-
第一章
Our material world(
物质世界
) is
composed of many substances
distinguished(
区别
) by their
chemical, mechanical, and electrical
properties(
特性
). They are
found in nature in various
physical
states(
物理状态
)---the familiar
solid, liquid, and gas, along
with(
连同
) the ionic
等离子体
) However,
the apparent diversity(
多样性
)
of kinds and forms of material is
reduced by the knowledge that there are
only a little over 100 distinct chemical
elements(
元
素
) and
that the chemical and physical features of
substances depend merely on the strength of
force bonds(
结合
)
between atoms.
我们的物质世界
(
物质世界
)
是由许多物质
(
以区别区别被其化工、机
械、
、
电气性能
(
特性
)
。
他们是在大自然中找到的材料在不同的物理状态
(
物理状态
)
——而且熟悉
的固体、
液体和气体
,
随着
(
连同
)
离子“等离子体
”
(
等离子体
)
然而
,
明显的多样性
(
多样性
)
各类形式的资料将减少
知识只有一个小超过
100
种特定的化学元素
(
元素
),
化学和物理特征
的物质的力量仅仅看力债券
(
结合
)<
/p>
之
间的原子。
In turn(
依次
),
the distinctions between the elements of nature
arise from(
起于
) the number
and arrangement of basic particles(
基本粒子
)
—
elec
trons(
电子
),
protons(
质子
), and
neutrons(
中
子
). At
both the atomic and nuclear levels, the structure
of elements is determined by internal
forces and
energy(
内力和内能
).
1.1 FORCES AND ENERGY
（力和能量）反
过来
(
依次
),
区别自然元素
(
源自起于
)
电话号码和安排基本粒
子
)-electron
s
基本粒子
(
电子
),
质子
((
质子
),
和中子
(
中子
)
。在两个原子与核水平
,
结构是由元素的内力
和能量
(
内力和
内能
)
。
11
力量和能量
(
力和能量
*
If
the
specific
heat
of
iron
is
o
o
o
0.45J/g·<
/p>
C, how much energy is required to bring
0.5kg of iron from 0
C to 100
C?
如果的比
热铁变形、
0.45J /
g
·需要多少能量将铁
0.5kg
从<
/p>
0(oC)
到
100(oC)
吗
?
*
State
the
concept
of
temperature.
What's the difference between the
Celsius scale and Kelvin scale?
国家温度的概念
。有何区别式
温标摄氏度的规模和吗
?
*
Give some
examples of SI units?
1.6
SUMMARY
（概要）
*
Associated
with
each
basic
type
of
force is
an energy, which may be transformed to another
form for practical addition of
thermal
energy
to
a
substance
causes
an
increase
in
temperature,
the
measure
of
particle
omagnetic
radiation
arising
from
electrical
devices,
atoms
or
nuclei
may
be
considered
as
composed
of
waves
or
of
can
be
converted
into
energy
and
vice
versa
2
（反之亦然）
; according to Einstein's
formula E = mc
.The energy of nuclear
fission is millions
of
times
as
large
as
that
from
chemical
is
fundamental
to
all
of
man's
endeavors
and indeed to his
survival.
举些例子
SI
单位简介
(
概要
? 1.6)
与相关各基本类型的力量是一种力量
,
它可以被
转化为实际使用另一种
形式的热能。增加对某种物质的温度升高引起了一场的方法、质点
运动。电磁辐射引起原子或核设备、电
子可以被看作是由波或是的光子。物质可以转化为
能量
,
反之亦然
(
反之亦然
);
根据爱因斯坦的公式
E =
mc2
。这些能量的核子分裂在内也远在数百万倍大能
量从化学反应。我们的基本人的努力
,
也正是为了他的
性命
第二章
原子与原子核
2.1 ATOMIC
THEORY
（原子理论）
A
complete
understanding
of
the microscopic
structure
of
matter
(
物质微观结构
)
and
the
exact
nature
of
the
forces acting
(
作用力的准确性质
) is yet to
(
有待于
) be realized. However,
excellent models have been developed
to
predict behavior to
an adequate degree
of accuracy for
most
practical purposes.
These models
are descriptive
(
描述的
) or
mathematical often based on analogy
(
类推
) with large-scale
process, on experimental data
(
实验
数据
), or on
advanced theory.
1.
< br>对物质的微观结构和作用力的准确性质的完全认识仍有待于实现。
然而，
为了实际的用途，
能足够精确地预
知物质在微观
世界行为的模型已经被研究出来。这些模型是描述性的或数学的，基于对大尺度过程的类推、实验数据
或先进的理论。
The
most
elementary
concept
(
元素概念
)
is
that
matter
is
composed
of
individual
particles
(
单个粒子
)
–
atoms
–
that retain their identity
(
同一性
,
特性
) as elements in ordinary
physical and chemical interactions. Thus
a collection of helium atoms
(
氦原子
) that forms a gas has a
total weight that is the sum of the weights of the
individual
atoms.
Also, when two
elements
combine (
结合
) to form a
compound (
化合物
)
(e.g., if carbon atoms
(
碳
原子
) combine
with oxygen atoms (
氧原子
) to
form carbon monoxide molecules
(
一氧化碳分子
)), the total weight
of the new substance is the sum of the
origin elements.
2.
< br>公认的物质的概念是：
物质是由单个粒子——原子组成，
在普通的化学和物理反应中原子保持了元素的特性。
因此，因此一团由氦原子组成的气体
的重量就是其中每一个原子重量的总和。同样，当两种元素结合成化合物时（例
如：碳原
子与氧原子结合成一氧化碳分子。），新物质的总重量是原先的元素的质量之和。
There are more than l00 known elements.
Each is given an atomic number
(
原子序数
) in the periodic table
of
the elements (
元素周期表
)
–
examples are
hydrogen (H) l, helium (He) 2, oxygen (O) 8, and
uranium (U) 92. The
symbol
Z
is given to the atomic
number, which is also the number of electrons in
the atom and determines its
chemical
properties (
性质
).
The atomic weight
(
原子质量
)
M
is the weight in grams of
a definite (
明确的
) number of
atoms, 6.02
?
10
,
which is A
vogadro’s
number
(
阿佛伽德罗常数
),
N
a
.
3.
有超过
100
种的已知元素。每种元素在元素周期表中都有一个给定的原子序数。例如氢（
H
）
1
，氦（
He
）
2
，
23
23
23
氧
（
O
）
8
以及
铀（
U
）
92
。
符
号
Z
表
示原
子序
数，这
也
正是
决定
着原
子化
学性质
的<
/p>
原子
中电
子的
数
目
。
原子量
M
（单位：克）是
6.02
?
10
个原子的质量之和。
6.02
?
10
就是阿佛伽德罗常数，用
N
a
来表示。
?
We can easily find the
number of atoms per cubic centimeter
(
每立方厘米
) in a substance if
its density
?
N<
/p>
?
N
a
in
grams per cubic centimeter is known. This
procedure (
程序
,
手续
) can be expressed as a
convenient (
便利的
)
formula for finding
N
, the number per cubic
centimeter for any material
如果每立方厘米内的物质密度
?
已知，我们就可以很容易地求
出每立方厘米中原子的个数。任何物质中每立方厘米的
原子数都法可以方便的用这个公式
算出。
2.2 GASES
(
气体
)
N
?
M
?
M
N
a
Substances in the
gaseous state (
气态
) are
described approximately by the perfect gas law
理想气体规律
(
方
程
), relating pressure, volume, and
absolute temperature (
绝对温度
),
pV=nkT.
An increase in the
temperature of the gas due to heating causes
greater molecular motion, which results in
an increase of particle bombardment (n
炮击；轰击
) of a container wall
and thus of pressure on the wall.
The
particles
of
gas,
each
of
mass
m
,
have
a
variety
of(
多种的
)
speeds
v
in
accord
with
与??一致
Ma
xwell’s
gas theory
(
麦克斯韦气体理论
) as shown in Fig.
2.1.
4.
气态的物质可以用与
压力、体积和绝对温度有关的理想气体规律方程
pV=nkT
来
近似地描述。温度上升将引
起分子运动的加剧——从而引起粒子对容器内壁的碰撞的增加
而导致其压力的增大。每种质量（
m
）的气体粒子具有的
不同速度与图
2.1
所示的麦克斯韦理论一致
。
The most
probable speed(
最概然速率
), at
the peak of Maxwellian distribution
(
麦克斯韦分布
) , is dependent
on temperature according to the
relation (
关系式)??.
The kinetic theory of gas (
气体动力学
) provides a basis for
calculating properties such as the specific
heat (
比热
).
Using the fact from Chapter l that the
average energy of gas molecules is proportional
(
成比例的
) to the
3
temperature,
, we can deduce (
推想
), that
the specific heat of a gas consisting only of
atoms
E
?
kT
is
, where
m
is the mass of one
atom.
c
?
k
m
5.
从麦克斯韦分布图上
可以看到，
在其峰值处出现的气体粒子的最概然速率，
按照这个
关系式??，
是与温度
3
2
3
2
2
紧密相关的。气体
动力学为计算诸如比热之类的一些性质提供了基础。用第一章中气体分子的平均能量正比于温度的
3
，在公式中
m
是一个原子的
质量。
事实，
E
?
kT
，我们可
以推断出单元子气体的比热
c
?
k
m
2.3 THE
ATOM AND
LIGHT(
原子与光
)
2
Until
the
20th
century
the
internal
structure
of
atoms
was
unknown,
but
it
was
believed
that
electric
charge
(
电荷
)
and
mass
were
uniform
(
统一的
).
Rutherfor
performed
(
执行
)
some
crucial
(
至关紧要的
)
experiments
in
which
gold
atoms
were
bombarded
by
charged
particles.
He
deduced
(
推断
)in
1911
that
most
of
the
mass
and
positive
charge
（正电荷）
of an
atom were concentrated (
集中的
)
in a nucleus of radius only about l0
times that of the atom,
and thus
occupying a volume of about 10
times
that of the atom. The new view of atoms paved the
way for (
为?
铺平道路
)
Bohr to find an explanation for the production of
light.
6.
