6.4 Nuclear and particle physics Flashcards
What is the proton number?
The number of protons inside the nucleus of a particular atom. Also known is the atomic number.
What is the nucleon number?
The number is nucleons (protons and neutrons) inside the nucleus of a particluar atom. Also known as the mass number.
What is the unified atomic mass unit?
1/12 of the mass of carbon-12 atom. 1 u = 1.661x10-27kg.
What is an isotope?
Atoms of the same element which contain the same amount of protons but varying numbers of neutrons.
Who was the first to propose new ideas surrounding atomic theory? What did he propose?
John Dalton.
He proposec elements were made of tny particles called atoms which would combine to form compounds.
Who discovered the electron?
J.J. Thomson- he suggested it was like a plum pudding.
What did J.J Thomspon discover while discovering the electron?
He found that a atom was 1800 times less massive than the smallest element.
Who’s exeperiment discovered the nucleus?
Ernest Rutherford.
What did Ernest Rutherfords experiment inculde?
He fired positivley alpha particles at a thin gold foil to see how the alpha particles were deflected- the detector was a zink sulfide screen that would produce a faint flash of light whenever an alpha particle hit it.
What is an alpha particle?
Helium atoms stripped of their electrons (positively charged).
What was the results from Ernest Rutherford’s experiement?
His colleagues Hans Geiger abd Ernest marsden showed most of the alpha particles past though the golf foil, however, a small numner were deflected through small angles (less than 90°) and about 1 in 8000 particles were deflected greated then 90°, causing it to bounce back in the direction it came from.
What was deducted from Ernest Rutherford’s scattering experiment?
- Most of the mass in an atom is contained in a small volume called it’s nucleus.
- Nuceus has a positive charge.
- Nucear diameter is considerable smaller than the diameter of the atom, meaning most of the atom is empty space.
Who proposed that int he nuclear model of the atom, electrons can only occupy certian orbits or energy levels around the nucleus?
Niels Bohr
What did Rutherford propose after discoving the nucleus?
Proposed the name for proton for the positively charges particle in the nucleus in the atom. He also suspected the nucleus contained a neural particle with a mass very close to that of a proton, simce the atomic mass of most elements was arounf twice that of the elements atomic numebr.
Who discovered the neutron? What did they show?
James Chadwick-he showed that the neitron has no charge and a mass very close to that of the proton.
What is the proton number also known as?
The atomic number and is also denoted as the letter Z.
What is the nucleon number also known as?
The mass number- often denoted as the letter A.
What are elements with different numebers of neutrons called?
Isotopes?
What defines an element?
It’s number of protons.
What is strong nuclear force?
The force that acts between ucleons and holds the nucleus together against the electrostatic repulsion of the protons.
What power of 10 of metres in fm?
x10-15m
What is the equation for coulmbs law?
F= Q x q/ 4πe0r^2
Is the value for coulmbs law in a nucleus going to be big or small?
Big
What is Newtons law of gravitation?
F= GMm/r^2
Describe the graph showing strong nuclear force with distance?
- The strong force provides a repulsive force between nucleons for distances of separation up to 0.5x10-15m.
- It is attractive between distances of about 0.5x10-15m and 3x10-15m.
- Beyong the distance of separation 3x10-15m between nucleons, the strong force approaches zero, it is a short-range force that does not act over large distances.
Is the value for Newton’s law of gravitation in a nucleus going to be big or small?
Small.
What is the force acting between protons keeping them together?
Strong nuclear force.
What particles does strong nuclear force act between?
Protons and neutrons
What happens to the strong nuclear force as you go further away from the nucleus?
It rapidly decreases with distance and does not extend much beyond adjacent protons and neutrons within the nucleus.
Why must the strong nuclear force become a repulsive force at a particular distance?
The strong nuclear force must bind nucleons together, but if it was just an attractive force then the nucleons would collapse in on themselves.
What does the graph look like showing how the strong nuclear force veries with distance?
What is the value of the strong force on nucleons inside the nucleus?
zero.
What happens the the stong force a nucleon experiences if it moves slightly further away to the nucleus?
It would experience a very strong force pulling it back.
How does the stong nuclear force keep the nucleus very stable?
Inside of nucleus, the n ucleons have a resultant force on them of zero. However, if a nucleon near the surface of the nucleus moves only slightly further away, it would have a. very large resultant force pulling back on it.
What are the forces on neutrons?
Since neutrons have no charge, there is no elecrical force, we can ignore the tiny gravitational forces leaving just the strong force.
What forces would 2 neutrons experience if they mived away from eachother?
They would experience a large force of attraction pulling them back together.
What forces would 2 neutrons experience if they moved closer?
