Radioactivity

definition: spontaneous

• radioactivity happens independently external conditions

what is radiation

• alpha/beta/gamma radiaitons

what is unstable?

• nuclei are liable to decay/has too much energy

what is random nature of decay?

• cannot predict which nuclei will decay next/cannot predict when nuclei will decay

ionising

• kinetic energy lost

  • remove electrons from atoms

describe an experiment to determine whether certain source emit alpha/beta/gamma radiation or whether there’s background radiation

• use a GM counter

• place the source of radiation close to the detector

• measure the background radiation by reading from the counter when the radiation source is turned off

• put paper in between the source and detector, if it’s alpha radiation, there should be a rapid drop in activity/counts immediately. Otherwise, no change/minor change in counts

• put aluminium between the source and detector. If beta radiation, should see a rapid drop in counts. If gamma, no change

• put lead between the source and detector, if gamma, should see an immediate drop in counts

• source should be put in a lead box to prevent them penetrating and risk of ionising cells

  To find half life

• counts should be measured over a period of time and repeated and take an average

• graph of activity vs time plotted to find half life of source

• for both experiment background radiation doesn’t need to be measured as count rate is much greater

why beta particles ionise more molecules at the end of its journey than at the beginning?

• beta particles travel slower and have less kinetic energy so there are more collisions with atoms/molecules toward the end of the range as beta particles take longer to travel a given length

In the radiation experiment to determine count rate, why sometimes low proportion of decays are recorded

• emission of radiation in all direction

• so some radiation may be absorbed by the windows

• some maybe absorbed by other materials in the sample

Why most of times in experiments it is better to use samples with longer half life

So activity won’t change significantly over time

What are the four scenarios when an atom may become unstable

• the atom having too many neutrons

• the atom having too few neutrons

• the atom having too much mass

• the atom having too much energy

How do unstable nuclei become more stable

• emit radiation to become more stable

What does beta-plus radiation consist of? What are the penetrating capabilities of beta-plus radiations

• High-energy positrons, when a proton turns into a neutron emitting a positron and an electron neutrino

• no range

Under what circumstance is alpha radiation emitted?

When is gamma radiation emitted?

When a nucleus has too much mass

When a nucleus has too much energy

Under what circumstance is beta minus radiation emitted

when is beta plus radiation emitted

When a nucleus has too many neutrons

When a nucleus has too many protons

Explain the process of beta minus decay

Where a neutron in the nucleus turns into a proton, and release an electron and an electron antineutrino

Explain why the decay constant of an isotope can be determined even though nuclear decay is random

• probability of decay(at a specific time) may be determined

• probability may be applied accurately because very large numbers involved