直到
20
世纪，原子的内部结构仍然是未知的，但是人们确信核电荷数与原子质
量是相同的。卢瑟福进行了
5
l5
-
l5
-5
一些重要的实验，包括用带电粒子轰击金原子。他在<
/p>
1911
年推断出：原子的质量和正电荷都集中在半径为
l0
分之一
的原子核，占原子体积的
10
分之一。关于原子的新观点为波尔解释光的产生铺平了道路。
The
measured
(
有规则的
)
distribution
of
light
among
the
different
wavelengths
(
波长
)
at
a
certain
temperature
can be explained
by the assumption (
假设
) that
light is in the form of photons. These are
absorbed and emitted
with
definite
(
一定的
)
amounts
of
energy
E
that
are
proportional
to
the
frequency
?
,
according
to
E
=
hv
,
where
h
is
Planck’s constant
, 6.63
×
l0
-34
J-sec. For examp1e, the energy corresponding
to(
相当于
) a frequency of
5.l
×
l0
is
(6.63
×
l0
)
(5.l
×
10
) =
3.4
×
l0
J, which
is seen to be a very minute
(
微小的
) amount of energy.
7.
14
1
4
-34
14
-19
< br>在一定温度不同波长光的有规则分布可以用光是光子形式存在的假设来解释。
这要
吸收或者放出一定数量的
-34
-34
14
-19
能量
E
，根据公式
E
=
hv
（这里的
< br>h
表示普朗克常量
6.63
×<
/p>
l0
J-sec
），能量与频率成正比
。例如：频率为
5.l
×
l0
的光的能量相当于
(6.63
×
l0
)
×
(5.l
×
10
) =
3.4
×
l0
J
，这通常被看做是非常微小的能量。
He(Bohr) assumed that the atom consists
of a single electron moving at constant speed in a
circular orbit
about
a
nucleus
--the
proton--as
sketched
in
Fig.
2.2.
Each
particle
has
an
electric
charge
of
l.6
×
l0
coulombs,
but the proton has
a mass that is 1836 times that of the electron.
(Figure 2.2 )
8.
波尔假设
（氢）
原子由一个单独的电子绕着一个核子——质子，
以圆形轨道作恒定速度的移动——见图
2.2
< br>，
-l9
-l9
每个粒子有
l.6
×
l0
库伦
的电量，质子的质量是电子质量的
1836
倍。
The
energy
of
the
photon
hv
is
equal
to
the
difference
between
energies
in
the
two
orbits.
The
smallest
orbit
has a radius
R
1
= 0.53
×
l0
m, while the
others have radii increasing as the square
(
平方
) of integers (called
quantum numbers
(
量子数
)). Thus if
n
is l, 2, 3, . . . , the
radius of the
n
th orbit is
R
n
=
n
R
l
.
9.
光子的能量
hv
等于两个轨道能量之差。最小轨道半径为
R
1
= 0.53
×
l0
m
，其它轨道半径随着整数的平
2
-l
0
-l0
2
方（量子数）增长。因此，
如果
n
是
1
、
2
、
3
??，
那么第
n
层轨道半径应为
R
n
=
n
R
l
。
The energy of
the atom system when the electron is in the first
orbit is
E
1
=
-l3.5 eV, where the negative
sign
(
负号
)
means
that
energy
must
be
supplied
to
remove
the
electron
to
a
great
distance
and
leave
the
hydrogen
as a positive ion
(
阳离子
). The energy when the
electron is in the
n
th orbit
is
E
n
=
E
1
/n
. The various
discrete
(
不连续的
)
levels are sketched (
绘图
) in
Fig. 2.4.
10.
当电
子在第一个轨道时，原子系统的能量为
E
1
=
-l3.5
eV
，负号表示把电子移到一个较远的距离只剩下阳
离子时外界必须提供的
能量。电子处于
n
轨道时，能量为
E<
/p>
n
= E
1
/
n
，各种不连续的等级见图
2.4
。
The electronic
structure
of
the other
elements
is
described by the shell model
(
壳模型
),
in
which a
limited
number of electrons can occupy a given
orbit or shell. The atomic number
Z
is unique
(
独特的
) for each chemical
2
2
element, and represents
(
描绘
) both the number of
positive charges on the central massive
(
结实的
) nucleus of
the atom and the number of electrons in
orbits around the nucleus.
The
chemical behavior of elements is determined by the
number of electrons in the outermost
(
最外面的
) or
valence
(
原子价
) shell.
11.
其它元素的电子模型是用壳模
型来描述的，
一定限制数量的电子能够占据一个给定的轨道或壳层。
对每一个
化学元素，原子序数
Z
是
唯一的，它代表了原子中央结实核子的正电荷数以及围绕核子的轨道的电子数。最外层的电
子数或化合价层，决定了元素的化学性质。
2.4
LASER BEAMS(
激光束
)
Ordinary
light
as
in
the
visible
range
(
可见区
)
is
a
mixture
of
many
frequencies,
directions,
and
phases(
状
态
).
In
contrast,
light
from
a
laser
(“Light
Amplification
by
Stimulated
Emission
of
Radiation”
)
consists
of a
direct beam of one color and with the waves in
step (
相干
).
Lasers
can be constructed from several materials. The
original one (1960) was the crystalline gem ruby
(
水晶红宝石
). Others
use gases such as a helium-neon(
氦
-
氖
) mixture, or liquids
with dye in them, or
semiconductors(
半导体
).
Lasers are
widely used where an intense
(
强烈的
) well-directed beam is
required, as in metal cutting
and
welding, eye surgery
(
眼部外科手术
) and other medical
applications, and accurate surveying and range
finding(
精确的测量和测距
).
Newer
applications
are
noise-free
phonographs
(
无噪声留声机
,
电唱机
),
holograms
(
全息摄影
) ( 3D
images), and communication between airplane and
submarine (
潜水艇
).
12.
普通光，例如可见光区，是由
许多频率、方向和状态不同的光混合而成的。相对的是，激光是由同一方向的
单一颜色的
光束组成，而且是相干波。激光的产生可以来源于多种材料。最早的一种是
1960
年使用的水晶红宝石。其
它的还可以用气体（如氦
< br>-
氖混合气体），或者染料液体，以及半导体来做激光发生器。激光可以被广泛地
应用于需要
良好方向性光
/
热束的地方
，例如金属的切割与焊接，眼部外科手术及它医疗应用还有精确的测量和测距上。新出现的
应用还包括无噪声留声机、全息摄影以及飞机和潜艇的通讯。
Most
elements
are
composed
of
particles
of
different
weight,
called
isotopes
(
同位素
).
For
instance,
hydrogen
has three isotopes
of weights in proportion l, 2, and 3 -ordinary
hydrogen, heavy hydrogen
(deuterium
氘
), and
tritium(
氚
).
The
nucleus
of
ordinary
hydrogen
is
the
positively
charged
proton(
带正电的质子
);
the
deuteron(
氘核
)consists
of
a
proton
plus
a
neutron,
a
neutral
particle(
中性粒子
)
of
weight
very
close
to
that
of
the
proton;
the
triton(
氚
核
) contains a proton plus two
neutrons.
13.
大多数元素是由重量不同的粒子构成，我们称之为
“同位素”
。
例如：氢元素有三种同位素，
原子量比为
1
：
2
：
3
——普通氢（氕）、重氢（氘）以及超重氢
(
氚
)
。普通氢的原子核是一个带正电的
质子；氘核由一个质子加一个
重量十分接近质子的中性粒子（中子）组成；氚核则是由一
个质子加两个中子组成。
2.6 SIZES AND
MASSES OF NUCLEI
(
核的大小和质量
)
The dimensions
(
尺寸
) of nuclei
(nucleus
的复数
) are found to be
very much smaller than those of atoms.
Since the
proton
weight
is much larger than
the electron weight, the
nucleus is
extremely dense. The
nuclei
of
other
isotopes
may
be
viewed
as
closely
packed
particles
of
matter-neutrons
and
protons-forming
a
sphere
whose
volume,
4/3
?
R
, depends on
A
, the number of nucleons. A
useful rule of thumb
(
凭经验的方法
) to calculate radii
of nuclei is R(cm) = l.4 x
10
1
-
l3
3
A
.
12
2
l/3
The
masses
of
atoms,
labeled
M
,
are
compared
on
a
scale
in
which
an
isotope
of
carbon
C
has
a
mass
of
exactly
12. For
1
H, the atomic mass is
M
= 1.007825, for
1
H,
M
= 2.0l4102, and so on. The atomic mass
of the proton is
1.007277, of the
neutron l.008665, the difference being only about
0.1%. The mass of the electron on this scale
is 0.000549.
14.
原子核的尺寸相较原子来说非常小。由于质子的重量远大于电子，所以，原子核的密度非
常大。
其它同位素的原子核可以被看做是由紧紧压在一起的粒
子（中子和质子）构成的一个体积（
4/3
?
< br>R
）由核子数
A
决定
的球体。根据经验可以算出原子核的半径为
R(cm) = l.4 x
10
12
1
-
l3
3
A
l/3
。原子的质量（记为
M
）是一个与有着精确质量
2
数
12
的同位素
C
的质量的比值。例如
1
H
原子的质量
M
= 1.00782
5
，
1
H
原子
的质量
M
= 2.0l4102
??质子的原子
量为
1.007277
，中子的为
l.008665
，两者相差只有大约
0.1%
。在这种比例下
电子的质量为
0.000549
。
The atomic mass unit (amu)
(
原子质量单位
), as 1/12 the mass
of
C, corresponds to
(
相应于
) an actual mass
of l.66
?
l0
g. To verify (
校验) this,
merely divide l g by Avogadro’s number 6.02
?
l0
. It is easy
to show
that 1 amu
is also
equivalent
to 931
MeV. We
calculate the actual
masses
of atoms and
nuclei by multiplying
(
乘
)
the mass in
atomic mass units by the mass of 1 amu.
15.
原子质量单位
amu
表示一个
C
原子质量的
1/12
，相应于实际的质量是
l.6
6
?
l0
克。要校验这个值，只
需用
1
克除以阿伏伽德罗常数
6.02
?
l0
2.7 BINDING
ENERGY(
结合能
)
The
force
of
electrostatic
repulsion
(
静电排斥
)
between
like
charges
(
同种电荷
),
which
varies
inversely
(
相
反地
)
as the square of their separation, would be
expected to be so large nuclei could not be
formed. The fact
that they do exist is
evidence (
证明
) there is an
even larger force of attraction. The nuclear force
(
核力
) is
of
very
short
range,
as
we
can
deduce
from(
从?推论出
)
the
above
rule
of
thumb.
The
nuclear
force
acts
only
when
the nucleons are very close to each
other, and binds them into a compact structure
(
紧凑结构
). Associated with
the net force is a potential energy of
binding(
结合势能
).
16.
