## dosimetry

This week, we’ve looked at calculating radiation doses.  The absorbed dose D, measured in Grays (Gy), takes into account the energy E absorbed and the mass m of the absorbing tissue.

$D = \displaystyle {E \over m}$

The higher the energy, the greater the absorbed dose.  If you are wondering why the absorbing mass is important, consider the different masses of tissue involved in a dental x-ray and a chest x-ray….

We also learned about equivalent dose in Sieverts (Sv). The equivalent dose H gives an indication of the potential for biological harm by considering the absorbed dose D and a weighting factor $W_R$.

$H=DW_R$

Different types of radiation have different weighting factors, e.g.

gamma1
x-ray1
beta1
alpha20

The more damaging forms of radiation have a larger weighting factor.

Absorbed dose and equivalent dose are usually expressed in smaller units; μGy, mGy, μSv, mSv.

In the UK, the population receives an average equivalent dose of 2.2mSv per year due to background radiation produced by cosmic rays, radon gas and materials dug up from the Earth’s crust, such as rocks and soil. In addition to this exposure to background radiation, the Government has set a further equivalent dose of 1mSv per year for members of the public.  This limit can be increased to 20mSv for people who work in the nuclear industry, certain medical occupations (such as radiographers) and airline pilots – all of whom will exceed the public limit in the course of their job.

This occupational increase for some individuals can be justified on the grounds that workers are not as vulnerable to the effects of radiation exposure since they are neither children (high rate of cell division so more chance of dna damage being copied) or elderly (reduced ability to repair damage).  In many cases, these workers will also be screened on a regular basis by occupational health staff at their place of work.

Here is a poster from the excellent xkcd site that explores examples of the different levels of equivalent dose.

Click on the picture for a larger version.

###### source: XKCD

Notice that the scale changes as you move through the poster from blue to green to red.

The dosimetry topic is comprehensively covered at BBC Bitesize.

## what do astronauts do?

We’ve been looking at the risks and benefits of space exploration.

Tim Peake, the British astronaut about to start work on the International Space Station, appeared on The One Show last week to talk about his training for the mission.

## national 4 – waves & radiation revision

Here are some summary notes to help with your revision for the waves and radiation unit assessment.  Your test is scheduled for Friday 24th April.
Extra revision materials and questions are available on BBC Bitesize.

## national 4 electricity & energy KU revision

Here are some old exam questions to help you to prepare for the resit of the E&E unit assessment.  Your resit is scheduled for Thursday of this week (see calendar dates on right of the screen).  You will get more thorough coverage of the appropriate key areas if you work through the BBC Bitesize pages and try their tests.

## national 4 dynamics & space KU revision

If you have to resit any of the national 4 unit assessments, the test paper will only contain knowledge questions.  The revision material on BBC Bitesize has multiple choice test questions but you should also practise making accurate statements if you want to pass the test.

Here is a selection of suitable questions I have extracted from old SQA papers.  Work through them and compare your responses to those given in the answer booklet (see next post).

Your Dynamics and Space resit will take place on Monday 30th March.

## viewing the solar eclipse

We spoke about the eclipse in class today.  It’s really important that you follow advice for watching the eclipse safely to avoid permanent damage to your eyes.

You can buy eclipse viewing glasses online.  They look like this

and only cost a few pounds per pair.  Make sure any glasses you buy have the CE mark on them.

Here is one UK retailer of eclipse viewing glasses who still has them in stock.

Although we’re not in the totality (100%) zone, Thurso is well placed to get a good view.  Here is a simulation for Orkney, our view will be very similar.  Click on the picture to start to animation.