Atomic And Nuclear Physics Engineering Essay

Black body Radiation A black organic structure is a theoretical object that absorbs 100 % of the radiation that hits it. Therefore it reflects no radiation and appears absolutely black. In pattern no stuff has been found to absorb all entrance radiation, but C in its graphite signifier absorbs all but about 3 % . It is besides a perfect emitter of radiation. At a peculiar temperature the black organic structure would breathe the maximal sum of energy possible for that temperature. This value is known as the black organic structure radiation. It would breathe at every wavelength of visible radiation as it must be able to absorb every wavelength to be certain of absorbing all entrance radiation. The maximal wavelength emitted by a black organic structure radiator is infinite. It besides emits a definite sum of energy at each wavelength for a peculiar temperature, so standard black body radiation curves can be drawn for each temperature, demoing the energy radiated at each wavelength. All objects emit radiation above absolute nothing. [ 1 ]

“ Black body radiation ” or “ pit radiation ” refers to an object or system which absorbs all radiation incident upon it and re-radiates energy which is characteristic of this radiating system merely, non dependent upon the type of radiation which is incident upon it. The radiated energy can be considered to be produced by standing moving ridge or resonating manners of the pit which is radiating. [ 2 ]

The sum of radiation given off in a peculiar frequence set should be relative to the sum of manners that is in that scope. Classical natural philosophies suggested that all manners have an equal opportunity of been produced and that the figure of manners goes up relative to the square of the frequence

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But the continual addition in predicted radiated energy with frequence called the ( ultraviolet calamity ) did non go on.

Manners per unit frequence per unit volume

Probability of busying manners

Average energy per manner


Equal for all manners



Quantized manners ;

Require hI? energy to excite upper manners, less likely

Table ( 1 )

Black body Radiation

Experimental set-up

DetectorFigure ( 2 )

A simple experiment set up to observe black body radiations to hold an object ( T1 ) maintained at a changeless temperature and the radiation that is been emitted by the light beginning will be detected by the setup that is sensitive at that peculiar wavelength following this a prism is used to divide the wavelength ( I» ) at a assortment of different angles ( I? ) .The wavelengths that will be detected will be quiet big so to do this easier we will mensurate the dI» difference in wavelengths around I» .This will be repeated for a scope of different angles and so in bend it will be done for a scope of values of I»

The measure that will be measured by the sensor for this will be

Beaming strength R

The consequences that will be obtained will be for a series of values R dI» for each of the different values of I» that are measured.we repetition this with a assortment of different temperatures and the information that is gathered can be plotted on a graph of beaming strength R against I» with the result looking as follows

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This consequence of this experiment tells us two of import consequences the first been

That the entire beaming strength ( R ) increases over all the wavelengths as the 4th power of temperature ( T ) this is equal to the entire strength is the country under the curve which gives us


R = radiant strength R

I? = Stefan-Boltzmann changeless = 5.6703 ten 10-8 W/m2 K4

T = Temperature ( Kelvin )

This is known as Stefan ‘s Law and is besides written in the signifier of

P = I?T4 A· A

The 2nd thing that was learned from this experiment was that the wavelength with the most intensity I»max ( in metres ) decreases in reverse proportion as the temperature increases so hence


So the invariable of proportionality was determined by experimentation so

I»max T = 2.898 x 10-3 mA·K

m = metres K = temperature

This experiment can be simulated on the nexus below on the undermentioned site to assist better understand these constructs

Figure ( 4 )

To recap what we know so far as the temperature increases the entire energy additions and the extremum of the spectrum displacements to smaller wavelengths towards the bluish side of the spectrum.

Figure ( 5 )

The dependance of R on I» that is described by Stefan ‘s and Wien ‘s Laws is an empirical consequence that is achieved we need to explicate these consequences based on the theories of thermodynamics and electromagnetism

To work out this job we construct a pit in which to pin down the radiation which is absolutely absorbing and breathing as shown in Figure ( 2 ) it should be remembered that it is the hole and non the box that acts as a black body. Radiation outside strikes the hole and gets trapped inside the pit with a really little opportunity of get awaying once more so it is assumed there will be no contemplations from the black body.

If our black body box is filled with electromagnetic standing moving ridges and the walls are made up of a metallic stuff so the electromagnetic radiation reflected back and Forth with a manner of an electric field at each wall

The expression used to prove this was to happen out the figure of standing moving ridges N with wavelengths that are between I» and dI» is

N ( I» ) dI» = dI»

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For the Classical thermodynamic consequence it was taught that each moving ridge contributes energy karat to the radiation in the box. The radiation in the box is at thermic equal with the wall temperature of the box. In that the radiation is reflected from the walls and so it is absorbed and re-emitted so rapidly by the atoms The atoms are said to hover at the same frequence of that of the radiation and the mean thermic KE ( Kinetic Energy ) of the atom is equal to half the karat ( Boltzmann invariable and the absolute temperature ) a consequence which is similar for ideal gas. So from the SHM ( Simple Harmonic Motion ) we can state that the average KE is equal to the average PE.Therefore the mean of the entire energy was equal to kT

