Radioactive Decay

Which of the following statements best describes the structure of a U-235 atom?

• 92 protons & 235 neutrons.

• 92 protons & 143 neutrons.

• 143 protons & 92 neutrons.

• 235 protons & 92 neutrons.

There are three stable isotopes of oxygen found in nature. In what ways do these isotopes vary?

• The number of neutrons and mass is different.

• The number of protons and mass is different.

• The number of electrons is different.

• The atomic numbers are different.

Which of the following best describes an alpha particle?

• A double charged hydrogen nucleus.

• An electron.

• A pulse of electromagnetic radiation.

• A double charged helium ion.

What is the product of the beta minus decay of Gold 198?

• 
• 
• 
• 

Plutonium 239 decays into uranium 235. What type of decay is this?

• Alpha

• Beta

• Gamma

• Neutron

Barium is a source of gamma radiation. What is the daughter isotope?

• 
• 
• 
• Cannot be determined

It is noted that the decay rate of a radioisotope drops from 384 Bq to 12 Bq over a period of 20 hours. What is the half life of the isotope?

• 1 hour.

• 4 hours.

• 5 hours.

• 20 hours.

A particular radio-isotope has a half life of 36 hours. If you started with 1.00 grams, how much of the original isotope would remain after 3 days?

• 0.25 grams

• 0.50 grams

• 0.75 grams

• 0.97 grams

Uranium 235 has a half life of around 700,000 years, while the isotope uranium 238 has a half life of 4.5 billion years. If you had two samples of equal mass, which would have the higher activity and why?

• Both samples are of the same element, so both will have the same activity.

• U235 decays at a quicker rate and will have a greater activity.

• U238 decays at a slower rate because it has a greater activity.

• Both samples are of the same mass, so both will have the same activity.

Carbon 14 is a radioisotope with a half life of around 5700 years. The proportion of carbon 14 reduces in organisms once they die, due to radioactive decay.

One particular sample shows that the amount of carbon 14 is only 95% of the normal level. The age of the sample is approximately:

• 5 years.

• 420 years.

• 5280 years.

• 5700 years.