More Soup (part 2) – The Hadrons

We have already looked at the leptons in part 1, so now we’re moving on to the hadrons. Please don’t forget that I’m keeping this purposefully simple and hopefully jargon-free(ish) to give the greatest degree of accessibility, to as wide an audience as possible.

A beginners guide to the Hadrons.

So ….what the hell is a hadron?
This a question many people ask but few find a satisfactorily simple answer to.
Simply put, a hadron is a composite subatomic particles made up of quarks and gluons. We’ll look at quarks in a little more detail further on in this post but for now we can just think of them as little building blocks. As for gluons, we’ll be looking at them in a future post (probably ‘More Soup – part 3’) but temporarily, just think of them as the force that binds the quarks together. This a somewhat simplistic view but suits our purposes for now.

Hadrons can be grouped into two main types. The mesons, that are made up of a quark and an antiquark, and the baryons, that are composed of three quarks.
To put this into a little bit of context lets use some examples. Some of the best and most commonly known baryons (a type of hadron) are the proton (p) and neutron (n) found in the atomic nuclei.

Both of these particles are stable when found in the nucleus. The neutron is unstable when outside of the nucleus (called a free neutron) and decays into a proton via the emission of an electron and an antineutrino.

The mesons, however, are a different kettle of fish!
Tending to be very short lived, with durations of 10-8 secs and shorter, the most common of the mesons are the Pion (pi-meson) and the Kaon (k-meson). There are many other varieties of meson, including the rho, B zero and eta-c meson but unlike the pion and kaon, these three, and most other mesons, are only detectable by the products of their decay.
What does this mean in real terms? Well ….. they are so short lived (10-23 secs in the case of eta-c) that the only way we can “see” them is to look for the ‘things’ they break down into when they decay into more stable products. It the case of eta-c (the charmed eta meson or ηc) the products could be a pair of photons or a trio of pions.

Pion decay in an early bubble chamber at CERN.

Like the leptons that we have looked at before, both the baryons and mesons have antiparticles that correspond to each positive particle. The proton (p) has an antiproton ( p ) and the positive pion (π+) has the negative pion (π) as an antiparticle. However, there are some mesons, such as the neutral pion (π0), that are there own antiparticle!
Quite unlike the leptons mentioned previously, all hadrons are affected by the strong interaction as well as the weak interaction, electromagnetism and gravitation. This is an important difference as it is this strong interaction that holds the nucleus together. Were it not so, why would the two protons in a helium nucleus stay together? The force of electrostatic repulsion would surely push them apart at a high velocity! We shall return to these binding forces in later posts.

So now we know what a hadron is, well …. we have a better idea anyway.
They are two or three of these little quark ‘building blocks’ stuck together. Great.
Quarks however …..erm ….. ok, off we go again.

Realistically, the quarks really deserve a whole “More Soup” post all to themselves, but what the hell, lets keep it simple and give you a quick guide now.

A quick guide to quarks.

As we’ve seen, these little guys are the very very simplest things that matter can be comprised of. They are held together in threes (baryons) or twos (mesons) and are a fundamental particle i.e. they’re not made of anything simpler – well thats what physicists currently think anyway.

Just like the leptons, they are categorised into six types or ‘flavours’, arranged into three generations.

In the first generation is the up (u) and down (d) quark. [both discovered SLAC 1968]
In the second generation are strange (s) and the charm (c) quark. [discovered SLAC 1968 and SLAC & Brookhaven 1974]
Lastly, in the third generation are the bottom (b) and top (t) quarks [discovered Fermilab 1977 and Fermilab 1995]
As before, each of these quarks has its own antiparticle – an antiquark e.g. the anti top quark (t) or the anti strange quark (s).
Note – All anti particles are designated with a little bar above the letter.

An example of some hadrons with their component quarks are listed below.
Proton (p) – up, up, down. (abbreviated to ‘uud’)
Neutron (n) – up, down, down. (udd)
Sigma minus (Σ) – down, down, strange (dds)
Charmed eta meson (ηc) – charm, anticharm (cc)
Pi minus meson (π) – down, antiup (du)

Before we leave this article, there are plenty of physicists out there who will be yelling about various qualities such as spin (isospin), parity (both C and G), strangeness, charm, charge, baryonic number and colour that can also apply to hadrons.
For you guys and gals – don’t worry. We’re taking this subatomic soup stuff a little at a time don’t forget. All those attributes will come up again later, in the future ‘More Soup (part 5) – Everything Else!’ post (probably).


Space Debris – Some creative thinking and “out there” solutions.

Quite a few people talk about the dangers of space debris. It trends on twitter in cycles and is a hot topic in the space world.
So, given my the exposure to the topic (mainly by the peeps on twitter) I did a little reading and then let my overactive imagination loose on the problem, well …. a section of the problem anyway.