What was done after this was to happen the R ( beaming strength ) from the energy denseness and multiply this by

Is a factor from geometry consideration of energy in a volume that is linked to Stefan ‘s jurisprudence

So after we consider all this information we are left with

Beaming strength ( R ) equal figure of moving ridges per unit volume multiplied by the energy per moving ridge multiplied by beaming energy per energy denseness

And we get

R ( I» ) = = Rayleigh-Jeans Law

R = Radiant strength

I» = wavelength

K = Boltzmann invariable

T = absolute temperature

degree Celsius = velocity of visible radiation

The job with utilizing the Rayleigh-Jean expression was that at long wavelengths, beaming strength ( R ) predicts the same consequences as the existent informations nevertheless at shorter wavelengths this does non work and a failure know as the UV calamity happens shown below

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This happened due to there been excessively much beaming strength been predicted at little I» or high frequences even thou the thermodynamics and the electromagnetism were in good understanding with many other experiments at the clip a new theory was required.Plank attempted to happen a manner to seek and cut down the figure of high frequence standing moving ridges by cut downing the figure of frequence oscillators in the pit wall. Board came up with the thought that an atom could merely absorb and re-emit energy ( Iµ ) in distinct packages called quanta. He besides assumed that the quanta was relative to the frequence of the radiation and so the consequence that Plank came up with was that when the frequences are big the energy will be big and no single moving ridge can hold more than karat of energy

E = n Iµ

E = energy

n = figure of quanta

Iµ = quanta

With the energy of each quanta been determined by

Iµ = H degree Fahrenheit

H = Plank ‘s invariable

f = frequence

When Plank recalculated the spectrum of radiation strength R he got a consequence that matched the experimental informations precisely

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Black body radiation in instrumentality

Infra ruddy thermometers avail of this engineering to mensurate the heat signature of objects utilizing the black body rule

Working Principle:

In nature, all objects above absolute zero temperature are ever sent to the infrared radiation energy of the environing infinite. Infrared radiation energy of the object size and the distribution by wavelength – and its surface temperature has a really close relationship. Therefore, through the infrared energy radiated by objects in their ain measurings, can accurately find its surface temperature, infrared temperature measuring which is based on an nonsubjective footing. Infrared thermometerA by the optical system, photoelectric sensor, amplifier and signal processing, show end product and other constituents. Optical system field of position of its end of assemblage infrared radiation energy. The field size of optical constituents by the thermometer is to find its location. Infrared energy is focused on the photoelectric sensor and into a corresponding electrical signal. The signal through the amplifier and signal processing circuit, and intervention algorithms in conformity with the instrument and the mark emissivity corrected temperature of the mark into the measured value. In add-on, the thermometer should besides see the mark and where the environmental conditions such as temperature, atmosphere, pollution and interfering factors such as the impact on the public presentation and the rectification method. [ 5 ]

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Typical IR-thermometer

Photoelectric Consequence

The photoelectric consequence is when a metal surface is lit up with a beam of visible radiation and negatrons are emitted from the surface of the metal in inquiry.

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The Photoelectric consequence describes the first ( 1st ) mechanism in which radiation interacts with the atom ( the photon gives up all its energy to e- )

The experiment chosen to demo the photoelectric consequence is performed in a vacuity tubing this is to forestall energy loss from negatron due to hits with molecules of air

The emanation rate of the negatron is measured utilizing an ammeter connected external to a circuit. The KE ( Kinetic Energy ) of the negatrons is determined by using a Vs ( halting electromotive force ) to the anode so the negatrons do non hold plenty KE to interrupt free and flight.

Most negatrons can non get the better of the Vs we can therefore state Vs is equal to the maximal negatrons ‘Kmax ‘ so we are left with

Kmax = electron volt

Kmax = upper limit negatron

vitamin E = charge

Vs = halting electromotive force

A diagram of the experiment is shown in Figure ( 2 ) below



Figure ( 2 )


The consequences we obtain from this experiment are as follows

The emanation rate of the negatron is dependent on how bright the visible radiation is clambering

The ‘ cut-off ‘ wavelength is wholly dependent on the metal been used I»c

The maximal KE of negatrons is dependent on I»

The Photo-current flows every bit shortly as light beginning is turned on

This experiment can be simulated on the nexus below on the undermentioned site

Simulation of Photoelectric consequence

Figure ( 3 )

Einstein developed a theory based on Plank ‘s thought of quantum energy to explicate the ascertained effects in this he assumed that a quantum of energy was a belongings of the radiation itself In this theory Einstein assumed that photons have an energy equal to the energy difference between next degrees of a black body In saying this we must retrieve that the energy of radiation that is absorbed in distinct packages of energy are called photons and is obtained by the undermentioned expression

Tocopherol =hf

E = Energy

H =Plank ‘s changeless

f = frequence

Along with the expression for the impulse of a photon that is given as

P = E/c

P = impulse

E = photon

degree Celsius = velocity of visible radiation

With these two equations we can unite them together to acquire a utile equation that relates to both the wavelength and the impulse of the photon

P = h/I»

