Nuclear and particle atom

The mass number

Is the number of nucleons

Properties of the strong nuclear force

It acts within the confines of the nucleus and decreases rapidly with distance. It is independent of charge and acts between nucleons. It overcomes the electrostatic repulsive forces between protons It becomes a negative force at a certain distance because if it was purely attractive then the nucleons would just collide with eachother and collapse in on themselves. it provides a repulsive force between nucleons for distances of separation up to around 0.5fm. it is attractive between distances of about 3fm and 0.5fm. Beyond 3fm between nucleons, the strong force reaches zero. Short range force. Inside the nucleus, the nucleons have a resultant force of 0. If 2 nuclei come close enough, the nucleons will feel attracted/ repelled due to the strong nuclear force. There is a graph which goes vertically down then comes back up like a hill. FORCE against nucleon separation. Bottom half is attraction and top half is repulsion.

Isotope

Different number of neutrons

INVESTIGATION : investigating the absorption of alpha beta and gamma.

Equipment: Data logging computer recording counts GM tube Absorbing material Radioactive source Paper, lead, aluminium Holder for absorbing material Always handle radioactive materials with a tool, not hands. We can investigate the penetrating power of alpha beta and gamma using a geiger muller tube and a counter to detect the radiation passing through sheets of different materials placed between the tube and the radioactive source. The number of ionizing events detected per second or per minute when no radioactive source is nearby is the background radiation count rate and it must first be measured and then subtracted from all recorded count rates. Different thicknesses of paper, aluminium and pieces of lead will be used to investigate what thickness of each material stops each radiation

Experiment to determine half life of protactinium

Equipment: GM tube Plastic bottle (generator) lined tray Oily layer inside solution of uranium salt (once shaken contains atoms of protactinium 234.) Stand and clamp ratemeter/ datalogging inferface and computor connected to gm tube to record results) Ensure generator (plastic bottle) is undamaged- do not attempt to handle it. Handle only to shake and keep over tray at all times. radioactive isotope Protactinium 234 has a half life of just over a minute, and we can determine the half life of it by monitering its decay using a gm tube connected to a ratemeter or a datalogging interface and computer. When the bottle containing the solution of uranium salt and the imiscable solvent is shaken most of the protactinium 234 present in the watery layer dissolves into the solvent. Once the 2 layers have seperated out, no more protactanium 234 moves into the oily layer since the half life of thorium 234 is 24 days, so regeneration of protactinium is very slow, therefore we can moniter the decay of a fixed amount of P from the oily layer from the beta radiation it emits. The alpha particles emitted by the uranium are absorbed by the plastic bottle so not detected by the gm tube. Before plotting a graph of count rate against time, the background radiation count rate value must be subtracted.

The decay constant

(lambda) is the probability that an individual nucleus will decay per unit time. Given by decay constant = A/N, and has dimensions of time^-1. Units are per second, per minute, per hour or per year.

Electron mass

1/1840

atom diameter

10^-10 m

Diameter of a nucleon

10^-15

1u

1u is an amu and it is equal to 1.66x10^-27

Activity

A, is the number of nuclear decays (the number of gamma rays emitted) per unit time. An activity of one decy per second is one Beckquerel. Over time the activity of a sample will decrease as there are fewer unstable nuclei left to decay. Activity is directly proportional to the number of undecayed nuclei present given by the equation A=lambdaN A= - change in N/ change in t

Decay equations

A=lambdaN A=- change in N /change in time= lambdaN A and N both are proportional and decrease exponentially so: A=A0e^-lambdat N=N0e^-lambdat lambda= ln(A0/A)/t ln2= lambda t1/2

Decay of uranium 238

An atom of uranium 238 undergoes alpha decay to become thorium 234. A gamma ray is then emitted by the excited thorium nucleus as it de- excites. Gamma has no mass so the mass of the throium does not decrease any further.

B minus decay- quark transformation

Beta minus decay can be explained in terms of the quark model. Nuetron turns into a proton- down quark turns into an up quark. d into u + (-e) + antinuetrino Charge is conserved because on the left the down quark has a charge of -1/3 , and on the right hand side the up quark has a charge of +2/3 and the electron has a charge of -e which added together is -1/3.

Decay constant

High decay constant- decay happens quicker and a higher chance it will decay Lower decay constant- likelihood of individual nucleus decaying is small and it will take a long time for it to stop being radioactive

Binding energy per nucleon

If you divide the total binding energy of a nucleus by the number of nucleons, you'll get the binding energy per nucleon. The larger the value, the more stable the nucleus.

