Radioactive decay and half-life

Which statement about α-radiation is correct?

• It is a stream of fast-moving electrons.

• It is a form of electromagnetic radiation.

• It is more highly ionising than γ-radiation.

• It is more penetrating than β-radiation.

A radioactive source produces a count rate on a detector of 1600 counts / s.

After 32 hours the count rate has fallen to 100 counts / s.

Both count rates have been corrected for background radiation.

What is the half-life of the source?

• 2.0 hours

• 6.4 hours

• 8.0 hours

• 16 hours

α, β and γ-radiations are emitted by radioactive substances.

Which statement is correct?

• α-radiation consists of charged particles and is the most highly ionising radiation.

• β-radiation consists of charged particles and is the most penetrating radiation.

• β-radiation consists of uncharged particles and is the least highly ionising radiation.

• γ-radiation consists of uncharged particles and is the least penetrating radiation.

A radioactive substance has a half-life of 2 weeks. At the beginning of an investigation, a sample

of the substance emits 3000 β-particles per minute.

How many β-particles will it emit per minute after 6 weeks?

• 0

• 375

• 500

• 1500

Compared with β-particles and γ-rays, α-particles

• are the only type of radiation to carry a charge.

• have the greatest ionising effect.

• have the greatest penetrating effect.

• have the smallest mass.

In a cathode-ray tube, a hot tungsten cathode releases particles by thermionic emission.

What are these particles?

• α-particles

• electrons

• protons

• tungsten atoms

The half-life of a radioactive substance is 10 minutes. A sample of the radioactive substance

contains 2000 nuclei.

How many radioactive nuclei were in the sample half an hour earlier?

• 250

• 4000

• 6000

• 16000

A radioactive substance emits a particle from the nucleus of one of its atoms. The particle

consists of two protons and two neutrons.

What is the name of this process?

• α-emission

• β-emission

• γ-emission

• nuclear fission

Why are some radioactive sources stored in boxes made from lead?

• Lead absorbs emissions from the radioactive sources.

• Lead decreases the half-life of radioactive sources.

• Lead increases the half-life of radioactive sources.

• Lead repels emissions from the radioactive sources.

When measuring the emissions from a radioactive rock brought into the laboratory, a teacher

mentions that background radiation must be taken into account.

What is this background radiation?

• infra-red radiation from warm objects in the laboratory

• infra-red radiation from the Sun

• ionising radiation from the radioactive rock brought into the laboratory

• ionising radiation in the laboratory when the radioactive rock is not present