## 8 argumenter mot kjernekraft 1

Hei verden ♥

I dag har jeg avsluttet undervisningen jeg har gitt i Nukleær Teknologi, og det skjedde med brask og bram og debatt 🙂 Det var utrolig gøy, og studentene var så flinke, og jeg kjente jeg ble skikkelig stolt av dem ♥ De kom dessuten opp med flere svar på vanlige innvendinger, som jeg ikke har tenkt over før, og det syns jeg var så inmari gøy å se!

De hadde fått litt forskjellige synspunkter på kjernekraft som de skulle sette seg inn i på forhånd, og i dag skulle de altså debattere seg i mellom. Jeg prøvde meg som debattleder (vi har aldri prøvd å kjøre debatt i undervinsingssammenheng før, så det får vi sikkert til – fritt etter min heltinne, Pippi Langstrømpe), og i min forberedelse til dette satte jeg sammen en liste med åtte vanlige argumenter mot kjernekraft. Disse må jeg selvsagt dele med dere her, med noen veldig korte tilsvar:

1 ♥ Kjernekraft er farlig

Kjernekraft er en av de aller tryggeste måtene å produsere energi på. I feks USA (som har en betydelig andel av verdens kjernekraftverk) har ingen privatpersoner noensinne blitt drept eller skadet på grunn av kjernekraft, i løpet av hele den 50 årige historien til sivil kjernekraft.

Det er tryggere å jobbe i et kjernekraftverk enn på et kontor.

2 ♥ Et kjernekraftverk kan eksplodere sånn som en atombombe

Det er fysisk umulig for reaktoren i et kjernekraftverk å eksplodere sånn som en atombombe (“atomeksplosjon”) – nei, Tsjernobyl var ikke en atomeksplosjon, det var “bare” en dampeksplosjon (som forsåvidt forteller noe om hvor heftig det at vann går over i gassform kan være…).

Atomvåpen er konstruert på en spesiell måte, og har veldig mye mer spaltbart materiale (MYE høyere anrikning) enn et kjernekraftverk, så det kan heller ikke skje ved et uhell at kjernekraftverket plutselig blir som en atombombe.

3 ♥ Kjernekraftverk slipper ut farlig(e mengder) stråling

Nei. Utslippene av stråling fra et kjernekraftverk er veldig små. Hvis man bor innenfor en 75 km radius til et kjernekraftverk vil du i gjennomsnitt få en ekstra stråledose hvert år på ca 0.0001 mSv som kommer fra kraftverket. For å sammenlikne så får den gjennomsnittlige nordmannen ca 4/4.5 mSv hvert år fra andre kilder (størstedelen er den såkalte naturlige bakgrunnsstrålingen).

4 ♥ Kjernekraft fører til (spredning av) kjernevåpen

Dette er en sånn type påstand det er vanskelig å si sikkert hva som er svaret, men et par ting er sikkert:

1. Land som feks Nord-Korea har klart å skaffe seg atomvåpen helt uten noen som helst hjelp eller støtte – de har ikke kjernevaåpen i dag fordi de fikk hjelp til å starte en sivil kjerneindustri som så ble til en våpenindustri
2. Kjernekraft er dessuten den beste måten å ufarliggjøre de våpnene som allerede eksisterer (hvis det er ønske om det, da, selvfølgelig); de består nemlig av helt fantastisk spaltbart material som er helt nydelig å bruke som brensel i et kjernekraftverk – og dermed gi oss den elektrisitetetn vi så gjerne vil ha

For land som har skrevet under på ikke-spredningsavtalen så er det ekstremt strengt og kontrollert, nettopp for å unngå spredning av kjernefysiske våpen.

5 ♥ Et kjernekraftverk produserer store mengder avfall

Denne er jo litt gøy å ta tak i… For det er faktisk ganske så motsatt: Kjernekraft produserer veldig SMÅ mengder avfall sammenliknet med andre energikilder.

Hvis man feks ser på alt brukt brensel som er produsert i alle kanadiske kjernekraftverk i løpet av de siste 50 årene så fyller disse 6 NHL hockey-baner (!)  En stor mengde av dette avfallet kan dessuten gjenvinnes, slik at den totale mengden avfall vil gå fra liten til bitteliten.

Dessuten, i motsetning til avfallet som produseres fra fossilt brensel, som bare slippes rett ut i luften, så blir avfallet fra kjernekraft tatt veldig godt hånd om.

6 ♥ Kjernekraft er i ferd med å fases ut uansett

Dette er faktisk på ingen måte sant. Det er over 400 reaktorer i verden i dag, og ca 60 stykker er i ferd med å bygges.

Men hvis man ser på tallene for andelen elektrisitet som kommer fra kjernekraft så har den gått ned de siste årene. Dette er ikke fordi det blir færre kjernekraftverk, men fordi det totalt sett i verden produseres mer elektrisitet, og økningen er større for andre måter å produsere energi på enn kjernekraft (feks kull...). Så andelen går ned, men i absolutte tall er det en økning.

