Answer the following question given this paragraph: These devices are not very sensitive to low levels of radiation, but more sensitive devices are also available that reliably measure the frequency of radioactive events. One such device is the Geiger counter. A Geiger counter is a tube filled with an inert gas that will conduct electricity when exposed to charged radiation, such as alpha or beta particles. When a charged particle enters the tube, it changes the electrical potential between the anode and the cathode, and this change in potential is registered by an electrical circuit as a single radioactive event. Geiger counters are fairly inexpensive and reliable, so they are useful in a wide range of applications. More complicated types of counters are also available, but are generally used only in sophisticated experiments. Q: What is the tube-like device used to reliably measure lower levels of radiation? A:

OPT: (1). Richter scale (2). weber counter (3). MRI machine (4). geiger counter
Answer:
(4).