Question

1)A sample of technetium-99 was used in a procedure to image the heart muscle of a patient 18 hours ago and now 2.50 mCi remain. What was the size of the original sample? (Technetium-99 has a half life of 6 hours.)

2)

Which of the following statements comparing beta decay and positron emission are NOT true?

Select the correct answer below:

Particles released during both types of decay processes have similar mass.

Particles released during both types of decay processes are deflected the same way in an electric field.

Both result in a change in atomic number with the release of charged particles.

Both types of radioactive decay processes tend to occur in isotopes with proton-to-neutron ratios that are out of balance.

3)

Which of the following correctly describes how a scintillation counter works?

Select the correct answer below:

A material called a scintillator produces electrical signals on exposure to ionizing radiation.

A material boils under the influence of ionizing radiation and produces bubbles which are detectable by optical means.

A material called a scintillator emits light on exposure to ionizing radiation, and the light is further converted to an electrical signal by an optical sensor.

A gas, called a scintillator, ionizes under the influence of radiation, and the ions are detected and converted to an electrical signal.

Answer 1

1)

Radioactive decay follows first order kinetics

hence,

final activity = initial activity $\times$_{$\frac{1}{2^{x}}$}

x is number of half life

for the given sample of technetium -99 ,

final activity = 2.50 mCi

half life = 6 hours

time passed = 18 hours

then , x = $\frac{18}{6}$ = 3

so,

2.50 = initial activity  $\times$_{$\frac{1}{2^{3}}$}

or, 2.50 = initial activity  $\times$_{$\frac{1}{8}$}

or,  initial activity = 8 $\times$ 2.50 = 20 mCi

2)

symbol of beta is ⁰e_-1

symbol of positron is  ⁰e₁

as they have same mass but opposite charge they are deflected in opposite way in electric field .

So statement 2 is not true.

3)

Scintillator is a material that absorb radiation and produces photon (light) and a optical sensor converts it into electrical signals .

hence third statement is correct.

"A material is called a scintillator emits light on exposure to ionizing radiation, and the light is further converted to an electrical signal by an optical sensor".