7 ♥ Kjernekraft kan ikke gjøre noe for avhengigheten av olje

Allerede i dag driver strøm produsert fra kjernekraft både elektriske tog, t-baner og biler. Kjernekraft har også vært brukt (og brukes i dag) i store båter - atomdrevne hangarskip og ubåter (disse drives direkte av en reaktor i båte, og ikke indirekte fra strøm 🙂 ). Denne typen bruk av kjernekraft kan (og bør?) selvsagt utvides.

Så, jo, kjernekraft kan absolutt gjøre noe med avhengigheten av olje 😉

8 ♥ Kjernekraft er dårlig for miljøet

Kjernekraftverk har ingen utslipp av drivhusgasser direkte, altså fra når de produserer kraft. Hvis man ser på hele livsløpet til en reaktor (tar med det som slippes ut når man produserer betong, bygger reaktoren, dekommisjonering av kraftverket osv), så er utslippene av drivhusgasser ca de samme som det man får fra fornybare kilder som for eksempel vind- og solkraft.

(Fantastisk sitat jeg skulle ønske jeg kunne ta æren for selv, men det er nok David McKay som er mannen bak dette - sååå sant!)

## Formelfredag: kunstig tyngdekraft 2

Ukens formel er egentlig ikke en ny formel, men endelig kan vi sette sammen ting fra tidligere innlegg, og løse praktiske problemer 🙂 Praktiske problemer av den typen du får når du skal være veldig lenge på et romskip, altså i vektløs tilstand. Med andre ord; ikke ting som er problemer for de fleste av oss...;)

I dette innlegget står det om Newtons andre lov, som kort fortalt sier at $$F = m\cdot a$$, og i innlegget fra forrige ukes formel står det om sentripetalakselerasjon - altså den akselerasjonen man har når man kjører rundt og rundt i en sirkel: $$a = \frac{v^2}{r}$$.

Sentripetalakselerasjon er nettopp det som gjør at vannet presses ut av klærne under sentrifugeringen i en vaskemaskinen. Trommelen snurrer rundt og de våte klærne går i sirkelbane inni maskinen. Det er små hull som gjør at vannet får lov til å renne ut mens klærne forblir på innsiden. Vått tøy minus vann er lik mindre vått tøy 🙂

I innlegget om Newtons andre lov skrev jeg om tyngdekraft. Hvis vi setter sammen idéen om sentrifugen med det vi vet om tyngdekraften på jorden har vi alt vi trenger for å finne ut hva slags romskip vi må ha for å lage "kunstig tyngdekraft" for astronauter i vektløs tilstand enten i bane rundt jorden eller kanskje på vei til Mars. Løsningen er nemlig at romskipet må ha en snurrende del sånn som dette:

Romskipet kan være formet som mye rart, men det viktige å få med seg her er den store donut'en (den er jo en slags sirkel med radius r). Hvis romskipet er vektløst vil en person som står inni kjenne at han/hun blir dyttet utover når det snurrer (tenk på tekoppen-karusellen 😉 ).

Vi kan nå kombinere de to formlene til å finne sammenhengen mellom radius på romskipet og farten det må snurre med for at en person inni opplever å bli dyttet mot gulvet akkurat like hardt som jorden drar deg ned mot gulvet. Vi starter med selve formelen

- oppskrift -

- hvorfor det blir sånn/forklaring -

Forklaringen kommer her (du kan gjerne hoppe over, hvis du ikke vil vite hvordan det er sånn, og gå rett ned til hva det betyr):

Newtons annen lov sier altså at $$F=m\cdot a$$, og her på jorden er a (det som kalles tyngdeakselerasjonen) 9.81$$\frac{m}{s^2}$$, så derfor blir tyngdekraften $$F=m\cdot 9.81$$. Når du kjører i en sirkel så er $$a=\frac{v^2}{r}$$, og siden du har en akselerasjon (som ikke er null), så blir den kraften du blir presset utover med $$F=m\cdot\frac{v^2}{r}$$ (her starter man også med Newtons annen, og setter man inn $$\frac{v^2}{r}$$ der det står a 🙂 )

Da har vi to forskjellige likninger som forteller om kraft: 1) $$F=m\cdot 9.81$$, og 2) $$F=m\cdot \frac{v^2}{r}$$. Poenget er at når vi er i det snurrende romskipet så vil vi at den kraften vi blir presset utover med skal være lik den tyngdekraften vi kjenner her på jorden, og derfor sier vi at $$F=m\cdot 9.81$$ på en måte er fasiten - det er det vi må få på vestre siden av likhetstegnet i likning 2). Dermed blir det seende sånn ut: $$m\cdot 9.81=m\cdot \frac{v^2}{r}$$. m er den samme på begge sider av likhetstegnet, så den kan vi bare ta bort (og det er jo litt heldig, for ellers ville det vært sånn at alle astronauter måtte hatt akkurat samme masse for at dette skulle funke, men heldigvis så er denne kraften uavhengig av massen din, eller det vi ofte kaller for vekt, da 😉 ). Så da ser det slik ut: $$9.81=\frac{v^2}{r}$$, og fra denne får vi likningen over ♥