同种电荷之间的静电斥力随着
它们距离的平方成反比变化，
可以想见其会大到核子无法形成的地步。
< br>我们可
以凭经验推断出——核力的作用范围一定非常短的。只有当核子之间靠得很
近时，核力才起作用将它们紧密地结合在
一起。与这种合力相关的是结合势能。
To disrupt
(
使分裂
)
a nucleus
and
separate it into
its component
(
组成的
)
nucleons,
energy must
be supplied
from
the
outside.
Recalling
Einstein's
relation
between
mass
and
energy,
this
is
the
same
as
saying
that
a
given
nucleus is lighter
than
the
sum of its
separate
nucleons, the
difference
being the binding
mass-energy.
Let the
mass of an atom including nucleus and
external electrons be
M
and
let
m
n and
m
H be the masses of the
neutron
and the proton plus matching
electron (
匹配电子
). Then the
binding energy is
B = total mass of
separate particles - mass of the atom
or
B =
Nm
n
+ Z m
H
- M.
17.
要想把一个原子核分裂成组成
它的核子，
必须从外部给它一定的能量。
回想爱因斯坦质能方程
，
也可以换个
说法：一个的原子核要比组成它的所有核子的质量
之和要轻，而这个差值就是其结合能。
CHAPTER 3
Radioactivity
（放射性）
Many
naturally
occurring
and
man-made
isotopes
have
the
property
of
radioactivity(
放射性
),
which
is the
spontaneous(
自发的
)
disintegration (decay) (
衰变
)
of the nucleus with the emission of a particle.
The process takes place in minerals
(
矿物质
) of the ground, in
fibers (
纤维
) of plants, in
tissues (
组
织
) of
animals, and in the air and water, all of which
contain traces (
痕迹
,
微量
) of radioactive elements.
< br>1
、许多天然和人造同位素都具有放射性，这是核子发射出粒子的自发衰变。这个
过程发生在地表的矿物中、植物的纤
维中、动物的组织中、空气和水中，所有的一切都存
在着放射性元素的痕迹（放射性元素无处不在）。
3.1
RADIOACTIVE DECAY
（放射性衰变
）
Many elements that are found in nature
or man-made are
radioactive(
放射性的
), emitting
alpha
partic1es(
?
),
beta particles (
?
)
(including electron or negatron and positron),
neutrinos(
中微子
) , and
gamma rays(
?
).
Some examples are as following:
2
、许多天然和人造的元素都具有放射性，能发射阿尔法
(
?
)
粒子、贝塔
(
?
)
粒子（包括电子或者负电子和正电子）、中
微子和伽马
(
?
)<
/p>
射线。举例如下：??
3.2 THE
DECAY LAW(
衰变规律
)
The
rate
at
which
a
radioactive
substance
disintegrates
(and
thus
the
rate
of
release
of
particles)
depends
on
the
isotopic
species(
种类，核素
),
but
there
is
a
definite
(
一定的)
“decay
law”
that
governs
(管
理
,
支配
) the process. In a given time period, say one
second, each nucleus of a given isotopic species
has
the same chance of decay. If we
were able to watch one nucleus, it might decay in
the next instant
(
立即
的
), or a few
days later, or even hundreds of years later.
23
12
-24
2
-24
23
12
。很明显：
1 amu
也相当于
931
兆电子伏
(E = mc
)
。我们
可以用原子质量
乘以每一原子质量单位的质量来计算原子和核子的确切质量。
3
、放射性物质的衰
变率（粒子释放率）决定于同位素的种类，但是也确定存在着“衰变规律”支配着这个过程。在一
个给定的时间段，
譬如一秒，给定同位素的每个核子都具有相同的衰变几率。如
果我们能对某个核子进行观察的话，
它可能
在下一个瞬间发生衰
变，也有可能在几天甚至几百年以后才发生衰变。
Such
statistical(
统计学的
) behavior
is described by a constant property of the atom
called
half-life
(
半衰期
). This time
interval(
间隔
), symbolized by
t
H
is the time required for
half of the nuclei
to decay, leaving
half of them intact(
完整无缺的
).
We should like to know how many nuclei of a
radioactive
species remain at any time.
If we start at time zero with
N
0
nuclei, after a length of
time t
H
there will
be N
0
/2; by the
time 2t
H
has elapsed
(
流逝
), there will be
N
0
/4; etc. A graph of the
number of nuclei as a
function of time
is shown in Fig. 3.l.
4
、这种统
计学上的表现可以用原子的一个恒定属性——半衰期来表示。这个用
t
< br>H
表示的时间间隔指的是一半的核子发
生衰变所需要的
时间。我们想知道在任意时间放射性核素的剩余量。如果在一开始有
N
< br>0
个核子，那么经过了
t
H<
/p>
的时间以后，
核子还剩下
N
0
/2
个；经过
2t
H
时，核子还剩下
N
0
/4
个??核子数与时间的函数关系可以用图
3.l
来表示。
(
For
any time t on the curve
(
曲线图
), the ratio of the
number of nuclei present to the initial
初
始
的
)
t
number
t
H
is
given
by
N
?
1
?
?
< br>?
?
N
0
?
2
?
Half-lives
range from very small fractions
(
小部分
,
片断
) of a second to billions
of (
数十亿
) years, with
each radioactive isotope
(
放射性同位素
) having a definite
half-life.
5
、曲线上任一时刻
t
，当前的核子数与初始的核子数的比率如下式表示：
半衰期从零点几秒到数十亿年不等，每种放射性同位素都有一个确定的半衰期。
N
?
1
?
?
?
< br>?
N
0
?
2
?
t
t
H
The
formula
for
N/N
0
is
not
very
convenient
for
calculations
except
when
t
is
some
integer
multiple
(
同
意
义
的
)
exponential
(
指
数
of
t
H
. Defining the decay
constant
?
(lambda), as the
chance of decay of a given nucleus each second, an
equivalent
We find that
?
=
0.693/t
H
几率，可以得到一个意义相同的指数方程：
我们可以得出
?
= 0.693/t
H
。
N
?
?
t
formu
la
的
?
e
)
N
0
for
decay
is
6
、
N/N0
这个公式并十分便于计算，除非
t
是
t
H
的整数倍。衰变常数
?
的定义是：一个原子核在单位时
间内发生衰变的
t
N
?
e
?
?
N
0
The number of disintegrations per
second (dis/sec) of a radioisotope is called the
activity, A.
Since the decay constant
?
is the chance of decay
each second of one nucleus, for N nuclei the
activity
is the product
(
乘积
)A =
?
unit dis/sec is called
the becquerel (Bq), honoring the scientist who
discovered radioactivity
(
放射性活度
). Another older and
commonly used unit of activity is the curie (Ci)
named after the French scientists
Pierre and Marie Curie who studied radium
(
镭
). The curie is 3.7
?
10
dis/sec, which is an early measured
value of the activity per gram of radium.
< br>7
、放射性同位素每秒衰变的原子数称为活度（记作
A<
/p>
）。既然衰变常数
?
是核子每秒衰变的几
率，
N
个核子的活度是
乘积
A=
?
N
。单位
dis/sec
称为“贝克勒尔”（
Bq
），用来纪念这位发现放射性活度的科学家。另一个更早的曾被普遍使用
的放射性活度的单位是
“居里”
（
C
i
）
，
这是以研究镭的法国科学家皮埃
尔和玛丽·
居里的名字命名的。
1
居里
等于
3.7
?
10
贝克。
3.3
MEASUREMENT OF HALF-
LIFE(
半衰期的测量
)
Finding the half-life of an isotope
provides part of its identification
(
鉴定
), needed for
beneficial
use
or
for
protection
against
radiation
hazard.
Let
us
look
at
a
method
for
measuring
the
half-life
of
a
radioactive
substance.
As
in
Fig.
3.2,
a
detector
探测器
(that
counts
the
number
of
particles
striking
it ) is placed near the source of
radiation (
放射源
).
8
、为了有益的应用或者是为防止辐射危害而需鉴定放射性核素，而找出它的半衰期，则
可为鉴定同位素提供线索。让
我们来看看一种检测放射性物质半衰期的方法。
如图
3.2
所示，
一个探
测器
（统计击打到它上的粒子数）
放置在放射源的附
近。
From
the number of counts observed in a known short
time interval, the counting rate
(
计数率
)is
10
10
computed. It is proportional to the
rates of emission of particles or rays from the
sample and thus to the
activity A of
the source. The process is repeated after an
elapsed time for decay. The resulting values of
activity
are
plotted
on
semi-
log
graph
paper
(
半对数坐标纸
)
as
in
Fig.
3.3,
and
a
straight
line
drawn
through
the
observed points.
From
any
pairs
of
points
on the
line
?
and
t
H
=
0.693/
?
can
be
calculated (see Exercise
3-8).
9
、计数率可以通过一段
时间间隔内的计数计算出来。计数率与样本发射粒子或射线的速率成正比，也就是说与活度
A
成正比。
在衰变发生的一段时间内重复这个过程：
把活度的结果标记在如图
3.3
那样的半对数坐
标纸上，
然后画一条直线穿
过这些观察点。从直线上任意两个点
可以计算出
?
，这样，半衰期
t
H
=
0.693/
?
就求出来了。
The measurement of the
activity of a radioactive substance is complicated
by the presence
(
存
在
) of
background radiation (
本底辐射
),
which is due to cosmic rays
(
宇宙射线
) from outside the
earth or
from the decay of minerals in
materials of construction
(
建筑物
) or in the earth. It is
always necessary
to
measure
the
background
counts
(
本底计数
)
and
subtract
(
减去
)
them
from
those
observed
in
the
experiment.
10
、<
/p>
放射性物质活度的测量因
“本底辐射”
的
存在而变得复杂，这源于地球之外的宇宙射线或来自建材抑或土壤中的矿
石的衰变。我们
经常需要测量本底计数并把它们从实验观测计数中减去。
CHAPTER 4 Nuclear Processes
（核过程）
Nuclear reactions
(
核反应
)---those in which
atomic nuclei
participate
(
参与
) ---may take place
spontaneously
(
自然地
), as in radioactivity,
or may be
induced
(
感应
,
诱发
) by
bombardment
(
轰击
,
撞击
)
with
a
particle
or
ray.
Nuclear
reactions
are
much
more
energetic
(
精力充沛的
,
高能的
)
than
chemical
reactions,
but
they
obey
the
same
physical
laws---
conservation
(
守恒
)
of
momentum
(
动量
),
energy,
number
of
particles,
and charge.
