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Flashcards in P2 9-16 Deck (33):

What is radioactive decay?

The nuclei of some atoms are unstable, and radioactive decay occurs when a nucleus from one of these atoms breaks down and emits radiation.


What are alpha, beta and gamma radiation stopped by?

Alpha - a few sheets of paper
Beta - a few mm of aluminium
Gamma - a few cm of lead


What is ionising radiation?

radiation causes electrons to be added or removed from atoms, forming charged ions.


Radiation in least to most ionising?

Gamma, beta alpha


What happens when DNA inside a cell is ionised?

- it changes the interactions inside the cell.
- The ionised parts repel or attract each other, so the cell does not behave as it should.
- Ionisation can also initiate chemical reactions that would not normally take place.
- Severe damage to the DNA may lead to cancer and cell death.


What precaution should you take when handling radioactive substances?

Shielding - e.g gloves. Denser shielding depending on radiation
Time - reduce time of exposure to radiation
Distance - e.g tongs. The further away you are, the better


Why do smoke alarms contain alpha radiation?

This ionises air inside the alarm and creates a very small electric current. When smoke enters the alarm, this current drops, setting off the alarm. If there is no smoke, there is no change in current and so the alarm stays quiet.


Why are beta particles used in paper mills?

Beta particles are quite penetrating, and not very ionising. In paper mills, sheets of paper pass between a beta source and a detector which counts them. Some beta particles don’t get through the paper. The thicker the paper, the fewer get through and so the counts recorded by the counter go down. If the counts fall too low, this shows that the paper is too thick and so the rollers squeeze together.


How can gamma rays be used to kill tumours?

A special machine called a gamma knife contains a movable source of gamma rays. The gamma rays are fired into the body and focused on the tumour. The source is moved around in order to reduce the exposure of the healthy tissue but provide a high enough dose to kill the cells inside the tumour.


How are gamma rays used as medical tracers?

A weak source of gamma rays is either swallowed by or injected into a patient. Gamma rays travel out of the body and special cameras are used to monitor the flow of the source around the body. Doctors can then identify problems such as blockages or leaks within internal organs. A similar technique can also be used to detect leaks in underground pipes.


How are gamma rays used in sterilising equipment?

The gamma rays are used to kill the bacteria on the instruments, making them safe for use in future operations.


What is a centripetal force?

A force that makes an object move in a circular path


How do scientists explore space?

If the body being explored is nearby (like the Moon), samples are often brought back to Earth for further study. if the object being studied is much further away, spacecraft have been launched into space to collect a range of information. Probes have been sent to almost every planet, and to most large moons. They collect data on the temperature, magnetic field strength, atmosphere and the strength of gravity on the planet or moon.


What are the risks of sending humans into space?

Large amounts of oxygen, food and water are needed. All this requires extra fuel and a much more complex spacecraft. As a result, manned spaceflight is much more expensive than sending unmanned spacecraft. Unmanned spacecraft need less maintenance and they can withstand conditions that would be lethal to humans. If there is a problem, this may be too late. If there is a problem, this may be too late, because signals take a long time to travel through space.


What are asteroids?

pieces of rock that orbit the Sun. They are too small to be classed as planets. Often they have unusual shapes. Most of them are not rounded, as gravity is not strong enough to pull them into spheres. It is thought that asteroids are left over from the formation of the Solar System.


How did the asteroid belt form?

It is thought Jupiter’s strong gravitational field (due to its large mass) prevented the asteroids in the asteroid belt from forming a planet. Jupiter’s gravity disrupted this process, breaking up clusters of asteroids which would otherwise have eventually formed a planet.


What is a comet?

a large ball of ice and dust. There are hundreds of comets orbiting the Sun, but unlike most asteroids their orbits are highly elliptical (squashed circles). This means that sometimes they are very far away from the Sun, further than even the most distant planets. At other times they are much closer to the Sun, and the closer they get the faster they move (as the Sun’s gravitational attraction is stronger the closer you get to it). When they are near the Sun, the solar wind melts part of the comet, and its distinctive tail of debris is formed.


