WO2017035322A1

WO2017035322A1 - Emulating detector output of a radioactive sample

Info

Publication number: WO2017035322A1
Application number: PCT/US2016/048610
Authority: WO
Inventors: Author J. HALL; Winston LAM; Mary Anne YUSKO; Roman Zaikin
Original assignee: Capintec, Inc.
Priority date: 2015-08-27
Filing date: 2016-08-25
Publication date: 2017-03-02

Abstract

A system and method for emulating detector output corresponding to spectrum data of emission counts and emission energy of a radioactive material detected by a detector. The system includes at least one digital to analog converter (DAC) configured to produce a voltage pulse at a predetermined frequency, and to modulate an amplitude of pulses; a CPU operably connected to the at least one DAC; memory operably connected to the CPU and configured to store data corresponding to the spectrum data; and software executable by the CPU and configured to analyze the spectrum data in order to control the frequency of the pulses and at least one DAC to adjust the amplitude of pulses.

Description

EMULATING DETECTOR OUTPUT

OF A RADIOACTIVE SAMPLE BACKGROUND OF THE DISCLOSURE

An overview of Gamma-Ray spectroscopy can be found at

https://en.wikipedia.org/wiki/Garnma_spectroscopy. As described therein, gamma rays are produced by radioactive sources in a spectrum of various energies and intensities. The spectrum can be analyzed to determine the radioactive constituents, or nuclides, in a sample. Gamma energy is measured within a range, typically, of a few keV to about 10 MeV. Gamma rays tend to be produced within a narrow range of energy, producing spikes of varying intensity within the range of energy.

To measure the spectrum, an energy -sensitive radiation detector provides a pulsed signal which is analyzed by a pulse sorter or multichannel analyzer (MCA). Examples of gamma detectors include sodium iodide (Nal) scintillation counters and germanium detectors, and solid state detectors. Alpha rays can also be detected, using a liquid scintillation detector, for example. The detector produces a voltage pulse, and in the case of a scintillation detector, a photomultiplier (PMT) produces the voltage pulse, which corresponds to emitted radiation.

The MCA digitizes the incoming signal from the detector pulses based on the amplitude of each pulse, and stores the obtained digital data in channels within memory corresponding to voltage/amplitude, or energy. Each channel, typically 1 to 4 bytes wide, stores the number of counts with the same amplitude that came from the detector within a period of time in which the spectrum was acquired.

The number of channels can therefore correspond to the resolution of the measurement system for a given range of energy. Common numbers of channels include 512, 1024, 2048, 4096, 8192, and 16384 channels.

For a given manner of organizing the channels or representing the processed spectrum data, emissions by particular nuclides will be the same. In this manner, the identity of nuclides within a sample is possible, typically with the aid of a computer processor configured to access data relating to known spectra.

Radiation detectors and MCAs can be calibrated by using radioactive samples having a composition that is known with certainty and specificity. These samples can be difficult to obtain, and can be hazardous to handle and use. SUMMARY OF THE DISCLOSURE

The disclosure relates to a system for emulating detector output corresponding to spectrum data of emission counts and emission energy of a radioactive material detected by a detector. The system comprises: at least one digital to analog converter (DAC) configured to produce a voltage pulse at a predetermined frequency, and to modulate an amplitude of pulses; a CPU operably connected to the at least one DAC; memory operably connected to the CPU and configured to store data corresponding to the spectrum data; and software executable by the CPU and configured to analyze the spectrum data in order to control the frequency of the pulses and at least one DAC to adjust the amplitude of pulses.

The at least one DAC can include a first DAC controlled by the CPU to generate pulses of a waveform shape corresponding to the detector and the radioactive material, and a second DAC controlled by the CPU to adjust an amplitude of pulses. The system can further include a LPF (low pass filter) connected to an output of the first DAC.

In some embodiments, the second DAC controls the amplitude of each pulse. The second DAC can be a two channel DAC, including a channel for controlling the overall amplitude corresponding to a desired FSR, and a channel for the adjustment of amplitude of pulses. The system can further include a source of a reference voltage signal connected to one of the at least one DAC.

