Ex) Article Title, Author, Keywords
New Phys.: Sae Mulli 2022; 72: 900-904
Published online December 31, 2022 https://doi.org/10.3938/NPSM.72.900
Copyright © New Physics: Sae Mulli.
Jong-Kwan Woo*, Dong Liu
Department of Physics, Jeju National University, Jeju 63243, Korea
Correspondence to:*E-mail: firstname.lastname@example.org
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
In this study, we will examine the Raman and Compton scattering theories to explain a mechanism of the blue light emitted by a UV germicidal lamp, whose average wavelength is between λ ≈ 260 nm and λ ≈ 360 nm. A germicidal lamp emits ultraviolet C light (UV-C), which has a wavelength between 100 nm and 280 nm. Man can typically see visible light with a wavelength between 380 nm and 780 nm, but cannot see UV light from a germicidal lamp. However, we can observe the blue light that emanates from a germicidal lamp (wavelength for blue from 465 nm to 482 nm and violet from 380 nm to 450 nm). There are various reasons why we can measure the blue light coming from a UV germicidal lamp. Because a germicidal UV lamp emits blue light, this study will focus on the scattering, particularly the Raman and Compton. We will make a suggestion for exploiting the scattering-induced redshifts for a tiny neutral particle around the atoms.
Keywords: Scattering, UV lamp, Germicidal lamp, Tiny neutral particles
We can see the blue light coming from a germicidal UV lamp with our unaided eyes. Its main wavelength was 253.7 nm. However, it stands to reason that humans cannot see UV light with the naked eye. As a result, I will investigate several sources of blue light from the UV germicidal lamp, such as blue light from the UV lamp, scattered light, etc. This investigation will highlight the UV germicidal lamp as the main source of blue light. We will also investigate the physical conditions that cause UV light to emit visible blue light. We will then suggest on how to search for a tiny particle that is present near atoms whose mass ( eV) is less than that of the electrons.
Figure 1 shows a schematic representation of the mercury (Hg) gas-filled germicidal lamp's UV light emitting mechanism. The four mechanisms by a germicidal lamp emits UV light through four processes, heating filament, thermal-emitting electron, electron scattering with Hg atoms, and UV emission.
A UV lamp's filament is heated in the first process. In the second method, a hot filament emits a thermal electron. The thermal electron strikes a mercury atom in the third process, causing it to be become excited. Finally, a UV light is emitted in the fourth process when the excited mercury atom is de-excited. Fundamentally, when an excited electron is de-excited, rather than when a nucleus is stimulated, the excited electron releases UV light. These four processes describe a mechanism by which a germicidal UV lamp emits UV radiation. The interaction between a thermal electron and a mercury atom in a lamp is shown in Eq. (1) as the source of UV light. The symbols
Through the transparency quarts tube of the lamp, the UV light is released. If the wall of the quart tube is coated with a fluorescent material, the UV light hits the fluorescent material, which causes the fluorescent light to be emitted. It is known as a fluorescent lamp.
When an electron hits a metal surface, either an X-ray or UV light is produce. We can determine the UV light's wavelength by emitted a simple calculation on an excited mercury atom. Early in the 20th century, Moseley calculated the relationship between X-ray wavelength and atomic number. Equation (1) can be used to calculate the wavelength of the wave caused by electron hitting a metal.
We call the UV light, whose wavelength is longer than 100 nm and shorter than 380 nm, corresponding to the higher energy of 5.23 eV and lower than 19.9 eV. The interaction between an electron and a mercury atom in a germicidal lamp produces many types of UV. The wavelengths of UV light from the mercury germicidal lamp are fixed, but the intensity of UV light varies with the conditions. Figure 2 shows the efficiency of the mercury lamp depending on the vapor pressure of the mercury lamp. Figure 2 was redrawn from a graph described in a chemical data book. Therefore, we can categorize the pressure of the mercury lamps into 3 regions. In region 1 (R1), especially at pressure of 0.01 mmHg, a UV light with wavelength
The distribution of UV light from a mercury lamp depends on the lamp's manufacture. Figure 3 shows the energy distribution of UV light made by a manufacturer. This graph was redrawn using the data provided by the manufacturer.
From the graph in Fig. 3, we see that a UV light with wavelength
In this study, I focused on the four UV lights whose wavelengths are less than 380 nm and whether they affect the amount of blue light and visible light. The wavelength of light, a type of electromagnetic wave, can be shifted for several reasons. For example, Raman scattering, Compton scattering, the Doppler's effect, etc. However, this investigation did not consider Doppler's effect because the UV source and detector do not move. Also, I did not consider that fluorescent light was produced by the interaction between UV light and fluorescent material surrounding the UV lamp.
We can calculate the shifted wavelength by the Compton scattering between a UV light and the electron of a mercury atom as
where λ and
We can calculate the shifted wavelength from the Raman scattering between a UV light and the electron of a mercury atom as
This result gives us the information that a small amount of the shifted frequency by Raman scattering could shift the UV light to visible light.
We investigated several ways to produce blue and visible light in UV germicidal mercury lamps. The blue light should come from the lamp itself, majorly. But several physics effects could shift the wavelength, which then makes the wavelength of UV light shift into the visible light range. A Raman scattering, a Compton scattering, a Doppler's effect, etc., could be the physical effects that shift the wavelengths of incident UV light. In this study, I focused on whether Raman scattering and Compton scattering can modify the wavelength of UV light from a germicidal lamp.
By the calculation, we know that a Raman scattering can shift the wavelength of the incident wave up to
Also, by the calculation, we know that a Compton scattering can shift the wavelength of the incident wave up to
We investigated whether the major reason UV light in a germicidal lamp shifted into the visible region is a Raman scattering rather than a Compton scattering when we consider only two scatterings.
We can consider another reason except for the Raman and Compton scattering described above. As we see, the effect of Compton scattering shifting is insignificant
This work was supported by the grant of NRF-2021R1F1A1061174.