A2 nuclear physics

Protactinium has a half-life of 70 s. A sample of protactinium is prepared and monitored over a period of time. Which of the following statements is correct?

• The activity of the protactinium will be zero after 140 s.
• The activity of the protactinium will be 25% of its initial value after 140 s.
• The activity of the protactinium will be 12.5% of its initial value after 280 s.
• The activity of the protactinium will never become zero.

In a famous thought experiment, Schrödinger imagined that a cat is locked in a box, along with a radioactive atom that is connected to a tube containing a deadly poison. If the atom decays, it causes the tube to smash and the cat to die. The random nature of radioactive decay means that the radioactive atom will

• decay after one half life
• probably decay after one half-life. 
• have a fixed probability of decaying in a given time interval
• have a number of possible decay paths. 

The fuel used in a nuclear fission reactor is uranium. Which of the following is required for fission to proceed?

• Neutrons must be removed from the reactor core.
• The reactor core must be very hot
• The uranium nuclei must absorb neutrons
• The uranium nuclei must absorb protons

A radioactive source is placed a few cm away from a detector. There is no change in the count rate when a thin aluminium foil is placed between the source and the detector, but the count rate is reduced to the background rate when a 0.5 cm aluminium plate is introduced. These observations show that the source must be emitting

• alpha and beta radiation
• beta and gamma radiation
• beta radiation only
• gamma radiation only

The force that causes protons and neutrons in the nucleus to attract to one another is the

• strong nuclear force
• electric repulsion
• gravity
• weak force

Fission and fusion are both nuclear processes. Which of the following statements is correct for both processes?

• Neutrons are released
• No harmful radiation is produced
• The binding energy per nucleon increases.
• The total mass increases

When measuring the count rate from a radioactive source it is usual to also measure the background count rate. The background count rate must be

• as large as possible for an accurate experiment
• measured when the source is in place
• recorded for the same time as the count rate
• subtracted from the count rate measured from the source

The ionising properties of radiations determine their penetrating power. Which of the following statements is correct?

• Alpha particles are not very ionising so they are stopped by thin paper
• Alpha particles are very ionising so they can only travel a few cm in air
• gamma radiation is very penetrating because it's very ionising
• gamma radiation is not very penetrating because it is very ionising

Radioactive decay is sometimes described as being spontaneous.  In this context spontaneous means 

• nothing can influence the decay
• the decay is random
• the decay can be predicted
• the decay is exponential

The total number of free neutrons immediately after a fission reaction 

• goes down
• goes up
• may increase or decrease
• must stay constant