The disclosure also relates to a method of simulating output of a radiation detector using spectrum data generated from detecting a radioactive sample, with the spectrum data including activity counts at varying energy levels corresponding to sequential channels corresponding to energy levels. The method comprises using at least one computer to execute software stored on non-transitory media. The software is configured to: construct a first memory array by sequentially setting each element of the first array to the number of counts in each of successive channels from the original spectrum having count values greater than zero, adding to the number of counts the total number of counts in the preceding array element; construct a second memory array by sequentially setting each element of the second array to the channel number of each successive channel from the original spectrum which has a count value greater than zero; and successively

a) generate a random number between zero and the value in the highest numbered element of the first memory array,

b) identify the lowest element number in the first array which is equal to or larger than the generated random number, c) identify the channel number in the second array stored in the element of the second array having a pointer equal to the pointer of the lowest element number identified for the first array, and

d) cause the output of a pulse signal in an output channel corresponding to the channel number identified, with the channel number corresponding to a particular energy level for the pulse.

In an exemplary embodiment, the pulses are output at a predetermined rate.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is an example of a PRIOR ART spectrum generated from detection of Cobalt-60 using an Nal Probe type detector;

FIG. 2 is an illustrative spectrum corresponding to a virtual isotope, to aid in understanding the disclosure;

FIG. 3 is a display screen image of a user interface of the device of FIG. 4;

FIG. 4 is a diagram of an illustrative example of a device of the disclosure for emulating output of a detection device outputting a signal corresponding to radioactivity detected;

FIG. 5A-5E are oscilloscope readings taken at the captioned locations within the device of FIG. 4;

FIG. 6 is a block diagram for calculating two tables which are used for spectrum replicating, based on original spectrum, in accordance with the disclosure;

FIG. 7 is an example of output of a CAPTUS MCA board report, the MCA board using an input produced by a device of the disclosure; and

FIG. 8 is an illustrative computing system, some or all of which can be used in carrying out the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely examples and that the systems and methods described below can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present subject matter in virtually any appropriately detailed structure and function. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the concepts.

The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms "including" and "having," as used herein, are defined as comprising (i.e., open language). The term "coupled," as used herein, is defined as "connected," although not necessarily directly, and not necessarily mechanically.

System 100 (FIG. 2) of the disclosure generates a spectrum signal which enables operation of a MCA (Multi-Channel Analyzer) type device, without a requirement for using real radioactive sources and detectors. More particularly, a device of the disclosure is connected to an MCA circuit board or device instead of a real detector with a real radioactive source. With the use of system 100, an MCA class device can be reliably designed, demonstrated, and repaired, without a requirement for using radioactive materials to produce an input signal. More particularly, system 100 generates one or more consistent spectrums or test patterns, at a stable count rate. Further, not only can a device of the disclosure produce spectrums of a real isotopes, but can also be used to create unique 'spectrums', which can be useful for MCA board testing or performance comparison.

FIG. 1 illustrates an actual spectrum emitted by an isotope as detected by a radiation emission detection device. More particularly, FIG. 1 is an output report from a CAPTUS

MCA board, the board obtaining input from a Nal Probe type detector and a sample of Co-60.

To aid in understanding the disclosure, FIG. 2 illustrates a simple, virtual spectra which corresponds to a real spectrum, but which contains a limited number of data points/channels, so that an example of the disclosure can be more easily understood. It should be understood that a system 100 of the disclosure can analyze complex spectrum of the type illustrated in FIG. 1, and use such spectrums to simulate corresponding output of a detection device.

With reference to FIGS. 3-6, and in particular FIG. 4, an illustrative system 100 of the disclosure includes a CPU 120/705 (hereinafter 120) that controls a selected isotope spectrum emulating process of the disclosure, and enables the display of information about a selected isotope, including a current count rate and an output signal full scale range (FSR) percentage, on an LCD or other display device 770. CPU 120 can be the same or a different processor than processor 705 of FIG. 7. CPU 120 can additionally process user input, for example scanning the state of a keypad 756 or mouse 757. Display device 770, or human interface devices 756, 757 can be embedded within a case (not shown) which houses system 100, or can be external peripherals. CPU 120 can further control the state of a digital POT

(potentiometer) 152 to adjust the contrast of LCD 770. Additionally, CPU 120 can save currently selected settings, including for example a selected isotope, count rate, and FSR percentage, to memory 715, which in an embodiment is nonvolatile EEPROM, so that these settings can be quickly loaded during a subsequent use of system 100 on power up.

