Sper scientific 840007 Bedienungsanleitung

SPER

SCIENTIFIC

RADIATION MONITORS

840007, 840026

INSTRUCTION MANUAL

TABLE OF CONTENTS

INTRODUCTION ....................................................... 2

CAUTION .................................................................. 2

BATTERY REPLACEMENT ...................................... 3

OPERATION ............................................................. 3

READINGS................................................................ 5

INTERPRETING READINGS .................................... 6

SPECIFICATIONS..................................................... 11

LIMITED WARRANTY ............................................... 12

NOTICE..................................................................... 12

INTRODUCTION

This manual contains valuable information about the nature

of ionizing radiation that should be understood by the user

so that accurate measurements can be made. Information

on the care of your Geiger counter is also included. If the

following instructions are followed, your radiation monitor

will give you many years of reliable service.

The radiation meters are very sensitive pieces of equip-

ment. Although housed in a high-impact case, the Geiger-

Mueller tube that senses radiation is fragile. If the unit is

dropped, the G-M tube may break. Exposure of the unit

above 40°C (100°F) may also cause the G-M tube to stop

functioning. The electronic circuitry is sensitive to high hu-

midity (over 90% R.H.).

CAUTION

DO NOT put the unit in a very hot place (such as a car's

glove box, especially on a summer day).

DO NOT allow the unit to get wet. However, if this should

happen, clean it with a towel and allow unit to air-dry for

several days (do not place in an oven or microwave).

DO NOT open the unit (except for battery replacement).

There are no adjustments inside for the 840007 that can be

made by the user, since the unit is calibrated at the factory.

For the 840026, see instructions on page 5.

BATTERY REPLACEMENT

The unit is powered by a 9-volt battery. With the on button

activated, the LED should be brightly lit. When the LED is

no longer bright or when the LED dims in the presence of a

radiation source, replace battery. To replace the battery:

1. Slide the plastic door off the unit located in the back.

2. Carefully replace the battery. DO NOT reach into the

unit through the battery compartment while unit is on.

G-M tube activation voltage is over 200 VDC.

3. Replace plastic door.

4. For extended operation and infrequent battery replace-

ment, use an alkaline battery.

OPERATION

The radiation monitor only operates while the push button

on the face of the unit is depressed. This feature makes the

operation very simple and conserves battery power. The

unit is designed to be held in the right hand, with the thumb

over the pushbutton (see Figures 1 and 2). The LED just

above the pushbutton indicates that the unit is on and will

give an indication of battery condition.

When the unit is turned on, a faint buzz may be audible in a

quiet room. This is normal and is caused by the transformer

that powers the G-M tube.

In most parts of the world, background radiation will cause

the speaker to click at random intervals, about one click

every few seconds. In areas where large deposits of natu-

ral radioactive minerals are found, or in an area that has

been contaminated with radioactive materials, the speaker

will click more frequently. This is called the "background

level." It should be taken into account when making meas-

urements on specific objects.

Since the incidence of clicks from radioactive sources is

random, several clicks can be heard in rapid succession,

while on other occasions several seconds may elapse be-

tween clicks. This is normal. Averaged over a period of

time, the click rate should remain relatively constant. A rea-

sonable average time should be at least two minutes or

more.

The Geiger-Mueller tube is located behind the slots in the

upper edge of the case. The surface of the tube is very thin

(0.004"). This allows beta radiation to penetrate and to be

detected with greater efficiency. (Beta rays and other types

of radiation will be discussed in the next section). This thin

surface is fragile and poking sharp objects through the slots

will damage the tube.

Your Geiger Counter is designed to be sensitive to:

1. Gamma radiation (which includes X-rays).

2. Beta radiation.

FIG. 1

Gamma radiation and X-rays can penetrate the plastic case

with comparative ease.

Beta radiation can most efficiently enter the case through

the slots. Although Beta radiation is easily detected, it is

difficult to measure accurately. Therefore, when a radioac-

tive object is being searched for Beta radiation, the open

slots in the case should be positioned in such a way that

they are exposed to the object (see Figure 1).

If the unit shows a significantly higher click rate in this posi-

tion, you can be reasonably certain the object is giving off

Beta radiation.

Now position the unit as shown in Figure 2. In this position,

where radiation cannot pass directly through the slots (Beta

radiation travels in straight lines for the most part) only

gamma and X-ray radiation from the object will be de-

tected.

THIS IS THE POSITION IN WHICH TO HOLD THE GEI-

GER COUNTER TO TAKE READINGS. It is important to

understand this, for misleadingly high meter readings can

result from allowing Beta rays to be measured with the

gamma rays. The meter scale is calibrated for gamma ra-

diation.

FIG. 2

READINGS

There are two Sper Scientific Radiation Monitor models:

840007 - 0.1 to 10mR/hr

840026 - 0 to 100mR/hr

All units are tested at the factory using gamma radiation.

The radioactive gamma source used in the factory is Ce-

sium-137 that has been Beta shielded with .062" of Alumi-

num, and measuring radioisotopes other than Cesium-137

introduces some error. The error caused by this is usually

very little. Note that in the case of X-rays, the unit is very

sensitive and subsequently meter readings should be di-

vided by about 5.

