For the photoelectric effect, they were deduced from the data of Hubbell [ 12 ]. Some typical spectra are shown in Figure 5 for 40 K. The low energy cut-off is determined by photoelectric effect and occurs at higher energy for high-Z media.
And for Th in pure water Figure 6. Computed energy spectra for 40 K in a dry C soil, b wet S soil, and c pure water [ 5 ]. Computed energy spectra for Th in pure water [ 5 ]. Similar features are also noticed for the more complex case of U and Th series.
There is a similarity in the degraded spectrum, even for two very different gamma sources for example, thorium and potassim Our results are in good agreement with those obtained by G.
Valladas [ 7 ] by the Monte-Carlo method for potassium in siliceous medium. The results are given in Table 2. Calculations are performed here with, as a TL dosimeter, CaSO 4 : Dy, but are readily feasible for any combination of known dosimeters and compositions. This can be explained by the fact that copper absorbs the lower part of the spectrum of energy for which the difference dose between the dosimeter and the soil is significant.
This is due to a smaller contribution of low energies to the 40 K spectrum no low energy lines. An important consequence of the foregoing is that, for the experimenter, copper or a close material is well used when the composition especially moisture of the soil is not well known. In general, it is difficult to determine the respective contribution of the potassium, uranium and thorium series to the total dose rate.
The results obtained with our program under the same conditions regarding the dosimeter, the surrounding environment, the capsules and the sources of the gamma rays are slightly superior to the theoretical results of G.
Valladas [ 7 ]. The gamma radiation self-absorption coefficient is of great interest in activation analysis. Since it is difficult to measure this coefficient, various calculation methods have been developed. Measuring the self-absorption coefficient is not a simple thing.
The physicists who have faced this problem, for a long time, have always used methods of statistical or non-statistical computation: Parallel beam methods, Monte-Carlo method and many other methods. In this chapter, we are presenting a method that we have developed, this which allows us control and calibrate the activation analysis experiments [ 13 ].
This method consists of simulating the interaction processes of gamma rays induced by neutron activation of various samples by using the Monte Carlo method adapted to experimental conditions. Different disk shaped red beet samples and standards were irradiated with 14 MeV neutrons. The induced gamma activities on the sodium, potassium, chlorine and phosphorus elements have been experimentally measured by means of hyper-pure germanium spectrometer. The analyzed beet samples and standards have a 23 mm diameter and a 6 mm thickness.
The different parameters of the nuclear reactions used cross section, isotopic abundance, etc. The produced nuclear reactions by irradiating the samples standards with 14 MeV neutrons. To take into account the activity measuring time, relation Eq. By combining relations Eq. The calculation of the paths lengths l 1 and 1 2 consists firstly on generating random numbers by using a programme based on a congruentia 1 method. The path length l 1 is given by [ 17 ]:. We have developed the following theory to calculate the path length 1 2 which is given by:.
To complete this study, we have developed another program based on the EGC method [ 18 ]. This program results in determining the energy loss predominant phenomenon that occurs when gamma rays interact with the absorber. Scheme shows changes in gamma-ray direction in the case of multiple interactions.
The measured N m and calculated N c activities of some different irradiated standards containing Na, K, Cl, and P are shown in Table 4.
Data obtained for different irradiated standards with a 14 MeV neutron flux by experimental N m and calculation N c methods. We notice that the results obtained by the two methods experimental and calculation are in good agreement with each other.
In the first part of the chapter, a careful study of the correcting factors linked to the environmental and experimental conditions is performed. In the second part, the calculation method was developed. It is very accurate, rapid, adapted to the experimental conditions, it does not necessitate the use of a very expensive detection chain, and can be used to determine the trace element concentrations in materials.
This technique is a good test for neutron activation analysis experiments. It allows these experiments to be calibrated in cases where it is difficult to achieve standards. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications.
Edited by Basim Almayahi. Edited by Waldemar Alfredo Monteiro. We are IntechOpen, the world's leading publisher of Open Access books.
Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract Gamma rays are high frequency electromagnetic radiation and therefore carry a lot of energy.
The common designations are radio waves, microwaves, infrared IR , visible light, ultraviolet UV , X-rays and gamma rays. Gamma rays fall in the range of the EM spectrum above soft X-rays. A picometer is one-trillionth of a meter. Gamma rays and hard X-rays overlap in the EM spectrum, which can make it hard to differentiate them. In some fields, such as astrophysics, an arbitrary line is drawn in the spectrum where rays above a certain wavelength are classified as X-rays and rays with shorter wavelengths are classified as gamma-rays.
Both gamma rays and X-rays have enough energy to cause damage to living tissue, but almost all cosmic gamma rays are blocked by Earth's atmosphere.
A few years later, New Zealand-born chemist and physicist Ernest Rutherford proposed the name "gamma rays," following the order of alpha rays and beta rays — names given to other particles that are created during a nuclear reaction — and the name stuck. Gamma rays are produced primarily by four different nuclear reactions: fusion, fission, alpha decay and gamma decay.
Nuclear fusion is the reaction that powers the sun and stars. It occurs in a multistep process in which four protons, or hydrogen nuclei, are forced under extreme temperature and pressure to fuse into a helium nucleus, which comprises two protons and two neutrons.
The resulting helium nucleus is about 0. The rest is in the form of neutrinos , which are extremely weakly interacting particles with nearly zero mass. In the later stages of a star's lifetime, when it runs out of hydrogen fuel, it can form increasingly more massive elements through fusion, up to and including iron, but these reactions produce a decreasing amount of energy at each stage.
Another familiar source of gamma rays is nuclear fission. Lawrence Berkeley National Laboratory defines nuclear fission as the splitting of a heavy nucleus into two roughly equal parts, which are then nuclei of lighter elements.
These waves are generated by radioactive atoms and in nuclear explosions. Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells. Gamma-rays travel to us across vast distances of the universe, only to be absorbed by the Earth's atmosphere.
Different wavelengths of light penetrate the Earth's atmosphere to different depths. Instruments aboard high-altitude balloons and satellites like the Compton Observatory provide our only view of the gamma-ray sky. Gamma-rays are the most energetic form of light and are produced by the hottest regions of the universe.
They are also produced by such violent events as supernova explosions or the destruction of atoms, and by less dramatic events, such as the decay of radioactive material in space. Things like supernova explosions the way massive stars die , neutron stars and pulsars, and black holes are all sources of celestial gamma-rays. How do we "see" using gamma-ray light? Gamma-ray astronomy did not develop until it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft.
The first gamma-ray telescope, carried into orbit on the Explorer XI satellite in , picked up fewer than cosmic gamma-ray photons! Unlike optical light and X-rays, gamma rays cannot be captured and reflected in mirrors.
0コメント