Components of a fission reactor

In a nuclear reactor the chain reaction is controlled by ensuring that on average only one of the neutrons produced by fission of uranium 235 causes subsequent fission. In practice some neutrons are absorbed by some uranium 238 but this does not undergo fission. Some are absorbed by the materials in the reactor, leaving a small excess. fission reactor has a concrete shield and fuel rods inside which contain the fissile material .

Plum pudding model

Model of the atom Negatively charged "raisins" Embedded in positive charged sponge giving an over all neutral charge.

Slowing down (Moderating the nuetrons)

Neutron only causes fission of a uranium 235 if it is travelling at the correct speed. It is more likely to be successful in causing fission if it is moving slower. Atoms of a moderator material always have to slow the neutrons down after they energy from a fission reaction before the cause fission of uranium 235. Methods of slowing down a neutron include: colliding the nuetron with a uranium nucleus- this causes a negligible loss of energy to the nuetron Colliding a neutron with a carbon nucleus- some loss of energy, more than when the nuetron collided with the uranium nucleus. colliding the neutron with a proton. The neutron loses all its energy here, and it stops, whilst the proton moves off. colliding the neutron with an electron- the neutrons speed here remains almost unchanged and the electron moves off with twice the speed of before. when neutrons energy from induced fission reactions they are highly energetic with a high ke so for them to induce further fission events they must be slowed down A neutron slows down the most when it collides with a particle that has a mass equal to its own mass.

Nuclear radius

Relationship between nuclear radius and nucleuon number (A) is given by R= r0A^1/3 where r0 is constant. R plotted against A looks like a square root graph. The nuclear radius is directly proportional to the cube root of the mass number, which means that when plotted against one another the graph will be a straight line through the origin and the gradient will be r0. r0 is the value if R when A=1 r0= 1.4 fm

Environmental impacts of nuclear waste.

Nuclear waste is radioactive material that is no longer useful. Sources include military weapons production and testing, nuclear power stations and hospitals. It can be classified as high level, intermediate level or low level depending on its activity. Waste can remain radioactive for any time between a fraction of a second to millions of years, depending on the types of isotopes that it contains. The fact that it can be active for long periods of time makes it dangerous. There is background radiation everywhere therefore everything on earth is exposed to ionizing radiation. Nuclear waste must be stored and shielded until it is no longer active. High level waste- produces LARGE amounts of ionizing radiation. Fuel rods removed from the core of a nuclear power station. High level waste produces heat as a result of the rapid decay of some of the short lived isotopes, so it needs cooling and shielding to block emissions. Intermediate level waste- material that has become radioactive from being inside a nuclear reactor. When a nuclear power station is decomissioned at the end of its working life, the reactors metal cladding is intermediate. Low level- items which are only slightly radioactive due to becoming contaminated with small amounts of radioactivity, such as protective clothing.

Atomic number

Number of protons in the nucleus

How to tell if radiation is charged

Put them in into an electric field- charged particles will experience a force in a magnetic field due to the motor effect.

Graphs of radioactive decay

Random nature of decay results in a graph that has a scatter of points about the theoretical exponential decay curve guven by the aa0e^ equation. Large activity= variation from mean not significant, but if only back ground radiation is measured, a great deal of radiation would be seen. High activity= back ground radiation is negligible. Graph of activity and time has a negative gradient and the activity starts at a max value and decreases as time increases.

Alpha particle experiment and conclusions

Rutherford, geiger and marsdon fired a beam of alpha particles at a thin gold foil to see how the alpha particles were deflected. Detector was a zinc sulfide screen that would produce a faint flash of light whenever an alpha particle hit it. Collected results showed that the vast majority traveled straight through the gold foil without being deflected. ( CONCLUSION: Most of the space inside an atom is empty space, therefore vast majority of mass of atom contained in a small volume(nucleus)) and the nucleus diameter is much smaller than the diameter of the atom. He found that the nucleus had a diameter in the region of 10^-14m. And the atom has one of 10^-10. 10,000 times greater. A small number were deflected through small angles, less than 90. (CONCLUSION: very few deflected- positive charge of atom occupies very little space. 1 in every 8000 was deflected through an angle of over 90, therefore it bounced back in the direction in which it came. (CONCLUSION: nucleus had a positive charge, because it repelled the alpha particles, which was concentrated in a small volume) The alpha particles were deflected by the nucleus, therefore almost entire mass of atom lies at the center in the nucleus.