- hva det betyr -

Et romskip som i bildet øverst har en eller annen radius, og da kan vi bruke formelen for å finne ut akkurat hvor fort det må snurre for å få lik tyngdekraft som på jorden!

v er hastighet ("fart"), r er radiusen i den sirkelen du beveger deg i (radiusen til romskipet), og 9.81 er 9.81$$\frac{m}{s^2}$$, eller det som kalles tyngdeakselerasjon som er det som gjelder her på jorden (ja, vi har faktisk hele tiden en akselerasjon ned mot bakken). Som alltid så må man måle hastigheten i m/s, og radius (eller en hvilken som helst avstand) i meter - ellers blir det bare krøll 😉

- fremgangsmåte -

Hvis vi har et romskip som har radius 100 meter (det er jo et ganske stort romskip, men fint tall å regne med). Da kan vi bruke formelen med én gang for å finne farten:$$v = \sqrt{r\cdot 9.81} = \sqrt{100 \cdot 9.81} = \sqrt{981} = \sqrt{981} = 31 \frac{m}{s}.$$

Det er jo egentlig ganske fort (111 km/t), men så var det jo et ganske stort romskip også. Å ha et stort romskip er viktig fordi et menneske er omtrent 2 meter, og vi vil jo ikke at føttene og hodet skal ha veldig forskjellig akselerasjon, så vi vil at menneskehøyden er liten sammenliknet med radien på sirkelen. Det kan jo hende et romskip som har halvparten så stor radius er greit nok, og da vil vi få farten

$$v = \sqrt{r\cdot 9.81} = \sqrt{50 \cdot 9.81} = \sqrt{490.5} = \sqrt{490.5} = 22.15\frac{m}{s}$$, en god del lavere fart, men mer enn halvparten! Denne farten ser vi at stemmer fra grafen under. Hver rosa prikk i grafen viser hva farten må være ved forskjellige radiuser.

Men hvor fort må den snurre da? Da tenker jeg på antall omdreininger (bedre kjent som RPM, revolutions per minute), slik vaskemaskiner og bilmotorer ofte oppgir. Hvis du står i romskipet vil du jo i løpet av en hel runde bevege deg akkurat like mye som omkretsen på sirkelen. Omkretsen har formelen $$O = 2\pi r$$, så i det første eksempelet er omkretsen

$$O = 2\pi r = 2\pi 100 = 2\cdot 3.14\cdot 100 = 628 m$$. Når vi har farten 31 meter per sekund vil det jo ta $$\frac{628}{31} = 20$$ sekunder å bevege seg en hel runde. På et helt minutt får vi 3 runder, altså 3 omdreininger i minuttet. For det litt mindre romskipet blir omkretsen $$O = 2\pi r = 2\pi 50 = 2\cdot 3.14\cdot 50 = 314 m$$. Antall sekunder per omdreining blir da $$\frac{314}{22.15} = 14.18$$, så omdreininger i minuttet blir $$60/14.18 = 4.23$$, mer enn for det store romskipet.

Sånn helt til slutt, fordi det er en fin avslutning på formelfredag, og uken sånn generelt: En vaskemaskin, hvor fort må den snurre for å få nøyaktig 9.81 $$\frac{m}{s^2}$$ akselerasjon? Skriv svaret i kommentarfeltet her eller på Facebook, eller send meg en snap, eller hva som helst ♥

## 10 facts about getting a PhD 3

I write about this work I'm doing all the time, but I have never written anything about what really constitutes a PhD, so I thought this week you'll get 10 FACTS about how to get a PhD:

