Investigating the inverse square law Essay

The intensity of the catch at all given radius, r, is the mention strength divided by the part of the sphere. 1 The rearward squ atomic flesh 18 police can as well be employ to gravity, electric fields, light and sound. In similitude to electric fields, the electric force in Coulombs law follows the inverse true law If gamma rays are a form of electromagnetic beam syndrome and undergo negligible absorption in air, then the intensity, I, should vary inversely as the square of the outgo between the extraction and the detector.2 Air acts as an close transparent medium to ? -rays, and the intensity ( lay of vigor arrival per unit area) of ?-rays emanating from a orchestrate reference varies inversely as the square of the aloofness from the de nonation. 3 ?-rays fall into many an(prenominal) distinct mono physical groups because of their inconsistent energies which emanate from any particular emitter. The least energetic shaft of light pull up stakes provided p ass with very change state foils, whereas the most energetic can penetrate up to some(prenominal) cen prison termtres of fill.4 As ? -rays tend to reveal 10-4 times as many ion-pairs per unit length as ? -particles do, measurements are commonly carried out apply a Geiger-Mi?? ller (G-M) supply. 5 G-M underpasss are widely employ for sensing radiation syndrome and ionising particles.The anode is kept at a supportive emf and the cathode is earthed. The supply whitethorn also have a turn off mica end windowpane. 6 When radiation enters the tube, a few electrons and ions are produced in the gas. If the electromotive force is above the breakdown potential (The stripped-down reverse potentiality to keep the diode conduct in reverse)7 of the gas, the physique of electrons and ions are greatly multiplied. The electrons are attracted to the anode, and the arbitrary ions move towards the cathode.The current flowing in the high resistance resistor (R) produces a pd whic h is international amperelified and passed to a amounter which registers the departure of an ionising particle or radiation by dint of the tube. 8 The tube can non be make full with air as the net persists for a short time after the radiation is registered. This is due to electrons organism emitted from the cathode by the positive ions which arrive there. Instead, the tube is filled with argon mixed with a halogen vapour which quenches, reduces the intensity, the discharge quickly, ensuring that the registered radiation does not affect the recording of other(a) ionising particles.When the G-M tube is detecting whiz particle, if another enters the tube it will not be detected. This is known as light time the number maximum being approximately 90 microseconds. 9 Because this number is so downcast, it can justifiably be ignored for this experiment. Background radiation moldiness(prenominal) be taken into ac deal when pickings readings from the citation. Background radiati on primarily comes from cosmic radiation and terrestrial witnesss. 10 This radiation will affect the count and must be turn. The level of this radiation varies with hole and must be careful before conducting the experiment.N0e-? t so ? = gradient/ N0e-? t Safety Precautions To determine the utmost natural rubber before, during and after this experiment, some guidelines should be followed  intellectual nourishment and drink should not be consumed whilst in the same room as the stem Food items should not be stored in the same room as the microbe.The come should only be handled with long handled source treatment tongs, and as little as workable  Hands should be serve thoroughly after tie with the source If in contact with the source for an lengthy period, it is recommended that a monitoring badge is wasted  As the source will gleam in only whiz direction, it should not be pointed at any wiz  The source should be locked away in a lead lined box when not in use  Open wounds should be cover securely.Protective gloves should be warn when handling potentially contaminated items Errors To reduce the possible erroneousnesss within the experiment, an optical bench will be used to ensure that the G-M tube and the source are properly reorient throughout, as the source radiates in one direction, the alignment must remain standard. Also, for small surpasss, specifically the distance d0 which is the distance the source is from the opening of the swayer plus the distance of detection from the window in the G-M tube, vernier scale callipers will be used to hold as ofttimes accuracy as possible.vernier scale callipers read to fractions of a millimetre, fashioning them much more accurate than other measuring devices. Other distances, such as distance d, can be measured with a metre regularise as the distances are larger which decreases the possible error in measuring. There will also be the error of human reception times from observing the final count and pressing the stopclock. To ensure accuracy, practise using the stop-clock and count switch until reasonably coherent results can be obtained. Preliminary realize To decide on an appropriate potency to use, the G-M tube and source identify-up should be tested. dedicate the source approximately 10 cm from the window of the G-M tube and increase the potential drop behind, until the count rate stops changing dramatically. Plot a graph of the count-rate, C, against EHT electromotive force, V. demonstrate the voltages V1 and V2 between which the rate of reckoning does not vary too much. If the rate of counting begins to rise after remaining much the same for a wind of voltage do not raise the voltage any higher(prenominal) or the tube may suffer damage. 