Radioactive decay

Spontaneous and random decay of an unstable nucleus into a more stable nucles by the emmission or alpha, beta or gamma radiation Spontaneous because it happens without being triggered or affected by external factors like temperature or pressure. It is random because it is not possible to determine exactly how many particles will decay each second nor which ones.

When alpha or beta or gamma are emitted

The emission of an alpha or beta will cause the original parent nucleus to change, it will become a nucleus of a different element called the daughter nucleus. When gamma rays are emitted, the nucleus does not change in terms of its nucleon composition, it loses energy to become more energetically stable. Mass- energy is conserved in nuclear reactions. The parent nucleus will recoil slightly due to conservation of momentum so has a very small amount of kinetic energy.

Stable and unstable nuclei

There is a graph plotting nuetron number (n) against the proton number (z) and there is a curved line on the graph which represents the zone of stability. Stable nuclei are found in this zone. Graph shows that as atomic number increases, there are relativly more nuetrons present than protons in stable nuclei. The zone of stability diverges from the line N=Z as the nuclei get heavier. Unstable nuclei emit a b or g radiation in order to get closer to the zone of stability.

A moderator

This is a substance used in a nuclear reactor which slows down the nuetrons so that they have a greater change of being absorbed by the fissile nuclear fuel. Moderator usually made of graphite.

Properties of quarks

UP quark: charge= +2/3 e Down quark: charge= -1/3e Strange quark: charge= -1/3e also has a strangeness of -1 Top quark: charge of 2/3 bottom quark has a charge of -1/3 charm has a charge of 2/3 they all have a bayron number of 1/3 Protons are UUD (2/3 +2/3 - 1/3)e = +e Neutron, UDD

KE Equation

We can equate kinetic energy to electric potential energy: 1/2mv^2= qQ/4PIrepsilon0 due to the conservation of energy, where r is the distance of closest approach. If an alpha particle is directed to a gold nucleus, the alpha particle must do some work against the electrostatic repulsion forces between the 2 positive charges. some Kinetic energy converted into electric potential.

Beta MINUS decay

Weak nuclear force responsible. A nuetron in the nucleus of the decaying radioactive nucleus transmutes into a proton AN ELECTRON (Beta minus particle) is released from the nucleus An electron antinuetrino is also released Beta minus decay occurs in nuclei which are low mass, unstable and have too many nuetrons relative to the zone of stability. Beta minus particle is an electron, it has a mass of 0 and a a charge of -1.

neutrino

a fundamental particle (lepton) with almost no mass and zero charge . each neutrino has an antimatter partner, called an antinuetrino

An alpha particle

a particle comprising of 2 neutrons and 2 protons ejected from the nucleus during radioactive decay. It is identical to a helium nucleus and is emitted due to its unusually high stability as a particle

an antiparticle

a particle of antimatter that has the same rest mass (mass at zero speed) but if charged it has the equal and opposite charge to it's corresponding particle eg a positron is e+ and an electron is e- Proton= antiproton they have opposite spin to corresponding particle When matter interacts with antimatter, annihilation occurs as their combined mass is converted to energy. Proton+antiproton= annihilation, and mass converts to energy in the form of photons. Even though a neutron has no charge, it still has an antimatter equivalent, its just made of anti quarks. p+p= p+p+p+P P being an anti proton. this equation works because the antiproton and the proton cancel eachother out, leaving just the original 2 protons, effectivley. The proton and anti proton come from the energy produced from the reaction.

Eeinsteins mass energy equation

a particles mass increases as its speed increases, not noticable at low speeds. This lead to his principle of the equivalence of energy and mass, which states that if energy is supplied to, or removed from an object, its mass changes by an equivilent amount. E=mc^2 change in energy= change in mass multiplied by the speed of light squared. If energy is absorbed their is an increase in mass and vice versa. Mass energy is conserved.

Beta plus decay

a proton in the nucleus breaks down into nuetron under the influence of the weak nucleur force a beta plus particle and an electron nuetrino are emmited. A beta plus particle is a positron. Beta plus occurs in nuclei where there are too many protons compared to nuetrons, relative to the zone of stability. Charge and mass must be conserved. Energy is released during beta decay due to the mass energy principle, because the decaying nucleus loses an elecron: mass decreases so an equivilent amount of energy is released: E=MC^2. Example: an isotope of flourine (flourine 18) undergoes beta plus decay into an isotope of oxygen a proton in the flourine nuclei will become a nuetron leading to a reduction in its atomic number from 9 to 8.

the strong nuclear force

acts between nucleons and holds the nucleus together against the electrostatic repulsion of the protons

Beta plus decay quark transformation

an up quark transmutes into a down quark Opposite to what you think- beta plus implies something becomes positive (plus) however an up quark becomes more down so its the opposite. u into d + (+e) + nuetrino charge is conserved: +2/3= (-1/3+1)

Isotopes

atoms of the same element which contain the same number of protons but can have a varying number of neutrons.

