AGREEMENT AND PLAN OF REORGANIZATION

                                      AMONG

                           THERMEDICS DETECTION INC.,

                             ORION ACQUISITION INC.,

                                 THERMEDICS INC.

                                       AND

                               ORION RESEARCH INC.

                          _____________________________

                                Dated May 6, 1998
                          _____________________________









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                                TABLE OF CONTENTS

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             SECTION 1 - THE REORGANIZATION
                   1.1  The Merger                               
                   1.2  Effective Time              
                   1.3  Closing
                   1.4  Certificate of Incorporation and By-Laws
                   1.5  Directors and Officers  
                   1.6  Conversion of Stock  
                   1.7  Payment for Orion Common Stock
                   1.8  Adjustments     
                   1.9       Lost Certificates        
                   1.10 No Fractional Shares


             SECTION 2 - REPRESENTATIONS AND WARRANTIES OF 
                       THERMEDICS AND ORION  

                   2.1  Organization and Qualification
                   2.2  Authority
                   2.3  Capitalization and Title to Shares
                   2.4  Subsidiaries and Other Affiliates
                   2.5  Financial Statements
                   2.6  Absence of Undisclosed Liabilities;         
                                                                    
                                                                    
                                            No Dealings with
                        Affiliates   
                   2.7  Taxes 
                   2.8  Properties
                   2.9  Hazardous Materials
                   2.10 Accounts Receivable
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                   2.11 Inventories                        
                   2.12 Purchase and Sale Commitments      
                   2.13 Governmental Authorizations   
                   2.14 Intellectual Property         
                   2.15 Insurance                               
                   2.16 Employee Benefit Plans 
                   2.17 Agreements and Documents 
                   2.18 Validity                           
                   2.19 No Changes                         
                   2.20 Litigation or Proceedings 
                   2.21 Compliance with Laws 
                   2.22 Labor Matters                      
                   2.23 Recalls                            
                   2.24 Brokers and Finders                
                   2.25 Powers of Attorney                 
                   2.26 No Termination of Relationship
                   2.27 All Information 
                   2.28 Statements True and Correct 


             SECTION 3 - REPRESENTATIONS AND WARRANTIES OF 
                   DETECTION AND ACQUISITION 

                   3.1  Organization 
                   3.2  Authority
                   3.3  Statements True and Correct 


             SECTION 4 - COVENANTS AND AGREEMENTS 

                   4.1  Conduct of Business 
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                   4.2  Corporate Examinations and Investigations 
                   4.3  Expenses 
                   4.4  Authorization from Others 
                   4.5  Consummation of Agreement 
                   4.6  Further Assurances 
                   4.7  Tax-Free Reorganization 
                   4.8  Listing of Shares 
                   4.9  Public Announcements and Confidentiality    
                   4.10      No Solicitation
                   4.11 Indemnification
                   4.12 Participation in Employee Benefit Plans
                   4.13      Certain Tax Matters


             SECTION 5 - CONDITIONS PRECEDENT TO THE 
                   OBLIGATIONS OF DETECTION AND ACQUISITION 
                   TO CONSUMMATE THE MERGER 

                   5.1  Representations, Warranties and Covenants
                   5.2  Articles of Merger 
                   5.3  Certificates 


             SECTION 6 - CONDITIONS PRECEDENT TO THE 
                   OBLIGATION OF THERMEDICS AND ORION 
                   TO CONSUMMATE THE MERGER 

                   6.1  Representations, Warranties and Covenants 
                   6.2  Articles of Merger 
                   6.3  Certificates 




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             SECTION 7 - TERMINATION, AMENDMENT AND WAIVER 

                   7.1  Termination
                   7.2  Effect of Termination 
                   7.3  Amendment 
                   7.4  Waiver 


             SECTION 8 - MISCELLANEOUS 

                   8.1  Notices
                   8.2  Survival and Materiality of Representations 
                   8.3  Entire Agreement 
                   8.4  Parties in Interest 
                   8.5  No Implied Rights or Remedies 
                   8.6  Headings 
                   8.7  Severability 
                   8.8  Counterparts 
                   8.9  Further Assurances 
                   8.10      Governing Law 


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                      AGREEMENT AND PLAN OF REORGANIZATION


             THIS AGREEMENT AND PLAN OF REORGANIZATION (this "Agreement")
        dated May 6, 1998 is among Thermedics Detection Inc.
        ("Detection"), a Massachusetts corporation, Orion Acquisition
        Inc. ("Acquisition"), a Massachusetts corporation and a
        wholly-owned subsidiary of Detection, Thermedics Inc.
        ("Thermedics"), a Massachusetts corporation, and Orion Research
        Inc. ("Orion"), a Massachusetts corporation and a wholly-owned
        subsidiary of Thermedics.  The parties wish to effect the
        acquisition of Orion by Detection through a merger of Acquisition
        with and into Orion on the terms and conditions hereof.  This
        Agreement is intended to be a "plan of reorganization" within the
        meaning of Section 368(a) of the Internal Revenue Code of 1986,
        as amended (the "Code").

             Accordingly, in consideration of the foregoing and the
        mutual representations and covenants contained herein, the
        parties hereto agree as follows:


                         SECTION 1 - THE REORGANIZATION

             1.1  The Merger.  Upon the terms and subject to the
        conditions hereof, and in accordance with the Business
        Corporation Law of the Commonwealth of Massachusetts (the
        "BCLM"), Acquisition shall be merged with and into Orion (the
        "Merger").  The Merger shall occur at the Effective Time (as
        defined in Section 1.2).  Following the Merger, Orion shall be
        the surviving corporation (the "Surviving Corporation") and the
        separate corporate existence of Acquisition shall cease.

             1.2  Effective Time.  As soon as practicable after the
        execution of this Agreement and satisfaction or waiver of all
        conditions to the Merger, the parties shall cause articles of
        merger (the "Articles of Merger") with respect to the Merger to
        be filed and recorded in accordance with Section 78 of the BCLM
        and shall take all such further actions as may be required by law
        to make the Merger effective.  The Merger shall be effective at
        such time as the Articles of Merger are duly filed with the
        Secretary of State of the Commonwealth of Massachusetts in
        accordance with the BCLM or at such later time as is specified in
        the Articles of Merger (the "Effective Time").  The date on which
        the Merger shall be effective is hereafter referred to as the
        _Effective Date._

             1.3  Closing.  Immediately prior to the filing of the
                  -------
        Articles of Merger, a closing (the "Closing") will be held at the
        offices of Thermo Electron Corporation, 81 Wyman Street, Waltham,
        Massachusetts (or such other place as the parties may agree) for 
                                     
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        the purpose of confirming satisfaction or waiver of all 
        conditions to the Merger.  The date on which the Closing occurs
        is referred to herein as the "Effective Date."

             1.4  Articles of Organization and By-Laws.  The Articles of
        Organization and By-laws of Acquisition, in each case as in
        effect immediately prior to the Effective Time, shall be the
        Articles of Organization and By-laws of the Surviving Corporation
        immediately after the Effective Time.

             1.5  Directors and Officers.  The directors and officers of
        Acquisition immediately prior to the Effective Time shall be the
        directors and officers of the Surviving Corporation immediately
        after the Effective Time.

             1.6  Conversion of Stock.

                  At the Effective Time, by virtue of the Merger and
        without any action on the part of Detection, Acquisition,
        Thermedics or Orion:

                  (a) Each share of common stock of Orion ("Orion Common
        Stock") outstanding immediately prior to the Effective Time,
        other than (A) shares held by Orion as treasury stock or shares
        held by any subsidiary of Orion and (B) shares owned beneficially
        by Detection, Acquisition or any other subsidiary of Detection,
        (the "Orion Shares") shall be converted into and become the right
        to receive a pro rata share of a total of 5,961,225 shares (the
        "Detection Shares") of common stock, $.10 par value per share, of
        Detection ("Detection Common Stock").  The Detection Shares are
        referred to herein as the "Merger Consideration."

                  (b) All shares of Orion Common Stock held at the
        Effective Time by Orion as treasury stock or by a subsidiary of
        Orion shall be canceled without any conversion thereof and no
        payment shall be made with respect thereto.

                  (c) All shares of Orion Common Stock owned
        beneficially at the Effective Time by Detection, Acquisition or
        any other subsidiary of Detection shall be cancelled without any
        conversion thereof and no payment shall be made with respect
        thereto.

