Natural Radioactivity and Background Radiation

Background radiation is a natural part of the environment. The largest source of background radiation exposure comes from the natural radioactivity in rocks and soil and the inhalation of naturally occurring radon that seeps from the ground into our buildings. We are also exposed to cosmic radiation and the natural radioactivity in food and in the body.

On average, Australians are exposed to about 1.5 mSv each year from natural sources, although for some the dose might be more than double that. On average, we also receive about 1.7 mSv per year from medical diagnoses and treatment. Continue reading “Natural Radioactivity and Background Radiation”

Black holes and neutron star collisions

The recent observations of gravitational waves from cosmic events opens a dramatic new window on the universe (first in 2015).  The first four events observed by gravitational waves were colliding black holes with masses between 7.5 and 35 solar masses. As black holes do not emit any radiation, there is no electromagnet radiation from the resultant black holes although the actual collision produces a gamma ray pulse which has been detected for one of the events. The amount of energy radiated away as gravitational energy from these black hole collisions is immense: between 1 and 3 solar masses of energy emitted in a short time of order or less than 100 seconds.

Even more interesting in terms of observations was the GW170817 event (published on 16 Oct 2017) which was caused by the collision of two neutron stars approximately 130 million years ago.  Continue reading “Black holes and neutron star collisions”

The Black Hole at the Centre of the Milky Way Galaxy

Recent observations by the W. M Keck Telescopes have provided clear evidence for the existence of a supermassive black hole at the centre of our Milky Way galaxy.  Because of dust, the galactic centre cannot be seen at visible, ultraviolet or soft x-rays wavelengths, but the W. M. Keck Telescopes have obtained incredible images of the stars and gas clouds at the centre of our Milky Way galaxy using infrared optics. Continue reading “The Black Hole at the Centre of the Milky Way Galaxy”

Neutrinos – present in vast numbers but barely interact with matter

The sun emits vast numbers of neutrinos which can pass through the earth with little or no interaction. Solar neutrinos shine down on us during the day, and shine up on us during the night after passing through the earth almost no absorption. Bahcall’s modeling of the solar neutrino flux led to the prediction of about 5 x 106 neutrinos/cm2s.

Since a typical adult has a cross section of about 30 cm x 100 cm i.e 3000 cm2, there are over 1 billion neutrinos from the sun passing through our bodies every second. Continue reading “Neutrinos – present in vast numbers but barely interact with matter”