Gamma rays

can penetrate paper and aluminium but are stopped by lead. The lead absorbs it. Undeflected in an electric field because gamma radiation is composed of photons and is uncharged. Travels at the speed of light has no mass its a wave. is a form of electromagnetic wave with wavelengths between 10^-16 and 10^-9. Its emitted from the nucleus during gamma decay.

Beta radiation

can travel a few m in air and would be stopped by aluminium. They travel in the opposite direction to alpha, towards the positive plate, thus they have a negative charge. Mass- 1/1840 Charge: beta minus has -e charge and beta plus is a positron which is anti matter so has a charge of +e. Travels at 0.99c. Particle Its a high speed electron emitted from the nucleus during beta decay. it is produced when a nuetron changes into a proton.

nucleon

collective term for any particle in the nucleus

Electrostatic force equation

coulombs law: f= Q^2/4PIr^2e0

unified atomic mass unit

defined as 1/12 of the mass of a carbon 12 atom. 1u= 1.661x10^-27kg.

Geiger muller tube

detects ionisations of gas molecules caused by radioactive emissions.

Equilibrium seperation of nuclear particles

for 2 nucleons to be in equilibrium, the resultant force on each of them must be zero. Nuetral, so no electrical charge, and we can ignore the gravitational force. This leaves the strong force. Graph shows that when d is 0.5x10-15, the strong force is zero. So if they move out or in from this they will have a massive resultant froce pushing them back. protons would have an electrical force of repulsion balancing the strong forces attraction. This electrical force is tiny so they will have similar seperation to nuetrons. Seperation of nuetrons within any nucleus is virtually independent of how many nucleons there are in the nucleus.

leptons

fundamental particles, electrons and neutrinos are leptons. Each lepton has its own neutrino which is also fundamental. Eg, an electron has its own neutrino which is produced in beta decay. All leptons experience the weak nuclear force but not the strong nuclear force.

Annihilation reactions

if a proton meets an anti proton, their ,mass dissapears and a large amount of energy is released as photons of EM radiation. This is annihiliation. Photons are produced to conserve momentum. The reverse can happen; a burst of em radiation from the annhilation of a particle antiparticle pair can result in the creation of a new pair of particles, this is pair production. if a gamma ray photon is near an atomic nucleus it can produce an electron positron pair. The photon must have enough energy to create the rest mass of the 2 particles, any extra energy it has will be kinetic energy.

A gamma ray

is a form of electromagnetic wave with wavelengths between 10^-16 and 10^-9. Its emitted from the nucleus during gamma decay.

Pair production

is the process of creating a particle anti particle pair from a high energy photon

A beta particle

its a high speed electron emitted from the nucleus during beta decay. it is produced when a nuetron changes into a proton.

Fusion with larger elements

larger elements need more energy for fusion energy because they have a larger charge. They nucleons need to get closer together so the strong nuclear force can initiate fusion. Its hard for them to get closer because they have more electrostatic force.

Nuclear radius graph

looks like the y= square root x graph. It starts to move away from the y axis at 1

MOLES EQUATIONs

m= n mr where m is mass, n is moles, and mr is the relative formula mass which can be measured in grams per mole or kilograms per mole. For potassium, which has a mass number of 40, it will be 40 g per mole or 0.040 kg/ mole. N= n Na where N is the number of atoms, and n is moles, and Na is avogadros constant.

The nucleon number

number of nucleons (protons and neutrons) inside the nucleus of a particular atom. also known as mass number

proton number

number of protons inside the nucleus of a particular atom. Also known as the atomic number

The binding energy

of a nucleus is the minimum energy required to separate the nucleus (protons and neutrons) into its constituent parts. Useful to think of binding energy as unbinding energy. Heavier nuclei contain more nucleons so they posses a greater aggregate binding energy. Eg uranium. Binding energy is equivilent to the work done to separate the constituent particles. Nucleons are bound together by the strong nuclear force, therefore work has to be done to separate the nucleons so when they are separated they gain potential energy and according to Einsteins mass energy principle they therefore gain more mass because an increase in energy results in an increased mass. Binding energy is not the energy holding the nucleus together.