What will an impact on the earth cause?

throw large amounts of hot rock and dust into the atmosphere. often explosive and so can lead to enormous countrywide (or larger) fires. This creates even more dust that may block out the Sun, with a devastating effect on life on Earth. The impact may lead to rapid climate change, resulting in the extinction of some species.


What is a popular theory about the formation of the moon?

back when the solar system was very young, a planet about the size of Mars crashed into the Earth. The two planets merged together, with the heavier elements such as iron sinking into the middle. The lighter (less dense) elements were thrown into orbit. This material eventually formed the Moon.


What is the Big Bang?

the Universe began from a very small, very dense and very hot initial point. It burst outwards in a giant explosion. All matter and space was created in the Big Bang.


What is red shift?

Light from distant galaxies has been stretched because these galaxies are moving away from us. As they move away, the wavelength of the light increases. Red light has the longest wavelength of any colour. So when the wavelength increases, the light shifts towards the red end of the spectrum.


What is cosmic microwave background radiation? (CMBR)

two scientists called Wilson and Penzias noticed that no matter where they pointed their special telescope, they detected a background hum. This electromagnetic radiation was everywhere. They explained that CMBR must be the heat left over from the Big Bang. As the small, hot Universe expanded, it cooled, and the radiation was stretched out. Today this radiation is in the microwave region of the electromagnetic spectrum. It is the same everywhere you look because it fills the Universe.


What is evidence for the Big Bang?

Red shift


How are stars formed?

A cloud of gas (mainly hydrogen) called a nebula begins to be pulled together by gravity. A large ball of gas forms in the centre of this cloud. As it gets denser, more gas is pulled in. The ball gets hotter and hotter, forming a proto-star. Eventually, it gets so big, and its centre gets so hot, that atoms are squashed together in a process called nuclear fusion. A star is now born.


What is the main sequence of a star?

The energy released in nuclear fusion pushes out against gravity and keeps the star stable. This can last for billions of years, and is described as the main sequence of the star.


How does a small star die?

Small stars gradually cool and expand to become a red giant. The outer layers of the star break away and form a planetary nebula. All that remains is the white-hot core of the star. This white dwarf gradually cools over time.


How does a large star die?

They eventually expand and cool, but grow much bigger than smaller stars. They turn into super-red giants. The star then explodes in a gigantic explosion called a supernova.


What happens during a supernova?

the core of the star is crushed down by immense gravitational forces. This can form a very dense kind of star just made up of neutrons. This neutron star spins very fast and sends pulses of radio waves to the Earth. If the star is even bigger, the core is crushed down into a tiny space – it forms a black hole.


What is a black hole?

gravity so strong that nothing can escape from them, not even light.Black holes have near in nite densities due to their tiny volumes. All the mass of the core is crushed down into a space smaller than an atom.


What was ptolemys model?

• The Earth was at the centre of the Universe (the centre of
• This Universe was surrounded by a background of fixed,
unchanging stars.


What was Copernicus's model?

He used precise measurements of the planets to build models describing their motion. He found he could not explain their paths unless the Sun was at the centre of the Universe. He proposed a Sun-centred model of the Universe.


How did galelio work of Copernicus's model to create his own?

Galileo read Copernicus’s work and decided to investigate further. Galileo developed a telescope with very powerful magnification. This allowed him to see things that were previously too small to observe. Galileo discovered that there were objects in the Universe that were not in orbit of the Earth. Observations of stars and Galileo’s evidence led to scientists changing their ideas about the Universe. The Earth-centred model of the Universe was eventually replaced by the Sun- centred model.


Why were Copernicus and galelios theories controversial?

They went against the ideas of the church at the time. Speaking out against these ideas was considered blasphemy, and this was a very serious crime at the time.