The energy of the radiation is sufficient to excite atoms in a material that may fluoresce, such as the phosphor used by Rutherford’s group. The resulting current is detected and registered as a count.Īnother radiation detection method records light produced when radiation interacts with materials.

(credit: TimVickers, Wikimedia Commons) (b) Voltage applied between the cylinder and wire in a Geiger tube causes ions and electrons produced by radiation passing through the gas-filled cylinder to move towards them. However, Geiger counters are very useful in producing a prompt output that reveals the existence and relative intensity of ionizing radiation.įigure 31.8 (a) Geiger counters such as this one are used for prompt monitoring of radiation levels, generally giving only relative intensity and not identifying the type or energy of the radiation. They do not detect every particle, since some radiation can pass through without producing enough ionization to be detected. The word count implies that there is no information on energy, charge, or type of radiation with a simple Geiger counter. Ionizing radiation passing through the tube produces free ion pairs (each pair consisting of one positively charged particle and one negatively charged particle) that are attracted to the wire and cylinder, forming a current that is detected as a count. A conducting cylinder with a wire along its axis is filled with an insulating gas so that a voltage applied between the cylinder and wire produces almost no current. These relatively inexpensive radiation detectors are based on the simple and sturdy Geiger tube, shown schematically in Figure 31.8(b). The clicking and buzzing sound we hear in dramatizations and documentaries, as well as in our own physics labs, is usually an audio output of events detected by a Geiger counter. (credit: Werneuchen, Wikimedia Commons)Īnother very common radiation detector is the Geiger tube. The amount of film darkening is related to exposure, but the darkening also depends on the type of radiation, so that absorbers and other devices must be used to obtain energy, charge, and particle-identification information.įigure 31.7 Film badges contain film similar to that used in this dental x-ray film and is sandwiched between various absorbers to determine the penetrating ability of the radiation as well as the amount. The process is not 100% efficient, since not all incident radiation interacts and not all interactions produce the chemical change. The quantum come from an α α-particle, β β-particle, or photon, provided it has more than the few eV of energy needed to induce the chemical change (as does all ionizing radiation). A quantum of energy interacts with the emulsion and alters it chemically, thus exposing the film. The mechanism for film exposure by ionizing radiation is similar to that by photons. Nuclear radiation is also captured on film, such as seen in Figure 31.7. Photographic film is still the most common detector of ionizing radiation, being used routinely in medical and dental x rays. The first direct detection of radiation was Becquerel’s fogged photographic plate. This section is a brief overview of radiation detection and some of its applications. This makes the detection of radiation by instruments more than an important research tool. Newspapers carry stories about unsuspecting victims of radiation poisoning who fall ill with radiation sickness, such as burns and blood count changes, but who never felt the radiation directly. It is well known that ionizing radiation affects us but does not trigger nerve impulses. Define and discuss radiation detectors.Explain the working principle of a Geiger tube.It is difficult to measure accurately the small change in activity that would occur in only 200 years.By the end of this section, you will be able to: (b) Suggest why the method of carbon dating is likely to be unreliable if a sample is: (ii) A piece of wood taken from an axe handle found on an archaeological site has 0.375 times as many carbon-14 atoms as an equal mass of living wood.Ĭalculate the age of the axe handle in years. (note that the question is written in 3sf - therefore answers should be given to 3sf too)

(i) The half-life of carbon-14 is 5740 years.Ĭalculate the radioactive decay constant in yr −1 of carbon-14. After a tree dies, the proportion of carbon-14 in it decreases due to radioactive decay. The carbon content of living trees includes a small proportion of carbon-14, which is a radioactive isotope.

A Level and AS level - UK KS 5 (Age 16 - 18).GCSE and 'O' Level - UK KS4 (Age 14 - 16).

Radioactive dating game