Density of the nucleus

p (row) = 3mn/(4pir0^3) where mn is the mass of a nucleon. When doing calculations with density we assume the nucleons are packed together with little or no empty space.

Hadrons

particles consisting of a combination. Hadrons are composed of quarks, quarks are fundamental particles because they cannot be broken down any further. Protons and neutrons are examples of hadrons. They are each composed of 3 quarks. All hadrons experience the strong nuclear force

Fundamental particles

particles which cannot be broken down into smaller components

Annihilation

process in which a particle and its antiparticle interact and their combined mass is converted to energy via E=mc^2

Alpha particles and alpha decay

stopped by a few cm of air or a sheet of paper. Move in the direction of an electric field, towards the negative plate. They are deflected less than beta radiation because alphas have more mass. Mass of 4 Charge of +2e Typical speed of emmision: 5% the speed of light 0.05c. Particle Fast moving helium nucleus. They compose of 2 nuetrons and 2 protons, so to conserve mass and total charge, the mass number of the radioactive nucleus that is decaying will decrease by 4 and its atomic proton number will decrease by 2. This conserquentlty will make it another element. They are ejected from the nucleus during radioactive decay. It is identical to a helium nucleus and is emitted due to its unusually high stability as a particle.

Classification of particles

subatomic particles can be divided into 2 groups: hadrons and leptons.

Half life

t1/2, is defined as the mean time taken for the activity of a source , or the number of undecayed nuclei present to halve. After 1 half life the activity will decrease to 1/2, after 2 half lives it will decrease to 1/4 of original value, after 3 it will decrease to 1/8 of the original sample. Half life of a radioactive source is inversely proportional to its decay constant

Carbon dating

technique used to determine the age of organic matter from the relative proportions of the carbon 12 and carbon 14 isotopes that it contains, using the half life of carbon 14.

Why isnt it the gravitational force holding the nucleus together

the force of gravity isnt strong enough.

quarks

these are components of Hadrons and have a fractional electric charge. They are believed to he fundamental particles. there are different types. up down bottom top strange charm.

Gamma rays in decay

they frequently accompanie alpha and beta , but never occur purley as gamma decay. Example: Colbalt-60 undergoes b minus decay Colbalt 60 source will emit an electron (beta minus particle) and then 2 gamma photons, and then will become the more stable isotope of nickel-60. emission of bminus particle leads to change in the atomic number whereas emission of gamma leads to a more energetically stable nucleus without a change in mass number or charge

Strong nuclear force

this acts between nucleons and holds the nucleus together against the electrostatic repulsion of the protons

A control rod

this is a rod which can be lowered into the core of a nuclear reactor, absorb neutrons and slow down the chain reaction. Control rods are usually made from boron. They allow on average one nuetron from previous reaction to cause subsequent fission.

weak nuclear force

this is felt by quarks and leptons. It can change quarks from one type to another or leptons from one type to another and is responsible for beta decay.

Mass defect

this is the difference in mass between the mass of a nucleus and the total mass of its separate nucleons. The total mass of the separated nucleons is always greater than the mass of the nucleus.

A chain reaction

this is the sequence of nuclear reactions produced when an induced nuclear fission triggers more than one further fission reaction.

Induced Nuclear fission

this occurs when a nucleus absorbs slow moving neutrons and the resulting unstable nucleus undergoes a fission reaction to split into 2 smaller nuclei and a small number of neutrons, releasing energy. In a nuclear power station, the energy released by nuclear fission heats water and changes it into steam, which is then blown onto turbines at high pressure, and the rotation of the turbines turns a generator to produce electricity. Fission produced energy because when it occurs, there is a decrease in mass so according to E=MC^2 mass is converted into energy and energy is released. When a slow moving nuetron is absorbed into a Uranium 235 nucleus, this makes the resulting nucleus (u 236) unstable, and this unstable nucleus very quickly (less than 10^-6 seconds) dis integrates into 2 unequal fragments which may decay into other fragments. One possible reaction is nuetron + uranium(235 92) - U(236 92)- Te(135 52)+ Zr(97 40) +4 nuetrons The daughter nuclei are more stable than the mother. they have more binding energy. The daughter nuclei are closer to the peak of the binding energy per nucleon curve. They go deeper into the potential energy well.

Nucleus diameter

x10^-14 mm