Fysikexperiment i forskning och samhälle, HT 2013

Fysikexperiment i forskning och samhälle, HT 2013

Lunds universitet / Fysiska institutionen / Fysikexperiment i forskning och samhälle FYSN11, HT 2009

What defines physics? What defines a physics experiment?

Consider and discuss in groups the two questions above. Define

a couple of points as answers to the questions.


The teachers’ answers

What characterises physics?

• Striving for understanding and formulating the principal laws of nature• Understanding the physical entities relevant for a physical system• Understanding the nature of and interactions between these entities


What characterises a physics experiment?

•Control over cause – action•Controlled conditions: Control of as many parameters as

possible – systematic change of parameters • Idealisation / Abstraction •Reproducibility•Fundament in theory and/or model•Deliberate perturbation of a system in order to determine

the system’s characteristics. Make the cause-study the action

The teachers’ answers


Boxes

Think of physics experiments that could deliver information about the box and its contents.

Which physical property would you like to determine?How would you determine this physical property?Why does your measurement allow measuring this particular physical property?What is the length scale of the physical property?What is the length scale of your experiment?


Boxes

Physical property Probe Measured quantity

mm µm nm pm fm <fm

Length scales of physical properties and measurements

Your measurement method


Rutherford scattering

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf


Characteristics of a physics experiment

•Control over cause – action•Controlled conditions: Control of as many parameters as

possible – systematic change of parameters • Idealisation / Abstraction•Reproducibility•Fundament in theory and/or model•Deliberate perturbation of a system in order to determine

the system’s characteristics

Rutherford scattering vs Characteristics of physics experiments

To what extent do these apply to the Rutherford scattering experiment?


Probes

In Out

In

Out


Probes

In Out

Photons / Electromagnetic fieldsElectrons

AtomsIons

NeutronsProtonsPositrons

AntiprotonsMuonsPions

Neutrinos...


Choice of probe

Determination of the properties: disturb by suitabe radiation

• Choose wavelength according to probed interaction

• Penetrate into (or emit from) interior or surface only?

• If you want to receive information on length scales:de Broglie wavelength = h/p of same order as (or smaller than) the structure studied

• Smaller structures … higher momentum … bigger machines

Characterisation of a piece of matter: which properties are you interested in?


de Broglie wavelengths

Wave-length

P=Ek if photon Ek if electr. Ek if p/n

10-9m(10-10m)

1.2keV/c (12keV/c)

1.4eV(140eV)

Thermal

10-12m 1.2MeV/c 0.79MeV 0.76keV

10-15m 1.2GeV/c 1.2GeV 0.59GeV

10-18m 1.2TeV/c 1.2TeV 1.2TeV


Common concepts in experimental Physics

Each group picks a concept from the list below. During the lectures the group identifies how this concept was relevant in the type of experimental studies that was covered in the lecture.

You write a small essay about your concept in relation to the experimental physics you learn bout in the lectures. 2 pages written text plus figures.A preliminary writeup is delivered before the two last lectures. It is peer reviewed by your fellow who give feedbacktogether with one teacher. You respond to the criticism by correcting your text and include the two last lectures. Writing is individual, analysing the concept vs study material may be collaborative

•Concepts other years:

•Elastic scattering•Inelastic scattering•Energy levels•Conservation rules (energy, momentum, charge..)•Timing•Excitation•Quantal effects•crossections


Examples of spectroscopic measurements

What do the following terms mean?

Spectrum – Spectroscopy

Where have you previously encountered these terms?



Spectrum = lat. apparition, appearance

Came into use in the 17thcentury for describingwhat is seen when light isshone through a prism

www.wikipedia.org



X-rayphotoelectronspectroscopy

X-ray absorptionspectroscopy

Time-dependentx-ray photoelectronspectroscopy


Nuclear probe onmeteorite, x-rays


Almost Rutherford

Gamma energies from 61Zn 40Ca + 24Mg → 61Zn +p+p+n+γ


Particle spectroscopyat high energy


HEP: often PT instead of kinetic energyEarly results from LHC (CMS exp)

Masses are the quantal states


Writing articles about physics

• Any text about physics should be properly referenced.

• You may quote other sources. But remember:Quotes must be marked clearly.You must always provide the reference of the source (even for internet texts!).Only an insignificant fraction of your text may be composed of literal quotes (i.e., no ”cut and paste”).

• Enough information should be provided that a reader can repeat the experiment

Documents

Fysikexperiment i forskning och samhälle, HT 2013