I was trying to find the meaning of passive gamma-ray emission through the internet. I haven't found any helpful article except some research paper just denoting the word passive ray emission. They also didn't define the meaning. When I searched for the picture it showed a graph with the number of counts vs energy that didn't dictate any information why it was passive. And what were the criteria for being an active gamma-ray emission? so it would be helpful if someone can explain it.
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2$\begingroup$ Where did you read the term passive gamma-ray emission? In what context was it being used? As far as I know it doesn't have a precise scientific meaning so its meaning would be whatever the author wanted it to mean in that context. $\endgroup$– John RennieCommented Apr 7, 2022 at 6:06
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I found this:
The use of passive gamma-ray and neutron detection and imaging technologies in security-sensitive areas and ports has had more impact than most other techniques in detecting and deterring illicit transportation and trafficking of illegal radioactive materials.
So it is a term used in detectors
Passive Gamma-Ray and Neutron Imaging Systems for National Security and Nuclear Non-Proliferation in Controlled and Uncontrolled Detection Areas: Review of Past and Current Status
From glancing through the article I conclude that the term "passive radiation" and "active radiation" comes from the filters used for detecting the radiation, which are called "passive" and "active"
There are generally two types of coded apertures: passive masks and active masks. In the case of passive masks, a highly absorbing material is used to stop and eliminate non-normally directed radiation quanta from reaching the detector.
These masks are used so that the detectors work efficiently to detect ambient radiation.
Passive physical collimation shows noticeable drawbacks over a considerable range of the energy spectrum, especially at high energies where radiation fields have enough energy to penetrate the opaque pattern of the mask . On the other hand, active coded aperture designs use radiation sensitive materials, such as B- and Gd-doped glass plates for detecting low energy neutrons, as part of the collimation and detection process, which allows the detection of radiation quanta with a wider energy range.
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2$\begingroup$ For me, it's not the gammas that are passive, it's the detection system. A passive detection system only uses radiation from the source. Active detection systems use their own source of radiation and detect what comes back: there are detections of this type using neutron activation methods. I could be wrong . $\endgroup$ Commented Apr 7, 2022 at 9:56
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$\begingroup$ @JeanJacques I agree with you, what I have called "the filters used", if you read the link it is what you say. $\endgroup$– anna vCommented Apr 7, 2022 at 11:06
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$\begingroup$ There is no use of the term "passive radiation" in these quote. Possibly the OP missunderstood the source he read. $\endgroup$– nasuCommented Apr 7, 2022 at 12:46
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$\begingroup$ @nasu my search gave this arxiv.org/abs/2009.11617 , in abstract " Passive Gamma Emission Tomography (PGET) " and this led to the links given in the answer $\endgroup$– anna vCommented Apr 7, 2022 at 12:59
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$\begingroup$ It is this weird thing with English that we put all the adjective together with no change in format to show to what they are attached. I read the title as well as the abstract to mean that the passive thing is the tomography. Not the radiation. I suppose you can have "active" tomography where you emit some radiation (x-ray as in CAT-scan or ultrasound as in ultrasound tomography). $\endgroup$– nasuCommented Apr 7, 2022 at 13:08