They would experience a large force of repulsion which would push them back towards equilibirum.
What forces act on protons?
They will have an electrical force of repulsion provided by the strong force.
What the separation of protons be different to the separation of neutrons?
Since the size of the elecrical force on protons is much smaller than the size of strong nuclear force at this range, the separation of protons will be almost exactly the same as the separation of neurons.
What is the separation of neucleons within any nucleus independent of?
Independent of how many neucleons there are in the nucleus.
In comparison to the radius of an atoms nucleaus what is the radius of the whole atoms like?
The radius of the whole atom is 10,000 times greater
How much of the atoms mass is contained in the nucleus?
99.9% of the atoms mass
What should the density of an atom as a whole be like compared to the densoty to the nucleus of the atoms nucleus?
The density of the whole should be considerably smaller than the density of the nucleus beacuse the majority of the atoms mass is found in the nucleus which volumes tiny compared to the rest of the atom.
What happens to the volume and nuclear radius as more protons and neutrons are added to a nucleus?
The volume and the nuclear volume will increase.
What does the graph look like of nuclear radius size against neucloen number look like?
What is the relationship between nuclear radius and nucleon number?
R=r0A^1/3
Where R= nuclear radius, r0= constant, A= nucleon number
What is the nuclear radius directly proportional to?
The cube root of the mass number.
What is the constant r0?
r0 is the value of R when A=1 (the size of the hydrogen nucleus radius)
Describe the graph R against A^1/3?
Will get a linear relationship and the gradient of the graph will be equal to the constant r0.
What is the value of the constant r0?
1.4x10^-15 or 1.4fm
What equation relates the radius of a nucleus to its mass number?
R=r0A^1/3
How can you simplify the equation R=r0A^1/3 to make A a whole value?
Raise both sides to the power of 3 to obtain R^3=r0^3A
What is an α-particle?
A particle comprising 2 protons and 2 neutrons ejected from the nucleus during radioactive decay. It’s identical to a helium nucleus and is emitted due to it’s unusually high stability as a particle.
What is a β-particle?
It’s a high-speed electron emitted from the nucleus during beta decay. It is produced when a neutron changes into a proton.
What is a γ-ray?
A form of elecromagnetic wave with wavelengths between 10^-16 and 10^-9. Emitted from the nucleus during gamma decay.
What is radioactive decay?
Radioactive decay is the spontaneous and random decay od an unstable nucleus into a more stable nucleus by the emission of alpha, beta and gamma radiation.
Why is radioactive decay described as being spontaneous?
It happens without being affected by any external factors such as temperture or pressure, or by chemical reactions or placing it in a electric or magnetic field.
Why is radioacitive decay described as random?
It is not possible to determine exactly how many particles will decay each second, nor which ones will decay or when a particular nucleus will decay.
How was radioacitivty initially detected?
It was first detected by the darkening of a photographic film or plate. Soon after this, the material zinc sulfide started to be used. Zink sulfide gives out faint flashes of light when alpha particles are incident on it, enabling actual counts to be made of how much radiation was being emitted.
What did Hans Geiger invent?
He invented the Geiger-Muller tube which detencts ionisation of gas molecules caused by radioactive decay.
What will stop the penetration of apha particles?
A few centimetres of air or a sheet of paper.
What would stop the penetration of beta particles?
Beta particles will travel through a few meters of air and be stopped by thin aluminium.
What would stop the penetration of gamma rays?
Gamma rays will penetrate both parer and aluminium but will stopped by thick lead.
When passed through an electric field, how do alpha particles act?
Alpha particles would move in the direction of the magnetic field, towards the negative plate and so have a positive charge.
When passed through an electric field, how do beta particles act?
Beta particles move in the opposite direction of the elctric fiels, so have a positive charge.
When passed through an electric field, how do gamma rays act?
Gamma rays were not defelected since gamma radiation is composed of photons and is uncharged.
What are the main properties of alpha particles? (Nature, mass, charge, typical speed of emission)
- Nature: helium nucleaus: 2 protons, 2 neutrons
- Mass/u: 4
- Charge: +2e
- Typical speed of emission: 5% of speed of light: 0.05c
What are the main properties of beta minus particles? (Nature, mass, charge, typical speed of emission)
- Nature: electron
- Mass: 1/1840 u
- Charge: -e
- Typical speed of emission: 99% of the speed of light
What are the main properties of beta-plus particles? (Nature, mass, charge, typical speed of emission)
Nauture: Positron
Mass: 1/1840 u
Charge: -e
Typical speed of emission: 99% of the speed of light
What are the main properties of alpha gamma rays? (Nature, mass, charge, typical speed of emission)
- Nature: electromagnetic radiation
- Mass: 0
- Charge: 0
- Typical speed of emission: speed of light
What investigation is done to investigate the absorbtion of alpha-particles, beta-particles and gamma rays?