                  (d) Each share of the common stock of Acquisition
        ("Acquisition Common Stock") outstanding immediately prior to the
        Effective Time shall be converted into and become one validly
        issued, fully paid and nonassessable share of common stock, $0.10
        par value per share, of the Surviving Corporation. 

             1.7  Payment for Orion Common Stock.

                  (a) At the Effective Time, the stock transfer books of
        Orion shall be closed and no transfers of Orion Common Stock may
        be made thereafter.  Promptly after the later of (i) the listing 
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        of the Detection Shares for trading on the American Stock
        Exchange, Inc. ("AMEX"), as contemplated by Section 4.8 below,
        and (ii)  the proper surrender by Thermedics of such certificates
        representing the Orion Shares, Detection shall cause its stock
        transfer agent to issue and deliver to Thermedics a certificate
        for the Detection Shares.  It shall be a condition of such
        payment and delivery that the surrendered certificate(s) be
        properly endorsed or otherwise in proper form for transfer and
        that Thermedics shall pay any transfer or other taxes required by
        reason of such payment or delivery or establish, to the
        satisfaction of Detection and the Surviving Corporation that such
        tax has been paid or is not applicable.  The date on which all of
        the conditions to the issuance of the certificate representing
        the Detection Shares shall have been met is referred to
        hereinafter as the "Payment Date." 

                  (b) Notwithstanding the provisions of subsection (a)
        of this Section 1.7, in the event that, notwithstanding
        Detection's best efforts, Detection is unable to obtain the
        approval of its stockholders of the listing of the Detection
        Shares for trading on AMEX on or before December 31, 1998, then,
        on December 31, 1998, Detection will pay to Holdings the sum of
        $65,800,000 in cash in lieu of issuing the Detection Shares.

             1.8  Adjustments.

                  (a) In the event Detection shall declare, pay, make or
        effect between the date of this Agreement and the Payment Date,
        (i) any stock dividend or other distribution in respect of the
        Detection Common Stock payable in shares of capital stock of
        Detection, (ii) any stock split or other subdivision of
        outstanding shares of Detection Common Stock into a larger number
        of shares, (iii) any combination of outstanding shares of
        Detection Common Stock into a smaller number of shares, (iv) any
        reclassification of Detection Common Stock into other shares of
        capital stock or securities, or (v) any exchange of the
        outstanding shares of Detection Common Stock, in connection with
        a merger or consolidation of Detection or sale by Detection of
        all or part of its assets, for a different number or class of
        shares of stock or securities of Detection or for the share of
        the capital stock or other securities of any other corporation,
        appropriate adjustment shall be made in the number of Detection
        Shares to be issued in connection with the Merger as may be
        required to put Holdings in the same position as if the record
        date, with respect to any such transaction or transactions which
        shall so occur, had been immediately after the Payment Date, or
        otherwise to carry out the intents and purposes of this
        Agreement.

                  (b) In the event Detection shall declare, pay, make or
        effect between the date of this Agreement and the Payment Date
        any dividend or other distribution in respect of the Detection
        Common Stock payable in cash or other property other than in
        shares of capital stock of Detection, then the Detection Shares 
                                       
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        to be issued in connection with the Merger shall be deemed to be
        outstanding as of the record date with respect to any such
        dividend or distribution, and the cash or other property 
        otherwise payable or distributable to Thermedics with respect to 
        such Detection Shares shall be held by Detection for the benefit
        of Thermedics; and Detection shall take all actions reasonably
        necessary to prevent such cash or other property from being or
        becoming subject to any lien, security interest or other
        encumbrance not for the benefit of Thermedics.  Upon the issuance
        of the Detection Shares to Thermedics pursuant to Section 1.7(a)
        above, such cash or other property shall likewise be distributed
        by Detection to Thermedics.  In no event shall Thermedics be
        entitled to receive interest on such dividends or distributions.
        In the event that Detection pays Thermedics cash consideration
        pursuant to Section 1.7(b) above, then such cash or other
        property held by Detection on behalf of Thermedics shall not be
        paid or distributed to Thermedics and Thermedics shall have no
        further interest therein or claim thereto.

             1.9  Lost Certificates.  In the event any certificate
        representing Thermedics' Orion Shares shall have been lost,
        stolen or destroyed, upon the making of an affidavit of that fact
        by Thermedics, Detection shall issue in exchange for such lost,
        stolen or destroyed certificate the consideration payable in
        exchange therefor pursuant to this Section 1.

             1.10 No Fractional Shares.  No certificates representing
        fractional Detection Shares shall be issued upon the surrender
        for exchange of the Orion Shares.  No fractional interest shall
        entitle the owner to vote or to any rights of a security holder.
        In lieu of a fractional share, Thermedics will receive upon
        surrender of the Orion Shares an amount in cash (without
        interest) determined by multiplying such fraction by $11.0379.

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                 SECTION 2 - REPRESENTATIONS AND WARRANTIES OF 
                              THERMEDICS AND ORION

             Except as set forth on the disclosure schedule delivered to
        Detection on the date hereof (the "Orion Disclosure Schedule"),
        Thermedics and Orion, jointly and severally, represent and
        warrant to Detection and Acquisition as follows.  The term
        "knowledge," when used in this Agreement, shall mean actual
        knowledge after reasonable investigation.

             2.1  Organization and Qualification. 

                  (a) Each of Thermedics and Orion is a corporation duly
        organized, validly existing and in good standing under the laws
        of its jurisdiction of incorporation and has full corporate power
        and authority to own, lease and operate its assets and to carry
        on its business as now being and as heretofore conducted.  Each
        of Thermedics and Orion is qualified or otherwise authorized to
        transact business as a foreign corporation in all jurisdictions 
        in which such qualification or authorization is required by law,
        except for jurisdictions in which the failure to be so qualified
        or authorized would not have a material adverse effect on the
        assets, properties, business, results of operations, condition
        (financial or otherwise) or prospects of Orion (the "Business of
        Orion").

                  (b) Thermedics and Orion have previously provided to
        Detection true and complete copies of their charter and By-laws
        as in effect on the date hereof, and neither of such corporations
        is in default thereunder.

             2.2  Authority.  Each of Thermedics and Orion has full
        right, power, capacity and authority to execute, deliver and
        perform this Agreement and to consummate the transactions
        contemplated hereby.  The execution, delivery and performance of
        this Agreement, the filing of the Articles of Merger and the
        consummation of the transactions contemplated hereby have been 
        duly and validly authorized by all necessary corporate action on
        the part of Thermedics and Orion. This Agreement has been duly
        and validly executed and delivered by each of Thermedics and
        Orion and constitutes the valid and binding obligation of
        Thermedics and Orion, enforceable against them in accordance with
        the terms hereof.  Neither the execution, delivery and
        performance of this Agreement, the filing of the Articles of
        Merger nor the consummation of the transactions contemplated
        hereby will (i) conflict with or result in a violation, breach,
        termination or acceleration of, or default under (or would result
        in a violation, breach, termination, acceleration or default with
        the giving of notice or passage of time, or both) any of the
        terms, conditions or provisions of the Articles of Organization
        or By-laws of Thermedics or Orion, as amended, or of any note,
        bond, mortgage, indenture, license, agreement or other instrument
                                       
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        or obligation to which either of Thermedics or Orion is a party
        or by which either of Thermedics or Orion or any of their
        respective properties or assets may be bound or affected; (ii)
        result in the violation of any order, writ, injunction, decree,
        statute, rule or regulation applicable to Thermedics or Orion or
        any of their respective properties or assets; (iii) result in the
        imposition of any lien, encumbrance, charge or claim upon any of
        Thermedics' or Orion's assets; or (iv) entitle any employee to
        severance or other payments by Orion or create any other
        obligation to an employee.  Except for the filing of the Articles
        of Merger, no consent or approval by, or notification to or
        filing with, any court, governmental authority or third party is
        required in connection with the execution, delivery and
        performance of this Agreement by Thermedics and Orion or the
        consummation of the transactions contemplated hereby.

             2.3  Capitalization and Title to Shares.

                  (a) The authorized capital stock of Orion consists of
        200,000 shares of Orion Common Stock, of which 100 shares are
        issued and outstanding as of the date hereof.  Thermedics is the 
        record and beneficial owner of all of such issued and outstanding
        shares.  All of the issued and outstanding shares of the capital
        stock of Orion are duly authorized and are validly issued, fully
        paid, nonassessable and free of preemptive rights. 

