Radiation Protection Course PDF

Common Radiation Transmission of energy via: Particles or Waves  Radiation Protection Course Atomic structure of helium Helium’s sub-atomic composition - + 2 protons...

Common Radiation Transmission of energy via: Particles or Waves  Radiation Protection Course Atomic structure of helium Helium’s sub-atomic composition - + 2 protons 2 neutrons + 2 electrons - The helium atom  Radiation Protection Course Atomic structure of helium Protons have a large mass and a positive charge. The number total number of + of protons identifies an protons and neutrons element. MASS NUMBER 4 Neutrons have a large mass He approximately equal to a ELEMENT proton’s mass. Neutrons have no charge. SYMBOL ATOMIC NUMBER 2 - Electrons have a very small mass and a negative charge. Electrons travel outside the nucleus. number of protons  Radiation Protection Course Alpha radiation α This type of radiation does not consists of photons but rather, particles. More specifically He 2+ particles, i.e. Helium nuclei. Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium -4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet , α. The symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+ or 4 2He 2+ indicating a helium ion with a +2 charge (missing its two electrons). Once the ions gains electrons from its environment, the alpha particle becomes a normal (electrically neutral) helium atom 42He.  Radiation Protection Course β Beta radiation This consists of a stream of electrons or positrons A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay.There are two forms of beta decay, β− decay and β+ decay. Gamma radiation Photons with higher energy than x-rays. Gamma, or γ-radiation is electromagnetic radiation of high frequency (very short wavelength). It consists of frequencies above 10 exahertz (or >1019Hz), and therefore have energies above 100 keV and wavelength less than 10 picometers, less than the diameter of an atom. γ  Radiation Protection Course X-Rays These are photons with low X-RAY TUBE HOUSING energy, in the range 120 eV to 120 (ASSEMBLY) HIGH VOLTAGE keV. They Have a shorter CABLES wavelength than UV rays and longer than gamma rays. X- radiation is also called Röntgen radiation. Named after Wilhelm Conrad Roentgen, the discoverer of its existence, and the man who named it X-radiation. The "X" COLLIMATOR standing for an unknown type of radiation.  Radiation Protection Course X-Ray Production The higher the atomic number of the X-ray target, the higher the yield. The higher the incident electron energy, the higher the probability of X-ray production. At any electron energy, the probability of generating X-rays decreases with increasing X-ray energy. electrons Low to High medium > 1MeV energy target energy (10-400keV) X-rays  Radiation Protection Course Neutron radiation This consists of a neutron stream (free neutrons). The stream of free neutrons reacts with nuclei of other atoms forming new isotopes resulting in a chain reaction. Nuclear fission or fusion, consists of the release of free neutrons from atoms in the first place. The chain reaction makes radiation this dangerous and harmful over great areas of space. Neutron Fission Fragment Energy Parent Atom Neutron Energy Neutron Fission Fragment  Radiation Protection Course Neutron Properties Composition: two down quarks and one up quark Rest Mass: 1.0086649 amu Uses of Neutrons Energy equivalent: 939.5656 MeV Electric charge: 0 ❑ Reactor start up ❑ Density gauges Half-life: 10.4 minutes (outside the nucleus) ❑ Moisture gauges Decay scheme: ❑ Well logging ❑ Activation analysis ❑ Gemstone colorization neutron proton + beta + ❑ Research (physics, medicine) antineutrino ❑ Triggers for nuclear weapons ❑ Radiography ❑ Instrument calibration  Radiation Protection Course NEUTRON SOURCES 2. (α ,n) Source: 1. Californium-252 source: Mixed a source (226Ra, 241Am,..) with A strong neutron source. One microgram light elements (9Be, Li,..) of californium-252 produces about It produce fast neutrons 3,000,000 neutrons per second. T1/2 Decay by both Alpha (97%) and Fission Source Neutron Energy (3%) (MeV) 226Ra + 9Be 5 1600 Year Cf-252 has a half-life of about 2.6 years 241Am + 9Be 5 433 Year It emits fast neutrons 239Pu + 9Be 4 24000 Year  Radiation Protection Course NEUTRON SOURCES 3. (γ,n) Reaction Source (Photo-neutron source): Mixed g source (23Na, 88Y,..) with light elements (9Be, 2H,..) Produce a defined energy of fast neutrons γ + 21 H --- 1 1 H +01 n γ + 94 Be --- 8 Be 1 n Disadvantage: 4 0 + Required gamma source with a high energy (need more shield for gamma ) Short half life of g source (need to be activated again)  Radiation Protection Course NEUTRON SOURCES 4. Neutron Generator D-D Reaction emits neutron with 2 MeV D-T reaction emits neutron with 14 Mev Neutron Fluence Rate The intensity of a neutron source is usually described by the fluence rate. This is often and incorrectly referred to as the flux. The neutron fluence rate (N) is the number of neutrons that pass through a specified area per unit time. Commonly employed units for this quantity are n/cm2/s (i.e., cm-2 s- 1).The direction of the neutrons is irrelevant.  