|
2.
Hardware, Software, and Instructions
This chapter will give detailed hardware specifications, both mechanical
and electronic, of the various Helgeson In Vivo Counters. It will also
describe the system software setup and software languages. Finally, this
chapter also includes a list of fundamental instructions on the use of
a computer, instructions which, most likely, all readers will already know,
but which are included to make this manual more complete.
Most of the “whole body” counters which are used in the nuclear power and
associated industries use a form of the “shadow shield” principle. This
principle is concisely described by Palmer and Roesch (Palmer, H.E. and
Roesch, W.C., “A Shadow Shield Whole-Body Counter,” Health Physics, Vol.11,
pp. 1213-1219, 1965) from which we quote:
“A shield surrounds all but one side of the detector. The subject is in
front of the open side. A shield behind the subject, the “shadow shield,”
is large enough and so placed that no photon traveling in a straight line
from that side can enter the detector without passing through the shield.
This shield “casts a shadow” over the opening in the detector shield. The
only rays that can reach the detector without attenuation by the shield
are those emitted from the subject or the shielding material and those
scattered from the subject or the shadow shield. The energy of the scattered
rays is determined by the Compton scattering law. Most of the scattered
photons will have energies below 0.3-0.4 MeV regardless of their initial
energy. This removes them from the energy range of interest in most whole-body
counting problems.”
While we are quoting Palmer and Roesch, let us hear what they have to say
about subject positioning (from the same reference, page 1215):
"In whole-body counting one desires to count a given isotope with the same
efficiency for different size people. To do this the ideal scan would be
made over a distance much beyond both ends of the body and at a considerable
height above the body. Then radioactive material at any position in a person
would pass through essentially the same sequence of positions relative
to the detector and would be counted with the same efficiency. In practice
the scan is usually limited to slightly more that the length of the body
and the crystal is kept only slightly above the body. Fortunately, there
are factors that offset these non-ideal conditions. When the height of
the crystal above the bed is fixed, increased absorption in larger people
seems to be offset by decreased separation, on the average, between the
source and crystal. Also, in the shadow shield, the detector shielding
limits the parts of the body from which rays can reach the crystal. Hence,
the scan need only go far enough past the ends of the body for the body
to outside the sensitive region."
2.1.
The Mechanical Structures
2.1.1.
“Classic Shadow Shield Whole Body Counters”
This counter is fabricated with external cladding of stainless steel so
that it may be decontaminated easily. Less costly models may be fabricated
of ordinary “black iron” sheets and painted. The “Classic Shadow Shield
Whole Body Counter” uses lead bricks for shielding. Each brick is 2 by
4 by 8 inches in the United States or 5 by 10 by 20 centimeters in Europe.
2.1.1.1.
Physical Specifications
The physical specifications of the “Classic Shadow Shield Whole Body Counter”
are given in Table 2-1, on the next page.
2.1.1.2.
Shielding
The shielding around the detector is 4 inches (10 centimeters) of lead.
The shielding under the bottom of the bed and in the sides is also 4 inches
thick, however, as the angle from the detector to the bed leaves the perpendicular,
wooden spacers are placed between some of the lead bricks to minimize the
weight but at the same time the “slant range” is maintained to at least
4 inches of lead. Lead is positioned on the bottom and the sides so that
the detector cannot view any object without the gamma rays first having
passed through a minimum of 4 inches of lead.
2.1.1.3.
Motors
The “Classic Shadow Shield Whole Body Counter” has one motor for the movement
of the bed on which the subject lies. This is typically a 90-volt D.C.
motor which may be manually controlled but is normally controlled by the
computer.
If collimators are present a second motor is used for collimator positioning.
This is also typically a 90-volt motor with both manual and computer control.
Frame2
2.1.2.
“Do-It-Yourself Whole Body Counters”
As is the case with the “Classic Shadow Shield Whole Body Counter,” this
counter is also fabricated with external cladding of stainless steel so
that it may be decontaminated easily. Less costly models may be fabricated
from ordinary “black iron” sheets and painted. The “Do-It-Yourself Whole
Body Counter” also uses lead bricks for shielding. Each brick is 2 by 4
by 8 inches in the United States or 5 by 10 by 20 centimeters in Europe.