In an embodiment of the disclosure, an 8-bit DAC 130 is used to generate a pulse waveform with fixed shape and amplitude for a selected isotope spectrum or test pattern, by converting stored data corresponding to a waveform shape for a particular nuclide or mixed sample, to analog data representative of the sample. An output of DAC 130 is thus a pulse signal as would be observed from a detector which is detecting a radioactive sample, and that can have a maximum amplitude equal to a reference voltage 150. The reference voltage can be adjustable, for example using CPU 120. It should be understood that a higher resolution DAC can be used.

DAC 130, combined with Low Pass Filter (LPF) 132, generates pulses with a fixed amplitude, functioning as a form of Reference Pulse generator. The selected spectrum is replicated by further changing the Reference Pulse amplitude by gaining or attenuating it. This process can be considered as Reference Pulse Amplitude Modulation and DAC 130 and LPF 132 participate in the circuitry 136 that performs such action. This Modulation, based on the algorithm of the disclosure, leads to the distribution of pulses of varying amplitude at the output of system 100, in order to approximate or be equal to the spectrum selected for replication.

Power for system 100 can be obtained from a 110/220v outlet, for instance via a wall mount power supply, or can be powered from a USB port of a computing device using a USB connector 144. An input voltage can be converted and regulated to a desired operating voltage for system 100, for example +/- 5 volts, using a voltage converter if needed, and a regulator, illustrated collectively as 146.

It should be understood that various alternative components can be substituted for the components described herein, in order to carry out the functionality described herein.

When emulating a radioactive source, a pulse of short duration, for example 2.5 microseconds, is required to be generated. Due to speed limitations of DAC 130, a limited number of samples per pulse can be produced, which, combined with DAC's limited settling time, can result in a DAC 130 output, which appears choppy if viewed on an oscilloscope, containing non-smooth steps between samples. If uncorrected, this can cause a false peak detection within the MCA or other device to which system 100 is providing an input. Accordingly, the disclosure provides a low pass filter (LPF) 132 connected to the output of DAC 130, which operates to anti-alias the output of DAC 130 by removing short-term fluctuations.

The output of LPF 132 is passed to a 2-stage 10-bit DAC 136, which performs two functions. A first stage, DAC-A, sets an output signal FSR percentage. This enables the simulation of various photomultiplier tube (PMT) detectors, which can have different output efficiencies (gain), and which can exhibit reduced output due to PMT aging.

A second stage of DAC 136, DAC-B, changes the amplitude for the pulse from LPF 132 output corresponding to the original spectrum data. The software algorithm employed by DAC 136 can be unique for each application, changing the gain depending upon the isotope or desired test signal. A DAC 136 having a resolution higher or lower than 10 bits can be used. A 10 bit DAC can provide a 1024 channel spectrum. The number of channels of the output spectrum should be equal to or exceed the resolution (number of channels) of the MCA board that the device is connected to. For example, a 10-bit DAC can be used for 256-, 512- and 1024-channel MCAs, but for 2048-channel MCAs, at least an 11-bit DAC is required, as well as original spectrum data acquired with at least a 2048-channel MCA board.

In order to simulate a PMT, system 100 provides an output with substantial current, which is enabled by amplifier 138. To protect the amplifier from damage caused by high voltage applied to the PMT during normal operation, protection and decoupling circuitry 140 is provided, including, for example, a high voltage decoupling capacitor to decouple 140 output from HV coming from a connected MCA board, and a TVS diode (not shown) for overvoltage protection during initial decoupling capacitor charging. More particularly, PMTs and other detector types typically require 50 to 1000 volts (HV) for proper functioning. In most cases, this voltage is generated by the MCA board. The detector is connected to the MCA board using a coax cable with a central wire used for dual purposes: (1) to provide a bias voltage from the MCA board to the detector, and (2) to provide a signal path from the detector to the MCA board. If this cable is disconnected from the detector, and then connected to system 100, the HV could damage system 100 without this decoupling and overvoltage protection. A connection between system 100 and the MCA can be made using, for example, a BNC connector 154 or any other suitable type of connector.

