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This announcement is neither an offer to purchase nor a solicitation of an offer
to sell Shares. The Offer is being made solely by the Offer to Purchase dated
March 10, 2000 and the related Letter of Transmittal and is being made to all
holders of Shares. The Offer is not being made to (nor will tenders be accepted
from or on behalf of) holders of Shares in any jurisdiction in which the making
of the Offer or the acceptance thereof would not be in compliance with the laws
of such jurisdiction. In any jurisdiction where the securities, blue sky or
other laws require the Offer to be made by a licensed broker or dealer, the
Offer shall be deemed to be made on behalf of the Purchaser by J.P. Morgan
Securities Inc., The Beacon Group Capital Services, LLC or one or more
registered brokers or dealers licensed under the laws of such jurisdiction.

NOTICE OF OFFER TO PURCHASE FOR CASH

ALL OUTSTANDING SHARES OF COMMON STOCK

OF

THERMEDICS DETECTION INC.

AT

$8.00 NET PER SHARE

BY

DETECTION ACQUISITION, INC.

AN INDIRECT WHOLLY-OWNED SUBSIDIARY OF

THERMEDICS INC.

Detection Acquisition, Inc., a Delaware corporation (the "Purchaser") and an
indirect wholly-owned subsidiary of Thermedics Inc., a Massachusetts
corporation ("Thermedics"), is offering to purchase all outstanding shares of
common stock, par value $0.10 per share (the "Shares"), of Thermedics Detection
Inc., a Massachusetts corporation (the "Company"), at a purchase price of $8.00
per Share, net to the seller in cash, without interest thereon, upon the terms
and subject to the conditions set forth in the Offer to Purchase dated March 10,
2000 (the "Offer to Purchase") and in the related Letter of Transmittal (which,
together with any amendments or supplements thereto, collectively constitute the
"Offer"). The Purchaser is a wholly-owned subsidiary of Corpak Inc. ("Corpak"),
a Massachusetts corporation and a wholly-owned subsidiary of Thermedics. Thermo
Electron Corporation, a Delaware corporation ("Thermo Electron"), owns a
majority of the outstanding shares of common stock of Thermedics.

 -------------------------------------------------------------------------------
                         THE OFFER AND WITHDRAWAL RIGHTS
                  WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
                  TIME, ON THURSDAY, APRIL 6, 2000, UNLESS THE
                               OFFER IS EXTENDED.
 -------------------------------------------------------------------------------

THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY TENDERED
AND NOT WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER THAT NUMBER OF SHARES
WHICH, TOGETHER WITH SHARES OWNED BY THERMO ELECTRON AND ITS SUBSIDIARIES,
INCLUDING THERMEDICS, CONSTITUTES AT LEAST NINETY PERCENT (90%) OF THE
OUTSTANDING SHARES OF THE COMPANY ON THE EXPIRATION DATE. THE OFFER IS ALSO
SUBJECT TO CERTAIN OTHER IMPORTANT TERMS AND CONDITIONS CONTAINED IN THE OFFER
TO PURCHASE.



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The Offer is the first step in Thermedics' plan to take the Company private. The
purpose of the Offer is to acquire the minority interest in the Company as part
of an overall reorganization of Thermo Electron. If the Offer is completed,
Thermo Electron, Corpak and the Purchaser together will own at least 90% of the
Shares. Promptly following the closing of the Offer, Corpak and Thermo Electron
plan to contribute their Shares to the Purchaser. Thermo Electron and Corpak
would then cause the Company to merge with and into the Purchaser in a so-called
"short-form" merger between the Company and the Purchaser (the "Merger").
Stockholders of the Company who do not tender their Shares in the Offer will not
be entitled to vote on the Merger. The consideration per Share in the Merger
(other than with respect to Shares held by stockholders, if any, who are
entitled to and perfect their appraisal rights under Massachusetts law) would be
the same as the Offer price of $8.00.