1. After you get a master's degree, you can continue with a PhD
2. The actual PhD work is 3 years, but many of us also have 25% teaching so that we have the job for 4 years in total (the teaching is normally done during the time you also work on the degree)
3. To be admitted to the PhD program at the University of Oslo, you have to have quite good grades; B as an average on the courses in your master's degree, and at least B on your master thesis
4. Most of the PhD degree is research, but you also have to take one semester (in total) with courses (one of the courses is a mandatory ethics course - which sounds like a good idea, but when I took the course, I thought it wasn't a particularly good course...:/ )
5. My courses were the ethics course, one called "Communicating Scientific Research", a statistics course (STK9900), and a nuclear structure course ("advanced nuclear structure and reactions")
6. The main part of the PhD is research; you have to do stuff that is new, and the results must be of such a quality that it's published in serious, peer reviewed joournals (if your work isn't worthy publishing, well, then that's too bad for you - no PhD!)
7. The actual "thesis" is a collection of the articles you write (often it's something like three), and an "introduction" where you sort of sow everything together (which can be challenging when you feel like your articles have almost nothing in common), and write in detail about the methods you've used, and experimental setup, and theory and stuff (for example, I write about nuclear power in general, nuclear reactions that are interesting and important for nuclear reactors, simulations of nuclear fuel, and the Oslo Cyclotron Laboratory, and of course there is some kind of conclusion after the articles 🙂 )
8. When everything is finished (your research, your article writing, your thesis writing, and your funding), the entire thing will be sent to a committee (experts in the field, of course 😉 ) that will read everything carefully and decide whether the thesis is worthy of defending, or not. (If they decide it's not at all worthy, you don't get a chance to make it better, and all your work is worthless for the degree - if still you want to get a PhD then, you have to start ALL.OVER.AGAIN.)
9. After the committee says the thesis is ok, you'll get the date for the thesis defence, and two weeks before this, you get the title of you trial lecture that you have to prepare for the thesis defence. This could be almost anything (is my impression), but it's normally related to your research
10. The last part is the day of the thesis defence: it starts with the trial lecture, and if this is approved, then you get to actually defend your thesis. The defence happens later the same day; first you give a short presentation of the work, and the two opponents will ask all kinds of questions about it and discuss with you. After they've finished, people in the audience can ask questions. All of this is public. At the end of the day, after the committee (hopefully) approves of your work, you have to have a dinner with the opponents and your supervisor, and maybe your friends and family <3
I guess you can say I've finished points 1-5, and more or less number 6, and now I'm mostly working on the rest of point number 6, and 7.
not sure which one is most correct for me, but I'm leaning towards the first...:P

This week my supervisor from Paris, Jon, is coming, and my goals for the work with him is to make a draft of an article about prompt fission gamma rays, discuss my thesis draft, finish my article about uranium-234 and send it off to all the co-authors. Really (!) hope we/I manage all this...!

## 10 facts about nuclear physcis

A normal misconception about nuclear physics is that it's all about nuclear power and/or atomic bombs, and that that's it. This is far from the truth, and therefore I think 10 facts about nuclear physics is a good idea today 🙂
1. nuclear physics is  all about the atomic nucleus - discovered by accident by Ernest Rutherford a century ago, when he was bombarding a thin gold foil with alpha particles
2. there's so much we don't know about the heart of the atom - the nucleus; and that's why we are a lot of people around the world still spending all of our lives to study it, and try to understand the nucleus and the nuclear force that holds it all together (how does it really work, and why, and how big can a nucleus actually get?)
3. all atoms have a nucleus - nuclear physics is as much about the non-radioactive nuclei (stable gold, stable oxygen, stable iron), as the radioactive ones (thorium, uranium, plutonium)
4. the "applied part" of my phd thesis is about nuclear power, which is of course also one part of nuclear physics - how to produce energy from big nuclei that splits in two (you get heat and you can boil water and you get steam and then you can generate electricity)
5. I don't want to lie; atomic bombs is also something that some people (not in Norway) study - knowledge about nuclear physics can be used in such a destructive way. As can most knowledge if I think of it...
6. knowledge about nuclear physics tells us about the creation of the elements - what happens in the sun and similar stars; how do they get their energy, and what happens there? In stars like our sun, elements all the way up to iron are produced
7. no elements that are heavier than iron can be produced in stars/the sun, but we know they exist  so they must have been created somehow (we know gold exist, we know thorium exist, we know there is lead - to give some examples), but not where they came from. Creation of these heavy elements is actually one of the great mysteries, and we think they are made in explosions or collisions in space. We use nuclear physics to try to figure out how and where all these elements are created.
8. one of the really nice applications of nuclear physics is radiation therapy. Atomic radiation may cause cancer, but it may also cure cancer <3
9. if you've ever had a CT scan, you've experienced applied nuclear physics. Think about it: it's kind of awesome that we can actually look inside the body, and get really great images of the inside, without even cutting it open...!
10. PET, which is short for positron electron tomography is another imaging technique in the nuclear medicine, where you actually detect gamma radiation from an electron that meets its anti particle, the positron (awesome, seriously!). And from this you can create beautiful three dimensional images of for example a tumour inside the body