The functioning of 8-bit DAC 130 and 10-bit, 2-Channel multiplying DAC 136 can be further understood with reference to FIGS. 5A-5E, in which FIG. 5 A illustrates a rough waveform shape generated by DAC 130, based upon reference voltage 150 and data input from CPU 120 corresponding to the signal (pulse) shape and width of the detector type selected. As can be seen, the low resolution of 8-bit DAC 130 produces some jitter; however, DAC 130 is selected to be able to produce a pulse width of 3 microseconds or less.

In an embodiment, for DAC 130, a settling time of ½ LSB is 100ns. To obtain a pulse width of about 3 microseconds at the LPF output, we write 8 predefined codes to DAC 130 within about a 1.3 microsecond period (FIG. 5A). The values of the codes can be readily found experimentally in order to obtain a pulse shape which is very close to the real detector output. It is of course possible to use a DAC with a much faster settling time and a higher resolution. Furthermore, it is possible to eliminate the use of a CPU from this process of generating a reference pulse. Instead, for example, a CPLD (Complex Programmable Logic Device) or the like can be used, and the CPU can simply generate a command to start off the process. This would facilitate a modest increase in output signal count rate.

As can be seen in FIG. 5B, the LPF 132 signal output has removed most of the jitter, and also increases the pulse width, in this example, by about one-half. More particularly, LPFs reduce signal amplitude by cutting higher harmonics. Pulse width is also changed due to a combination of LPF parameters and the final speed of the Operational Amplifier used for implementing the LPF.

The analog pulse output of LPF 132 is sent to 10-bit 2-Channel multiplying DAC 136, where the output amplitude will be amplified or attenuated to fit the channel designated by CPU 120. In this example, a serial interface is used to control both DACs (DAC-A and DAC- B of FIG. 5). The channel indicated by CPU 120 corresponds to a voltage level programmed through DAC 136. Each successive channel typically corresponding to a stepped increase in voltage level, a representative example of which is shown in FIG. 5D.

Being a 2-Channel device, DAC 136 can also be used to adjust the overall output, as shown in FIG. 5C, in which a full scale range (FSR) can be applied to set a maximum output, or the output can be adjusted to represent an age or other specific output level of a PMT which is being simulated.

In an embodiment, a maximum count rate is about 26 kcps. Most limitations on count rate are imposed by CPU speed, where the CPU is unable to calculate the value of a new code for the next pulse any faster. However, a substantially faster output is possible by using a faster CPU, or, for example, by using programmable logic for channel calculation, as needed to simulate a particular detector and isotope activity. In theory, a maximum count rate cannot exceed l/(Pulse period). For a 3 microsecond pulse this equates to about 330 kcps. As a practical matter, this value will be reduced by the time required for calculation of a new channel, for loading the calculated code to DAC, for setting up the DAC, and other operations, based upon the specific hardware and software implementations selected. Finally, the output of amplifier 138 is illustrated in FIG. 5E.

Timer 142, implemented for example with a programmable interrupt timer (PIT), enables software of the disclosure to provide at least two interrupt servicing procedures. More particularly, a first interrupt has a fixed period, for example 20 Hz, which is used as a system tick for capturing human input, for example a keypad status. The keypad can be used, for example, to:

1. Change of detector type, for example to a WELL, PROBE or TEST SIGNAL;

2. Change the Isotope to be simulated, or the Test Signal pattern;

3. Change the Count Rate;

4. Change the FSR percentage; or

5. Adjust LCD or display contrast.

These changes can be displayed on display 770 for the convenience of a user of system 100, and can be stored in memory 715.

The second interrupt specifies a Count Rate of the output signal. Its period is variable and can be changed thru a Count Rate setting accessible to a user of system 100 though a user interface, which can include a keyboard 756 and display output 770, or which can be accessed through a serial or browser interface, if desired. It should be understood that a wide variety of features can be added to system 100, which are not described for this embodiment, including other interfaces. During this interrupt, CPU 120 performs at least these actions:

1. causes a pulse signal to be generated;

2. calculates new channel number values, using a software or hardware random generator, for designating the various channels of the 2-stage 10-bit DAC-B 136 which corresponds to an observed spectrum of an isotope selected. This leads to the output signal amplitude distribution being close to that of the spectrum of the selected isotope. During this calculation two tables or memory Arrays 1 and 2 are used, described in detail below, which are generated based on a real, previously acquired spectrum of the selected isotope, and which are stored in memory accessible to the CPU; and

3. sequentially writes calculated values to the 10-bit DAC-B 136 corresponding to the channel to which the next pulse output is to be sent.

