ymbelydredd - radiation (Welsh, Science)
Sorry folks, this is my subject and your assumptions are not correct. What kind of radiation? Light? Heat? What wavelength? Oh, you mean ionising radiation? It still depends on the circumstances! 'Radiation is dangerous' - 'Ymbelydredd yw peryglus' I tried 'can be dangerous' but on my iPad in the app, I can only signal a comment, not type it. I have tried all afternoon in the programme on the ipad but my connection is too poor. so here I am in the evening. I have suffered the need to deal with nervous young people who hear 'radioactive' and turn to flee! I know you are not teaching physics, or Health Physics (my profession), but please can we have 'may be' in front of dangerous. A sentence like, "We must take care when dealing with radioactive material." That is true!!!! And less likely to terrify Diolch yn fawr for your attention.
ymbelydredd is usually used in the sense of radioactivity. pelydriad is a more general term for radiation, such as in pelydriad heulol (solar radiation). I have updated the definitions to reflect that.
I take your point though, and I'll see if there is enough available vocabulary by that stage of the course to offer a more informative sentence.