Radiation Detection

By:Kelly Garnes

Michelle GreenShilpa GoyalAnand Jain

Okechukwu Nwogu

The early pioneers equipped only with crudely constructed, large scale machines, their human senses, and classical theory

were seeking to see into into the interiors of atoms. Were it not for the spectroscopes and cloud chambers of their time, atomic theory could never have advanced as rapidly as it

did.

History of Radiation

Detection

The X-RAY

The x-ray, discovered by German physicist Wilhelm

Konrad Roentgen on November 8, 1895, was reported to the

world shortly after the first of the year 1896. Roentgen's

discovery was a scientific bombshell, and was received with

extraordinary interest by both scientist and laymen. The X-Ray

brought harmful radiation into the scientific scope.

THE ERAWith the discovery of harmful types of radiation,

protection and detection efforts became prevalent. Here is

the early chronology of radiation protection efforts.

Pioneer Era (1895-1905), briefly described above, in which

recognition of the gross somatic hazard occurred, and

relatively simple means devised to cope. Dormant Era

(1905-1925), in which the major concern was toward

applications, but in which great gains were made in

technical and biological knowledge which were later applied

to protection. Era of Progress (1925-1945), which saw the

development of radiation protection as a science in its own

right along with the birth of health physics in the

Manhattan District.

The Progressive Era was by far the most

important portion of the radiation protection movement.

It was the Manhattan District of U.S. Army Corps of

Engineers that the name "health physics" was born, and

great advances were made in radiation safety. From the

onset, the leaders of the Manhattan District recognized

that a new and intense source of radiation and

radioactivity would be created, and thus, in the summer of

19424, asked Ernest O. Wollan, a cosmic ray physicist at

the University of Chicago, to form a group to study and

control radiation hazards. Thus, Wollan was the first to

bear the title of health physicist. He was soon joined by

Carl G. Gamertsfelder, recently graduated physics

baccalaureate, and Herbert M. Parker, the noted

British-American medical physicist. By mid 1943, six others

had been added: Karl Z. Morgan, James C. Hart, Robert R.

Coveyou, O.G. Landsverk, L.A. Pardue and John E. Rose.

Their activities included development of appropriate monitoring instruments, developing physical controls,

administrative procedures, monitoring areas and [personnel, radioactive waste disposal.

It was in the Manhattan District that many of the modern concepts of protection were born, including the rem unit, which

took into account the biological effectiveness of the radiation, and the maximum permissible concentration (MPC) for inhaled

radioactivity.

It was in the Manhattan District that modern day radiation protection effects, born in the early days of x-ray and radium,

realized their maturity.

The Manhattan District

Radiation Detection and the Future

Radiation detection instrumentation over the past 100 yrs

has played a significant role in ushering in the atomic age

and the numerous outreaching applications which followed.

While largely unnoticed by the public at large, radiation

detection instrumentation has revolutionized the world we

live in today and will most likely continue to go

undetected in the future as it leads us in our endeavor to

restore the environment.

There are many sources of Natural Radiation. Randon gas exists in most parts of US at different levels and is produced from naturally occurring Uranimum-238 in the soil. It can be a problem in some areas since the gas can enter the house through basement. Another gas called Thorium-232 also exists in the soil. Both Uranium and Thorium decay into numerous other radioactive isotopes before decaying into a stable element, lead.

Natural Radiation

Types of Detectable Radiation

There are three types of radiation that may be detected with a Geiger counter:

Alpha Particles: Helium nuclei, generally emitted from heavy elements such as uranium and thorium. Alpha particles only travel a few inches in the air, and can be stopped by a piece of paper. Special Geiger tubes with a mica window are necessary to detect them, as other windows will stop alpha particles.

Beta Rays: Electrons moving at extremely high (often relativistic) speeds. They are more penetrating than alpha particles. They can pass through light elements, such as paper and aluminum (but only small thicknesses).

