1. Radon gas has a half-life of 3.83 days. If 2.94 g of radon gas is present at

Question

1. Radon gas has a half-life of 3.83 days. If 2.94 g of radon gas is present at time t = 0, what mass of radon will remain after 1.90 days have passed?

----g

2. A person whose mass is 73.0 kg is exposed to a whole-body dose of 23.0 rad. How many joules of energy are deposited in the person's body?

------j

3. A "clever" technician decides to heat some water for his coffee with an x-ray machine. If the machine produces 31 rad/s, how long will it take to raise the temperature of a cup of water by 51°C? Ignore heat losses during this time. (Use

4186 J/kg · °C

for the specific heat of water.)

-----days.

4. Suppose a virus has a mass of 6.12 1018 kg. Calculate its rest energy in joules and MeV.

(a) joules
J

(b) MeV
MeV

Explanation / Answer

Question 1:

Mass, M = 2.94*(1/2)(1.90/3.83)

remaining mass of radon, M = 2.0845 g

Question 2:

1 rad is the dose causing 0.01 joule of energy to be absorbed per kilogram of matter.

23 rads then causes 0.23 J to be released per kilogram.

73 kg * 0.23 J/kg

the number of joules of energy deposited in the person's body = 16.79 J

Question 4:

From Einstein relationship for energy,

E = m*c2

('m' is mass and 'c' is speed of light)

E = 6.12*10-18 * (3 *108)2

(a) E = 0.5508 J

Since,

1 J = 1/(1.6*10-19) MeV

E = 0.5508/(1.6*10-19)

(b) E = 3.4425*1018MeV

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