Impression of space junk in LEO and higher orbits

Lets first set the scene. Space debris, or space junk, is the ever-increasing collection of used rocket stages, defunct satellites, and collision fragments that circle the planet. The problem is mainly found in low earth orbit (LEO) but not exclusively.
Wow, there’s a lot of crap up there !!!

So why is it such a problem?? Well…. with the amount of junk that’s now up there the low earth orbit is becoming a very packed place and if we don’t do something about it soon, spaceflight and in fact any launches, even to put satellites in orbit, will prove very difficult. With so many objects in the same or overlapping orbits, the chance of collisions is on the increase. The main problem with this is that an impact between two pieces of debris, generates even more debris and can even create clouds of debris. This resultant net increase in the amount of debris raises the probability for further impacts, with propagation runaway becoming a real possibility (the Kesseler Syndrome).

There have been numerous suggestions of how to remove the larger pieces (spent rocket stages and old satellites etc.) most of which relay on having another satellite intercept the junk and attach either an active thrust device (ion engine or conventional thruster) or a passive inductive drag device such as a solar sail. Other methods include laser ablation to induce momentum and setting off small thermonuclear devices to vaporise unwanted debris.
These methods are the most likely ones to be used, barring the thermonuclear option (probably!).

Below are some of the thoughts I personally had whilst considering the issue over a couple of days. Some of them are only semi-serious and the others may even verge on the ridiculous. But, thinking about it, being creative, highlighting the issue and talking about it has to be a good thing …… right ??? And before anyone shoots me down, there may well be overlap with a number of other much better ideas already out there. These are just a few of my own (possibly ill-informed) ramblings.

Spider Webs
I was looking at a spider web the other day whilst daydreaming (as you do!). What an elegant design! Super strong thread and highly sticky. What a good way to catch stuff, but could this be translated into a much much larger scale to trap bits of junk in space? I don’t know….. maybe ??
Using monofilament threads made into a net and coated in glue, this could be spread out from an orbital delivery container, using very small thrusters to “pull” the corners apart.
The questions and problems that arise from this are pretty obvious though.

  • The net would need to be massive and collision fragment clouds tend to be spread over a very wide area.
  • The thread would need to be super strong to resist the impact of targets travelling in excess of 15,000 mph
  • The net would have to be very dense, having very small holes, to catch the small stuff

Based on the above, does this render the glue net defunct ?? Hmmmmm…… not necessarily.
Lets say that you made it target specific with regards to debris size and used it only in the area of a cloud that has the highest spacial density of fragments. Maybe some sort of carbon fibre thread could be used. Would the glue be strong enough to hold that fragment even after such a momentary contact? Would the fibres that the net was made of be strong enough not to just be shredded by the impact? The trick would be not necessarily to have the net taut but very very baggy to give the maximum amount of absorption of momentum. Should even a few of the fragments be caught up, the net could then be “encouraged” into a degrading orbit using the thrusters that erected it in the first place.

Catcher’s Mitt
The catchers mitt idea is really just a development of the net, but the material used would be a solid sheet and would need momentum absorbing properties much like a Whipple shield. Whether this would better be a stuffed or spaced variety would be best decided by experimental design and testing. The idea would be to manoeuvre this large shield around inside the debit field orbit to “catch” whatever fragmentary debris were possible until the “mitt” were so degraded by impacts that it lost any further usefulness and itself became a risk of possible fragmentation from impacts.
It could then be manoeuvred into a graveyard orbit or urged into a more rapidly decaying orbit.
DARPA currently have a program codenamed “catcher’s mitt”, looking at tethers and solar sails for altering the orbits of large items of junk.

Interestingly, the previously mentioned solar sails need to be ‘erected’ or expended when in orbit. The net and mitt ideas also require an expanding mechanism technology to deploy them. Although I have mentioned the possibility of using small thrusters for the net idea, another way might be considered. Were the backs of all these sheets and surfaces covered in a web of tiny hollow pipes, a liquid (or maybe a gas) could be pumped through them causing them to unfurl much like the wings of an emerging dragonfly. I’m sure I can’t be the first person to think of this.

