PHYS 3330 Module 1 Self Assessment Practice Problems

Module 1 Self Assessment Practice Problems

1.1
A current of 1.0 µA flows into a condenser of capacity 100 nF for 5.0 s. Calculate the potential difference between the plates of the condenser.
Answer: 50 V

1.2
An x-ray tube operates at 80 kV. Calculate the kinetic energy gained by an electron accelerated through this potential difference. Express your answer in joules and electronvolts.
Answer: 1.28 x 10^-14 J, 80 keV

1.3
A linear accelerator used in radiation therapy delivers 2.5 MeV of energy per electron. If the accelerator produces a beam current of 100 µA, calculate the beam power in watts.
Answer: 250 W

1.4
A diagnostic x-ray tube operates at 120 kV and draws a current of 200 mA. Calculate
(a) the electrical power consumed by the tube in watts
(b) the resistance of the tube in ohms
Answer: (a) 24,000 W (b) 600,000 ohms

1.5
After a full course of treatment, a tumor received a dose of 4000 rad. Express this dose
(a) in grays
(b) in MeV/g
Answer: (a) 40 Gy (b) 2.5 x 10¹¹ MeV/g

1.6
An x-ray exposure measurement yields a reading of 250 mR. Convert this exposure to
(a) R (roentgen)
(b) C/kg (coulombs per kilogram of air)
Answer: (a) 0.250 R (b) 6.45 x 10^-5 C/kg

1.7
A radiation therapy machine delivers an absorbed dose rate of 3 Gy/min to a tumor. Express this dose rate in rad/hour.
Answer: 18,000 rad/h

1.8
A radioisotope sample has an activity of 37 MBq. Express this activity
(a) in mCi (millicuries)
(b) in disintegrations per second
Answer: (a) 1 mCi (b) 3.7 x 10⁷ disintegrations per second

1.9
How many protons and how many neutrons are there in a nucleus of the most common isotope of
(a) silicon ²⁸Si
(b) rubidium ⁸⁵Rb
(c) thallium ²⁰⁵Tl
Answer: (a) 14 p and 14 n (b) 37 p and 48 n (c) 81 p and 124 n

1.10
Compare the number of electrons/g for ¹²C to the number of electrons/g for ⁴⁰Ar.
Answer: 3.0114 x 10²³ electrons/g and 2.714 x 10²³ electrons/g