With reference to FIG. 3, a display 770, in this example an LCD display is shown, which includes several fields corresponding to the simulation to be performed. One or more of these fields have been selected by a user of system 100 using a keyboard or other input device, or an uploaded data file, or any other manner of programming of CPU 102, which controls the display, which is known or is hereinafter developed.

More particularly, at the upper left, 'PROBE' is indicated, representing that system 100 will be simulating/emulating a Probe type detector. In this embodiment, other programmed simulations include a Well type detector, and a Test pattern. It should be understood that any type of detector can be simulated by system 100. In this embodiment, DAC 130 generates pulses with fixed amplitude, and software executed by CPU 120 controls DAC-B 136 to adjust for observed differences in spectrums obtained with either Probe or Well type detectors.

At the upper right, 'Csl37' is selected, indicating the type of isotope that is to be simulated. Memory /storage 715 can contain spectrum data corresponding to many different isotopes which are selectable by a user of system 100 for simulation as described herein.

At the lower left, '26 kcps' is selected, corresponding to the rate at which pulses will be output by system 100, in this case 26 thousand counts per second, although lower and higher speeds can be selected, bound only by the speed of the various components described herein, and in particular the speed of CPU 120 and DACs 130 and 136.

At lower right, ' 100% FSR' has been selected, to indicate 100% of the Full Scale Range of the stored spectrum data, although any other percentage can be selected by a user of system 100. This field allows a user to simulate an aging of a particular detector, or other characteristic of a detector which affects an output range of the detector. If a user selects 50% FSR, for example, the maximum amplitude of the signal at the output will be 1/2 of its value at 100% FSR.

CPU 120/705 executes software for emulating detector output corresponding to spectrum data for a real isotope, the software configured to carry out the calculations and execute the actions described above and in the following detailed example.

Table 1 presents a simplified example of real world spectrum data, graphically presented in FIG. 2. The example is simplified because, typically, there would be 1024 channels, each corresponding to a different, progressively higher voltage level for observed pulses from a real world sample. Additionally, the counts would be substantially higher, for example tens of thousands of counts per channel. However, the calculations provided for the sample data, below, would be the same for data representing a real sample.

Tables 2 and 3 provide examples of computer Arrays 1 and 2 of the disclosure, which in this example are based upon the data of Table 1. Arrays 1 and 2 are used in accordance with the disclosure for generating output data corresponding to pulse data of one or more selected isotopes, and which are created using data from a spectrum previously acquired for a real sample of one or more isotopes.

Table 1: Illustrative Spectrum Data

Table 2: Array 1

To create Array 1, the following algorithm of the disclosure is used:

la. The first element of Array 1 is set to the number of counts of the first channel from the original spectrum having a count value greater than 0. Alternatively stated, all initial channels having a zero value are ignored. With respect to the spectrum of Table 1, the first element of Array 1 corresponds to channel 2 of this illustrative spectrum, having a value of 5. There are only 7 array items, as there are only 7 values in Table 1 that are greater than zero. In accordance with the disclosure, channels with the number of count equal to zero are skipped to avoid uncertainty during calculation of the code value for the DAC that is responsible for output signal amplitude modulation (a 10-bit DAC-B in this embodiment). By skipping channels from the illustrative spectrum with zero number of count, Array 1 becomes strictly monotonous and this is important for further calculations.

lb. The value of every subsequent element of Array 1 is set to the count value of the next non-zero channel of Table 1 plus the value of the previous element of Array 1. In this manner, each subsequent element of Array 1 represents a running total count value.

As such, Array 1 has a number of elements equal to the number of channels in a given spectrum having a count not equal to zero. Further, the first element of the table stores the number of counts of the first channel having a non-zero value; the last value stores the total counts for the entire spectrum; and the number of elements is not larger than the total number of channels in the spectrum.