1
、核反应（有原子核参与）可能会自然发生，如放射性，或可能被粒子或
射线轰击诱发。核反应比化学反应剧烈的多，
但它们遵守同样的物理定律
-----
动量、能量、粒子数、电荷守恒。
The number of possible
nuclear reactions is extremely large because there
are about 2000 known
isotopes
and
many
particles
that
can
either
be
projectiles
(
发射体
,
入射粒子
)
or
products
(
产物
)---photons,
electrons, protons, neutrons, alpha
particles, deuteron (
氘核
),
and heavy charged
particles(
重带电粒子
).
In this chapter we emphasize
(
强调
,
着重
) induced reactions,
especially those involving neutrons.
2<
/p>
、
可能发生核反应的数量是非常大的，
因
为有大概
2000
种已知的同位素以及许多粒子，
他们既可是发射体又可能是产
物
-------
光子、电子、质子、中子，
α
粒子，氘核，
重带电粒子。在这一章中我们强调辐射引发的反应，尤其是包含中子
的反应。
4.1 TRANSMUTATION OF
ELEMENTS
（元素的嬗变
）
The
conversion
of
one
element
into
another,
a
process
called
transmutation
(
变形
,
嬗变
),
was
first
achieved in 19l9 by
Rutherford in England. He bombarded nitrogen
(
氮
) atoms with alpha
particles from a
radioactive source to
produce an oxygen isotope and a proton. (Fig.4.1)
energy.
3
、一种元素转变成另一种的过程称为嬗变，
1919
在
英格兰被卢瑟福实现。他用放射源发出的
α
粒子轰击氮核产生了
一
种氧的同位素和一个质子。
由于核
子间的静电斥力，带正电的
α
粒子要进入氮核是困难的。除非<
/p>
α
粒子具有几兆电子伏的能量。
Nuclear
transmutations
can
also
be
achieved
by
charged
particles
that
are
electrically
accelerated
to high speeds.
4
、在电场中加速到高速的带电粒子也可以实现核嬗变。
Since the neutron
is a neutral (
中性的
) particle
it does not experience electrostatic repulsion
(
静电排斥
) and can
readily penetrate (
穿透
) a
target nucleus (
靶核
).
Neutrons are thus especially useful
as
projectiles
to
induce
reactions.
Several
examples
：
The
conversion
of
mercury
(
汞
)
into
gold,
the
alchemist
(
炼金术士
)'s dream,
is described by
It
is
difficult
for
the
positively
charged(
带正电子的
)
alpha
particle
to
enter
the
nitrogen
nucleus
because of the electrical forces
(
静电斥力
) between nuclei. The
alpha particle thus must have several MeV
5
、因为中子是中性的粒子，它不受
静电排斥所以能够轻易穿透靶核。中子作为入射粒子诱发的反应时非常有用的。这
里有几
个例子：炼金术士的梦想，把汞变成黄金，如下列化学式所示：
A
shorthand
(
简化
)
notation (
符号
)
is
used
to
represent
(
描绘
)
nuclear
reactions.
Let
an
incoming
particle
(
入射粒子
)
a
strike
a
target
nucleus
X
to
produce
a
residual
nucleus
(
余核
)
Y
and
an
outgoing
particle
(
出射粒子
) b, with
equation a + X = Y+ b. The reaction may be
abbreviated (
缩写
) X(a, b)Y. <
/p>
6
、我们可以用简化了的符号来描绘核反应。让一个入射粒子轰击
靶核
X
产生一个余核和一个出射粒子
b
，满足方程
a+X=Y+b
。这个反应
可缩写为
X(a,b)Y
。
The
interpretation
(
解释
) of nuclear
reactions often involves the concept of
compound nucleus
(
复合核
). This
intermediate
(
中间的
,
中级的
) stage is
formed by the combination of a projectile and
target
nucleus. It has extra energy of
excitation and breaks up into the outgoing
particle or ray and the residual
nucleus.
7
、核反应的解释
通常牵涉到复合核的概念。这个中间阶段是由一个入射粒子和靶核组合而成。它有更多的激发能把复
合核分解为出射粒子或射线和剩余核。
—————
————————————————————————————————————————
4.2 ENERGY AND MOMENTUM
CONSERVATION
（能量与动量守恒
）
units).
8
、质能守恒是任何
核反应必定遵守的规律。回顾第一章，我们知道：总质量是静止质量
m
< br>和动量
E
k
的总和。
The calculations
just completed tell us the total kinetic energy of
the product particles but do
not
reveal
(
显示
)
how much
each has, or what the speeds are. To find this
information we must apply
the
principle
of
conservation
of
momentum
(
动量守恒法则
).
Recall
that
the
linear
momentum
(
线动量
)
p
of
a
material
particle of mass
m
and speed
v
is
p=
mv
. This relation is correct in both
the
classical
(
经典的
)
and
relativistic
(
相对论的
)
senses.
The total momentum of the interacting particles
before and after the
collision is the
same.
9
、刚才的计算结果求出了产出粒子的总动量但并
没有算出其中每一个粒子的动量，或是速度。我们须用动量守恒法则
来算出这些数据。一
个质量为
m
速度为
v
< br>的物质粒子的线动量
p=mv
。这个关系在经典力学的和
相对论的领域都是适用的。
在碰撞前后，这些相互作用的粒子的总动量总是守恒的。
4.3 REACTION
RATES
（反应率
）
We
can perform
a set of
imaginary
experiments that will
clarify
(
阐明
) the idea of
cross section
2
The
conservation
of
mass-energy
is a firm
(
坚定的
,
严格的
)
requirement
for
any
nuclear
reaction.
Recall from
Chapter l that the total mass is the sum of the
rest mass
m
0
and
the kinetic energy
E
k
(in mass
(
截面
). Picture, as
in Fig. 4.2(a) a tube of
end
area
(
截面积
) 1
cm
containing only one target particle.
A single projectile is
injected
(
注入
)
parallel
to
(
平行于
) the tube
axis, but its exact location is not
specified. It is clear that the chance
of collision, labeled
?
(sigma) and called the
microscopic
cross
section
(
微观截面
), is the ratio of the
target area to the area of the tube, which is 1. <
/p>
10
、我们可以进行一套假想的实验来阐明截面的概念。如图
4.2
（
a
）一个
截面积为
1
cm
的试管仅含有一个靶
粒子。从
平行于试管的
X
轴注入一个入
射粒子，但它的准确位置是不确定的。很明显，一个入射粒子碰撞的几率，即微观截面（记为
σ
），等于靶面积与试管的截面积的比值。
In a time of one second,
the number of them (projectiles) that pass through
the target volume is
2
nv
, and since
the chance of collision (
碰撞
)
of each with one target atom is
?
, the number of
collisions
is
nvN
?
. We can thus
define the reaction rate
(
反应率
) per unit volume,
R =
nvN
?
1
1
、一秒钟的时间内，通过给靶区的入射粒子数是
nv
，一个靶原子的碰撞几率是
σ
，碰撞数是
nvN
σ
。我们可以定义
每单位体积内的反应率为
R =
nvN
?
When a particle such as a neutron
collides
with a target nucleus, there
is a certain
chance of each of several
reactions. The simplest is elastic scattering
(
弹性散射
), in which the neutron
is
visualized
(
想象
,
形象化
) as bouncing
(
弹跳
) off the nucleus and
moving
in a
new
direction with a
change
in
energy. Such a collision, governed by classical
physics (
经典物理
), is
predominant (
主要的
,
突出的
) in
light
elements.
12
、当一个粒子如中子与靶核相撞，
有一定的几率发生几种反应中的一种。最简单的是弹性散射，在反应中，可以想像
中子从
核子中弹开并以某种的能量向新的方向飞去了。这种遵循经典物理学的碰撞，在轻元素中尤为突出。
In
the
inelastic
scattering
(
非弹性散射
)
collision,
an
important
process
for
fast
neutrons
in
heavy
The
cross section
?
s
is the chance of a collision that results in
neutron scattering. The neutron
elements, the neutron becomes a part of
the nucleus.
may
instead
be
absorbed
by
the
nucleus,
with
cross
section
?
a
.
Since
?
a
and
?
s
are
chances
of
reaction,
their
sum is the chance for collision or
total cross section
?
=
?
a
+
?
s
.
1
3
、在非弹性散射碰撞中，重元素中的快中子的一个重要过程，是中子变成核子的一部分
。
微观截面
?
s
是导致中子散射的几率。中子可能反被核子吸收，微观截面为
?
a
。因为
?
a
和
?
s
是反应的机会，它们的
和是碰撞的几率或总微观截面
?
=
?
a
+
?
s
4.4 PARTICLE ATTENUATION
(
粒子衰减
)
Visualize an experiment in
which a stream of particles of common speed and
direction is allowed
to strike the
plane surface of a substance as in Fig.4.4.
14
、想象一个实验中一束粒子如图
4.4
那样以同样的速度和方向撞击物质的水平表面。
Collisions
with
the
target
atoms
in
the
material
will
continually remove
projectiles from the stream,
which will
thus diminish (
使??减少
) in
strength with distance, a process we label
attenuation (
衰减
).
15
、
与材料中靶原子的碰撞会不断地把入射粒子从粒子束
弹出，
这将使得其可穿透的深度大大降低，
这个过程我们称之<
/p>
衰减。
4.5 NEUTRON
CROSS SECTIONS
(
中子截面
)
The cross section for
neutron absorption in materials depends greatly on
the isotope bombarded
and on the
neutron energy. For consistent
(
一致的
)
comparison
and use, the
cross
section is often cited
(
引
用
) at 0.0253
eV, corresponding to neutron speed 2200m/sec.
The dependence of
absorption cross section on energy is of two
types, one called l/
v
, in
which
?
a varies inversely
(
相反地
) with neutron speed,
the other called resonance
(
共振
), where there is a very
strong absorption at certain neutron
energies.
16
、
中子在物质中的吸收截面极大依赖于被轰击的同位素和中子能量。
为了
比较和使用上的一致，
通常引用
0.0253eV
的
截面，相对应的中子速度为
2200m/sec
。
吸收截面对于能量的依赖有两种类
型，一个称
1/v
，
?
a
与中子速度成反比，另一个叫共振，对一定能量
的中子吸收
非常强。
4.6
NEUTRON SLOWING AND DIFFUSION
（中子慢化与扩散）
When
fast
neutrons,
those
of
energy
of
the
order
of
2
MeV,
are
introduced
into
a
medium,
a sequence
(
序列
)
of
collisions
with
nuclei
takes
place.