2.1.2.1.
Physical Specifications
The physical specifications of the “Do-It-Yourself Whole Body Counter”
are given in Table 2-2, on the next page.
2.1.2.2.
Shielding
The shielding around the detector is 4 inches (10 centimeters) of lead.
The shielding under the bottom of the bed and in the sides is 2 inches
thick, however, the stainless steel has been fabricated so 4 inches of
lead may be inserted if additional shielding is necessary without the gamma
rays first having passed through a minimum of 4 inches of lead. If the
extra lead is not used, the spaces are filled with wood.
2.1.2.3.
Motors
The “Do-It-Yourself Whole Body Counter” has one motor for the movement
of the bed on which the subject lies. This is typically a 90-volt D.C.
motor which may be manually controlled but is normally controlled by the
computer.
If collimators are present a second motor is used for collimator positioning.
This is also typically a 90-volt motor with both manual and computer control.
Frame4
2.1.3.
“Quicky” In Vivo Counters
The “Quicky” In Vivo Counters are fabricated from ordinary “black iron”
sheets and painted. Molten lead is poured for the shielding around the
detectors and behind the subject.
2.1.3.1.
Physical Specifications
The physical specifications of the “Quicky” In Vivo Counters are given
in Table 2-3, on the next page.
2.1.3.2.
Shielding
The shielding around the detectors is 2 inches (5 centimeters) of poured
lead. The shielding under the bottom of the bed and in the sides is 2 inches
thick, however, the stainless steel has been fabricated so 4 inches of
lead may be inserted if additional shielding is necessary without the gamma
rays first having passed through a minimum of 4 inches of lead. If the
extra lead is not used, the spaces are filled with wood.
2.1.3.3.
Hardware for External Contamination Measurements
The proportional counters used by Helgeson have been designed with the
following objectives:
-
making them strong to resist warpage,
-
resistant to the breaking of wires by choosing materials with very similar
coefficients of thermal expansion,
-
large area of the beta particle entrance window to maximize sensitivity
regardless of the location of the beta source,
-
thin mylar windows to minimize the loss of the low energy end of the beta
spectrum, yet thick enough to minimize breakage,
-
a protective grid over the mylar to minimize punctures by sharp objects,
and
-
relatively thin boundary walls to maximize the sensitive counting area
and minimize the loss of counts between adjacent detectors.
The subject of Proportional Counters is sufficiently important that we
are devoting a separate chapter, Chapter , to the theory of proportional
counters and the routing of the P-10 gas through a typical “Quicky” system.
Frame6
2.2.
The Computer System(s)
Frame8
The “HELGE” software will work on any 286, 386, or 486 computer. The speed
with which the software works is, obviously, a function of the capabilities
of the central processing unit. Because the 386 and 486 computers have
so many additional capabilities over those of the 286, we have yet to install
a system which uses only a 286 CPU. In fact, with such a small price differential
between a 386 with co-processor and a 486, most of the newer systems being
installed use the 80486 CPU. (Table 2-4.)
2.2.1.
Disk Organization and Storage
There may be three disk drives on your system:
- 1. The “A” Floppy drive for 5.25 inch floppies.
- 2. The “B” Floppy drive for 3.5 inch floppies.
- 3. The “C” Hard Disk drive, typically of 40 MBytes or more.
The two floppy disk drives are used primarily for file transfers and program
updates.
The “C” disk is divided into several parts:
-
the Root directory which contains all of the fundamental files for starting
the computer,
-
the “DOS” directory which contains the MS-DOS files,
-
the “HSSPROGRAMS” directory which contains all of the Helgeson programs,
command files, menus, etc., and
-
other directories containing utility programs.
The “HSSPROGRAMS” directory will have names such as “QUICKY1,” “DIYSNAI,”
“DIYSHPGE,” etc. The directory contains all of the Helgeson programs. It
also has two sub-directories, “SUPPORTS” and “WB1.” The “SUPPORTS” directory
contains all of the supporting files, parameters, etc. The “WB1” directory
contains only the data from whole body counts, such as the original data
and the short “answer” files. A “tree” of the directory structure is shown
in Figure 2-1, below.
| Frame10 |
| Figure 2-2. The Tree Structure
of the “C” Disk. |
There are several other directories which are required for some of the
Miscellaneous Programs menu, such as RADDECAY, PCPLUS, and UTIL.