                  (b) Except as set forth above, there are not as of the
        date hereof, and at the Effective Time there will not be, any
        other shares of capital stock of Orion authorized or outstanding
        or any subscriptions, options, conversion or exchange rights,
        warrants, repurchase or redemption agreements, or other
        agreements or commitments obligating Orion to issue, transfer,
        sell, repurchase or redeem any shares of its capital stock or
        other securities of Orion.  To the knowledge of Thermedics and
        Orion, there are no written shareholder agreements, voting
        trusts, proxies or other agreements, instruments or
        understandings with respect to the voting of the capital stock of
        Orion.  The books and records of Orion, including without
        limitation the books of account, minute books, stock certificate 
        books and stock ledgers, are complete and correct and accurately
        reflect the conduct of the business and affairs of Orion.

             2.4  Subsidiaries and Other Affiliates. 

                  (a) The Orion Disclosure Schedule sets forth all
        Subsidiaries of Orion and the jurisdiction in which each is
        incorporated.  All shares of the capital stock of each Subsidiary
        owned by Orion are owned free and clear of any charges, liens,
        encumbrances, security interests or adverse claims.  As used in
        this Agreement, "Subsidiary" means any corporation or other legal
        entity of which a party to this Agreement owns, directly or
        indirectly, fifty percent (50%) or more of the stock or other
        equity interest entitled to vote for the election of directors
        and representations, warranties and covenants referring to Orion
                                       
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        contained herein shall be deemed to mean Orion and each of its
        Subsidiaries, both separately and together as a consolidated
        whole, unless and except to the extent expressly indicated
        otherwise.

                  (b) There are not as of the date hereof, and at the
        Effective Time there will not be, any other shares of capital
        stock of any Subsidiary of Orion authorized or outstanding or any
        subscriptions, options, conversion or exchange rights, warrants,
        repurchase or redemption agreements, or other agreements or
        commitments obligating any Subsidiary of Orion to issue,
        transfer, sell, repurchase or redeem any shares of its capital
        stock or other securities.  There are no shareholder agreements,
        voting trusts, proxies or other agreements, instruments or
        understandings with respect to the voting of the capital stock of
        any Subsidiary of Orion.

                  (c) Except for its Subsidiaries, Orion does not,
        directly or indirectly, own any material equity interest in any
        corporation, partnership, joint venture or other entity.

             2.5  Financial Statements.  Orion has delivered to Detection
        prior to the execution of this Agreement true and complete copies
        of:  (a) the audited consolidated balance sheet of Orion as at
        January 3, 1998 (the "Balance Sheet"), (b) Orion's audited
        consolidated statements of earnings and cash flows for the fiscal
        year ended January 3, 1998, (c) the audited consolidated balance
        sheet of Orion as at December 28, 1996, and (d) Orion's audited
        consolidated statements of earnings and cash flows for the fiscal
        year ended December 28, 1996 (collectively, the "Financial
        Statements").  The Financial Statements have been prepared from,
        and are in accordance with, the books and records of Orion and
        fairly present the financial condition, results of operations,
        and cash flows of Orion as at the dates and for the periods
        indicated, in each case in accordance with generally accepted
        accounting principles applied on a basis consistent with previous
        years.

             2.6  Absence of Undisclosed Liabilities; No Dealings with 
        Affiliates.  As of the date of the Balance Sheet, Orion had no
        material liabilities or obligations of any nature, whether
        accrued, absolute, contingent or otherwise and whether due or to
        become due (including without limitation, liabilities as
        guarantor or otherwise with respect to obligations of others or
        liabilities for taxes due or then accrued or to become due),
        required to be reflected or disclosed on the Balance Sheet that
        were not adequately reflected or reserved against on the Balance
        Sheet.  Orion has no liabilities of the type required to be
        reflected or disclosed on a balance sheet in accordance with
        generally accepted accounting principles, other than liabilities
        (i) adequately reflected or reserved against on the Balance
        Sheet, (ii) incurred since the date of the Balance Sheet in the
        ordinary course of business and consistent with past practice,
        (iii) that would not, in the aggregate, have a material adverse
                                       
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        effect on the Business of Orion, or (iv) disclosed in this
        Agreement.  Orion does not have any contractual arrangement with
        or commitment to or from any of its stockholders, officers,
        management, directors or employees (or their family members)
        other than such as may have been entered into in the normal
        course of employment, including, without limiting the generality
        of the foregoing, being directly or indirectly a joint investor
        or coventurer with respect to, or owner, lessor, lessee, licenser
        or licensee of, any real or personal property, tangible or
        intangible, owned or used by, or a lender to or debtor of, Orion.

             2.7  Taxes.  Orion has accurately prepared and duly and
        timely filed all federal, state, local or foreign tax and other
        returns and reports (_Tax Returns_) which were required to be
        filed, in respect of all income, franchise, excise, sales, use,
        property (real and personal), payroll and other taxes, levies,
        imports, duties, license and registration fees, charges or
        withholdings of any nature whatsoever (collectively "Taxes_).
        None of the federal, state, local or foreign Tax returns of Orion
        has been audited or examined by the governmental authority having
        jurisdiction.  No waivers of any statutes of limitation are in 
        effect in respect of any Taxes.  There are no claims pending or,
        to the best of its knowledge, threatened, against Orion for past
        due Taxes. All Taxes incurred but not yet due have been fully
        accrued on the books of Orion or full reserves have been
        established therefor; the reserves indicated on the Balance Sheet
        are also adequate to cover all Taxes that may become payable by
        Orion in future periods in respect of any transactions or sales
        occurring on or prior to the date of the Balance Sheet.  Without
        limiting the generality of the foregoing, Orion has withheld or
        collected from each payment made to each of its employees,
        consultants or non-U.S. payees, the amount of all Taxes required
        to be withheld or collected therefrom, and has paid the same to
        the proper tax receiving officers or authorized depositories.
        Orion has no liability for Taxes of any person other than Orion
        (a) under Regulation Sec. 1.1502-6 (or any similar provision of
        federal, state, local or foreign law, (b) as a transferee or
        successor, (c) by contract or (d) otherwise.

             2.8  Properties.  Except as set forth on the Orion
        Disclosure Schedule, Orion owns and has good title to all of the
        assets and properties reflected as owned by it on the Balance
        Sheet or acquired by Orion since the date of the Balance Sheet
        (except personal property sold or otherwise disposed of in the
        ordinary course of business since the date of the Balance Sheet),
        free and clear of any lien, claim or other encumbrance, except
        for (i) the liens, claims or other encumbrances reflected on the
        Balance Sheet, (ii) assets and properties disposed of, or subject
        to purchase or sales orders, in the ordinary course of business
        since the date of the Balance Sheet, (iii) liens, claims or other
        encumbrances securing the liens of materialmen, carriers,
        landlords and like persons, all of which are not yet due and
        payable, (iv) liens for taxes not yet delinquent and (v) liens,
        claims, other encumbrances or defects in title that, in the
                                      
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        aggregate, are not material to the Business of Orion.  Orion owns
        or has a valid leasehold interest in all of the buildings,
        structures, leasehold improvements, equipment and other tangible
        property material to the Business of Orion, all of which are in
        good and sufficient operating condition and repair, ordinary wear
        and tear excepted, for the conduct of its business in accordance
        with past practices and Orion has not received notice that any of
        such property is in violation in any material respect of any
        existing law or any building, zoning, health, safety or other
        ordinance, code or regulation.

             2.9  Hazardous Materials. 

                  (a) Orion has previously made available to Detection a
        true and correct list of all Hazardous Materials (as hereinafter
        defined) generated, used, handled or stored by Orion, the proper
        disposal of which will require any material expenditure by Orion.
        There has been no generation, use, handling, storage or disposal
        of any Hazardous Materials in violation of common law or any
        applicable environmental law at any site owned or premises leased
        by Orion during the period of Orion's ownership or lease that 
        could have a material adverse effect on the Business of Orion.
        Nor has there been or is there threatened any release of any
        Hazardous Materials on or at any such site or premises during
        such period in violation of common law or any applicable
        environmental law or which created or will create an obligation
        to report or remediate such release, which release or failure to
        report or remediate could have a material adverse effect on the
        Business of Orion.  For purposes of this Agreement, "Hazardous
        Material" means any medical waste, flammable, explosive or
        radioactive material, or any hazardous or toxic waste, substance
        or material, including substances defined as "hazardous
        substances," "hazardous materials," "solid waste" or "toxic
        substances" under any applicable laws or ordinances relating to
        hazardous or toxic materials and substances, air pollution
        (including noise and odors), water pollution, liquid and solid
        waste, pesticides, drinking water, community and employee health,
        environmental land use management, stormwater, sediment control,
        nuisances, radiation, wetlands, endangered species, environmental
        permitting, petroleum products, and all rules and regulations
        promulgated pursuant to any such laws and ordinances.