The 840026 was calibrated. For how often you have to cali-

brate your unit, check with your local NRC. However, you

must calibrate after each repair or change of G-M tube.

Since the 840026 radiation monitor has an oscillator, it can

be readily adjusted/calibrated by turning the screw on the

oscillator with a small screwdriver in the desired direction:

turning clockwise to decrease the reading; counter clock-

wise to increase. This calibration should be done at a li-

censed laboratory.

In addition to the analog meter, a special extended range

has been designed into the 840007 unit. At radiation levels

that are in excess of the meter scale, the unit will emit

beeps, at a rate that increases as the radiation level in-

creases. Although this range is not as accurate as the dis-

played range, beeping will begin approximately at 15mR/hr.

A continuous beep occurs approximately at 20mR/hr.

These built-in ranges greatly simplify operation and allow

reasonably quick and accurate measurements to be made.

The meter is not intended to indicate levels below 0.1 mR/

hr., therefore, readings taken below this level should be

considered extremely crude. However, such low level

measurements can be made by simply counting the clicks

over a period of time, much like taking a person's pulse,

and expressing the result as clicks (or counts) per minute.

0.1 mR/hr, on the meter corresponds to about 330 counts

per minute.

INTERPRETING READINGS

Health physics, the field that pertains to radiation and its

effects on man, is very complex, and theories and con-

clusions are constantly being updated as information be-

comes available. Data from occupational exposure, animal

studies, and events like Hiroshima and Nagasaki have

fairly well established the maximum safe exposure limits for

man. Whether low level radiation causes cancer and birth

defects is still being debated. Delayed effect, which could

take years to develop, is difficult to study, and therefore,

there are no well-defined lower limits on ionizing radiation.

Two publications entitled "Hormesis with Ionizing Radia-

tion," 1980 and "Radiation Hormesis," 1991 (CRC Press,

Boca Raton) present over one thousand examples of statis-

tically valid data showing no physiological harm in verte-

brates from whole body exposures to low dose radiation

(<20mGy/y).

As previously mentioned in the section on operation, the

units mR/hr (milli-Roentgen per hour, or 1/1000th of a Ro-

entgen per hour) pertain only to gamma radiation. Often

other units of measurement similar to mR/hr are used. The

term "REM" (Roentgen Equivalent Man) includes the af-

fects of beta, alpha and neutron radiation. Measurement in

REMs is more complete as radiation affects man, but such

measurements are a complicated combination of many

measurements each made with specialized detectors.

It is important to note that the field intensity from a radioac-

tive object decreases very quickly with distance.

If the object is very small, increasing the distance from the

object by a factor of two decreases the radiation level by a

factor of four. This is called a square law situation, which

demonstrates the dependence of proximity on dose for

small radioactive sources. Larger sources, such as a large

deposit of radioactive minerals, will show much less of this

effect. In trying to estimate the danger of radioactive mate-

rials, it is important to take into account many aspects of

the situation. For instance, the radiation level at the face of

a radium-dial watch may be 3mR/hr, but the measurement

taken from the back of the watch may be 0.3mR/hr.

Another interesting point concerns the energy of the radia-

tion. Geiger Counters will register one click whenever they

detect a ray or particle of radiation hitting them. These tiny

high speed bundles of energy are like short bursts of light.

Some are extremely energetic, while others are not. Geiger

Counters cannot determine the energy of the impinging ray,

they only detect its presence. Sper Scientific models

840007 and 840026, detect Beta and gamma radiation

starting at approximately 30KeV and up to 1.5 MeV.

The opposite is the case for cosmic rays, which have enor-

mous energy — some millions of times more energetic than

anything found here on earth. The compensation figure for

radiation of this type is difficult to estimate, due to the ex-

treme range of energies that have been measured.

RADIATION — WHAT IS IT?

Nuclear physics is a very complex field, however, the basic

principles can be simply explained.

All matter is composed of atoms. Atoms alone and bonded

together in molecules form all the things around us, includ-

ing ourselves. These atomic units are extremely small; so

small, in fact, that a single grain of table salt contains ap-

proximately 1,000,000,000,000,000,000 atoms (this is not a

misprint). It is impossible to see an atom, except with a so-

phisticated electron microscope, so many of our present

day theories on the structure and composition of single at-

oms are based largely on the study of radiation given off

from unstable (radioactive) substances.

Atoms are composed of three basic particles: protons, neu-

trons and electrons. Electrons are extremely light, nega-

tively charged particles that exist as a cloud around the

center, or nucleus, of the atom. Sometimes the electrons

are said to occupy orbits around the nucleus. These elec-

trons are attracted to the nucleus because of the positively

charged protons that, along with the neutrons, make up the

nucleus. Atoms bond together in molecules when one atom

gives up or shares an electron with another atom. Chemical

reactions utilize this bonding process.