The
neutrons
are
deflected
(
偏离
)
in
direction
on
each
collision,
they lose energy, and they tend to
migrate (
移动
) away from their
origin.
17
、当能量为
2
MeV
的快中子被引入媒介，中子会与原子核发生一系列的碰撞。每次碰撞后中子都将偏
离原来的方向，
损失能量，而且它们趋向从原来的位置移走。
The process of
diffusion
(
扩散
) of gas
molecules
is familiar to us.
If a bottle of
perfume
(
香
水
) is opened,
the
scent
(
香味
) is quickly observed, as
the molecules of the substance
migrate
away from
the
source.
Since
neutrons
in
large
numbers
behave
as
a
gas,
the
descriptions
of
gas
diffusion
may
be
applied.
18
、我们熟悉气体分子的扩散过程。当打开一瓶香水时，因为物质分子的散出，我们很快闻到香
味。大量中子的行为和
气体一样，用于描述气体扩散的方法也可以用于描述中子扩散。<
/p>
We can guess
that the larger the neutron speed v and the larger
the transport
mean free path (
平
均自由程
)
?
< br>t
,
the more neutron flow will take place.
Theory and measurement show that if
n
varies in the
?
?
v
dn
j<
/p>
?
t
z
-dir
ection, the net flow of neutrons across a unit
area each second, the net current density, is
3
dz
19
、我们可以
猜到中子的速度
v
越大平均自由程
?<
/p>
t
越远，而且将会产生更多的中子流。理论和测量显示：如果
n
在
z
?
?
v
dn
轴方向发生改
变，每秒穿过单位面积的净中子流（净流密度）是
j
?
t
3
dz
4.7
SUMMARY(
总结
)
Chemical and
nuclear equations have similarities
(
相似性
) in the form of
equations and in the
The
bombardment
(
轰击
)
of
nuclei
by
charged
particles
or
neutrons
produces
new
nuclei
and
particles.
requirements on
conservation (
守恒
) of
particles and charge.
Final energies
are found from mass differences and final speeds
from conservation of momentum
(
动量守恒
).
20
、化学和核子方程在方程的组成和粒子电量守恒是相似的。
< br>带电的粒子或中子轰击原子核产生新的原子核和粒子。最终的能量来自质量差异以及速度来自动量守恒。< /p>
The
cross
section
for
interaction
of
neutrons
with
nuclei
is
a
measure
of
the
chance
of
collision.
Reaction
rates
depend
mutually
(
相互地
)
on
neutron
flows
and
macroscopic
cross
section
(
微观截面
).
A
stream
of
uncollided (
未经碰撞的
) particles
is reduced exponentially
(
指数的
; logarithmic
对数的
) as it passes
through a medium
(
媒介
).
21
、
中子和原子核的反应的截面积是碰撞几率的量度。
反应率
在中子流和微观截面上相互依赖。
一股未经碰撞的粒子当
它穿过
媒介时是呈指数减少的。
Neutron absorption cross sections
(
吸收截面
) vary
(
改变
) greatly with target
isotope and with
neutron energy, while
scattering cross sections
(
散射截面
) are relatively
constant. Neutrons are slowed
readily
by collisions with light nuclei and migrate
(
移动
) from their point of
origin. On reaching thermal
energy they
continue to disperse (
散开
),
with the net flow dependent on the spatial
variation of flux.
22
、
中子吸收截面因靶同位素和中子能量改变很大，
然而散射截面相对来说是一定
的。
中子通过与轻原子核碰撞轻易减
速并从它们的原先位置移开
。达到一定热能时继续散开，净流依赖空间连续的改变。
CHAPTER 5 Radiation and Materials
(
辐射与物质
)
The word “radiation” will be taken to
embrace (包含
) all particles, whether
they are of material
or electromagnetic
origin. We include those produced by both atomic
and nuclear processes and those resulting
from electrical acceleration, noting
that there is no essential
(
本质的
) difference between
X-rays from atomic
collisions and gamma
rays from nuclear decay; protons can come from a
particle accelerator, from cosmic rays
(
宇宙射线
) , or from
a nuclear reaction in a reactor (
反应堆).
The word “materials” wil1 refer to (涉及
)
bulk
(
大多数
)
matter, whether of mineral or biological origin,
as well as to the particles of which the matter is
composed, including molecules, atoms,
electrons, and nuclei.
1.
“辐射
”
这个词涵盖了所有的粒子，
不论他们来自某种物质还是电磁场
。
我们如果将那些由原子和核过程产生的以及
那些来自电子加速
的粒子加以比较的话，可以发现由原子碰撞产生的
X
射线和核子
衰变产生的
γ
射线并没有本质上的区别；
质子可以由粒子加速产生，也可以来源于宇宙射线或反应堆中的核反应。
“物质”这个
词涉及大多数物体，无论是矿物质还
是生物组织，也包括组成物质的粒子：分子、原子、
电子和核子。
When
we
put
radiation
and
materials
together,
a
great
variety
of
possible
situations
must
be
considered.
Bombarding
particles may have low or high energy, they may be
charged, uncharged, or photons; they may be heavy
or light in the scale of masses. The
targets may be similarly
(
同样地
) distinguished, but
they may also exhibit
(
展示
) degrees
o
f binding that range from none (“free”
particles), to weak (atoms in molecules and
electrons
in atoms), to strong
(nucleons in nuclei).
2.
当我们
把放射物和物质放在一起，
很多种可能的情况必须要考虑。
轰击
粒子的能量或高或低，
可能带电、
不带电或是
< br>光子；它们的质量可能或重或轻。靶物质可能有同样的区别，但它们可能也显示结合的程度，从没有（“自 由”粒子），到
弱（分子中的原子以及原子中的电子），再到强（原子核中的核子）。<
/p>
5.1 EXCITATION AND
IONIZATION BY ELECTRONS
(
电子所致激发与电离
)
These processes occur in
the familiar fluorescent light-bulb
(
日光灯
), in an X-ray machine
(X
光机
),
or in
matter exposed to beta particles. If an electron
that enters a material has a very low energy, it
will
merely migrate
(
移动
) without affecting the
molecules significantly
(
值得注意的
). If its energy is
larger, it
may impart
(
给予
) energy to atomic
electrons as described by the Bohr theory
(
波尔理论
) (Chapter 2), causing
excitation
of
electrons
to
higher
energy
states
(
能态
)
or
producing
ionization,
with
subsequent
(
并发的
)
emission
of light.
3.
这些过程发生在熟悉的日光灯中
，
X
光机中，或暴露在贝塔粒子下的物质中。如果一个进入物质
的电子能量很低，则
电子仅仅在物质中发生移动而不会显著地影响其分子。
如果它的能量稍大，
它可能如波尔理论描述的那样给予原子中的电子
以能量，导致电子激发到高能态或产生电离并发出光。
P49
第二段
Beta particles as electrons
from nuclear reactions have energies in the range
0.0l-l MeV, and thus
are capable of
(
能够
) producing large amounts
of ionization as they penetrate
(
穿透
) a substance. As a rough
rule
of
thumb
(
经验方法
),
about
32
eV
of
energy
is
required
to
produce
one
ion
pair
(
离子对
).
The
beta
particles
lose energy with
each event, and eventually are stopped. For
electrons of l MeV energy, the range
(
射程
), as
the
typical distance of penetration, is no more than a
few millimeters (
毫米
) in
liquids and solids or a few
meters in
air.
4.
如同来自核反应中的电子，贝塔粒子的能量范围
是
0.0l-l MeV
，并且当它们穿透物质时能够产生大量
的电离作用。
粗略地估计，产生一个离子对大概需要
32
eV
的能量。贝塔粒子在每次碰撞中都会损失能量，直到最终停下。
对
l
MeV
能量
的电子，其射程，即穿透距离，在液体和固体不超过几毫米，在气体中也不过几米远而已。
< br>
5.2
HEAVY CHARGED PARTICLE SLOWING BY ATOMS
(
原子对重带电粒子的慢化
)
Charged particles such as protons,
alpha particles, or ions such as the fragments of
fission (
裂变
碎片
)
are
classed as
(
分类为
) heavy
particles,
being
much more massive
(
厚重的
) than the
electron.
For
the same
particle energy they have far less
speed than an electron, but they are less readily
deflected (
偏转
) in their
motion than electrons because of their
inertia (
惯性
) . The mechanism
(
机制
) by which heavy ions
slow down in
matter is primarily
electrostatic interaction
(
静电相互作用
) with atomic
electrons.
5.
带电的粒子如质子、阿尔法粒子、
离子（例如裂变碎片），由于它们比电子重得多，可以归类为重粒子。同样粒子能
量下它
们的速度远小于电子，
因为惯性它们比电子不易发生偏转。
重离
子在物质中慢化的原因主要是由于其与原子中电子的
静电相互作用。
(P49
倒数
12
行
)It is found that
(
业已发现
) the kinetic energy
lost in one collision is proportional
to (
正比于
) the
square of Z, the number of external electrons in
the target atom, and inversely proportional
to (
反比于
) the
kinetic energy of the projectile.
6.
业已发现在一次碰撞中损失的动能正比于靶原子内部电子数
Z
的平方，
靶原子中的外层的电子数量，
反比于入
射粒子
的动能。
5.3
HEAVY CHARGED PARTICLE SCATTERING BY NUCLEI
(
核对重带电粒子的散射
)
When
a
high-speed
charged
ion
such
as
an
alpha
particle
encounters
(
遇到
)
a
very
heavy
charged
nucleus,
the mutual (
相互的
)
repulsion (
排斥
) of the two
particles causes the projectile to move on a
hyperbolic (
双
曲线的
) path, as in Fig. 5.2. Such a collision can take
place in a gas or in a solid if the incoming
particle
passes close to the nucleus. <
/p>
7.
当一个像阿尔法粒子的高速带电离子遇到一个非常重的带电核
，
两个粒子的相互排斥导致入射粒子以双曲线的轨迹移
动，如图
5.2
。在气体或固体中当入射粒子从靠近核子的地方通过时，
这样的碰撞就可能发生。
The
projectile is scattered
(
散射
)
through an angle
(
角
) that depends on the
detailed nature of the
collision, i.e.,
the initial (
初始的
) energy and
direction of motion of the incoming ion relative
to (
相对于
)
the
target nucleus, and the magnitude
(
数量
) of electric charge
(
电荷
) of the interacting
particles
(
相互作
用粒子
). Unless
the energy of the bombarding particle is very high
and it comes within the short range of the
nuclear force, there is a small chance
that it can enter the nucleus and cause a nuclear
reaction.