2.3. Networking (if used)
 |
| Figure 2-2. Simplified schematic diagram of a Token Ring Network.
|
The communications between two computers is carried out by an IBM Token
Ring Network program shown in Figure 2-2, below. Disk “C” the File Server
computer is equivalent to Disk “P” on any of the in vivo computers. Demographic
information for an individual may be entered at a separate computer, such
as at a “Personnel Entry and Termination station,” or on “Quicky A,” “Quicky
B,” or “DIYS A,” and the data are immediately available to all other stations.
Disk “P” on the File Server computer contains the Personnel File Data Base
and the Answer File Data Base. Once every ten minutes the entire Personnel
Data Base may be copied from the File Server to the other counters to ensure
that all files are in synchronization.
The typical networking hardware and software used by Helgeson Scientific
Services is called the “Invisible Network.” It is fully compatible with
Novell. The specifications are given in Table 2-5 on Page 2-12.
The following paragraphs are taken from the literature of a supplier of
typical network hardware and software:
A Local Area Network is a hardware and software system that connects individual
Personal Computers together to form an integrated whole. Usually, the Personal
Computers are in the same office or department, in close proximity to each
other.
With the Invisible Ethernet-16, you can build a high-performance Local
Area Network at low cost. You can share expensive equipment such as large
fixed disks and laser printers. You can send messages from one computer
to another with electronic mail. And most valuable of all, you can share
computer data such as databases, accounting records, spreadsheets, and
word-processing documents.
Many of the most popular software titles are now available in special network
versions. With Invisible Ethernet-16, you can tap the power of network
software, while continuing to use your existing single-user software.
Invisible Ethernet-16 uses industry-standard Ethernet technology, recognized
around the world as offering high reliability and high performance.
Unlike other Ethernet-based products, the Invisible Ethernet-16 is designed
specifically for use in a small business, office, or department. It has
the same performance and features as IBM’s big networks, but is simpler,
less expensive, and easier to install. Where IBM’s networks are tailored
to the needs of large corporations, Invisible Ethernet-16 is tailored to
the needs of small business.
Features:
-
Complete system includes Ethernet board and network software.
-
16-bit design for high performance.
-
Includes NET/30 Network Operating System.
-
Compatible with IBM’s NetBIOS standard.
-
In addition to NET/30, Invisible Ethernet-16 also runs the IBM PC LAN Program,
Novell Netware, Torus Tapestry, CBIS Network-OS, and other Net BIOS-compatible
operating systems.
-
Operates at 10.0 Mbps (million bits per second).
The Invisible Ethernet Cable connects the computers that form the network.
Each piece of cable has a BNC plug at either end. One end of the cable
plugs into the “T” connector on one Invisible Ethernet Adapter, and the
other end of the cable plugs into the “T” connector on another Invisible
Ethernet Adapter.
Since each “T” connector has two jacks, each card can be connected to two
other cards. This allows the computers in the network to be daisy chained.
For example, if there are five computers in the network, they can be connected
together as follows:
1——-2——-3——-4——-5
In this example, computer #2 is connected to both computer #1 and computer
#3. Computer #3 is connected to both computer #2 and computer #4. Computer
#4 is connected to both computer #3 and computer #5.
This type of wiring is called “daisy chain” because each computer is connected
both to the next computer and also to previous computer, just like the
links in a chain. Each computer in the middle of the chain is connected
to two other computers. The two computers at the ends of the chain are
each connected to only one other computer.
Frame15
2.4. Software
2.4.1. Setup Requirements
The software is pre-loaded on the disk so you should not have any reason
to load software. There will be certain “messages” which may have to be
changed and there are many operating parameters which may be changed to
suit your particular needs. These are all discussed in Chapter 9.
2.4.1.1. The AUTOEXEC.BAT File
The AUTOEXEC.BAT file is shown in Figure 2-3, below.
