Types of Radiation — Edexcel GCSE Combined Science 1SC0 - Physics Revision Notes & Topical Questions

Section 1 of 10Radioactive decay

Emission

• Emission the emission of radiation from an unstable nucleus is spontaneous and random in direction.

Equal probability

• Equal probability any nucleus is equally likely to decay.

Unpredictable

• Unpredictable it cannot be known which nucleus will decay next or when.

Unaffected

• Unaffected the rate of decay is unaffected by the surrounding conditions.

Probability

• Probability only the probability of decay in a given time can be estimated.

Section 2 of 10Unstable nuclei

Cause

• Cause an imbalance of the forces in the nucleus, commonly from too many protons or neutrons or from the nucleus being very large.

Example

• Example carbon-14 has two extra neutrons compared with stable carbon-12.

Emission

• Emission unstable nuclei emit a high-energy particle or wave, which takes energy away and makes the nucleus more stable.

Ionising radiation

• Ionising radiation all three types can knock electrons from atoms and make ions.

Section 3 of 10Alpha particles

Alpha particles

Nature

• Nature a helium nucleus, two protons and two neutrons, written ⁴₂He.

Charge and mass

• Charge and mass charge +2 and a relatively large mass of about 4 u.

Source

• Source emitted by heavy nuclei such as uranium and americium-241.

Range

• Range a few centimetres in air, stopped by a thin sheet of paper or the dead outer layer of skin.

Section 4 of 10Beta particles

Beta particles

Nature

• Nature a fast-moving electron that comes from the nucleus.

Charge and mass

• Charge and mass charge −1 and a very small mass (about 1/1840 u).

Origin

• Origin formed when a neutron changes into a proton and an electron.

Range

• Range a few tens of centimetres to about a metre in air, stopped by a few millimetres of aluminium or Perspex.

Source

• Source nuclei with too many neutrons, such as carbon-14 and strontium-90.

Section 5 of 10Gamma rays

Nature

• Nature electromagnetic waves with the highest energy of the electromagnetic spectrum.

Charge and mass

• Charge and mass no charge and no mass, travelling at the speed of light.

Penetration

• Penetration reduced but never completely stopped by a few centimetres of lead or metres of concrete.

Range

• Range very long in air, with no sharp range, only reduced intensity as thickness increases.

Source

• Source usually follows alpha or beta decay from a nucleus with excess energy.

Section 6 of 10Comparison table

Property	Alpha	Beta	Gamma
Nature	Helium nucleus	High-energy electron	Electromagnetic wave
Charge	+2	−1	0
Relative mass	4	1/1840	0
Range in air	A few cm	A few tens of cm	Very long
Stopped by	Paper	A few mm of aluminium	Thick lead reduces it
Penetrating power	Low	Moderate	High
Ionising ability	High	Moderate	Low

• Trend
  • from alpha to gamma the range and penetrating power increase and ionisation decreases.

Section 7 of 10Investigating penetration

1

Place a GM tube at a fixed distance from the source.

2

Place absorbers in turn between them: paper, 5 mm aluminium and thick lead.

3

Record the count rate for each and subtract the background rate.

4

Compare the readings to identify the radiation.

1Falls to background with paper

• Falls to background with paper alpha only.

2Paper has no effect but aluminium reduces it

• Paper has no effect but aluminium reduces it beta.

3Aluminium has little effect but thick lead reduces it

• Aluminium has little effect but thick lead reduces it gamma.

4Thin aluminium

• Thin aluminium beta passes through aluminium thinner than a few millimetres.

Section 8 of 10More from the specification

1Radiation penetrating power

• Radiation penetrating power measuring attenuation through various shielding thicknesses provides an empirical means to distinguish alpha, beta,
  • and gamma emissions.

2Properties of Nuclear Radiations

• Radioactive decay emits alpha particles, beta particles (high-speed electrons or positrons),
  • (helium-4 nuclei)
• and gamma rays, each possessing distinctive ionizing power.
  • (high-frequency photons)

3Penetrating Power Through Materials

• Alpha radiation is stopped by a sheet of paper, beta particles penetrate paper but are absorbed by a few millimetres of aluminium,
• and gamma rays require thick lead or dense concrete shielding.

4Deflection in Electric and Magnetic Fields

• In electric and magnetic fields, positively charged alpha particles and negatively charged beta particles are deflected in opposite directions,
• while neutral gamma rays pass straight through undeflected.

5Radioactive Half-Life and Detection

• The half-life of an isotope is the time taken for half the radioactive nuclei in a sample to decay or for activity measured by a Geiger-Müller detector to decrease by half.

6Half-life

• Time for half the nuclei of an isotope to decay.

7Isotope

• Atom of the same element with a different number of neutrons.

8Detector

• An instrument that records the particles produced in collisions.

9Electric field

• Region of space in which a charge experiences a force.

10Magnetic field

• Area around a magnet where its effects can be detected.

11Decay equation

• An equation in nuclide notation with balanced nucleon and proton numbers.

12Kinetic energy

• K = ½mv², energy of motion.

Section 9 of 10Key terms

Term	Meaning
Radioactive decay	Spontaneous random emission of radiation from an unstable nucleus.
Alpha particle	Helium nucleus emitted from a nucleus.
Beta particle	Fast electron emitted from a nucleus.
Gamma ray	Electromagnetic wave emitted from a nucleus.
Penetrating power	How far radiation travels through a material.

Section 10 of 10Exam technique

1

Saying gamma is stopped by paper — it is the most penetrating.

2

Believing alpha particles are the most penetrating because they are the largest.

3

Thinking gamma has charge — it has none.

4

Saying radioactive decay can be predicted for a single nucleus — it is random.