RGPu Dose Measurements and Inverse Square Law
Howdy All,
Yesterday I posted several 7 Ci reactor grade plutonium sources, and today I’m coming back with some dose rate updates.
First off, the contact dose rate I mentioned yesterday was significantly lower than what I measured today. Depending on a triangle’s position, I saw as high as 2.5 mSv/hr. Absolutely wild. This is on the order of 1 CT scan (of a limb) per hour for perspective. Around a day of direct exposure at this level would exceed current annual dose limits. And it’s only gamma dose (maybe including some betas that escape the zirconium casing).
However, it’s important to take into account proper tissue weighing factors and that this dose is in the short field. Meaning the difference in hourly dose rate between the front of your body (if you were looking at the source) and your back will be significantly different. The total dose you’d actually receive would be significantly less than what’s read on the detector.
That being said, distance is your friend.
At 30mm, the dose rate drops to 167 uSv/hr. Doubling this distance a couple times, we get to 480mm, and the dose rate drops to a very manageable 3.84 uSv/hr (around 10x background levels).
While the dose doesn’t necessarily drop as 1/r^2, it’s close. I calculated the trend to be close to 1/r^1.1, which is expected given the system geometry. The detector presents a rather large solid angle to the source.