                  (b) Orion has previously made available to Detection
        copies of all documents concerning any environmental or health
        and safety matter that could have a material adverse effect on
        the Business of Orion, if any, and copies of any environmental
        audits or risk assessments, site assessments, documentation
        regarding off-site disposal of Hazardous Materials, spill control
        plans and material correspondence with any governmental authority
        regarding the foregoing.

             2.10 Accounts Receivable.  All accounts and notes
                  -------------------
        receivable of Orion shown on the Balance Sheet and all accounts
        and notes receivable acquired by Orion subsequent to the date of
                                       
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        the Balance Sheet have arisen in the ordinary course of business
        and have been collected, or are in the process of collection and
        are collectible in the ordinary course of business and in any
        event within nine months from the Effective Date, in the
        aggregate recorded amounts thereof, less the applicable
        allowances reflected on the Balance Sheet with respect to the
        accounts and notes receivable shown thereon, or set up consistent
        with past practice on the books of Orion with respect to the
        accounts and notes receivable acquired subsequent to the date of
        the Balance Sheet.

             2.11 Inventories.  All Inventories (as defined below) of
        Orion are of a quality and quantity usable and saleable in the
        ordinary course of business, except for obsolete items and items
        of below- standard quality, all of which are in the aggregate
        immaterial to the Business of Orion.  Items included in such
        Inventories are carried on the books of Orion, and are valued on
        the Balance Sheet, at the lower of cost or market.  The value of
        obsolete materials and materials of below-standard quality or
        quantity has been written down on Orion's books of account to
        realizable market value.  The term "Inventories" includes all 
        stock of raw materials, work-in-process and finished goods,
        including but not limited to finished goods purchased for resale,
        held by Orion for manufacturing, assembly, processing, finishing,
        sale or resale to others, from time to time in the ordinary
        course of business of Orion in the form in which such inventories
        then are held or after manufacturing, assembling, finishing,
        processing, incorporating with other goods or items, refining or
        the like.


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             2.12 Purchase and Sale Commitments.  No outstanding
        purchase commitments by Orion are in excess of the normal,
        ordinary and usual requirements of Orion, and the aggregate of
        the contract prices to which Orion has agreed in any outstanding
        purchase commitments is not so excessive when compared with
        current market prices for the relevant commodities or services
        that a material loss is likely to result.  No outstanding sales
        commitment by Orion obligates Orion to sell any product or
        service at a price which, because of currently prevailing and 
        projected costs of materials or labor, is likely to result, when
        all such sales commitments are taken in the aggregate, in a
        material loss to Orion. There are no suppliers to Orion of
        significant goods or services with respect to which practical
        alternative sources of supply, or comparable products, are not
        available on comparable terms and conditions.

             2.13 Governmental Authorizations.  Orion has all
        governmental permits, licenses, franchises, concessions, zoning
        variances and other approvals, authorizations and orders
        (collectively "Permits") material to the Business of Orion.  Such
        Permits constitute all the permits which are required under all
        applicable local, state, federal or foreign laws and regulations
        for the operation of the Business of Orion.  All such Permits are
        presently in full force and effect, Orion is in compliance with
        the requirements thereof, no suspension or cancellation of any of
        them is threatened so far as is known to Orion, and the Merger
        will not adversely affect the validity or effectiveness of, and
        will not require, for retention thereof after the Merger, the
        consent or approval of any party to, or any other person or
        governmental authority having jurisdiction of, any such Permit.
        Orion has no knowledge of any fact or circumstance which would
        prevent, limit or restrict it from continuing to operate its
        business in the present manner, and no new requirements
        pertaining to the manner of operating its business have been
        issued or announced by any governmental authority during the past
        year nor are there any disputes pending between Orion and any
        governmental authority relating to Orion's operations as
        presently being conducted or actively considered.  Orion has
        furnished or made available to Detection all reports and
        applications filed by it with any governmental authority in the
        last three years.

             2.14 Intellectual Property.  Orion owns, or is licensed to
        use, or otherwise has the right to use all patents, trademarks,
        service marks, trade names, trade secrets, franchises, and 
        copyrights, and all applications for any of the foregoing, and
        all technology, know-how and processes necessary for the conduct
        of its businesses as now conducted (collectively, the
        "Proprietary Rights").  A list of all such copyrights,
        trademarks, tradenames and patents, and all applications
        therefor, has been furnished or made available to Detection.
        Orion is not aware of any claim by any third party that the
        Business of Orion as currently conducted or proposed to be
                                      
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        conducted infringes upon the unlicensed Proprietary Rights of
        others, nor has Orion received any notice or claim from any third
        party of such infringement by Orion.  Orion is not aware of any
        infringement by any third party on, or any competing claim of
        right to use or own any of, the Proprietary Rights of Orion.
        Orion has the right to use, free and clear of claims or rights of
        others, all customer lists and computer software material to its
        business as presently conducted.  To the best knowledge of Orion,
        none of the activities of the employees of Orion on behalf of
        Orion violates any agreements or arrangements which any such
        employees have with former employers in a way which is materially
        adverse to the Business of Orion.

             2.15 Insurance.  Orion is not in default with respect to any
        provisions of any policy of general liability, fire, title or
        other form of insurance held by it, is current in the payment of
        all premiums due on such insurance and has not failed to give any
        notice or present any claim thereunder in due and timely fashion,
        except for claims that are immaterial in both the nature of the
        claim and in the amount of such claim.  Orion maintains insurance
        on all of its assets and its business (including products
        liability insurance) from insurers which to its knowledge are
        financially sound and reputable, in amounts and coverages and
        against the kinds of risks and losses reasonably prudent to be
        insured against by corporations engaged in the same or similar
        businesses.  No basis exists which would jeopardize the coverage
        under any such insurance.  No such insurance will be terminated
        or cancelled by reason of the execution, delivery and performance
        of this Agreement, the filing of the Articles of Merger or the
        consummation of the transactions contemplated hereby.  Orion has
        previously furnished or made available to Detection all policies
        of general liability, fire, title or other forms of insurance
        held by Orion and a description of all claims pending thereunder
        other than health or dental insurance claims.

             2.16 Employee Benefit Plans. 

                  (a) Orion has made available or furnished to Detection
        true and complete copies of each pension, profit-sharing,
        deferred compensation, incentive compensation, severance pay,
        retirement, welfare benefit or other plan or arrangement
        providing benefits to employees or retirees, including both those
        that do and do not constitute employee benefit plans within the
        meaning of Section 3(3) of the Employee Retirement Income
        Security Act of 1974, as amended ("ERISA"), currently maintained
        or contributed to by Orion or Thermedics for the benefit of 
        Orion's employees or retirees (each, a "Plan").

                  (b) Except as set forth on the Orion Disclosure
        Schedule, (i) each such Plan that is an "employee pension benefit
        plan" within the meaning of Section 3(2) of ERISA is being
        operated and administered in compliance with Section 401(a) of
        the Code, a favorable determination letter has been obtained from
        the Internal Revenue Service (the "IRS") for such Plan, and there
                                       
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        is no accumulated funding deficiency, as defined in Section
        302(a)(2) of ERISA or Section 412 of the Code, with respect to
        such Plan; (ii) there has been no non-exempt "prohibited
        transaction" within the meaning of Section 406 of ERISA or
        Section 4975 of the Code involving the assets of any Plan nor any
        "reportable event" within the meaning of Section 4043 of ERISA
        with respect to any Plan; (iii) all required employer
        contributions to such Plan have been made (or, in the case of
        contributions not yet due, have been accrued on the Balance
        Sheet); (iv) Orion has made available to Detection as to each
        such Plan a true and correct copy of (w) the annual report (Form 
        5500) filed with the IRS for each of the three most recent plan
        years, (x) each plan, trust agreement, group annuity contract and
        insurance contract, if any, relating to such Plan, (y) each
        actuarial report prepared for each of the last three years for
        each Plan and (z) each summary plan description distributed to
        participants in each Plan and each summary of material
        modifications to each Plan (as defined in ERISA); and (v) each
        such Plan is, and at all relevant times has been, in compliance
        with ERISA, the Code and the terms of such Plan.  Neither Orion,
        Thermedics nor any Subsidiary of Thermedics has ever participated
        in a "multiemployer pension plan" as defined in Section 3(37) of
        ERISA.