There should be no reason to change it.
files = 100
buffers = 30
lastdrive = z
fcbs = 16,8
stacks = 32,128
device = c:\net30\cache.sys
device = c:\dos\ansi.sys
device = c:\qemm\qemm.sys ram
rem device = c:\dos\ramdrive.sys 16 128 4 /e
device = c:\net30\n30dev.sys
cd DIYSV50
mainmenu.exe
|
| Figure 2-3, This is a typical "AUTOEXEC.BAT" file. |
2.4.1.2.
The CONFIG.SYS File
files = 100
buffers = 30
lastdrive = z
fcbs = 16,8
stacks = 32,128
device = c:\net30\cache.sys
device = c:\dos\ansi.sys
device = c:\qemm\qemm.sys ram
rem device = c:\dos\ramdrive.sys 16 128 4 /e
device = c:\net30\n30dev.sys
|
| Figure 2-4, This is a typical "CONFIG.SYS" file. |
2.4.2.
Software Languages
Most of the “HELGE” software is written in Borland’s Turbo Pascal, Version
6.0. For data base work an extension to Turbo Pascal called “Topaz,” allows
us to write data to a file that is in the same format as a standard dBase
file.
2.5.
General Instructions
In this chapter we shall discuss some of the fundamental instructions necessary
for operating the Helgeson systems. Many of the readers will already have
a basic knowledge of Personal Computers (PC’s), so this will just be a
refresher course. Those of you who are using a PC for the first time will
want to pay special attention to the instructions in this chapter because
it will affect how well you may use these programs.
2.5.1.
Screen Display on Boot-Up
The screen display on booting the computer is shown in Figure 2-5, on the
next page.
C:\ Echo off
Net/30 Networking Operating System Version 2.20
Copyright 1991 Invisible Software Inc.
... Loading SHARE.EXE ...
... Loading TransBios and NetBIOS ...
Invisible Ethernet: Address=199, Speed=10 Mbps, IRQ=11, I/O=300
... Loading Server
Net/30-EMS File Server Version 2.20
Copyright 1991 Invisible Software Inc.
One Moment Please ...
Command completed successfully
...Loading Re-director ...
Net/30-EMS Re-Director Version 2.20
Copyright 1991 Invisible Software Inc.
One moment please
P: == \\Server\C:\
LPT1: == \\Server\1
... Loading Mail
Copyright 1991 Invisible Software Inc.
Net/30-EMS Resident Mail
Copyright 1991 Invisible Software Inc.
Command completed successfully
(Editor’s Note: At this point the program will automatically start.)
|
| Figure 2-5, This is a typical screen display during boot-up if a network is present. |
2.5.2.
Typing Instructions
2.5.2.1
General Typing Information
The computer keyboard looks like an expanded version of a standard typewriter
keyboard. There are groups of keys to the right and left of the regular
typewriter keys, and several special purpose keys.
The computer keys act just like the keys on a typewriter. The characters
you type appear on the terminal screen, instead of on a piece of paper.
NOTE
A computer takes things literally.
So, you cannot use the letters O
(“Oh”) and l (lower case “L”)
for the numbers 0 (“zero”) and 1 (one).
Use the “Shift” key to get capital letters just as you would with a typewriter.
When two symbols are pictured on a key, the “Shift” key gives you the upper
one.
The “Lock” key (on some keyboards it will be labeled “Caps Lock”) makes
all the letter keys upper case, but it does not affect the number keys
or the punctuation keys. You will still have to use the “Shift” key to
get to the upper symbols on the number row. The “Lock” key toggles: that
is, if you press it once it will be on, and you press it a second time
and it is off. Note: If “Caps Lock” is on and you use the shift key while
typing alphabetical characters, you will receive the lower case character.
The “tab” key, typically found in the second row from the top on the extreme
left hand side, moves you to the right, usually 8 spaces. This key is used
infrequently in the HELGE software.
2.5.2.2.
Special Keys
2.5.2.2.1
How Do You Delete a Character?
When you are typing an entry, and you make a mistake, there is a key that
will allow you to delete characters to the left of where the cursor is
currently located. On some keyboards this is labeled the “delete” or “rub
out” key and on others it merely shows an arrow pointing to the left, or
an arrow pointing to the left with an “X” through it. Thus, when you are
typing an entry, this key moves you one space to the left, wiping out the
character it passes over. Important: Do not confuse the “back space” key
with the “delete” or “rub out” key. Some keyboards have both of these keys
and the use of “back space” instead of “delete” can cause confusion to
the software.
