试题与答案

放射治疗中X线半价层用于表达() A.X射线的强度 B.X射线的能谱 C.X射线的穿

题型:单项选择题

题目:

放射治疗中X线半价层用于表达()

A.X射线的强度

B.X射线的能谱

C.X射线的穿透能力

D.X射线的平均能量

E.X射线的百分深度剂量

答案:

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(1)镭核衰变方程为: 22688Ra→ 22286Ra+ 42He(2)镭核衰变放出α粒子和氡核,分别在磁场中做匀速圆周运动,α粒子射出y轴时平行于x轴,设α粒子在磁场中的轨道半径为R,其圆心位置如图d-1中O′点,有(l-R)2+(...

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题型:阅读理解

Bill Javis took over our village’s news-agency at a time of life when most of us only wanted to relax. He just thought he would like something but not too much to do, and the news-a­gency was ready-made. The business produced little enough for him, but Bill was a man who only wanted the simplicity and order and regularity of the job. He had been a long-serving sailor, and all his life had done everything by the clock.

Every day he opened his shop at 6:00 a. m. to catch the early trade; the papers arrived on his doorstep before that. Many of Bill’s customers were city workers, and the shop was convenient for the station. Business was tailing off by 10 o’clock, so at eleven sharp Bill closed for lunch. It was hard luck on anybody who wanted a paper or magazine in the after­noon, for most likely Bill would be down on the river bank, fishing, and his neatest competitor was five kilometers away. Sometimes in the afternoon-, the evening paper landed on the doorway, and at 4 o’ clock Bill reopened his shop. The evening rush lasted till seven, and it was worthwhile.

He lived in a flat above the ship, alone. Except in the very bad weather, you always knew where to find him in the af­ternoon, as I have said. Once, on a sunny afternoon, I walked home along the river bank from a shopping trip to the village. By my watch it was three minutes past four, so I was aston­ished to see Bill sitting there on his little chair with a line in the, water. He had no luck, I could, see, but he was making no effort to move. “What’s wrong, Bill?” I called out from the path.

For answer, he put a hand in his jacket and took out a big, golden object. For a moment I had no idea what it could be, and then it suddenly went off with a noise like a fire en­gine. Stopping the bell, Bill held the thing up and called back, "Ten to four, you see, and this is dead right. "

I had never known anyone carrying a brass alarm clock round with him before.

5. Bill Javis became a news-agent when ________.

A. he need the money.                        B. he decided to take things easy

C. he was quite an old man                 D. he gave up clock-repairing

6. Bill opened the shop so early in the day because ________.

A. he liked to do as much as possible before he went to work

B. the shop had to be open when the morning papers came

C. he was never sure of time

D. it was then that he did a lot of business

7. On that sunny afternoon, the writer was surprised when he saw Bill because ________.

A. he thought it was late for Bill to be still fishing

B. he thought Bill was ill, since he was not moving at all

C. Bill had not caught anything, and that seemed strange

D. Bill stayed in his flat

8. From the information given in the passage, who or what do you think was wrong?

A. The bell was; it must have gone off at the wrong time.

B. Bill was; he had dropped off to sleep.

C. The writer’s watch was fast.

D. Bill’s clock was wrong; it was old.

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