山形第一天

Last time I visited Osaka, I made a conclusion that Japanese girls are not that pretty. They are merely cute, but not pretty. This fact really disappointed me since I had always expected that there should be many beautiful girls in Japan because they are usually pretty in Japanese drama.

But this time in Tokyo, I found these Japanese dramas did not lie. 

In Tokyo station, beautiful office ladies are so many. Maybe the most pretty ones are always gathered in the largest city. Just like the situation in Taipei of Taiwan. The pretty comes and goes. I really want to enjoy appreciating them but I can't do that too apparently. Because my parents are with me. I better be a good boy XD.

And I think this is the most important thing of the day.

Way back home

As I had expected, it's a terribly long trip home.

Getting up at eight, I went to Illini terminals at nine to take Amtrak train. To my disappointment, the train delayed for one hour. Not until today, I have seen the amtrak as the most reliable transportation to Chicago( I wondered if there is an grammar error of this sentence). This reminded me the rail trains in Taiwan which delay all the time. I wondered if I could ask for a ticket fee return.

And then, I took CTA subway to O'Hare airport. I don't know it's because of my unluckiness or what, the train stopped after one or two stops and all passengers were requested to take off. And after several minuets, all passengers were asked to take on the very same train again. Thank god I had pretty adequate buffer for transferring.

With two McDonald's meals for lunch and dinner, I found I always choose McDonald's in airport.

And now I am in LA airport. This is the most uncomfortable airport I have ever been in USA. It's crowded. Many places are under refurnishing or something( or supposed to be?). It's dark in the check-in hall and , especially, in the food court.

Finally, I were home. To my curiosity, I did not feel very excited. Further more, the humid and warm air made me uncomfortable. Maybe I am really not a homesick type of person I think.

class review NPRE 441 5/4

Regulations
ICRP 26/30 Philosophy( dose equivalent (rem or Sv) and effective dose equivalent,Stochastic and Nonstochastic effect.)

Because different radiations cause different biological effect, so we define:
dose equivalent is equal to dose by quality factor.

Because different tissues respond differently to radiations, so we define:
effective dose equivalent is equal to dose equivalent by tissue weighting factor W(tissue). It only applies to stochastic case.

For nonstochastic case, we consider a 50 year organ dose.
For stochastic case, we consider doses upon whole body.

we also have limitation on intake dose( also stochastic and non-stochastic).

NPRE 441 5/1

Photon shielding:

Secondary protection barrier( for scattered photons and leakage radiation), depending on ratio of scattering to incident radiation scattering field size, exposure rate on scatterer....

Distance between "source and scatterer" and "scatterer and objective place" are related to allowable value as well as occupancy factor and others.

Eventually, I want to find the required barrier thickness. Usually we would find K or B, attenuation factor) first, then we can use some table or figure to find the corresponding required wall thickness.

Beta ray shielding:

Gotta consider both electrons  and bremsstrahlung radiation. To calculate the bremsstrahlung part, we first find the fraction of energy emitted as bremsstrahlung. And then to find the required thickness of wall. 

Neutron shielding:

For fast neutron.

Use table 9.5, we could find the relation of neutron energy and neutron flux that cause a 0.01 Sv/h.

Once we know the attenuation cross section, we can know the flux distribution of neutron in the wall. At the end point of wall, the flux of neutron should equal the required value. This is, we could find the required wall thickness.

For thermal neutron.

Gotta consider gamma capture reaction. Usually, we assume a uniformly distributed gamma source. Then we have equation to fine the dose rate on the surface of the sphere. 

So, we have dose rate from fast and thermal neutrons and gamma rays. One way to reduce gamma ray radiation, we could add some lower energy emitter like boron(0,48Mev).

Spring is coming

When flower blooms, the spring is coming.
I came to USA in summer and now it's spring.
So, I have experienced all of four seasons in America.

This is photo I took this afternoon.

This is in summer, the first day I came to UIUC.

This is in fall.

This is in winter

NPRE 441 4/29

When it comes to photons radiation protection, we should not only consider the originally incident photos but also should take care of the scattered photons and characteristic x-rays that follow because these following photons contribute to the dose as well. A build up factor is called for counting this fact.

Build up factor depends on (1)source (photons) energy (2)the distance traveled and (3)the nature of the medium. With build up factor, we could calculate the dose more precisely.

In order to satisfy the Requirements for structural shielding for X-ray facilities, we consider the following factors. (1)the maximum voltage that X-ray tube is used. This is related to the incident photos energy. (2)maximum current(mA) of beam current, which relate to flux of radiation. (3)work load of the X-ray tube. (4)the use factor. The fraction of workload that the beam is pointed directly to. (5)the occupancy factor.

class review NPRE 455 4/28

By operating integration of energy over E_g to E_g-1 on energy dependent neutron diffusion equation, we can get definitions of some group constant like group absorption cross section, group scattering cross section weighed by flux.

For diffusion coefficient, it's weighed by gradient of flux, not flux itself. It is reasonable because the diffusion depends on gradient of flux, not flux.

It's interesting that we have flux dependence( or gradient of flux) , which we have not known yet, in the definition of group constants. This is called a recursive problem. To tackle this, we assume the spatial part and energy part of flux is separable. And then, we further assume that we know the energy dependence. For example, we assume a Maxwellian-Boltzmann distribution for thermal neutrons.

Since the difficulty of group parameter constants are already solved, we can easily write down the two group diffusion equation. What following is similar in one group. We will have two kind of problems, source problems and criticality problems.