238 1 239
92U + 0 → 92
What is the likely decay mode?
Just gained a neutron, therefore neutron rich
β minus decay
239 239 0 −¿
92 → 94Pu + −1e
A 60 kg laboratory worker receives a whole-body x-ray exposure of 0.50 mSv.
The x-ray wavelength is 0.15 nm.
How many x-ray photons are absorbed in the worker’s body?
(X rays have an RBE of 1.)
1240 1240 -15
E photon λ = 0.15nm = 1.3 x 10 J
Dose: 0.5 mGy RBE is 1)
0.5 mGy = 0.5 x 10 J/kg
0.5 x 10 J/kg x 60 kg = 0.03 J absorbed
1.3x10 J/photon = 2.3 x 10 photons
The effects of radiation on tissue in the body depend on the susceptibility. Rapidly-
dividing tissues are the most susceptible
Tumors are extremely susceptible.
Bone marrow is very susceptible.
The lining of the digestive tract is quite susceptible.
The brain is not very susceptible.
Damaging bone marrow: 2 Sv Damaging the brain: 50 Sv
Radiation can cause or cure cancer.
Using Radiation to Treat
Collimator allows gamma rays to penetrate only along certain lines
The paths of the allowed gamma rays intersect at the tumor
The I in the seeds decays to Te, which emits low-energy x rays and gamma
“Hot spots” mean the isotope is present.
The scan shows metabolic activity, not the bone structure. It shows areas where
fractures have occurred.
SPECT scan – single photon emission computed tomography
Positron emission tomography
The positron annihilates with an electron to produce two oppositely directed gamma
Coincidence detection of two gamma rays means that the positron source is along that
Creating positrons for use