8.
入射粒子以某一个角度散射，
这角度取决于碰撞的具体性质，
比如，
入射离
子的初始能量、
相对靶核的运动方向以及
相互作用粒子的电荷数
。除非碰撞粒子的能量非常高并且它在短程核力范围内，否则它很难有机会进入核子并引发核反应。
5.4 GAMMA RAY INTERACTIONS WITH
MATTER (
?
射线与物质的相互作用
We now turn to a group of three related
processes involving (
使?陷于
)
gamma ray photons produced by
nuclear
reactions. These have energies as high as a few
MeV. The interactions include simple scattering of
the
photon, ionization by it, and a
special nuclear reaction known as pair production.
(a)
Photon-Electron
Scattering
(
光电散射
)
(b)
Photoelectric Effect
(
光电效应
)
(c)
Electron-Positron Pair Production
(
电子对产生效应
)
9.
现在我们转向于与核反应产生的
γ
射线
光子有关的三个过程，
这些光子的能量可达几兆电子伏。
反应包
括简单的光子
散射、电离，以及众所周知的一个特殊核反应——电子对效应。
(a) Photon-Electron
Scattering
（
光电散射
）
One
of the easiest processes to visualize
(
设想
,
显现
) is the interaction of a
photon of energy E=hv
and an electron
of rest mass m
0
. Although
the electrons in a target atom can be regarded as
moving and bound
to their nucleus, the
energies involved are very small (eV) in
comparison with those of typical gamma rays (keV
or MeV). Thus the electrons may be
viewed as (
被视为
) free
stationary (
固定的
) particles.
The collision may be
treated by the
physical principles of energy and momentum
conservation.
10.
设想中最简单的核反应
的过程之一是能量为
hv
的光子与静止质量为
< br>m
0
的电子的反应。尽管靶原子中的电子可看做
是被他们的核子所束缚着绕核运动，其间的能量（
eV
< br>）与那些典型的
γ
射线（
KeV
或
Mev
）相比非常小。因此，这种电
子可
被视为自由的温定粒子。碰撞过程遵守能量和动量守恒定律。
2
(P51
倒数
11
行
)(Fig.
5.3)
the
photon
is
deflected
in
its
direction
and
loses
energy,
becoming
a
photon
of
new
energy
E’=
hv’.
The
electron
gains
energy
and
moves
away
(
离开
)
with
high
speed
v
and
total
mass-energy
mc
,
leaving the atom ionized. In this Compton effect
(
康普顿效应
), named after its
discoverer, one finds that
the greatest
photon energy loss occurs when it is scattered
backward (l80o) from the original direction.
11.
光子偏离原来的方向并损失一定的能量，变成能量为
E’= hv’
的光子。电子获得能量以很高的速度
v
离开原子，
其总质能为
mc
，而原子则变成了离子。在以其发现者命名的康普顿效应中，人们发现当光子发生
l80
散射时其能量损失最
大。
(P53)The probability
of
Compton
scattering
(
康普顿散射
)
is expressed
by
a
cross section
(
截面
), which
is smaller for larger gamma energies as
shown in Fig. 5.4 for the element lead
(
铅
plumbum), a common
material
for shielding against X-rays
or gamma rays. We can deduce
(
推论
) that the chance of
collision increases with
each
successive (
逐次的
,
相继的
) loss of energy by the
photon, and eventually the photon disappears.
12.
康普顿散射发生的概率可用截面表示，如图
Fig.
5.4
，对一种常用于防护
X
射线或
γ
射线的铅来说，伽马能量
越大
反应截面越小。我们可以推断，碰撞几率随着光子能量的持续丧失而上升，最终光子
消失。
(b) Photoelectric Effect
（光电效应
）
This process is in competition with
(
与?竞争
) scattering. An
incident photon of high enough energy
dislodges
(
驱逐
)
an
electron
from
the
atom,
leaving
a
positively
charged
ion.
In
so
doing,
the
photon
is
absorbed
and thus lost (see
Fig. 5.5). The cross section for the photoelectric
effect decreases (
减少
) with
increasing
(
增加
)
photon energy, as sketched in Fig.5.4 for the
element lead (
铅
).
13
．
这个过程可与散射相媲美。
能
量足够高的光子导致原子中的电子被驱逐出来，
留下一个带正电的离子，
而这个光子
最终会被吸收而消失。如
Fig.5.4<
/p>
中描绘的铅元素的吸收截面那样，光电效应的截面随光子能量的增加而减少。
The above two
processes are usually treated separately even
though both result in ionization. In the
Compton
effect,
a
photon
of
lower
energy
survives
(
生还
),
but
in
the
photoelectric
effect,
the
photon
is
eliminated
(
消除
).
In
each
case,
the
electron
released
may
have
enough
energy
to
excite
or
ionize
other
atoms
by
the
mechanism
(
机制
) described
earlier. Also, the ejection
(
排出物
) of the electron is
followed by light emission or X-ray
production, depending on whether an
outer shell or inner shell is involve
1
4.
以上两个过程虽然都导致电离，但它们通常被区别对待。在康普顿效应中，能量较低
的光子仍然存在，但在光电效
应中，光子消失。在两种情况下，被释放的电子有足够的能
量通过前面描述的机制去激发或使其他原子电离。同样，伴随着
被打出的电子，放出光还
是
X
射线，取决于它处于外壳层还是内壳层。
< br>
The
third
process
to
be
considered
is
one
in
which
the
photon
is
converted
into
matter.
This
is
entirely
in
accord
with
Einstein’s
theory
of
the
equivalence
of
mass
and
energy
(质能关系式
).
In
the
presence
of
a
nucleus,
as
sketched in Fig. 5.6, a gamma ray photon
disappears and two particles appear---an electron
and a positron.
15.
第三个过程被认为
是光子转变成物质的过程。完全符合爱因斯坦的质能关系式的理论。如
Fig.
5.6
所示，一个伽马
射线光子撞击一个核子
，光子消失以后产生了两个新的粒子——一个负电子和一个正电子。
2
o
(P53
倒数第
1
行
)Since
these
are
of
equal charge
but of
opposite sign, there
is no
net charge
after the
reaction, just as before, the gamma ray
having zero charge. The law of conservation of
charge is thus met. The
total
new
mass
produced
is
twice
the
mass-energy
of
the
electron,
2(0.5l)
=
l.02
MeV,
which
means
that
the
reaction
can occur (
发生
)
only if the gamma ray has at least this amount of
energy. The cross section for the process
of pair production rises from zero as
shown in Fig. 5.4 for lead.
16.
< br>因为电量相同而电性相反，所以在反应后没有净电荷。如反应前一样，伽马射线的电荷为零，符合电荷守恒 定律。
新产物的总质能是电子的两倍，
2(0.5l)
=
l.02
MeV,
这意味着只有伽马射线的能量至少有这么多时这个反应才有可能发生。
铅产生
电子对效应的截面从零开始上升，如图
Fig.
5.4
所示。
< br>(P54
倒数第
2
行
)
The
reverse
process
(
逆过程
)
also
takes
place
(Fig.
5.7).
when
an
electron
and
a
positron
combine, they are annihilated (
湮没
) as material particles,
and two gamma rays of energy totaling
at least l.02 MeV are released. That
there must be two photons is a consequence of the
principle of momentum
conservation.
17.
当正负电子结合时，
逆过程也会发生<
/p>
(
如图
5.7)
，
作为物质粒子它们发生湮没，
同时发射出的两束总能量至少有
l.02
MeV
的伽马射线。根据动
量守恒定律的推断，必然有两个（方向相反、能量相等的）光子产生。
Figure 5.4 shows that the
total gamma ray cross section curve
(
曲线
) for lead (Pb), as the
sum of the
components
for
Compton
effect,
photoelectric
effect,
and
pair
production,
exhibits
a
minimum
around
3
MeV
energy.
This implies that gamma rays in this
vicinity (
附近
) are more
penetrating (
有穿透力的
) than
those of higher or
lower energy.
In
contrast with
(
与?对比
)
the case
of
beta
particles and
alpha
particles, which
have
a
definite
range
(
确定的射程
), a certain fraction
of incident gamma rays can pass through any
thickness of material.
18.
如
图
5.4
所示铅的伽马射线反应总截面曲线（总截面是康普顿效
应，光电效应截面以及电子对效应截面之和）显示
最小截面出现在
3 MeV
能量处。这就表明当伽马射线的能量在
3MeV<
/p>
左右时，其穿透力最强。与有确定的射程的阿尔法粒子
和贝塔粒子
相比，某些伽马射线的能够穿透任何厚度的物质。
5.5
NEUTRON REACTIONS
（中子反应）
For completeness, we
mention the interaction of neutrons with matter.
Neutrons may be scattered by
nuclei
elastically
or
inelastically,
may
be
captured
(
俘获
)
with
resulting
gamma
ray
emission,
or
may
cause
fission
(
裂变
). If their
energy is high enough, neutrons may induce
(
引起
,
诱发
) (n, p) and (n,
?
) reactions as well.
19.
出于完整性的考虑，我们介绍一下中子和物质的反应。中子可能与核发
生弹性散射和非弹性散射，也可能会被俘获
而放出伽马射线，甚至可能导致裂变。如果它
们的能量足够高，中子也会引发
(n,
p)
和
(n,
?
)
反应。
We are now in a position to
understand the connection between neutron
reactions and atomic processes.
When a
high-speed neutron strikes the hydrogen atom in a
water molecule, a proton is ejected
(
逐出
), resulting
in chemical dissociation
(
离解
,
分裂
) of the
H
2
O. A similar effect takes
place in molecules of cells in any
biological tissue
(
生物组织
). Now, the proton as a
heavy charged particle passes through matter,
slowing and
creating ionization along
its path. Thus two types of radiation damage
(
辐射危害
) take place---primary
and
secondary
(
初级与次级
).
20.
我们现在能够理解中子反应和原子反应之间的联系。
当一个高速的中子撞击
水分子中的氢原子，
一个质子会被逐出，
导致
< br>H
2
O
的化学分解。类似的过程
发生在任何生物组织的细胞中。质子作为重带电粒子穿过物质，在慢化过程中产生电离。
因而产生两种辐射危害——初级电离与次级电离。
After many collisions, the neutron
arrives at a low enough energy that it can be
readily absorbed.