Gamma Rays: Electromagnetic waves, similar to light, but at a much higher energy. Much more penetrating than alpha or beta radiations. High-energy gamma rays can pass through several inches of metal. Note that X-Rays and Gamma Rays are really the same thing, the term X-Ray is used when the radiation is produced by electrons striking a material, such as in an X-Ray tube.

The two types of radiation detectors are: GM-10 and GM-45. These are sensitive and affordable ionizing radiation detectors and are called Geiger counters. They are capable of detecting extremely small amounts of radiation. They can connect to almost any personal computer – and this allows you to measure, record, and display radiation readings over any time period. GM-10 and GM-45 Geiger counters are also self powered off the computer’s serial port and therefore, are ideal for use in the filed or any location.

Types of Radiation Detectors

The typical background levels that are detected with the GM-10 are about 10 CPM – which can be higher in the basement of homes with randon levels. A GM-10 on an airplane flight recorded a level of over 400 CPM and this is only due to the larger amount of cosmic radiation that is present at high altitudes.

The Geiger counter detects the ionization produced by a radioactive particle. The counter records as a particle is detected each time. The number of events recorded over a period of time indicates the amount of radiation present. When this is done over one minute intervals, it is called “counter per minute” or CPM. The higher the CPM, the higher the radiation levels.

The difference between the GM-10 and GM-45 is the size of the radiation sensor. The GM-45 sensor has 24 times the surface area of that in the GM-10 making it more sensitive, especially for alpha and beta radiation sources. That means that it can detect weaker levels of radiation.

GM-10

GM-45

There is a size difference between the GM-10 and GM-45 detectors. The surface area of the GM-45 detector is 24 times as large. This means that it is much more sensitive for alpha and beta radiation, and somewhat more sensitive for gamma / x-ray radiation. That is, it will be able to detect much smaller (weaker) levels of such radiation.

Specifications of Detectors

Bringin’ down the house…

Noise and radiation detection

• Radiation detector output signals are usually weak and require amplification before they can be used.

• The nature of the input pulse and discriminator determines the characteristics that the preamplifier and amplifier must have.

• Two stage amplification is usually used to increase the signal-to- noise ratio.

One and Two stage amplification

Dad, where does noise come from? • The detector is away from the readout. • A shielded cable transmits the output to the

amplifier. The output signal may be 0.01 volts. • A gain of 1000 is needed to increase this to 10

volts (a usable output pulse voltage). • There is always a pickup of noise in the long cable

run; this noise can amount to 0.001 volts.

• If all amplification were done at the remote amplifier, the 0.01-volt pulse signal would be 10 volts, and the 0.001 noise signal would be 1 volt, for a signal-to-noise ratio of 10.

• Dividing the total gain between two stages of amplification will reduce the ratio.

• A preamplifier near the detector eliminates cable noise because of the short cable length.

• Radiation impinges on a sensor and creates an electrical signal.

• The signal level is low and must be amplified to allow digitization and storage.

• Both the sensor and amplifiers cause noise.1. Fluctuations in signal introduced by sensor2. Noise from electronics The detection limit and measurement accuracy are

determined by the signal-to-noise ratio.

Dad, where does noise come from?

Sure sounds good, but does it do?

Electronic noise affects all measurements:1. Detect presence of hit:• Noise level determines minimum threshold, so

that if the threshold is too low, the output signal is dominated by noise hits.

2. Energy measurement:• Noise “smears” signal amplitude.3. Time measurement• Noise alters time dependence of signal pulse

How to optimize the signal-to-noise ratio?1. Increase signal (amplification) and reduce

noise2. For a given sensor and signal: reduce

electronic noise

Signal-to-Noise Ratio

It’s noise to you, but fluctuations within a power spectrum to me.

• All signals exhibit undesirable fluctuations that are called noise – the frequency of noise is a power spectrum.