                  (c) Except as set forth on the Orion Disclosure
        Schedule, Orion has no obligation to provide any welfare benefits
        to retired or former employees other than continuation of welfare
        benefits as required by applicable law.

                  (d) Orion has no liability under or with respect to
        any employee benefit plans or arrangements that it no longer
        maintains or in which it no longer participates.

             2.17 Agreements and Documents.  Orion has previously
        furnished or made available to Detection true, correct and
        complete copies of each document that is referred to or otherwise
        related to any of the following items referred to in this Section
        2.17:

                  (a) each document related to interests in real
        property owned, leased or otherwise used or claimed by Orion;










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                  (b) (i) each agreement of Orion made in the ordinary
        course of business which involves aggregate future payments by or
        to Orion of more than one hundred fifty thousand dollars
        ($150,000) in the case of payments to Orion (including current 
        firm purchase orders for Orion products), seventy five thousand
        dollars ($75,000) in the case of payments by Orion, or any
        agreement made in the ordinary course of business whose term
        extends beyond one year after the date hereof; (ii) each
        agreement containing any covenant restricting the freedom of
        Orion to compete in any line of business or with any person; and
        (iii) each agreement of Orion not made in the ordinary course of
        business which is or was to be performed after the date hereof;

                  (c) all employment or similar compensation agreements
        of Orion which may not be terminated by Orion without penalty
        within thirty days after the Closing;

                  (d) all bonus, incentive compensation, deferred
        compensation, profit-sharing, stock option, retirement, pension,
        severance, indemnification, insurance, death benefit or other
        fringe benefit plans, agreements or arrangements of Orion (or
        applying to Orion) in effect, or under which any amounts remain
        unpaid, on the date hereof or to become effective after the date 
        hereof;

                  (e) all labor unions or other organizations
        representing, purporting to represent or attempting to represent
        any employees of Orion, and all collective bargaining agreements
        of Orion with any labor unions or other representatives or
        employees;

                  (f) each agreement or other instrument or arrangement
        defining the terms on which any indebtedness of Orion (or a
        guarantee by Orion of indebtedness) is or may be issued; and

                  (g) the names and addresses of all banks in which
        Orion has accounts or lines of credit, and with respect to each
        such account or line of credit, the names of all persons
        authorized to drawn thereon. 

                  Orion is not a party to any oral contract or agreement
        which would be required to have been furnished or made available
        to Detection under this Section 2.17 had such contract or
        agreement been committed to writing.

             2.18 Validity.  There is no default or claimed or purported
        or alleged default, or basis on which with notice or lapse of
        time or both (including notice of this Agreement), a default
        would exist, in any obligation on the part of any party
        (including Orion) to be performed under any lease, contract,
        plan, policy or other instrument or arrangement referred to in
        Section 2.17 or otherwise in this Agreement.

                                      
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             2.19 No Changes.  Since the date of the Balance Sheet there
        has not been:

                  (a) any material adverse change in the Business of
        Orion;

                  (b) any material damage, destruction or loss (whether
        or not covered by insurance) adversely affecting the Business of
        Orion;

                  (c) any declaration, setting aside or payment of any
        dividend, or other distribution, in respect of Orion's capital
        stock or any direct or indirect redemption, purchase or other
        acquisition of such stock;

                  (d) any option to purchase Orion's capital stock
        granted to any person, or any employment or deferred compensation
        agreement entered into between Orion and any of its stockholders,
        officers, directors, employees or consultants;

                  (e) any issuance or sale by Orion of any stock, bonds
        or other corporate securities, or any partial or complete
        formation, acquisition, disposition or liquidation of Orion;

                  (f) any labor union activity (including without
        limitation any negotiation, or request for negotiation, with
        respect to any union representation or any labor contract)
        respecting Orion;

                  (g) any statute, rule or regulation, or, to the best
        of Orion's knowledge, any government policy, adopted which may
        materially and adversely affect the Business of Orion;

                  (h) any mortgage, lien, attachment, pledge,
        encumbrance or security interest created on any asset, tangible
        or intangible, of Orion, or assumed, either by Orion or by
        others, with respect to any such assets;

                  (i) any indebtedness or other liability or obligation
        (whether absolute, accrued, contingent or otherwise) incurred, or
        other transaction (except that reflected in this Agreement)
        engaged in, by Orion, except those in the ordinary course of
        business that are individually, or in the aggregate to one group
        of related parties, less than ten thousand dollars ($10,000);

                  (j) any obligation or liability discharged or
        satisfied by Orion, except items included in current liabilities
        shown on the Balance Sheet and current liabilities incurred since
        the date of the Balance Sheet in the ordinary course of business
        which are individually, or in the aggregate to one group of
        related parties, less than ten thousand dollars ($10,000) in
        amount;

                  (k) any sale, assignment, lease, transfer or other
                                       
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        disposition of any tangible asset of Orion, except in the
        ordinary course of business, or any sale, assignment, lease,
        transfer or other disposition of any of its patents, trademarks,
        trade names, brand names, copyrights, licenses or other
        intangible assets;

                  (l) any amendment, termination or waiver of any
        material right belonging to Orion;

                  (m) any increase in the compensation or benefits
        payable or to become payable by Orion to any of its officers or
        employees;

                  (n) any transaction or contract with Thermedics; or

                  (o) any other action or omission by Orion, or the
        passage of any resolution, other than in the ordinary course of
        business.

             2.20 Litigation or Proceedings.  Orion is not engaged in, or
        a party to, or, to the best of Thermedics' or Orion's knowledge,
        threatened with, any claim or legal action or other proceeding
        before any court, any arbitrator of any kind or any governmental
        authority, nor does any basis for any claim or legal action or
        other proceeding or governmental investigation exist.  There are
        no orders, rulings, decrees, judgments or stipulations to which
        Orion is a party by or with any court, arbitrator or governmental
        authority affecting the Business of Orion.

             2.21 Compliance with Laws.  Orion (i) has not been and is
        not in violation of any applicable building, zoning, occupational
        safety and health, pension, export control, environmental or
        other federal, state, local or, to the best of its knowledge,
        foreign, law, ordinance, regulation, rule, order or governmental
        policy applicable to the Business of Orion; (ii) has not received
        any complaint from any governmental authority, and to the best
        knowledge of Orion, none is threatened, alleging that Orion has
        violated any such law, ordinance, regulation, rule, order or
        governmental policy; (iii) has not received any notice from any
        governmental authority of any pending proceedings to take all or
        any part of the properties of Orion (whether leased or owned) by
        condemnation or right of eminent domain and, to the best
        knowledge of Orion, no such proceeding is threatened; and (iv) is
        not a party to any agreement or instrument, or subject to any
        charter or other corporate restriction or judgment, order, writ,
        injunction, rule, regulation, code or ordinance, which materially
        and adversely affects, or might reasonably be expected materially
        and adversely to affect the Business of Orion.

             2.22 Labor Matters.  There are no labor organizing
        activities, election petitions or proceedings, labor strikes,
        disputes, slowdowns, work stoppages or unfair labor practice 
        complaints pending or, to the best of Orion's knowledge,
        threatened against Orion or between Orion and any of its
                                       
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        employees.

             2.23 Recalls.  There is no basis for the recall, withdrawal
        or suspension of any approval by any governmental authority with
        respect to any product sold or proposed to be sold by Orion.  
        None of Orion's products is subject to any recall proceedings and
        to the best of its knowledge no such proceedings have been
        threatened.  No product of Orion has ever been recalled.

             2.24 Brokers and Finders.  Neither Orion nor Thermedics has
        employed any broker, agent or finder or incurred any liability on
        behalf of Orion or for any brokerage fees, agents' commissions or
        finders' fees in connection with the transactions contemplated
        hereby.