Nuclear physics is seriously awesome <3<3<3

## 10 differences of the RBMK and a PWR 7

Since it was 30 years since the Chernobyl accident on Tuesday, I was thinking it would be a good idea with 10 facts related to that as a little "comeback" of Friday Facts (so sorry that I don't manage to make these facts every week, it's just that lately I've either been travelling, or really busy with my PhD, which I sort of have to prioritize sometimes 😉 ). Or, not just ten facts, but ten differences between the Chernobyl type RBMK reactor ("reaktor bolshoy moshchnosty kanalny", meaning high-power channel reactor), and the standard pressurized water reactor (PWR).
Let's go!
1. PWR is the most common type of reactor in the world operated in countries like USA,  Belgium, Brazil, China, Finland, France, Germany, India, Japan (the Fuksuhima reactor was not a PWR, though), Russia, Spain, and Sweden, and several more. The RBMK was a Soviet develloped design - only built in the former Soviet Union.
2. the PWR uses water as both moderator (for slowing down all the neutrons from really high energies, to really low energy - which is what we want <3 ) and as cooling medium, but the RBMK uses graphite as moderator, and water as cooling medium. Normally we say that the PWR is light water (light water is what we normally just call "water", instead of heavy water) moderated and cooled, and the RBMK is graphite moderated and light water cooled.
3. the RBMK was designed with a positive void coefficient; I'll don't go in detail on that now (if you want me to, I can make a separate blogpost about what this means), but in short it is the reason why the RBMK is unstable under certain conditions
4. the tip of the control rods of the RBMK actually didn't control the reactor/absorb the neutrons -it was made out of graphite that speeds up the fission process, instead of a material that actually shuts it down
5. the control rods of the RBMK could be withdrawn completely from the reactor - even if it wasn't allowed (no one should EVER be able to overrun safety systems, like it was done the night of the accident)
6. it took almost half a minute to insert the control rods into the RBMK reactor; on a PWR it takes around a second or so
7. a PWR needs fuel which is enriched to 5% uranium-235, but the RBMK only needed 2% - so it was economical with the fuel
8. the RBMK could have its fuel changed while it was running. This, together with the low enrichment (no 7) made it ideal as a producer of weapons plutonium
9. a PWR is passively safe, but the RBMK definitely wasn't
10. the Chernobyl reactor didn't have any outer barrier; meaning the reactor was placed more or less in a warehouse rather than a full containment building. Therefore, when the reactor actually exploded, the radioactive inside of it could get out, and fresh air (oxygen...!) could get in, making a strong fire that lasted for days

These are just the first ten big differences I could think of, but there are even more.
When I, or other nuclear scientists, say that Chernobyl could never happen in a modern, Western reactor, it's not because we just don't want to see reality or something silly like that, but it's because of these facts listet above - which makes that accident physically impossible in, for example a PWR...!
testing of reactor grade concrete - the concrete stays intact, as the plane is just disintegrated (plane vs concrete: plane 0, concrete 1)
PS: There are still some RBMKs operating in the world today, but major modifications have been made to these reactors.

## Ten facts about depleted uranium 1

As we were approaching the Tenerife airport yesterday, I suddenly remembered something...
The thing is, I have this weird fascination for accidents and catastrophes (Titanic, bombings of Hiroshima and Nagasaki, the Chernobyl accident, and more or less all accidents from "air crash investigation ") - which is probably one of the main reasons I was interested in nuclear physics in the first place. If you're like me, you might know which thing, or accident, I came to think about as we were approaching the airport? It was of course the Tenerife accident of March 1977, involving two Boeing-747, that crashed at the runway, killing close to 600 people. If you're weird like me, you probably don't think I'm completely crazy for googling the accident. (If you're not like me, you might think I'm insane for reading all I could find about the deadliest air crash ever, just before I'm about to go on a six hours flight :v )
First I found a very interesting and well written article, but after I had read this, and still wanted more, I kept scrolling, and suddenly I saw the two words depleted uranium. I don't think it was from the most serious web page ever, but I was inspired by it to make ten facts about this mysterious material - check fact number 10 for why the Tenerife air crash and depleted uranium have anything to do with each other:

