Fission bombs versus Fusion Bombs - PowerPoint Presentation

Slide1

Fission bombs versus Fusion Bombs

Bikini Atoll H-bomb Test, 2013: $500/month plus free medical care from US

GovSlide2

Today’s Plan

Particle Detectors

Bubble Chamber exampleCherenkov radiation QuizSlide3

Elements of a multi-purpose particle spectrometer

Vertexing

(measure displaced vertices due to weak interaction decays). Silicon strip and pixel detectors.Tracking (measure charged tracks in a magnetic field;

use the radius of curvature to deduce the momentum)Particle identification

(Use Cerenkov emission or time of flight (TOF)) to distinguish

pions

from

kaons

etc…Calorimetry (measure energy deposited in electromagnetic or hadronic showers)Muons (measure muons that penetrate steel or other heavy absorber).

Special purposeexperiments also have some of these componentsSlide4

A bubble chamber photograph

Donald Glaser,

1960 Nobel Prize in Physics for the bubble chamber

1968 Physics Nobel for Luis Alvarez:

"for his decisive contributions to elementary particle physics, in particular

the discovery of a large number of resonance states

, made possible through his development of the technique of using

hydrogen bubble chamber

and data analysis"

Fermilab

bubble chamberSlide5

How to measure the radius of curvature and momentum from

three points

in a bubble chamber or tracking detector. From the radius curvature or sagitta one can obtain the momentum.

Taylor expansion

cos

θ

≈

1

– θ2/2

So measure the “

sagitta

”, s, and determine p

R

RSlide6

The Geiger counter/The Proportional Counter

Two versions:

An avalanche discharge is produced near the wire (independent of the charge deposited).

When operated in proportional mode at lower HV (the ionization is proportional to the charge deposited in the tube).

Question: What is the E field produced near a wire in a cylinder ?

What is the potential difference across the tube ?

Ans

: E~1/r,

integrate to obtain ΔV=ln

(r0/ra)

Wire at positive HV; Why ?Slide7

Multi-wire proportional chamber (MWPC)

Georges

Charpak

, 1992 Nobel Prize in Physics

10

5

amplification factor near the wire.

Can cover large areas with planes of MWPC’s. This enabled many discoveries and fundamental experiments in particle physics.Slide8

MWPCs were followed by Drift Chambers

Similar to MWPC’s but provide two coordinates (one from the drift time of the ionization cloud to the wire. (spatial resolution is ~3 X times better than a MWPC).

MWPC’s can handle higher rates than drift chambers. Solid state detectors based on silicon are even more robust.Slide9

A fixed target experiment

Uses dipole magnets as momentum analyzers (“prisms”) and drift chambers and MWPC for tracking

In the case of a non-uniform B field or multiple magnets

A single dipole with field BSlide10

TPC (Time Projection Chambers)

Alessandro

Bettini

(left) and Dave

Nygren

(right), inventor of the TPC

Principle of the time projection chamber

3-D tracking AND

dE

/dx measurements.ATLAS

Also used by Prof.

Vahsen

for directional dark matter detection.Slide11
Slide12

What is the vector momentum of each pion ?

Argonne Bubble Chamber event

Measure the radii of curvature and scale.Slide13

Let’s now calculate the energy momentum 4-vectors for each pion

.

However, the mass of the K

0

meson is 497.7 MeV

How do we calculate the invariant mass of the pi-pi system ?Slide14

We identified the π

+ π- parent, it is a K

0 meson !

Let’s try to identify the X particle.

Question: how can we do this ?

Introduce missing mass

Let’s calculate

E

miss

firstSlide15

Compare to known strange particles

Aha, the missing X particle is a

Σ

.Slide16

Shielding by dipoles on left

1934 Nobel Prize in Physics,

Pavel

CherenkovSlide17

Cherenkov radiation: another mechanism for relativistic charged particles

If a particle travels faster than the phase velocity (“speed”) of light in a medium, Cherenkov radiation is produced.

Recall n=c/v, where n is the index of refraction.

OB=

ct

/n (Cherenkov

wavefronts

)

OA=vt (particle moving to the right)

How does C radiation depend on frequency ?Slide18

Cerenkov radiation by electrons

Cerenkov radiation by electrons (few MeV range) produces the “spooky blue glow” in the cooling pools of nuclear reactors

Optical analogue of sonic boom

Radiation comes out in a cone in 3d

Remember the frequency dependence.Slide19

The phototubes in the

SuperKamkiokande

detector being serviced. The detector is located at the Kamioka

mine in Gifu prefecture, Japan

Cerenkov detectors can operate

in the

threshold

mode

orIn the ring imaging mode

Question: What is meant by threshold mode ?Slide20

Particle identification using Cerenkov radiation

Question: What is this event display ?

Bettini

p42

For water, n=1.33, the Cerenkov threshold is

E=0.775 MeV for electrons;

E=213 MeV for

muonsSlide21
Slide22

Example: In the experiment of O. Chamberlain et al in which the anti-proton was discovered, the anti-proton momentum was approximately p=1.2

GeV. What is the minimum refractive index needed to have the antiprotons above Cerenkov

threshold ?

Need γ and then β. How we do find

γ

? Slide23

EM shower development in a calorimeter

From Rossi, B. (1952);

High-Energy Particles

; Prentice-Hall