Bouncing Rocks and Debrisflectors
The idea behind this last strategy came about after remembering a childhood holiday spent on a pebble beach in the south of England. I can clearly remember throwing fist sized beach cobbles at a large rounded car size lump of rock a good distance away in the sea and then being amazed at how the rocks appeared to bounce or ricochet off the curved surface almost with an apparent complete preservation of momentum.
That was just the seed thought as its really the ricochet bit that is of interest.
Let say that it were feasible to get a relatively strong surface into space (we’ll come back to some ideas in a bit) that could be manoeuvred into the path of the debris – would this be capable of deflecting smaller items back towards the atmosphere to harmlessly burn up on re-entry???
Similarly to the catchers mitt idea, this “debrisflector” would have to be actively manoeuvred around inside an oncoming debris field to intercept the maximum number of objects. This also assumes that the surface could be made hard enough and correctly angled.
One other thought for the debrisflector would be to induce an ultrasonic vibration in the surface. This might then mitigate damage done to the surface by impacts (ricochets) extending the lifespan and usability of the unit.

So how could the reflecting surface be made strong enough to resist impacts and reflect properly, yet lightweight enough to be delivered to orbit in the first place??
One idea would be to use a composite sheet made of some form of metallic surface with a doped and strengthened aerogel backing. It could potentially be delivered in sections and assembled in orbit although this could potentially introduce weak spots at the joins.
The other main issue with reflection is the possibility that the object may not “ricochet” in whole pieces but may create an even worse problem in further clouds of collision spall. The only mitigating factor is that this cloud would then be directed towards the atmosphere for a relatively rapid re-entry.

So ……. a few ideas. None of them great, but maybe it’ll starts someone’s ball rolling. Good luck 😉

More Soup (part 1) – The Leptons

Time for another post so I thought I’d go back to the particle physics.

Wow there’s a lot of subatomic particles.
The more I stir this quantum soup, the more I need to get to grips with my mesons, baryons, quarks, antineutrinos and lambda particles. Not forgetting, of course, the gluons, photons and bosons!
Ok …. so lets start explaining what’s what. I want to keep it really simple for now, so it’s as accessible as possible.
Most particles already get grouped together to form families, so I’m thinking some sort of list or glossary might be in order!

Evidence of neutrino interactions in a bubble chamber.

Let’s start with……..

A beginners guide to the Leptons.

Leptons are fundamental particles. By fundamental, we mean that they are composed of nothing smaller (by current thinking). They are divided into two main groups: the charged leptons (ie electrons) and the neutral leptons (ie. neutrinos).
These leptons are further classified into six distinct types, also known as flavours, occurring in what is known as three generations. Lots of sub atomic particles have favours and generations as we’ll see in subsequent posts but lets not worry about this now.

In the first generation is the electron (e) and the electron neutrino (Ve).

In the second generation are muon (μ) and the muon neutrino (Vμ).

Lastly, in the third and final generation are the tau (τ) and tau neutrino (Vτ)

This last lepton, the tau neutrino, was only discovered eleven years ago in 2000 at Fermilab in the US and indicates just how recently new discoveries are being made in the field of particle physics.

Each of these six fundamental particles also has a corresponding anti particle. Its exact opposite, if you like. An example of this would be an electron (e) and the corresponding antiparticle, an anti-electron , often called a positron (e+). They  differ from each other only in that some of their properties have equal magnitude but opposite sign.

All leptons have some intrinsic properties like mass, charge and spin (that’s quantum spin by the way). Unlike hadrons, they are not affected by the strong interaction, only by weak interaction, electromagnetism (except neutrinos which are electrically neutral) and gravitation.

Ok … so now we know what they are and how we classify them but ….. what exactly do they do and where can we find some ??
I guess most people know about electrons. Go back to some fairly standard secondary school science and we are told that they spin round the nucleus of an atom and are divided up into “energy shells”. Sort of like this —>

However that’s not really the case. We need to really think more along the line of an electron cloud – a little like an electron probability map. This diagram (left) shows what I mean. The purple spot in the centre representing the nucleus and the haze around the outside representing the probability of finding an electron in that location. The darker the haze the greater the chance that an electron could be found there.
Its all to do with quantum mechanics and a gentleman called Heisenberg. He came up with a principle – the aptly named Heisenberg Uncertainty Principle – that stated that you could not know a particles exact speed and position with 100% certainty. This is better stated as – the more precisely one of these qualities is known, the less precisely the other one can be determined.

But, again… I digress, so …. back to the leptons then.

Electrons (wherever they are!) control most of the chemical properties of the elements and govern how elements react with each other. They are very light weight, having a very small mass and are very stable.
Muons are heavier, with taus being the real heavyweights. Both muons and taus are very very unstable and short lived with lifespans ranging from 2.1×10-6 in the case of muons, to 2.9×10−13 for taus. Both muons and taus can only be created by high energy collisions such as those created by cosmic rays or in particle accelerators. Both particles break down readily, via particle decay, explaining their short lifespans. Muons decay into electrons and various neutrinos. Taus however, are much more complicated and are the only leptons that can decay to various hadrons as well as other leptons.

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