P6.1 Flashcards
What are atomic nuclei composed of
They are composed of both protons and neutrons
What is the charge of the nucleus of an element
Positive
What does the charge of the nucleus depend on
The number of protons
Why do the nuclei of different elements have different masses
Same number of protons
Different number of neutrons
What is an isotope
Atom of the same element with same atomic number but different mass number as different amount of neutrons
How can atoms of the same element differ in mass
They are isotopes so have a different number of neutrons but same number of protons
What format is carbon with 11 subatomic particles written in, and how many neutrons and protons does it have?
Carbon -11 Mass number (total protons and neutrons nucleus) - atomic number (no of protons or no of e-) So 12 - 6 = 5 there are 5 neutrons
What does a stable atom mean
They donβt break down or decay
What do the unstable nucleus of atoms emit
They emit radiation, which can be made up of particles or waves
What are materials that emit radiation called
Radioactive
What are the 4 types of radiation emitted by an unstable nuclei
Alpha - particle - a - itβs the nucleus of a helium atom - 4 2 He
Beta- particle - B - itβs a fast moving electron - 0 -1e
Gamma- wave - upside down Y- a wave of the EM spectrum - no equation
Neutron - particle- n - itβs a particles in the nucleus - 1 0 n
What do the bottom and top numbers of equations show
Top = mass relative to proton Bottom = charge
Where do beta particles come from as a nucleus doesnβt have electrons?
Neutrons are not stable so they can decay to make a proton and electron
How can you detect radiation?
Geiger MΓΌller tube pr Geiger counter - clicks when radiation enters it ( each click = tiny current produced when the radiation ionises atoms f the gas inside the tube)
What are the penetrating powers of alpha, beta and gamma?
Alpha stops with paper or skin
Beta travels through paper and stole by aluminium
Gamma travels through paper and aluminium and stops mostly by lead but some may still go through
(Most penetrating power)
What is the radiation emitted by a radioactive material called
Ionising radiation = this means that the radiation can remove e- from atoms to produce positively charged ions
Describe the property of radiation of alpha, beta and gamma
Alpha - large relative mass - +2 charge - high ionising power - short range
Beta - small relative mass - -1 charge - medium ionising power - medium range
Game - no relative mass - no charge - low ionising power - long range
What needs to be done to ionise an atom
Energy needs to be transferred to it
Why does alpha radiation have a short range?
Alpha particles transfer more energy to the material they travel through than gamma rays as they have a higher ionising power. This means that they used their energy to ionise the materials they have come in contact with, meaning they have a shorter range,
What range are the radiation the most dangerous at ?
- short range alpha
- mid range beta
- long range gamma
Name 3 isotopes of hydrogen
Protium - 1 proton and 0 neutron (used in fuel cells and making plastics) - most common
Deuterium- 1 proton and 1 neutrons ( used in nuclear fusion) -very few
Tritium - 1 proton and 2 neutrons ( use pd in thermonuclear fusion weapons) - very rare
What happens in alpha decay?
Ξ±
An alpha particle is emitted which is made of 2 neutrons and 2 protons
Therefore, the top number -4
bottom number - 2 (charge of proton is +2)
Mass and charge is conserved
What happens in beta decay?
Ξ²
A neutron decays into a proton and an electron
Top number is the same as we lose a neutron and gain a proton and electron
Bottom number +1 as you gain a proton
What happens in gamma decay?
Ξ³
Gamma rays donβt have mass or charge as itβs an EM wave
Therefore there is no change to the mass and atomic number
What happens in neutron decay?
Neutron decay happens in the decay of some nuclei when they emit a neutron.
Top number -1 as one neutron emitted
Bottom number is same as there is no change in charge but the nucleus is more stable
How do materials emit radiation ?
Materials emit radiation at random
What can a Geiger counter measure?
It measures the radiation (photons/particles) emitted per second
What is the particles emitted per second called and what is it measured in?
Itβs called the activity/ count rate
Measure in becquerels (Bq)
What does one Bq equal to
One becquerel is one count (wave/particle) per second.
What can counts per minute be used to measure?
Itβs used to measure lower activities.
What is half life?
The activity of a material decreases with time. The time it takes for the activity to half is its half life. This is the same as the time for the nuclei of half the atoms to decay.
Is decay and half life constant or random?
The probability that one nucleus decays in one second is fixed. This means that the decay is random and also means the half life is constant.
What happens to atoms that decay
They donβt disappear and instead after emitting alpha or beta particles, they change to the atom of a different element and eventually become stable.
What does the half life of a radioactive material depend on and do isotopes of an element have the same half life?
It can be very short or very long depending on the material. The half lives of different isotopes of an element will be different.
How do calculate the ration of final to initial activity using half life and what is this known as?
Itβs the net decline.
After 1 half life = 1:2
After 2 half lives = 1:4
How are electrons in atoms arranged?
- electrons occupy fixed energy shells around the nucleus of atom
- diff atom = diff energy levels
- electrons occupy the lowest possible energy level, at the smallest distance from nucleus
What model do we used to model electron radiation
In the Photon model electromagnetic radiation is emitted and absorbed as packets of energy called photons
What is the energy of each photon proportional to
Itβs proportional to the frequency
How are electrons βexcitedβ?
It takes a photon exactly the right energy to βexciteβ an electron to a higher energy level. Electron moves from the lower to higher energy level and we say that the atom is in an excited state
What happens when light of all frequencies is passed through hydrogen gas?
