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Hoofdstuk 7

Beoordeling 8.2
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  • Samenvatting door een scholier
  • 3e klas vwo | 1035 woorden
  • 13 juni 2019
  • 5 keer beoordeeld
  • Cijfer 8.2
  • 5 keer beoordeeld

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Physics



7.1 Types of radiation



- Electromagnetic waves are the movements of electrons in the antenna which move up and down at a high frequency. Electromagnetic waves always have the same speed in a vacuum which is 299,792,458 = 3.0 x 10? m/s and is called the speed of light. Frequency is the number of waves created every second. Wavelength is the distance between two succesive wave peaks (or wave throughs). The symbol for wavelength is λ and is called lambda. A phone uses waves with wavelengths 10-40 cm. Every wavelength has just one frequency and vice versa.



- Electromagnetic radiation is energy that is transmitted at the speed of light through oscillating electric and magnetic fields such as light, radio waves, infrared, ultra violet, X-rays and gamma rays. Red light has the longest wavelength and violet the shortest. Light is the only electromagnetic radiation you can see.



 - When electromagnetic radiation falls on an opject, 3 things can happen:




  1. It passes through, when eg. sunlight passes through a glass window.

  2. It is reflected, when eg. light is reflected by a mirror or white wall.

  3. It is absorbed, when eg. a dark object heats up in the sunlight.



X-rays are a type of radiation that can go through many solid substances, allowing hidden objects such as bones and organs in the body to be photographed.



You can calculate the wavelength by dividing the propagation speed (distance covered by second) by the frequency (number of waves per second) by the formula: λ = c / f.   



7.2 Atoms



Atoms are molecules split into even smaller particles. An element is a substance that cannot be broken down further because it only constists of one type of atom. A proton has a positive electrical charge that´s found in the nucleus of all atoms. The mass of a proton is 1.6726219 × 10-27 . Because the positive charge is also really small, nuclear forces hold the protons together. Neutrons are part of the nucleus of an atom too and have no electrical charge. The mass of a neutron is almost the same as a proton. An electron is a negatively charged particle with a mass of 9.10938356 × 10-31. The charge of an electron is the same as a proton but have the opposite sign, and two of the same will repel eachother. The number of protons and electrons in an atom are always equal which tells us atoms are electrically neutral.



The number of protons in an atom will determine what kind of element it is, which is represented as atomic number. The number of electrons in an atom will determine which isotope it is. Mass numbers indicates the total number of protons + neutrons.



7.3 Ionising radiation



-Radiation that can break down molecules is called ionising radiation. Radio waves, infrared and light are not ionisting, UV is slightly ionising and X-rays and gamma radiation can harm your health. Radioactive means emitting radiation by itself and is described by having or producing the energy that comes from the breaking up of atoms. Naturally radioactive is when radioactive substances are natural in origin. Artificially radioactive is when radioactive substances are created by people themselves. A dosimeter is an instrument which registers how much radiation people have been exposed to. Unstable nuclei are radiactive substances which can change suddenly and commit ionising radiation. Stable nuclei therefore doesn´t change. Whether a nuclei is stable or unstable is affected by the stability of protons and neutrons in the atomic nucleus. -Radioactive decay is the variation of ways in which unstable atomic nuclei can change. Three important forms of radioactive decay:




  1. Alpha decay happens when an alpha particleis emitted by the nucleus. Its nucleus the same as helium, atomic nr of 2 and mass nr of 4. Which you can add to make a stable substance.

  2. Beta decay is a fast moving electron emitted from the nucleus of an atom undergoing radioactive decay. As a result of beta decay, the nucleus has one fewer neutron but one extra proton. Therefore the atomic number increses by one, ad mass number stays the same.

  3. For gamma decay, the nucleus does not physically change, a nuclide undergoing gamma decay does not undergo transmutation.



7.4  Protection against radiation



Physicist use the word radiation for ‘something’ that moves away from the source. That’s why particles and waves are both called radiation but have different aspects.



Types of penetrating power:




  1. Alpha radiation cannot penetrate deeply into substances, because its large, and loses energy quickly when it collides with atoms.

  2. Beta radiation penetrates further than alpha radiation. Beta particles are therefore much smaller and can penetrate more deeply.

  3. Gamma radiation consists of waves that propagate at the speed of light. Those are very penetrating.



How much damage ionising radiation makes depends on the amount of energy absorbed; the greater the amount, the more damage and the type of radiation; alpha radiation causes more damage than beta or gamma radiation. The equivalent dose is a measure of the amount of damage caused inside someones body by radiation, measured in sieverts (Sv). When a radioactive source isn’t shielded well, ionising radiation can reach your body from the outside which is called irradiation. Gamma is here the most dangerous.



Rules for working with radioactive sources:




  1. Make sure distance is as large as possible. Here, radiation spreads and become weaker and weaker.

  2. The time for which you are irradiated has to be as short as possible. The shorter the time, the less energy your body absorbs.

  3. Use shielding material that absorbs radiation. The greater the density, the more effectively the radiation is shielded.



Radioactive contamination are radioactive substances which are released into the environment, enter your body by for example breathing, drinking and eating and can land on your skin. Radiotherapy is a method used by doctors by using ionising radiation to irradiate tumors.



7.5 Activity and half life



Half life is the prediction of how long it will be before half of all the atomic nucleus will decay (t1/2). After that time, half the unstable nuclei have dacayed and the activity of the source has decreased by half. The decay curve is a graph that plots the activity of an amount of substance against time.


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