Radiation Protection Course Measuring the Neutron Source Strength The neutron emission rates for alpha neutron, gamma neutron, and spontaneous fission neutron sources can be determined with the manganese sulfate bath technique. The source is positioned in the center of a tank filled with a solution of manganese sulfate (the bath must be large enough to moderate all the neutrons). By quantifying the Mn-56 (2.6 hr) production via gamma spectrometry, the neutron emission rate can be calculated. The manganese solution is inside the spherical tank and the source is lowered through the top. The white neutron detector on the right side of the tank is used to measure neutron leakage. This value is used to make corrections to the calculated neutron emission rate. Image courtesy of NPL.  Radiation Protection Course Alpha Neutron Sources AmBe Sources AmBe (“ambee”) sources are a mix of Am-241 and Be-9. Yield: ca. 2.0 to 2.4 x neutrons/sec. per Ci 106 neutrons/sec. per GBq ca. 5.4 to 6.5 x 104 Half-life:neutron Average 432.2energy: years 4.2 MeV (11 max) Neutron dose rate: 2.2-2.7 mrem/hr at 1 m/Ci 0.59-0.73 uSv/hr at 1m/GBq Gamma dose rate: 2.5 mrem/hr at 1 m/Ci 0.68 uSv/hr at 1m/GBq  Radiation Protection Course Alpha Neutron Sources PuBe Sources PuBe (“pewbee”) sources are a mix of Pu-239 or Pu-238 and Be-9. Yield: ca. 1.5 to 2.0 x 10 neutrons/second per Ci Half-life: 24,114 years Average neutron energy: 4.2 – 5 MeV (11 max) Neutron dose rate: 1.3-2.7 mrem/hr at 1 m/Ci 0.35-0.73 uSv/hr at 1m/GBq Gamma dose rate: 0.1 mrem/hr at 1 m/Ci 0.027 uSv/hr at 1 m/GBq  Radiation Protection Course Alpha Neutron Sources RaBe Sources RaBe (“raybee”) source, a mix of Ra-226 and Be-9 Yield: ca. 15 x 106 neutrons/sec. per Ci ca. 40 x 104 neutrons/sec. per GBq Half-life: 1,600 years Average neutron energy: 3.6 MeV (13.2 MeV max) Gamma exposure rates of these sources can be high. There is also the problem of leakage. RaBe sources have been used in moisture gauges sold by Seaman Nuclear - until recently radium has been unregulated by the NRC.  Radiation Protection Course Alpha Neutron Sources Alternatives to Beryllium Beryllium is the most common low Z material to be used in alpha- neutron sources because of its relatively high neutron yield. Nevertheless, fluorine, lithium and boron have also been used. Am-F and Am-Li sources have average neutron energies of 1.5 and 0.5 MeV respectively.  Radiation Protection Course Alpha Neutron Sources Source Construction The alpha emitter and beryllium must be in intimate The source is doubly encapsulated. The inner and outer contact, e.g., by mixing powdered beryllium metal capsules are usually fabricated of stainless steel (type with an oxide of the alpha emitter. This mixture is then compressed into a cylindrical shape for 304) and the end caps are TIG welded. Space is left within the encapsulation. Another approach is to employ a inner capsule to allow for the gradual buildup of helium that metallic alloy of the beryllium and the alpha results from the alpha emissions. emitting actinide. Typical AmBe sources. Largest pictured is 60 x 30 mm. Image courtesy of NPL..  Radiation Protection Course Gamma-Neutron Sources A “typical” photo-neutron source might consist of an inner aluminum-encapsulated gamma-emitting core (e.g., 1 inch diameter) surrounded by an eighth of an The major advantage of photo-neutron inch of the neutron emitting target. sources is that the emitted neutrons are very close to being monoenergetic. The overall shape of the source might be cylindrical or spherical. Their major disadvantage is the very high activity of the gamma source-only one gamma ray in one million (or so) might produce a neutron.The resulting gamma In the case of an antimony-beryllium source, the core exposure rates can pose a significant is antimony that has been activated in a reactor. radiological hazard. Aluminum wall Gamma- emitting core Neutron-emitting target (H-2 or Be)  Radiation Protection Course Gamma-Neutron Sources Sb-Be Source – Antimony-Beryllium Source Characteristics A mix of Sb-124 and Be-9. Yield: ca 0.2-0.3 x 106 neutrons/sec. per Ci ca. 0.54-0.81 x neutrons/sec. per GBq 104 Half-life: 60 days Neutron Gamma energy: energy: 1.69 0.024MeV MeV Neutron dose rate: 0.18-0.27 mrem/hr at 1 m/Ci 0.049-0.073 uSv/hr at 1m/GBq Gamma dose rate: 1000 mrem/hr at 1 m/Ci 270 uSv/hr at 1m/GBq