             2.25 Powers of Attorney.  Orion has no powers of attorney
        or similar authorizations outstanding.

             2.26 No Termination of Relationship.  As of the date hereof,
        Thermedics and Orion are unaware, and have no reason to expect,
        that any relationship between Orion and a distributor, customer,
        supplier, lender, employee or other person will be terminated or
        adversely affected as a result of the Merger.

             2.27 All Information.  Detection has been furnished in
        writing prior to the execution of this Agreement all information
        as to the Business of Orion material to a reasonable buyer's
        determination to enter into this Agreement and to consummate the
        transactions contemplated hereby.

             2.28 Statements True and Correct.  The statements contained
        herein or in any written documents prepared and delivered by or
        on behalf of Thermedics or Orion pursuant to the terms hereof are
        true, complete and correct in all material respects, and such
        documents do not omit any material fact required to be stated
        herein or therein or necessary to make the statements contained
        herein or therein not misleading.


                 SECTION 3 - REPRESENTATIONS AND WARRANTIES OF 
                            DETECTION AND ACQUISITION

             Detection and Acquisition, jointly and severally, represent
        and warrant to Thermedics and Orion as follows.

             3.1  Organization.   Each of Detection and Acquisition is a
        corporation duly organized, validly existing and in good standing
        under the laws of its state of incorporation and has full
        corporate power and authority to own, lease and operate its
        assets and to carry on its business as now being and as
        heretofore conducted.  All outstanding shares of Acquisition
        capital stock are owned by Detection, free and clear of any
        charges, liens, encumbrances, security interests or adverse
        claims.
                                      
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             3.2  Authority.  Each of Detection and Acquisition has full
        right, power, capacity and authority to execute, deliver and
        perform this Agreement and to consummate the transactions
        contemplated hereby. The execution, delivery and performance of 
        this Agreement, the filing of the Articles of Merger and the
        consummation of the transactions contemplated hereby have been
        duly and validly authorized by all necessary corporate action on
        the part of Detection and Acquisition.  This Agreement has been
        duly and validly executed and delivered by each of Detection and
        Acquisition and constitutes the valid and binding obligation of
        Detection and Acquisition, enforceable against them in accordance
        with the terms hereof.  Neither the execution, delivery and
        performance of this Agreement, the filing of the Articles of
        Merger nor the consummation of the transactions contemplated
        hereby will (i) conflict with or result in a violation, breach,
        termination or acceleration of, or default under (or would result
        in a violation, breach, termination, acceleration or default with
        the giving of notice or passage of time, or both) any of the
        terms, conditions or provisions of the Articles of Organization
        or By-laws of Detection, as amended, or Articles of Organization
        or By-laws of Acquisition, as amended, or of any note, bond,
        mortgage, indenture, license, agreement or other instrument or
        obligation to which either Detection or Acquisition is a party or
        by which Detection or Acquisition or any of their respective
        properties or assets may be bound or affected; (ii) result in the
        violation of any order, writ, injunction, decree, statute, rule
        or regulation applicable to Detection or Acquisition or any of
        their respective properties or assets; or (iii) result in the
        imposition of any lien, encumbrance, charge or claim upon any of
        Detection's or Acquisition's assets.  Except for the filing of
        the Articles of Merger and the listing of the Detection Shares
        for trading on the AMEX, no consent or approval by, or
        notification to or filing with, any court, governmental authority
        or third party is required in connection with the execution,
        delivery and performance of this Agreement by Detection and
        Acquisition or the consummation of the transactions contemplated
        hereby. 

             3.3  Statements True and Correct.  The statements contained
        herein or in any written documents prepared and delivered by or
        on behalf of Detection or Acquisition pursuant to the terms
        hereof are true, complete and correct in all material respects,
        and such documents do not omit any material fact required to be
        stated herein or therein or necessary to make the statements
        contained herein or therein not misleading.


                      SECTION 4 - COVENANTS AND AGREEMENTS

             4.1  Conduct of Business.  Except with the prior written
        consent of Detection, which will not be unreasonably withheld or
        delayed, and except as otherwise contemplated herein, during the
        period from the date hereof to the Effective Time, Thermedics and
                                       
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        Orion shall observe the following covenants:

                  (a) Affirmative Covenants Pending Closing.  Thermedics
        and Orion shall:

                      (i) Preservation of Personnel.  Use all reasonable
             efforts to preserve intact Orion's business organization and
             keep available the services of Orion's present employees, in
             each case in accordance with past practice, it being
             understood that Orion's termination of employees with poor
             performance ratings shall not constitute a violation of this
             covenant;

                      (ii)    Insurance.  Use all reasonable efforts to
             keep in effect casualty, public liability, worker's
             compensation and other insurance policies applicable to
             Orion in coverage amounts not less than those in effect at
             the date of this Agreement;

                      (iii)   Preservation of the Business; Maintenance
             of Properties.  Use all reasonable efforts to preserve the
             Business of Orion, advertise, promote and market its
             products and services in accordance with past practices over
             the last twelve months, keep its properties intact, preserve
             its goodwill, maintain all physical properties in such
             operating condition as will permit the conduct of Orion's
             business on a basis consistent with past practice;

                      (iv)    Intellectual Property Rights.  Use all
             reasonable efforts to preserve and protect Orion's
             Proprietary Rights; and

                      (v) Ordinary Course of Business.  Operate Orion's
             business solely in the ordinary course.

                  (b) Negative Covenants Pending Closing.  Thermedics
        and Orion will not:

                      (i) Disposition of Assets.  Sell or transfer, or
             mortgage, pledge or create or permit to be created any lien
             on, any of Orion's assets other than sales or transfers in
             the ordinary course of business or the creation of liens
             under existing arrangements disclosed hereunder and liens
             permitted under Section 2.8;

                      (ii)    Liabilities.  Permit Orion to (A) incur
             any obligation or liability other than in the ordinary
             course of business, (B) incur any indebtedness for borrowed
             money in excess of $100,000 or (C) enter into any contracts
             or commitments involving payments by Orion of $100,000 or
             more other than purchase orders and commitments for
             inventory, materials and supplies in the ordinary course of
             business;

                                
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                      (iii)   Compensation.  Except as required by
             applicable law or any existing employment or severance
             agreement, (A) change the compensation or fringe benefits of
             any Orion officer, director, employee or agent, except for
             ordinary merit increases for employees other than officers
             based on periodic reviews in accordance with past practices,
             or (B) enter into or modify any employment, severance or
             other agreement with any officer, director or employee of
             Orion or any benefit plan (it being understood that Orion's
             hiring of at will employees in the ordinary course of
             business shall not constitute a violation of this covenant)
             or (C) enter into or modify any agreement with any
             consultant, except for agreements terminable upon not more
             than one year's notice that are consistent with Orion's past
             practices with respect to consulting agreements.

                      (iv)    Capital Stock.  Make any change in the
             number of shares of Orion's capital stock authorized, issued
             or outstanding or grant any option, warrant or other right
             to purchase, or to convert any obligation into, shares of
             Orion's capital stock, or declare or pay any dividend or
             other distribution with respect to any shares of Orion's
             capital stock, or sell or transfer any shares of its capital
             stock;

                      (v) Charter and By-Laws.  Amend the Articles of
             Organization or By-laws of Orion;

                      (vi)    Acquisitions.  Make any material
             acquisition of property other than in the ordinary course of
             the Business of Orion; or

                      (vii)   License Agreements.  Enter into or modify
             any license, technology development or technology transfer
             agreement between Orion and any other person or entity.

             4.2  Corporate Examinations and Investigations.  Prior to
        the Effective Time, Detection shall be entitled, through its
        employees and representatives, to have such access to the assets,
        properties, business and operations of Orion, as is reasonably
        necessary or appropriate in connection with its investigation of
        Orion with respect to the transaction contemplated hereby.  Any
        such investigation and examination shall be conducted at
        reasonable times and under reasonable circumstances so as to
        minimize any disruption to or impairment of Orion's business and
        each party shall cooperate fully therein.  No investigation by
        Detection shall diminish or obviate any of the representations,
        warranties, covenants or agreements of Thermedics or Orion
        contained in this Agreement.  In order that Detection may have
        full opportunity to make such investigation, Thermedics and Orion
        shall furnish the representatives of Detection with all such
        information and copies of such documents concerning its affairs
        as Detection may reasonably request and cause their officers,
        employees, consultants, agents, accountants and attorneys to
                                       
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        cooperate fully with Detection's representatives in connection
        with such investigation.