If it is captured by
the proton in a molecule of water or some other
hydrocarbon (
碳氢化合物
), a gamma
ray is
released,
as
discussed
in Chapter
4. The
resulting
deuteron
recoils
(
氘核反冲
)
with
energy that
is
much smaller
than that of the gamma ray, but still
is far greater than the energy of binding
(
结合能
) of atoms in the water
molecule. Again dissociation
(
分裂
) of the compound
(
混合物
) takes place, which can
be regarded as a form of
radiation
damage.
21.
在许多次碰撞后中子达到了一个低得可
以被容易地吸收的能量。如第四章讨论的那样，如果中子被水分子中的质子
或一些其他碳
氢化合物吸收，
则会释放出伽马射线。
氘核反冲的能量比伽马射
线反冲的能量小的多，
但仍比水分子中原子的
结合能大得多。化
合物再次发生分裂，这被看做是辐射损伤的形式之一。
总结
Radiation of especial interest includes
electrons, heavy charged particles, photons, and
neutrons
Each of the particles tends to
lose energy by interaction with the electrons and
nuclei of matter,
特别重要的辐射包括电子，重带电粒子，光子和中子。
and each creates ionization in
different degrees.
每个粒子在与物质的电子和核子的反应过程中
会丧失能量，每次在不同程度上产生离子。
The ranges of beta particles and alpha
particles are short, but gamma rays penetrate
(
穿透
) in accord
with an exponential law
(
指数规律
). Gamma rays can also
produce electron-positron pairs. Neutrons of both
high
and low energy can create
radiation damage in molecular materials.
贝塔粒子和阿尔法粒子的射程很短，
但伽马射线穿透符合指数规律。
伽马射线也可以产生正负电子对。
能量高和低的中
子都
可以在物质分子中产生辐射损伤。
CHAPTER 6
Fission (
裂变
)
Out of many nuclear
reactions known, that resulting in fission has at
present (
目前
) the greatest
practical significance
(
意义
). In this chapter we
shall describe the mechanism
(
机制
) of the process,
identify
(
识别
,
鉴别
) the byproducts
(
副产品
), introduce the concept
(
概念
) of the chain reaction
(
链式反应
), and look
at the energy yield
(
出产
) from the consumption
(
消费
) of nuclear fuels
(
核燃料
).
1.
目前，在许多已知的核反应中，导致裂变的反应最有实用意义。在这一章中我们将描述这一过程的机制，
认识其副
产物，介绍链式反应的概念，搞清楚从核燃料的消耗中产出的能量。
6.1 THE FISSION
PROCESS(
裂变过程
)
The absorption
(
吸收
) of a neutron by most
isotopes
involves radiative
capture (
辐射俘获
), with the
excitation energy
(
激发能
) appearing as a gamma
ray. In certain heavy elements, notably (
特别地
,
尤其
) uranium
(
铀
) and plutonium
(
钚
), an alternate
(
交替的
) consequence is
observed---the splitting
(
分裂
) of the nucleus
into
two massive
fragments (
重碎片
),
a process
called
fission.
Figure
6. 1 shows the sequence
(
序列
)
of
events,
using
the reaction with U-235 to illustrate
(
举例
).
2.
< br>大多数核素吸收中子的过程都涉及辐射俘获，
同时激发能以伽马射线的形式出现。
在某些重元素中，
特别是铀和钚，
可以
观察到一个交替的结果
---
核子分裂成两个重碎片，这个过程
称为裂变。图
6.
l
以铀
-235
的反应为例显示了这一过程。
In Stage A, the neutron
approaches (
接近
) the U-235
nucleus. In Stage B, the U-236 nucleus has been
formed,
in
an
excited
state
(
激发态
).
The
excess
(
过度的
,
额外的
)
energy
in
some
cases
may
be
released
as
a
gamma
ray, but more
frequently (
常常
,
频繁地
), the energy causes
distortions (
变形
) of the
nucleus into a
dumbbell
shape (
哑铃形状
), as
in Stage C. The parts of the nucleus oscillate
(
振荡
) in a manner analogous
to (
类似于
)
the
motion
of
a
drop
of
liquid.
Because
of
the
dominance
(
优势
)
of
electrostatic
repulsion
over
nuclear
attraction,
the two parts can separate, as in Stage
D. They are then called fission fragments
(
裂变碎片
), bearing
(
具有
)
most of the energy released.
3.
在
A
阶
段，中子接近
U-235
核。在
B
阶段，
U-236
核形成并处于激发态。<
/p>
C
阶段：在一些情况下过多的能量以伽马射
线的形式释放出来，但更有可能的是，能量导致核子变形成哑铃状。，
D
阶段：核子的各部分的振荡在一定程度上类似于一
滴液体的运动。因为静电斥
力大于核引力，这两个部分可能分离。它们被称作裂变碎片，具有大部分的释放能。
They
fly
apart
at
high
speeds,
carrying
some
166MeV
of
kinetic
energy
out
of
the
total
of
around
200MeV
released in the whole process. As the
fragments (
碎片
) separate,
they lose atomic electrons, and the resulting
high-speed
ions
lose
energy
by
interaction
with
the
atoms
and
molecules
of
the
surrounding
medium.
The
resultant
thermal energy is recoverable
(
可重获的
) if the fission takes
place (
发生
) in a nuclear
reactor. Also shown in
the diagram are
the prompt (
瞬发
)
gamma rays and fast neutrons that are
released at the time of splitting.
4. <
/p>
它们带着
166MeV
的动能以高速飞离
，而整个过程中释放的总能量大概是
200MeV
。当碎片分开
，它们的原子失去电
子，
高速运动的离子与周围介质中的原子和
分子反应损失能量。
如果裂变发生在核反应堆中，
发出的热能可
持续获得。图表
中也显示了分裂时放出的伽马射线和快中子。
6.2 ENERGY CONSIDERATIONS
(
裂变能量
)
The absorption
of a neutron by a nucleus such as U-235 gives rise
to (
引起
) extra internal
energy (
内
能
) of
the product, because the sum of masses of the two
interacting particles is greater than that of a
normal
U-236 nucleus.
235U + n
→
(236U)*,
where the asterisk
([`?st
?
risk]
星号
)
signifies (
表示
) the excited
state (
激发态
). The mass in
atomic mass
units of (U-236)* is the
sum 235.043925 + 1.008665 = 236.052590. However,
U-236 in its ground state
(
基态
) has
a
mass
of
only
236.045563,
lower
by
0.007027amu
or
6.5MeV.
This
amount
of excess
energy
(
过剩能量
)
is
sufficient
(
充分的
) to cause
fission.
5.
一个核子（比如
U-235
）吸收一个中子后引起产物的内能过多，因为两个参加反应的粒子的总质
量比普通的
U-236
核子大。
235U + n
→
(236U)*,
< br>这里的星号表示激发态。
(U-236)*
的重量用原子
质量单位表示的总数是
235.043925 + 1.008665 = 236.0
52590.
然而，
U-236
的基态
的质量仅为
236.045563
，比前者低了
0.007027amu
或
6.5MeV
。
过剩能量足够导致裂变的发生。
The above calculation did not include
any kinetic energy brought to the reaction by the
neutron, on
the
grounds
that
(
由于，因为
)
fission
can
be
induced
by
absorption
in
U-235
of
very
slow
neutrons.
Only
one
natural
isotope (
天然同位素
),
235U, undergoes (
经历
) fission
in this way, while 239Pu and 233U are the main
artificial
isotopes
(
人工同位素
) that do so. Most
other heavy isotopes require significantly larger
excitation energy to
bring
the
compound
nucleus
(
复合核
)
to
the
required
energy
level
for
fission
to
occur,
and
the
extra
energy
must
be
provided by the motion of the incoming neutron.
6.
因为铀
235
< br>吸收慢中子可以诱发裂变反应，以上的计算没有包括中子带到反应中的任何动能。只有一种天然同位素
铀
235
以及人工同位素中的钚
239
和铀
233U
以这
种方式发生裂变。绝大多数其他重同位素需要极大的激发能来使复合核达
到发生裂变所需
的能量，额外的能量必须由入射中子的运动提供。
The precise terminology
(
术语学
) is as follows: fissile
(
裂变的
) materials are those
giving rise to
fission with slow
neutrons; many isotopes are fissionable
(
可裂变的
), if enough energy is
supplied. It is
advantageous
to
use
fast
neutrons--of
the
order
of
1MeV
energy--to
cause
fission.
As
will
be
discussed
in
Chapter
l3,
the
fast
reactor
(
快堆)
permits
the
“
breeding
”(增殖
)
of
nuclear
fuel.
In
a
few
elements
such
as
californium
(
锎
Cf),
spontaneous
fission
(
自发裂变
)
takes
place. The isotope 252Cf,
produced artificially
by a
sequence
(
一
连串的
)
of neutron absorption, has a half-life of 2.646
yr, decaying by alpha emission (97%) and
spontaneous
fission (3%).
7.
准确的术语如下：由慢中子可以引起的裂变物质称为易裂变物质；如果提供足够的能量，
许多同位素是可裂变的。
使用能量为
1MeV
< br>以上的快中子产生裂变是有利的。
在
13
章我们将讨论快堆使核燃料增值。一些元素
（例如锎）
能自发地发
生裂变。同位素锎
252
是
经过一系列中子吸收而人工制造的，半衰期为
2.646
年，发
生
α
衰变占
97%
，自发裂变占
3%
。
It may be surprising that
the introduction of only 6.5MeV of excitation
energy can produce a reaction
yielding
(
出产
)
as much as
200MeV. The explanation
(
解释
)
is that
the excitation triggers
(
引起
) the
separation
of
the
two
fragments
(
碎片
)
and
the
powerful
electrostatic
force
(
静电力
)
provides
them
a
large
amount
of
kinetic
energy. By
conservation of mass-energy
(
质能转换
), the mass of the
nuclear products is smaller than the mass
of the compound nucleus
(
复合核
) from which they emerge
(
形成
).
8.
< br>这可能会很令人惊讶，仅仅引入
6.5MeV
的激发能就
可以导致产生多达
200MeV
能量的反应。对此的解释是激发
能引
起两个碎片的分离，
同时，
强大的
静电力给它们提供巨大的动能。通过质能转换，
核反应产物的质量比由它们形成的复合核
的质量小。
6.3
BYPRODUCTS OF FISSION
(
裂变产物
)
Accompanying
(
伴随
) the fission process is
the release of several neutrons, which are all-
important
for the practical application
to a self-sustaining (
自行持续
)
chain reaction. The numbers that appear
?