Table 4 illustrates one possible software routine which can be used in the creation of Array 1 as described above. Table 4: Example Software Routine for Creating Array 1

II a1 [j] is an element of Array 1 with index 'j', and Channel[i] holds the number of counts // for the channel ΐ from original (illustrative) spectrum j=1 ; for (i=0; i< (Number of Channels in original (illustrative) spectrum); i++)

{

if (Channel [i] != 0 )

{

k= i

a1 [j] =∑ (Channel [k]);

k=0;

j⁺⁺;

}

Table 3 illustrates Array 2, created using the data of original (illustrative spectrum) Table 1. To create Array 2, the following algorithm is used:

2a. The first element of Array 2 is set to the first channel number from the original

(illustrative) spectrum Table 1 having a count value greater than zero.

2b. Each subsequent array element stores the channel number of the next channel from original (illustrative) spectrum Table 1 that has a count number greater than zero. It is noted that as a practical matter, each element of Array 2 stores the code value for the DAC that provides an output signal amplitude to correspond to desired channel.

Table 5 illustrates one possible software routine which can be used in the creation of Array 2 as described above.

Table 5: Example Software Routine for Creating Array 2

II a2[j] is an element of Array 2 with index 'j', and Channel[i] holds the number of

// counts for the channel Ί' from original (illustrative) spectrum j = 1 ;

for (i=0; i< (Number of Channels in the original (illustrative) spectrum); i++)

{

if ((Channel [i]) != 0 )

{

a2[j] = i;

j⁺⁺;

}

// Note: As a practical matter, algorithms 1 and 2 can be combined in one routine) For the virtual illustrative spectrum of Table 1 , it was given that there were only 7 nonzero count values, and therefore there are only 7 elements for each of Array 1 and 2. For real isotope spectrums, both tables can have, for example, 1024 elements, or up to the number of elements as there are channels in the spectrum.

In an embodiment, if the original spectrum has more channels than a particular embodiment of system 100 can generate, a few channels from the original spectrum can be summed to downgrade the number of channels to the required value. This is straightforward when the number of channels of the original spectrum are a multiple of the number of channels that the generator can produce. If this is not the case, additional processing is needed to calculate Arrays 1 and 2. Similarly, if the MCA has a higher resolution (number of channels) than system 100 can provide, the output spectrum will have a stepped aspect. Accordingly, it is advantageous for system 100 to have a resolution (number of channels) which is as high as possible, and for the original spectrum for replication to have a number of channels equal to, or a multiple of, the number of channels available within a particular design embodiment of system 100.

If 1024 channels are to be analyzed, each element of array 2 should be a 16-bit integer, in order to be able to store a sufficiently large number. For array 1, the required data width can be derived from the total number of counts in the spectrum. However, as CPUs are readily available which perform 32 bit moves and arithmetic, it may be convenient to store data as 32-bits (4 bytes), which should provide adequate storage for all values likely to be used.

The foregoing algorithms are diagrammatically shown in FIG. 6, in which the first channel having a number of counts not equal to zero is determined in steps 502, 504 and 506, for a 1024 channel system. At 508, Tables 1 and 2, corresponding to Arrays 1 and 2, respectively, are initialized. More particularly, the first element of Table 1 is initialized with the first non-zero count value of the real spectrum, and the first element of Table 2 is initialized with the channel number of the first non-zero value in the real spectrum. The remainder of the channels of the original spectra are analyzed at 510, and at 512, the cumulative count values are stored in Table 1, and the channel number of non-zero counts are stored in Table 2, until all channels in the real spectrum have been analyzed.

Once Arrays 1 and 2 are formed, they can be used to generate a signal which is sent to the MCA or other receiving device over time, and which reflects the original spectrum data corresponding to a real radioactive sample.

To generate this signal, the following algorithm is used: 3a. A random number is generated between 0 and the total count value, which can be obtained from the last element of Array 1 (in this case, 105).

3b. The values of Array 1 are sequentially iterated to find the first count value which is greater than or equal to the generated random number.

3c. The Array Index associated with the selected element of step 3b is used as an array index within Array 2, whose corresponding value is a channel number of the MCA to which a new 'pulse' is sent. As previously mentioned, as a practical matter, Array 2 contains a code value that should be loaded into the DAC-B to send a new pulse to the desired channel.