Using a Geiger Muller tube and counter to detect the radiation passing through sheets of different materials placed between the tube and the radiative source.
The background radition count rate (amount of inonising evens detected per second/ per minute when no radiation source is nearby) is subtracted from all recorded count rates.
Use paper and aluminium foils and pieces of lead of different thivknesses to investigate what thickness to investigate what thickness of each material stops each type of radiation.
What is beta-minus decay?
In beta-minus decay in a neutron in the nucleus breaks down into a proton under thee influence the of weak nuclear force, and a beta-minus particle and an electron antineutrino are emitted. A beta-minus particle is positron.
What beta-plus decay?
In beta-plus decay, a proton in the nucleus breaks down into a neutron under the influsence of the weak nuceur force, and a beta-plus particle and an electron neutrino are emitted. A beta-plus particle is a positron.
When nuclei undergo radioacitive decay, what must be conserved?
Both the number of particles and the total charge must be conserved.
What is an alpha particle?
An alpha paricle in a fast-moving helium nucleus.
What is an alpha particle composed of?
Since it is a fast moving helium atoms, it is composed of 2 protons and 2 neutrons.
What happens to an element when it undergoes alpha decay?
Since an element is defined to its atomic number, the nucleus will become that of another element.
What is responsible for both types on beta decay?
The weak nuclear force.
Describe what happens in the nucleus during beta-minus deacy.
A neutron in the nucleus of an atom changes to a proton, and an elecrton and and electron antineutrino are released from the nucleus. This electron that is ejected is the beta-minus particle.
When does beta-minus decay occur?
Beta-minus decay occurs in nuclei that are unstable, low in mass and have too many neutrons relative to the zone of stability.
How is charge conserved when beta-minus decay occurs?
Since the beta-minus is an elecron, it has a mass of nearly 0 and a charge of -1. To conserve total charge the atomic number of the radioacive nucleus that is decaying will increase by one. The mass number does not change.
What is an example of beta-minus decay?
The decay of carbon-14 to nitrogen-14 with the emission of an electron and an antineutriono.
What is the quark transformation of beta-minus decay?
A down (d) quark changes to an up (u) quark.
Describe what happens in beta-plus decay?
Beta-plus decay occurs when a proton within a nucleus turns into a neutron. This results in the ejection of a positron and a neutrino from the nucleus.
When does beta-plus decay occur?
Beta-plus emission occurs in nuclei where are too many protons compared to the number of neutrons , relative to the zone of stability.
What is an exaple of beta-plus decay?
When of flouride-18 into oxygen-18 with the emission of a positron and an elecrton nutrino.
What does the graph showing the number of neutrons plotted against the number of protons for stable isotopes show?
The graph shows as the atomic number increases, there are relatively more neutrons the=an protons in a stable nucleus.
What does the zone of stability show?
Shows the region where stable nuclei are found.
What does the zone of stability do an the line N=Z (neutrons=protons) as the nuclei get heavier?
The zone of stability curve diverges from the line N=Z.
What hadron is this?
Proton
What hadron is this?
Neutron
Why does the line show variation in activity in the graph of activity against time for a radioacitive source?
Background radiation causes variation to be seen in the graph.
What graph can half life be estimated from?
Half life can be estimated from a graph of number of particles against time or a graph of the corrected count rate.
What graph can half life be estimated from?
Half life can be estimated from a graph of number of particles against time or a graph of the corrected count rate.
What is does a graph showing half life look like?
What does the slope of a tangent show?
∆N/∆t
How can you find the decay constsnt and the half life from this graph?
- From ∆N/∆t=-λN we can find the decay constant λ by finding the gradient at any point. The half-life can then be found from ln2=λt1/2.
- Alternatively, graphic methords usued a logarithmic plot. From A=A0e^-λt, if we rearrange and take natural logs, we get: lnA0=LnA-λt. A graph of lnA against t should be a straight line, of gradient -λ.
What does the graph of binding energy per nucleon plotted plotted against nucleon number look like?
What does this graph show?
It shows that the nuclei of low and high nucleon number have smaller binding energy of those nuclei with a nucleon number of about 56.
Using the graph, what will happen when 2 low nucleon number elements combine to a higher nucleon number element (nuclear fusion?
This will result in the release of energy.
Using the graph, what will happen when a heavy nucleus is split into 2 lighter nuclei? (nuclear fission)
It will release energy.
Using the graph, what is similar between nucleau fusion and nucear fission?
After nuclear fission and nuclear fusion, energy will be released feom both.