1. depleted uranium is what you get when you take natural uranium, and you enrich it to get enriched uranium for nuclear fuel - the "waste" from this process is the depleted uranium (natural uranium minus enriched uranium equals depleted uranium, to sort of make into an equation <3) reason why it's called "depleted" is that it's depleted in the fissile uranium-235
2. natural uranium is made by uranium-238, uranium-235, and uranium-234. The uranium-238 isotope makes up 99.275%, uranium-235 is 0.72%, and uranium-234 is just 0.0054%. Depleted uranium is made up by typically 99.799% uranium-238, 0.2% uranium-235, and 0.001% uranium-234
3. depleted uranium is often called just DU
4. it's the least radioactive kind of uranium: depleted uranium is less radioactive than natural uranium - meaning it's close to not radioactive at all. Uranium-238 has an activity of 12 445 Bequerels per gram, uranium-235: 80 011 Bequerels per gram, and uranium-234: 231 million Bequerels per gram. The total activity of natural uranium is therefore: 25 280 Bequerel from 1 gram (meaning that 25 280 atoms of the uranium - either 234, 235, or 238 is changed into another atom every second :D), and the activity of depleted uranium is about half the activity: typically 14 600 Bequerels per second. (Don't be fooled by long halflifes - the longer the halflife, the less radioactivity... Activity/radioactivity sort of tells us how fast a material is turning into something stable: if the radioactivity is very high, the halflife is short. If it's very very low, the halflife is long. Uranium-238 has a halflife of 4.5 billion years, and is not at all very radioactive.)
5. the gamma dose rate from a 30 mm DU-bullet (of 271 grams) at a distance of 1 m is 7 nano sieverts per hours, which is almost not distinguishable from the normal background radiation of typically 100 nano sieverts per hour. If you take 10 kg of DU and disperse it over 1000 m2 the result is a gamma dose rate of 4 micro sieverts per year (the average background radiation from gamma in Norway is 0.5 milli sieverts)
6. DU is extremely dense, and therefore very heavy. Natural uranium is already a metal of high density, with 18.9 g/cm3, and DU is even more dense: 19.1 g/cm3 - making it almost 70% denser than lead
7. because of the extreme density, it's used as ammunition; since a projectile made from DU has a bigger kinetic energy than if it were made by lead, and therefore it will penetrate or destroy almost anything. Also, if a DU bullet hits a tank, all the energy that it's carrying will turn it into dust, and the heat generated will make it burn. If you're in a tank that's hit by a DU projectile - it's not exactly the radioactivity you should fear...
8. DU is actually the best kind of shielding you can make to protect yourself against gamma- or X-rays. It's even better than lead, since uranium has 92 protons in the nucleus, compared to only 82 in lead. (You could also shield with natural uranium, but since natural uranium has more of the uranium-235 isotope than depleted uranium, and 235 is more radioactive than 238 and DU, you would rather use DU than natural uranium)
9. uranium (thus also depleted uranium) is a heavy metal, like lead, and this fact is the main reason it's not very healthy - not the radioactivity. You take natural uranium, and make into something that's about half as radioactive as it already was. It's not like you make a new radioactive material.
10. depleted uranium is also used as counterweight in airplanes like the Boeing-747; that carries around 250 kg of DU. I didn't know this until I started reading all I could find about the 1977 Tenerifie aircrash. I definitely learned something new, and now I want to learn more about counterweights 🙂
Luckily we got home safely after a great week of vacation, and I think I'm ready for a couple of very busy months. I've made a nice plan for this week, that includes talking about cold fusion on the radio tomorrow. Sorry I haven't been "here" last week, but I needed the vacation, and Alexandra needed her mother to be there, on vacation with her, and not on the cell or the computer all the time...:)

Friday Facts on a Sunday again - I'm starting to think I should just call it "facts"... Well, I'll try a little bit more, and see if I manage to get back on track with actually having FRIDAY facts on FRIDAYS again 😛
Anyway: this day started super super early; the alarm rung at 3:15, and at 7 we took off from Gardermoen airport, with Tenerife as our destination. I feel almost silly to have one week of vacation now, just after Easter, but it just had to be this way this time. Since we've been flying today, I thought the perfect theme for facts is cosmic radiation...:
1. cosmic radiation is a mixture of particles, like protons, neutrons, alphas, and electrons, and gamma- and X-rays. Most of it comes from outside our solar system, and a small part comes from the sun
2. when the solar activity is high, there is more radiation coming towards the earth (since the small part that comes from the sun becomes larger 🙂 )
3. our atmosphere works as a radiation shield for us; the cosmic rays come into it and interact, so that the rays/particles are either stopped completely, or at least lose their energy - which is a good thing for us here on Earth 🙂
4. the intensity of the cosmic radiation changes with altitude - which is sort of logic, since you move “closer to space” if you climb up on a high mountain, or you get on a plane, so that there’s less atmosphere to stop whatever rays that are coming towards us from outer space. When you go from sea level to around 1600 meters above sea level, the intensity of the cosmic radiation doubles. If you go to 5000 meters, the radiation is 8 to 10 times more intense than at sea level, and if you’re on a plane, at 8500 meters above sea level,  the level of radiation is 40 times higher than at the ground
5. pilots and air attendants are actually classified as radiation workers; even though I work in a nuclear physics lab, with the cyclotron (that produces ionizing radiation), and with actual radioactive substances, they receive a higher dose each year than I have ever received
6. there are four factors that decides how big of a dose you will receive: solar activity (more activity from the sun means more particles bombarding Earth), time (if you spend a lot of time in a plane, 10 000 meters above sea level, you will of course receive a larger dose than if you spend little time at these altitudes), altitude (the higher you go, the more radiation - see point number 4), latitude (the shielding is better around equator that towards the poles - at typical flight altitudes, the difference between the cosmic ray dose rates at the equator and high latitudes is about a factor of two to three)
7. normal, average annul dose from cosmic radiation is 0.35 milli Sievert (this is not much - in Norway, we receive around 2 milli Sivert from radon gas, 0.6 from medical use, 0.55 from external gamma radiation, 0.35 from internal gamma radiation, and then just 0.35 from cosmic 😉 )
8. the annual dose for pilots and air attendants is somewhere between 2 and 3 milli Sivert per year; which means that if you work on a plane, your dose is well below the normal annual limit for radiation workers that is 20 milli Sievert, but more than the general public is allowed to receive (still not much - it just means that the dose limits for “members of the public” is really really strict 😉 )
9. the dose you receive on a long distance flight (like Oslo-Tokyo back and forth) is four times bigger than the total dose the average Norwegian receives from fallout from the Chernobyl accident in April 1986, from that year and 50 years into the future. (This does NOT mean that you receive a big dose from being on a plane, but that the dose we get from Chernobyl in Norway is small.)
10. flying to the Mediterranean will get you an extra dose from cosmic radiation, equal to one meal of reindeer meat with a radioactivity of 10 000 Bq/kg. A pilot receives something equal to 100 such meals every year. If you have been scared into believing it's dangerous to eat Norwegian reindeer meat because of the radioactive downfall from Chernobyl 30 years ago, then you definitely shouldn't fly… (hint: fly as much as you want to, and eat the reindeer you want to - it's not doses that are dangerous to you; they might even be positive 🙂 )
Back and forth to Tenerife is about 13 hours on a plane, in roughly 10 000 meters altitude. This means that when we get back to Oslo, we've all received an extra dose of radiation of 0.065 milli Sieverts (this is just a very rough average estimate, since I haven’t really taken into account where we are flying, or where in it 11-year cycle the sun is just now - I actually have no idea of that , but maybe some of you guys know? 😛 ).
PS: I didn't manage all my goals, but at least I did "finish" my article draft, and I sent it off to supervisor Jon on Friday. Also, I'm planning on plotting some stuff while I'm here - not exactly working, but sort of maintenance 😉