             4.3  Expenses.  Whether or not the Merger is consummated,
        Detection, Thermedics and Orion shall bear their respective 
        expenses incurred in connection with the preparation, execution
        and performance of this Agreement and the transactions
        contemplated hereby, including without limitation, all fees and
        expenses of agents, representatives, counsel and accountants.

             4.4  Authorization from Others.  Prior to the Effective
        Date, the parties shall use all reasonable efforts to obtain all
        authorizations, consents and permits of others required to permit
        the consummation of the transactions contemplated by this
        Agreement.

             4.5  Consummation of Agreement.  Each party shall use all
        reasonable efforts to perform and fulfill all conditions and
        obligations to be performed and fulfilled by it under this
        Agreement and to ensure that to the extent within its control or
        capable of influence by it, no breach of any of its respective
        representations, warranties and agreements hereunder occurs or
        exists on or prior to the Effective Time, all to the end that the
        transactions contemplated by this Agreement shall be fully
        carried out in a timely fashion.

             4.6  Further Assurances.  Each of the parties shall execute
        such documents, further instruments of transfer and assignment
        and other papers and take such further actions as may be
        reasonably required or desirable to carry out the provisions
        hereof and the transactions contemplated hereby. 

             4.7  Tax-Free Reorganization.  Detection, Acquisition,
        Thermedics and Orion agree that no party shall take any action
        directly or indirectly that would prevent the Merger from
        qualifying as a tax-free reorganization under Section 368(a) of
        the Code.

             4.8  Listing of Shares.  Promptly after the Effective Date,
        Detection shall take all action necessary in accordance with
        applicable law to convene a meeting of its stockholders to be
        held for the purpose of approving the listing of the Detection
        Shares for trading upon AMEX in accordance with Section 712 of
        AMEX's Listing Standards, Policies and Requirements.  Orion
        acknowledges and agrees that such meeting may be held subsequent
        to Detection's 1998 annual meeting.  In connection with such
        meeting, Detection's Board of Directors shall recommend to the
        Detection stockholders the approval of the listing of the
        Detection Shares pursuant to this Agreement.  Detection shall use
        all reasonable efforts to obtain all votes and approvals of the
        Detection stockholders necessary for the listing of the Detection
        Shares and all related matters under the BCLM, and its Articles
        of Organization and By-laws.  Thermedics hereby agrees to vote
        all of the shares of Detection Common Stock held by it as of the
                                       
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        record date of any such meeting in favor of the listing of the
        Detection Shares and all such related matters.

             4.9  Public Announcements and Confidentiality.  Any press
        release or other information to the press or any third party with
        respect to this Agreement or the transactions contemplated hereby
        shall require the prior approval of Detection and Orion, which
        approval shall not be unreasonably withheld, provided that a
        party shall not be prevented from making such disclosure as it
        shall be advised by counsel is required by law.

             4.10 No Solicitation.  Thermedics and Orion will not (i)
        solicit or initiate discussions with any person, other than
        Detection, relating to the possible acquisition of Orion or all
        or a material portion of the assets or any of the capital stock 
        of Orion or any merger or other business combination with Orion
        (an "Acquisition Transaction") or (ii) except to the extent
        reasonably required by fiduciary obligations under applicable law
        as advised by legal counsel, participate in any negotiations
        regarding, or furnish to any other person information with
        respect to, any effort or attempt by any other person to do or to
        seek any Acquisition Transaction.  Thermedics and Orion agree to
        inform Detection within one business day of its receipt of any
        offer, proposal or inquiry relating to any Acquisition
        Transaction.

             4.11 Indemnification. 

                  (a) Right to Indemnification.  Detection and
        Thermedics (as the case may be, the "Indemnitee") shall be
        indemnified on its respective demand made to the other (the
        "Indemnitor") for the full amount of all damages (as defined
        below) suffered by it as a direct or indirect result of:

                      (i) the inaccuracy of any representation or
             warranty made by the Indemnitor in or pursuant to this
             Agreement; and

                      (ii)    any failure by the Indemnitor to perform
             any obligation or comply with any covenant or agreement
             specified in this Agreement.

        For the purpose of this Section 4.11, (a) references to Detection
        shall be deemed to mean Detection and Acquisition; (b) the term
        "damages" shall be determined and computed by reference to the
        effect of the compensable event on the Indemnitee, and shall be
        deemed to include (i) all losses, liabilities, expenses or costs
        incurred by the Indemnitee, including reasonable attorneys' fees,
        and (ii) interest at a rate per annum equal to that announced
        from time to time by BankBoston as its "base rate" (or the legal
        rate of interest, if lower) from the date 30 days after notice of
        any such claim for indemnification is given to the Indemnitor, or
        if an unliquidated claim, from such later date as the claim is
        liquidated, to the date full indemnification is made therefor;
                                       
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        and (c) damages shall not include any amounts for which the
        Indemnitee actually receives payment under an insurance policy,
        excluding self-insured amounts and deductible amounts. 

                  (b) Indemnification Procedures.  The Indemnitee shall 
        give the Indemnitor notice of any claim, action or proceeding by
        a third party which is reasonably likely to result in a claim for
        indemnification under this Section 4.11.  The Indemnitor shall
        have the right, at its expense, to defend, contest, protest,
        settle and otherwise control the resolution of any such claim,
        action or proceeding.  The Indemnitee shall have the right to
        participate in any such legal proceeding, subject to the
        Indemnitor's right of control thereof, at the expense of the
        Indemnitee and with counsel selected by the Indemnitee.

                  (c) Limitations on Indemnification.  Detection's and
        Thermedics' rights to be indemnified pursuant to Section 4.11
        shall survive the Effective Date of this Agreement indefinitely.

             4.12 Participation in Employee Benefit Plans.  Thermedics
        and Orion will take whatever actions may be required to continue
        in effect without interruption the participation of Orion in the
        employee benefit plans in which Orion is participating as of the
        Effective Date, until such time as Orion may choose not to 
        participate in those plans.

             4.13 Certain Tax Matters.

                  (a) Allocation of Certain Taxes.  In the case of any
        Tax that is attributable to a taxable period which begins before
        the Effective Date and ends after the Effective Date, the amount
        of Taxes attributable to the period prior to the Effective Date
        (the _Pre-Effective Period_) and the period subsequent to the
        Effective Date (the _Post-Effective Period_) shall be determined
        as follows:

                      (i) Thermedics and Detection agree that if Orion
             is permitted but not required under applicable foreign,
             state or local Tax laws to treat the Effective Date as the
             last day of a taxable period, Thermedics and Detection shall
             treat such day as the last day of a taxable period.

                      (ii)    Except to the extent provided in clause
             (i) of this subsection 4.13(a), in the case of ad valorem
             Taxes imposed on Orion and franchise or similar Taxes
             imposed on Orion based on capital (including net worth or
             long-term debt) or number of shares of stock authorized,
             issued or outstanding, such Taxes shall be allocated between
             the Pre-Effective Period and the Post-Effective Period based
             upon the respective number of days in each such period.

                      (iii)   Except to the extent provided in clauses
             (i) and (ii) of this subsection 4.13(a), all other Taxes
             shall be allocated between the Pre-Effective Period and the
                                       
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             Post-Effective Period based upon an interim closing of the
             books of Orion as of the end of the day of the Effective
             Date, and the computation of the Tax for each resulting
             period as if the period were a separate taxable period;
             provided, however, that in no event shall the hypothetical
             Tax for any period be less than zero.

                  (b) Tax Sharing Agreements.  Any Tax sharing agreement
        between Orion and Thermedics or any other related corporation
        shall be terminated as of the Effective Date and, after the
        Effective Date, Orion shall not be bound thereby or have any
        liability thereunder.

                  (c) Waivers of Carrybacks.  Orion and Thermedics
        agree, to the maximum extent permitted, to elect to waive the
        carryback of any loss, credit or deduction incurred in or
        attributable to any taxable period (or portion thereof) after the
        Effective Date to any taxable period (or portion thereof) prior
        to the Effective Date.  