For purposes of the Offer, the Purchaser will be deemed to have accepted for
payment, and thereby purchased, Shares validly tendered and not properly
withdrawn if, as and when the Purchaser gives oral or written notice to American
Stock Transfer & Trust Company (the "Depositary") of the Purchaser's acceptance
for payment of such Shares pursuant to the Offer. Upon the terms and subject to
the conditions of the Offer, payment for Shares so accepted for payment pursuant
to the Offer will be made by deposit of the aggregate purchase price therefor
with the Depositary, which will act as agent for tendering stockholders for the
purpose of receiving payment from the Purchaser and transmitting such payment to
stockholders whose Shares have been accepted for payment. UNDER NO CIRCUMSTANCES
WILL INTEREST ON THE PURCHASE PRICE FOR SHARES BE PAID, REGARDLESS OF ANY
EXTENSION OF THE OFFER OR ANY DELAY IN MAKING SUCH PAYMENT. In all cases,
payment for Shares tendered and accepted for payment pursuant to the Offer will
be made only after timely receipt by the Depositary of (i) certificates
evidencing Shares ("Share Certificates") or timely confirmation of a book-entry
transfer of such Shares into the Depositary's account at the Book-Entry Transfer
Facility (as defined in the section of the Offer to Purchase captioned "The
Tender Offer -- Acceptance For Payment And Payment For Shares") pursuant to the
procedures set forth in the section of the Offer to Purchase captioned "The
Tender Offer -- Acceptance For Payment And Payment For Shares," (ii) the Letter
of Transmittal (or a facsimile thereof), properly completed and duly executed,
with any required signature guarantees, or an Agent's Message (as defined in the
section of the Offer to Purchase captioned "The Tender Offer -- Acceptance For
Payment And Payment For Shares") in connection with a book-entry transfer and
(iii) any other documents required by the Letter of Transmittal.

The term "Expiration Date" means 12:00 midnight, New York City time, on
Thursday, April 6, 2000, unless and until the Purchaser, in its sole discretion,
shall have extended the period during which the Offer is open, in which event
the term "Expiration Date" shall mean the latest time and date at which the
Offer, as so extended by the Purchaser, shall expire.

Subject to the applicable rules and regulations of the Securities and Exchange
Commission, the Purchaser expressly reserves the right, in its sole discretion,
at any time and from time to time, to extend the period during which the Offer
is open for any reason, including the failure to satisfy any of the conditions
specified in the section of the Offer to Purchase captioned "The Tender Offer --
Certain Conditions Of The Offer," and thereby delay acceptance for payment of,
or payment for, any Shares, by giving oral or written notice of such extension
to the Depositary. Any such extension will be followed as promptly as
practicable by a public announcement thereof, such announcement to be made no
later than 9:00 a.m., New York City time, on the next business day after the
previously scheduled Expiration Date. During any such extension, all Shares
previously tendered and not properly withdrawn will remain subject to the Offer,
subject to the right of a tendering stockholder to withdraw such stockholder's
Shares.

