P6 Radioactivity

Question 1

Recap: Properties of Sub-Atomic

Answer 1

Subatomic Particles/Relative Mass/Relative Charge
Proton 1.00000 +1
Neutron 1.0000 0
Electron 0.0005 -1

Question 2

What are isotopes?

Answer 2

Isotopes are variations of an atom of an element with different numbers of neutrons but same number of protons. They are written in the format carbon-12 and carbon-14 with the number referring to the total number of nucleons.

Question 3

Why do atoms emit radiation?

Answer 3

When electrons move from a high to a low energy level, they emit radiation because of the change in energy. If an atom has an unstable nuclei, it will emit radiation.

Question 4

What is alpha, beta, gamma and neutron radiation? What is it / Equation

Answer 4

Radiation / Type / What is it? / Equation

Alpha / Particle / Helium nucleus / He 4 : 2

Beta / Particle / Fast-moving electron / e 0 : -1

Gamma / Electromagnetic wave on spectrum/ none

Neutron / Particle / Nucleon Particle / n 1 : 0

Question 5

What are the penetrating powers of alpha, beta and gamma?

Answer 5

Alpha can be stopped by paper.
Beta travels through paper but is stopped by aluminium.
Gamma is the most penetrating and is mostly stopped by a few cm lead but some can still get through.

Question 6

What is radiation? How does radiation interact with the atoms it collides with?

Answer 6

Radiation is the emission or transmission of energy in the form of waves or particles. Radiation emitted by radioactive material can be ionising radiation like alpha and beta. This means that the radiation like alpha can knock off electrons from the atoms producing ions and beta particle leave its atom with one more proton and joins another atom. When gamma radiation hits an atom, it may excite an electron.

Question 7

What are the properties of alpha, beta and gamma?

Answer 7

Alpha / Large / +2 charge / high ionising power / short range
Beta / Small / -1 charge / medium ionising power / medium range
Gamma / none / none / low ionising power / long range

Question 8

What happens in the decay of alpha, beta and gamma?

Answer 8

Alpha decay is where 2 protons and 2 neutrons join up to form an alpha particle which is emitted from the nucleus.
Beta decay is where a neutron decays to a proton and an electron. The proton remains in the nucleus so the atomic number goes up by one, but the electron is emitted as a beta particle.
Gamma decay does not affect the nucleus but if it has the right frequency, it can excite and electron. Gamma radiation is mostly found alongside alpha or beta.

Question 9

How do you measure the activity of a radioactive material?

Answer 9

A Geiger counter beeps when it is detecting radiation however, this is never regular as radiation is random. The Geiger counter absorbs radiation and transmits an electrical pulse to a counting machine. A Geiger counter measures radiation emitted per second in becquerels (Bq) and this is called the activity.

Question 10

What is half life?

Answer 10

Half life is the average time it takes for a number of radioactive atoms to halve in number and activity.
The activity of radioactive material halves after the same amount of days every time. If the half life of a material is 18 days, the next time its activity halves is in another 18 days.

Question 11

What happens when electromagnetic radiation is absorbed?

Answer 11

Electromagnetic radiation can be split into photons proportional with frequency. When they absorb the right energy, an electron moves from a low to a high energy level becoming ‘excited’.
Beta particles can be absorbed by an atom needing an electron.

Question 12

What is irradiation and contamination?

Answer 12

Irradiation happens when the radioactive material is outside the body but travels into by penetration.
Contamination is when the radioactive material is taken into your body

Question 13

What are tracers?
What are gamma knives?

Answer 13

Tracers detect cancers. They are proteins that specific human organs absorb and get injected into the patient’s body. A gamma camera is then used to detect when the tracer is concentrated.

Gamma rays are emitted from outside the body and focused onto the cancerous area as a “gamma knife”

Question 14

What is nuclear fission?

Answer 14

When a large nucleus splits into fragments and emits neutrons, it is called nuclear fission. The nucleus often absorbs a neutron. Then it splits and produces two smaller nuclei, and two or three neutron

Question 15

What is a fissionable nuclei?

Answer 15

Uranium-235 and Uranium-239 are fissionable as they can be split easily

Question 16

What nuclei are produced after the fission of uranium?

Answer 16

Krypton 94, Barium 139

Question 17

Why is fission an exothermic reaction?

Answer 17

All fission products are moving and so they collide with and heat up matter around them. By releasing energy in the form of heat to the surroundings, fission is exothermic

Question 18

Where is fission used?

Answer 18

Fission process is used in a nuclear power station to heat water to produce steam that drives turbines and generators to power electronics.

Question 19

How can fission be a chain reaction?

Answer 19

You need a neutron to start a fission reaction, but the reaction also produces a neutron. These neutrons can then trigger other fission reactions starting a chain reaction

Question 20

How do engineers control the chain reaction?

Answer 20

Engineers control the chain reaction by using boron rods to absorb some of the neutrons.

Question 21

What is nuclear fusion?

Answer 21

Lighter, smaller nuclei can join together to make more stable nuclei in a process called nuclear fusion.

Question 22

What are the reactants of typical nuclear fusion?

Answer 22

Nuclei in fusion are opposingly charged and so repel. Therefore, most fusion reaction involve isotopes of hydrogen. Hydrogen 2 (Deuterium) and Hydrogen 3 (Tritium) fuse to form a helium nucleus and a neutron.

Question 23

What are the conditions for fusion?

Answer 23

High temperatures so the nuclei move at fast speeds
High pressures to keep the nuclei close enough to fuse

This is to overcome the electrostatic forces of repulsion

Question 24

Where does the lost mass end up after fusion? Formula

Answer 24

The tiny amount of mass lost produces an extremely large amount of energy in the form of radiation.

E = mc^2

(E = energy, m = change in mass, c = the speed of light)