Some frequencies are absorbed and create a hydrogen absorption spectrum. This shows the set of radiation absorbed by an atom when excited electrons move to a higher energy shell.
What does a black line represent in a hydrogen absorption spectrum?
Black line = absorbed
How can an atom be ionised and what rays can ionise atoms?
If a photon has enough energy, it can completely remove the electron from an atom and it becomes ionised. UV, X-rays and gamma ray frequencies can ionise atoms.
How can you excite an electron
You can excite the electrons in the atoms of the gas by passing electric current through
When do atoms emit radiation?
When they move from a higher to a lower level.
What does the emission spectrum show?
The emission spectrum shows the set of frequencies of radiation emitted by an atom when excited electrons move to lower energy shells. Colour = emitted electrons
What does the frequency of radiation emitted depend on?
It depends on the difference in energy of the two energy levels. The energy change can take place in one go, or two or more. If there were two or more changes then the emitted photons will have less energy, lower frequencies, and longer wavelengths than one go
What is the largest energy difference from an energy level?
Just below ionisation which varies in different atoms
What are the highest energy photons from a hydrogen atom
They are in the UV part of the EM spectrum
What type of photons can carbon atoms emit?
They can emit X-ray photons
Where are gamma rays emitted from and what are they the highest energy radiation ?
They emitted from the nuclei. Protons and neutrons occupy energy levels in the nucleus, where the energy involved is much higher, so the radiation emitted is of a higher energy.
How does a smoke detector work?
- a radioactive material fires alpha particles at a smoke detector
- if there is smoke between the radioactive material and the smoke detector, then fewer alpha particles will reach the detector
- this will set off the smoke alarm
How is blood flow in the body imaged using radiation?
- Gamma emitting isotopes are injected into the body
- we can trace the gamma emoting particles as they travel in the blood around the body
- we can use the detected signal to image the organs in the body
Why are ions reactive?
- the system or ions are in a high energy state and need to lose energy
Explain why nuclear radiation is so dangerous to the human body?
- nuclear radiation = highly ionising
- if ions are created inside or near the body = react with body cells
- cells become damages
- damaged cells continue to replicate giving rise to a tumour
If alpha , beta and gamma rays are placed between an electric field between positive and negative metal plate, which way will they bend?
- alpha = charge of +2 = negative plate
- beta = charge of -1 = positive plate
- gamma = no charge = straight through
Why do metal ions emit light when heated?
When metal ions are heated, energy is transferred to their e-. This makes their e- move into higher electron shells. When they move back to their normal shell levels, energy is transferred to the surroundings as radiation, which is seen as light.
How are alpha, beta and gamma rays deflected in a magnetic field?
- only alpha and beta experience deflection (gamma has no mass)
- deflection of beta is greater than alpha due to its small mass
How can you use a Geiger counter to work out the type of radiation a radioactive material was emitting?
- place radioactive source in front of counter and nothing in between and record activity
- place paper in between counter and source and if activity falls itβs alpha
- place thin metal foil in between counter and source and if activity falls itβs beta
- if activity doesnβt stop being recorded after placing thin metal foil = gamma (gamma passes through everything = decreases)
- a radioactive source can emit more than one type of radiation
Are neutrons more, less or similarly ionising to alpha particles?
- alpha and beta = highly ionising due to possessing a charge
- neutrons have 0 charge = canβt exert a force of repulsion/ attraction upon other particles
- smaller than alpha particles =can more easily pass by other particles
- neutrons = less ionising than alpha = more penetrating
What happens to the count rate when a source is moved away and why?
- decreases as radiation has to travel further through the air before reaching the detector so more of the radiation is likely to hit air particles on the way and be absorbed and so not reach the detector
Which radiation produces a new element?
- alpha and beta as the number of protons changes
What happens when an atom is ionised?
- if outer electron absorbs radiation with enough energy, it can move so far that it leaves the atom = now a free e-
- loses an e- and becomes positive
- can lose more than one e-
What does nuclear radiation do?
- alpha, beta and gamma can ionise atoms and ionising power is different for all of the,
- alpha has most so canβt travel very far in a substance without hitting an atom an ionising it and gamma is least
How do fluorescent light bulbs produce light?
- electrons are accelerated through the mercury vapour which ionises some of the mercury atoms, producing more free electrons
- when this flow of free e- collides with the e- in other mercury atoms, the e- in the mercury atoms are excited to higher energy levels
- when the excited e- return to their original energy levels, they emit radiation in the UV range of the EM spectrum
- compound called phosphor coats the inside of the tube and absorbs this radiation, exciting itβs electrons to higher energy levels and these e- cascade down the energy levels, emitting many diff frequencies of radiation, all in the visible part of the EM spectrum
Why do mercury atoms and atoms in the phosphor coasting emit different forms of EM radiation?
Electrons move between different energy levels in the mercury atoms and atoms in the phosphor coating, releasing different amounts of energy. The part of the EM spectrum that is radiation is from depends on the energy of the radiation
How can net decline of radioactive substance be calculated?
- itβs how much the activity (or no of undeclared nuclei) decreases by over a period of time = normally a ratio
- calculate how much the substance has declined in total by doing start activity- end activity = net decline
- write it as a ratio by doing net decline in activity/ original activity (as a fraction)
