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Interaction of Radiation with Matter
Published in William H. Hallenbeck, Radiation Protection, 2020
Neutron shielding usually involves three steps: moderation of neutron kinetic energy, neutron capture, and shielding against secondary gamma radiation. The probability of fast neutron capture is very low for most materials. Hence, fast neutrons must be moderated to slow neutron energies to increase the probability of neutron capture. Fast neutrons can be efficiently moderated by elastic collisions with hydrogen in hydrogen-containing materials, e.g., water, paraffin, plastics, and concrete. However, hydrogen is a poor slow neutron absorber and also produces a capture gamma by the (n,γ) reaction: n+1H1→1H2+Eγ(2.22MeV) Lead shielding may be required due to the gamma radiation. The natural isotopic abundance of H-1 is 99.98%.
Human physiology, hazards and health risks
Published in Stephen Battersby, Clay's Handbook of Environmental Health, 2016
David J. Baker, Naima Bradley, Alec Dobney, Virginia Murray, Jill R. Meara, John O’Hagan, Neil P. McColl, Caryn L. Cox
Unstable isotopes (radionuclides) decay and, in so doing, release energy as subatomic particles (alpha or beta), or X- or gamma rays.Alpha radiation is mainly emitted by the isotopes of heavier elements. It consists of helium nuclei, which are made up of two protons and two neutrons, and are tightly bound together to create a particle. This is a relatively large subatomic particle with 2 units of positive charge. Alpha particles are densely ionising and are stopped by the dead layer of the skin so they only constitute a hazard if taken into the body. Because the radiation is particulate and charged, alpha radiation interacts both physically and electrically with the media it passes through and transfers all of its inherent energy into material it interacts with. This energy excites electrons in the absorbing material, causing electrons to be released from their atomic orbits, to produce ions.Beta radiation is mainly emitted by intermediate and lighter elements. It consists of high-speed electrons that originate in the atomic nucleus and carry 1 unit of negative charge. Beta particles can penetrate the body up to a few centimetres. Beta particles produce a similar ionisation to alpha particles, but are much lighter and more penetrative. Beta particles will penetrate a sheet of paper and have a range in air of a few metres.Gamma radiation consists of quanta of energy emitted as an electromagnetic wave. It is non-particulate and uncharged. X-radiation is electromagnetic radiation that differs from the other forms mentioned above in that it is non-nuclear in origin. It is normally generated electrically, although it can be generated when atomic electrons undergo a change in orbit, such as when beta particles react with other matter. Gamma radiation and X-radiation are extremely penetrative with a very large range in air. Most X- and gamma rays will pass through the human body. However, if absorbed, they can ionise matter. Lead shielding is needed to protect against X- and gamma rays.
Residence time distribution studies using radiotracers in chemical industry—A review
Published in Chemical Engineering Communications, 2018
Meenakshi Sheoran, Avinash Chandra, Haripada Bhunia, Pramod K. Bajpai, Harish J. Pant
While using the radiotracers, safety concern is very important. According to Vaz (2015), most of the radiological accidents occur due to the lack of awareness, no safety programs, failure of equipment, orphan source (lost, stolen and abandoned). Another main issue is related to the waste disposal. The waste produced from radiological activities should be minimized using the guidelines of radiological safety provided by IAEA (2006). Radiological and environmental aspects of the radiotracers are based on as low as reasonably achievable principle. All safety measures should be considered to avoid the unnecessary exposure of the radiation to human beings. The exposure to the radiation can be minimized by decreasing the exposure time around the radioisotope and increasing the distance from the radiation source. One should use the optimum thickness of shielding against the radiation exposure. Concrete or lead shielding is preferred for gamma radiation. The annual dose limit of the exposure is 1 mSv for public and 20 mSv for a person working in radiation environment (IAEA, 2006, 2011). All radioactive sites have to be routinely checked and monitored for the detection of any radiological accident (Mishra, 2004). The radiation survey meters are used to monitor the radiation nearby the working place and dosimeters are used for personal safety. The rules and regulations for safety are continuously reviewed and revised from time to time (IAEA, 2011).
CdZnTe quasi-hemispherical detector for gamma–neutron detection
Published in Journal of Nuclear Science and Technology, 2019
Lei Bao, Gangqiang Zha, Jian Li, Lijian Guo, Jiangpeng Dong, Wanqi Jie
The pulse height spectrum obtained from 241AmBe source without the lead house is shown in Figure 8(a), and all of the peaks appeared in the spectrum were summarized in Table 1. 241Am decay gamma peak at 59.5 keV can be seen clearly. The peak located at 120 keV is the true coincidence summing (TCS). TCS effect for gamma rays occurs simply when two gamma photons are emitted in coincidence from the decay of the same nuclide, and they are recorded simultaneously within the resolving time of the detector [26]. The enlarged part from 500 to 2500 channel is given in the illustration in Figure 8(a). Gamma-ray peaks located at 315, 338, and 367 keV are recorded, which could be attributed to the inelastic neutron scattering. The positron annihilation peak at 511 keV and the double escape peak at 1201 keV caused by 2.2 MeV hydrogen neutron capture gamma-ray are observed. Apart from the background gamma rays, we also found 113Cd(n,γ)114Cd neutron capture reaction gamma rays at 558 and 651 keV. The energy resolution for gamma-ray was determined to be 14.28 keV FWHM at 558 keV, which is adequate to distinguish between neutron and background gamma rays events. The count rate at 558 keV peak is 1.25 cps and we reasoned that the thermal neutron flux is at least 1.25 ÷ 12.2% = 10.24 n/cm2·s, where 12.2% is the maximum detection efficiency calculated above. This suggests that the 7 cm rectangle polyethylene is not enough to moderate fast neutrons. The spectrum of the detector shielded with the lead house is shown in Figure 8(b). The peaks at 558 and 651 keV still exist. The lead shielding reduces the background gamma rays while allowing a large percentage of the thermal neutrons to pass through. Hence, the peaks were attributed to the neutron capture reaction of 113Cd(n,γ)114Cd. From the discussions above, we can find that the quasi-hemispherical CdZnTe detector is able to discriminate the neutron events under high dose gamma-ray background conditions and simultaneously register neutron and gamma events, especially with relatively low energy gamma rays (<558 keV). The quasi-hemispherical CdZnTe detector may meet some demand to measure and distinguish gamma and neutron radiation, simultaneously. For example, Boron neutron capture therapy is based on high linear energy transfer radiation released from the neutron capture reaction 10B(n,α)7Li, in which a prompt gamma photon of 478 keV is emitted with a probability of 94% [27,28]. Such an arrangement could be used to determine the optimal time to start the patient treatment as real-time monitoring of the development of the boron distribution in the tumor and healthy tissues would be possible.