B - Factary

Background Radiation

See also, Big Bang.

This is the 'warm' after-glow of the universe’s Big Bang. Following any explosion there is usually some residue of radiation. This normally takes the form of heat (infrared radiation). Many scientists searched for this after-glow, which would provide another piece of evidence for the universe’s Big Bang. However, in the end, it was found purely by accident by two American astronomers, Penzias and Wilson. They were actually looking for something else at the time and thought the 'buzz' in their equipment was due to some birds which were roosting in their horn-shaped telescope. As a consequence they had the birds shot. However, the buzz remained. After much thought and consultation they finally decided that their telescope really was detecting the after-glow of the Big Bang. The elusive Background Radiation had finally been found.

Becquerel (Bq)

The unit of nuclear radioactivity.

It is a measure of the 'activity' of a sample of a radioactive substance when the nuclei of its atoms split apart (nuclear fission). It is measured in 'the number of disintegrations per second'. One Bq is one disintegration per second.

Within 1 gm of the radioactive element radium approximately 40 billion atoms every second will break apart (the fission process) and produce dangerous radiation. That gram of radium therefore has a radioactivity measure of 3.7 x 10¹⁰ Bq.

Radium has a half-life of 1600 years and so loses only 1% of its radioactivity every 25 years.

Becquerel, Henri (1852-1908)

The French Scientist who discovered radioactivity by accident.

In 1896 he was experimenting with chemicals containing uranium which were known to 'fog' photographic film (make the film go black without it being exposed to light). He had set up an experiment in which he wrapped some film in light-tight black paper and placed the uranium chemical on top of the paper. At the time he and others thought it was the action of sunlight on the chemical that made it give off strange rays (possibly the newly discovered X-rays) that affected the film and Becquerel was planning to test this. However, because on a couple of days it was cloudy, he put his experiment in a draw away from light. Afterwards he decided to develop the film anyway, expecting only very little blackening of the film because the chemical had not been exposed to sunlight. To his surprise the film was blacker than he'd ever seen.

OK, so far it was all an accident and not planned, but the reason scientists get credit for such work is that they go on to interpret correctly the results they get.

How would you have interpreted Becquerel's result?

He realised that the blackening of the film meant that something was being emitted from the chemical without needing any help from sunlight and that such an effect must be a property of certain elements (in this case uranium). He was then able to perform further experiments to investigate the nature of what was being emitted and showed that the 'radiation' was in fact in the form of charged particles, not the electromagnetic radiation (X-rays) he had first thought.

Beta particle (e^-)

See also, nuclear radiation.

This is another name for an electron. It was given the name 'beta' by early experimenters who were not sure of the true nature of the strange radiation they had discovered and because it was the second one they had discovered.

Beta particles can be easily stopped by a metal shield, for example 5mm of aluminium. They are weakly ionizing and have only a small effect on living organisms. However, if you receive a large enough 'dose' of them they could be harmful. The dose received would depend upon how 'strong' the source of the radiation is, how far away you are from it and how long you're exposed to it.

A stream of beta particles is known as a cathode ray. Cathode rays can be found in TV sets. They can be created by heating up a thin piece of tungsten wire and accelerating the electrons which are emitted by using electric and magnetic fields. When an electron hits a TV screen it makes it glow because there are special powders or phosphors on the inside of the screen whose atoms emit light when struck by an electron.

Big Bang

The theory that all matter in the universe started off at the same point as pure energy. Since then all of the matter we know to exist has been created and has formed vast structures, such as stars and galaxies. In astronomy, the theory of the Big Bang is now the most popular explanation for the creation of the universe. The existence of the Background Radiation is a strong piece of evidence in favour of the Big Bang theory.

Billion

Internationally, this almost always now means a thousand million (1 000 000 000 or 10⁹). That's the way it's used in the Sun|trek material, rather than the old UK definition which was a million million (1 000 000 000 000 or 10¹²).

Black Hole

A region of space which has so much mass concentrated in it and is so dense, that its gravitational pull is strong enough to prevent any nearby object, or even light, escaping the pull of its gravity. We can't see a black hole, but we can see the effect of material being sucked into it.

For the Earth to become a black hole all the mass of the Earth would have to be compressed into a sphere of diameter 1.7 cm - yep that's less than 2 centimetres and that would be one very compact object.

Blueshift

See Doppler Shift.

Bow shock

The bow shock is the leading edge of the Earth's magnetic field in its interaction with the solar wind.

The characteristic shapes and boundaries are similar to the bow waves of ships, bullets, supersonic jets etc. They all compress or squash the material in front of them.

Byte (and bits)

Computers work on the basis of being able to distinguish between two states, for example on or off, 0 or 1, yes or no, heads or tails - however you want to describe it. The electronics in computers is designed to have these two options. Each electronic element that can either be on or off (0 or 1) is called a 'bit'. But only counting 0 or 1 on its own is rather restrictive (you might say it was a bit restrictive) so let's put two bits together and use them to represent a single number. Then we can have:

(0,0) = 0
(0,1) = 1
(1,0) = 2
(1,1) = 3

So now we can count from 0 to 3 by just using the values 0 and 1 - it's getting better. The general rule is that the range of numbers you can count is given by 0 to (2^N-1) where N is the number of bits being used.

It is normal practice to put 8 bits together to represent a number. We can then count from 0 to (2⁸ -1) or 0 to 255. Such a combination of bits is called a BYTE. Several bytes can be used together to represent even larger numbers. When we start talking about storing large amounts of numbers (or characters) we need some new words and we use prefixes to make them. A prefix is simply a group of characters attached to the front of another word which indicates a number. For instance, the prefix KILO means 1000. The word kilogram, therefore, means 1000 grams.

In computer-speak, the first word we come across is KILOBYTE, and immediately we hit a problem. Bits and bytes, and computers in general, like powers of 2 (4,8,16,32 etc) while in general life we much prefer powers of 10 (100,1000 etc.) - so what exactly is a kilobyte? It's a bit of a cheat actually. Computer language borrowed the 'kilo' prefix but then they fiddled it to mean 'about 1000', so that kilobyte actually means 1024 bytes. Why 1024? - well 2¹⁰ = 1024, not 1000. Unfortunately it gets worse so that when computer people talk of 1 megabyte they actually mean:

2¹⁰ x 2¹⁰ = 1024 x 1024 = 1,048,576 bytes
- not all that close to a million bytes. How confusing!

What's the origin of the words bit and byte?

The word 'bit' dates back to 1948, when computers were just becoming modern machines. An article written by C.E. Shannon in a technical journal of the time credits J.W. Tukey with its first use. The word comes from 'binary digit', but it also means a 'small part'. A bit of a neat play on words, eh?! You might also imagine that since it deals with two things (0s and 1s) it is only fair the word contains the letters 'bi' as in bicycle and binoculars.

On the other hand it’s not clear where the word byte comes from. It means 'eight bits' and was probably first used by someone working at the computer firm IBM around 1964. One suggestion is that the word could have come from BInary digiT Eight? The letter ' I ' was then substituted by a ' Y ' to save any confusion with the word bit! Maybe you could come up with your own version of where the word came from?

back to top