Tuesday, 21 April 2015

Kawau Island copper mines

Visited Kawau Island off the east coast of New Zealand in the Hauraki gulf last weekend. In 1844 copper was discovered on the Island and a mine was set up next to the coast. The chimney you see below is the engine house that housed a big steam engine to pump water out of the mine.

Here is the description of the history of the site.

I loved to see the amazing copper carbonate deposits around the copper mine and on the rocks around the area.

The rocks around the site were clearly a greenish-blue copper carbonate colour.

 However the rocks around the cave entrance were more of blue colour.

This indicates the fresh water around the cave, probably flows over the rocks when it rains, is hydrating the copper and giving rise to the classic Cu2+ colour.

The basic copper carbonate is green-blue colour and is called Malachite (Cu2CO3(OH)2).
 The hydrated copper carbonate is a blue colour and is called Azurite (Cu3(CO3)2(OH)2).
Azurite is broken down into Malachite over time. Here is an excellent picture of a rock caught during the transition.

Sarah Thompson in the Photon Factory works on pigments and their photo degradation. So I was interested to see if this breakdown is important for Azurite pigments.
Raphael, Madonna and Child Enthroned with Saints, The Metropolitan Museum of Art
Sure enough in Raphael's Madonna and Child Enthroned with Saints the Virgin's mantle is darkened and a green colour due to Malachite where orginally it would have been a dark blue Azurite.

A painting with it particulary well preserved is Hans Holbein's Lady with a Squirrel and a Starling.

Hans Holbein the Younger, Lady with a Squirrel and a Starling, National Gallery, London
 It was a great day and the views from the boat were well worth the trip.

Thursday, 9 April 2015



Keen to do a science and technology fair project but don't know where to start. Check out a website a group of students and teachers (including I) put together in 2012 to give students resources to do science and technology fair projects and teachers the resources to integrate science and technology fair projects with NCEA. I have just added a Facebook page and added in a new forum to the wiki. Also if you a teacher or student and want to contribute that would be great.

There are five main sections of the website including

Steps - What are the steps to complete a science or technology project? What are some tips and tricks to making award winning projects.
Pathways - A teachers resource for NCEA integration with science and technology projects.
Forum - Need help with your science and technology fair project or need help with ideas check out the forum.
Other projects - Get inspired with other students projects and where they have taken them.
Mentoring - Want to get connected with groups and researchers that can help you with your topic. Fill in the form and we can get back to you with people that can help.

Monday, 6 April 2015

Lunar Eclipse

This Saturday stayed up with some leaders from Easter camp out at Bucklands beach to watch the lunar eclipse. Thanks to Jack Fowler we captured the whole event on his iphone pushed up against the eyepiece of my small 76 mm Newtonian telescope with a moon filter. Here are the shots.

Thanks also to the group that stayed up till 1pm with me to capture the eclipse that started at around 11pm.

Tuesday, 27 January 2015

We have only just worked out how sodium explodes in water

This classic experiment is one of the many explosions that encouraged me to pursue a career in chemistry. But ever wonder why it explodes I thought that the generation of hydrogen on the surface had a part to play this does explain the burning but for an explosion you need to have a large enough surface area to have a reaction fast enough to really get a boom. If you know anything about the thermite reaction or flour bombs a huge surface area allows the reaction to proceed fast enough to build up pressure and explode. Also unlike gun powder which already has the fuel and oxidant mixed together only at the sodium water interface can you get the reaction so surface area is crucial. Using a high speed camera and some neat simulations researchers have just work out how sodium increases it's surface area enough to cause an explosion.

Put most simply sodium quite easily gives up its outer most electron and becomes the positive sodium ion. What they found was that when sodium is put into water the water sucks the electrons from the surface of the sodium metal. Without the electron you just have positive ions which repel each other this causes small needle like fingers of sodium to extend into the water. This greatly increases the surface area causing hydrogen gas build up and allows for the big explosion.

The high speed images show the needle like filaments. The crucial frame is 0.4ps 5th image from the top middle column where you can see the needles of sodium and potassium (potassium is added to make a liquid metal for easier dropping). The next frame shows the explosion at the surface.

Now comes the awesome simulations. So using quantum calculations they modeled nano drops and show the electrons (blue in the image below) moving into the water and then the sodium ions breaking apart as there are no longer any electron glue to hold them together.
Scaling up the simulations using some assumptions that reduce the amount of computer processing time they showed a larger drop exploding at the surface.

Check out the movie they put together and the paper. I wonder what other elementary reactions are still not fully understood.

Monday, 8 December 2014

10 billion frames per second videos of single pulses of light

There has been quite some buzz about doing ultrafast photography. This involves using ultra short pulses of light to illuminate a scene and take images at billions of frames per second. However there is always a trick and in this case the pulse of light is not the same pulse of light throughout the movie. What you do is repeat the measurement and delay the opening of the shutter on the camera. This is the same way we take ultra-fast spectrum of molecules we rely on the repeatability of the measurement and change when we observe the molecules after firstly exciting them. Here is a video made up of hundred of different pulses that when you put them altogether you can see how a pulse of light hits an apple.
An exciting new paper by Liang Gao et al. in nature shows a way to take a movie of a single pulse of light. This opens up the ability to see non-repeatable events such as nuclear explosions, optical rogue waves or gravitational waves. These events happen on the femtosecond (10-15s) timescale that are one off events.

Before we get into the nuts and bolts of how it works here are the amazing movies they captured of a single pulse of light.

Light hitting a mirror will be reflected at the same angle it approaches the mirror. Something else you can see if the evanescent field (light tunnels through the material) which decays away exponentially over time. We can use this to perform spectroscopy on a surface.
Light will travel slower in a lower refractive index material here is a comparison of air and resin where the light in the resin is travelling slower.
Refraction occurs at the surface of a lower refractive index material and a higher refractive index material.
This is my favourite, Seeing the glow of molecules after they have been excited. They capture a phenomenon called fluorescence where light of a higher energy (green in this case) is absorbed by the molecule (Rhodamine) the excited molecules loses some of that energy to vibrations and then drops down to the ground state emitting lower energy light (red).

Here are all of the different experiments.

So how does it work. Here is my basic explanation feel free to correct me in the comments. Firstly an ultrafast laser pulse is needed these are generated using special laser cavities that bounce a laser pulse inside a cavity hundreds of times each time they destructively interfere inbetween pulses and constructively interfere only for a few femtoseconds - if you have ever made a diffraction pattern in on a wall (spatially) think of this as a diffraction pattern in time (temporally). The camera used is quite similar to the old CRT TVs but in reverse instead of electrons being scanned over a phosphorous screen that converts the electrons to light. Light hits a phosphorous screen where the photons of light are converted to electrons these are accelerated towards a camera sensor like in a cellphone and an image is created. However you apply a voltage ramp across the path of the electrons so they are deflected depending on when they arrive (you reduce the voltage as a function of time). This means electrons from light that arrived earlier will be deflected more by the electric field than electrons from light that arrives near the end. You can think of this as sophisticated light painting where you get a blur of colour by keeping the shutter open on a camera. 
Here is a schematic of the optics used.

Now how do you extract out a video from a blured image on the image sensor. You need some sort of pattern that will be the same at every time step. The way they do this is using a coded mask that randomly patterns the image of the object. You can see this in the diagram below.

Using matrix methods on the computer you can reconstruct a whole video from a single blurred image. What do you want to observe at 10 billion frames per second?

Gao, L.; Liang, J.; Li, C.; Wang, L. V. Nature 2014, 516, 74–77.