Choosing a radiation monitor
When you think about it buying a radiation monitor is a rather odd thing to do.
For most of us radioactivity or ionising radiation is something we rarely think about, except
when it hits the headlines, following a serious incident, leak or explosion, and
that’s when the trouble begins.
The fact is, the only people
who actually need radiation monitoring equipment for health and safety reasons are
those involved in the handling of radioactive materials, or can reasonably expect
to encounter potenially hazardous radioactive sources in the course of their work. The devices they
use are usually highly specialised and supported by trained experts and
technicians who know how to interpret the readings they provide. At the risk of losing sales we have to say that this is not
what we are about here at anythingradioactive..
By the way, it's important to distinguish between ionising and non-ionising radiation. The latter are electromagnetic fields coming from from the likes of mobile phones and radio transmitters and none of our instruments are designed to respond to it. The jury is still out on the health effects of electromagnetic (EM) radiation and we're not about to get into that debate. You should also be wary of electromagnetic detectors being wrongly described as Geiger Counters.
Let’s
take a look at the different types of radiation monitor that we sell, starting
with the classic Geiger Counter that everyone has heard of and seen in the movies . A lot of devices
are mistakenly or misleadingly referred to as Geiger Counters so let’s sort
that one out straight away. To qualify as a pukka Geiger Counter an instrument should employ
a device called a Geiger Müller tube, which detects radioactive particles or
waves and, by some means or other, is able to count or log the ‘clicks’
generated by the tube when it detects radioactivity.
The dosimeter family also includes things like film badges
and ‘Pen’ type dosimeters. These are passive devices that
record radioactive dosage over time. They cannot be used for detecting or as
warning devices as the measurements they take are analysed at preset intervals,
hours or days after exposure. The last category of instrument is the CDV-715 Survey Meter; unfortunately now out of stock. Like the CDV-700 they were produced in the US in the 1960s and 70s, at the height of the Cold War.
These are not Geiger Counters – they have no Geiger tube – instead they use a device called an Ion Chamber for detecting very high levels of radioactivity that would be present in the aftermath of a nuclear war. In short they are totally useless for detecting the sort of radiation levels you are ever likely to encounter in the normal course of events. In fact, if you ever see the needle move in anger you have probably just survived a nuclear attack and you really shouldn’t be booking any holidays…
A lot of CDV-715s turn up on ebay, sometimes at absurdly inflated prices, (we have seen them priced at over £1000...) and misleadingly labelled as Geiger Counters. Do not be misled! As a matter of interest they can be modified to make them a little more sensitive and we will happily direct you to the instructions but it’s a complicated job and they are still hopelessly insensitive for doing anything interesting or useful, other than as doorstops! Nevertheless, they are superbly well-made and a good source of vintage electronic components. They're interesting examples of cold war memorabilia and conversation pieces...
Last but not least is another class of radiation detecting or measuring instrument that technically are not Geiger Counters as they do not use Geiger Müller detection tubes, yet often have readouts scaled in counts per second or minute, as well as microsieverts. Instruments in this category include Mini Monitors with Types D, E, 42 and 44 probes. A number of devices and technologies are in use but they mostly into rely on a process called scintillation. The idea is certain organic (e.g. Sodium Iodide) and plastics (Polyvinyltoluene) in crystalline form emit brief flashes of light when struck by Gamma radiation (and X-Rays). The flashes of light are extremely weak and generally not visible to the naked eye, so the crystals are mounted onto devices like photomultipliers and solid state light detectors that amplify to flashes so they can be counted or measured. In the case of Sodium Iodide detection crystals the brightness and duration of the flashes are an indication of the type of radiation and can be used to identify the radioactive isotopes it is coming from. These types of probe can also be many times more sensitive to (gamma) radiation that other detectors and some models, like our Mini Monitor 900 with a type 44A probe can pick up the tiny amounts of gamma radiation coming from such everyday things as household smoke detectors (ionisation type).
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