## Ten facts about neutrinos 2

Friday again - facts again <3
You know the drill, say no more:

1. a neutrino is a en elementary particle
2. a neutrino is not a neutron - neutrons are made up of quarks, and are thus not elementary particles
3. there are three types of neutrinos: they're called electron neutrino, muon neutrino, and tau neutrino (they all also have an antiparticle)
4. the name neutrino actually means "little neutron", but I have to tell that story another time...;) (In short: Pauli proposed that there should be a particle called a neutron, before the actual neutron was discovered. Then, what we know today as a neutron was discovered before the neutrino, and by that time the term neutron was taken, and this particle became a neutrino).
5. neutrinos don't have any electric charge (so they are not at all affected by the electromagnetic force), and they're almost massless - but only almost...! They do have a tiny tiny tiny mass: the heaviest one is more than 4 million times lighter than the electron (the next lightest particle). Since they are so light, neutrinos move at a speed more than 80% of the speed of light at room temperature
6. neutrinos are created in radioactive decay (like beta-decay), nuclear reactions (like in a reactor when a heavy nucleus fission, or in the sun when light nuclei fuse), when cosmic rays hit atoms, and in supernovae. Most of the neutrinos here on Earth come from the nuclear reactions that take place in the Sun <3
7. every second, a trillion trillion neutrinos pass through your body, and since they do have (a tiiiiiny) mass, this means that there's a constant flow of matter through your body ALL THE TIME. Since their mass is so small, they don't add up to much mass - about 0.0000000000001 kg of neutrinos will pass through your body in a lifetime 😀 (If you add up the mass of all neutrinos that have passed through every single person who ever lived, over everyone's total lifetime, the sum is 0.15 kg)
8. neutrinos are extremely difficult to detect, so you need really huge detectors if you want to try... For example, the OPERA detector (a good neutrino detector) consists of 1000 tonnes of mass to try to catch a neutrino, but even if this detector was a block of lead a light-year in length, you'd only have a 50% chance of stopping a neutrino!
9. they are often called ghost particles, since they can actually change from being one kind to being another - an electron neutrino changing into being a muon neutrino changing into being a tau neutrino (this is weird: like if you went into a Mercedes and drove for a while, and then suddenly the car changed into being a BMW, and then when you arrived at your destination you were driving and Audi. W. E. I. R. D.)
10. in 2011 neutrinos were sort of detected to move faster than light - which shouldn't be possible. Of course it turned out to be an experimental mistake, and we are still very very certain that Einstein's theory of special relativity is true <3

Bonus facts: According to my colleague, Cecilie, neutrinos fabulous 😀 Happy Friday!

## Friday FACTS: Black holes

Happy Friday!