2.5.2.2.2.
The “Control” Key
The “CTRL” key is used to double the capacity of some other keys. For example,
in some of the indirect command files (you will learn about these later)
you may wish terminate the command file because you have made some mistakes
or you have changed your mind. Under these circumstances it is appropriate
to type “CTRL-Z”. This is accomplished by holding down the “CTRL” key and
pressing the “Z” key while you still hold the “CTRL” key down. Anytime
the Instruction Manual calls for the use of the “CTRL” key, remember that
you have to hold this key down while you type another key.
2.5.2.2.3. The “ALT” Key
The “ALT” key is similar to the “Control” key since it allows you to double
the capacity of some other keys. It is used for several commands in the
“HELGE” software.
2.5.2.2.4.
The “Enter” Key
The “Enter” key is sometimes called the “Return” key, or “carriage return”
key, because it is in the same location as the carriage return on a typewriter
keyboard. This key causes our software to “enter” what you have typed or
to carry out a menu command. It means, “go ahead, do it!”
During the balance of this Instruction Manual we shall use the symbol:
<ENTERƒ>
to symbolize the pressing of the “return” or “enter” key. Thus, the following
instruction means “type your menu selection followed by the return key:”
Enter selection (0 for menu): 2<ENTERƒ>
Please note in the example above that the part which had been typed by
the computer was in bold-face type, while the response by the operator
was underlined. This convention is used throughout the Instruction Manual.
2.5.2.2.5. The “Escape” Key
The “ESC” key is used infrequently, primarily when one is working with
the Keyboard Editor. Its location differs on different keyboards. For example,
on the standard “101-key” keyboard it is immediately to the left of the
numeral “1.”
2.5.2.2.6. Default Entries
At a number of places in the “HELGE” software you will encounter what we
call “default entries.” These are opportunities to accept the usual mode
of operation but at the same time to allow you to change the mode of operation
should you wish. For example, in the program for plotting the Quality Control
charts, the computer asks the following question:
* Print the file? [Yes]
This statement is telling you is that we usually want to print the file.
If you wish to do so, all you have to do is press the <ENTERƒ> key because
the default answer is shown as “Yes.” The letter in the square brackets
([ ]) is called the “Default” answer to the question. In the above example,
the letter “Y” stands for the English affirmative response “yes.”
If you did not want to print the file, you would have answered the question
by pressing “N<ENTERƒ>.”
In all parts of our software the default answer is expressed in the language
of the operator, that is, English for those people using English, Spanish
in Spanish speaking countries, etc.
Thus, we can summarize by saying that “default” values are printed and
are there for you to accept or reject. If you choose to accept them, all
you need to do is to press the <ENTERƒ> key. If you choose to reject them,
you must type the alternative choice followed by the <ENTERƒ> key.
2.5.3. Using the Mouse
Version 4.2 (and following versions) of the “HELGE” software allows use of the mouse in certain
portions of the programs. If you do not have a mouse, you will see a rectangle
or a white arrow near the center of the screen that may be partially obscurring
a character. An example of this is shown in Figure 2-6, at the top of the
next page. Look at Option 7, “System Diagnostics.” You see that the letter
“o” of “Diagnostics” is partially hidden by a grey rectangle (it will appear
red on the screen). This is the normal location of the mouse cursor when
it has not been used, or when a mouse is not connected to the system. Many
of the screen captures shown throughout this instruction manual will have
the mouse cursor at some other location because in the preparation of the
manual we have deliberately moved the cursor to a location that will not
interfere with the understanding of the picture. Figure 2-7, at the bottom
of the next page, is an example. In this screen capture we have moved the
mouse cursor to the right of the menu block and now it appears as a solid
black rectangle.
Frame25
|
| Figure 2-6, This picture shows the "Main Menu" screen with the rectangular mouse cursor interfering with the "o" in the word "Diagnostics" in Option 7. |
2.6.