3d. Steps 3a to 3c are repeated to generate a distribution of pulses or counts over time, which correspond to the original spectrum data, which is reflective of a real world radioactive sample. The frequency of pulses corresponds to the selected count rate.

For example, given a random number of 30, the first value in Array 1 which is greater than or equal to 30 is the value of 35, corresponding to Array 1 index number 3. In Array 2, array index 3 corresponds to the value 4. Thus, a pulse is sent to channel 4 of the MCA. Additional random values are chosen, and additional pulses are sent to the corresponding MCA channels, at a rate that corresponds to the count rate chosen by the user to correspond to a real sample.

In one embodiment, a user is enabled to select from 10 preset values for a count rate. The number of presets and count rate range is ultimately a function of the component specification of an implementation of system 100, including cost factors. Further, each pulse is generated as a result of an interrupt processing routine, and there are many ways that an interrupt can be generated. Thus, the limitation in terms of count rate is defined by a minimum interval between two consecutive interrupts, which (interval) should never be less than maximum time for interrupt processing.

Over time, the count and distribution of pulses generated by system 100 within the various channels corresponding to energy levels, if plotted, would match the original spectrum with sufficient accuracy to result in the same analysis result by the MCA as the original real sample.

Accordingly, system 100 executes software for carrying out the algorithms described above, in such a manner that an input spectrum corresponding to a real isotope or nuclide can be analyzed, converted to Arrays 1 and 2, and then simulated using system 100. By connecting system 100 to a multichannel analyzer or other device configured to accept input from a multichannel detector, the effect of an isotope on the detector can be simulated without a requirement for the presence of either the detector or an isotope, as system 100 replaces both simultaneously, and with a high level of reproducibility. The multichannel recipient device can thus be used for testing, manufacturing, quality control, demonstration, manufacturing calibration, or any other purpose, without the use of radioactive materials.

FIG. 7 illustrates output from a CAPTUS MCA board, the board obtaining input from system 100, correctly identifying Co-60 using a Probe detector.

System 100 of the disclosure provides for replacement/simulation of PMT-based detectors, as well as other types of detectors. Additional interfaces and features can be provided by incorporating multiple processors and additional components beyond those described for the embodiment herein. Additionally, specially designed ASICs can be used which may exhibit advantageous characteristics with respect to a general purpose CPU, including a higher count rate, higher resolution, and a more robust user interface with a wider number of available parameter and range selections, at a relatively reduced cost. It is further possible to use an advanced external generator instead of an internal 8-bit DAC to generate a reference pulse, or to provide additional inputs.

Example Computing System

FIG. 8 illustrates the system architecture for a computer system 700, such as a process controller, or other processor on which or with which the disclosure may be implemented. The exemplary computer system of FIG. 8 is for descriptive purposes only. Although the description may refer to terms commonly used in describing particular computer systems, the description and concepts equally apply to other systems, including systems having architectures dissimilar to FIG. 8. Computer system 700 can control temperatures, motors, pumps, flow rates, power supplies, ultrasonic energy power generators, and valves, using actuators and transducers. One or more sensors, not shown, provide input to computer system 700, which executes software stored on non-volatile memory, the software configured to receive inputs from sensors or from human interface devices, in calculations for controlling system 200.

Computer system 700 includes at least one central processing unit (CPU) 705, or server, which may be implemented with a conventional microprocessor, a random access memory (RAM) 710 for temporary storage of information, and a read only memory (ROM) 715 for permanent storage of information. A memory controller 720 is provided for controlling RAM 710. A bus 730 interconnects the components of computer system 700. A bus controller 725 is provided for controlling bus 730. An interrupt controller 735 is used for receiving and processing various interrupt signals from the system components.

Mass storage may be provided by DVD ROM 747, or flash or rotating hard disk drive 752, for example. Data and software, including software 400 of the disclosure, may be exchanged with computer system 700 via removable media such as diskette, CD ROM, DVD, Blu Ray, or other optical media 747 connectable to an Optical Media Drive 746 and

Controller 745. Alternatively, other media, including for example a media stick, for example a solid state USB drive, may be connected to an External Device Interface 741, and

Controller 740. Additionally, another computing device can be connected to computer system 700 through External Device Interface 741, for example by a USB connector, BLUETOOTH connector, Infrared, or WiFi connector, although other modes of connection are known or may be hereinafter developed. A hard disk 752 is part of a fixed disk drive 751 which is connected to bus 730 by controller 750. It should be understood that other storage, peripheral, and computer processing means may be developed in the future, which may advantageously be used with the disclosure.