I'm at Anders (not my Anders, but my good friend) and Charlotte's fantastic cabin at Nordseter (Sjusjøen). We just had a nice dinner, we're drinking wine, talking, and there's a fire in the fireplace <3 I'm about to put away my laptop for the weekend, but before I do that, what could fit better now than ten facts about black holes? Close to nothing 😀 Here goes:
1. Black holes are called “black” because they swallow all light, and no light (or anything) can ever escape it
3. Black holes are super super super dense, and NOTHING have a higher density than a black hole
4. It's not really like what people think of as a hole, but maybe more like what we would normally think of as a sphere. But then again, it has the "traplike" properties of a hole (since you can fall into is, as if it was a hole in the ground), so you can probably think about it as a three dimensional hole 😉
5. A black hole with the size of a sugar cube weighs the same as the entire earth: 1000000000000000000000000kg (24 zeros!) - 1 septillion kilos 😀
6. We know nothing about what happens inside black holes
7. If a black hole came into our solar system it would swallow the earth. This is extremely unlikely, but it’s still more likely than for example winning the lottery ten times in a row (but less likely than being struck by lightening)
8. Black holes have a horizon (or really an "event horizon", which is the boarder of the black hole) where time stands still (at least it looks like it’s standing still if we are looking at a person who is falling into it) this horizon is the point of no return, where it's absolutely impossible to escape falling into the hole. It's really just like as a a clock runs a bit slower closer to sea level than up on a space station, a clock run really slow near black holes, and this all have to do with gravity
9. If you fall into a black hole you would be stretched (to death) like spaghetti, since whatever part of your body that reaches the horizon first will feel soooo much more gravity (since the hole is so dense and heavy) than the rest of the body that's outside the horizon
10. When black holes collide, they make gravitational waves - which were discovered last Thursday!
By the way: today I managed to finally make this figure I was talking about yesterday, so then I'm one step closer to a new article. Next week I want to finish the rest of the figures to the article, and then I'm suddenly quite close to finishing the thing.
PS. This week I just have to give you a sort of fact number 11: we don't believe that inside black holes you find book shelves. (Hint: "Interstellar")

## Fuel on a Friday – 10 Facts

I can’t believe it’s Friday already.
This week has just gone by so fast. It started with Alexandra still being sick on Monday, and then on Tuesday I went to Stavanger, and spent around 50 hours there - giving two talks, and talking to so many interesting people. (I think I’ll have to write about some of my thoughts about the Norwegian oil industry - just not right now.) Yesterday I got home, and the evening was spent with Anders; we shared a bottle of wine, he worked on his code and I scanned all my receipts from the trip, and sorted them into the right folders (not fun doing, but it feels GREAT when you’re done, especially when you realise you’ve spent roughly 9000NOK on travelling, that you of course want, and will get, back ;)). Then we made the working your ass off thai chili, and around that time I got a migraine…:/
However, today is Friday, and luckily I woke up this morning feeling great again - hopefully there'll be many months before I get another migraine attack!
So Friday is luckily NOT equal to migraine, but it IS equal to FACTS! It's finally time for ten Friday Facts about Fuel - nuclear fuel, of course:
1. the fuel in a nuclear power plant is placed inside the reactor core. Mostly all the fuel soaked in water because water is great for cooling the fuel, which is the same as removing the heat - which is exactly what we want; we want water to be heated so that we can produce steam and thus generate electricity with a turbine <3
2. we often call it "burning" the fuel, but it's no real burning going on - the fuel is the place where the fission chain reaction happens (the energy from nuclear power comes from fission of nuclei inside the fuel 🙂 ), so when I talk about (nuclear) fuel I mean material where there’s a chain reaction going on.
3. nuclear fuel is made out of slightly radioactive elements; it can either be uranium, plutonium, or thorium
4. a small part of the fuel has to be fissile; meaning it has to have a really big chance of splitting if it's hit by a neutron. The fissile material can be either uranium-233, uranium-235, or plutonium-239
5. thorium is NOT fissile, so thorium must be mixed with something that is. This means that in thorium based fuels it is actually not the nuclei of the thorium atoms itself that fissions - thorium is first transformed into uranium-233, and then this uranium nucleus is the one that fissions and releases energy 😀
6. the fissile part of the fuel is typically just 5% of the total of the fuel. The rest of the fuel (so, the majority of the fuel, really) is either thorium-232 or uranium-238.
7. the "flame" in nuclear fuel is the neutron. There is of course no real flame, and there is also no burning (see point number 2.), but I think that calling the neutron "the flame" is a nice analogy, since the neutron is what makes the nucleus fission and then release all the energy <3
8. the most common nuclear fuel is called UOX, which is for uranium oxide, meaning that it’s not pure metallic uranium (uranium as an element is a metal), but uranium and oxygen ( the oxides are used rather than the metals themselves because the oxide melting point is much higher than that of the metal and because it cannot actually burn, since it's already in the oxidized state.)
9. used fuel can (and should, in my opinion!) be recycled, since it has a lot of material that is really useful (actually: typically only half a percent of all the fuel fissions during the years it's in the reactor, so if you throw away all that's left after a couple of years, you throw away A LOT of resources). If you recycle these materials - which can be uranium-235 that just hasn't fissioned yet, or plutonium-239 that has been made during the time the fuel was in the reactor - you have to mix them with fresh fissile material, and when you do this the fuel is called MOX. MOX is short for Mixed Oxides 😀
10. if you get really got at recycling, and you have the kind of reactors that are optimized for this type of MOX fuel (see point number 9.), you can actually end up getting 200 times more energy from the fuel than you normally get today!
- my fuel when I got to Stavanger airport yesterday: Chablis and Cæsar salad - as I started going through all the receipts (a lot!) rom just two days travelling -