Initial Procedures for Setting Up a Counter
There are several steps that must be taken before using a counting system.
These are:
-
Setting the high voltage, gain, zero intercept,
-
Determining the “gain factor,
-
Determining the speed control coefficients, and
-
Modifying the parameters to suit your needs.
Each of these will be discussed below.
2.6.1.
Initial setup of High Voltage, Gain, and Zero Intercept
When any product that is manufactured by Helgeson Scientific Services is
about to be used for the very first time for gamma spectral data accumulation,
it is necessary to establish a proper high voltage, the proper gain, and
the zero intercept. This document will show the actual adjustment of the
various controls.
The objective is to collect data and nominal gain of 5 keV per channel
and a zero intercept that will meet the standard conditions established
in the document IDO-16880. The sources being used are 60-cobalt for the
high energy reference points at 1173.32 KeV and 241-americium for the low
energy reference point at 59.54 keV. From Heath’s document we find that
at a nominal gain of 5-keV per channel, the lower 60-cobalt for the should
fall in channel 230.37 and 241-americium photopeak should fall in channel
14.28.
Figure 2-1 shows the background spectrum that was obtained at high voltage
setting of 500 volts. There is nothing special about this voltage, it
could have been anything between approximately 400 volts and 1200 volts,
but experience has shown that the sodium iodide detectors work best at
voltage of approximately 800 to 900 volts. The amplifier gain was found
to be at 4.05 out of a possible 10.0. Since the zero control is a screwdriver
adjustment, it is not possible to state the actual numerical value. This
spectrum does not show anything that is recognizable as a typical sodium
iodide spectrum with potassium (found in the glass of the photomultiplier
tube and in the environment) as the only radioactive material in the background.
It is obvious that this high voltage is not adequate to meet our objective
of a nominal 5-KeV per channel.
|
| Figure 2-7, This is the spectrum when the high voltage is arbitrarily set at 500 volts. |
How can we achieve these objectives? There are several methods:
-
Change the high voltage, gain and zero settings and test repeatedly, or
-
Establish the difference in channels, set the high voltage and gain to
meet this difference, then adjust the zero control to put the 241-americium
in the correct channel.
We shall choose the second method because if you choose the first method,
you will find that you may have to adjust all three, high voltage, gain,
and zero, after each change of one of them.
Table 2-7, below shows the various energies and correct channels. The next
to the bottom row shows the difference in energies, 1113.67 and the difference
in channels, 216.09, showing that the effective gain is 5.15 keV per channel.
| Energy | Channel |
| 60-cobalt, lower peak | 1173.21 | 230.27 |
| 241-americium | 59.54 | 14.28 |
| Differences | 1113.67 | 216.09 |
| | Effective KeV/Channel | 5.1537 |
| Table 2-7, Energies, their Center Channels, and Differences |
Since the previous figure was not recognizable as a typical sodium iodide
spectrum, the next step was to raise the high voltage by 100 volts to see
if the spectrum was somewhat recognizable. This screen is shown in Figure
2-8, below, where the high voltage was set to 600 volts.
|
| Figure 2-8, This is the spectrum when the high voltage is set at 600 volts.
|
It is helpful to put a markers in channels 14 and 230. This may be done several ways, but
the easiest is to type the letter “M” and the number “14," then type ”M"
and the number “230.” (After each change of high voltage press ALT-R to
start a new data accumulation.) You may also use the ability of the software
to put up a marker by moving the cursor to the center of a channel and
pressing “pg up.” The computer will tell you the center channel using
the method of Zimmerman. (You may erase all markers by pressing “u*” or
by pressing “u” followed by the marker number. If you erase marker one
first of all, the old marker to now becomes marker one.)
We shall now look at the center channels of 241-americium and 60-cobalt as we change the high voltage.
