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UPDATE: 2023-11-07
A BRIEF INTRODUCTION TO RADIOACTIVITY MONITORING AT HOME
This is an ongoing paper, as I've the time I'll update that gopher page.
I'm not a physicist, just a geiger counter nerd so I apologize in
advance for many errors I can make during the redaction of that paper.
Contact: blizzard@sdf.org
1. Ionizing radiation is everywhere
Really, you don't need to hack in the Chernobyl Exclusion Zone to find
some atom's nucleus going crazy and shot some particles or waves.
Radiation is a naturally occurring phenomenon you can find from
radioactive minerals in nature (Uranium etc...), radon gas rising
from soil, in the rain or concentrating in your basement (harmful).
Also you can find raadioactive stuff in your home:
. Tiles are generally a little radioactive. Sometimes they were
coated with uranium or depleated uranium oxide years ago.
. Grandma clocks with luminous radium painted dials
. Dust concentrated from air filters and vacuum filters may be radioactive
due to radon gas decay daughters and remain radioactive for few hours.
. Ashes, due to Potassium40 and maybe Cesium137 (that isotope is
produced in technological nuclear events. Large part of that Cs137 was
spread in Chernobyl accident, Fukushima, other minor accidents and n
nuclear wepons explosions
. Bananas, mushrooms, berries... are all a little bit radioactive.
If berries and mushrooms are grown in soil containing radioactive
minerals or Cs137 they may be noticeably radioactive.
. Sea... is radioactive due to Carbon14, Potassium40 (as bananas),
deuterium, tritium, etc...
. Cosmic radiation
. You!
So basically we are surrounded by radioactive stuff but with a simple
geiger counter we may check for some radiation, ignoring other types
or overstimate/understimate how harmful is. That paper will guide
you to buy hinstruments, check for radiation and evaluate the scenario.
1.1 Types of radiation
Radioactivity is a nuclear event. It means that the atom nucleus is
involved. Also when we talk about nuclear radioactivity, we refer to
ionizing radiation: an energetic event that has the power to ionize
atoms (ie. taking off electrons from an atom) and that may be dangerous.
There are 3 main types of radiation(in fact there are more):
. ALPHA
Alpha radiation are particles made by 2 protons and 2 neutrons
(basically an helium nucleus). Heavy elements like uranium are usually
alpha emitters. Alpha radiation is massive and easly stopped by a paper
sheet or human death skin layer. External contact is mainly safe
(heavy metals btw are chemically poisonous often) but internal contact
is really dangerous. So the main problem with alpha emitters are
ingestion or breathing the dusts. Generally, radiation from inside
the body is the worst form of exposition; that way is good to use
respirators in a contaminated environment.
Due to the low pentration capability of that kind of radiation, only
certain geiger counters may be able to measure alphas.
. BETA
Beta radiation are basically electrons. A beta emitter may generate
beta- electrons or beta+ positrons (that hapens sometimes in your
bananas but as the positrons are antiparticles, they suddenly
annihilates with other banana atoms, generating 2 gamma rays
traveling in opposite directions like in PET tomography).
Beta radiation is more penetrant than alpha particles. It can
travel for few meters and reach body organs. BTW aluminum foils are
able to stop beta particles, as many metal plates would do.
A magnet may bend a flux of beta radiation.
Beta effects on body are mainly thermal effects.
Cheap geiger counters are able to measure high energy betas.
. GAMMA
Gamma rays are indeed the most popular form of radiation.
Gammas are waves/photons, exactly like visible light but much more
energetic and at the right end of the electromagnetic spectrum.
When an atom needs to dissipate energy (for example is in an
excitated state etc...) it emits gamma rays.
X-rays are a kind of gamma rays, generated by human devices or
radiation-matter interaction (Bremsstrahlung radiation).
Gammas are high penetrating rays, and to stop large part of that
radiation you need to sheild with thick lead plates, concrete
walls (bunker style) or water pools. But it's so hard or almost
impossible to stop completely that kind of radiation.
Gamma ray bursts are generated also in catastrophic cosmic events
like star collapse.
That is the easiest radiation to measure. The simplest geiger is
capable to count only gamma rays but that events are the ones
involved in the complex meaasurement of dosimeters with scintillation
technology and gamma spectroscopy (a method to check the isotope
involved in the radioactive emission we are measuring).
2. Buying a geiger counter
A Geiger Counter is a device capable of counting radioactive decays of a
certain type. It basically counts!
The main element of a geiger counter is the Geiger Muller tube. That tube
is composed by a metal or glass shield and a metal needle passing inside
the tube. Between the tube itself and the needle inside there is a
difference of potential that in many common tubes is about 400Volts.
As the needle doesn't touch the tube shield, no current passes between
the two, so the circuit is not closed.
BTW the tube is filled with a gas in low pressure. That gas ionizes when
a radioctivity event (ex. a gamma ray) passes through the tube. That
ionization breaks the electric insulation between the needle and the tube,
the circuit closes and a speaker clicks! Or a more complex circuit counts
how many radioactive particles have hit the tube in one minute.
So a geiger counter's main measuring unit is the CPM (Counts per minute)
or the CPS (Counts per second). The sensitivity of a geiger counter is
basically defined by two main characteristics: the surface of the probe
and the capability of the probe to be penetrated by radiation.
The main difference between geiger counters is in fact in the
radioactivity type they can measure: we have only gamma/X geiger counters,
beta/gamma/X geiger counters or alpha/beta/gamma/X geiger counters.
The first type of geigers are generally suitable to measuring background
radiation of the environment we live. Also we can find really cheap counters
capable of measuring only gamma and x-rays. Usually the tube is well
protected in the case and sometimes is shielded by a lead foil to make some
sort of energy compensation for the "dosimetry" (we talk about that later).
They are also pretty tough.
2.1 Dosimeters
2.2 Scintillators
3. Radioactivity background
4. Check for radioactive spots
5. Radioactivity in food
6. Radon