             SECTION 5 - CONDITIONS PRECEDENT TO THE OBLIGATIONS OF
               DETECTION AND ACQUISITION TO CONSUMMATE THE MERGER

             The obligation of Detection and Acquisition to consummate
        the Merger is subject to the satisfaction or waiver, at or before
        the Effective Time, of the following conditions:

             5.1  Representations, Warranties and Covenants.  The
        representations and warranties of Thermedics and Orion contained
        in this Agreement shall be true and correct in all material
        respects on and as of the Effective Time with the same force and
        effect as though made on and as of the Effective Time (with such
        exceptions as may be permitted under or contemplated by this
        Agreement) and there shall not have been any material adverse
        change in the Business of Orion since the date hereof.
        Thermedics and Orion shall have performed and complied in all
        material respects with all covenants and agreements required by
        this Agreement to be performed or complied with by them on or
        prior to the Effective Time and shall have obtained all required
        consents and approvals.  Thermedics and Orion shall have
        delivered to Detection a certificate, dated the Effective Time,
        to the foregoing effect.

             5.2  Articles of Merger.  Orion shall have executed and
        delivered the Articles of Merger.

             5.3  Certificates.  Thermedics and Orion shall have
        furnished Detection and Acquisition with such certificates of
        public officials and of Thermedics and Orion officers as may be
        reasonably requested by Detection and Acquisition.


              SECTION 6 - CONDITIONS PRECEDENT TO THE OBLIGATION OF
                                       
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                  THERMEDICS AND ORION TO CONSUMMATE THE MERGER

             The obligation of Thermedics and Orion to consummate the
        Merger is subject to the satisfaction or waiver, at or before the
        Effective Time, of the following conditions:















                                      
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             6.1  Representations, Warranties and Covenants.  The
        representations and warranties of Detection and Acquisition
        contained in this Agreement shall be true and correct in all
        material respects on and as of the Effective Time with the same
        force and effect as though made on and as of the Effective Time
        (with such exceptions as may be permitted under or contemplated
        by this Agreement) and there shall not have been any material
        adverse change in the Business of Detection since the date
        hereof.  Detection shall have performed and complied in all
        material respects with all covenants and agreements required by
        this Agreement to be performed or complied with by it on or prior
        to the Effective Time and shall have obtained all required
        consents and approvals.  Detection and Acquisition shall have
        delivered to Orion a certificate, dated the Effective Time, to 
        the foregoing effect.

             6.2  Articles of Merger.  Acquisition shall have executed
        and delivered the Articles of Merger.

             6.3  Certificates.  Detection and Acquisition shall have
        furnished Thermedics and Orion with such certificates of public
        officials and of Detection and Acquisition officers as may be
        reasonably requested by Thermedics and Orion.


                  SECTION 7 - TERMINATION, AMENDMENT AND WAIVER

             7.1  Termination.  This Agreement may be terminated at any
        time prior to the Effective Time as follows:

                  (a) by Thermedics upon written notice to Detection if
        Detection or Acquisition has materially breached any
        representation, warranty, covenant or agreement contained herein
        and has not cured such breach within ten (10) business days of
        receipt of written notice from Thermedics;

                  (b) by Detection upon written notice to Thermedics if
        Thermedics or Orion has materially breached any representation,
        warranty, covenant or agreement contained herein and has not
        cured such breach within ten (10) business days of receipt of
        written notice from Detection;

                  (c) by either party if any court of competent
        jurisdiction or United States governmental body shall have issued
        an order, decree or ruling or taken any other action restraining,
        enjoining or otherwise prohibiting the Merger and such order,
        decree or ruling shall have become final and nonappealable; or

                  (d) at any time with the written consent of Thermedics
        and Detection.

             7.2  Effect of Termination.  If this Agreement is
        terminated as provided in Section 7.1, this Agreement shall 
                                      
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        forthwith become void and have no effect, without liability on
        the part of any party, its directors, officers or stockholders,
        other than the provisions of this Section 7.2, Section 4.3
        relating to expenses and Section 4.9 relating to publicity and
        confidentiality to the extent provided therein.  Nothing
        contained in this Section 7.2 shall relieve any party from
        liability for any breach of this Agreement occurring before such
        termination.

             7.3  Amendment.  This Agreement may not be amended except
        by an instrument signed by each of the parties hereto.

             7.4  Waiver.  At any time, any party hereto may (a) extend
        the time for the performance of any of the obligations or other
        acts of any other party hereto or (b) waive compliance with any
        of the agreements of any other party or any conditions to its own
        obligations, in each case only to the extent such obligations,
        agreements and conditions are intended for its benefit; provided
        that any such extension or waiver shall be binding upon a party 
        only if such extension or waiver is set forth in a writing
        executed by such party.


                            SECTION 8 - MISCELLANEOUS

             8.1  Notices.  All notices, requests, demands, consents and
        other communications which are required or permitted hereunder
        shall be in writing, and shall be deemed given when actually
        received or if earlier, one day after deposit with a nationally
        recognized air courier or express mail, charges prepaid or three
        days after deposit in the U.S. mail by certified mail, return
        receipt requested, postage prepaid, addressed as follows:

         
                  If to Detection or Acquisition:

                       Thermedics Detection Inc.
                       220 Mill Road
                       Chelmsford, Massachusetts  01824
                       Attention:  President

                  With a copy to:

                       Thermo Electron Corporation
                       81 Wyman Street
                       Waltham, Massachusetts  02254
                       Attention:  General Counsel

                  If to Thermedics or Orion:

                       Thermedics Inc.
                       470 Wildwood Street
                       Woburn, Massachusetts  01888
                       Attention:  President
                                      
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                  With a copy to:

                       Thermo Electron Corporation
                       81 Wyman Street
                       Waltham, Massachusetts  02254
                       Attention:  General Counsel

        or to such other address as any party hereto may designate in
        writing to the other parties, specifying a change of address for
        the purpose of this Agreement.

             8.2  Survival and Materiality of Representations.  Each of
        the representations, warranties and agreements made by the
        parties hereto shall be deemed material and shall survive the
        Effective Date and the consummation of the transactions
        contemplated hereby. All statements contained in any certificates
        or other instruments delivered by or on behalf of the 
        parties pursuant hereto or in connection with the transactions
        contemplated hereby shall be deemed material and shall constitute
        representations and warranties by the person making such
        statement.

             8.3  Entire Agreement.  This Agreement, including the
        exhibits, the Orion Disclosure Schedule and the other documents
        referred to herein, supersedes any and all oral or written
        agreements or understandings heretofore made relating to the
        subject matter hereof and constitutes the entire agreement of the
        parties relating to the subject matter hereof.

             8.4  Parties in Interest.  All covenants and agreements,
        representations and warranties contained in this Agreement made
        by or on behalf of any of the parties hereto shall bind and inure
        to the benefit of the parties hereto, and their respective
        successors, assigns, heirs, executors, administrators and
        personal representatives, whether so expressed or not.

             8.5  No Implied Rights or Remedies.  Except as otherwise
        expressly provided herein, nothing herein expressed or implied is
        intended or shall be construed to confer upon or to give any
        person, firm or corporation, other than the parties hereto, any
        rights or remedies under or by reason of this Agreement.

             8.6  Headings.  The headings in this Agreement are inserted
        for convenience of reference only and shall not be a part of or
        control or affect the meaning hereof.

             8.7  Severability.  If any provision of this Agreement
        shall be declared void or unenforceable by any judicial or
        administrative authority, the validity of any other provision
        shall not be affected thereby.

             8.8  Counterparts.  This Agreement may be executed in
        several counterparts, each of which shall be deemed an original, 
                                       
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        but all of which together shall constitute one and the same
        instrument.

             8.9  Further Assurances.  Thermedics and Orion will execute
        and furnish to Detection and Acquisition all documents and will
        do or cause to be done all other things that Detection may
        reasonably request from time to time in order to give full effect
        to this Agreement and to effectuate the intent of the parties.

             8.10 Governing Law.  This Agreement shall be governed by
        the law of the Commonwealth of Massachusetts applicable to
        agreements made and to be performed wholly within such
        jurisdiction, without regard to the conflicts of laws provisions
        thereof.


             IN WITNESS WHEREOF, the parties have caused this Agreement
        to be duly executed as of the date first written above.


        THERMEDICS DETECTION INC.       ORION ACQUISITION INC.


        By: /s/James Barbookles         By: John W. Wood
        Name: James Barbookles          Name: /s/ John W. Wood
        Title: President                Title: President



        THERMEDICS INC.                 ORION RESEARCH INC.


        By: /s/ John T. Keiser          By: James Barbookles
        Name:      John T. Keiser                                  Name:
        /s/ James Barbookles
        Title: President                Title: President