(nu)
range
from
l
to
7,
with
an
average
in
the
range
2
to
3
depending
on
the
isotope
and
the
bombarding
neutron
energy.
For example, in U-235 with slow
neutrons the average number
?
is 2.42. Most of these are
released instantly,
the
so-
called
prompt neutrons
(
瞬发中子
),
while
a small
percentage,
0.65%
for
U-235, appear
later
as
the
result
of radioactive decay
of certain fission fragments. These delayed
neutrons (
缓发中子
) provide
considerable
inherent
(
固有的
) safety and
controllability (
可控性
) in the
operation of nuclear reactors.
9.
裂变过程同时伴随着少量中子的释放，这对自行持续链式
反应是极其重要的。中子数目
?
的范围从
1
到
7
不等，平
均是
2
到
3
个，这取决于同位素和轰击中子的能量。例如，慢中子轰击
U-235
平均产生的中子数
?
为
2.4
2
。大部分中子都
是瞬间释放出来的，即所谓的瞬发中子，对<
/p>
U-235
，某一个裂变碎片发生放射性衰变而放出的中子到后来
才出现。这种中子
只占
0.65%
这样
很小的比例。这些缓发中子为核反应堆在运行过程中的固有安全性和可控性提供了有力的保障。
< br>
The nuclear reaction
equation (
核反应方程式
) for
fission resulting from neutron absorption in U-235
may be written in general form
(
通式
), letting the chemical
symbols for the two fragments be labeled F1 and F2
to indicate many possible ways of
splitting. Thus
235U + n
→
A1Fl + A2F2 +
?
n + energy.
The
appropriate (
适当的
) mass
numbers and atomic numbers are attached. One
example, in which the fission
fragments
are isotopes of krypton (
氪
)
and barium (
钡
), is
235U + n
→
90Kr +
144Ba + 2n + E.
Mass numbers ranging
from 75 to l60 are observed, with the most
probable at around 92 and l44 as sketched
in Fig.6.3.
10.
U
-235
吸收中子产生的裂变的核反应方程式可以用一个通式表示。两个碎片的化学元素
用
F1
和
F2
表示，这个通式
可以用来表示许多可能的分裂方式。如下
235U + n
→
A1Fl +
A2F2 +
?
n
+
能量
适当的质量数和原子序数可以
被附上（代入）。举个例子，反应中裂变碎片是氪和钡的同位素
235U + n
→
90Kr +
144Ba + 2n + E.
质量数范围为
75
到
160
不等，最有可能是
92
到
144
这个范围。
如图
6.3
所示。<
/p>
The
total
energy
from
fission,
after
all
of
the
particles
from
decay
have
been
released,
is
about
200MeV.
This
is
distributed
among
the
various
processes
as
shown
in
Table
6.1.
The prompt
gamma
rays
(
瞬发
?
)
are
emitted
as a
part of fission; the rest are fission product
(
裂变产物
) decay gammas.
Neutrinos (
中微子
) accompany
the
beta particle emission, but since
they are such highly penetrating
(
穿透性
) particles their energy
cannot be
counted
as
part
of
the
useful
thermal
energy
yield
of
the
fission
process.
Thus
only
about
l90MeV
of
the
fission
energy is effectively available.
11.
在衰变过程中所有粒子被释放出来之后，裂变放出的总能量大约为<
/p>
200 MeV
。这些能量分配给如表格
6.1
所示的各
种过程。瞬发
?
作为裂变的一部分被放出；其它是伽马衰变的裂变产物。中微子连同贝塔粒子一起发射出来，但
由于它是如
此高穿透性粒子，它的能量不能计为裂变过程产生的有用的热能。因此仅仅只
有
l90MeV
的裂变能是可以有效利用的。
< br>
Although
fission
is
the
dominant
(
占优势的
)
process,
a
certain
fraction
of
the
absorptions
of
neutrons
235U + n
→
236U +
?
The U-236 is
relatively stable (
稳定的
),
having a half life of
2.34
×
l07 yr. About 14% of
the absorptions
are of this type, with
fission occurring in the remaining 86%. This means
that
?
(eta), the number of
neutrons
produced per absorption in
U-235 is lower than
?
, the
number per fission. Thus using
?
= 2.42,
?
is (0.86)
(2.42)=2.07. The effectiveness
(
效力
) of any nuclear fuel
(
核燃料
) is sensitively
dependent on the value of
?
.
12.
尽管裂变是主要过程，但是铀中一小部分吸收中子仅仅
导致辐射俘获，根据
235U + n
→
236U +
?
U-236
是相对稳定的，半衰期
2.34
×
l
0
年。大概
14%
< br>的中子吸收是这种形式，剩余的
86%
发生裂变。这就意
味着在每
次
U-235
吸收中产生的中
子数
?
(eta)
低于每次裂变释放出
的中子数量
?
。因此当
?
= 2.42,
则
?
为
(0.86) (2.42)=2.07
。
任何核燃料的效力都
与
?
的值紧密相关。
The
possibility of a chain reaction
was
recognized as
soon as
it was known
that
neutrons
were
released
in
the
fission
process.
If
a
neutron
is
absorbed
by
the
nucleus
of
one
atom
of
uranium
and one neutron
is produced, the
latter
can
be
absorbed
in
a
second
uranium
atom, and so
on. In
order to sustain
(
维持
) a chain
reaction as in a nuclear reactor or in a nuclear
weapon, the value of
?
must
be somewhat (
稍
微
)
above l because of processes that complete with
absorption in uranium, such as capture in other
materials
and escape from the system.
一旦知道裂变反应中放出的中子链式反应的可能性就可被发现
。如果一个铀原子吸收一个中子并产生一个中子，
7
in
uranium merely result in radiative capture
(
辐射俘获
), according to
后者可被下一个铀原子吸收，
如此下
去。
为了在核反应堆或核武器维持链式反应，
?
的值必须稍微高于
1
因为过程中包括铀
中的吸收，比如在其他物质中俘获以及逃离这个系统。
The size of
?
has two important
consequences. First, there is a possibility of a
growth of neutron
population with time.
After all extraneous (
外来的
)
absorption and losses have been accounted for
(
考虑
), if
one
absorption
in
uranium
ultimately
(
最后
)
gives
rise
to
say
1.1
neutrons,
these
can
be
absorbed
to
give
(l.l)(l.l)
=
l.2l,
which
produce
1.33l,
etc.
The
number
available
increases
rapidly
with
time.
Second,
there
is
a
possibility
of using the
extra neutron, over and above
(
除?之外
) the one required to
maintain (
维持
) the chain
reaction,
to produce new fissile
materials (
裂变材料
).
replace that used up, while
?
的大小有两个重要的影响。首先，随时间中子数增殖是可能的
。在考虑了所有的外来吸收和损耗，如果铀中的
一次吸收最后产生
1.1
个中子，这些可被吸收产生
(l.l)(l.l) =
l.2l,
产生
1.33l,
等等。数
量虽时间迅速增加。其次，使
用额外的中子是可能的，
除一个用
来维持链式反应之外，
来产生裂变材料。
“转化”
包括产生的一些新的能量来替代用完的，
然而“增殖”发生在当产生的多于消
耗的时候。
Out of the
hundreds of isotopes found in nature, only one is
fissile, 235U. Unfortunately, it is the
less abundant
(
丰富的
) of the isotopes of
uranium, with weight percentage in natural uranium
of only 0.7ll, in
comparison,
with
99.3
%
of
the
heavier
isotope
238U.
The
two
other
most
important
fissile
materials,
plutonium-239
and uranium-
233, are
“artificial” in the sense that they are
man
-made by use of neutron irradiation
(
照射
)
of two
fertile (
富饶的
) materials,
respectively (
分别地
),
uranium-238 and thorium-232.
< br>在自然界发现的成百上千的同位素中，只有一种是可裂变的，
235U.
遗憾的是，铀的同位素是不丰富的，自然界
的铀
235
的重量比例仅为
0.711
，与
此对照，铀
238
占
99.3
%
。其他两个最重要的可裂变的材料，环
23
9
和铀
233
，它们是
人造的，是用中子照射两中富饶的材料，分别是铀
238
和杜
232.
The
reactions by which 239Pu is produced are
238U + n
→
239U
239U
→
239Np + e- 239Np
→
239Pu + e-
while the yielding 233U are
232Th + n
→
233Th
233Th
→
233Pa + e- 233Pa
→
233U + e-
6.4
ENERGY FROM NUCLEAR
FUELS(
核燃料产生的能量
)
The practical
significance
(
实际意义
)
of
the
fission
process is revealed
(
显示
)
by
calculation of the
amount
of
uranium
that
is
consumed
(
消耗
)
to
obtain
a
given
amount
of
energy.
Each
fission
yields
l90MeV
of
useful
energy, which is also
(l90MeV)(l.60
×
l0-13
J/MeV)=3.04
×
l0-11J. Thus the
number of fissions required to obtain
l
W-sec of energy is
1/(3.04
×
l0-11) =
3.3
×
1010. The number of
U-235 atoms consumed in a thermal reactor
(
热
堆
) is larger by
the factor 1/0.86 = 1.l6 because of the formation
of U-236 in part of the reactions.
裂变的实际意义显示在通过计算消耗的铀产生的能量。每次裂变产生
l
90MeV
有用能量，也即
(l90MeV)(l.60
×
l0-13 J/MeV)=3.04
×<
/p>
l0-11J.
这样获得
l W-sec
能量所需的裂变数是
1/(3.04
×
l0-11) = 3.3
×
1010
.
热堆消耗掉的
U-235
原子数因因
子
1/0.86 =
1.l6
存在而更大，因为反应的一部分要形成铀
236.
is
power is
在核反应堆一天的运行中每兆瓦热能，燃烧的铀
235
是
In one
day's operation of a reactor per megawatt of
thermal power, the number of U-235 nuclei burned
(l0
6
W)( 3.3
?
10
10
fission
s/W-sec)(86,400 sec/day)
(0.86
fissions/absorptions)
= 3.32
?
10
21
absorptions/d
ay
Then since 235 g corresponds to
Avogadro's number of atoms
6.02
×
1023, the U-235 weight
consumed at l MW
(3.32
?
10
21
day
-1
)(235g)
?
1.3g/day.
(6.02
?
10
23
)
In other words, 1.3 g of
fuel is used per
megawatt(
兆瓦
)-day of useful
thermal energy released. In
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