Except as otherwise provided in the section of the Offer to Purchase captioned
"The Tender Offer -- Withdrawal Rights," tenders of Shares made pursuant to the
Offer are irrevocable. Shares tendered pursuant to the Offer may be withdrawn at
any time prior to the Expiration Date and, unless previously accepted for
payment by the Purchaser pursuant to the Offer, may also be withdrawn at any
time after May 8, 2000. In order for a withdrawal to be effective, a written,
telegraphic or facsimile transmission notice of withdrawal must be timely
received by the Depositary at one of its addresses set forth on the back cover
of the Offer to Purchase. Any such notice of withdrawal must specify the name of
the person who tendered the Shares to be withdrawn, the number of Shares to be
withdrawn and the name of the registered holder of the Shares to be withdrawn,
if different from that of the person who tendered such Shares. If Share
Certificates to be withdrawn have been delivered or otherwise identified to the
Depositary, then, prior to the physical release of such Share Certificates, the
tendering stockholder must also submit the serial numbers shown on such Share
Certificates to the Depositary, and the signatures on the notice of withdrawal
must be guaranteed by an Eligible Institution (as defined in the section of the
Offer to Purchase captioned "The Tender Offer -- Procedures For Accepting The
Offer And Tendering Shares"), unless such Shares have been tendered for the
account of an Eligible Institution. If Shares have been tendered pursuant to the
procedures for book-entry transfer, as set forth in the section of the Offer to
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Purchase captioned "The Tender Offer -- Procedures For Accepting The Offer And
Tendering Shares," any notice of withdrawal must specify the name and number of
the account at the Book-Entry Transfer Facility to be credited with the
withdrawn Shares and must otherwise comply with the procedures of the Book-Entry
Transfer Facility. Withdrawals may not be revoked, and any Shares properly
withdrawn will thereafter be deemed not to have been validly tendered for
purposes of the Offer. However, withdrawn Shares may be retendered at any time
prior to the Expiration Date by following the procedures described in the
section of the Offer to Purchase captioned "The Tender Offer -- Procedures For
Accepting The Offer And Tendering Shares." All questions as to the form and
validity (including the time of receipt) of any notice of withdrawal will be
determined by the Purchaser, in its sole discretion, whose determination will be
final and binding.

The information required to be disclosed by Rule 14d-6(d)(1) and Rule
13e-3(e)(i) of the General Rules and Regulations under the Securities Exchange
Act of 1934, as amended, is contained in the Offer to Purchase and is
incorporated herein by reference.

The Company has provided the Purchaser with the Company's stockholder list and
security position listings for the purpose of disseminating the Offer to holders
of Shares. The Offer to Purchase, the related Letter of Transmittal and, if
required, other relevant material will be mailed to record holders of Shares
whose names appear on the Company's stockholder list and will be furnished to
brokers, dealers, commercial banks, trust companies and similar persons whose
names, or the names of whose nominees, appear on the Company's stockholder list
or, if applicable, who are listed as participants in a clearing agency's
security position listing for subsequent transmittal to beneficial owners of
Shares.

The receipt of cash for Shares pursuant to the Offer will be a taxable
transaction for U.S. federal income tax purposes.

THE OFFER TO PURCHASE AND THE RELATED LETTER OF TRANSMITTAL CONTAIN IMPORTANT
INFORMATION WHICH SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE WITH
RESPECT TO THE OFFER.

Tendering stockholders of record who tender Shares directly will not be
obligated to pay brokerage fees or commissions or, except as set forth in
Instruction 6 of the Letter of Transmittal, stock transfer taxes on the purchase
of Shares by the Purchaser pursuant to the Offer. Stockholders who hold their
Shares through a bank or a broker should check with such institution as to
whether it charges any service fees. The Purchaser will pay the expenses of the
Depositary, D.F. King & Co., Inc., who is acting as the information agent (the
"Information Agent"), and J.P. Morgan Securities Inc. and The Beacon Group
Capital Services, LLC, who are acting as dealer managers (collectively, the
"Dealer Managers"), in connection with the Offer.

Questions and requests for assistance or for additional copies of the Offer to
Purchase, the Letter of Transmittal and all other tender offer materials may be
directed to the Information Agent or the Dealer Managers as set forth below, and
copies will be furnished promptly at the Purchaser's expense. No fees or
commissions will be paid to brokers, dealers or any other persons (other than
the Dealer Managers and the Information Agent) for soliciting tenders of Shares
pursuant to the Offer.

The Information Agent for the Offer is:

D.F. King & Co., Inc.
77 Water Street, 20th Floor
New York, NY 10005
Bankers and Brokers Call Collect: (212) 269-5550
All Others Call Toll Free: (800) 290-6433

The Dealer Managers for the Offer are:

J.P. Morgan Securities Inc.
60 Wall Street
New York, NY 10260
(877) 869-0656

The Beacon Group Capital Services, LLC
399 Park Avenue

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New York, NY 10022
(212) 339-9100


March 10, 2000