User input to computer system 700 may be provided by a number of devices. For example, a keyboard 756 and mouse 757 are connected to bus 730 by controller 755. An audio transducer 796, which may act as both a microphone and a speaker, is connected to bus 730 by audio controller 797, as illustrated. It will be obvious to those reasonably skilled in the art that other input devices, such as a pen and/or tablet, Personal Digital Assistant (PDA), mobile/cellular phone and other devices, may be connected to bus 730 and an appropriate controller and software, as required. DMA controller 760 is provided for performing direct memory access to RAM 710. A visual display is generated by video controller 765 which controls video display 770. Computer system 700 also includes a communications adapter 790 which allows the system to be interconnected to a local area network (LAN) or a wide area network (WAN), schematically illustrated by bus 791 and network 795.

Operation of computer system 700 is generally controlled and coordinated by operating system software, such as a Windows system, commercially available from Microsoft Corp., Redmond, WA. The operating system controls allocation of system resources and performs tasks such as processing scheduling, memory management, networking, and I/O services, among other things. In particular, an operating system resident in system memory and running on CPU 705 coordinates the operation of the other elements of computer system 700. The present disclosure may be implemented with any number of commercially available operating systems.

One or more applications, such as an HTML page server, or a commercially available communication application, may execute under the control of the operating system, operable to convey information to a user.

All references cited herein are expressly incorporated by reference in their entirety. It will be appreciated by persons skilled in the art that the present disclosure is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. There are many different features to the present disclosure and it is contemplated that these features may be used together or separately. Thus, the disclosure should not be limited to any particular combination of features or to a particular application of the disclosure. Further, it should be understood that variations and modifications within the spirit and scope of the disclosure might occur to those skilled in the art to which the disclosure pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present disclosure are to be included as further embodiments of the present disclosure.

Claims

THE CLAIMS What is claimed is:

1. A system for emulating detector output corresponding to spectrum data of emission counts and emission energy of a radioactive material detected by a detector, the system comprising:

at least one digital to analog converter (DAC) configured to produce a voltage pulse at a predetermined frequency, and to modulate an amplitude of pulses;

a CPU operably connected to the at least one DAC;

memory operably connected to the CPU and configured to store data corresponding to the spectrum data;

software executable by the CPU and configured to analyze the spectrum data in order to control the frequency of the pulses and at least one DAC to adjust the amplitude of pulses.

2. The system of claim 1, wherein the at least one DAC includes a first DAC controlled by the CPU to generate pulses of a waveform shape corresponding to the detector and the radioactive material, and a second DAC controlled by the CPU to adjust an amplitude of pulses.

3. The system of claim 2, further including a LPF (low pass filter) connected to an output of the first DAC.

4. The system of claim 2, wherein the second DAC controls the amplitude of each pulse.

5. The system of claim 2, wherein the second DAC is a two channel DAC, including a channel for controlling the overall amplitude corresponding to a desired FSR, and a channel for the adjustment of amplitude of pulses.

6. The system of claim 1, further including a source of a reference voltage signal connected to one of the at least one DAC.

7. A method of simulating output of a radiation detector using spectrum data generated from detecting a radioactive sample, the spectrum data including activity counts at varying energy levels corresponding to sequential channels corresponding to energy levels, the method comprising:

using at least one computer to execute software stored on non-transitory media, the software configured to:

construct a first memory array by sequentially setting each element of the first array to the number of counts in each of successive channels from the original spectrum having count values greater than zero, adding to the number of counts the total number of counts in the preceding array element;

construct a second memory array by sequentially setting each element of the second array to the channel number of each successive channel from the original spectrum which has a count value greater than zero;

successively

b) identify the lowest element number in the first array which is equal to or larger than the generated random number,

c) identify the channel number in the second array stored in the element of the second array having a pointer equal to the pointer of the lowest element number identified for the first array, and d) cause the output of a pulse signal in an output channel corresponding to the channel number identified, the channel number corresponding to a particular energy level for the pulse.

8. The method of claim 7, wherein pulses are output at a predetermined rate.