Radioactivity Flashcards
What was the original model of the atom?
Tiny particles that could not split.
What and when was the plum pudding model?
Discovered in 1897, used until 1911. By JJ Thompson. Belief that electrons were embedded inside a positively charged sphere to make a neutral atom. Due to discovery of electrons.
When and what was the nuclear model?
Proposed in 1911. Nucleus contains most of the mass and all of the positive charge, very small, negative electrons orbit the nucleus. Most of an atom is therefore empty space. Based on the results of Rutherford’s experiment.
What is Rutherford’s experiment?
Alpha particle scattering - a beam of alpha particles was fired at a thin gold sheet.
What were the results and conclusions drawn from Rutherford’s experiment?
Most particles passed through the sheet - an atom is mostly empty space.
A few were deflected by large angles - the nucleus is positively charged so will deflect positive alpha particles.
Very few were deflected backwards - the mass of an atom is concentrated in a very small space, as collisions with the nucleus directly were rare.
What is the currently accepted atomic model?
Energy level model - electrons occupy energy levels at specific distances from nucleus, nucleus made of protons + neutrons.
Explain the use of radiation in tracers.
Radioactive isotope injected into patient, radiation is picked up by a camera and tracks flow of substance through organs. Gamma used to pass through body. Low enough half-life to not remain in the body for ages, but long enough to be useful for tracing / imaging.
Explain the use of radiation in radiotherapy beams.
Beam of gamma is aimed at cancerous cells to kill them. Gamma used to penetrate into body. Half-life is up to a few years, as patient is only exposed and not contaminated.
Explain the use of radiation in radiotherapy implants.
Small rod of radioactive material is implanted inside a tumour. Used beta or gamma depending on how far into the tissue it needs to penetrate. Half-life should be long enough to kill cancer but short enough to not be radioactive after treatment finishes.
What is the activity A of a source?
Measured in becquerel, 1 Bq = 1 decay per second. Number of nuclei that decay a second.
What is the formula for activity?
A = deltaN / deltaT, number of nuclei remaining at time T. so - lambda N
What is background radiation?
The radiation that is constantly present around us, mostly due to air, medical uses, food/drink, cosmic rays and ground/buildings.
What is the decay constant?
lambda, s^-1, the probability of an individual nucleus decaying per second.
How do you calculate the decay constant from half-life?
Half-life = ln2 / decay constant. So decay constant = ln2 / half-life.
What is the formula for radioactive decay, and what do the symbols stand for?
N = N(0) e ^ - lambda t, N0 is number of nuclei in sample at time t = 0. Shows exponential decay.
