you safe from radiation and starve to death.