Figure 2-10 shows that the center of the 241-americium photopeak is in channel
18.5 (look in the lower right corner of the screen). Figure 2-11 shows the
center of the 1173.21 keV 60-cobalt photopeak is in channel 206.8. The
difference in channels is 188.3, showing that the high voltage (and/or
the gain) is not high enough.
|
| Figure 2-9, the 241-americium peak center is channel 18.5 when the high voltage is set at 1000 volts. (Look in the lower right hand corner of the picture. |
|
| Figure 2-10, the 60-cobalt peak center is channel 206.8 when the high voltage is set at 1000 volts. (Look in the lower right hand corner of the picture.) |
Raising the voltage another 100 volts (to a total of 1100 volts) is too
much, as seen in Figures 2-11 and 2-12. The americium photopeak is now in
channel 28.9 and 60-cobalt photopeak is in channel 382.6, giving a difference
of 353.7 channels. This says that we should go back to the previous high
voltage setting and start using the fine tuning available from the 10-turn
potentiometer on the high voltage power supply.
|
| Figure 2-11, The 241-americium peak in in channel 28.9 when the high voltage is set at 1100 volts. |
 |
| Figure 2-12, The 60-cobalt peak in in channel 382.6 when the high voltage is set at 1100 volts. |
Figures 2-13 and 2-14 were obtained with a high voltage setting of 1070.0 volts
and the amplifier gain potentiometer set at 5.00. The americium photopeak
is now in channel 20.7 and 60-cobalt photopeak is in channel 243.6. Under
these conditions the difference in channels is 222.9. Since it is desirable
to have the amplifier gain potentiometer set about midscale (5.00), we
shall reduce the high voltage to 1065.0.
.jpg)
|
| Figure 2-13, The 241-americium peak is in channel 22.3 when the high voltage is set at 1070.0 volts. |
|
| Figure 2-14, The 60-cobalt peak is in channel 243.6 when the high voltage is set at 1070.0 volts. |
Figures 15 and 16 show that we now have the americium in channel 20.5 and
60-cobalt at channel 234.7 for a difference of 214.2 channels. This is
near to the difference in channels that we want, 216.09 channels. Therefore,
we are very close to the desired difference. It is time to stop changing
the high voltage, leave it at 1065.0 volts and to change the gain potentiometer
until we come to a channel difference of 216.09.
|
| Figure 2-15, The 241-americium peak is in channel 20.5 when the high voltage is set at 1065 volts. |
 |
| Figure 2-16, The 60-cobalt peak is in channel 232.6 when the high voltage is set at 1065.0 volts. |
Setting the gain potentiometer at 5.10, we obtained center channels of
21.6 and 240.1, for a difference of 218.5 channels or, we are still 2.41
channels to high in terms of gain. We are actually close enough, however, that we
can start to modify the zero adjustment on the back of the PCA2 card.
As was stated earlier, this is a screwdriver adjustment, see Figure 2-20 on
the bottom of the next page. Turning it clockwise adds more channels at
the left side. Since we want the americium photopeak to be in channel
14.28 and it currently is in channel 21.6, let us start by making one full
360 degree rotation of the zero. Figures 2-18 and 2-19 show the results where
the 241-americium is in channel 14.4 and the 60-cobalt is in channel 232.6,
making the diffenence equal to 217.8 channels.. We are now close enough
to the correct settings that we can do the balance of the adjustments using
Option 2 from the Main Menu, “Calibrations,” and Sub-Menu 1, “Energy vs.
Channel,” to finish the adjustments.
|
| I think that I have duplicated some pictures. |
|
| I think that I have duplicated some pictures. |
|
| Figure 2-17, This picture shows the zero adjustment on the PCA-2 card. It is next to the “IN” coaxial cable connector that comes from the amplifier and detector. |
2.6.2
Determining the “Dial Gain Factor”
The determination of the “Dial Factor(s)” is documented in Chapter 11,
Section 11.6, “Energy Calibration, Part 6, Determining the Dial Factors.”
2.6.3
Determining the Speed Control Coefficients
This subject is discussed in Chapter 17, “Linear and Rotational Speed Calibrations”
| This chapter is not on the web as of June 17, 2003 at 9:40 AM. Check frequently as it is being put into "HTML" format at the present time. |
2.6.4
Modifying the Parameters
Modification of the parameters and why you may want to do this is documented
in Chapter 9, “Examine/Change Parameters.”
| This chapter is not on the web as of June 17, 2003 at 9:40 AM. Check frequently as it is being put into "HTML" format at the present time. |
This is the end of Chapter 2, “Hardware, Software, and Instructions.”
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