In all atoms, the number of electrons (and therefore the

number of negative charges) equals the number of protons

(positive charges). The number of protons or electrons in

an atom determines the chemical nature of the atom, and

each element has its own unique number (example: hydro-

gen = 1, helium - 2 etc.). The number of neutrons, how-

ever, may not always be the same in every atom of a par-

ticular element. Atoms of an element with different numbers

of neutrons are called isotopes. Every atom of a particular

element has the same atomic number, but different iso-

topes of a given element have different atomic weights.

It is the variable number of neutrons in the nucleus of an

atom that leads to a process called nuclear decay that

causes radiation. When an atom has too many or too few

neutrons in its nucleus, it will have a tendency to rearrange

itself spontaneously into a new combination of particles that

are more stable. In this decay process, bundles of excess

energy are shot out of the nucleus in one of a number of

ways.

When the neutrons are excessive, a neutron can

convert itself to a proton and shoot out an electron

at very high speed, known as beta radiation.

A proton may be converted to a neutron to cause

an unusual particle called a positron to be ejected

from the nucleus.

In still another process, the nucleus, in a vain

atempt to stabilize itself, kicks out two protons and

two neutrons all together as one particle, called an

alpha particle.

The energy released in each decay can be enormous. This

decay process is utilized in atomic reactors and bombs.

When certain very heavy isotopes of uranium or plutonium

(or several other isotopes) decay, they may split apart. This

process is called fission. In fission, the entire nucleus splits

apart, causing two new atoms and releasing a very large

amount of energy. This process is not very predictable, for

the nucleus can split in many ways, yielding a wide variety

of new atoms and even some free neutrons. The free neu-

trons, when released, can be absorbed by other fuel atoms,

causing them, in turn, to fission -- leading to a continuous

or (if not controlled) explosive chain reaction. Due to the

wide range of new atoms produced in the fission process,

many of the daughter products are not stable and will, in

turn, decay themselves, leading to hazardous nuclear

waste and fallout.

In all of the above processes, another kind of radiation,

gamma, is almost always released. Unlike the particles pre-

viously mentioned, gamma radiation consists of tiny, dis-

crete bundles of energy called quanta. Light, X-rays and

gamma rays can all be described as quanta, the difference

being the total energy packed into each bundle.

In nuclear decay some energy in the unstable nucleus is

dissipated to its surroundings in the form of heat and radia-

tion in the instant that it decays. The nucleus may remain in

its unstable state for billions of years, and then suddenly

decay spontaneously. The time required for half of the at-

oms of a particular isotope to decay is called the half-life of

that isotope. For an isotope with a half-life of 1 year, the

pure isotope substance would be only 50% pure after one

year, half of the original atoms having decayed into some

other substance. After another year, 25% of the original

material would remain, and so on. Natural radioactive ma-

terials in our world are only those with very, very long half-

lives. Uranium-238, for example, has a half-life of 4 billion

years, and exists today only because not enough time has

elapsed since its creation for it to decay away to negligible

levels. It is thought that the universe was created from a

huge mass of subatomic particles and energy — the Big

Bang Theory.

Of the elements and their isotopes that constitute our

planet, the vast majority are quite stable, the result of bil-

lions of years of nuclear decay. The amount of radiation

given off from natural radioactive minerals in the earth's

crust is a major constituent of background radiation. For the

most part, it is quite low, due to the long time required for

the remaining radioisotopes to decay. In atomic reactions

(either natural or forced by man) the decay process is sped

up by the effect of neutrons given off in the fission process

interacting with more unstable isotopes to cause immediate

decay. While this allows the energy of the isotope to be

harvested in a conveniently short time, the unstable decay

products produced generally have short half-lives, on the

order of seconds to centuries, and are very radioactive. As

a result of this process, considerable larger quantities of

short half-life (high decay rate) isotopes become a part of

the world we live in. This is the basis for the controversy

and concerns on the subject of nuclear power generation,

waste disposal, and nuclear weapons.

INTERACTION OF RADIATION WITH MATTER

The particles and photons that result from nuclear decay

carry most of the energy released from the original unsta-

ble nucleus. The value of this energy is expressed in elec-

tron Volts, or eV. The energy of beta and alpha rays is in-

vested in the particles' speed. A typical beta particle from

Cesium-137 has an energy of about 500,000 eV, and a

speed that approaches that of light. Beta energies can

cover a wide range, and many radioisotopes are known to

emit betas at energies in excess of 10 million eV. The

penetration range of typical beta particles is only a few mil-

limeters in human skin.

Alpha particles have even shorter penetration ranges than

beta particles. Typical alpha energies are on the order of 5

million eV, with ranges so short that they are extremely dif-

ficult to measure. Alphas are stopped by a ~nin sheet of

paper, and in air only travel a few inches at most before

coming to a stop. Therefore, alpha particles cannot be de-

tected without being in close contact with the source, and

even then only the alphas coming from the surface of the

source can be detected. Alphas generated within the

source are absorbed before reaching the surface. Due to

short range, alpha particles are not a serious health hazard

unless they are emitted from within the body when their

high energy, in close contact with sensitive living tissue, is

an extreme hazard. Fortunately, almost all alpha-emitting

substances also emit gamma rays, allowing for their detec-

tion.

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