H = Plank ‘s invariable

I» ( lambda ) = wavelength

Einstein besides noted that the Electron is bound in metal with energy W – ‘work map ‘and that different metals have different work maps Cu, nickel, Ag, e.t.c An negatron is released from the metal surface if the photon energy is equal to the work map so

hafnium & lt ; ( less than ) W no photoelectric consequence

hafnium & gt ; ( greater than ) an negatron is knocked free and the extra energy is KE

So Kmax = H degree Fahrenheit -W

Kmax = upper limit negatron

H =Plank ‘s changeless

f = frequence

W = work map

So if the photon is precisely equal to W when Kmax = 0 so the above equation becomes

W = H degree Fahrenheit = hc/I»c

W = work map

H = Plank ‘s Changeless

f = frequence

degree Celsius = velocity of visible radiation

hc =planks changeless x velocity of visible radiation

I»c = cutoff wavelength

Therefore we are left with an equation that is

I»c = hc/W

I»c = cutoff frequence

hc = board ‘s changeless x velocity of visible radiation

W = work map

With these expressions now know it was possible to plot a graph of frequence versus negatron kinetic energy and find the relationship between them is additive

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We can so take the secret plan of the KE ( Kinetic Energy ) versus the frequence and the mean of this incline of informations will give us the value of Plank ‘s changeless as shown below

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The account of the photoelectric consequence was a important discovery in natural philosophies as it represented the first univocal grounds of dichotomy ; the phenomenon whereby visible radiation can act as a moving ridge in some state of affairss and as a watercourse of atoms ( or quanta of energy ) in others. This dichotomy formed a basis of the new quantum theory and was subsequently found to be a cosmopolitan truth of the micro universe -A entities known asA ‘particles ‘ such as negatrons and even atoms were in bend found to exhibit wave behaviour [ 3 ]

Compton Effect

Compton Effect is the 2nd ( 2nd ) mechanism

The Compton Effect is energetic incident radiation that spreads from slackly bound negatrons. Part of the energy of incident radiation is given to the electron-electron this is so released from the atom a part of energy is re-radiated as a longer wavelength in electromagnetic radiation in a different way.

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The Compton Effect as a wave re-radiated or scatters the electromagnetic moving ridge which is less energetic than the incident radiation ( the energy gone into the negatron ) but has the same wavelength

The Compton Effect as a atom gives us a different anticipation for the scattered radiation in that the photon gives up some of its energy to e- and is so scattered and shifted to a longer wavelength ( I» )

Before dispersing happens the photon has energy that is obtained by

E = H degree Fahrenheit = H c/ I»

E = Energy

H = Plank ‘s invariable

degree Celsius = velocity of visible radiation

I» = frequence

And additive impulse P is given by

P = E / degree Celsius

P = impulse

E = energy

degree Celsius = velocity of visible radiation

The negatron at remainder has energy of me c2

me = Electron remainder mass

degree Celsius = velocity of visible radiation

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After dispersing the photon and the negatron have energy and impulse as shown in the old diagram If we want to mensurate the way and the energy of the scattered photon we need to use the preservation of energy and of impulse to accomplish the derivation for the expression for Compton dispersing equation shown below taken from the Hyper Physics web site

Compton Scattering Equation

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In his account of the Compton sprinkling experiment, Arthur Compton treated the x-ray photons as atoms and applied preservation of energy and preservation of impulse to the hit of a photon with a stationary negatron. Using the Planck relationship and the relativistic energy look, preservation of energy takes the signifier

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Conservation of impulse requires

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Where p=E/c is used for the photon impulse. Squaring this equation utilizing the scalar merchandise gives

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Again utilizing the Planck relationship and the relativistic energy look:

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The energy preservation look above can be squared to give

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These two signifiers can be equated to give

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This can be rearranged to

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And eventually to the standard Compton expression:

I»’- I» =

I» = wavelength of incident photon

I» ‘ =wavelength of the scattered photon

H = Plank ‘s invariable

me = electron at remainder mass

degree Celsius = velocity of visible radiation

I? = sprinkling angle

The measure is known as the Compton wavelength of the negatron it must be remembered that the Compton wavelength is non a true wavelength but it is a alteration in the wavelength itself to turn out this an experiment can be done to verify what happens by detecting extremums in wave forms

At the different incident angle which is greater than zero there will be two extremums that will be observed

The wavelength of one of the extremum does non alter this is due to the tightly bound negatrons therefore there is no energy lost by the negatron to the photon

The wavelength of the 2nd extremum will change depending on the angle that is incident upon it this is predicted by Compton Formula

Figure ( 3a )

Figure ( 3b )

a?†I»Figure ( 3c ) Figure ( 3d )

I» = wavelength of the incident quantum

I» ‘ = is the scattered quantum

It showed be noted that the maximal wavelength addition is when a?†I»max = 2I»c this occurs when the photon is scattered straight backwards. Since this is the soap difference that can go on it would be incorrect to utilize this for wavelengths 100s of times larger than this as the consequences would be inadmissible ( strong UV visible radiation ) . For this ground it is merely important for X-ray and gamma beam dispersing