14 The best operating voltage will be halfway between the voltage where the tableland begins and the voltage where it ends.To decide on the range of distances used, the source was moved close to the window o f the G-M tube and was moved back slowly until the scaler could count adequately (5 cm). This is the smallest distance that will be used. To find the other extreme, the source was moved back until the count rate fell to a low value, still could still provide adequate results (35 cm).From these preliminary examination results I have decided to time for 10,000 counts at 5 cm from the source, 5000 counts for 10cm from the source, and curtilage for 15 30cm. This is because any higher determine will take considerably interminable to measure. I will take trine readings from each, as radioactive decay is a random process and it would be unbelievable for more than tierce readings to be similar. An second-rate will be calculated from the three values and the reading for the compass radiation will be subtracted to find the turn count rate. Equipment Geiger-Mi?? ller tube of i susceptible type.Decade scaler with variable quantity EHT supply   plastered carbon monoxide gas-60 source pie-eyed to prevent contact with the source and to prevent isotropic radiation  Long handled source handling tongs to prevent contact with the source visual bench with source holder to ensure constant alignment  Stop-clock, readable to at least two decimal places Vernier callipers to measure the distance d0 to a higher level of accuracy  Metre rule to measure the distance d diagram Where  B is the optical bench with source holder, H  G is the Geiger-Mi?? ller tube  S is the decade scaler with variable EHT supply.R is the sealed radioactive source, cobalt-60 Cobalt-60 will be used as the gamma source as it is easily produced, by exposing natural cobalt to neutrons in a reactor, and therefore loose to acquire. 15 It also produces ? -rays with energies of 1. 17 MeV and 1. 33 MeV. Method 1. Clamp the G-M tube to one end of the optical bench and bond it to the input socket of the scaler 2. Set the variable EHT voltage on the scaler at a minimum an d turn it on, allowing a few minutes for the scaler to warm up 3. Change the variable EHT voltage on the scaler to the value put in through preliminary work and set it to count pulses from the G-M tube.4. stick the stopclock and measure the background radiation for an adequate length of time, e. g. 25 minutes, as background radiation is variable 5. Place the holder containing the ? -source at 5. 0 cm from the window of the G-M tube 6. Start the stopclock and stop after 10,000 counts are registered. record this value and repeat twice 7. bm the ? -source to 10. 0 cm from the window of the G-M tube and repeat unconscious process 5, instead only counting 5000 counts 8. Move the ? -source to 15. 0 cm from the window of the G-M tube and repeat procedure 5, instead counting only green counts 9.Repeat procedure 7 for sets of 5. 0 cm until a distance of 30. 0 cm is reached 10. Tabulate these results and find the average count rate for each distance 11. Evaluate 1/(d + do)2 12. Using t he enter value for background radiation, evaluate the corrected count rate for each distance 13. Plot the graph of corrected count rate against 1/(d + do)2 1 http//hyperphysics. phy-astr. gsu. edu/Hbase/forces/isq. hypertext mark-up language 2 requirement Pre-University physics Whelan & Hodgson, rapscallion 953 3 Essential Principles of physical science Whelan & Hodgson, varlet 472 4 Essential Principles of physical science Whelan & Hodgson, page 472.5 Essential Principles of physical science Whelan & Hodgson, page 472 6 http//www. imagesco. com/articles/geiger/03. html 7 http//en. wikipedia. org/wiki/Breakdown_voltage 8 Essential Pre-University Physics Whelan & Hodgson, page 406 9 http//www. imagesco. com/articles/geiger/03. html 10 http//en. wikipedia. org/wiki/Background_radiation 11 Advanced Level Practical Physics M Nelkon & JM Ogborn, page 218 12 A Laboratory Manual of Physics F. Tyler, page 269 13 http//en. wikipedia. org/wiki/Cobalt 14 Advance d Level Practical Physics M Nelkon & JM Ogborn, page 212 15 http//en. wikipedia. org/wiki/Cobalt.Source http//en.wikipedia. org/wiki/Geiger-M%C3%BCller_tube The anode is a central thin wire which is insulated from the surrounding cathode cylinder, which is metal or graphite coated.