• Noise can be periodic or nonperiodic. • - Periodic noise is high frequency - Nonperiodic noise is low frequency and

white noise

So many to choose from!• Detector noise originates in the detector and can be

classified as:- Thermal due to the thermal agitation of current carriers in a resistive element.

- the most common example of noise due to velocity fluctuations

• Temperature noise is due to fluctuations of the electric signal through heat exchange.

• Generation-recombination noise due to generation-recombination processes.

• Contact noise due to current fluctuations across electrical contacts.

• Radiation noise due to statistical fluctuations in the "arrival" of the photons.

• Dark current noise due to the sum of noise currents in the absence of a signal, including

• fluctuations of thermionic emission, of leakage current, of corona discharge charge carriers and other physical effects.

• Shot noise is the sum of the radiation noise and the statistical component of the dark current noise.

Finding resolution

• Resolution: distinguishing signal levels- recognize structure and improve sensitivity- signal to background ratio improves with better resolution as signal counts compete with fewer background counts

• Signal variance is greater than baseline variance - resolution is determined by signal and noise.

• Baseline fluctuations can have many origins but noise is the basic limit.

• Solution:Tailor frequency response of measurement system to optimize signal-to-noise ratio.Frequency response of measurement system affects both signal amplitude and noise.

Apply a filter to make the noise spectrum white (constant over frequency). Then the optimum filter has an impulse response that is the signal pulse mirrored in time and shifted by the measurement time.

This is an “acausal” filter, i.e. it must act before the signal appears.

- only useful if the time of arrival is known in advance.

- Not good for random events– need time delay buffer memory adds complexity!

Hidden Detectors?

• Radiation and Terrorism A 34-year-old man was treated for Graves disease.

Twenty-four hours after treatment, his radioactive iodine uptake was 63%. Later that week, he was strip-searched twice at Manhattan subway stations. Police identified him as emitting radiation and detained him for further questioning.

Radiation Badges

• NJ Company develops radiation badges

• Laboratory has created a small device that can detect if someone was exposed to radiation.

• Price of $5.

Radiation Pills• Radiation Plant Workers

Offered Pill • Tiny pill known as

potassium iodide that blocks the thyroid from radioactive iodine.

• Pills are available at pharmacies and on the Internet, no matter where you live. Cost about $16 for a package of 14 pills.

Current Threat of RadiationWhat is a “dirty bomb”?

•A radiation threat or "Dirty Bomb" is the use of common explosives to spread radioactive materials over a targeted area.

•A “dirty bomb,” also known as a radiological weapon, is a conventional explosive such as dynamite packaged with radioactive material that scatters when the bomb goes off.

•A dirty bomb kills or injures through the initial blast of the conventional explosive and by airborne radiation and contamination—hence the term “dirty.”

•Such bombs could be miniature devices or as big as a truck bomb.

•It is not a nuclear blast.

•The force of the explosion and radioactive contamination will be more localized.

•While the blast will be immediately obvious, the presence of radiation will not be clearly defined until trained personnel with specialized equipment are on the scene.

•As with any radiation, you want to try to limit exposure.

Dirty Bomb: Description

Radiation Threat

3. Shielding: If you have a thick shield between yourself and the radioactive materials more of the radiation will be absorbed by the thick shield, and you will be exposed to less.

2. It is not a nuclear blast. The force of the explosion and radioactive contamination will be more localized. In order to limit the amount of radiation you are exposed to, think about shielding, distance and time.

1. A radiation threat or "Dirty Bomb" is the use of common explosives to spread radioactive materials.

6. Local authorities may not be able to immediately provide information on what is happening and what you should do. However, you should watch TV, listen to the radio, or check the Internet often for official news and information as it becomes available.

4. Distance: The farther away you are from the radiation the lower your exposure.

5. Time: Minimizing time spent exposed will also reduce your risk.

Radiation Threat (Con’t)

Thank you.

Hope you enjoyed it!